Co-reporter:Jie Ma, Zhi-Zhou Li, Xue-Dong Wang, and Liang-Sheng Liao
Crystal Growth & Design September 6, 2017 Volume 17(Issue 9) pp:4527-4527
Publication Date(Web):August 23, 2017
DOI:10.1021/acs.cgd.7b00910
Self-assembly of small organic π-conjugated molecules into micro- and nanostructures has drawn much attention because of their wide applications in miniature optoelectronic devices. Many efforts have been focused on the controlled fabrication of organic micro/nanostructures, which are determined by various factors including kinetic and thermodynamic process but still remain poorly understood. In our research, two π-conjugated molecules of (E)-3-(4-(diphenylamino)phenyl)-1-(4-fluoro-2-hydroxyphenyl)prop-2-en-1-one (DFHP) and (E)-3-(4-(bis(4-methoxyphenyl)amino)phenyl)-1-(4-fluoro-2-hydroxyphenyl)prop-2-en-1-one (DFPHP) with a small difference of substituent groups were designed and synthesized. By the solution-exchange method, DFHP are self-assembled into amorphous microspheres while DFPHP tend to grow into crystalline rhombic microcrystals. The head of DFHP organic molecules can form hydrogen bonds with ethanol molecules and the tail of DFHP dissolves in the dichloromethane (DCM) phase, which exhibits amphiphilic nature, contributing to the self-assembly of microspheres. In a contrast, both the head and the tail of DFPHP can have hydrogen bonds with the ethanol molecules, which leads to the ordered DFPHP molecular packing and then the formation of rhombic microcrystals. Furthermore, based on simulated growth/equilibrium morphology, DFHP form the amorphous microspheres other than the crystalline microcrystals due to the lower attachment energy (Etotal = −43.5 kcal/mol) as compared with that (Etotal = −53.1 kcal/mol) of DFPHP. Our demonstration can indeed builds the structure–morphology relationship for rational fabrication of organic micro/nanostructures, which would contribute to integrated optoelectronics.
Co-reporter:Yongxi Li, Jiu-Dong Lin, Xiaozhou Che, Yue Qu, Feng Liu, Liang-Sheng Liao, and Stephen R. Forrest
Journal of the American Chemical Society November 29, 2017 Volume 139(Issue 47) pp:17114-17114
Publication Date(Web):November 16, 2017
DOI:10.1021/jacs.7b11278
The absence of near-infrared (NIR) solar cells with high open circuit voltage (Voc) and external quantum efficiency (EQE) has impeded progress toward achieving organic photovoltaic (OPV) power conversion efficiency PCE > 15%. Here we report a small energy gap (1.3 eV), chlorinated nonfullerene acceptor-based solar cell with PCE = 11.2 ± 0.4%, short circuit current of 22.5 ± 0.6 mA cm–2, Voc = 0.70 ± 0.01 V and fill factor of 0.71 ± 0.02, which is the highest performance reported to date for NIR single junction OPVs. Importantly, the EQE of this NIR solar cell reaches 75%, between 650 and 850 nm while leaving a transparency window between 400 and 600 nm. The semitransparent OPV using an ultrathin (10 nm) Ag cathode shows PCE = 7.1 ± 0.1%, with an average visible transmittance of 43 ± 2%, Commission d’Eclairage chromaticity coordinates of (0.29, 0.32) and a color rendering index of 91 for simulated AM1.5 illumination transmitted through the cell.
Co-reporter:Feng Liang, Yuan Liu, Yun Hu, Ying-Li Shi, Yu-Qiang Liu, Zhao-Kui Wang, Xue-Dong Wang, Bao-Quan Sun, and Liang-Sheng Liao
ACS Applied Materials & Interfaces June 14, 2017 Volume 9(Issue 23) pp:20239-20239
Publication Date(Web):May 25, 2017
DOI:10.1021/acsami.7b05629
A facile but effective method is proposed to improve the performance of quantum dot light-emitting diodes (QLEDs) by incorporating a polymer, poly(9-vinlycarbazole) (PVK), as an additive into the CdSe/CdS/ZnS quantum dot (QD) emitting layer (EML). It is found that the charge balance of the device with the PVK-added EML was greatly improved. In addition, the film morphology of the hole-transporting layer (HTL) which is adjacent to the EML, is substantially improved. The surface roughness of the HTL is reduced from 5.87 to 1.38 nm, which promises a good contact between the HTL and the EML, resulting in low leakage current. With the improved charge balance and morphology, a maximum external quantum efficiency (EQE) of 16.8% corresponding to the current efficiency of 19.0 cd/A is achievable in the red QLEDs. The EQE is 1.6 times as high as that (10.5%) of the reference QLED, comprising a pure QD EML. This work demonstrates that incorporating some polymer molecules into the QD EML as additives could be a facile route toward high-performance QLEDs.Keywords: additive; charge balance; light-emitting diodes; morphology; quantum dots;
Co-reporter:Yilong Lei;Yanqiu Sun;Liangsheng Liao;Shuit-Tong Lee;Wai-Yeung Wong
Nano Letters February 8, 2017 Volume 17(Issue 2) pp:695-701
Publication Date(Web):December 27, 2016
DOI:10.1021/acs.nanolett.6b03778
In contrast to those for their polymeric counterparts, the controlled construction of organic heterostructured architectures derived from π-conjugated organic molecules has been rare and remains a great challenge. Herein, we develop a simple single-step solution strategy for the realization of organic heterostructures comprising coronene and perylene. Under a sequential crystallization process, an efficient doping step for coronene and perylene domains enables their perfect lattice matching, which facilitates facet-selective epitaxial growth of perylene domains on both the tips and the side surfaces of the preformed seed microwires by manipulating the growth pathways of the two pairs of materials. The present synthetic route provides a promising platform to investigate the detailed formation mechanism of complex organic heterostructures with specific topological configurations, further directing the construction of more functional heterostructured materials.Keywords: facet-selective growth; organic heterostructured architectures; sequential crystallization; structural matching; π-conjugated organic molecules;
Co-reporter:Miao-Miao Xue;Chen-Chao Huang;Yi Yuan;Ye-Xin Zhang;Man-Keung Fung
Chemical Communications 2017 vol. 53(Issue 1) pp:263-265
Publication Date(Web):2016/12/20
DOI:10.1039/C6CC09486D
A new electron-withdrawing moiety (BFPz) has been used for the first time as an acceptor in OLEDs and its corresponding core unit (2-Br-BFPz) was synthesized. Combined with an electron-donating moiety triphenylamine, a novel fluorescent material with a D–A structure named TPA-BFPz was synthesized. Encouragingly, the EQE values of non-doped and doped blue OLEDs reach 3.68% and 4.42%, respectively.
Co-reporter:Amjad Islam, Qiang Wang, Lei Zhang, Tao Lei, Ling Hong, Rongjuan Yang, Zhiyang Liu, Ruixiang Peng, Liang-Sheng Liao, Ziyi Ge
Dyes and Pigments 2017 Volume 142(Volume 142) pp:
Publication Date(Web):1 July 2017
DOI:10.1016/j.dyepig.2017.03.061
•Novel emissive molecules containing phenanthroimidazole, triphenylamine, carbazole and pyrene units are developed.•Deep blue emission is exhibited by these fluorescent materials.•High thermal stability of materials and low operating voltage of device are observed.•Non-doped OLEDs are constructed with high efficiency and low roll-off.Two phenanthroimidazole derivatives containing triphenylamine, carbazole and pyrene units were designed and synthesized. Highly efficient non-doped deep blue organic light emitting diodes (OLEDs) were fabricated by using these materials as emissive layer. The non-doped devices demonstrated high efficiency (4.24 cd/A, 3.67 lm/W, 4.66%), low efficiency roll-off at higher current densities, and stable deep blue emissions with CIEy around 0.10, which are excellent results for deep-blue OLED devices. This study reveals that the combination of phenanthroimidazole and donor-linker-acceptor strategy has a great potential for developing high performance deep-blue OLEDs.
Co-reporter:Ya-Kun Wang;Sheng-Fan Wu;Si-Hua Li;Yi Yuan;Fu-Peng Wu;Sarvendra Kumar;Zuo-Quan Jiang;Man-Keung Fung
Advanced Optical Materials 2017 Volume 5(Issue 24) pp:
Publication Date(Web):2017/12/01
DOI:10.1002/adom.201700566
AbstractThough urgently required, high performance near-infrared (NIR) emitters are still rare given the challenge of obtaining high photoluminance quantum efficiency (PLQY) at the same time ensuring NIR emission. The major issue lies in the design strategy for which strong electron donating/withdrawing moieties with high PLQY should be integrated with a scrumptious way. Herein, a novel donor–acceptor–acceptor (D–A–A) type NIR emitter comprising highly polar cyano group (CN) together with rigid benzo[c][1,2,5]thiadiazole as tandem acceptor and 4,4′-dimethyltriphenylamine as donor is successfully designed. This constructing strategy not only allows the D/A maintain their intrinsic electron-donating/withdrawing characteristics, but also retains high PLQY. In merits of these features, excellent external quantum efficiency (EQE) of 3.8% with peak emission at 692 nm for 15% doped device is achieved. Encouragingly, impressive EQE of 3.1% with the peak emission at 708 nm is also successfully achieved without doping technique. It is believed that these efficiencies are the best or among the best comparing to those of the reported NIR organic light-emitting diodes with similar electroluminescence peak. Notably, efficiency roll-offs of both doped and nondoped device are also quite flat.
Co-reporter:Khan Qasim;Baoping Wang;Yupeng Zhang;Pengfei Li;Yusheng Wang;Shaojuan Li;Shuit-Tong Lee;Wei Lei;Qiaoliang Bao
Advanced Functional Materials 2017 Volume 27(Issue 21) pp:
Publication Date(Web):2017/06/01
DOI:10.1002/adfm.201606874
A specially designed n-type semiconductor consisting of Ca-doped ZnO (CZO) nanoparticles is used as the electron transport layer (ETL) in high-performance multicolor perovskite light-emitting diodes (PeLEDs) fabricated using an all-solution process. The band structure of the ZnO is tailored via Ca doping to create a cascade of conduction energy levels from the cathode to the perovskite. This energy band alignment significantly enhances conductivity and carrier mobility in the CZO ETL and enables controlled electron injection, giving rise to sub-bandgap turn-on voltages of 1.65 V for red emission, 1.8 V for yellow, and 2.2 V for green. The devices exhibit significantly improved luminance yields and external quantum efficiencies of, respectively, 19 cd A−1 and 5.8% for red emission, 16 cd A−1 and 4.2% for yellow, and 21 cd A−1 and 6.2% for green. The power efficiencies of these multicolor devices demonstrated in this study, 30 lm W−1 for green light-emitting PeLED, 28 lm W−1 for yellow, and 36 lm W−1 for red are the highest to date reported. In addition, the perovskite layers are fabricated using a two-step hot-casting technique that affords highly continuous (>95% coverage) and pinhole-free thin films. By virtue of the efficiency of the ETL and the uniformity of the perovskite film, high brightnesses of 10 100, 4200, and 16,060 cd m−2 are demonstrated for red, yellow, and green PeLEDs, respectively. The strategy of using a tunable ETL in combination with a solution process pushes perovskite-based materials a step closer to practical application in multicolor light-emitting devices.
Co-reporter:Yi Yuan;Yun Hu;Ye-Xin Zhang;Jiu-Dong Lin;Ya-Kun Wang;Zuo-Quan Jiang;Shuit-Tong Lee
Advanced Functional Materials 2017 Volume 27(Issue 26) pp:
Publication Date(Web):2017/07/01
DOI:10.1002/adfm.201700986
Significant effort has been made to develop novel material systems to improve the efficiency of near-infrared organic light-emitting diodes (NIR OLEDs). Of those, fluorescent chromophores are mostly studied because of their advantages in cost and tunability. However, it is still rare for fluorescent NIR emitters to present good color purities in the NIR range and to have high external quantum efficiency (EQE). Here, a wedge-shaped D-π-A-π-D emitter APDC-DTPA with thermally activated delayed fluorescence property and a small single-triplet splitting (ΔEst) of 0.14 eV is presented. The non-doped NIR device exhibits excellent performance with a maximum EQE of 2.19% and a peak wavelength of 777 nm. Remarkably, when 10 wt% of APDC-DTPA is doped in 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene host, an extremely high EQE of 10.19% with an emission peak of 693 nm is achieved. All these values represent the best result for NIR OLEDs based on a pure organic fluorescent emitter with similar device structure and color gamut.
Co-reporter:Wen-Cheng Chen, Yi Yuan, Shao-Fei Ni, Ze-Lin Zhu, Jinfeng Zhang, Zuo-Quan JiangLiang-Sheng Liao, Fu-Lung WongChun-Sing Lee
ACS Applied Materials & Interfaces 2017 Volume 9(Issue 8) pp:
Publication Date(Web):February 10, 2017
DOI:10.1021/acsami.6b14638
Organic materials containing arylamines have been widely used as hole-transporting materials as well as emitters in organic light-emitting devices (OLEDs). However, it has been pointed out that the C–N bonds in these arylamines can easily suffer from degradation in excited states, especially in deep-blue OLEDs. In this work, phenanthro[9,10-d]imidazole (PI) is proposed as a potential donor with higher stability than those of arylamines. Using PI as the donor, a donor–acceptor type deep-blue fluorophore 1-phenyl-2-(4″-(1-phenyl-1H-benzo[d]imidazol-2-yl)-[1,1′:4′,1″-terphenyl]-4-yl)-1H-phenanthro[9,10-d]imidazole (BITPI) is designed and synthesized. Results from UV-aging test on neat films of BITPI and other three arylamine compounds demonstrate that PI is indeed a more stable donor comparing to common arylamines. An OLED using BITPI as an emitter exhibits good device performances (EQE over 7%) with stable deep-blue emission (color index: (0.15, 0.13)) and longer operation lifetime than the similarly structured device using arylamine-based emitter. Single-organic layer device based on BITPI also shows superior performances, which are comparable to the best results from the arylamine-based donor–acceptor emitters, suggesting that PI is a stable donor with good hole transport/injection capability.Keywords: deep-blue OLED; donor−acceptor emitter; high efficiency; high stability; phenanthro[9,10-d]imidazole;
Co-reporter:Ting Xu, Ye-Xin Zhang, Bo Wang, Chen-Chao Huang, Imran MurtazaHong Meng, Liang-Sheng Liao
ACS Applied Materials & Interfaces 2017 Volume 9(Issue 3) pp:
Publication Date(Web):December 30, 2016
DOI:10.1021/acsami.6b13077
A novel exciplex-forming host is applied so as to design highly simplified reddish orange light-emitting diodes (OLEDs) with low driving voltage, high efficiency, and an extraordinarily low efficiency roll-off, by combining N,N-10-triphenyl-10H-spiro [acridine-9,9′-fluoren]-3′-amine (SAFDPA) with 4,7-diphenyl-1,10-phenanthroline (Bphen) doped with trivalent iridium complex bis(2-methyldibenzo[f,h]quinoxaline) (acetylacetonate)iridium(III) (Ir(MDQ)2(acac)). The reddish orange OLEDs achieve a strikingly high power efficiency (PE) of 31.80 lm/W with an ultralow threshold voltage of 2.24 V which is almost equal to the triplet energy level of the phosphorescent reddish orange emitting dopant. The power efficiency of the device with the exciplex-forming host is enhanced, achieving 36.2% mainly owing to the lower operating voltage by the novel exciplex forming cohost, compared with the reference device (23.54 lm/W). Moreover, the OLEDs show extraordinarily low current efficiency (CE) roll-off to 1.41% at the brightness from 500 to 5000 cd/m2 with a maximal CE of 32.87 cd/A (EQEmax = 11.01%). The devices display a good reddish orange color (CIE of (0.628, 0.372) at 500 cd/m2) nearly without color shift with increasing brightness. Co-host architecture phosphorescent OLEDs show a simpler device structure, lower working voltage, and a better efficiency and stability than those of the reference devices without the cohost architecture, which helps to simplify the OLED structure, lower the cost, and popularize OLED technology.Keywords: efficiency roll-off; exciplex-forming host; hole-transport-material-free; OLED; reddish orange phosphorescence;
Co-reporter:Ying-Li Shi;Feng Liang;Yun Hu;Ming-Peng Zhuo;Xue-Dong Wang
Nanoscale (2009-Present) 2017 vol. 9(Issue 39) pp:14792-14797
Publication Date(Web):2017/10/12
DOI:10.1039/C7NR04542E
Efficient electron-injection into the emitting layer (EML) plays a pivotal role in the fabrication of high performance blue quantum dot light-emitting diodes (QLEDs). Herein, we reduce the electron-transporting barrier at the ITO/ETL (electron-transporting layer) interface from 0.7 eV to 0.4 eV by spin-coating a polyethylenimine ethoxylated (PEIE) film (8 nm) on the ITO substrate. Meanwhile, the electron-injection barrier was reduced from 0.5 to 0.1 eV at the ETL/QD interface by employing the incorporation of PEIE (0.1 wt%) into a ZnO layer. These above two interfacial modifications jointly decrease the electron barrier and make the electron transportation easier. As a result, the optimized QLEDs with the 460 nm emission peak exhibit a maximum external quantum efficiency (EQE) of 7.85%, which is enhanced by 1.4 fold compared with the reference device (5.68%). It is demonstrated that the facile interfacial modification by the organic polymer PEIE contributes to the fabrication of high-efficiency blue QLEDs.
Co-reporter:Ying-Li Shi;Feng Liang;Yun Hu;Xue-Dong Wang;Zhao-Kui Wang
Journal of Materials Chemistry C 2017 vol. 5(Issue 22) pp:5372-5377
Publication Date(Web):2017/06/08
DOI:10.1039/C7TC00449D
For the purpose of fabricating solution-processed quantum-dot light-emitting diodes (QLEDs) with high performance, the efficient hole–electron recombination at low current density is particularly pivotal. Herein, to enhance the charge balance of the QLED device, we employed lithium bis(trifluoromethylsulfonyl)imide (Li-TFSI) as a p-type dopant into the hole-transporting material (HTM) of poly(9-vinlycarbazole) (PVK). In the experiment, the increased conductivity and the enhanced charge mobility of the Li-TFSI-doped PVK layer were confirmed by the J–V curves of the hole-only devices and conductive atomic force microscopy (c-AFM). Furthermore, on combining ultraviolet photoelectron spectroscopy (UPS) and the absorption spectra, it was found that the highest occupied molecular orbital (HOMO) of the Li-TFSI-doped PVK layers gradually shifted closer to the Fermi level upon increasing the doping ratios from 0 to 4.5 wt%. Therefore, the hole-injecting barrier decreases from 1.17 eV to 0.64 eV. As a result, the maximum current efficiency and the highest external quantum efficiency (EQE) of our fabricated QLED devices can reach as high as 15.5 cd A−1 and 11.46%, respectively. It was demonstrated that the p-type dopant Li-TFSI in the HTM can contribute to the fabrication of high-performance solution-processed light-emitting diodes.
Co-reporter:Yun Hu;Qiang Wang;Ying-Li Shi;Meng Li;Lei Zhang;Zhao-Kui Wang
Journal of Materials Chemistry C 2017 vol. 5(Issue 32) pp:8144-8149
Publication Date(Web):2017/08/17
DOI:10.1039/C7TC02477K
All-inorganic perovskite materials, i.e. cesium lead halide (CsPbX3 (X = I, Br, Cl)), have attracted much attention in the application of photoelectronic devices, especially in solar cells and light-emitting diodes (LEDs). However, the solubility issue of CsPbX3 restricts their utilization in solution-processed devices. Herein, we demonstrated efficient all-inorganic perovskite LEDs (PeLEDs) via co-evaporation of cesium bromide (CsBr) and lead bromide (PbBr2) based on a vacuum thermal evaporation process. The molar ratio of CsBr to PbBr2, which can be adjusted via the co-evaporation ratio, is proved to be very critical to the device performance. Excess CsBr in the perovskite layer causes poor surface morphology and affects the charge transport. With an optimization of the molar ratio, the PeLEDs based on the equimolar CsBr and PbBr2 exhibit the best green electroluminescence (EL) performance with a maximum external quantum efficiency (EQE) of 1.55%. Meanwhile, the full width at half-maximum (FWHM) of the green EL spectrum is as narrow as 18.5 nm, which can offer high color purity and large color space in display applications.
