Co-reporter:Feng Jin, Jianyu Yuan, Wenping Guo, Lu Han, Yalong Xu, Chuanxiang Sheng, Wanli Ma, and Haibin Zhao
The Journal of Physical Chemistry C September 21, 2017 Volume 121(Issue 37) pp:20126-20126
Publication Date(Web):September 8, 2017
DOI:10.1021/acs.jpcc.7b04984
All-polymer solar cells composed of wide-band-gap polymer poly(1-{4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]-benzo[1,2-b:4,5-b′]dithiophen-2-yl}-3-methyl-5-(4-octylphenyl)-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione) (PTP8) as the donor and poly[1,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)] [P(NDI2OD-T2), also known as Activink N2200] as the acceptor exhibit a broad absorbance in the range 300–900 nm, thanks to complementary absorption of near-infrared light by N2200. Although N2200 shows reasonably high electron mobility, the contribution of the photogenerated excitons in N2200 to the power conversion of the PTP8/N2200 solar cell is insignificant. Here, the hole transfer from N2200 to PTP8 in PTP8/N2200 blend films was investigated by utilizing ultrafast transient absorption spectroscopy. The spectral fingerprints of ground-state bleaching and hole polaron-induced absorption of PTP8 are identified under selective excitation of the N2200 component and unambiguously indicate hole transfer from N2200 to PTP8. The hole transfer is slow (∼100 ps), comparable to the geminate exciton recombination rate, consequently limiting the transfer efficiency and carrier generation. The hole-transfer efficiency depends on the PTP8/N2200 weight ratio, showing a highest value of ∼14.1% in the 3:2 film.
Co-reporter:Feng Jin, Guanqun Ding, Yuning Wang, Jianyu Yuan, Wenping Guo, Haochen Yuan, Chuanxiang Sheng, Wanli Ma, and Haibin Zhao
The Journal of Physical Chemistry C April 27, 2017 Volume 121(Issue 16) pp:8804-8804
Publication Date(Web):April 5, 2017
DOI:10.1021/acs.jpcc.7b03001
Ultrafast transient absorption (TA) spectroscopy was employed to investigate the thermal annealing effect on the charge transfer (CT) in bulk heterojunction (BHJ) all-polymer solar cells (all-PSCs) utilizing an n-type polymer P(NDI2OD-T2) (Polyera, N2200) as acceptor and a low bandgap polymer PBPT as donor. The CT generates hole polarons residing in the PBPT and electron polarons belonging to N2200, manifested in the TA spectra of the BHJ films as the long-lived absorption peak centered at ∼850 nm. The CT is most efficient in the film annealed at 160 °C and its efficiency declines monotonically when enhancing or reducing the annealing temperature, displaying a positive correlation with the power conversion efficiency (PCE) of the corresponding solar cell devices. This correlation is analyzed in terms of the crystallinity and phase separation, which are the key factors determining the performance of all-PSCs. Our results can provide valuable guidance for the fabrication of BHJ all-PSCs to improve their PCE.
Co-reporter:Yannan Zhang, Jianyu Yuan, Jianxia Sun, Guanqun Ding, Lu Han, Xufeng Ling, and Wanli Ma
ACS Applied Materials & Interfaces April 19, 2017 Volume 9(Issue 15) pp:13396-13396
Publication Date(Web):April 3, 2017
DOI:10.1021/acsami.7b02075
We have investigated a series of commercially available alkenyl carboxylic acids with different alkenyl chain lengths (trans-2-hexenoic acid (CA-6), trans-2-decenoic acid (CA-10), 9-tetradecenoic acid (CA-14)) for use as solvent additives in polymer–polymer non-fullerene solar cells. We systematically investigated their effect on the film absorption, morphology, carrier generation, transport, and recombination in all-polymer solar cells. We revealed that these additives have a significant impact on the aggregation of polymer acceptor, leading to improved phase segregation in the blend film. This in-depth understanding of the additives effect on the nanomorphology in all-polymer solar cell can help further boost the device performance. By using CA-10 with the optimal alkenyl chain length, we achieved fine phase separation, balanced charge transport, and suppressed recombination in all-polymer solar cells. As a result, an optimal power conversion efficiency (PCE) of 5.71% was demonstrated which is over 50% higher than that of the as-cast device (PCE = 3.71%) and slightly higher than that of devices with DIO treatment (PCE = 5.68%). Compared with widely used DIO, these halogen-free alkenyl carboxylic acids have a more sustainable processing as well as better performance, which may make them more promising candidates for use as processing additives in organic non-fullerene solar cells.Keywords: aggregation; alkenyl carboxylic acid; all-polymer solar cells; blend morphology; processing additives;
Co-reporter:Jianyu YuanMichael J. Ford, Yannan Zhang, Huilong Dong, Zhi Li, Youyong Li, Thuc-Quyen NguyenGuillermo C. Bazan, Wanli Ma
Chemistry of Materials 2017 Volume 29(Issue 4) pp:
Publication Date(Web):January 24, 2017
DOI:10.1021/acs.chemmater.6b05365
Narrow band gap conjugated polymers with a D–A–D′–A repeat unit architecture, namely, PF-0, PF-1a, PF-1b, and PF-2, were designed and synthesized. By precisely controlling the orientation of the asymmetric fluorobenzo[c][1,2,5]thiadiazole (FBT) fragments as well as incorporating different electron acceptors benzothiadiazole (BT) and difluorobenzo[c][1,2,5]thiadiazole (DFBT), regioregularity and graded fluorination have been achieved over the polymer backbone. There are evident differences between the properties of PF-1a and PF-1b due to different regioselectivity within the polymer backbone. In addition, the fluorinated analogues can exhibit increased light absorbance, higher electron density in the solid state, a lower-lying valence band, and more ordered solid film structure. The monofluorinated polymer PF-1b with the optimal regioselectivity and bis-fluorinated polymer PF-2 demonstrated improved charge transport as well as thermally resistant film structure (up to 300 °C) in organic field-effect transistors. Moreover, the fluorinated polymers exhibit dramatically increased efficiency from 5.58% to 8.42% in solar cells with lower amount of processing additive, indicating the important role of fluorination and regioselectivity in determining polymer properties. Thus, our systematical study on fluorination may provide an effective approach to precisely control the polymer regioselectivity and improve device performance as well as long-term durability under various environmental stresses.
Co-reporter:Jianyu Yuan;Michael J. Ford;Guillermo C. Bazan
Journal of Materials Chemistry A 2017 vol. 5(Issue 19) pp:8903-8908
Publication Date(Web):2017/05/16
DOI:10.1039/C7TA02510F
In comparison with many reported high-efficiency polymer solar cells, only 0.5% (v/v) additive is necessary to optimize a polymer/fullerene (PSFSiF/PC71BM) system, and the power conversion efficiency (PCE) was boosted from 2.4% to 8.0%. 2D grazing incidence wide angle X-ray scattering (GIWAXS) is utilized to understand the relevant structural features in the blend films prepared under different processing conditions, and the BHJ morphology is also examined using atomic force microscopy (AFM) and transmission electron microscopy (TEM) techniques.
Co-reporter:Yu Lei, Jianxia Sun, Jianyu Yuan, Jinan Gu, ... Wanli Ma
Journal of Materials Science & Technology 2017 Volume 33, Issue 5(Volume 33, Issue 5) pp:
Publication Date(Web):1 May 2017
DOI:10.1016/j.jmst.2016.06.028
A widely-used naphthalenediimide (NDI) based electron acceptor P(NDI2OD-T2) with different number-average molecular weight (Mn) of 38 (N2200L), 56 (N2200M), 102 (N2200H) kDa were successfully prepared. The effect of molecular-weight on the performance of all-polymer solar cells based on Poly(5-(5-(4,8-bis(5-decylthiophen-2-yl)-6-methylbenzo[1,2-b:4,5-b’]dithophen-2-yl)thiophen-2-yl)-6,7-difluoro-8-(5-methylthiophen-2-yl)-2,3-bis(3-(octyloxy)phenyl)quinoxaline) (P2F-DE):N2200 was systematically investigated. The results reveal that N2200 with increased Mn show enhanced intermolecular interactions, resulting in improved light absorption and electron mobility. However, the strong aggregation trend of N2200H can cause unfavorable morphology for exciton dissociation and carrier transport. The blend film using N2200 with moderate Mn actually develops more ideal phase segregation for efficient charge separation and transport, leading to balanced electron/hole mobility and less carrier recombination. Consequently, all-polymer solar cells employing P2F-DE as the electron donor and N2200M as the electron acceptor show the highest efficiency of 4.81%, outperforming those using N2200L (3.07%) and N2200H (3.92%). Thus, the Mn of the polymer acceptor plays an important role in all-polymer solar cells, which allows it to be an effective parameter for the adjustment of the device morphology and efficiency.
Co-reporter:Xiangxiang Zhu, Zeke Liu, Guozheng Shi, Jinan Gu, ... Wanli Ma
Journal of Materials Science & Technology 2017 Volume 33, Issue 5(Volume 33, Issue 5) pp:
Publication Date(Web):1 May 2017
DOI:10.1016/j.jmst.2017.01.018
Colloidal quantum dots (CQDs), especially lead chalcogenide CQDs, are regarded as promising materials for the next generation solar cells, due to their large absorption coefficient, excellent charge transport, and multiple exciton generation effect. We successfully synthesized highly-crystalline, monodispersed, well-alloyed PbSxTe1-x nanocrystals via a one-pot, hot injection reaction method. Energy-filtered transmission electron microscopy suggested that the S and Te anions were uniformly distributed in the alloy nanoparticles. The photovoltaic performance of CQD solar cells based on ternary PbSxTe1-x was reported for the first time. The photovoltaic devices using PbSxTe1-x were more efficient than either the pure PbS or the PbTe based devices. In addition, the PbSxTe1-x based devices showed a significantly improved stability than that of the PbTe based devices.