Co-reporter:Zhi-Zhou Li;Xue-Dong Wang
Journal of Materials Chemistry C 2017 vol. 5(Issue 27) pp:6661-6666
Publication Date(Web):2017/07/13
DOI:10.1039/C7TC02013A
Organic nano/microcrystals with desirable optical/electrical properties and a regular morphology are extensively applied in various optoelectronic devices at the microscale, but the morphology/luminescence-modulation of organic microstructures remains to be a great challenge. Herein, we utilize a protonation/de-protonation process to simultaneously modulate both the luminescence and the morphology of blue-emissive two-dimensional (2D) organic microcrystals, which are self-assembled from 1,4-bis((E)-2-(3-methylpyridin-4-yl)vinyl)benzene (MSP) by a facile solution-exchange method. Impressively, 1D color-tunable MSP·nHCl (n is an integer) organic microwires can be obtained by the protonation process activated by the addition of an acid (such as hydrochloric acid). When n = 2 or n > 2, these obtained MSP·2HCl or MSP·nHCl microcrystals with a 1D wire-morphology emitted yellow light and red light, respectively.
Co-reporter:Junming Li;Shou-Cheng Dong;Andreas Opitz;Norbert Koch
Journal of Materials Chemistry C 2017 vol. 5(Issue 28) pp:6989-6996
Publication Date(Web):2017/07/20
DOI:10.1039/C7TC02248D
Modern high-efficiency organic light-emitting diodes (OLEDs) based on phosphorescence and thermally activated delayed fluorescence (TADF) rely on host materials that are optimized with respect to many properties simultaneously, including thermal stability, photophysical properties, energy levels, and charge carrier transport. Responding to this challenge, we synthesized and investigated carbazole/dibenzothiophene derivatives as potential hosts, in which carbazole acts as electron donating and dibenzothiophene as electron withdrawing unit. Within this series, the carbazole/dibenzothiophene fraction and the linking phenyl spacer length were systematically varied. Through comprehensive assessment of all material parameters mentioned above and the performance of these host in phosphorescent and TADF OLEDs, we could reliably identify the most suitable molecule for applications and provide guidelines for further material development. With 9-(3′-(dibenzo[b,d]thiophen-4-yl)-[1,1′-biphenyl]-3-yl)-9H-carbazole, bearing one carbazole and one dibenzothiophene unit linked with biphenyl in meta position, we achieved high external quantum efficiency for blue (17.9%) and green (19.4%) modern OLEDs.
Co-reporter:Bo Wang;Zhao-Kui Wang;Jian Liang;Meng Li;Yun Hu
Journal of Materials Chemistry C 2017 vol. 5(Issue 41) pp:10721-10727
Publication Date(Web):2017/10/26
DOI:10.1039/C7TC03529B
The high cost of vacuum thermal evaporation and the challenging fabrication of multilayer devices by the solution processing method restrict the commercialization of organic light-emitting diodes (OLEDs). Herein, we introduce a flash evaporation method where an organic film pre-coated on a silicon wafer is re-deposited by sudden exposure to high temperature (∼1000 °C) in a rough vacuum to fabricate small molecule-based multilayer OLEDs. The flash-evaporated organic films maintain the original molecular structure after flash evaporation. Compared with the random molecular orientation of spin-coated small molecule films, flash-evaporated films have a high degree of molecular orientation perpendicular to the substrate surface. As a result, flash-evaporated OLEDs exhibit improved efficiency with low roll-off compared with spin-coated devices. The successful fabrication of a flexible, large-area (20 × 20 mm2) OLED suggests the great potential of the flash evaporation method for fabricating flexible and large area OLEDs with low cost in the future.
Co-reporter:Ming-Peng Zhuo;Feng Liang;Ying-Li Shi;Yun Hu;Rong-Bin Wang;Wei-Fan Chen;Xue-Dong Wang
Journal of Materials Chemistry C 2017 vol. 5(Issue 47) pp:12343-12348
Publication Date(Web):2017/12/07
DOI:10.1039/C7TC04575A
Through a facile solid-state mechanochemical method, we have prepared WO3 nanobelts with a length of ∼80 nm and a width of ∼10 nm, which were doped into PEDOT:PSS as a hybrid hole-injecting layer (HIL) for conventional red quantum dot light-emitting diodes (QLEDs). The work function (WF) of the hybrid HIL was enhanced from 4.91 to 5.25 eV and the hole-injecting barrier was decreased from 0.89 to 0.55 eV. Notably, an optimal red QLED based on the hybrid HIL PEDOT:PSS:WO3 (4.0 wt%) achieved a satisfactory reduction in the driving voltage at the luminance of 100 cd A−1 from 5.18 V (pristine PEDOT:PSS) to 2.97 V. Moreover, the optimal device exhibits a maximal current efficiency of 15.5 cd A−1 and a high external quantum efficiency (EQE) of 10.60%, which are nearly two-folds higher than those (8.0 cd A−1 and 5.82%) of the reference device based on pristine PEDOT:PSS. It was demonstrated that doping these as-prepared WO3 nanobelts into the PEDOT:PSS could be an effective route toward high-performance QLEDs.
Co-reporter:Yongxi Li;Lian Zhong;Bhoj Gautam;Hai-Jun Bin;Jiu-Dong Lin;Fu-Peng Wu;Zhanjun Zhang;Zuo-Quan Jiang;Zhi-Guo Zhang;Kenan Gundogdu;Yongfang Li
Energy & Environmental Science (2008-Present) 2017 vol. 10(Issue 7) pp:1610-1620
Publication Date(Web):2017/07/12
DOI:10.1039/C7EE00844A
Low-bandgap polymers/molecules are an interesting family of semiconductor materials, and have enabled many recent exciting breakthroughs in the field of organic electronics, especially for organic photovoltaics (OPVs). Here, such a low-bandgap (1.43 eV) non-fullerene electron acceptor (BT-IC) bearing a fused 7-heterocyclic ring with absorption edge extending to the near-infrared (NIR) region was specially designed and synthesized. Benefitted from its NIR light harvesting, high performance OPVs were fabricated with medium bandgap polymers (J61 and J71) as donors, showing power conversion efficiencies of 9.6% with J61 and 10.5% with J71 along with extremely low energy loss (0.56 eV for J61 and 0.53 eV for J71). Interestingly, femtosecond transient absorption spectroscopy studies on both systems show that efficient charge generation was observed despite the fact that the highest occupied molecular orbital (HOMO)–HOMO offset (ΔEH) in the blends was as low as 0.10 eV, suggesting that such a small ΔEH is not a crucial limitation in realizing high performance of NIR non-fullerene based OPVs. Our results indicated that BT-IC is an interesting NIR non-fullerene acceptor with great potential application in tandem/multi-junction, semitransparent, and ternary blend solar cells.
Co-reporter:Zhao-Kui Wang;Meng Li;Ying-Guo Yang;Yun Hu;Heng Ma;Xing-Yu Gao
Advanced Materials 2016 Volume 28( Issue 31) pp:6695-6703
Publication Date(Web):
DOI:10.1002/adma.201600626
Co-reporter:Ya-Kun Wang;Zhong-Cheng Yuan;Guo-Zheng Shi;Yong-Xi Li;Qian Li;Fei Hui;Bao-Quan Sun;Zuo-Quan Jiang
Advanced Functional Materials 2016 Volume 26( Issue 9) pp:1375-1381
Publication Date(Web):
DOI:10.1002/adfm.201504245
Chemical doping is often used to enhance electric conductivity of the conjugated molecule as hole-transporting material (HTM) for the application in optoelectronics. However, chemical dopants can promote ion migration at the electrical field, which deteriorates the device efficiency as well as increases the fabrication cost. Here, two star HTMs, namely 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine) 9,9′-spirobifluorene (Spiro-OMeTAD) and poly(triarylamine) are subjeted to chemical combination to yield dopant-free N2,N2,N2′,N2′,N7,N7,N7′,N7′-octakis(4-methoxyphenyl)-10-phenyl-10H-spiro[acridine-9,9′-fluorene]-2,2′,7,7′-tetraamine (SAF-OMe). The power conversion efficiencies (PCEs) of 12.39% achieved by solar cells based on pristine, dopant-free SAF-OMe are among the highest reported for perovskite solar cells and are even comparable to devices based on chemically doped Spiro-OMeTAD (14.84%). Moreover, using a HTM comprised of SAF-OMe with an additional dopant results in a record PCE of 16.73%. Compared to Spiro-OMeTAD-based devices, SAF-OMe significantly improves stability.
Co-reporter:Xiang-Yang Liu, Feng Liang, Yi Yuan, Zuo-Quan Jiang and Liang-Sheng Liao
Journal of Materials Chemistry A 2016 vol. 4(Issue 33) pp:7869-7874
Publication Date(Web):25 Jul 2016
DOI:10.1039/C6TC02180H
Two novel materials, 10-(6-(dibenzo[b,d]furan-1-yl)pyrazin-2-yl)-9,9-diphenyl-9,10-dihydroacridine (PrFPhAc) and 10-(6-(dibenzo[b,d]thiophen-1-yl)pyrazin-2-yl)-9,9-diphenyl-9,10-dihydroacridine (PrTPhAc), were designed and synthesized by introducing heterocyclic pyrazine between 9,10-dihydroacridine and dibenzofuran/dibenzothiophene moieties. The basic properties, such as thermal, photophysical and electrochemical properties, were systematically investigated and compared. Both the materials have suitable triplet energies for red phosphorescent organic light-emitting diodes, and dibenzofuran (DBF) derivative PrFPhAc was finally achieved with superior external quantum efficiency of 22%.
Co-reporter:Bo Wang, Lei Zhang, Yun Hu, Xiao-Bo Shi, Zhao-Kui Wang and Liang-Sheng Liao
Journal of Materials Chemistry A 2016 vol. 4(Issue 27) pp:6570-6574
Publication Date(Web):14 Jun 2016
DOI:10.1039/C6TC01624C
Carrier injection plays an important role in determining the device performance of organic light-emitting diodes (OLEDs). 1,4,5,8,9,11-Hexaazatriphenylene hexacarbonitrile (HAT-CN) has been widely used as an effective material to promote the hole injection when fabricating vacuum deposited OLEDs. However, serious crystallization occurs in solution-processed HAT-CN films, which weakens its hole injection ability in OLEDs. Herein, we demonstrate a solution-processed composite film as the hole injection layer (HIL) in OLEDs developed by mixing HAT-CN with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ). The crystallization is suppressed effectively by optimizing the mixing ratio. In addition, a doping of HAT-CN:F4-TCNQ composite film contributes to a decreased hole injection barrier, which can be reflected from the current density–voltage curve. Furthermore, HAT-CN:F4-TCNQ is successfully combined with MoO3 doped copper phthalocyanine-3,4′,4′′,4′′′-tetra-sulfonated acid tetra sodium salt (TS-CuPc) as bi-HIL in solution-processable blue phosphorescent OLEDs, which exhibit a maximum current efficiency of 16.7 cd A−1.
Co-reporter:Ya-Li Deng, Lin-Song Cui, Yuan Liu, Zhao-Kui Wang, Zuo-Quan Jiang and Liang-Sheng Liao
Journal of Materials Chemistry A 2016 vol. 4(Issue 6) pp:1250-1256
Publication Date(Web):06 Jan 2016
DOI:10.1039/C5TC03793J
A new red phosphorescent material Ir(dmppm)2(dmd), which is a pyrimidine-based iridium(III) complex, has been synthesized and successfully used to fabricate solution-processed red and white organic light-emitting diodes (OLEDs). Due to its excellent solubility in common organic solvents and its good compatibility with the host material, a record current efficiency of 27.2 cd A−1 so far with satisfactory Commission International de l'Eclairage (CIE) coordinates of (0.60, 0.40) has been achieved for partially solution-processed red OLEDs by using Ir(dmppm)2(dmd) as a dopant. Furthermore, the fabricated two-component “warm-white” OLEDs based on the Ir(dmppm)2(dmd) red emitter demonstrate a maximum current efficiency of 28.9 cd A−1, which can meet the call for physiologically-friendly indoor illumination.
Co-reporter:Femi Igbari, Meng Li, Yun Hu, Zhao-Kui Wang and Liang-Sheng Liao
Journal of Materials Chemistry A 2016 vol. 4(Issue 4) pp:1326-1335
Publication Date(Web):17 Dec 2015
DOI:10.1039/C5TA07957H
The fabrication and device parameters of inverted planar heterojunction (PHJ) organic–inorganic lead mixed-halide (CH3NH3PbI3−xClx) perovskite based solar cells (PSCs) using a:CuAlO2 as the hole selective buffer layer between the ITO electrode and PEDOT:PSS were demonstrated. Thin films of a:CuAlO2 were derived from a pre-fabricated polycrystalline CuAlO2 ceramic target by using the direct current (d.c.) magnetron sputtering technique. The one-step spin coating method was used to prepare the perovskite layer. A short circuit current density (Jsc) of 21.98 mA cm−2, an open circuit voltage (Voc) of 0.88 V, a fill factor (FF) of 0.75 and a power conversion efficiency (PCE) of 14.52% were achieved for the optimized device. These improved device parameters were also accompanied by improved stability as a result of sandwiching the ambient stable a:CuAlO2 layer with decent conductivity between the ITO and the PEDOT:PSS layers. The versatility of this material application was also demonstrated as a similar improvement in device performance and stability, which was observed by using the prepared a:CuAlO2 in another perovskite solar cell system based on CH3NH3PbI3 prepared by the two-step spin-coating method.
Co-reporter:Xiang-Yang Liu, Feng Liang, Yi Yuan, Lin-Song Cui, Zuo-Quan Jiang and Liang-Sheng Liao
Chemical Communications 2016 vol. 52(Issue 52) pp:8149-8151
Publication Date(Web):08 Jun 2016
DOI:10.1039/C6CC02856J
A thermally activated delayed fluorescence material 2,6-bis(9,9-diphenylacridin-10(9H)-yl)pyrazine was designed and synthesized. The twisted configuration made it possesses very small singlet–triplet splitting. A red electroluminescent device based on this new host material is able to achieve ∼26% external quantum efficiency and relatively flat efficiency roll-off.
Co-reporter:Lei Zhang, Ye-Xin Zhang, Yun Hu, Xiao-Bo Shi, Zuo-Quan Jiang, Zhao-Kui Wang, and Liang-Sheng Liao
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 25) pp:16186-16191
Publication Date(Web):June 9, 2016
DOI:10.1021/acsami.6b01304
Blue phosphorescent organic light-emitting diode (PhOLED) with a high maximum external quantum efficiency (EQE) of 26.6% was achieved using a new material, 2,8-bis(9,9-dimethylacridin-10(9H)-yl)dibenzo[b,d]furan (DBF-DMS) with a small bandgap, as the host. The device with DBF-DMS showed improved performance compared with that with 1,3-di-9-carbazolylbenzene, which is ascribed to the enhancement in carrier injection and transporting abilities and material stability of DBF-DMS. A lifetime of more than 100 h (time to 50% of the initial luminance, 1000 cd/m2 with an EQE of 19.6%) in the other DBF-DMS-based device is obtained by further utilizing better device structure. This is a report indicating that host material with a small bandgap like DBF-DMS can be successfully utilized toward blue PhOLEDs with high performance.
Co-reporter:Miao-Miao Xue, Chen-Chao Huang, Yi Yuan, Lin-Song Cui, Yong-Xi Li, Bo Wang, Zuo-Quan Jiang, Man-Keung Fung, and Liang-Sheng Liao
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 31) pp:20230
Publication Date(Web):July 20, 2016
DOI:10.1021/acsami.6b05064
Borane is an excellent electron-accepting species, and its derivatives have been widely used in a variety of fields. However, the use of borane derivatives as host materials in OLEDs has rarely reported because the device performance is generally not satisfactory. In this work, two novel spiro-bipolar hosts with incorporated borane were designed and synthesized. The strategies used in preparing these materials were to increase the spatial separation of the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) in the molecules, tune the connecting positions of functional groups, and incorporate specific functional groups with desirable thermal stability. Based on these designs, phosphorescent OLEDs with borane derivatives as hosts and with outstanding device performances were obtained. In particular, devices based on SAF-3-DMB/FIrpic exhibited an external quantum efficiency (EQE) of >25%. More encouragingly, the device was found to have quite a low efficiency roll-off, giving an efficiency of >20% even at a high brightness of 10000 cd/m2. Furthermore, the EQE of the three-color-based (R + G + B) white OLED employing SAF-3-DMB as a host was also as high as 22.9% with CIE coordinates of (x, y) = (0.40, 0.48). At a brightness of 5000 cd/m2, there was only a 3% decrease in EQE from its maximum value, implying a very low efficiency roll-off.Keywords: borane derivatives; high efficiency; low efficiency roll-off; molecular orbital spatial separation; spiro-bipolar hosts
Co-reporter:Xiang-Yang Liu, Feng Liang, Lei Ding, Qian Li, Zuo-Quan Jiang, Liang-Sheng Liao
Dyes and Pigments 2016 Volume 126() pp:131-137
Publication Date(Web):March 2016
DOI:10.1016/j.dyepig.2015.11.016
•It was explored to synthesize derivatives of 9,10-dihydroacridine via the C3 position.•The materials showed high thermal stability and high triplet energy.•Blue & red PHOLED devices exhibited over 10% external quantum efficiencies with low roll-off.A new intermediate, 3-bromo-9,9-diphenyl-9,10-dihydroacridine, based on 9,10-dihydroacridine was synthesized and thereby a new host material, 2,6-bis(9,9,10-triphenyl-9,10-dihydroacridin-3-yl)pyridine, via the intermediate was designed and prepared. This intermediate directed a meta-derivation and could make the resulted host retain triplet energy of 2.68 eV. Besides, the rigid backbone along with the substituted phenyl rings at C9 position could benefit the thermal and morphological stabilities of host. According to these features arise from the key intermediate, blue and red phosphorescent organic light-emitting diodes were fabricated and external quantum efficiencies above 10% were achieved with relative flat roll-off.
Co-reporter:Lei Ding, Shuai Du, Lin-Song Cui, Fang-Hui Zhang, Liang-Sheng Liao
Organic Electronics 2016 Volume 37() pp:108-114
Publication Date(Web):October 2016
DOI:10.1016/j.orgel.2016.06.012
•Two novel spirobifluorene hosts were designed with high triplet energy.•Both materials showed high glass transition temperatures over 150 °C.•The FIrpic based PHOLEDs hosted by SF3Cz1 and SF3Cz2 exhibited high EQEs of 18.1% and 19.7% respectively.•Two-color warm white PHOLEDs hosted by SF3Cz1 and SF3Cz2 also achieved high EQEs and low efficiency roll-offs.Two novel spiro-based host materials, namely 3-(9,9′-spirobi[fluoren]-6-yl)-9-phenyl-9H-carbazole (SF3Cz1) and 9-(3-(9,9′-spirobi[fluoren]-6-yl)phenyl)-9H-carbazole (SF3Cz2) were designed and synthesized. Due to the meta-linkage of spirobifluorene backbone, both SF3Cz1 and SF3Cz2 possess triplet energies over 2.70 eV, indicating they could serve as suitable hosts for blue and even white phosphorescent organic light-emitting diodes (PHOLEDs). The fabricated bis(4,6-(difluorophenyl)-pyridinato -N,C′)picolinate (FIrpic) based PHOLEDs hosted by SF3Cz1 and SF3Cz2 exhibited excellent performance with maximum external quantum efficiencies (EQEs) of 18.1% and 19.7%, respectively. Two-color warm white PHOLEDs fabricated by utilizing SF3Cz1 and SF3Cz2 as hosts also achieved high EQEs and low efficiency roll-offs. The results demonstrate that SF3Cz1 and SF3Cz2 are promising hosts for blue and white PHOLEDs.
Co-reporter:Xun Tang, Min Qian, Dong-Ying Zhou, Lei Ding, Yun Hu, Liang-Sheng Liao
Organic Electronics 2016 Volume 28() pp:217-224
Publication Date(Web):January 2016
DOI:10.1016/j.orgel.2015.10.037
•A modification layer is used to oxidize surface contaminants on electrodes.•“Dirty” substrate with the modification layer is useful to make electronic devices.•High-performance organic light-emitting diodes can be fabricated using the layer.An organic molecule, hexaazatriphenylene hexacarbonitrile (HAT-CN), is found that it can be used not only as a hole-injecting material but also a surface modification material to clean contaminated substrate electrodes for the fabrication of organic electronic devices. As an example, HAT-CN can modify or “clean” indium-tin-oxide (ITO) anode surface in organic light-emitting diodes (OLEDs). Negative effect from ITO surface contamination on the electroluminescence performance of OLEDs can be dramatically reduced with this modification layer. As a result, the OLEDs with the same device architecture but with different ITO surface conditions, even with intentional contamination, can all exhibit substantially identical and superior electroluminescence performance. The surface modification function of this material is feasibly useful for the real fabrications of OLEDs as well as for advanced research on other organic electronic devices.An organic modification layer, which is capable of modifying or “cleaning” the surface of a substrate electrode due to its strong oxidizing property, may let people use “dirty” substrate without going through a painful and time-consuming cleaning process to fabricate high performance organic electronic devices. Taking organic light-emitting diodes (OLEDs) as example, no matter the substrate electrodes are contaminated or not (i.e. with quite different surface conditions), the electroluminescent characteristics from the OLEDs are almost identical and superior if a “cleaning” layer is formed on the substrate electrodes.