Co-reporter:Jianyu Yuan, Wenping Guo, Yuxin Xia, Michael J. Ford, Feng Jin, Dongyang Liu, Haibin Zhao, Olle Inganäs, Guillermo C. Bazan, Wanli Ma
Nano Energy 2017 Volume 35(Volume 35) pp:
Publication Date(Web):1 May 2017
DOI:10.1016/j.nanoen.2017.03.050
•The fundamental loss mechanisms using non-fullerene polymer acceptor N2200.•Dynamics study using ultrafast transient transmission spectroscopy.•Geminate recombination in all-polymer solar cells was firstly investigated relative to polymer/PCBM device.•Unfavorable face-to-edge orientation at the polymer/polymer interface hinders the non-fullerene device performance.Current all polymer solar cells still suffer from low fill factors (FF) and short-circuit current density (Jsc) compared with the conventional polymer/fullerene system. Herein in this work, devices using PTP8 as the electron donor and [70]PCBM as well as widely used polymer N2200 as the electron acceptor were systematically studied and compared. The major loss mechanisms in the all polymer solar cells were investigated to understand their relatively lower performance than the PTP8/fullerene system. By performing in-depth analysis on ultrafast transient transmission spectroscopy results, we estimated that in PTP8/N2200 device nearly half of the charges recombine geminately, which is confirmed as the major factor hindering the device performance of all polymer solar cells compared with polymer/fullerene system. Through thorough morphology analysis, the low charge generation efficiency is attributed to the reduced crystallinity of N2200 in the blend film and the unfavorable face-to-edge orientation at the donor/acceptor heterojunction. Coupling these results with knowledge from efficient polymer/fullerene systems, the future design of new polymers can devote to increase the attraction between the π face of donor and acceptor, leading to enhanced face-to-face orientation at the heterojunction, while maintaining a high π-π stacking order for each polymer.Download high-res image (497KB)Download full-size image
Co-reporter:Guozheng Shi;Yongjie Wang;Zeke Liu;Lu Han;Jie Liu;Yakun Wang;Kunyuan Lu;Si Chen;Xufeng Ling;Yong Li;Si Cheng
Advanced Energy Materials 2017 Volume 7(Issue 15) pp:
Publication Date(Web):2017/08/01
DOI:10.1002/aenm.201602667
This study reports the fabrication of stable, high-performance, simple structured tandem solar cells based on PbS colloidal quantum dots (CQDs) under ambient air. This study also reveals detailed device engineering to deposit each functional layer in the subcells at low temperature to avoid damage to the PbS CQDs and meanwhile makes the fabrication process compatible to flexible plastic substrate. Two efficient recombination layers (RLs) are rationally designed to connect the two subcells in series. The use of solution-processed RL with an organic PEDOT:PSS (poly(3,4-ethylenedioxythiophene): polystyrene sulfonate) interlayer leads to the fabrication of the tandem devices in solution process. The use of robust inorganic RL containing an ultrathin Au interlayer results in more efficient device performance and remarkably improved device lifetime. The optimal PbS CQDs tandem cells based on inorganic RL demonstrate a high power conversion efficiency approaching 9%. This efficiency is more than two times higher than the previous record of 4.2%, which has been kept for more than five years. The remarkable stability, high performance, and low-temperature processing of these tandem devices may provide insight into the commercialization of flexible and large-area CQDs tandem solar cells in the near future.
Co-reporter:Guanqun Ding, Jianyu Yuan, Feng Jin, Yannan Zhang, Lu Han, Xufeng Ling, Haibin Zhao, Wanli Ma
Nano Energy 2017 Volume 36(Volume 36) pp:
Publication Date(Web):1 June 2017
DOI:10.1016/j.nanoen.2017.04.061
•First report of ITIC in application of high efficiency all-polymer nonfullerene solar cells.•The champion PCE of all-polymer nonfullerene solar cells is increased from 6.00% to 7.01% by adding 6 wt% ITIC in total.•ITIC addition is beneficial to optimized blend morphology, enhance charge carrier generation and balance charge carrier mobility.•Universal capability for application in all-polymer solar cells adopting either P3HT or PTB7.In the current research field of non-fullerene solar cells, the device performance of all polymer solar cells (all-PSCs) lags significantly behind those based on polymer donor and molecule acceptor. To further improve the device performance of all-PSCs, the small molecule electron acceptor ITIC was introduced for the first time to the all-PSCs based on PTP8/P(NDI2HD-T). The combinative polymer/molecule acceptor P(NDI2HD-T)/ITIC with only a small amount of ITIC, 15 wt% in acceptors and 6 wt% in total, can significantly improve the device PCE from 6% to over 7%, which is among the highest-efficiencies for reported all-PSCs. The improved device performance can be attributed to the broadened absorption and optimized blend morphology, which can further enhance charge carrier generation and balance charge carrier mobility in the ternary blend. More importantly, we discovered that this strategy can be successfully applied to all-PSCs based on other polymer donors like widely spread P3HT or PTB7. Therefore, our work not only reveals the detailed effect of polymer-small molecule acceptor alloy in all-PSCs, but also suggest that the ternary cell strategy of polymer donor/polymer:molecule acceptor may become a general and facile approach to further boost the performance of current all-PSCs.Download high-res image (186KB)Download full-size image
Co-reporter:Jianyu Yuan;Niva A. Ran;Michael J. Ford;Ming Wang;Mahesh Kumar Ravva;Cheng-Kang Mai;Xiaofeng Liu;Jean-Luc Brédas;Thuc-Quyen Nguyen;Guillermo C. Bazan
Journal of Materials Chemistry A 2017 vol. 5(Issue 35) pp:18618-18626
Publication Date(Web):2017/09/12
DOI:10.1039/C7TA05442D
Two regioregular narrow bandgap conjugated polymers with a D′–A–D–A repeat unit architecture, namely PIFCF and PSFCF, were designed and synthesized. Both polymers contain strictly organized fluorobenzo[c][1,2,5]thiadiazole (FBT) orientations and different solubilizing side chains for solution processing. Compared to the previously reported asymmetric pyridyl-[2,1,3]thiadiazole (PT) based regioregular polymer, namely PIPCP, PIFCF and PSFCF exhibit wider bandgaps, tighter π–π stacking, and improved hole mobilities. When incorporated into solar cells with fullerene acceptors, the Eloss = Eg − eVoc values of PIFCF and PSFCF devices are increased compared to solar cells based on PIPCP. Determination of Ect in these solar cells reveals that, relative to PIPCP, PIFCF solar cells lose more energy from Eg − Ect, and PSFCF solar cells lose more energy from both Eg − Ect and Ect − eVoc. The close structural relationship between PIPCP and PIFCF provides an excellent framework to establish molecular features that impact the relationship between Eg and Ect. Theoretical calculations predict that Eloss of PIFCF:PC61BM would be higher than in the case of PIPCP:PC61BM, due to greater Eg − Ect. These findings provide insight into the design of high performance, low voltage loss photovoltaic polymeric materials with desirable optoelectronic properties.
Co-reporter:Kunyuan Lu;Yongjie Wang;Jianyu Yuan;Zequn Cui;Guozheng Shi;Shaohua Shi;Lu Han;Si Chen;Yannan Zhang;Xufeng Ling;Zeke Liu;Lifeng Chi;Jian Fan
Journal of Materials Chemistry A 2017 vol. 5(Issue 45) pp:23960-23966
Publication Date(Web):2017/11/21
DOI:10.1039/C7TA07014D
New-generation solar cells based on colloidal lead chalcogenide (PbX) quantum dots (CQDs) are promising low-cost solution-processed photovoltaics. However, current state-of-the art CQDs are all using an inverted device architecture. The performance gap between CQD solar cells with conventional and inverted structures is much larger than that for other solution-processed photovoltaics such as organic and perovskite solar cells, which may restrict the future development of CQD solar cells. Here, we reported a record-high power conversion efficiency of 8.45% for conventionally structured PbS QD solar cells by the introduction of a unique conjugated polymer PDTPBT as the anode buffer layer. With the modification of the anode, the device performance was largely improved through a dramatic enhancement in open circuit voltage (Voc), which can be attributed to the enhanced hole extraction to the anode after PDTPBT modification. Meanwhile, the polymer layer can also efficiently improve charge separation and reduce interfacial charge recombination as well as reverse saturation current density, which result in significantly enhanced Voc. More importantly, our results proposed a new conventional architecture for QD solar cells which can avoid the complex processing of metal oxides and is free of light-soaking. This new device structure may offer more flexibility in future device design and show potential advantages in large-scale manufacturing by simplifying the fabrication process.