Co-reporter:Femi Igbari, Qi-Xun Shang, Yue-Min Xie, Xiu-Juan Zhang, Zhao-Kui Wang and Liang-Sheng Liao
RSC Advances 2016 vol. 6(Issue 34) pp:28801-28808
Publication Date(Web):14 Mar 2016
DOI:10.1039/C6RA02700H
An approach to achieve improved performance in pentacene-based organic field effect transistors (OFETs) using high-k AlOx prepared by a low temperature sol–gel technique as a thin buffer layer on a SiO2 gate dielectric was demonstrated. The maximum processing temperature for the AlOx thin layer was 150 °C. The resulting all-inorganic SiO2/AlOx bilayer gate dielectric system exhibited a low leakage current density <1 × 10−8 A cm−2 under an applied electric field strength of 1.8 MV cm−1, a smooth surface with an rms of 0.11 nm and an equivalent dielectric constant (k) of 4.13. The OFET fabricated as a result of this surface modification exhibited a significantly improved field effect mobility of 0.81 cm2 V−1 s−1 when compared with a reference device with a SiO2 single layer gate dielectric, which had a lower mobility of 0.28 cm2 V−1 s−1.
Co-reporter:Zhao-Kui Wang, Xiu Gong, Meng Li, Yun Hu, Jin-Miao Wang, Heng Ma, and Liang-Sheng Liao
ACS Nano 2016 Volume 10(Issue 5) pp:5479
Publication Date(Web):April 29, 2016
DOI:10.1021/acsnano.6b01904
Perovskite crystallization and interface engineering are regarded as the most crucial factors in achieving high-performance planar heterojunction (PHJ) perovskite solar cells (PSCs). Herein, we demonstrate a thin perylene underlayer via a solution-processable method. By using branch-shaped perylene film as a seed-mediated underlayer, crystalline perovskites with fabric morphology can be formed, which allows for obvious improvement in absorption by a light scattering effect. With its deep highest occupied molecular orbital (HOMO) level, perylene also plays an important role in the energy-level tailoring of poly(3,4-ethylenedioxythiophene): poly(styrenesulphonate) (PEDOT:PSS) and CH3NH3PbIxCl3–x. In addition, perylene and perovskites form a fully crystalline heterojunction, which is beneficial for minimizing the defect and trap densities. Due to these merits, a maximum power conversion efficiency of 17.06% with improved cell stability is achieved. The finding in this work provides a simple route to control perovskite crystallizaition and to optimize the interfaces in PHJ PSCs simultaneously.Keywords: induced crystallization; interface engineering; perovskite solar cells; perylene underlayer; stability
Co-reporter:Yongxi Li, Deping Qian, Lian Zhong, Jiu-Dong Lin, Zuo-Quan Jiang, Zhi-Guo Zhang, Zhanjun Zhang, Yongfang Li, Liang-Sheng Liao, Fengling Zhang
Nano Energy 2016 Volume 27() pp:430-438
Publication Date(Web):September 2016
DOI:10.1016/j.nanoen.2016.07.019
•Ten-fused ring with selenium atom make the absorption edge of IDTIDSe-IC red-shift to 850 nm.•Combined with polymer J51, the absorption of active layer can cover all the visible region.•Effective exciton dissociation is achieved under very small HOMO offset ~0.12 eV.•High JSC of 15.16 mA/cm2, VOC of 0.91 V as well as high efficiency over 8% are achieved.A non-fullerene electron acceptor bearing a novel backbone with fused 10-heterocyclic ring (indacenodithiopheno-indacenodiselenophene), denoted by IDTIDSe-IC is developed for fullerene free polymer solar cells. IDTIDSe-IC exhibits a low band gap (Eg=1.52 eV) and strong absorption in the 600–850 nm region. Combining with a large band gap polymer J51 (Eg=1.91 eV) as donor, broad absorption coverage from 300 nm to 800 nm is obtained due to complementary absorption of J51 and IDTIDSe-IC, which enables a high PCE of 8.02% with a VOC of 0.91 V, a JSC of 15.16 mA/cm2 and a FF of 58.0% in the corresponding PSCs. Moreover, the EQE of 50–65% is achieved in the absorption range of IDTIDSe-IC with only about 0.1 eV HOMO difference between J51 and IDTIDSe-IC.A non-fullerene electron acceptor bearing a novel backbone with fused 10-heterocyclic ring (indacenodithiopheno-indacenodiselenophene), denoted by IDTIDSe-IC was developed for fullerene free polymer solar cells. This molecule exhibits low band gap (Eg=1.52 eV), strong absorption in the 600-850 nm region. When using a large band gap polymer J51 (Eg=1.91 eV) as donor, complementary absorption of the polymer donor and acceptor was obtained. The PSC based on J51:IDTIDSe-IC gives a high PCE of 8.02% with a VOC of 0.91 V, a JSC of 15.16 mA cm−2 and a FF of 58.0%. Moreover, the HOMO difference between J51:IDTIDSe-IC is as small as ~0.1 eV, which indicates the small driving force for hole transfer.
Co-reporter:Lin-Song Cui;Yue-Min Xie;Ya-Kun Wang;Cheng Zhong;Ya-Li Deng;Xiang-Yang Liu;Zuo-Quan Jiang
Advanced Materials 2015 Volume 27( Issue 28) pp:4213-4217
Publication Date(Web):
DOI:10.1002/adma.201501376
Co-reporter:Xiao-Bo Shi;Yun Hu;Bo Wang;Lei Zhang;Zhao-Kui Wang
Advanced Materials 2015 Volume 27( Issue 42) pp:6696-6701
Publication Date(Web):
DOI:10.1002/adma.201503003
Co-reporter:Lei Ding;Shou-Cheng Dong;Zuo-Quan Jiang;Hua Chen
Advanced Functional Materials 2015 Volume 25( Issue 4) pp:645-650
Publication Date(Web):
DOI:10.1002/adfm.201403402
High-efficiency blue phosphorescence devices with external quantum efficiencies above 25% are developed using a new bipolar host material, diphenyl(10-phenyl-10H-spiro[acridine-9,9′-fluoren]-2′-yl)phosphine oxide (POSTF), which is constructed in orthogonal molecular structure with a spiro-coree. The separation of bipolarity from effective spiro-fluorene-triphenylamine (STF) structure is elucidated and its versatility in device is evaluated by two kinds of sky-blue phosphors. Noticeably, large-size white light-emitting panel (150 mm × 150 mm) is fabricated with max power efficiency of 75.9 l m W−1 using this new host.
Co-reporter:Xiu Gong;Meng Li;Xiao-Bo Shi;Heng Ma;Zhao-Kui Wang
Advanced Functional Materials 2015 Volume 25( Issue 42) pp:6671-6678
Publication Date(Web):
DOI:10.1002/adfm.201503559
A key issue for perovskite solar cells is the stability of perovskite materials due to moisture effects under ambient conditions, although their efficiency is improved constantly. Herein, an improved CH3NH3PbI3−xClx perovskite quality is demonstrated with good crystallization and stability by using water as an additive during crystal perovskite growth. Incorporating suitable water additives in N,N-dimethylformamide (DMF) leads to controllable growth of perovskites due to the lower boiling point and the higher vapor pressure of water compared with DMF. In addition, CH3NH3PbI3−xClx · nH2O hydrated perovskites, which can be resistant to the corrosion by water molecules to some extent, are assumed to be generated during the annealing process. Accordingly, water additive based perovskite solar cells present a high power conversion efficiency of 16.06% and improved cell stability under ambient conditions compared with the references. The findings in this work provide a route to control the growth of crystal perovskites and a clue to improve the stability of organic–inorganic halide perovskites.
Co-reporter:Yan-Qiu Sun, Yi-Long Lei, Xu-Hui Sun, Shuit-Tong Lee, and Liang-Sheng Liao
Chemistry of Materials 2015 Volume 27(Issue 4) pp:1157
Publication Date(Web):December 26, 2014
DOI:10.1021/cm5027249
A series of crystalline mixed cocrystal microtubes comprising organic charge-transfer (CT) complexes has been prepared. The emission colors of the mixed cocrystal microtubes can be tailored from green to orange at low dopant concentrations (0 < x ⩽ 5%), while their hexagonal cross sections can transform into square ones gradually at higher concentrations (0.15 < x < 1). In addition, we can further extend the solvent-processed synthetic route to other CT pairs based on structural compatibility consideration.
Co-reporter:Min Qian, Meng Li, Xiao-Bo Shi, Heng Ma, Zhao-Kui Wang and Liang-Sheng Liao
Journal of Materials Chemistry A 2015 vol. 3(Issue 25) pp:13533-13539
Publication Date(Web):20 May 2015
DOI:10.1039/C5TA02265G
Anode modification by doping silver nano-particles (Ag NPs) into poly(3,4-ethylene dioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) and cathode interfacial modification by inserting solution-processed bathophenanthroline (sBphen) in CH3NH3PbI3−xClx based planar perovskite solar cells are investigated. Prior to the optical effect such as localized surface plasmon resonance, the Ag-NPs distributed in PEDOT:PSS mainly cause an improvement in the electrical property of PEDOT:PSS–Ag NPs composite films. The sBphen interfacial layer modified the surface morphology of perovskite/phenyl-C61-butyric acid methyl ester (PC61BM) films by filling the voids on the surface of perovskite/PC61BM effectively, which led to an obvious improvement in the fill factor. Accordingly, an efficient device with a power conversion efficiency of 15.75% was achieved due to the simultaneous cathode and anode interfacial modification.
Co-reporter:Mei-Feng Xu, Hong Zhang, Su Zhang, Hugh L. Zhu, Hui-Min Su, Jian Liu, Kam Sing Wong, Liang-Sheng Liao and Wallace C. H. Choy
Journal of Materials Chemistry A 2015 vol. 3(Issue 27) pp:14424-14430
Publication Date(Web):08 Jun 2015
DOI:10.1039/C5TA02730F
CH3NH3PbI3 is commonly used in perovskite solar cells due to its long diffusion length and good crystallinity. In this paper, in the one-step approach using CH3NH3I and PbCl2 for forming the perovskite, we present a new low temperature annealing approach of gradually increasing the temperature to fabricate perovskite films. Various temperatures and temperature ranges for the formation of perovskite films have been studied. Using the gradual annealing process, we can tune the amount of chlorine in the atomic ratio of chlorine/iodine from 1.2 to 4.0%. Meanwhile, the gradual annealing process influences the quality of the perovskite film and importantly the device performance. The results show that through the optimized process, the film quality is improved with high surface coverage and good photoluminescence and reproducibility. We find that a higher amount of chlorine in the perovskite film plays a positive role in the device performance in the approach for achieving a power conversion efficiency of 14.9% with no obvious hysteresis.
Co-reporter:Xun Tang, Lei Ding, Yan-Qiu Sun, Yue-Min Xie, Ya-Li Deng, Zhao-Kui Wang and Liang-Sheng Liao
Journal of Materials Chemistry A 2015 vol. 3(Issue 48) pp:12399-12402
Publication Date(Web):19 Oct 2015
DOI:10.1039/C5TC03108G
Green phosphorescent inverted organic light-emitting diodes (IOLEDs) with 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN)/aluminium/n-doped 4,7-diphenyl-1,10-phenanthroline (Bphen) used as an electron injection layer (EIL) were demonstrated. The IOLED shows the lowest driving voltage of 4.5 V at 10000 cd m−2 to date. The electron injection effects of different interlayers were further investigated by ultraviolet photoelectron spectroscopy (UPS) and evaluating the electron injection efficiency. For application in large-sized OLEDs, a 120 × 120 mm2 flexible IOLED was successfully fabricated based on this inverted structure.
Co-reporter:Xiang-Yang Liu, Feng Liang, Lei Ding, Shou-Cheng Dong, Qian Li, Lin-Song Cui, Zuo-Quan Jiang, Hua Chen and Liang-Sheng Liao
Journal of Materials Chemistry A 2015 vol. 3(Issue 35) pp:9053-9056
Publication Date(Web):10 Aug 2015
DOI:10.1039/C5TC01828E
The introduction of spiro-acridine-fluorene (SAF) can affect the electronic structure of the whole molecule, which made SAF-based materials exhibit totally different photophysical properties from conventional spirobifluorene-based materials. With these properties, an external quantum efficiency of nearly 25% was achieved for sky-blue phosphorescent organic light-emitting diodes.
Co-reporter:Ya-Li Deng, Yue-Min Xie, Lei Zhang, Zhao-Kui Wang and Liang-Sheng Liao
Journal of Materials Chemistry A 2015 vol. 3(Issue 24) pp:6218-6223
Publication Date(Web):18 May 2015
DOI:10.1039/C5TC00851D
The authors develop an aqueous solution-processed hole injection layer, MoO3 doped copper phthalocyanine-3,4′,4′′,4′′′-tetra-sulfonated acid tetra sodium salt (TS-CuPc), in organic light-emitting diodes (OLEDs) via an environmentally-friendly and easy fabrication process. The generation of a charge transfer complex in TS-CuPc:MoO3 composite films is confirmed by absorption spectra and X-ray photoemission spectroscopy (XPS) measurements. Enhanced hole injection in OLEDs is attributed to the decreased hole barrier at the ITO side, which is in agreement with the Schottky thermal emission evaluation. The efficient modification of ITO by TS-CuPc:MoO3 is further confirmed by ultraviolet photoemission spectroscopy (UPS) measurements.
Co-reporter:Yue-Min Xie, Lin-Song Cui, Yuan Liu, Feng-Shuo Zu, Qian Li, Zuo-Quan Jiang and Liang-Sheng Liao
Journal of Materials Chemistry A 2015 vol. 3(Issue 20) pp:5347-5353
Publication Date(Web):23 Apr 2015
DOI:10.1039/C5TC00523J
A new host material BCz–Si for blue and white phosphorescent organic light-emitting devices was designed and synthesized. The introduction of the triphenylsilyl moiety into the BCz unit can efficiently tune the HOMO/LUMO energy levels and maintain high triplet energy. Its carrier mobility, thermal, photophysical, and electrochemical properties were also systematically investigated. The high triplet energy of BCz–Si ensures efficient energy transfer from the host to the triplet emitter FIrpic. The blue device using BCz–Si as a host material achieved a maximum quantum efficiency of 21.0%, corresponding to a current efficiency and power efficiency as high as 46.5 cd A−1 and 45.8 lm W−1, respectively; meanwhile, high efficiency white phosphorescent OLEDs hosted by BCz–Si were also fabricated with a maximum external quantum efficiency of 24.6%, 70.5 cd A−1 for two-color based and 21.5%, 50.1 cd A−1 for three color based devices.
Co-reporter:Xiao-Bo Shi, Min Qian, Dong-Ying Zhou, Zhao-Kui Wang and Liang-Sheng Liao
Journal of Materials Chemistry A 2015 vol. 3(Issue 8) pp:1666-1671
Publication Date(Web):15 Jan 2015
DOI:10.1039/C4TC02596B
The authors demonstrate a honeycomb structured organic light-emitting diode (OLED) with high enhancements greater than 2.0 fold and 2.3 fold in current efficiency and power efficiency, respectively. The dispersion relationships in both planar and nano-honeycomb structured OLEDs are calculated through numerical simulations utilizing the finite-difference time-domain method and measured through the electroluminescence spectra. There is good agreement between the numerically calculated and the experimentally measured dispersion relationships for the nano-honeycomb structured OLEDs. Improved light out-coupling efficiency is mainly attributed to the efficient extraction of the waveguide and the surface plasmon polariton (SPP) loss modes in the devices. Particularly, most of the extracted energy is verified to be originated from the SPP loss mode in honeycomb structured OLEDs.
Co-reporter:Zhao-Kui Wang, Meng Li, Da-Xing Yuan, Xiao-Bo Shi, Heng Ma, and Liang-Sheng Liao
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 18) pp:9645
Publication Date(Web):April 21, 2015
DOI:10.1021/acsami.5b01330
Planar structure has been proven to be efficient and convenient in fabricating low-temperature and solution-processing perovkite solar cells (PSCs). Interface control and crystal film growth of organometal halide films are regarded as the most important factors to obtain high-performance PSCs. Herein, we report a solution-processed PEDOT:PSS-GeO2 composite films by simply incorporating the GeO2 aqueous solution into the PEDOT:PSS aqueous dispersion as a hole transport layer in planar PSCs. Besides the merits of high conductivity, ambient stability and interface modification of PEDOT:PSS-GeO2 composite films, the formed island-like GeO2 particles are assumed to act as growing sites of crystal nucleus of perovskite films during annealing. By the seed-mediation of GeO2 particles, a superior CH3NH3PbI3–xClx crystalline film with large-scale domains and good film uniformity was obtained. The resulting PSC device with PEDOT:PSS-GeO2 composite film as HTL shows a best performance with 15.15% PCE and a fill factor (FF) of 74%. There is a remarkable improvement (∼37%) in PCE, from 9.87% to 13.54% (in average for over 120 devices), compared with the reference pristine PEDOT:PSS based device.Keywords: GeO2 nanoparticles; hole interfacial layer; perovskite solar cells; solution-processing;
Co-reporter:Lin-Song Cui, Yuan Liu, Xiang-Yang Liu, Zuo-Quan Jiang, and Liang-Sheng Liao
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 20) pp:11007
Publication Date(Web):May 6, 2015
DOI:10.1021/acsami.5b02541
Two phosphorescent Ir(III) complexes Ir(ppm)2(acac) and Ir(dmppm)2(acac) were synthesized and characterized with emission ranged at 584/600 nm and high photoluminescence quantum yields (PLQYs) of 0.90/0.92, respectively. The angle-dependent PL spectra analysis reveals that the two orange iridium(III) complexes embodied horizontal orientation property. The high photoluminescence quantum yield and high horizontal dipoles ratio determine their excellent device performance. The devices based on Ir(ppm)2(acac) and Ir(dmppm)2(acac) achieved efficiencies of 26.8% and 28.2%, respectively, which can be comparable to the best orange phosphorescent devices reported in the literature. Furthermore, with the introduction of FIrpic as sky-blue emitter, phosphorescent two-element white organic light-emitting devices (OLEDs) have been realized with external quantum efficiencies (EQEs) as high as 25%, which are the highest values among the reported two-element white OLEDs.Keywords: horizontal orientation; iridium complex; orange emission; organic light-emitting diodes; pyrimidine; warm-white;
Co-reporter:Lei Zhang, Feng-Shuo Zu, Ya-Li Deng, Femi Igbari, Zhao-Kui Wang, and Liang-Sheng Liao
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 22) pp:11965
Publication Date(Web):May 13, 2015
DOI:10.1021/acsami.5b01989
The electrical doping nature of a strong electron acceptor, 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HATCN), is investigated by doping it in a typical hole-transport material, N,N′-bis(naphthalen-1-yl)-N,N′-diphenylbenzidine (NPB). A better device performance of organic light-emitting diodes (OLEDs) was achieved by doping NPB with HATCN. The improved performance could, in principle, arise from a p-type doping effect in the codeposited thin films. However, physical characteristics evaluations including UV–vis absorption, Fourier transform infrared absorption, and X-ray photoelectron spectroscopy demonstrated that there was no obvious evidence of charge transfer in the NPB:HATCN composite. The performance improvement in NPB:HATCN-based OLEDs is mainly attributed to an interfacial modification effect owing to the diffusion of HATCN small molecules. The interfacial diffusion effect of the HATCN molecules was verified by the in situ ultraviolet photoelectron spectroscopy evaluations.Keywords: carrier injection; charge transfer; doping; electron acceptor; interfacial diffusion; organic light-emitting diodes;
Co-reporter:Da-Xing Yuan, Xiao-Dong Yuan, Qing-Yang Xu, Mei-Feng Xu, Xiao-Bo Shi, Zhao-Kui Wang and Liang-Sheng Liao
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 40) pp:26653-26658
Publication Date(Web):14 Sep 2015
DOI:10.1039/C5CP03995A
Perovskite film generally has rough surface morphology due to the voids between the grain domains. Smoothed interface contact between the perovskite layer and the top electrode is critical for planar perovskite solar cells. We reported high efficiency bromine–iodine based perovskite solar cells with a flattening cathode interface by incorporating a solution-processed bathocuproine (sBCP) interfacial layer at the cathode side. Compared with vacuum evaporated bathocuproine (eBCP), sBCP demonstrated an excellent surface modification effect at the cathode side with very smaller charge transfer resistance. Accordingly, a high fill factor exceeding 85% and a power conversion efficiency exceeding 13% in CH3NH3PbI3−xBrx based perovskite solar cells were achieved. The largely improved fill factor was attributed to the smooth film morphology and full surface coverage of perovskite films modified by the solution-processed BCP layer.