Co-reporter:Zeke Liu;Haoran Mu;Si Xiao;Rongbin Wang;Zhiteng Wang;Weiwei Wang;Yongjie Wang;Xiangxiang Zhu;Kunyuan Lu;Han Zhang;Shuit-Tong Lee;Qiaoliang Bao
Advanced Materials 2016 Volume 28( Issue 18) pp:3535-3542
Publication Date(Web):
DOI:10.1002/adma.201504927
Co-reporter:Wenping Guo;Jianyu Yuan;Haochen Yuan;Feng Jin;Lu Han;Chuanxiang Sheng;Haibin Zhao
Advanced Functional Materials 2016 Volume 26( Issue 5) pp:713-721
Publication Date(Web):
DOI:10.1002/adfm.201503556
Ultrafast charge transfer dynamics in hybrid blend films of a low band-gap polymer poly(2,6-(N-(1-octylnonyl)dithieno[3,2-b:20,30-d]pyrrole)-alt-4,7-(2,1,3-benzothiadiazole)) (PDBT) and PbS quantum dots (QDs) are studied by using ultrafast transient transmission spectroscopy. It is observed that the transient bleaching signal arising from excitons of the PDBT displays a much faster recovery, within the time delay of ≈5 ps, in hybrid films than in the neat PDBT film. In contrast, the bleaching signal resulting from the electron filling of the QDs in hybrid films shows an extra rising component during ≈1–5 ps, which is absent in the pristine QDs. These results indicate the ultrafast electron transfer from the lowest unoccupied molecular orbital energy level of the PDBT to the conduction band of the QDs in the time scale of several ps after laser excitation. A transient absorption signal within 1 ps in the hybrid films is also found, indicating the emergence of charge transfer states (CTs). The CTs formed at the interface of the hybrid blend may facilitate the charge separation and transfer. It is estimated that over 80% of the photoexcited electrons in the PDBT may be transferred into the QDs. The transfer efficiencies show a positive correlation with the power conversion efficiencies of the corresponding hybrid solar cells.
Co-reporter:Shaohua Shi;Jianyu Yuan;Guanqun Ding;Michael Ford;Kunyuan Lu;Guozheng Shi;Jianxia Sun;Xufeng Ling;Yong Li
Advanced Functional Materials 2016 Volume 26( Issue 31) pp:5669-5678
Publication Date(Web):
DOI:10.1002/adfm.201601037
By the introduction of different building blocks and side-chains, a series of donor–acceptor type polymer acceptors containing naphthalene diimide have been successfully prepared. The theoretical and experimental results show that the molecular design effectively tunes the energy levels, solubility, and coplanarity of the acceptor polymers. The intermolecular packing, which has been considered as a key factor in the bulk heterojunction morphology, has been adjusted by changing the coplanarity. As a result of improved morphology and fine-tuned energy levels, a power conversion efficiency of 6.0% has been demonstrated for the optimized devices, which is among the highest-efficiencies for reported all-polymer solar cells. The improved device performance may be attributed to the resemble crystallinity of the donor/acceptor polymers, which can lead to the optimal phase separation morphology balancing both charge transfer and transport.
Co-reporter:Jianyu Yuan, Caitlin McDowell, Cheng-Kang Mai, Guillermo C. Bazan, and Wanli Ma
Chemistry of Materials 2016 Volume 28(Issue 20) pp:7479
Publication Date(Web):September 21, 2016
DOI:10.1021/acs.chemmater.6b03189
In contrast to the great efforts on developing novel donor (D)–acceptor (A) copolymers, research on investigating the backbone composition of conjugated polymer is rare. In this contribution, we disclose the design and synthesis of a ternary D1–D2–A–D2 structured conjugated polymer PBSF. Compared to the typical D–A polymer with fixed D/A moiety number, the ternary structure can tune the optical and electrical properties more comprehensively and delicately. Precisely control of the ternary fragments relative to the backbone vector was achieved, further promoting sufficient planar structure, strong intermolecular packing, and excellent charge transport. Finally, the additive and annealing-free polymer solar cells based on PBSF and phenyl-C71-butyric acid methyl ester ([70]PCBM; PCE = 7.4%) or cheap, nonfunctionalized C70 (PCE = 5.3%) demonstrate excellent performance using either chlorinated or nonhalogenated “green” solvent. We believe that this novel and efficient ternary structure may spark future polymer design to achieve sustainable-processed photovoltaic devices for practical mass production.
Co-reporter:Yong Li, Kunyuan Lu, Xufeng Ling, Jianyu Yuan, Guozhen Shi, Guanqun Ding, Jianxia Sun, Shaohua Shi, Xiu Gong and Wanli Ma
Journal of Materials Chemistry A 2016 vol. 4(Issue 26) pp:10130-10134
Publication Date(Web):06 Jun 2016
DOI:10.1039/C6TA03284B
In this contribution, we disclose the fabrication and characterization of efficient planar-heterojunction perovskite solar cells using novel amino-based fulleropyrrolidine (C60–N) as the electron transporting material (ETM). Compared to the widely spread [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), we found that C60–N can both efficiently reduce the work function of the metal cathode and passivate the trap states of the perovskite surface, further resulting in improved carrier transport, photovoltaic performance and stability. Devices using C60–N as the ETM exhibit a high power conversion efficiency (PCE) of 16.6%, significantly higher than the 12.3% of PCBM based ones. In addition, we found that C60–N can also significantly enhance the film PL lifetime and decrease the surface roughness. These findings provide insight into the selection and design of new ETMs with desirable properties.
Co-reporter:Jiangsheng Yu, Guanqun Ding, Jiefeng Hai, Enwei Zhu, Xinxing Yin, Zhongsheng Xu, Baojing Zhou, Fujun Zhang, Wanli Ma and Weihua Tang
Physical Chemistry Chemical Physics 2016 vol. 18(Issue 11) pp:7978-7986
Publication Date(Web):16 Feb 2016
DOI:10.1039/C5CP07942J
Four isostructural donor–acceptor alternating polymers of benzodithiophene (BDT)/naphthodifuran (NDF) and benzoselenadiazole (BSe)/benzothiadiazole (BT) have been developed and evaluated for organic photovoltaics. The substitution of one-atom (Se for S) in the accepting units exerts remarkable impact on the optoelectronic properties of polymers. Extended absorption, narrowed bandgap and higher HOMO energy levels were observed for Se-containing polymers in comparison to their S-containing counterparts. Theoretical calculations confirmed the measurable effect on energy levels as found in experimental studies. Bulk-heterojuction solar cells based on the BDT–BSe copolymer and [6,6]-phenyl-C71-butyric acid methyl ester (1:2, w/w) blend films deliver the best PCE of 5.40%. BSe-based polymers showed enhanced photovoltaic performances than BT-based polymers. The device performance is found to be strongly dependent on the processing conditions and morphology of the active layers.
Co-reporter:Jianyu Yuan, Wanli Ma
Organic Electronics 2016 Volume 39() pp:279-287
Publication Date(Web):December 2016
DOI:10.1016/j.orgel.2016.10.021
•High performance and molecular donor-polymeric acceptor nonfullerene solar cells achieved by properly selection of molecular donor.•Investigation of end-group effect on optical property, structural order and hole transport.•The effect of molecular donor crystallinity on nonfullerene blend film morphology.In order to specifically investigate the low efficiency of small molecule donor-polymer acceptor (M-P) nonfullerene organic solar cells, we have successfully modify the synthesis of a series of D-π-A-π-D conjugated molecules containing diketopyrrolopyrrole (DPP) and different end groups. By incorporation of end group with different size of π-conjugation (benzene, naphthalene and pyrene), we further improved the fill factor (FF) and short current density (Jsc) of the donors molecule. Our experimental results and theoretical calculations have proven that the size of the end groups can influence the molecule crystallinity, mobility and intermolecular packing by altering the molecular coplanarity. As the result of improved crystallinity, morphology and fine-tuned mobilities, we demonstrated an increased FF, a high Jsc of ∼4.5 mA/cm2 and a power conversion efficiency of 2.05%, which is among the highest efficiency reported for M-P nonfullerene solar cells. Our results provide opportunities and possibilities of achieving higher performance M-P nonfullerene solar cells in the future.
Co-reporter:Jianxia Sun, Jinan Gu, Jianyu Yuan, Zequn Cui, Kunyuan Lu, Shaohua Shi, Guanqun Ding, Wanli Ma
Organic Electronics 2016 Volume 33() pp:227-234
Publication Date(Web):June 2016
DOI:10.1016/j.orgel.2016.03.032
•High performance (PCE = 5.35%) achieved for all-PSCs through introduction of electron-withdrawing fluorine atoms to polymer acceptor unit and change the alkyl side chain in polymer donor unit.•Systematical modifications on the chemical structure of the donor polymers in all-PSCs.•Investigation of introduction of electron-withdrawing fluorine atoms to polymer acceptor unit effect on optical property, polymer coplanarity, intermolecular packing and balanced carrier transport.•Investigation of change alkyl side chain in polymer donor unit effect on film morphology and hole transport.We successfully designed and synthesized a series of BDT-Qx-T based polymers as the donor polymer used in all polymer solar cells (all-PSCs). Their properties were finely tuned by side-chain modification and the introduction of electron-withdrawing fluorine atoms to polymer acceptor unit. Then we systematically investigated the effect of molecular structure on the polymer morphology and photovoltaic properties in all-PSCs. We revealed that the fluorination can optimize polymer energy level and improve the polymer coplanarity, leading to enhanced intermolecular packing and balanced carrier transport. Meanwhile, the substitution of dodecyl for 2-ethylhexyl side chains can result in improved film morphology and hole transport. As a result of the synergistic effect between fluorination and side-chain modification, we achieved a high PCE of 5.35% for the optimized all-PSCs. More importantly, our approach may become a general and effective way to tailor the polymer molecular structure for achieving high performance all-PSCs.
Co-reporter:Jianyu Yuan, Kunyuan Lu, Michael Ford, Guillermo C. Bazan, Wanli Ma
Organic Electronics 2016 Volume 32() pp:187-194
Publication Date(Web):May 2016
DOI:10.1016/j.orgel.2016.02.026
•High performance and low fullerene content polymer solar cells achieved by dual structure modifications on both polymer and PCBM.•Investigation of side-chain effect on optical property, structural order and hole transport.•Correlation between bulkier side-chain and fullerene molecule aggregation in blend film.The molecular structures of both donor polymer and acceptor fullerene were adjusted and their effect on the donor/acceptor blend ratio in the polymer solar cells was investigated. We found that increasing the side-chain rigidity of the donor polymer or bulkiness of the fullerene can both effectively reduce the fullerene intercalation into polymer side chains, realizing efficient electron transport at higher polymer/fullerene ratio. Especially, by using a bulkier fullerene molecule, all the three adopted polymers exhibit remarkably stable device performance over a wide range of blend ratio (from 1:0.5 to 1:1.0), which can't be achieved by using conventional PC61BM. Moreover, using bulky PC61BAd together with a high side-chain density polymer PTP8, the optimal device performance could be obtained at a surprisingly low blend ratio of 1:0.6, which may lead to more thermally stable and cost-effective devices.
Co-reporter:Jinan Gu, Jianyu Yuan, Wanli Ma
Organic Electronics 2016 Volume 34() pp:229-236
Publication Date(Web):July 2016
DOI:10.1016/j.orgel.2016.04.011
•High performance and low fullerene content polymer solar cells achieved by structure modifications on polymer.•Investigation of molecular weight effect on optimal fullerene content.•Systematically morphological characterization of molecular weight effect on fullerene molecule aggregation in blend film.In this contribution, a donor-acceptor (D-A) copolymer PTP8, consisting of alternating benzodithiophene and thienopyrroledione with conjugated side-chains on both donor and acceptor units, was sucessfully prepared. We further investigated the effect of polymer molecular weight on polymer physicochemical properties, solar cell device performance, polymer-PCBM blend morphology, and, most importantly, polymer/PCBM blend ratio. We found that increasing the molecular weight of the donor polymer can both effectively improve the device performance and simultaneously stabilize solar cell efficiency over a wide range of polymer/PCBM blend ratios (from 1:0.5 to 1:1.0), which may lead to more thermally stable and cost-effective devices. Through intensive morphological investigation, we propose a sound morphological evolution for PTP8/PCBM blends with different molecular weights at low fullerene content.
Co-reporter:Qi-Jun Sun, Jun Peng, Wen-Hua Chen, Xiao-Jian She, Jie Liu, Xu Gao, Wan-Li Ma, Sui-Dong Wang
Organic Electronics 2016 Volume 34() pp:118-123
Publication Date(Web):July 2016
DOI:10.1016/j.orgel.2016.04.023
•A low-cost and low-temperature solution process is developed to prepare excellent Al2O3 gate dielectric.•Both p-type and n-type high-performance low-voltage organic field-effect transistors are realized utilizing Al2O3 dielectric.•High quality of Al2O3 dielectric results in high operating stability of organic field-effect transistors.•A flexible low-power complementary inverter with a large gain is achieved utilizing Al2O3 dielectric.Organic-based complementary inverter could be a key component in future flexible and portable electronic products, which require low-power operation, high operating stability and flexible compatibility at the same time. A simple method for making excellent Al2O3 gate dielectric is developed toward the target, and it is a low-cost solution process with a low annealing temperature compatible with plastic substrates. Utilizing the Al2O3 dielectric, both p-type and n-type low-voltage organic field-effect transistors (OFETs) are realized. The device operating voltage is down to ±3 V, and the On/Off ratio is up to 106. The hole and electron field-effect mobilities are 2.7 cm2/V and 0.2 cm2/V, respectively, and the subthreshold swing is as small as about 110 mV/decade. The high quality of the Al2O3 dielectric results in high operating stability of the devices. The p-type and n-type OFETs are integrated to achieve a low-power complementary inverter with a large gain, which can be successfully fabricated on a flexible substrate.
Co-reporter:Xiao Yang, Xiaoliang Yan, Wei Wang, Xiangxiang Zhu, Heng Li, Wanli Ma, ChuanXiang Sheng
Organic Electronics 2016 Volume 34() pp:79-83
Publication Date(Web):July 2016
DOI:10.1016/j.orgel.2016.04.020
•PL of MAPbI3−xBrx films red-shift excited by CW laser.•PL of MAPbI3−xBrx films don't shift excited by small repetition pulsed laser.•Ref-shift of PL is due to photoinduced metastable sub band states in film.•Photoinduced metastable states can be restored spontaneously.•Two-step mechanism is needed to explain the metastable modification.We have used photoluminescence (PL) and photomodulation (PM) spectroscopy to investigate the reversible spectral changes of PL in CH3NH3PbI3−xBrx films, where x is 1.7. In an as-prepared film, the peak of PL spectra shifts from ∼640 nm near bandedge to ∼750 nm after excitation by a continuous wave (CW) or a pulsed laser with high repetition rate, but keeps at 640 nm excited by same pulsed laser with the repetition rate smaller than 500 Hz. The PM spectroscopy also shows the formation of sub bandgap states after illumination which is responsible for the red shift of PL. The light induced modification of optical properties is reversible after keeping the film out of illumination for several hours at room temperature. We analyze the photoinduced modification to be two-steps processes: the temporary sub bandgap states were first photogenerated in perovskite film, if those states interacting with more coming photons within their lifetimes, light induced metastable states responsible for red-shift of PL will be formed. This instability reduces the electronic bandgap and generates more traps which will degrade the performance of the related photovoltaic devices.
Co-reporter:Guobing Zhang, Jie Zhang, Guanqun Ding, Jinghua Guo, Hongbo Lu, Longzhen Qiu, Wanli Ma
Polymer 2016 Volume 93() pp:213-220
Publication Date(Web):14 June 2016
DOI:10.1016/j.polymer.2016.04.011
•Two polymers based on pyrrolo[3,4-d]pyridazine-5,7-dione unit were synthesized and characterized.•The LUMO and bandgap were lowered by introducing a more electron deficient unit.•The polymers maintained the deep HOMO level and the devices exhibited a PCE of 3.66% with a high Voc of 0.91 V.Two donor–acceptor polymer semiconductors based on highly electron-deficient pyrrolo[3,4-d]pyridazine-5,7-dione unit were synthesized by Stille cross-coupling polymerization, and their thermal property, photophysical property, electrochemical property, microstructure, application as organic thin-film transistors, and photovoltaic property were investigated. Because of the strong electron-accepting characteristic of pyrrolo[3,4-d]pyridazine-5,7-dione, the new polymers (P1 and P2) exhibited much wider absorption, smaller bandgaps (1.70 vs 1.98 eV), and deeper LUMO levels (−3.60 vs −3.37 eV) than those of a phthalimide-based polymer PBDT-PhBT (Figure 1). The fabricated organic thin-film transistor devices exhibited hole-transport behavior, and the highest mobility of 1.14 × 10−3 cm2 V−1 s−1 was obtained. The bulk-heterojunction solar cells based on the two polymers as the electron donors and PC71BM as the electron acceptor showed a high open-circuit voltage and achieved a power conversion efficiency of 2.71% and 3.66% for polymers P1 and P2, respectively.
Co-reporter:Jianyu Yuan, Aidan Gallagher, Zeke Liu, Yaxiang Sun and Wanli Ma
Journal of Materials Chemistry A 2015 vol. 3(Issue 6) pp:2572-2579
Publication Date(Web):24 Sep 2014
DOI:10.1039/C4TA03995E
Solution-processed hybrid solar cells (HSCs), composed of conjugated polymers and semiconducting PbS nanocrystals, are promising candidates for the next-generation photovoltaic devices. Through deliberate molecular design, a series of new organic donor–acceptor polymers bearing varying optical band-gaps (1.25–1.65 eV) and suitable HOMO (highest occupied molecular orbital) energy levels (∼5.0 eV) were synthesized. Due to improved device architecture, we achieved the highest power conversion efficiency (PCE) of 4.23% to date for polymer–PbS based HSCs. Furthermore, the correlation between the polymer molecular structure and hybrid blend morphologies was systematically investigated using 2-dimensional grazing incidence X-ray diffraction, atomic force microscopy and scanning transmission electron microscopy. We believe our findings can be beneficial to the future molecular design toward highly efficient polymer–PbS HSCs.
Co-reporter:Lu Han, Jie Liu, Ningning Yu, Zeke Liu, Jinan Gu, Jialing Lu and Wanli Ma
Nanoscale 2015 vol. 7(Issue 6) pp:2461-2470
Publication Date(Web):15 Dec 2014
DOI:10.1039/C4NR05707D
Nanocrystal array solar cells based on lead chalcogenide quantum dots (QDs) have recently achieved a high power conversion efficiency of over 8%. The device performance is expected to further increase by using 1-dimensional nanorods (NRs), due to their improved carrier transport over zero-dimensional quantum dots. However, previously reported PbSe NRs have not been used in solar cells mainly because of their large diameters, resulting in a small bandgap unsuitable for photovoltaic application. In this work, we have demonstrated a new method for synthesizing monodisperse ultra-small PbSe NRs with the diameter approaching 2 nm (Eg > 1.2 eV), which can be attributed to the use of diphenylphosphine (DPP) and trans-2-octenoic acid (t-2-OA). The introduction of trace DPP can greatly lower the reaction temperature, leading to reduced diameters for the obtained PbSe NRs as well as largely increased yield. The use of short-chain t-2-OA together with oleic acid as capping ligands results in high monomer reactivity, fast nucleus diffusion and high growth rate, which realize the anisotropic growth of ultra-small PbSe NRs at low reaction temperatures. The PbSe NRs show n-type properties and high electron mobility as measured using field-effect transistors. The PbSe NRs with narrow diameters also demonstrate a suitable bandgap for photovoltaic application. They are used for the first time in solar cells and their improved efficiency is demonstrated when used together with QDs.