Co-reporter:Da-Xing Yuan, Adam Gorka, Mei-Feng Xu, Zhao-Kui Wang and Liang-Sheng Liao
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 30) pp:19745-19750
Publication Date(Web):12 Jun 2015
DOI:10.1039/C5CP02705E
In this work, NH2CHNH2PbI3 (FAPbI3) was employed for light harvesting in inverted planer perovskite solar cells for the first time. Except for the silver cathode, all layers were solution-processed under or below 140 °C. The effect of the annealing process on device performance was investigated. The FAPbI3 solar cells based on a slowed-down annealing shows superior performance compared to the CH3NH3PbI3 (MAPbI3)-based devices, especially for the short circuit current density. A power conversion efficiency of 13.56% was obtained with high short circuit current density of 21.48 mA cm−2. This work paves the way for low-temperature fabrication of efficient inverted planer structure FAPbI3 perovskite solar cells.
Co-reporter:Min Qian, Xiao-Bo Shi, Jie Ma, Jian Liang, Yuan Liu, Zhao-Kui Wang and Liang-Sheng Liao
RSC Advances 2015 vol. 5(Issue 117) pp:96478-96482
Publication Date(Web):04 Nov 2015
DOI:10.1039/C5RA18132A
Aluminum and silver (Al/Ag) stacked films are utilized as the anode in ITO free top-emitting organic light-emitting devices (TEOLEDs). Serious short circuit issues can be resolved since the stacked metal films can increase the crystallinity and smoothen the surface morphology to suppress the poor infiltration between pure Ag and glass substrates. Optical simulations are carried out based on a transfer matrix method and microcavity effect to guide the real fabrications of the fluorescent TEOLEDs. The stacked Al (56 nm)/Ag (44 nm) anode based TEOLEDs demonstrate a better device performance than that of the Al-only anode based devices. The proposed stacked metal electrode provides a simple and convenient way to fabricate TEOLEDs with suppressed electrical short circuits.
Co-reporter:Min Qian, Xiao-Bo Shi, Yuan Liu, Zhi-Ming Jin, Xue-Liang Wang, Zhao-Kui Wang, Liang-Sheng Liao
Organic Electronics 2015 Volume 25() pp:200-205
Publication Date(Web):October 2015
DOI:10.1016/j.orgel.2015.06.030
•An optical energy loss mechanism in OLEDs is introduced based on CPS theory.•Theoretical calculations of both OCE and EQE in OLEDs are carried out.•The simulation results are further validated experimentally.An optical energy loss mechanism including the surface plasmon polariton (SPP) loss, wave guide (WG) mode and substrate mode in organic light-emitting diodes (OLEDs) is introduced based on CPS theory. The theoretical calculations of both the out-coupling efficiency (OCE) and the external quantum efficiency (EQE) of OLEDs are proposed. MATLAB tools are applied to simulate the optical model and provide the results of the two efficiencies. It is demonstrated that, the OCE and the EQE in a green phosphorescence OLED with optimized device structure can reach up to 20% and 27%, respectively (intrinsic quantum efficiency q = 90% assumed). The simulation results based on the theoretical model are further validated experimentally.
Co-reporter:Yue-Min Xie, Lin-Song Cui, Feng-Shuo Zu, Femi Igbari, Miao-Miao Xue, Zuo-Quan Jiang, Liang-Sheng Liao
Organic Electronics 2015 Volume 26() pp:25-29
Publication Date(Web):November 2015
DOI:10.1016/j.orgel.2015.07.018
•Two unipolar host materials can achieve effective separation in frontier molecular orbitals.•Both materials showed high glass transition temperatures over 130 °C.•A blue PHOLED device based on BCz–DBF exhibited a maximum EQE of 25%, which is among the best results of blue hosts.•Tri-color white emission over 21% EQE is also achieved by BCz–DBF.New host materials (BCz–DBT and BCz–DBF) are synthesized by regrouped 3,3-bicarbazole (BCz) and dibenzothiophene (DBT)/dibenzofuran (DBF). Their thermal, electrochemical, electronic absorption and photoluminescent properties are also carefully investigated. The materials exhibit high glass transition temperatures (Tg) of 134 °C and 139 °C, respectively. This kind of molecular design can effectively achieve high triplet energies and suitable highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO/LUMO) energy levels. High external quantum efficiencies (EQE) of sky blue (EQE = 25%) and three-color white (EQE = 21.4%) phosphorescent OLEDs have been achieved by using BCz–DBF as the host material.
Co-reporter:Fu-Peng Wu, Yue-Min Xie, Lin-Song Cui, Xiang-Yang Liu, Qian Li, Zuo-Quan Jiang, Liang-Sheng Liao
Synthetic Metals 2015 Volume 205() pp:11-17
Publication Date(Web):July 2015
DOI:10.1016/j.synthmet.2015.03.023
•A NPO linkage is constructed to obtain high triplet energy.•A NPO linkage serves as a bipolar core for host material.•A bicarbazole backbone gives good hole transportability to host material.•A blue PHOLED device based on PBCz-PO host exhibited a maximum EQE of 13.4%.A new bipolar host material (PBCz-PO) consisting a phosphinic amide is developed to show a resonance effect. It possesses quite high triplet energy (2.76 eV), and this high triplet energy make it suitable to be blue host in phosphorescent organic light-emitting diodes (PHOLEDs). The device with PBCz-PO as a host and FIrpic as a dopant achieved a maximum current efficiency (ηc) of 31.5 cd/A, a maximum power efficiency (ηp) of 31.0 lm/W and a maximum external quantum efficiency (EQE) of 13.4% as well as low driving voltage.
Co-reporter:Ye-Xin Zhang, Lei Ding, Xiang-Yang Liu, Zuo-Quan Jiang, Hua Chen, Shun-Jun Ji, Liang-Sheng Liao
Organic Electronics 2015 20() pp: 112-118
Publication Date(Web):
DOI:10.1016/j.orgel.2015.02.014
Co-reporter:Liang-Sheng Liao
NPG Asia Materials 2015 7(3) pp:e163
Publication Date(Web):2015-03-01
DOI:10.1038/am.2015.9
If you have ever compared the image quality of a laser display and a liquid-crystal display side by side, you might never forget the striking color images from the laser display, which has a color gamut >140% of the standard of the National Television Standards Committee of USA (NTSC). However, the laser display is expensive and bulky in size. Can we expect a vivid display product that is inexpensive, lightweight, flexible, portable, self-emitting, highly stable and highly efficient? Quantum dot light-emitting diodes (QLEDs) would be the best answer. In Nature, Jin and colleagues1 described how a high-performance QLED can be produced through a solution process. The team has fabricated a high-performance, solution-processed red LED that is superior or comparable to state-of-the-art vacuum-deposited organic red LEDs in terms of color purity, quantum efficiency and operational lifetime.Solution-processed QLEDs have been investigated owing to the advantages of low-cost fabrication and their compatibility with flexible substrates.2 However, the overall performance of the QLEDs was inferior to that of the organic LEDs. Jin and Peng’s team1 made great progress in device fabrication. Their deep-red QLEDs exhibit not only a saturated color peak at 640 nm with a full-width at half-maximum (FWHM) of 28 nm corresponding to Commission Internationale de l’Eclairage (CIE) color coordinates of (0.71, 0.29) but also high external quantum efficiencies of up to 20.5% and a long operational lifetime of >100 000 h at 100 cd m−2. There are two important ‘tricks’ for their success. One trick is the synthesis of phase-pure zinc blend CdSe–CdS core shell quantum dots with 10 monolayers for the CdS shell, which possesses a photoluminescence quantum yield of >90%. The other is the insertion of an insulating layer polymethylmethacrylate between the quantum dot layer and an oxide electron-transporting layer that can balance charge recombination in the device and preserve the outstanding properties of the quantum dots.These fabrication techniques present no fundamental obstacles to the improvement of green or blue QLEDs. Recently, both high-efficiency green QLEDs (at 516 nm, FWHM of 21 nm and CIE ~(0.08, 0.78))3 and deep-blue QLEDs (at 452 nm, FWHM of 31 nm and CIE ~(0.153, 0.027))4 have been reported. If we draw the CIE coordinates according to the above-specified red, green and blue colors, we can see the color gamut shown in Figure 1. Once the overall performance of the green and the blue QLEDs can be further improved similar to that of the red QLEDs, a high-efficiency and vivid display with a striking color gamut of >140% of NTSC can certainly be obtained. This extremely high-performance QLED could also be potentially useful as high-efficiency solid-state lighting.
Co-reporter:Zhao Wei, Liang Feng, Jin Zhi-Ming, Shi Xiao-Bo, Yin Peng-Hui, Wang Xue-Ren, Sun Cheng, Gao Zhan-Qi and Liao Liang-Sheng
Journal of Materials Chemistry A 2014 vol. 2(Issue 33) pp:13226-13231
Publication Date(Web):18 Jun 2014
DOI:10.1039/C4TA02369B
An Ag/AgVO3 plasmonic photocatalyst was synthesized via in situ reduction of AgVO3 by NaBH4 at room temperature. The Ag/AgVO3 showed high photocatalytic activity due to the relatively high conductivity and electron-storing capacity of Ag nanoparticles, which facilitate the charge transfer between AgVO3 and Ag nanoparticles. FDTD simulation indicates that the formed Ag nanoparticles induce SPR leading to the increased electric field and the enhanced absorption of visible light.
Co-reporter:Lei Ding, Yan-Qiu Sun, Hua Chen, Feng-Shuo Zu, Zhao-Kui Wang and Liang-Sheng Liao
Journal of Materials Chemistry A 2014 vol. 2(Issue 48) pp:10403-10408
Publication Date(Web):03 Nov 2014
DOI:10.1039/C4TC02082K
An intermediate connector (IC) consisting of lithium (Li) doped 4,7-diphenyl-1,10-phenanthroline (BPhen)/Al/tetrafluoro-tetracyanoquinodimethane (F4-TCNQ)/1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN) is developed for fabricating tandem white organic light-emitting diodes (WOLEDs). An investigation of the charge generation and separation process in Bphen:Li/Al/F4-TCNQ/HAT-CN, which is carried out by analysis of the current–voltage and capacitance–voltage characteristics, shows that the proposed IC structure is suitable as a connecting unit in tandem OLEDs. The tandem WOLED based on a silicon compound host material of 10-phenyl-2′-(triphenylsilyl)-10H-spiro [acridine-9,9′-fluorene] (SSTF) with the proposed IC structure exhibits a maximum current efficiency of 159.2 cd A−1 and a maximum power efficiency of 69.4 lm W−1. For application in large-area OLEDs, a 150 × 150 mm2 tandem lighting panel with maximum efficiencies of 231.8 cd A−1 and 52.9 lm W−1, correlated color temperature of 3000 K and Commission International de I'Eclairage (CIE) coordinates of (0.34, 0.45) is also demonstrated.
Co-reporter:Yuan Liu, Lin-Song Cui, Xiao-Bo Shi, Qian Li, Zuo-Quan Jiang and Liang-Sheng Liao
Journal of Materials Chemistry A 2014 vol. 2(Issue 41) pp:8736-8744
Publication Date(Web):27 Aug 2014
DOI:10.1039/C4TC01619J
Two novel materials, SF2BCz and SF3BCz, which combine spirobifluorene (SF) and carbazole units by meta- and para-bonding, have been designed and synthesized by a straightforward process as hosts in phosphorescent organic light-emitting diodes (PhOLEDs), and their thermal and electronic absorption and photoluminescent properties investigated. The meta-linkage of SF enables SF3BCz to possess high triplet and energy levels and good thermal stability. Blue PhOLEDs featuring SF3BCz as a host give high performance and low roll-off, with an efficiency of 41.4 cd A−1 (39.8 lm W−1) at 100 cd m−2 and 39.7 cd A−1 (29.8 lm W−1) at 1000 cd m−2. In addition, SF3BCz has been adopted as a universal host for white PhOLEDs, with a maximum external quantum efficiency of 21.3% for two-color and 19.8% for three-color-based white devices. By adopting tandem technology, a four-color-based white PhOLED was also successfully constructed, achieving 40% external quantum efficiency and a stable color spectrum.
Co-reporter:Xiao-Dong Yuan, Jian Liang, Yun-Chu He, Qian Li, Cheng Zhong, Zuo-Quan Jiang and Liang-Sheng Liao
Journal of Materials Chemistry A 2014 vol. 2(Issue 31) pp:6387-6394
Publication Date(Web):12 Jun 2014
DOI:10.1039/C4TC00867G
Two novel carbazole derivatives, 3,3′-(2,6-dimethyl-1,4-phenylene)bis(9-phenyl-9H-carbazole) (DMCz) and 3,3′-(2,3,5,6-tetramethyl-1,4-phenylene)bis(9-phenyl-9H-carbazole) (TMCz), are designed and synthesized as host materials for blue phosphorescent organic light emitting diodes (PHOLEDs). Both the materials possess sufficiently high glass transition temperatures and triplet energies for the blue dopant Ir-complex iridium(III) bis(4,6-(difluorophenyl)-pyridinato-N,C′)picolinate (FIrpic, 2.65 eV). The device using DMCz as the host material showed a better performance than that of TMCz with a maximum power efficiency of 36.0 ± 0.7 lm per W, a maximum current efficiency of 43.7 ± 0.6 cd per A and a maximum external quantum efficiency (EQE) of 18.5 ± 0.1%.
Co-reporter:Yuan Liu, Lin-Song Cui, Mei-Feng Xu, Xiao-Bo Shi, Dong-Ying Zhou, Zhao-Kui Wang, Zuo-Quan Jiang and Liang-Sheng Liao
Journal of Materials Chemistry A 2014 vol. 2(Issue 14) pp:2488-2495
Publication Date(Web):15 Jan 2014
DOI:10.1039/C3TC32301C
Organic light-emitting diodes (OLEDs) have attracted tremendous interest and have already become a prevalent technology in MP3 players, smartphones and cameras. In response to the calls for the large-scale application of OLEDs, the complicated and costly processes for preparing a device is a major challenge which should be addressed. Herein, a novel bipolar host material, 26PyzCz, which contains a pyrazine/carbazole hybrid, has been designed and synthesized. 26PyzCz-based single-layer (SL) fluorescent (F)–phosphorescent (P) OLEDs with various colors have been successfully fabricated. Green and orange SL phosphorescent OLEDs (PHOLEDs) have exhibited efficiencies as high as 63.3 and 62.1 cd A−1 at 1000 cd m−2, and 55.7 and 53.8 cd A−1 at 10000 cd m−2, respectively. Meanwhile, a SL warm white OLED based on fluorescent blue and phosphorescent orange has demonstrated excellent performance, with a maximum current efficiency of 27.5 cd A−1 and a maximum power efficiency of 21.6 lm W−1. In addition, the charge carrier behavior have been evaluated by impedance spectroscopy, which revealed that the dopant trapping effect plays a critical role in charge balance and exciton generation in the SL PHOLEDs.
Co-reporter:Yuanyuan Han, Lei Zhang, Xiujuan Zhang, Kaiqun Ruan, Linsong Cui, Yuming Wang, Liangsheng Liao, Zhaokui Wang and Jiansheng Jie
Journal of Materials Chemistry A 2014 vol. 2(Issue 1) pp:201-207
Publication Date(Web):16 Oct 2013
DOI:10.1039/C3TC31722F
Graphene shows great promise as a transparent conductive electrode to replace conventional indium tin oxide (ITO) for optoelectronic applications. However, the wide applications of graphene in fields such as organic light emitting diodes (OLEDs) are restricted by the difficulty in obtaining a clean and flat graphene surface, as the large residue generated during graphene transfer can lead to a large short circuit current and consequently degradation of the device performance. Here, we report a novel sandwich method to achieve the efficient transfer of graphene with an ultra-clean and flat surface onto a flexible substrate for OLED applications. Differing from the conventional poly(methyl methacrylate) (PMMA)-supported transfer technique, an organic small molecular buffer layer, e.g., a 2-(diphenylphosphory) spirofluorene (SPPO1) layer, was inserted between PMMA and graphene, forming a PMMA/SPPO1/graphene sandwich structure. The separation of PMMA from graphene, along with the large solubility of SPPO1 in clean solvent, results in a substantial reduction of PMMA residue on the graphene. As expected, flexible OLED devices based on the PMMA/SPPO1 transferred graphene films exhibited a much enhanced performance compared to their counterparts fabricated from PMMA transferred films. Our results demonstrate the great potential of the sandwich transfer technique for the fabrication of high-performance OLED devices, as well as other optoelectronic devices.
Co-reporter:Mei-Feng Xu, Ying-Jie Liao, Feng-Shuo Zu, Jian Liang, Da-Xing Yuan, Zhao-Kui Wang and Liang-Sheng Liao
Journal of Materials Chemistry A 2014 vol. 2(Issue 24) pp:9400-9404
Publication Date(Web):08 Apr 2014
DOI:10.1039/C4TA01441C
The authors demonstrate an aqueous solution-processed Cs2CO3 thin film with an adjustable work function via MoO3 and/or Na2WO4 doping. The doped Cs2CO3 as a cathode interfacial layer is successfully used in poly(3-hexyl-thiophene) (P3HT)/indene-C60 bisadduct (IC60BA) heterojunction based solar cells with improved open-circuit voltage and unaffected short-circuit current density. X-ray photoelectron spectroscopy (XPS) evaluation was conducted to verify the formation of the new composites of W–O–Cs and Mo–O–Cs after doping of MoO3 and/or Na2WO4 into Cs2CO3. The change of the work function of MoO3- and/or Na2WO4-doped Cs2CO3 was further confirmed by ultraviolet photoelectron spectroscopy (UPS) measurements.
Co-reporter:Lei Ding, Xun Tang, Mei-Feng Xu, Xiao-Bo Shi, Zhao-Kui Wang, and Liang-Sheng Liao
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 20) pp:18228
Publication Date(Web):September 22, 2014
DOI:10.1021/am5051108
Lithium hydride (LiH) is employed as a novel n-dopant in the intermediate connector for tandem organic light-emitting diodes (OLEDs) because of its easy coevaporation with other electron transporting materials. The tandem OLEDs with two and three electroluminescent (EL) units connected by a combination of LiH doped 8-hydroxyquinoline aluminum (Alq3) and 1,4,5,8,9,11–hexaazatriphenylene-hexacarbonitrile (HAT-CN) demonstrate approximately 2-fold and 3-fold enhancement in current efficiency, respectively. In addition, no extra voltage drop across the intermediate connector is observed. Particularly, the lifetime (T75%) in the tandem OLED with two and three EL units is substantially improved by 3.8 times and 7.4 times, respectively. The doping effect of LiH into Alq3, the charge injection, and transport characteristics of LiH-doped Alq3 are further investigated by ultraviolet photoelectron spectroscopy (UPS) and X-ray photoemission spectroscopy (XPS).Keywords: intermediate connector; LiH; long lifetime; n-type dopant; tandem OLEDs
Co-reporter:Yan-Qiu Sun, Yi-Long Lei, Jing Gao, Xu-Hui Sun, Sheng-Huang Lin, Qiao-Liang Bao, Qing Liao, Shuit-Tong Lee and Liang-Sheng Liao
Chemical Communications 2014 vol. 50(Issue 74) pp:10812-10814
Publication Date(Web):24 Jul 2014
DOI:10.1039/C4CC04794J
Two-dimensional (2D) hexagonal microsheets of 8-hydroxyquinoline zinc (Znq2) were synthesized readily via a mixed solvent induced self-assembly method. The 2D optical waveguiding properties of the microsheets have been clearly revealed by both fluorescence microscopy and confocal microscopy. In addition, the reversible vapochromic properties of the microsheets have also been demonstrated when the Znq2 is exposed to HCl and NH3 vapors.
Co-reporter:Qian Li, Lin-Song Cui, Cheng Zhong, Zuo-Quan Jiang, and Liang-Sheng Liao
Organic Letters 2014 Volume 16(Issue 6) pp:1622-1625
Publication Date(Web):March 3, 2014
DOI:10.1021/ol5002494
The intrinsic asymmetry of 1,2,4-oxadiazole was utilized to synthesize three isomers, DCzmOXD-1, DCzmOXD-2, and mCzmOXD, and high triplet energies over 2.80 eV made them good candidates for host materials in blue OLEDs. The best efficiencies of 23.0 cd A–1/20.5 lm W1–/11.2% in CE/PE/EQE were achieved by DCzmOXD-1 with derivation at the β-carbon position of 1,2,4-oxadiazole.
Co-reporter:Ye-Xin Zhang, Lei Zhang, Lin-Song Cui, Chun-Hong Gao, Hua Chen, Qian Li, Zuo-Quan Jiang, and Liang-Sheng Liao
Organic Letters 2014 Volume 16(Issue 14) pp:3748-3751
Publication Date(Web):July 3, 2014
DOI:10.1021/ol501603b
The C3 meta-position of fluorene is utilized to construct high-triplet energy compounds. Incorporating a spiroacridine structure, two new host materials SAFDPA and SAFCz were facilely obtained. Their thermal and photophysical properties are fully investigated. The best efficiencies of 19.4%/21.5% of blue/white devices are achieved by SAFCz.
Co-reporter:Zhi-Ming Jin;Wei Gu;Xiao-Bo Shi;Zhao-Kui Wang;Zuo-Quan Jiang
Advanced Optical Materials 2014 Volume 2( Issue 6) pp:588-596
Publication Date(Web):
DOI:10.1002/adom.201300504
An intense surface-enhanced Raman scattering (SERS) effect is realized by depositing Ag nanoparticles (NPs) into the nanogaps of a Ag substrate. The nanogaps are formed by the thermal annealing of a Ag film on a silicon substrate. This SERS substrate has an enhancement factor (EF) of 2.3 × 106 and a strong signal enhancement that is 20 times higher than that of substrates without the Ag NPs within the nanogaps. Moreover, the reproducibility is improved with the decreased relative standard deviation of mapping data, which falls from 23.9% down to 12.1%. Its performance is as good as commercial substrates. The electromagnetic distribution between the nanoparticles and nanogaps is simulated by the finite-difference time-domain method, which suggests that the additional enhancement of the SERS effect can be mainly attributed to the remarkable increase of the local electromagnetic field coupling among the Ag NPs, which is at least 12 times higher than that of conventional samples with bare Ag NPs.
Co-reporter:Qian Li, Lin-Song Cui, Cheng Zhong, Xiao-Dong Yuan, Shou-Cheng Dong, Zuo-Quan Jiang, Liang-Sheng Liao
Dyes and Pigments 2014 Volume 101() pp:142-149
Publication Date(Web):February 2014
DOI:10.1016/j.dyepig.2013.09.029
•Novel 1,2,4-oxadiazole based host materials were facile synthesized and used in organic light-emitting diodes.•Their thermal stabilities and optical energy levels revealed that they were suitable for good host materials.•High triplet energies were achieved.•Good blue phosphorescence were obtained.Two novel bipolar host materials, namely 3,5-bis(4-(9H-carbazol-9-yl)phenyl)-1,2,4-oxadiazole (pCzmOXD) and 3,5-bis(3-(9H-carbazol-9-yl)phenyl)-1,2,4-oxadiazole (mCzmOXD) were designed and synthesized, by incorporating a new block 1,2,4-oxadiazole as the n-type moiety and changing its linking pattern with carbazole. As expected, high triplet energy (over 2.81 eV) for mCzmOXD was achieved due to the intrinsic meta-linkage of 1,2,4-oxadiazole. When both materials were applied in blue phosphorescent organic light-emitting diodes, good performance of 13.0 cd A−1/16.0 cd A−1 were achieved for pCzmOXD and mCzmOXD in iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,C′2]bis[(4,6-difluorophenyl)pyridinato-N,C2′] picolinate (FIrpic)-based devices, respectively.
Co-reporter:Dong-Ying Zhou, Xiao-Bo Shi, Yuan Liu, Chun-Hong Gao, Kun Wang, Liang-Sheng Liao
Organic Electronics 2014 Volume 15(Issue 12) pp:3694-3701
Publication Date(Web):December 2014
DOI:10.1016/j.orgel.2014.10.015
Co-reporter:Kevin P. Klubek, Shou-Cheng Dong, Liang-Sheng Liao, Ching W. Tang, Lewis J. Rothberg
Organic Electronics 2014 Volume 15(Issue 11) pp:3127-3136
Publication Date(Web):November 2014
DOI:10.1016/j.orgel.2014.08.038
•We evaluate blue PHOLED devices using Ir(iprpmi)3 as the emitting dopant.•The charge recombination zone is controlled by varying the Ir(iprpmi)3 concentration.•External quantum efficiencies (EQE) greater than 20% have been achieved.•Devices with Ir(iprpmi)3 have improved lifetimes over those using the classic light-blue dopant FIrpic.A blue phosphorescent emitter based on tris[1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazole]iridium(III), Ir(iprpmi)3, as the dopant and 3,3′-bis(N-carbazolyl)biphenyl, mCBP, as the host have been evaluated in OLED devices. By optimizing the dopant concentration and the materials for the electron and hole-transport layers, external quantum efficiencies greater than 20% have been achieved. Improved device lifetimes over those using the classic light-blue dopant FIrpic have also been achieved. These improvements can be attributed to the control of the electron-hole recombination and emission regions within the emitter layer as well as the choice of material for the transport layers.
Co-reporter:Yan-Hui Lou, Lei Zhang, Mei-Feng Xu, Zhao-Kui Wang, Shigeki Naka, Hiroyuki Okada, Liang-Sheng Liao
Organic Electronics 2014 Volume 15(Issue 1) pp:299-305
Publication Date(Web):January 2014
DOI:10.1016/j.orgel.2013.11.001
•Charge transport and electronic traps in P3HT:PCBM blends was evaluated in dark and illumination.•Charge transport properties were analyzed based on current–voltage characteristics measurements.•Electronic trap density was evaluated by a differential method.•The charge transport was strongly associated with the trap states distribution.A direct comparison of charge transport and electronic traps in representative polymer–fullerene blend, poly (3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM), is carried out in dark and illuminated conditions based on the measurements of temperature-dependent current–voltage characteristics. In dark condition, the charge transport presents a transition from Ohmic to trap-limited current. While the trap-filled space charge limited current is observed under illumination at the same applied bias. From evaluations of trap density and energy distribution by a differential method, it is reveal that the diverse charge transport in dark and illuminated conditions is mainly caused by the different trap states distribution, which strongly affects the space charges and the electrical field in P3HT: PCBM blends.Graphical abstract
Co-reporter:Lin-Song Cui, Yuan Liu, Qian Li, Zuo-Quan Jiang, Liang-Sheng Liao
Organic Electronics 2014 Volume 15(Issue 7) pp:1368-1377
Publication Date(Web):July 2014
DOI:10.1016/j.orgel.2014.03.028
•The HOMO energy levels of carbazole-based host materials can be independently turned with simple spacers.•A blue PHOLED device incorporating PBCz host achieved a maximum EQE of 19.5%.•Two-color, all-phosphor WOLEDs was achieved with an EQE of 24.6%.•The three colors WOLEDs was demonstrated a high EQE of 19.1%.A series of host materials, 3,3′-linked carbazole-based molecules have been designed with phenyl and biphenyl spacers. Their optical and electrical properties can be fine-tuning by the spacers. Their HOMO energy levels depend on HOMO distributions within the range of −5.64 to −5.96 eV. On the other hand, the three compounds have similar LUMO energy levels and triplet energies. Their thermal, photophysical, electrochemical and carrier mobilities properties were also systematically investigated. The relationship between the molecular structures and optoelectronic properties are discussed. A blue PHOLED device incorporating PBCz achieved a maximum external quantum efficiency, current efficiency, and power efficiency of 19.5%, 45.5 cd/A and 43.8 lm/W, respectively. Moreover a two-color, all-phosphor and single-emitting-layer WOLED hosted by PBCz was also achieved with a maximum external quantum efficiency, current efficiency and power efficiency of 24.6%, 76.3 cd/A and 69.4 lm/W respectively. Furthermore, we also utilized this versatile host for three-component RGB white PHOLEDs and show excellent performance. For example, combination of PBCz with FIrpic, Ir(ppy)2(acac) and Ir(MDQ)2(acac) in the active layer, the resulting WOLEDs showed three evenly separated peaks and gave a high efficiency of 49.2 cd/A. The efficient PHOLEDs demonstrated that the versatile host PBCz has great potential for applications in the solid-state lighting.Graphical abstract
Co-reporter:W. Zhao, Y. Jin, C.H. Gao, W. Gu, Z.M. Jin, Y.L. Lei, L.S. Liao
Materials Chemistry and Physics 2014 Volume 143(Issue 3) pp:952-962
Publication Date(Web):14 February 2014
DOI:10.1016/j.matchemphys.2013.10.026
•A p–n heterojunction photocatalyst CuFe2O4/Bi4Ti3O12 was prepared by ball milling.•Water is added during the wet milling process to make the powders milled efficiently and dispersed highly.•The photocatalytical mechanism is discussed according to p–n junction principles.••O2− and h+ are the main reactive species for the degradation of methyl orange.The synthesis of Bi4Ti3O12 and CuFe2O4 powders was achieved using a conventional solid-state reaction and the Sol–Gel method, respectively. A novel p–n heterojunction photocatalyst CuFe2O4/Bi4Ti3O12 was subsequently prepared through ball milling. The structures, morphologies, and optical properties of the photocatalysts were comprehensively characterized. The transmission electron microscopy (TEM) images showed a clear interface between CuFe2O4 and Bi4Ti3O12, indicating that a heterojunction between CuFe2O4 and Bi4Ti3O12 was formed during ball milling. In addition, the photocatalytic activity was evaluated based on the photocatalytic degradation of methyl orange (MO). The results indicated that the photocatalytic activity of the p–n heterojunction photocatalyst CuFe2O4/Bi4Ti3O12 was higher than that of Bi4Ti3O12 alone. The enhanced photocatalytic activity could be attributed to the formation of a heterojunction between CuFe2O4 and Bi4Ti3O12, which suppressed the recombination of photogenerated electron–hole pairs. We also investigated the effects of procedure time and dispersant (H2O) during ball milling on the photocatalytic activity. The mechanisms underlying the observed photocatalytic activity were also described based on the semiconductor energy band theory and p–n junction principle. Moreover, the analysis of the radical scavengers confirmed that •O2− and h+ were the primary reactive species to cause the degradation of the MO.
Co-reporter:Dong-Ying Zhou ; Hossein Zamani Siboni ; Qi Wang ; Liang-Sheng Liao ;Hany Aziz
The Journal of Physical Chemistry C 2014 Volume 118(Issue 41) pp:24006-24012
Publication Date(Web):September 24, 2014
DOI:10.1021/jp508228z
The use of exciplex-forming hosts has recently emerged as an avenue to obtain very high efficiency with phosphorescent dopants in organic light-emitting devices (OLEDs). The exact electroluminescence (EL) mechanism, however, is still not clearly understood. In this work, we use time-resolved photoluminescence measurements and find that the EL mechanism is primarily based on efficient energy transfer from the exciplex to the emitter guest. By altering the distance between the guest and the exciplex-formation interface, we further uncover that this energy transfer occurs mostly by the Dexter mechanism. The results explain the high efficiency of phosphorescent OLEDs based on an exciplex-forming host and shed light on the reasons behind the significant difference in the efficiency of OLEDs utilizing exciplex-forming hosts when used with phosphorescent versus fluorescent emitters.
Co-reporter:Shou-Cheng Dong, Lei Zhang, Jian Liang, Lin-Song Cui, Qian Li, Zuo-Quan Jiang, and Liang-Sheng Liao
The Journal of Physical Chemistry C 2014 Volume 118(Issue 5) pp:2375-2384
Publication Date(Web):January 15, 2014
DOI:10.1021/jp412107g
A series of systematical designed host materials based on dibenzothiophene (DBT) were synthesized. Their physical properties were comprehensively characterized and compared with classic carbazole analogues. The different electron donating abilities of DBT and carbazole play an important role in the structure–property correlations. In this report, we demonstrate that the charge transport balance of host materials can be manipulated by utilizing the less electron-donating nature of DBT with proper design. Both the experimental data and theoretical calculations indicated possible bipolar property in meta-linked materials based on DBT. Through single carrier devices, an atypical bipolar transporting property was found in m-TPDBT. The meta- and ortho-linked DBT based materials exhibit decent performance in FIrpic based PHOLEDs. The best performed m-TPDBT was used as host in white phosphorescent organic light emitting diodes (PHOLEDs). Promising results were achieved with both double and single emitting layer configurations. A maximum power efficiency of 41.0 lm W–1 was achieved for warm white devices.
Co-reporter:Yi Long Lei ; Liang Sheng Liao ;Shuit Tong Lee
Journal of the American Chemical Society 2013 Volume 135(Issue 10) pp:3744-3747
Publication Date(Web):March 4, 2013
DOI:10.1021/ja3114278
We report a simple yet versatile solution route for constructing heterojunctions from luminescent organic charge-transfer (CT) complexes through a two-step seeded-growth method. Using this method, we achieved anisotropic and selective growth of anthracene–1,2,4,5-tetracyanobenzene (TCNB) complexes onto the tips of naphthalene–TCNB microtubes, resulting in the formation of microdumbbells. Significantly, the two-component microdumbbells appear as dual-color-emitting heterojunctions arising from integration of two distinct color-emitting materials. We further elucidated the two-step seeded-growth mechanism of the dumbbell-like organic heterostructures on the basis of structural analysis of the two crystals and surface–interface energy balance. In principle, the present synthetic route may be used to fabricate a wide range of sophisticated dual- or multicolor-emitting organic heterostructures via judicious choice of the CT complexes.
Co-reporter:Jianfeng Lu, Xiaobao Xu, Kun Cao, Jin Cui, Yibo Zhang, Yan Shen, Xiaobo Shi, Liangsheng Liao, Yibing Cheng and Mingkui Wang
Journal of Materials Chemistry A 2013 vol. 1(Issue 34) pp:10008-10015
Publication Date(Web):20 Jun 2013
DOI:10.1039/C3TA11870C
In this study, new push–pull alkoxy-wrapped zinc porphyrin dyes with intramolecular donor–π–acceptor structures have been designed and synthesized for dye-sensitized solar cells (DSCs). The linkers based on thiophene or 2,3-dihydrothieno[3,4-b][1,4] dioxine with cyanoacetic acid can broaden the spectral response of porphyrins into the near-IR region (∼850 nm), which is mainly attributed to the cyanoacetic acid group. However, porphyrins with cyanoacrylic acid as an anchoring group lead to a faster charge recombination rate at the dye-sensitized heterojunction interface, which lowers the device photovoltaic performance. By using porphyrins with a rigid π-linker feature structure that is 5-ethynylthiophene-2-carboxylic acid, highly efficient DSC devices with a power conversion efficiency of 9.5% can be obtained. Spectral, electrochemical, photovoltage transient decay and impedance measurements are performed to reveal the influence of π-conjugated linkers and anchoring groups upon the optoelectronic features of porphyrin dyes in DSCs.
Co-reporter:Lin-Song Cui, Yuan Liu, Xiao-Dong Yuan, Qian Li, Zuo-Quan Jiang and Liang-Sheng Liao
Journal of Materials Chemistry A 2013 vol. 1(Issue 48) pp:8177-8185
Publication Date(Web):15 Oct 2013
DOI:10.1039/C3TC31675K
Two novel bipolar host materials, BCzSCN and BCzSPO, consisting of an electron deficient cyano or diphenylphosphine oxide acceptor linked to a bicarbazole donor, were designed and synthesized. Their thermal, photophysical and electrochemical properties were systematically investigated. Both BCzSCN and BCzSPO show high triplet energies of over 2.75 eV and could be developed for application in blue phosphorescent organic light-emitting diodes (PHOLEDs), and further for white PHOLEDs. Moreover, the characterization of hole-only and electron-only devices based on BCzSCN and BCzSPO indicate their rather balanced hole/electron injection and transport properties. Blue PHOLEDs containing BCzSCN and BCzSPO as the hosts and FIrpic as a dopant exhibited excellent performance, with maximum external quantum efficiencies of 19.3% and 17.1% respectively. In particular, blue PHOLEDs adopting BCzSCN and BCzSPO exhibited extraordinary low efficiency roll-offs of 5.2% and 7.6% at a brightness of 1000 cd m−2, respectively. Meanwhile, the all-phosphor near-white devices hosted by the two materials were also fabricated, and high external quantum efficiencies of 22.0% and 21.3% were achieved.
Co-reporter:Shou-Cheng Dong, Yuan Liu, Qian Li, Lin-Song Cui, Hua Chen, Zuo-Quan Jiang and Liang-Sheng Liao
Journal of Materials Chemistry A 2013 vol. 1(Issue 40) pp:6575-6584
Publication Date(Web):09 Aug 2013
DOI:10.1039/C3TC31336K
Four novel host materials were designed and synthesized, incorporating fluorene-spiro-annulated triphenylamine–carbazole (ST–SCz) and dibenzothiophene (DBT) blocks. A meta-linking strategy was applied by introducing DBT moieties to ST–SCz skeletons at the C3 position of the fluorene backbones. As expected, high triplet energies (over 2.80 eV) were achieved in all four materials despite the different linking positions on the DBT. All four materials show a high Tg from 149 to 163 °C, which benefits from their spiro-structure. Their thermal, electrochemical and photo-physical properties were fully characterized. Highly efficient blue and white PHOLEDs were fabricated using these four materials as the hosts. Triphenylamine-containing STDBT4 and STDBT2 demonstrate better device performance due to their relatively high-lying HOMO compared to carbazole-containing SCzDBT4 and SCzDBT2. Maximum ηext of 19.6% and 18.4% (STDBT4 and STDBT2) were achieved for FIrpic-based devices, and 23.7% and 22.2% (STDBT4 and STDBT2) were achieved for two color-based white PHOLEDs with double emitting layers, using PO-01 as a yellow dopant. Finally, a highly efficient single-emitting layer white PHOLED with maximum efficiencies of 24.0%, 77.0 cd A−1 and 63.2 lm W−1 and CIE coordinates of (0.38, 0.48) was realized using the device configuration of ITO/HAT–CN/TAPC/STDBT4: 8 wt% FIrpic: 0.8 wt% PO-01/TmPyPB/Liq/Al. The device shows good color stability and low efficiency roll-off. Even at a high luminance of 10000 cd m−2, it still maintains very high efficiencies of 17.9%, 56.4 cd A−1 and 26 lm W−1.
Co-reporter:Lin-Song Cui, Shou-Cheng Dong, Yuan Liu, Qian Li, Zuo-Quan Jiang and Liang-Sheng Liao
Journal of Materials Chemistry A 2013 vol. 1(Issue 25) pp:3967-3975
Publication Date(Web):18 Apr 2013
DOI:10.1039/C3TC30410H
A series of novel blue phosphorescent host materials, namely, CTP-1, CTP-2 and CTP-3 have been designed and synthesized through the Suzuki–Miyaura cross-coupling reaction between N-phenylcarbazole and biphenyl. Their thermal, photophysical and electrochemical properties were systematically investigated. These novel hosts show excellent thermal stability and high glass transition temperatures (Tg) ranging from 113 to 127 °C. The triplet energies of these three materials are significantly higher than that of (4,4′-bis(N-carbazolyl)-2,2′-biphenyl) (CBP, 2.56 eV) and that of the most popular blue phosphorescent material iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,C2′] picolinate (FIrpic, 2.65 eV). These three novel materials have superior thermal and electronic properties for blue and white phosphorescent OLEDs. Blue emitting devices with an Ir-complex FIrpic as the phosphorescent dopant have been fabricated and show high efficiency with low roll-off. In particular, 40.4 cd A−1 at 100 cd m−2 and 38.2 cd A−1 at 1000 cd m−2 were achieved when CTP-1 was used as the host material. On the basis of this work, an all-phosphor white device with a current efficiency of 64.5 cd A−1 at 100 cd m−2 and 61.9 cd A−1 at 1000 cd m−2 has also been fabricated.