Co-reporter:Long Hu, Weiwei Wang, Huan Liu, Jun Peng, Hefeng Cao, Gang Shao, Zhe Xia, Wanli Ma and Jiang Tang
Journal of Materials Chemistry A 2015 vol. 3(Issue 2) pp:515-518
Publication Date(Web):24 Nov 2014
DOI:10.1039/C4TA04272G
Here, we applied colloidal quantum dots (CQDs) as an effective p-type hole-transporting material (HTM) for planar heterojunction perovskite solar cells. By tuning the size of PbS CQDs, we engineered the energy alignment of the valence and conduction band of this new HTM with the perovskite light harvester and achieved conversion efficiencies up to 7.5%. Absorption of PbS CQDs also extends the absorption spectrum of perovskite solar cells into the infrared region.
Co-reporter:Jianyu Yuan and Wanli Ma
Journal of Materials Chemistry A 2015 vol. 3(Issue 13) pp:7077-7085
Publication Date(Web):09 Feb 2015
DOI:10.1039/C4TA06648K
By adopting a series of donor–acceptor (D–A) polymers containing Benzo[1,2-b:4,5-b′]dithiophene (BDT) and thieno[3,4-c]pyrrole-4,6-dione (TPD) with different numbers of alkyl aromatic side-chains, we demonstrate a high optimized PCE of 4.35% for all-polymer solar cells by incorporating an n-type polymer N2200. Through systematic characterization of tapping mode atomic force microscopy (AFM), 2-dimensional grazing-incidence X-ray diffraction (2d-GIXD), photoluminescence spectra and peak force-kelvin probe force microscopy (PF-KPFM), we have shown that the introduction of alkyl aromatic side chains to the donor polymer backbone is beneficial for the intermolecular π–π stacking and hence improves the polymer crystallinity as well as hole mobility. More importantly, we discovered that conjugated side-chains and additives can work synergistically to restore the intermolecular stacking of donor–acceptor polymers in the as-cast amorphous blend film and meanwhile develop fine phase segregation for efficient exciton dissociation and transport. As a result, the donor polymer PTP8 with fully alkyl aromatic side chains demonstrated an improved short-circuit current density (Jsc), a high open-circuit voltage (Voc) of ∼1.00 V and a power conversion efficiency (PCE) of 4.35% after the addition of 0.5% DIO, which is among the highest reported efficiencies for all polymer solar cells.
Co-reporter:Weiwei Wang, Jianyu Yuan, Guozheng Shi, Xiangxiang Zhu, Shaohua Shi, Zeke Liu, Lu Han, Hai-Qiao Wang, and Wanli Ma
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 7) pp:3994
Publication Date(Web):January 30, 2015
DOI:10.1021/am506785k
Inverted planar heterojunction perovskite solar cells employing different polymers, poly{[N,N′-bis(2-octyldodecyl)-1,4,5,8-naphthalene diimide-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (N2200), poly{[N,N′-bis(alkyl)-1,4,5,8-naphthalene diimide-2,6-diyl-alt-5,5′-di(thiophen-2-yl)-2,2′-(E)-2-(2-(thiophen-2-yl)vinyl)thiophene]} (PNVT-8), and PNDI2OD-TT as electron-transporting material (ETM) have been investigated for the first time. The best device performance was obtained when N2200 was applied as the ETM, with JSC of 14.70 mA/cm2, VOC of 0.84 V, and fill factor (FF) of 66%, corresponding to a decent power conversion efficiency (PCE) of ∼8.15%. Which is very competitive to the parameters (JSC 14.65 mA/cm2, VOC 0.83 V, FF 70%, and PCE 8.51%) of the reference device employing conventional PCBM as the ETM. The slightly lower FF could be mainly accounted for by the increased recombination in the polymer contained devices. This work demonstrated that polymeric materials can be used as efficient ETM in perovskite solar cells, and we believe this class of polymeric ETMs will further promote the performance of perovskite photovoltaic cells after extended investigation.Keywords: characterization; device performance; electron conductor; perovskite solar cell; planar heterojunction; polymer;
Co-reporter:Jianyu Yuan, Yu Liu, Huilong Dong, Xiaobo Shi, Zeke Liu, Youyong Li and Wanli Ma
Polymer Chemistry 2015 vol. 6(Issue 43) pp:7550-7557
Publication Date(Web):02 Sep 2015
DOI:10.1039/C5PY00893J
In order to reveal the correlation between molecular structures and the corresponding film morphology as well as polymer/fullerene blend ratio, a new donor–acceptor (D–A) polymer poly-(benzodithiophene-naphthothiophenedione) (PTN8) based on and was synthesized, which was intentionally designed to further increase the molecular structure bulkiness of our previously reported polymer poly-(benzodithiophene-thienopyrroledione) (PTP8). The experimental results and theoretical calculations indicate that both polymers have similar solubilities, optical properties and energy levels, while the structural modification has a significant impact on the polymer intermolecular packing and crystallinity by altering the backbone coplanarity. The different molecular geometries lead to significantly different device performances, optimal fullerene loadings and efficiency dependence on blend ratios. Therefore molecular geometry should be carefully considered when rationally designing polymers for reducing the use of fullerene.
Co-reporter:Guidong Ge, Jinan Gu, Jiangsheng Yu, Enwei Zhu, Jiefeng Hai, Linyi Bian, Fujun Zhang, Zhongsheng Xu, Wanli Ma and Weihua Tang
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 12) pp:7848-7856
Publication Date(Web):2015/02/12
DOI:10.1039/C5CP00349K
Three dialkylthio benzo[1,2-b:4,5-b′]dithiophene (S-BDT) based polymers have been developed using different accepting units to tune their bandgaps. The polymer:PC71BM solar cells achieved the highest power conversion efficiency (PCE) of 4.51% without any post-treatment (such as annealing and solvent additive) in conventional single-cell devices. Joint photophysical, electrical and computational studies on the polymer based solar cells revealed the considerable impact of molecular planarity on polymer design. The polymer:PC71BM devices processed with 1,8-diiodooctane for improving their morphology afforded an improved PCE value of 5.63%, with a Voc of 0.83, a Jsc of 10.24 mA cm−2 and a FF of 66.3%.
Co-reporter:Yaxiang Sun, Zeke Liu, Jianyu Yuan, Jianmei Chen, Yu Zhou, Xiaodong Huang, Wanli Ma
Organic Electronics 2015 Volume 24() pp:263-271
Publication Date(Web):September 2015
DOI:10.1016/j.orgel.2015.06.010
•A PCE of 5.31% was obtained which was the highest efficiency reported for polymer/PbSe based hybrid solar cells (HSCs).•The open circuit voltage of HSCs showed a great improvement compared to that of PbSe Schottky junction devices.•The role of polymer in HSCs has been systematically investiated.By using a series of polymers in the polymer/PbSe planar heterojunction hybrid solar cells (HSCs), we found that the open circuit voltage of HSCs showed a great improvement compared to that of PbSe Schottky junction solar cells, which might be attributed to the formation of interface dipole, resulting in decreased interfacial resistance, increased built-in electrical field, as well as reduced exciton recombination at interface. Meanwhile, polymers with higher PL quenching have more favorable hole transfer which lead to better device performance. In addition, the energy levels and surface energy of the polymers might largely affect their interaction with PbSe NCs, leading to different interfacial morphologies and influencing the charge transfer efficiency. Furthermore, the optimized HSCs showed a remarkable PCE of 5.31% which was the highest efficiency reported for polymer/PbSe based HSCs. We believe this HSC efficiency can be further improved by selecting polymers with rationally designed structures.By using a series of polymers in the polymer/PbSe planar heterojunction hybrid solar cells (HSCs), an optimized PCE of 5.31% was obtained which was the highest efficiency reported for polymer/PbSe based HSCs. We believe this HSC efficiency can be further improved by selecting polymers with rationally designed structures.
Co-reporter:Guozheng Shi
The Journal of Physical Chemistry C 2015 Volume 119(Issue 45) pp:25298-25306
Publication Date(Web):October 19, 2015
DOI:10.1021/acs.jpcc.5b08861
The combinative effects of thermal annealing and additive processes on the performance of all-polymer bulk heterojunction (BHJ) solar cells with composites of different donor polymers (PTQ1, P3HT, PTB7-Th) and poly[1,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)P(NDI2OD-T2) [PolyeraActivInk N2200] were investigated. We found that devices treated with both processes show significant improved performance compared with those treated with either process alone. To reveal the mechanism of this enhancement in device performance, the optical and electrical properties of all-polymer blends were carefully investigated in the PTQ1/N2200 system. The synergetic effect of both processes can largely enhance the polymer aggregation, especially for N2200, leading to improved absorbance, improved charge mobility, and thus higher device performance. In addition, the device efficiency can be further enhanced by postannealing which can improve the interface between the active layer and Al cathode, as revealed by atomic force microscopy investigations. Moreover, the approaches reported here provide a simple and versatile method to optimize all-polymer solar cells and may help pave the route for this emerging system to overtake the state-of-the-art polymer/fullerene solar cells.