Co-reporter:Mei-Feng Xu, Xiao-Zhao Zhu, Xiao-Bo Shi, Jian Liang, Yue Jin, Zhao-Kui Wang, and Liang-Sheng Liao
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 8) pp:2935
Publication Date(Web):March 19, 2013
DOI:10.1021/am4001979
This paper investigates the effects of localized surface plasmon resonance (LSPR) in an inverted polymer/fullerene solar cell by incorporating Au and/or Ag nanoparticles (NPs) into the TiO2 buffer layer. Enhanced light harvesting via plasmonic resonance of metal NPs has been observed. It results in improved short-circuit current density (Jsc) while the corresponding open-circuit voltage (Voc) is maintained. A maximum power conversion efficiency of 7.52% is obtained in the case of introducing 30% Ag NPs into the TiO2, corresponding to a 20.7% enhancement compared with the reference device without the metal NPs. The device photovoltaic characteristics, photocurrent properties, steady-state and dynamic photoluminescences of active layer on metal NP-doped TiO2, and electric field profile in metal NP-doped TiO2 layers are systematically investigated to explore how the plasmonic effects of Au and/or Ag NPs influence the OSC performance.Keywords: localized surface plasmon resonance; metal nanoparticles; polymer solar cells;
Co-reporter:Mei-Feng Xu, Xiao-Bo Shi, Zhi-Ming Jin, Feng-Shuo Zu, Yang Liu, Lei Zhang, Zhao-Kui Wang, and Liang-Sheng Liao
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 21) pp:10866
Publication Date(Web):October 9, 2013
DOI:10.1021/am4030565
A simple and cheap method for depositing solution-processed GeO2 (sGeO2) film is proposed utilizing the weak solubility of GeO2 in water. X-ray photoelectron spectroscopy analysis reveals that a pure GeO2 thin film can be formed by casting its aqueous solution. This method can avoid the difficulty of vacuum evaporation by its high melting point. The sGeO2 film has been used successfully as an anode interfacial layer in poly(3-hexylthiophene) (P3HT) and indene-C60 bisadduct (IC60BA)-based bulk heterojunction organic solar cells with improved power conversion efficiency and device stability compared with that using conventional poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS); the improvement of the power conversion efficiency and the device stability are estimated to be 9% and 50%, respectively. The calculations of optical intensity in a whole cell demonstrate that a thin layer of sGeO2 could function as an optical spacer in the based bulk heterojunction (BHJ) organic solar cells (OSCs) for enhancing the light harvesting in the active layer. Interfacial evaluation by impedance spectroscopy shows that the sGeO2-based cell exists less charge carrier recombination and lower contact resistance. More importantly, the sGeO2 film processing is very simple and environmentally friendly, which has potential applications in green and low-cost organic electronics in the future.Keywords: device stability; GeO2 aqueous solution; interfacial layer; optical space effect; organic solar cells; solution processing;
Co-reporter:Shih-Han Chang, Chun-Fu Chang, Jia-Ling Liao, Yun Chi, Dong-Ying Zhou, Liang-Sheng Liao, Tzung-Ying Jiang, Tsao-Pei Chou, Elise Y. Li, Gene-Hsiang Lee, Ting-Yi Kuo, and Pi-Tai Chou
Inorganic Chemistry 2013 Volume 52(Issue 10) pp:5867-5875
Publication Date(Web):April 26, 2013
DOI:10.1021/ic302829e
A tetradentate bis(pyridylpyrazolate) chelate, L, is assembled by connecting two bidentate 3-(trifluoromethyl)-5-(2-pyridyl)pyrazole chelates at the 6 position of the pyridyl fragment with a phenylamido appendage. This chelate was then utilized in the synthesis of three osmium(II) complexes, namely, [Os(L)(CO)2] (4), [Os(L)(PPh2Me)2] (5), and [Os(L)(PPhMe2)2] (6). Single-crystal X-ray structural analyses were executed on 4 and 5 to reveal the bonding arrangement of the L chelate. Phosphine-substituted derivatives 5 and 6 are highly emissive in both solution and the solid state, and their photophysical properties were measured and discussed on the basis of computational approaches. For application, fabrication and analysis of organic light-emitting diodes (OLEDs) were also carried out. The OLEDs using 5 and 6 as dopants exhibit saturated red emission with maximum external quantum efficiencies of 9.8% and 9.4%, respectively, which are higher than that of the device using [Ir(piq)3] as a red-emitting reference sample. Moreover, for documentation, 5 and 6 also achieve a maximum brightness of 19540 cd·m–2 at 800 mA·cm–2 (11.6 V) and 12900 cd·m–2 at 500 mA·cm–2 (10.5 V), respectively.
Co-reporter:Lin-Song Cui, Shou-Cheng Dong, Yuan Liu, Mei-Feng Xu, Qian Li, Zuo-Quan Jiang, Liang-Sheng Liao
Organic Electronics 2013 Volume 14(Issue 7) pp:1924-1930
Publication Date(Web):July 2013
DOI:10.1016/j.orgel.2013.04.037
•Novel phosphine-oxide based host materials were facile synthesized and used in organic light-emitting diodes.•The substituted position is meta-position, which is rarely developed in the previous work.•As expected, the higher triplet energy and good thermal stability were obtained.•The better performance with deep blue phosphorescence was achieved as compared to its well-known isomer.This study investigated the use of a novel modification in molecular design to get two new electron-transport host materials, SF3PO and BSF3PO. By linking the phosphine oxide moieties at meta-position of spirobifluorene rings, higher triplet energies could be easily achieved for these two new materials. The steric spirobifluorene structures could guarantee their good thermal stabilities. According to these properties, their applications as host materials for deep blue phosphorescent organic light-emitting diodes (PHOLEDs) were explored. As expected, the deep blue emitting devices with Ir-complex FIr6 as phosphorescent dopants and SF3PO and BSF3PO as hosts had been fabricated and showed high efficiency of 28.5 and 22.0 cd/A, respectively, which were significantly higher than that of the para-linked analogue SPPO1.Graphical abstract
Co-reporter:Chun-Hong Gao, Dong-Ying Zhou, Wei Gu, Xiao-Bo Shi, Zhao-Kui Wang, Liang-Sheng Liao
Organic Electronics 2013 Volume 14(Issue 4) pp:1177-1182
Publication Date(Web):April 2013
DOI:10.1016/j.orgel.2013.02.013
A high efficiency phosphorescent organic light-emitting diode (OLED) has been fabricated by introducing a double exciton-blocking layer (d-EBL) between the hole-transporting layer and the light-emitting layer in the device. The device exhibits a yellow emission with a maximum current efficiency of 58.5 cd/A at 117 cd/m2, corresponding to the power efficiency of 50.9 lm/W, which is two times improved compared with that of devices having only one traditional single exciton-blocking layer (s-EBL). The efficiency improvement has been investigated through the electroluminescence (EL) spectral analyses in the phosphorescent guest-doped and the non-doped OLEDs. The results demonstrate that the electrons are blocked and the excitons are confined more effectively in the d-EBL-based devices than that in the s-EBL-based devices. In addition, over two times improvement in the lifetime is also achieved in the devices with the d-EBL compared with the devices having a traditional s-EBL.Graphical abstractHighlights► A double exciton-blocking layer is used in a PHOLED. ► Remarkable enhancements in EL efficiency and stability are achieved. ► The mechanism of better electron and exciton confining capability is investigated. ► The exciton–exciton annihilation can be suppressed as well in the device.
Co-reporter:Jinyong Zhuang, Wanfei Li, Wenming Su, Yuan Liu, Qi Shen, Liangsheng Liao, Ming Zhou
Organic Electronics 2013 Volume 14(Issue 10) pp:2596-2601
Publication Date(Web):October 2013
DOI:10.1016/j.orgel.2013.06.029
•Homoleptic tris(phenyl-imidazole) iridium(III) complex Ir(dbi)3 as a sky-blue dopant.•A maximum current efficiency and external quantum efficiency (EQE) of 61.5 cd A−1 and 23.1% obtained.•High efficiencies of 53.5 cd A−1 and 20.1% EQE achieved at the luminance of 1000 cd m−2.Homoleptic triscyclometalated iridium(III) complex Ir(dbi)3 was used as a dopant for sky blue phosphorescent organic light-emitting diodes (PHOLEDs). Its photophysical, thermal, electrochemical properties as well as the device performances were investigated. Ir(dbi)3 exhibited high quantum yield of 0.52 in solution at room temperature. A maximum current efficiency and external quantum efficiency (EQE) of 61.5 cd A−1 and 23.1% were obtained, which are the highest ever reported for blue homoleptic iridium complexes. High efficiencies of 53.5 cd A−1 and 20.1% EQE were achieved even at the luminance of 1000 cd m−2.Graphical abstract
Co-reporter:Yan-Hui Lou, Mei-Feng Xu, Lei Zhang, Zhao-Kui Wang, Shigeki Naka, Hiroyuki Okada, Liang-Sheng Liao
Organic Electronics 2013 Volume 14(Issue 10) pp:2698-2704
Publication Date(Web):October 2013
DOI:10.1016/j.orgel.2013.07.017
•A physical investigation was carried out in MoO3-doped pentacene films.•The charge transport properties were analyzed based on current-voltage characteristics measurements.•Trap density in MoO3-doped pentacene was evaluated by a differential method.•Conducting mechanism in MoO3-doped pentacene was investigated via Mo 3d valence state analysis.Molybdenum trioxide (MoO3) doped organic semiconductors have shown attractive applications in organic electric devices. The authors carried out an investigation on the origin of enhanced photoelectric characteristics in MoO3-doped pentacene films. Electrical properties including charge transport, trap density and conductivity in bulk MoO3-doped pentacene films were investigated through fundamental measurements of current-voltage characteristics. Electrical structure and conducting mechanism in MoO3-doped pentacene films were further evaluated by X-ray diffraction and X-ray photoelectron spectroscopy measurements. The experimental results suggest that the improved conductivity in MoO3-doped pentacene film was partly associated with the increased ratio of low Mo oxidation state (Mo4+) with a fact of better conducting property of MoO2 than that MoO3.Graphical abstract
Co-reporter:Shou-Cheng Dong, Chun-Hong Gao, Xiao-Dong Yuan, Lin-Song Cui, Zuo-Quan Jiang, Shuit-Tong Lee, Liang-Sheng Liao
Organic Electronics 2013 Volume 14(Issue 3) pp:902-908
Publication Date(Web):March 2013
DOI:10.1016/j.orgel.2013.01.012
Two host materials, DBTSF2 and DBTSF4, were designed and synthesized, incorporating dibenzothiophene (DBT) and spirobifluorene (SF) blocks. Their thermal, electrochemical and photo-physical properties were fully characterized. DBTSF4, which adopted an ortho-linkage between DBT and SF moieties, showed a significantly higher T1 energy of 2.82 eV as compared to its para-linkage analogue DBTSF2 (2.49 eV). Their applications as host for green, blue and white phosphorescent organic light-emitting diodes (PHOLEDs) were explored. The DBTSF4 based blue PHOLED has a highest current efficiency of 23.5 cd A−1. And using DBTSF4 as a single host, two-color based white PHOLEDs were achieved from cold white emission with CIE coordinate of (0.31, 0.43) to yellowish warm white emission (0.44, 0.49) with maximum current efficiencies varying from 35.8 to 52.3 cd A−1 and maximum external quantum efficiencies from 13.1% to 16.9% respectively. The white PHOLED devices also showed a low efficiency roll-off even at 10,000 cd m−2.Graphical abstractHighlights► Novel dibenzothiophene based host materials were facilely synthesized and used in organic light-emitting diodes. ► Their thermal stabilities and optical energy levels revealed that they are suitable for good host materials. ► Good blue, green and warm white device performances were obtained. ► Quite low efficiency roll-offs were also achieved.
Co-reporter:Mei-Feng Xu, Lin-Song Cui, Xiao-Zhao Zhu, Chun-Hong Gao, Xiao-Bo Shi, Zhi-Ming Jin, Zhao-Kui Wang, Liang-Sheng Liao
Organic Electronics 2013 Volume 14(Issue 2) pp:657-664
Publication Date(Web):February 2013
DOI:10.1016/j.orgel.2012.12.016
The authors demonstrate an effective anode interfacial layer based on aqueous solution-processed MoO3 (sMoO3) in poly (3-hexylthiophene) (P3HT) and indene-C60 bisadduct (ICBA) based bulk-heterojunction organic solar cells (PSCs). Various sMoO3 concentration (0.03–0.25 wt%) was obtained by dissolving MoO3 powder into deionized water directly with weak solubility. The characteristics of sMoO3 films evaluated by atomic force microscope (AFM) and scanning electron microscope (SEM) suggest that the sMoO3 films continuously cover the entire indium tin oxide (ITO) surface. The sMoO3 based PSCs exhibit comparable power conversion efficiency with poly (3,4-ethylenedioxythiophene)–polystyrenesulfonic acid (PEDOT:PSS) based devices. However, even more importantly, the stability of sMoO3 based devices have been greatly improved in air under continual light-illumination at 52 mW/cm2. Further evaluations on Mo valence states and work function of sMoO3 films by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) demonstrate that the aqueous solution-processed MoO3 could act as an better anode interfacial layer than the conventional PEDOT:PSS.Graphical abstractHighlights► Water-soluble MoO3 (sMoO3) was used to form a thin layer in organic solar cells. ► The preparation of sMoO3 layer is simple and environment-friendly. ► sMoO3 based devices are comparable to that of PEDOT:PSS in conversion efficiency. ► A better stability was obtained from sMoO3 based devices.
Co-reporter:Xiao-Zhao Zhu, Yuan-Yuan Han, Yuan Liu, Kai-Qun Ruan, Mei-Feng Xu, Zhao-Kui Wang, Jian-Sheng Jie, Liang-Sheng Liao
Organic Electronics 2013 Volume 14(Issue 12) pp:3348-3354
Publication Date(Web):December 2013
DOI:10.1016/j.orgel.2013.10.003
•A single layer graphene was modified with TiOx and PEDOT:PSS.•The sheet resistance of the modified graphene was reduced by 86% from 628 Ω/sq to 86 Ω/sq.•The work function of the modified graphene was increased by 0.82 eV from 4.30 eV to 5.12 eV.•Enhanced charge injection and transport were achieved from the modified graphene.There are many challenges for a direct application of graphene as the electrodes in organic electronics due to its hydrophobic surfaces, low work function (WF) and poor conductance. The authors demonstrate a modified single-layer graphene (SLG) as the anode in organic light-emitting diodes (OLEDs). The SLG, doped with the solution-processed titanium suboxide (TiOx) and poly(3,4-ethylenedio-xythiophene)/poly(styrene sulfonic acid) (PEDOT:PSS), exhibits excellent optoelectronic characteristics with reduced sheet resistance (Rsq), increased work function, as well as over 92% transmittance in the visible region. It is notable that the Rsq of graphene decreased by ∼86% from 628 Ω/sq to 86 Ω/sq and the WF of graphene increased about 0.82 eV from 4.30 eV to 5.12 eV after a modification by using the TiOx–PEDOT:PSS double interlayers. In addition, the existence of additional TiOx and PEDOT:PSS layers offers a good coverage to the PMMA residuals on SLG, which are often introduced during graphene transfer processes. As a result, the electrical shorting due to the PMMA residues in the device can be effectively suppressed. By using the modified SLG as a bottom anode in OLEDs, the device exhibited comparable current efficiency and power efficiency to those of the ITO based reference OLEDs. The approach demonstrated in this work could potentially provide a viable way to fabricate highly efficient and flexible OLEDs based on graphene anode.Graphical abstract
Co-reporter:Yi-Long Lei;Yue Jin;Dong-Ying Zhou;Wei Gu;Xiao-Bo Shi;Shuit-Tong Lee
Advanced Materials 2012 Volume 24( Issue 39) pp:5345-5351
Publication Date(Web):
DOI:10.1002/adma.201201493
Co-reporter:S. D. Cai, C. H. Gao, D. Y. Zhou, W. Gu, and L. S. Liao
ACS Applied Materials & Interfaces 2012 Volume 4(Issue 1) pp:312
Publication Date(Web):November 28, 2011
DOI:10.1021/am2013568
Simplified phosphorescent organic light-emitting diodes (OLEDs) using only two kinds of hosts and comprising either a neat MoOx hole-injecting layer (HIL) or a MoOx-doped 4,4′-bis(carbazol-9-yl)biphenyl (CBP) HIL were studied. The devices having the MoOx-doped CBP HIL are superior to the device having the neat MoOx HIL in terms of power efficiency and operational lifetime. Impedance spectroscopy studies revealed that both the reduced hole-injecting barrier height at the anode/doped HIL interface and the reduced bulk resistivity in the doped CBP HIL contribute to the improvement in electroluminescence characteristics. When increasing the MoOx volume percentage from 5 to 10% and then to 20%, the hole-injecting barrier height is decreased from 0.63 eV to 0.36 eV and then to 0.18 eV. The power efficiency of the device with a 20 vol % of MoOx-doped CBP HIL is more than two times that of the device with a neat MoOx HIL measured at a driven current of 5 mA/cm2. Moreover, the lifetime of the device with a 20 vol % of MoOx-doped CBP HIL is more than three times that of the device with a neat MoOx HIL estimated at an initial luminance of 1000 cd/m2. The MoOx-doped HIL further ensures the feasibility of the simplified phosphorescent OLEDs for potential applications.Keywords: doped hole-injecting layer; electroluminescence characteristics; hole injection properties; impedance spectroscopy; MoOx; phosphorescent OLEDs;
Co-reporter:Chun-Hong Gao, Shi-Duan Cai, Wei Gu, Dong-Ying Zhou, Zhao-Kui Wang, and Liang-Sheng Liao
ACS Applied Materials & Interfaces 2012 Volume 4(Issue 10) pp:5211
Publication Date(Web):September 24, 2012
DOI:10.1021/am3011324
An ultrathin layer of indium trichloride (InCl3) is thermally evaporated on the indium tin oxide (ITO) anode to enhance the hole injection in simplified phosphorescent organic light-emitting diodes (PHOLEDs). Comparing with the device with ultraviolet (UV)-ozone treatment, the device modified by InCl3 exhibits a maximum current efficiency of 82.2 cd/A measured at about 2000 cd/cm2 and 36% improvement in power efficiency measured at 20 mA/cm2. More importantly, more than three times improvement in half lifetime estimated at an initial luminance of 1000 cd/cm2 is achieved. The investigations using ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, and the bias- and temperature-dependent current density–voltage characteristics in the related hole-dominated devices have revealed that the improved device performance is mainly attributed to the enhanced hole injection resulting from the lowered hole injection barrier height in the InCl3-modified devices.Keywords: hole injection; indium trichloride; phosphorescent OLEDs; surface modification; thermal evaporation; work function;
Co-reporter:Shou-Cheng Dong, Chun-Hong Gao, Zhao-Hu Zhang, Zuo-Quan Jiang, Shuit-Tong Lee and Liang-Sheng Liao
Physical Chemistry Chemical Physics 2012 vol. 14(Issue 41) pp:14224-14228
Publication Date(Web):28 Jun 2012
DOI:10.1039/C2CP41535F
A new class of host materials DBFSF (DBFSF2 and DBFSF4) is facilely synthesized through a Suzuki coupling reaction between dibenzofuran and spirobifluorene. Their thermal, electrochemical, electronic absorption and photoluminescent properties are fully investigated. High glass transition temperatures (Tg) of 115 °C and 124 °C are observed for DBFSF2 and DBFSF4, respectively, due to the introduction of bulky spirobifluorene groups. As expected, the DBFSF4 with a twisted-linkage exhibits higher triplet energy than DBFSF2 and can be used in blue and green phosphorescent OLEDs. Electrophosphorescent devices with DBFSF2 and DBFSF4 as hosts were fabricated. Besides the good current efficiencies of 22.2 cd A−1 for blue and 64.4 cd A−1 for green, low efficiency roll-off has also been achieved for both devices.
Co-reporter:X.Z. Zhu, C.H. Gao, M.F. Xu, W. Gu, X.B. Shi, Y.L. Lei, Z.K. Wang, L.S. Liao
Synthetic Metals 2012 Volume 162(Issue 24) pp:2212-2215
Publication Date(Web):31 December 2012
DOI:10.1016/j.synthmet.2012.10.021
An InCl3 dipole layer is inserted into a copper phthalocyanine (CuPc) and fullerene (C60) based organic photovoltaic cell (OPV) to modify the indium-tin-oxide (ITO) anode surface. The work function of the ITO is improved from 4.63 eV to 5.47 eV. In addition, a 30% enhancement in absorption coefficient is achieved due to the strong interaction between CuPc and InCl3 molecules, which induces a configuration change of the CuPc stacks from perpendicular to parallel along the ITO substrate. Therefore, the power conversion efficiency of the OPV devices has a 30% improvement because of the improved work function of the ITO anode and the enhanced absorption coefficient of the devices.Graphical abstractHighlights► The work function of InCl3 modified ITO can be increased from 4.63 eV to 5.47 eV. ► Optical absorption enhancement can be obtained from a CuPc film grown on the ITO. ► 30% improvement in performance of the OPV devices can be then achieved.
Co-reporter:Cheng-Huei Lin ; Yuan-Chieh Chiu ; Yun Chi ; Yu-Tai Tao ; Liang-Sheng Liao ; Meu-Rurng Tseng ;Gene-Hsiang Lee
Organometallics 2012 Volume 31(Issue 11) pp:4349-4355
Publication Date(Web):May 25, 2012
DOI:10.1021/om300325y
Treatment of [IrCl3(tht)3] (tht = tetrahydrothiophene) with a stoichiometric amount of PPh3 gave the monosubstitution product [Ir(tht)2(PPh3)Cl3] (5), whose synthesis, particularly that leading to the effective preparation of OLED phosphors, was studied and optimized to achieve the best product yields. Thus, the independent treatment of 5 with 2,4-difluorophenylpyridine (dfppyH) or with variable amounts of benzyldiphenylphosphine (bdpH) gave rise to the formation of the cyclometalation products [Ir(dfppy)(tht)(PPh3)Cl2] (7), [Ir(bdp)(bdpH)(tht)Cl2] (8), and [Ir(bdp)(PPh3)(tht)Cl2] (10), depending on the stoichiometry and conditions employed. Upon further treatment with 5-pyridyl-3-trifluoromethyl-1H-pyrazole (fppzH), these Ir(III) complexes 7, 8, and 10 were capable of yielding the phosphors [Ir(dfppy)(fppz)2] (1), [Ir(bdp)2(fppz)] (4), and [Ir(bdp)(fppz)2] (2), respectively. The general mechanism en route to their formation was studied and discussed.
Co-reporter:Xia Sun ; Dong-Ying Zhou ; Lihua Qiu ; Liang-Sheng Liao ;Feng Yan
The Journal of Physical Chemistry C 2011 Volume 115(Issue 5) pp:2433-2438
Publication Date(Web):January 6, 2011
DOI:10.1021/jp1099656
Improvement of electron injection is one of the most effective ways for obtaining highly efficient low-voltage organic light-emitting diodes (OLEDs). Here, we report the study on the unidentate sodium−quinolate complexes as the electron injection layer for OLEDs. Sodium−quinolate complexes, 8-hydroxyquinolinolatosodium (Naq), 2-methyl-8-hydroxyquinolinolatosodium (NaMeq), and 2-(diphenylmethyl)-8-hydroxyquinolatosodium (Ph2Naq) were synthesized and characterized by 1H NMR, 13C NMR, FTIR, UV−vis, and photoluminescence (PL) spectroscopy. The produced sodium−quinolate complexes are thermally stable amorphous compounds with high glass transition and decomposition temperatures. These complexes were used as the electron injection materials for multilayer OLEDs. In the case of OLEDs using 2-methyl-9,10-bis(naphthalene-2-yl)anthracene (MADN) as the electron transport layer (ETL), Naq and NaMeq show much better performance than LiF in OLED devices.
Co-reporter:Da-Xing Yuan, Xiao-Dong Yuan, Qing-Yang Xu, Mei-Feng Xu, Xiao-Bo Shi, Zhao-Kui Wang and Liang-Sheng Liao
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 40) pp:NaN26658-26658
Publication Date(Web):2015/09/14
DOI:10.1039/C5CP03995A
Perovskite film generally has rough surface morphology due to the voids between the grain domains. Smoothed interface contact between the perovskite layer and the top electrode is critical for planar perovskite solar cells. We reported high efficiency bromine–iodine based perovskite solar cells with a flattening cathode interface by incorporating a solution-processed bathocuproine (sBCP) interfacial layer at the cathode side. Compared with vacuum evaporated bathocuproine (eBCP), sBCP demonstrated an excellent surface modification effect at the cathode side with very smaller charge transfer resistance. Accordingly, a high fill factor exceeding 85% and a power conversion efficiency exceeding 13% in CH3NH3PbI3−xBrx based perovskite solar cells were achieved. The largely improved fill factor was attributed to the smooth film morphology and full surface coverage of perovskite films modified by the solution-processed BCP layer.
Co-reporter:Da-Xing Yuan, Adam Gorka, Mei-Feng Xu, Zhao-Kui Wang and Liang-Sheng Liao
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 30) pp:NaN19750-19750
Publication Date(Web):2015/06/12
DOI:10.1039/C5CP02705E
In this work, NH2CHNH2PbI3 (FAPbI3) was employed for light harvesting in inverted planer perovskite solar cells for the first time. Except for the silver cathode, all layers were solution-processed under or below 140 °C. The effect of the annealing process on device performance was investigated. The FAPbI3 solar cells based on a slowed-down annealing shows superior performance compared to the CH3NH3PbI3 (MAPbI3)-based devices, especially for the short circuit current density. A power conversion efficiency of 13.56% was obtained with high short circuit current density of 21.48 mA cm−2. This work paves the way for low-temperature fabrication of efficient inverted planer structure FAPbI3 perovskite solar cells.
Co-reporter:Lin-Song Cui, Yuan Liu, Xiao-Dong Yuan, Qian Li, Zuo-Quan Jiang and Liang-Sheng Liao
Journal of Materials Chemistry A 2013 - vol. 1(Issue 48) pp:NaN8185-8185
Publication Date(Web):2013/10/15
DOI:10.1039/C3TC31675K
Two novel bipolar host materials, BCzSCN and BCzSPO, consisting of an electron deficient cyano or diphenylphosphine oxide acceptor linked to a bicarbazole donor, were designed and synthesized. Their thermal, photophysical and electrochemical properties were systematically investigated. Both BCzSCN and BCzSPO show high triplet energies of over 2.75 eV and could be developed for application in blue phosphorescent organic light-emitting diodes (PHOLEDs), and further for white PHOLEDs. Moreover, the characterization of hole-only and electron-only devices based on BCzSCN and BCzSPO indicate their rather balanced hole/electron injection and transport properties. Blue PHOLEDs containing BCzSCN and BCzSPO as the hosts and FIrpic as a dopant exhibited excellent performance, with maximum external quantum efficiencies of 19.3% and 17.1% respectively. In particular, blue PHOLEDs adopting BCzSCN and BCzSPO exhibited extraordinary low efficiency roll-offs of 5.2% and 7.6% at a brightness of 1000 cd m−2, respectively. Meanwhile, the all-phosphor near-white devices hosted by the two materials were also fabricated, and high external quantum efficiencies of 22.0% and 21.3% were achieved.
Co-reporter:Lin-Song Cui, Shou-Cheng Dong, Yuan Liu, Qian Li, Zuo-Quan Jiang and Liang-Sheng Liao
Journal of Materials Chemistry A 2013 - vol. 1(Issue 25) pp:NaN3975-3975
Publication Date(Web):2013/04/18
DOI:10.1039/C3TC30410H
A series of novel blue phosphorescent host materials, namely, CTP-1, CTP-2 and CTP-3 have been designed and synthesized through the Suzuki–Miyaura cross-coupling reaction between N-phenylcarbazole and biphenyl. Their thermal, photophysical and electrochemical properties were systematically investigated. These novel hosts show excellent thermal stability and high glass transition temperatures (Tg) ranging from 113 to 127 °C. The triplet energies of these three materials are significantly higher than that of (4,4′-bis(N-carbazolyl)-2,2′-biphenyl) (CBP, 2.56 eV) and that of the most popular blue phosphorescent material iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,C2′] picolinate (FIrpic, 2.65 eV). These three novel materials have superior thermal and electronic properties for blue and white phosphorescent OLEDs. Blue emitting devices with an Ir-complex FIrpic as the phosphorescent dopant have been fabricated and show high efficiency with low roll-off. In particular, 40.4 cd A−1 at 100 cd m−2 and 38.2 cd A−1 at 1000 cd m−2 were achieved when CTP-1 was used as the host material. On the basis of this work, an all-phosphor white device with a current efficiency of 64.5 cd A−1 at 100 cd m−2 and 61.9 cd A−1 at 1000 cd m−2 has also been fabricated.
Co-reporter:Yuan Liu, Lin-Song Cui, Xiao-Bo Shi, Qian Li, Zuo-Quan Jiang and Liang-Sheng Liao
Journal of Materials Chemistry A 2014 - vol. 2(Issue 41) pp:NaN8744-8744
Publication Date(Web):2014/08/27
DOI:10.1039/C4TC01619J
Two novel materials, SF2BCz and SF3BCz, which combine spirobifluorene (SF) and carbazole units by meta- and para-bonding, have been designed and synthesized by a straightforward process as hosts in phosphorescent organic light-emitting diodes (PhOLEDs), and their thermal and electronic absorption and photoluminescent properties investigated. The meta-linkage of SF enables SF3BCz to possess high triplet and energy levels and good thermal stability. Blue PhOLEDs featuring SF3BCz as a host give high performance and low roll-off, with an efficiency of 41.4 cd A−1 (39.8 lm W−1) at 100 cd m−2 and 39.7 cd A−1 (29.8 lm W−1) at 1000 cd m−2. In addition, SF3BCz has been adopted as a universal host for white PhOLEDs, with a maximum external quantum efficiency of 21.3% for two-color and 19.8% for three-color-based white devices. By adopting tandem technology, a four-color-based white PhOLED was also successfully constructed, achieving 40% external quantum efficiency and a stable color spectrum.
Co-reporter:Xiao-Dong Yuan, Jian Liang, Yun-Chu He, Qian Li, Cheng Zhong, Zuo-Quan Jiang and Liang-Sheng Liao
Journal of Materials Chemistry A 2014 - vol. 2(Issue 31) pp:NaN6394-6394
Publication Date(Web):2014/06/12
DOI:10.1039/C4TC00867G
Two novel carbazole derivatives, 3,3′-(2,6-dimethyl-1,4-phenylene)bis(9-phenyl-9H-carbazole) (DMCz) and 3,3′-(2,3,5,6-tetramethyl-1,4-phenylene)bis(9-phenyl-9H-carbazole) (TMCz), are designed and synthesized as host materials for blue phosphorescent organic light emitting diodes (PHOLEDs). Both the materials possess sufficiently high glass transition temperatures and triplet energies for the blue dopant Ir-complex iridium(III) bis(4,6-(difluorophenyl)-pyridinato-N,C′)picolinate (FIrpic, 2.65 eV). The device using DMCz as the host material showed a better performance than that of TMCz with a maximum power efficiency of 36.0 ± 0.7 lm per W, a maximum current efficiency of 43.7 ± 0.6 cd per A and a maximum external quantum efficiency (EQE) of 18.5 ± 0.1%.
Co-reporter:Yuan Liu, Lin-Song Cui, Mei-Feng Xu, Xiao-Bo Shi, Dong-Ying Zhou, Zhao-Kui Wang, Zuo-Quan Jiang and Liang-Sheng Liao
Journal of Materials Chemistry A 2014 - vol. 2(Issue 14) pp:NaN2495-2495
Publication Date(Web):2014/01/15
DOI:10.1039/C3TC32301C
Organic light-emitting diodes (OLEDs) have attracted tremendous interest and have already become a prevalent technology in MP3 players, smartphones and cameras. In response to the calls for the large-scale application of OLEDs, the complicated and costly processes for preparing a device is a major challenge which should be addressed. Herein, a novel bipolar host material, 26PyzCz, which contains a pyrazine/carbazole hybrid, has been designed and synthesized. 26PyzCz-based single-layer (SL) fluorescent (F)–phosphorescent (P) OLEDs with various colors have been successfully fabricated. Green and orange SL phosphorescent OLEDs (PHOLEDs) have exhibited efficiencies as high as 63.3 and 62.1 cd A−1 at 1000 cd m−2, and 55.7 and 53.8 cd A−1 at 10000 cd m−2, respectively. Meanwhile, a SL warm white OLED based on fluorescent blue and phosphorescent orange has demonstrated excellent performance, with a maximum current efficiency of 27.5 cd A−1 and a maximum power efficiency of 21.6 lm W−1. In addition, the charge carrier behavior have been evaluated by impedance spectroscopy, which revealed that the dopant trapping effect plays a critical role in charge balance and exciton generation in the SL PHOLEDs.
Co-reporter:Xiang-Yang Liu, Feng Liang, Lei Ding, Shou-Cheng Dong, Qian Li, Lin-Song Cui, Zuo-Quan Jiang, Hua Chen and Liang-Sheng Liao
Journal of Materials Chemistry A 2015 - vol. 3(Issue 35) pp:NaN9056-9056
Publication Date(Web):2015/08/10
DOI:10.1039/C5TC01828E
The introduction of spiro-acridine-fluorene (SAF) can affect the electronic structure of the whole molecule, which made SAF-based materials exhibit totally different photophysical properties from conventional spirobifluorene-based materials. With these properties, an external quantum efficiency of nearly 25% was achieved for sky-blue phosphorescent organic light-emitting diodes.
Co-reporter:Xiang-Yang Liu, Feng Liang, Yi Yuan, Zuo-Quan Jiang and Liang-Sheng Liao
Journal of Materials Chemistry A 2016 - vol. 4(Issue 33) pp:NaN7874-7874
Publication Date(Web):2016/07/25
DOI:10.1039/C6TC02180H
Two novel materials, 10-(6-(dibenzo[b,d]furan-1-yl)pyrazin-2-yl)-9,9-diphenyl-9,10-dihydroacridine (PrFPhAc) and 10-(6-(dibenzo[b,d]thiophen-1-yl)pyrazin-2-yl)-9,9-diphenyl-9,10-dihydroacridine (PrTPhAc), were designed and synthesized by introducing heterocyclic pyrazine between 9,10-dihydroacridine and dibenzofuran/dibenzothiophene moieties. The basic properties, such as thermal, photophysical and electrochemical properties, were systematically investigated and compared. Both the materials have suitable triplet energies for red phosphorescent organic light-emitting diodes, and dibenzofuran (DBF) derivative PrFPhAc was finally achieved with superior external quantum efficiency of 22%.
Co-reporter:Yuanyuan Han, Lei Zhang, Xiujuan Zhang, Kaiqun Ruan, Linsong Cui, Yuming Wang, Liangsheng Liao, Zhaokui Wang and Jiansheng Jie
Journal of Materials Chemistry A 2014 - vol. 2(Issue 1) pp:NaN207-207
Publication Date(Web):2013/10/16
DOI:10.1039/C3TC31722F
Graphene shows great promise as a transparent conductive electrode to replace conventional indium tin oxide (ITO) for optoelectronic applications. However, the wide applications of graphene in fields such as organic light emitting diodes (OLEDs) are restricted by the difficulty in obtaining a clean and flat graphene surface, as the large residue generated during graphene transfer can lead to a large short circuit current and consequently degradation of the device performance. Here, we report a novel sandwich method to achieve the efficient transfer of graphene with an ultra-clean and flat surface onto a flexible substrate for OLED applications. Differing from the conventional poly(methyl methacrylate) (PMMA)-supported transfer technique, an organic small molecular buffer layer, e.g., a 2-(diphenylphosphory) spirofluorene (SPPO1) layer, was inserted between PMMA and graphene, forming a PMMA/SPPO1/graphene sandwich structure. The separation of PMMA from graphene, along with the large solubility of SPPO1 in clean solvent, results in a substantial reduction of PMMA residue on the graphene. As expected, flexible OLED devices based on the PMMA/SPPO1 transferred graphene films exhibited a much enhanced performance compared to their counterparts fabricated from PMMA transferred films. Our results demonstrate the great potential of the sandwich transfer technique for the fabrication of high-performance OLED devices, as well as other optoelectronic devices.
Co-reporter:Xun Tang, Lei Ding, Yan-Qiu Sun, Yue-Min Xie, Ya-Li Deng, Zhao-Kui Wang and Liang-Sheng Liao
Journal of Materials Chemistry A 2015 - vol. 3(Issue 48) pp:NaN12402-12402
Publication Date(Web):2015/10/19
DOI:10.1039/C5TC03108G
Green phosphorescent inverted organic light-emitting diodes (IOLEDs) with 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN)/aluminium/n-doped 4,7-diphenyl-1,10-phenanthroline (Bphen) used as an electron injection layer (EIL) were demonstrated. The IOLED shows the lowest driving voltage of 4.5 V at 10000 cd m−2 to date. The electron injection effects of different interlayers were further investigated by ultraviolet photoelectron spectroscopy (UPS) and evaluating the electron injection efficiency. For application in large-sized OLEDs, a 120 × 120 mm2 flexible IOLED was successfully fabricated based on this inverted structure.
Co-reporter:Ya-Li Deng, Lin-Song Cui, Yuan Liu, Zhao-Kui Wang, Zuo-Quan Jiang and Liang-Sheng Liao
Journal of Materials Chemistry A 2016 - vol. 4(Issue 6) pp:NaN1256-1256
Publication Date(Web):2016/01/06
DOI:10.1039/C5TC03793J
A new red phosphorescent material Ir(dmppm)2(dmd), which is a pyrimidine-based iridium(III) complex, has been synthesized and successfully used to fabricate solution-processed red and white organic light-emitting diodes (OLEDs). Due to its excellent solubility in common organic solvents and its good compatibility with the host material, a record current efficiency of 27.2 cd A−1 so far with satisfactory Commission International de l'Eclairage (CIE) coordinates of (0.60, 0.40) has been achieved for partially solution-processed red OLEDs by using Ir(dmppm)2(dmd) as a dopant. Furthermore, the fabricated two-component “warm-white” OLEDs based on the Ir(dmppm)2(dmd) red emitter demonstrate a maximum current efficiency of 28.9 cd A−1, which can meet the call for physiologically-friendly indoor illumination.
Co-reporter:Ya-Li Deng, Yue-Min Xie, Lei Zhang, Zhao-Kui Wang and Liang-Sheng Liao
Journal of Materials Chemistry A 2015 - vol. 3(Issue 24) pp:NaN6223-6223
Publication Date(Web):2015/05/18
DOI:10.1039/C5TC00851D
The authors develop an aqueous solution-processed hole injection layer, MoO3 doped copper phthalocyanine-3,4′,4′′,4′′′-tetra-sulfonated acid tetra sodium salt (TS-CuPc), in organic light-emitting diodes (OLEDs) via an environmentally-friendly and easy fabrication process. The generation of a charge transfer complex in TS-CuPc:MoO3 composite films is confirmed by absorption spectra and X-ray photoemission spectroscopy (XPS) measurements. Enhanced hole injection in OLEDs is attributed to the decreased hole barrier at the ITO side, which is in agreement with the Schottky thermal emission evaluation. The efficient modification of ITO by TS-CuPc:MoO3 is further confirmed by ultraviolet photoemission spectroscopy (UPS) measurements.
Co-reporter:Bo Wang, Lei Zhang, Yun Hu, Xiao-Bo Shi, Zhao-Kui Wang and Liang-Sheng Liao
Journal of Materials Chemistry A 2016 - vol. 4(Issue 27) pp:NaN6574-6574
Publication Date(Web):2016/06/14
DOI:10.1039/C6TC01624C
Carrier injection plays an important role in determining the device performance of organic light-emitting diodes (OLEDs). 1,4,5,8,9,11-Hexaazatriphenylene hexacarbonitrile (HAT-CN) has been widely used as an effective material to promote the hole injection when fabricating vacuum deposited OLEDs. However, serious crystallization occurs in solution-processed HAT-CN films, which weakens its hole injection ability in OLEDs. Herein, we demonstrate a solution-processed composite film as the hole injection layer (HIL) in OLEDs developed by mixing HAT-CN with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ). The crystallization is suppressed effectively by optimizing the mixing ratio. In addition, a doping of HAT-CN:F4-TCNQ composite film contributes to a decreased hole injection barrier, which can be reflected from the current density–voltage curve. Furthermore, HAT-CN:F4-TCNQ is successfully combined with MoO3 doped copper phthalocyanine-3,4′,4′′,4′′′-tetra-sulfonated acid tetra sodium salt (TS-CuPc) as bi-HIL in solution-processable blue phosphorescent OLEDs, which exhibit a maximum current efficiency of 16.7 cd A−1.