Co-reporter:Jianyu Yuan;Huilong Dong;Ming Li;Xiaodong Huang;Jun Zhong;Youyong Li
Advanced Materials 2014 Volume 26( Issue 22) pp:3624-3630
Publication Date(Web):
DOI:10.1002/adma.201305577
Co-reporter:Jun Peng, Xinxin Wang, Jie Liu, Xiaodong Huang, Jing Xiao, Sui-Dong Wang, Hai-Qiao Wang and Wanli Ma
Journal of Materials Chemistry A 2014 vol. 2(Issue 5) pp:864-869
Publication Date(Web):18 Nov 2013
DOI:10.1039/C3TC32020K
Inverted organic light-emitting diodes (IOLEDs) can effectively improve device stability because they concentrate the air-stable anode and high work function (WF) metal oxide hole-injection layer (HIL) at the top of the devices. In this work, we report a facile solution-processed ultra-thin alumina film used as an electron-injection layer in IOLEDs and present significantly improved device performance. We achieved a high current efficiency of 5.12 cd A−1 at 10 mA cm−2 and the best current efficiency approaching 5.5 cd A−1 at 40 mA cm−2 without doping of an emission layer (EML) for a single Alq3-based green fluorescent IOLED, and a high current efficiency for a green phosphorescent IOLED as well. Furthermore, the extrapolated 50% decay lifetime (t50) shows that our Alq3-based green fluorescent IOLED is about 5 times more stable than the conventional OLED.
Co-reporter:Jialing Lu, Jianyu Yuan, Wenping Guo, Xiaodong Huang, Zeke Liu, Haibing Zhao, Hai-Qiao Wang and Wanli Ma
Polymer Chemistry 2014 vol. 5(Issue 16) pp:4772-4780
Publication Date(Web):14 Apr 2014
DOI:10.1039/C4PY00357H
A class of polymers (POT-DH, POT-HCN and POT-DCN) were synthesized and they contain the same donor (BDT) and acceptor units but different numbers of cyano (CN)-groups, i.e. 0, 1 and 2. We investigated for the first time the effects of different CN-group numbers on the optoelectronic, molecule packing, film morphology and photovoltaic properties of three conjugated polymers. With increased CN-group number, broader absorption, smaller optical bandgap and lower HOMO level can be obtained. The planarity of polymers also decreases with increasing CN-groups, leading to different inter-molecular packing and morphology. The incorporation of two CN-groups results in poor morphology, inefficient charge transfer and very low device performance. Due to the optimized POT-HCN polymer possessing the most balanced properties, the best PCE of 4.21% was demonstrated by POT-HCN with one CN-group. Thus we believe that, by controlling the number of introduced CN-groups, we can generally fine-tune the planarity and LUMO/HOMO levels of this class of polymers to achieve desired optoelectronic properties and morphology for high photovoltaic performance. This also provides a feasible way for optimizing other photovoltaic semiconducting polymers by adjusting the number of electron-withdrawing units.
Co-reporter:Shugang Li, Jianyu Yuan, Ping Deng, Wanli Ma, Qing Zhang
Dyes and Pigments 2014 Volume 106() pp:121-127
Publication Date(Web):July 2014
DOI:10.1016/j.dyepig.2014.03.002
•The polymers based on diketopyrrolopyrrole and isoindigo were studied and compared.•The polymer based on diketopyrrolopyrrole showed absorption extended into near IR region.•The polymer based on isoindigo showed little absorption in near IR region.•The isoindigo based polymer showed lower HOMO/LUMO energy than DPP based polymer.Two new donor/acceptor π-conjugated polymers with functional dyes, either diketopyrrolopyrrole or isoindigo as the electron accepting units and 5,10-bis(2,3-didecylthiophen-5-yl)-naphtho[1,2-b:5,6-b′]difuran as an electron donating units have been synthesized. The photo-physical, electrochemical and photovoltaic properties of the new polymers have been studied and compared. With the same donor unit, the diketopyrrolopyrrole based polymer showed low bandgap and broad absorption extended into near IR region. The isoindigo based polymer showed little absorption in near IR region. However, the isoindigo based polymer showed more efficient absorption than diketopyrrolopyrrole based polymer in the most of visible region (from 300 to 690 nm) in solution. The isoindigo based polymer showed lower HOMO and LUMO energy levels than diketopyrrolopyrrole based polymer. The isoindigo polymer based solar cell devices consistently showed higher open circuit voltages than the diketopyrrolopyrrole polymer based devices.
Co-reporter:Xiaodong Huang, Zhichun Zhai, Jianyu Yuan, Jun Peng, Tao Yang, Hai-Qiao Wang, Wanli Ma
Organic Electronics 2014 Volume 15(Issue 6) pp:1235-1243
Publication Date(Web):June 2014
DOI:10.1016/j.orgel.2014.03.018
•It is a facile method to prepare metal oxides for interfacial layer in PSC.•Good device performance can be achieved with the prepared metal-oxide interfacial layers.•Applicability was demonstrated with both polymer P3HT and PBDT-T8-TPD.We report a facile approach to prepare metal oxides for the interfacial layer in polymer solar cells (PSCs), in which the precursor solutions were obtained by dissolving commercial metal oxide/hydroxide in ammonia water. This approach can be adopted as a general method to prepare various solution-processable metal oxides for interfacial layers in PSCs, such as MoOx, VOx, WOx and ZnOx. The photovoltaic performance of PSCs buffered by these metal-oxide layers was studied and the applicability of these interfacial layers was demonstrated both with P3HT and a low band-gap polymer PBDT-T8-TPD.Graphical abstract
Co-reporter:Jialing Lu, Jun Peng, Yuchen Wang, Jianyu Yuan, Chuanxiang Sheng, Hai-Qiao Wang, Wanli Ma
Synthetic Metals 2014 Volume 188() pp:57-65
Publication Date(Web):February 2014
DOI:10.1016/j.synthmet.2013.11.019
•Four copolymers composed of donors and acceptors were designed and synthesized.•Influence of side chain and π-bridge on polymer's properties was studied.•Broader absorption and narrower band-gap were achieved for the synthesized polymers.•Deep HOMOs between −5.48 eV and −5.37 eV were confirmed for all the polymers.•Prospectively high Vocs of the devices based on the four polymers were achieved.Four new homologous copolymers (POP, POT, PTP and PTT), composed of benzo[1,2-b:4,5-b′]dithiophene (BDT) donors and fumaronitrile (BCNV) acceptors, were designed and synthesized. The effects of different side-chains of BDT units and different π-bridges of BCNV acceptors on polymers’ thermal, optical, electrochemical, chain geometric, hole-transporting properties and photovoltaic performance were systematically investigated. POT and PTT exhibit broader absorption and narrower bandgaps than POP and PTP due to the replacement of phenyl π-bridges with thienyl groups. All polymers show relatively deep highest occupied molecular orbitals (HOMOs) between −5.48 eV and −5.37 eV. Prospectively high open circuit voltages (Vocs) of the devices based on the four polymers were accomplished. The highest Voc 0.975 V was obtained with PTP. However, the obtained PCEs are still relatively low. We consider this is related to the polymers’ poor backbone planarity, relatively low LUMO levels or low polaron photogeneration efficiency resulted from BCNV.
Co-reporter:Long Hu, Jun Peng, Weiwei Wang, Zhe Xia, Jianyu Yuan, Jialing Lu, Xiaodong Huang, Wanli Ma, Huaibing Song, Wei Chen, Yi-Bing Cheng, and Jiang Tang
ACS Photonics 2014 Volume 1(Issue 7) pp:547
Publication Date(Web):June 18, 2014
DOI:10.1021/ph5000067
The new emerging organometal trihalide perovskite holds great potential for high-efficiency, low-cost solar cells because of its high solar to electricity conversation efficiency (>16%) achieved within 4 years of research and its low-temperature solution processing. In this Letter we introduce NiO as the hole-collecting and -conducting layer in perovskite solar cells. Through a modified sequential deposition strategy, we successfully fabricated high-quality CH3NH3PbI3 onto a planar NiO layer and built a planar inverted ITO/NiO/CH3NH3PbI3/PCBM/Al photovoltaic device. A device efficiency of 7.6% was achieved with an impressively high open-circuit voltage (Voc) of 1.05 V. Our study demonstrates the potential application of a deep work function NiO layer for perovskite solar cells.Keywords: NiO; perovskite; sequential deposition; solar cell
Co-reporter:Zeke Liu;Yaxiang Sun;Jianyu Yuan;Huaixin Wei;Xiaodong Huang;Lu Han;Weiwei Wang;Haiqiao Wang
Advanced Materials 2013 Volume 25( Issue 40) pp:5772-5778
Publication Date(Web):
DOI:10.1002/adma.201302340
Co-reporter:Zhichun Zhai;Xiaodong Huang;Meifeng Xu;Jianyu Yuan;Jun Peng
Advanced Energy Materials 2013 Volume 3( Issue 12) pp:1614-1622
Publication Date(Web):
DOI:10.1002/aenm.201300272
By application of thermal annealing and UV ozone simultaneously, a solution-processed NiOx film can achieve a work function of approximately –5.1 eV at a temperature below 150 °C, which allows the processing of NiOx that is compatible with fabrication of polymer solar cells (PSCs) on plastic substrates. The low processing temperature, which is greatly reduced from 250–400 °C to 150 °C, is attributed to the high concentration of NiOOH species on the film surface. This concentration will result in a large surface dipole and lead to increased work function. The pretreated NiOx is demonstrated to be an efficient buffer layer in PSCs based on polymers with different highest occupied molecular orbital energy levels. Compared with conventional poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate)-buffered PSCs, the NiOx-buffered PSCs achieve similar or improved device performance as well as enhanced device stability.
Co-reporter:Jianyu Yuan;Zhichun Zhai;Huilong Dong;Jing Li;Zuoquan Jiang;Youyong Li
Advanced Functional Materials 2013 Volume 23( Issue 7) pp:885-892
Publication Date(Web):
DOI:10.1002/adfm.201201535
Abstract
A series of polymers containing benzo[1,2-b:4,5-b′]dithiophene and N-alkylthieno[3,4-c]pyrrole-4,6-dione are designed. By incorporating different alkylthienyl side chains, the fill factor (FF) and open circuit voltage (Voc) of the copolymers are further improved. The experimental results and theoretical calculations show that the size and topology of the side chains can influence the polymer solubility, energy levels, and intermolecular packing by altering the molecular coplanarity. As a result of improved morphology and fine-tuned energy levels, an increased FF and a high Voc of 1.00 V are achieved, as well as a power conversion efficiency of 6.17%, which is the highest efficiency ever reported for polymer solar cells with a Voc over 1 V.