Co-reporter:Jianfeng Lu, Xiaobao Xu, Kun Cao, Jin Cui, Yibo Zhang, Yan Shen, Xiaobo Shi, Liangsheng Liao, Yibing Cheng and Mingkui Wang
Journal of Materials Chemistry A 2013 - vol. 1(Issue 34) pp:NaN10015-10015
Publication Date(Web):2013/06/20
DOI:10.1039/C3TA11870C
In this study, new push–pull alkoxy-wrapped zinc porphyrin dyes with intramolecular donor–π–acceptor structures have been designed and synthesized for dye-sensitized solar cells (DSCs). The linkers based on thiophene or 2,3-dihydrothieno[3,4-b][1,4] dioxine with cyanoacetic acid can broaden the spectral response of porphyrins into the near-IR region (∼850 nm), which is mainly attributed to the cyanoacetic acid group. However, porphyrins with cyanoacrylic acid as an anchoring group lead to a faster charge recombination rate at the dye-sensitized heterojunction interface, which lowers the device photovoltaic performance. By using porphyrins with a rigid π-linker feature structure that is 5-ethynylthiophene-2-carboxylic acid, highly efficient DSC devices with a power conversion efficiency of 9.5% can be obtained. Spectral, electrochemical, photovoltage transient decay and impedance measurements are performed to reveal the influence of π-conjugated linkers and anchoring groups upon the optoelectronic features of porphyrin dyes in DSCs.
Co-reporter:Zhao Wei, Liang Feng, Jin Zhi-Ming, Shi Xiao-Bo, Yin Peng-Hui, Wang Xue-Ren, Sun Cheng, Gao Zhan-Qi and Liao Liang-Sheng
Journal of Materials Chemistry A 2014 - vol. 2(Issue 33) pp:NaN13231-13231
Publication Date(Web):2014/06/18
DOI:10.1039/C4TA02369B
An Ag/AgVO3 plasmonic photocatalyst was synthesized via in situ reduction of AgVO3 by NaBH4 at room temperature. The Ag/AgVO3 showed high photocatalytic activity due to the relatively high conductivity and electron-storing capacity of Ag nanoparticles, which facilitate the charge transfer between AgVO3 and Ag nanoparticles. FDTD simulation indicates that the formed Ag nanoparticles induce SPR leading to the increased electric field and the enhanced absorption of visible light.
Co-reporter:Mei-Feng Xu, Ying-Jie Liao, Feng-Shuo Zu, Jian Liang, Da-Xing Yuan, Zhao-Kui Wang and Liang-Sheng Liao
Journal of Materials Chemistry A 2014 - vol. 2(Issue 24) pp:NaN9404-9404
Publication Date(Web):2014/04/08
DOI:10.1039/C4TA01441C
The authors demonstrate an aqueous solution-processed Cs2CO3 thin film with an adjustable work function via MoO3 and/or Na2WO4 doping. The doped Cs2CO3 as a cathode interfacial layer is successfully used in poly(3-hexyl-thiophene) (P3HT)/indene-C60 bisadduct (IC60BA) heterojunction based solar cells with improved open-circuit voltage and unaffected short-circuit current density. X-ray photoelectron spectroscopy (XPS) evaluation was conducted to verify the formation of the new composites of W–O–Cs and Mo–O–Cs after doping of MoO3 and/or Na2WO4 into Cs2CO3. The change of the work function of MoO3- and/or Na2WO4-doped Cs2CO3 was further confirmed by ultraviolet photoelectron spectroscopy (UPS) measurements.
Co-reporter:Femi Igbari, Meng Li, Yun Hu, Zhao-Kui Wang and Liang-Sheng Liao
Journal of Materials Chemistry A 2016 - vol. 4(Issue 4) pp:NaN1335-1335
Publication Date(Web):2015/12/17
DOI:10.1039/C5TA07957H
The fabrication and device parameters of inverted planar heterojunction (PHJ) organic–inorganic lead mixed-halide (CH3NH3PbI3−xClx) perovskite based solar cells (PSCs) using a:CuAlO2 as the hole selective buffer layer between the ITO electrode and PEDOT:PSS were demonstrated. Thin films of a:CuAlO2 were derived from a pre-fabricated polycrystalline CuAlO2 ceramic target by using the direct current (d.c.) magnetron sputtering technique. The one-step spin coating method was used to prepare the perovskite layer. A short circuit current density (Jsc) of 21.98 mA cm−2, an open circuit voltage (Voc) of 0.88 V, a fill factor (FF) of 0.75 and a power conversion efficiency (PCE) of 14.52% were achieved for the optimized device. These improved device parameters were also accompanied by improved stability as a result of sandwiching the ambient stable a:CuAlO2 layer with decent conductivity between the ITO and the PEDOT:PSS layers. The versatility of this material application was also demonstrated as a similar improvement in device performance and stability, which was observed by using the prepared a:CuAlO2 in another perovskite solar cell system based on CH3NH3PbI3 prepared by the two-step spin-coating method.
Co-reporter:Yan-Qiu Sun, Yi-Long Lei, Jing Gao, Xu-Hui Sun, Sheng-Huang Lin, Qiao-Liang Bao, Qing Liao, Shuit-Tong Lee and Liang-Sheng Liao
Chemical Communications 2014 - vol. 50(Issue 74) pp:NaN10814-10814
Publication Date(Web):2014/07/24
DOI:10.1039/C4CC04794J
Two-dimensional (2D) hexagonal microsheets of 8-hydroxyquinoline zinc (Znq2) were synthesized readily via a mixed solvent induced self-assembly method. The 2D optical waveguiding properties of the microsheets have been clearly revealed by both fluorescence microscopy and confocal microscopy. In addition, the reversible vapochromic properties of the microsheets have also been demonstrated when the Znq2 is exposed to HCl and NH3 vapors.
Co-reporter:Xiang-Yang Liu, Feng Liang, Yi Yuan, Lin-Song Cui, Zuo-Quan Jiang and Liang-Sheng Liao
Chemical Communications 2016 - vol. 52(Issue 52) pp:NaN8151-8151
Publication Date(Web):2016/06/08
DOI:10.1039/C6CC02856J
A thermally activated delayed fluorescence material 2,6-bis(9,9-diphenylacridin-10(9H)-yl)pyrazine was designed and synthesized. The twisted configuration made it possesses very small singlet–triplet splitting. A red electroluminescent device based on this new host material is able to achieve ∼26% external quantum efficiency and relatively flat efficiency roll-off.
Co-reporter:Miao-Miao Xue, Chen-Chao Huang, Yi Yuan, Ye-Xin Zhang, Man-Keung Fung and Liang-Sheng Liao
Chemical Communications 2017 - vol. 53(Issue 1) pp:NaN265-265
Publication Date(Web):2016/12/01
DOI:10.1039/C6CC09486D
A new electron-withdrawing moiety (BFPz) has been used for the first time as an acceptor in OLEDs and its corresponding core unit (2-Br-BFPz) was synthesized. Combined with an electron-donating moiety triphenylamine, a novel fluorescent material with a D–A structure named TPA-BFPz was synthesized. Encouragingly, the EQE values of non-doped and doped blue OLEDs reach 3.68% and 4.42%, respectively.
Co-reporter:Junming Li, Shou-Cheng Dong, Andreas Opitz, Liang-Sheng Liao and Norbert Koch
Journal of Materials Chemistry A 2017 - vol. 5(Issue 28) pp:NaN6996-6996
Publication Date(Web):2017/06/26
DOI:10.1039/C7TC02248D
Modern high-efficiency organic light-emitting diodes (OLEDs) based on phosphorescence and thermally activated delayed fluorescence (TADF) rely on host materials that are optimized with respect to many properties simultaneously, including thermal stability, photophysical properties, energy levels, and charge carrier transport. Responding to this challenge, we synthesized and investigated carbazole/dibenzothiophene derivatives as potential hosts, in which carbazole acts as electron donating and dibenzothiophene as electron withdrawing unit. Within this series, the carbazole/dibenzothiophene fraction and the linking phenyl spacer length were systematically varied. Through comprehensive assessment of all material parameters mentioned above and the performance of these host in phosphorescent and TADF OLEDs, we could reliably identify the most suitable molecule for applications and provide guidelines for further material development. With 9-(3′-(dibenzo[b,d]thiophen-4-yl)-[1,1′-biphenyl]-3-yl)-9H-carbazole, bearing one carbazole and one dibenzothiophene unit linked with biphenyl in meta position, we achieved high external quantum efficiency for blue (17.9%) and green (19.4%) modern OLEDs.
Co-reporter:Zhi-Zhou Li, Xue-Dong Wang and Liang-Sheng Liao
Journal of Materials Chemistry A 2017 - vol. 5(Issue 27) pp:NaN6666-6666
Publication Date(Web):2017/06/16
DOI:10.1039/C7TC02013A
Organic nano/microcrystals with desirable optical/electrical properties and a regular morphology are extensively applied in various optoelectronic devices at the microscale, but the morphology/luminescence-modulation of organic microstructures remains to be a great challenge. Herein, we utilize a protonation/de-protonation process to simultaneously modulate both the luminescence and the morphology of blue-emissive two-dimensional (2D) organic microcrystals, which are self-assembled from 1,4-bis((E)-2-(3-methylpyridin-4-yl)vinyl)benzene (MSP) by a facile solution-exchange method. Impressively, 1D color-tunable MSP·nHCl (n is an integer) organic microwires can be obtained by the protonation process activated by the addition of an acid (such as hydrochloric acid). When n = 2 or n > 2, these obtained MSP·2HCl or MSP·nHCl microcrystals with a 1D wire-morphology emitted yellow light and red light, respectively.
Co-reporter:Ying-Li Shi, Feng Liang, Yun Hu, Xue-Dong Wang, Zhao-Kui Wang and Liang-Sheng Liao
Journal of Materials Chemistry A 2017 - vol. 5(Issue 22) pp:NaN5377-5377
Publication Date(Web):2017/05/09
DOI:10.1039/C7TC00449D
For the purpose of fabricating solution-processed quantum-dot light-emitting diodes (QLEDs) with high performance, the efficient hole–electron recombination at low current density is particularly pivotal. Herein, to enhance the charge balance of the QLED device, we employed lithium bis(trifluoromethylsulfonyl)imide (Li-TFSI) as a p-type dopant into the hole-transporting material (HTM) of poly(9-vinlycarbazole) (PVK). In the experiment, the increased conductivity and the enhanced charge mobility of the Li-TFSI-doped PVK layer were confirmed by the J–V curves of the hole-only devices and conductive atomic force microscopy (c-AFM). Furthermore, on combining ultraviolet photoelectron spectroscopy (UPS) and the absorption spectra, it was found that the highest occupied molecular orbital (HOMO) of the Li-TFSI-doped PVK layers gradually shifted closer to the Fermi level upon increasing the doping ratios from 0 to 4.5 wt%. Therefore, the hole-injecting barrier decreases from 1.17 eV to 0.64 eV. As a result, the maximum current efficiency and the highest external quantum efficiency (EQE) of our fabricated QLED devices can reach as high as 15.5 cd A−1 and 11.46%, respectively. It was demonstrated that the p-type dopant Li-TFSI in the HTM can contribute to the fabrication of high-performance solution-processed light-emitting diodes.
Co-reporter:Mei-Feng Xu, Hong Zhang, Su Zhang, Hugh L. Zhu, Hui-Min Su, Jian Liu, Kam Sing Wong, Liang-Sheng Liao and Wallace C. H. Choy
Journal of Materials Chemistry A 2015 - vol. 3(Issue 27) pp:NaN14430-14430
Publication Date(Web):2015/06/08
DOI:10.1039/C5TA02730F
CH3NH3PbI3 is commonly used in perovskite solar cells due to its long diffusion length and good crystallinity. In this paper, in the one-step approach using CH3NH3I and PbCl2 for forming the perovskite, we present a new low temperature annealing approach of gradually increasing the temperature to fabricate perovskite films. Various temperatures and temperature ranges for the formation of perovskite films have been studied. Using the gradual annealing process, we can tune the amount of chlorine in the atomic ratio of chlorine/iodine from 1.2 to 4.0%. Meanwhile, the gradual annealing process influences the quality of the perovskite film and importantly the device performance. The results show that through the optimized process, the film quality is improved with high surface coverage and good photoluminescence and reproducibility. We find that a higher amount of chlorine in the perovskite film plays a positive role in the device performance in the approach for achieving a power conversion efficiency of 14.9% with no obvious hysteresis.
Co-reporter:Min Qian, Meng Li, Xiao-Bo Shi, Heng Ma, Zhao-Kui Wang and Liang-Sheng Liao
Journal of Materials Chemistry A 2015 - vol. 3(Issue 25) pp:NaN13539-13539
Publication Date(Web):2015/05/20
DOI:10.1039/C5TA02265G
Anode modification by doping silver nano-particles (Ag NPs) into poly(3,4-ethylene dioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) and cathode interfacial modification by inserting solution-processed bathophenanthroline (sBphen) in CH3NH3PbI3−xClx based planar perovskite solar cells are investigated. Prior to the optical effect such as localized surface plasmon resonance, the Ag-NPs distributed in PEDOT:PSS mainly cause an improvement in the electrical property of PEDOT:PSS–Ag NPs composite films. The sBphen interfacial layer modified the surface morphology of perovskite/phenyl-C61-butyric acid methyl ester (PC61BM) films by filling the voids on the surface of perovskite/PC61BM effectively, which led to an obvious improvement in the fill factor. Accordingly, an efficient device with a power conversion efficiency of 15.75% was achieved due to the simultaneous cathode and anode interfacial modification.
Co-reporter:Xiao-Bo Shi, Min Qian, Dong-Ying Zhou, Zhao-Kui Wang and Liang-Sheng Liao
Journal of Materials Chemistry A 2015 - vol. 3(Issue 8) pp:NaN1671-1671
Publication Date(Web):2015/01/15
DOI:10.1039/C4TC02596B
The authors demonstrate a honeycomb structured organic light-emitting diode (OLED) with high enhancements greater than 2.0 fold and 2.3 fold in current efficiency and power efficiency, respectively. The dispersion relationships in both planar and nano-honeycomb structured OLEDs are calculated through numerical simulations utilizing the finite-difference time-domain method and measured through the electroluminescence spectra. There is good agreement between the numerically calculated and the experimentally measured dispersion relationships for the nano-honeycomb structured OLEDs. Improved light out-coupling efficiency is mainly attributed to the efficient extraction of the waveguide and the surface plasmon polariton (SPP) loss modes in the devices. Particularly, most of the extracted energy is verified to be originated from the SPP loss mode in honeycomb structured OLEDs.
Co-reporter:Yue-Min Xie, Lin-Song Cui, Yuan Liu, Feng-Shuo Zu, Qian Li, Zuo-Quan Jiang and Liang-Sheng Liao
Journal of Materials Chemistry A 2015 - vol. 3(Issue 20) pp:NaN5353-5353
Publication Date(Web):2015/04/23
DOI:10.1039/C5TC00523J
A new host material BCz–Si for blue and white phosphorescent organic light-emitting devices was designed and synthesized. The introduction of the triphenylsilyl moiety into the BCz unit can efficiently tune the HOMO/LUMO energy levels and maintain high triplet energy. Its carrier mobility, thermal, photophysical, and electrochemical properties were also systematically investigated. The high triplet energy of BCz–Si ensures efficient energy transfer from the host to the triplet emitter FIrpic. The blue device using BCz–Si as a host material achieved a maximum quantum efficiency of 21.0%, corresponding to a current efficiency and power efficiency as high as 46.5 cd A−1 and 45.8 lm W−1, respectively; meanwhile, high efficiency white phosphorescent OLEDs hosted by BCz–Si were also fabricated with a maximum external quantum efficiency of 24.6%, 70.5 cd A−1 for two-color based and 21.5%, 50.1 cd A−1 for three color based devices.
Co-reporter:Lei Ding, Yan-Qiu Sun, Hua Chen, Feng-Shuo Zu, Zhao-Kui Wang and Liang-Sheng Liao
Journal of Materials Chemistry A 2014 - vol. 2(Issue 48) pp:NaN10408-10408
Publication Date(Web):2014/11/03
DOI:10.1039/C4TC02082K
An intermediate connector (IC) consisting of lithium (Li) doped 4,7-diphenyl-1,10-phenanthroline (BPhen)/Al/tetrafluoro-tetracyanoquinodimethane (F4-TCNQ)/1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN) is developed for fabricating tandem white organic light-emitting diodes (WOLEDs). An investigation of the charge generation and separation process in Bphen:Li/Al/F4-TCNQ/HAT-CN, which is carried out by analysis of the current–voltage and capacitance–voltage characteristics, shows that the proposed IC structure is suitable as a connecting unit in tandem OLEDs. The tandem WOLED based on a silicon compound host material of 10-phenyl-2′-(triphenylsilyl)-10H-spiro [acridine-9,9′-fluorene] (SSTF) with the proposed IC structure exhibits a maximum current efficiency of 159.2 cd A−1 and a maximum power efficiency of 69.4 lm W−1. For application in large-area OLEDs, a 150 × 150 mm2 tandem lighting panel with maximum efficiencies of 231.8 cd A−1 and 52.9 lm W−1, correlated color temperature of 3000 K and Commission International de I'Eclairage (CIE) coordinates of (0.34, 0.45) is also demonstrated.
Co-reporter:Shou-Cheng Dong, Yuan Liu, Qian Li, Lin-Song Cui, Hua Chen, Zuo-Quan Jiang and Liang-Sheng Liao
Journal of Materials Chemistry A 2013 - vol. 1(Issue 40) pp:NaN6584-6584
Publication Date(Web):2013/08/09
DOI:10.1039/C3TC31336K
Four novel host materials were designed and synthesized, incorporating fluorene-spiro-annulated triphenylamine–carbazole (ST–SCz) and dibenzothiophene (DBT) blocks. A meta-linking strategy was applied by introducing DBT moieties to ST–SCz skeletons at the C3 position of the fluorene backbones. As expected, high triplet energies (over 2.80 eV) were achieved in all four materials despite the different linking positions on the DBT. All four materials show a high Tg from 149 to 163 °C, which benefits from their spiro-structure. Their thermal, electrochemical and photo-physical properties were fully characterized. Highly efficient blue and white PHOLEDs were fabricated using these four materials as the hosts. Triphenylamine-containing STDBT4 and STDBT2 demonstrate better device performance due to their relatively high-lying HOMO compared to carbazole-containing SCzDBT4 and SCzDBT2. Maximum ηext of 19.6% and 18.4% (STDBT4 and STDBT2) were achieved for FIrpic-based devices, and 23.7% and 22.2% (STDBT4 and STDBT2) were achieved for two color-based white PHOLEDs with double emitting layers, using PO-01 as a yellow dopant. Finally, a highly efficient single-emitting layer white PHOLED with maximum efficiencies of 24.0%, 77.0 cd A−1 and 63.2 lm W−1 and CIE coordinates of (0.38, 0.48) was realized using the device configuration of ITO/HAT–CN/TAPC/STDBT4: 8 wt% FIrpic: 0.8 wt% PO-01/TmPyPB/Liq/Al. The device shows good color stability and low efficiency roll-off. Even at a high luminance of 10000 cd m−2, it still maintains very high efficiencies of 17.9%, 56.4 cd A−1 and 26 lm W−1.
Co-reporter:Shou-Cheng Dong, Chun-Hong Gao, Zhao-Hu Zhang, Zuo-Quan Jiang, Shuit-Tong Lee and Liang-Sheng Liao
Physical Chemistry Chemical Physics 2012 - vol. 14(Issue 41) pp:NaN14228-14228
Publication Date(Web):2012/06/28
DOI:10.1039/C2CP41535F
A new class of host materials DBFSF (DBFSF2 and DBFSF4) is facilely synthesized through a Suzuki coupling reaction between dibenzofuran and spirobifluorene. Their thermal, electrochemical, electronic absorption and photoluminescent properties are fully investigated. High glass transition temperatures (Tg) of 115 °C and 124 °C are observed for DBFSF2 and DBFSF4, respectively, due to the introduction of bulky spirobifluorene groups. As expected, the DBFSF4 with a twisted-linkage exhibits higher triplet energy than DBFSF2 and can be used in blue and green phosphorescent OLEDs. Electrophosphorescent devices with DBFSF2 and DBFSF4 as hosts were fabricated. Besides the good current efficiencies of 22.2 cd A−1 for blue and 64.4 cd A−1 for green, low efficiency roll-off has also been achieved for both devices.
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