Co-reporter:Wei Yue, Xiaodong Huang, Jianyu Yuan, Wanli Ma, Frederik C. Krebs and Donghong Yu
Journal of Materials Chemistry A 2013 vol. 1(Issue 35) pp:10116-10119
Publication Date(Web):24 Jul 2013
DOI:10.1039/C3TA12701J
A low band gap polymer PBDPDP-DTP, with alternating benzodipyrrolidone (BDP) unit and dithienopyrrole, was synthesized and characterized. A PCE of 2.60% and a Voc of up to 0.74 V were realized in PSCs, which demonstrated the strong potential of BDP as the electron deficient unit in the design of donor–acceptor conjugated polymers for PSCs.
Co-reporter:Kunyuan Lu, Jianyu Yuan, Jun Peng, Xiaodong Huang, Linsong Cui, Zuoquan Jiang, Hai-Qiao Wang and Wanli Ma
Journal of Materials Chemistry A 2013 vol. 1(Issue 45) pp:14253-14261
Publication Date(Web):25 Sep 2013
DOI:10.1039/C3TA12935G
Small molecules TPDA, TPDB, and TPDH, comprising the same backbone TPD (N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine) and different carboxyl side chains were designed and synthesized as hole-transporting materials in polymer solar cells. These small molecules demonstrated improved solubility in polar solvents due to the introduction of the weakly acidic carboxyl groups. The lengths of the side chains can also influence the film forming ability. Compared to conventional PEDOT:PSS, these small molecules showed higher transmittance in the visible range as revealed by UV-vis measurements. Desirable energy-level alignment for efficient hole-transporting and electron-blocking ability was indicated by their absorption and UPS spectra. Without applying any post-treatment to these buffer layers, comparable and improved device performances were achieved compared with PEDOT:PSS buffered control devices. A high power conversion efficiency of 6.51% was realized by a TPDB buffered device employing a low band gap polymer PBDTTPD as the active material, which showed ∼15% efficiency enhancement over the control devices. Equally important, better device stability was demonstrated by using TPDB as the new hole-transporting layer.
Co-reporter:Jianyu Yuan, Zhichun Zhai, Jing Li, Jialing Lu, Xiaodong Huang, Zhongjie Xu and Wanli Ma
Journal of Materials Chemistry A 2013 vol. 1(Issue 39) pp:12128-12136
Publication Date(Web):05 Aug 2013
DOI:10.1039/C3TA12210G
A series of donor–acceptor (D–A) polymers based on furan-bridged benzodithiophene and different acceptor blocks were designed and synthesized. By incorporating various acceptors with differing electron-withdrawing abilities into the same polymer backbone, we were seeking to reveal the correlation between molecular structures and the corresponding film morphology as well as photovoltaic performance. The experimental results and theoretical calculations indicate that the selection of acceptor units has significant impacts on the polymer energy levels and backbone coplanarity, leading to differing intermolecular packing. By using atomic force microscopy and transmission electron microscopy, we also observed that the size and topology of the alkyl-chains on acceptors can tune the polymer solubility and result in different film morphology. As a result of optimized morphology, we demonstrated power conversion efficiencies over 5% for the new polymer based devices, which are among the highest efficiencies of reported furan bridged D–A polymers.
Co-reporter:Jianyu Yuan, Yaping Zang, Huilong Dong, Guojun Liu, Chong-an Di, Youyong Li and Wanli Ma
Polymer Chemistry 2013 vol. 4(Issue 15) pp:4199-4206
Publication Date(Web):15 May 2013
DOI:10.1039/C3PY00501A
An existing donor–acceptor polymer was modified by introducing a furan π-bridge into its backbone, aiming to extend the π-conjugation and achieve higher performance in organic field effect transistors (OFETs). The effect of a furan-bridge on polymer thermal, optical and electrochemical properties was systematically investigated. OFETs demonstrated an unexpected reduced hole mobility for the furan-bridge containing polymer. Theoretical simulation indicated that the polymer coplanarity became worse after the incorporation of the furan-bridge due to the modified atomic interaction between adjacent building blocks in the backbone. X-ray diffraction and atomic force microscopy results further confirmed that the furan containing polymer had a less ordered intermolecular packing in film due to the reduced coplanarity.
Co-reporter:Guobing Zhang, Jianyu Yuan, Peng Li, Jingxuan Ma, Hongbo Lu, Longzhen Qiu and Wanli Ma
Polymer Chemistry 2013 vol. 4(Issue 11) pp:3390-3397
Publication Date(Web):22 Mar 2013
DOI:10.1039/C3PY00251A
Two new conjugated polymers based on benzodithiophene (BDT) and alkyl-benzotrithiophene (alkyl-BTT, P1), or acyl-benzotrithiophene (acyl-BTT, P2) were synthesized by a Stille cross-coupling reaction. The polymers were characterized by gel permeation chromatography (GPC), ultraviolet-visible (UV-vis) absorption as well as electrochemical cyclic voltammetry (CV) tests. Compared to the alkyl-BTT-based polymer (P1), the acyl-BTT-based polymer (P2) displayed a lower optical bandgap and a lower HOMO energy level. Polymer solar cells (PSCs) also confirmed that P2-based devices possessed better photovoltaic properties than those of P1-based devices. The optimized photovoltaic devices were fabricated with an active layer of a blend P2 and PC71BM using 2 vol% 1,8-diiodooctane (DIO) as a solvent additive, and a PCE of 4.20% was obtained, with a Voc as high as 0.96 V under AM 1.5G illumination at 100 mW cm−2 with a solar simulator.
Co-reporter:Shugang Li, Jianyu Yuan, Ping Deng, Wanli Ma, Qing Zhang
Solar Energy Materials and Solar Cells 2013 Volume 118() pp:22-29
Publication Date(Web):November 2013
DOI:10.1016/j.solmat.2013.07.049
•The UV–vis absorption spectra of polymer PIDNDF1 recorded in dilute solution and as thin-film were both red-shifted compared with those of polymer PIDNDF2.•The HOMO energy levels of PIDNDF1 and PIDNDF2 are similar at −5.40 eV. There is only slight difference in the LUMO energy levels of these two polymers.•The dihedral angle between naphthodifuran and isoindigo was 26.89° for the model compound of PIDNDF2, which was almost twice that of the model compound of PIDNDF1 (14.61°).•The performances of PSC devices based on these two polymers are different. The maximum PCE of PIDNDF1 was 1.83% with PC61BM, which was more than twice that of PIDNDF2.New polymers based on two different angular-shaped naphthodifurans (NDFs) have been synthesized. The optical, electrochemical and photovoltaic properties of the new polymers were investigated. The UV–vis absorption spectra of polymer PIDNDF1 recorded in dilute solution and as thin-film were both red-shifted compared with those of polymer PIDNDF2. The HOMO energy levels of PIDNDF1 and PIDNDF2 were similar at −5.40 eV. There was slight difference in the LUMO energy levels of these two polymers. The maximum power conversion efficiency (PCE) of PIDNDF1 based solar cell devices was 1.83%, which was more than twice that of PIDNDF2 based device. The difference on the device performance resulted from the shapes of NDF repeating units and backbone geometries of polymers.Two novel angular-shaped naphthodifurans (NDFs) based conjugated polymers (PIDNDF1 and PIDNDF2) have been successfully synthesized and characterized.
Co-reporter:Jianyu Yuan, Xiaodong Huang, Huilong Dong, Jialing Lu, Tao Yang, Youyong Li, Aidan Gallagher, Wanli Ma
Organic Electronics 2013 Volume 14(Issue 2) pp:635-643
Publication Date(Web):February 2013
DOI:10.1016/j.orgel.2012.12.003
Two new donor–acceptor (D–A) polymers composed of benzo[1,2-b:4,5-b′]dithiophene (BDT) as donor and thiadiazolo[3,4-c]pyridine (PyTZ) as acceptor were designed and synthesized. Compared to the polymer based on BDT and 4,7-dithien-2-yl-2,1,3-benzothiadiazole (DTBT), the planarity, energy levels, and band-gaps of the new polymers were fine adjusted by incorporating conjugated alkylthienyl side chains to BDT and substitute a stronger acceptor PyTZ for 2,1,3-benzothiadiazole. The new polymers exhibit broad absorption from 300 to 800 nm in both solution and film state. The polymer band gaps and energy levels are close to the optimal values. As a result, power conversion efficiencies (PCEs) of 4.84% and 5.11% were obtained for inverted polymer solar cells based on these new polymers. The PCEs are significantly higher than those of the BDT–DTBT based polymers (2–4%).Graphical abstractBriefs: Two new D–A polymers composed of BDT as donor and PyTZ as acceptor were designed and synthesized. The new polymers exhibit broad absorption from 300 to 800 nm in both solution and film state, and their band gaps and energy levels are close to the theoretical values of the efficacious donor polymers. As a result, PCEs of 4.84% and 5.11% were obtained for inverted PSCs based on these new polymers.Highlights► Two new D–A polymers composed of BDT as donor and thiadiazolo[3,4-c] pyridine as acceptor were designed and synthesized. ► Through structure, band-gap and energy level modulations, we obtained materials with excellent photovoltaic properties. ► The optimized inverted polymer solar cells exhibit high power conversion efficiencies of 4.84% and 5.11%.
Co-reporter:Tao Yang, Zuoquan Jiang, Xiaodong Huang, Huaixin Wei, Jianyu Yuan, Wei Yue, Youyong Li, Wanli Ma
Organic Electronics 2013 Volume 14(Issue 9) pp:2184-2191
Publication Date(Web):September 2013
DOI:10.1016/j.orgel.2013.05.017
•Two new fullerene derivatives with spiro-structure were designed and synthesized.•The performance was optimized by adjusting D/A ratio, using annealing and additive.•The optimal PCE of PSCs using DBSCBA is 10% higher than that of devices using PCBM.Two new dibenzosuberane-substituted fullerene derivatives, dibenzosuberane-C60 mono-adduct (DBSCMA) and bis-adduct (DBSCBA) were synthesized using a classical cyclopropanation reaction via a tosylhydrazone route for application as acceptor materials in polymer solar cells (PSCs). DBSCBA shows good solubility in common organic solvents and both derivatives were characterized by 1HNMR, 13C NMR, MALD-TOF, elemental analysis and UV–vis absorption measurements. The shift of fullerene energy levels induced by the dibenzosuberane substitution was investigated by using theoretical simulations and ultraviolet photoelectron spectroscopy. Bulk-heterojunction PSCs based on poly (3-hexylthiophene) (P3HT) and dibenzosuberane-C60 derivatives were fabricated and optimized by adjusting the donor/acceptor ratio and using thermal annealing and solvent additive. The morphologies of the active layers processed under different conditions were also examined by atomic force microscopy. When tested under an illumination of AM 1.5 G at 100 mW/cm2, the highest power conversion efficiency of the devices using DBSCBA is 3.70% which is superior to that of conventional P3HT:PCBM devices.Graphical abstractBriefs: We have successful synthesized two fullerene derivatives, dibenzosuberane-C60 mono-adduct (DBSCMA) and bis-adduct (DBSCBA) with new spiral structure by cyclopropanation reaction for use as acceptor materials in polymer solar cells. The introduced dibenzosuberane groups improve the fullerene energy level alignment and the two new fullerene derivatives show slightly higher absorption in the visible region than conventional PCBM. After systematical optimization, a high power conversion efficiency of 3.70% was obtained for the devices using DBSCBA under an illumination of AM 1.5 G at 100 mW/cm2, which is 10% higher than that of P3HT:PCBM control device. The improved PCE is attributed to the optimal morphology and enhanced absorbance of DBSCBA in the visible region.
Co-reporter:Jing Li, Xiaodong Huang, Jianyu Yuan, Kunyuan Lu, Wei Yue, Wanli Ma
Organic Electronics 2013 Volume 14(Issue 9) pp:2164-2171
Publication Date(Web):September 2013
DOI:10.1016/j.orgel.2013.05.012
•A new electron-transporting material DPPA was synthesized by modifying BCP.•DPPA outperforms BCP and ZnO as electron transporting layer in polymer solar cells.•The HOMO of DPPA is deeper than BCP, making it a better hole-blocking material.•DPPA shows a higher tolerance and flexibility for processing conditions than BCP.•A fast and economical approach was demonstrated to obtain buffer layer materials.A new electron-transporting material 4,7-diphenyl-1,10-phenanthroline-2,9-dicarboxylic acid (DPPA) was synthesized by modifying a n-type small molecule bathocuproine (BCP). The introduced carboxyl groups make DPPA soluble in polar solvent and compatible with large-scale solution-processing techniques. The anchoring of carboxyl on ZnO (or ITO) substrates helps to form a DPPA electron transporting layer, building an improved interfacial contact between the substrate and active layer. Furthermore, the highest occupied molecular orbital level of DPPA shifts to −6.45 eV, which is 0.38 eV deeper than that of BCP, suggesting enhanced hole-blocking. Inverted polymer solar cells using P3HT:PCBM blend as the active layer and DPPA modified ZnO as the electron transporting layer were fabricated. A power conversion efficiency (PCE) of 3.55% was obtained, which is about 10% higher than that of the conventional ZnO buffered devices (3.25%). The DPPA was also used to replace ZnO as the sole electron-extracting layer, resulting in an improved PCE of 3.46%, which indicates that DPPA-ETL/ITO forms a better cathode than conventional ZnO/ITO.Graphical abstractA new electron-transporting material 4,7-diphenyl-1,10-phenanthroline-2,9-dicarboxylic acid (DPPA) was synthesized by modifying a n-type small molecule bathocuproine (BCP). DPPA inherits the excellent electron collecting and transporting property from BCP. In addition, DPPA demonstrated more stable and efficient performance than BCP under various processing conditions, likely due to the improved film quality and better hole-blocking. More importantly, this work brings up a fast and economical approach to obtain efficient, solution-processible buffer layer materials by modifying the existing functional molecules with corresponding electron-withdrawing/donating groups.
Co-reporter:Jianyu Yuan, Xiaodong Huang, Fengjiao Zhang, Jialing Lu, Zhichun Zhai, Chongan Di, Zuoquan Jiang and Wanli Ma
Journal of Materials Chemistry A 2012 vol. 22(Issue 42) pp:22734-22742
Publication Date(Web):11 Sep 2012
DOI:10.1039/C2JM34004F
Three low-band-gap donor–acceptor (D–A) copolymers containing benzo(1,2-b:4,5-b′)dithiophene (BDT), 3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (TDP) or 3,6-di(furan-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (FDP) were designed and synthesized. Their thermal stability, optical and electrochemical properties, device performances for organic field effect transistors (OFETs) and polymer solar cells were systematically investigated. The device performances were significantly enhanced by the introduction of conjugated alkylthienyl side chains to the BDT core and the substitution of thiophene with furan moieties in polymer backbone. Compared to alkoxy side chains, conjugated alkylthienyl chains resulted in higher coplanarity, increased thermal stability (Td increased from 364 °C to 417 °C) and a lower HOMO level (from −5.10 eV to −5.24 eV). The incorporation of furan evidently improved the polymer solubility, leading to a finer phase separation morphology as proved by atomic force microscopy and transmission electron microscopy. After optimization, the designed polymer showed excellent performance in both OFETs and PSCs with an optimal hole mobility of 0.16 cm2 V−1 s−1 and a high power conversion efficiency of 5.54%.
Co-reporter:Shugang Li, Jianyu Yuan, Ping Deng, Wanli Ma, Qing Zhang
Solar Energy Materials and Solar Cells (November 2013) Volume 118() pp:22-29
Publication Date(Web):1 November 2013
DOI:10.1016/j.solmat.2013.07.049
•The UV–vis absorption spectra of polymer PIDNDF1 recorded in dilute solution and as thin-film were both red-shifted compared with those of polymer PIDNDF2.•The HOMO energy levels of PIDNDF1 and PIDNDF2 are similar at −5.40 eV. There is only slight difference in the LUMO energy levels of these two polymers.•The dihedral angle between naphthodifuran and isoindigo was 26.89° for the model compound of PIDNDF2, which was almost twice that of the model compound of PIDNDF1 (14.61°).•The performances of PSC devices based on these two polymers are different. The maximum PCE of PIDNDF1 was 1.83% with PC61BM, which was more than twice that of PIDNDF2.New polymers based on two different angular-shaped naphthodifurans (NDFs) have been synthesized. The optical, electrochemical and photovoltaic properties of the new polymers were investigated. The UV–vis absorption spectra of polymer PIDNDF1 recorded in dilute solution and as thin-film were both red-shifted compared with those of polymer PIDNDF2. The HOMO energy levels of PIDNDF1 and PIDNDF2 were similar at −5.40 eV. There was slight difference in the LUMO energy levels of these two polymers. The maximum power conversion efficiency (PCE) of PIDNDF1 based solar cell devices was 1.83%, which was more than twice that of PIDNDF2 based device. The difference on the device performance resulted from the shapes of NDF repeating units and backbone geometries of polymers.Two novel angular-shaped naphthodifurans (NDFs) based conjugated polymers (PIDNDF1 and PIDNDF2) have been successfully synthesized and characterized. Download full-size image
Co-reporter:Jiangsheng Yu, Guanqun Ding, Jiefeng Hai, Enwei Zhu, Xinxing Yin, Zhongsheng Xu, Baojing Zhou, Fujun Zhang, Wanli Ma and Weihua Tang
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 11) pp:NaN7986-7986
Publication Date(Web):2016/02/16
DOI:10.1039/C5CP07942J
Four isostructural donor–acceptor alternating polymers of benzodithiophene (BDT)/naphthodifuran (NDF) and benzoselenadiazole (BSe)/benzothiadiazole (BT) have been developed and evaluated for organic photovoltaics. The substitution of one-atom (Se for S) in the accepting units exerts remarkable impact on the optoelectronic properties of polymers. Extended absorption, narrowed bandgap and higher HOMO energy levels were observed for Se-containing polymers in comparison to their S-containing counterparts. Theoretical calculations confirmed the measurable effect on energy levels as found in experimental studies. Bulk-heterojuction solar cells based on the BDT–BSe copolymer and [6,6]-phenyl-C71-butyric acid methyl ester (1:2, w/w) blend films deliver the best PCE of 5.40%. BSe-based polymers showed enhanced photovoltaic performances than BT-based polymers. The device performance is found to be strongly dependent on the processing conditions and morphology of the active layers.
Co-reporter:Jun Peng, Xinxin Wang, Jie Liu, Xiaodong Huang, Jing Xiao, Sui-Dong Wang, Hai-Qiao Wang and Wanli Ma
Journal of Materials Chemistry A 2014 - vol. 2(Issue 5) pp:NaN869-869
Publication Date(Web):2013/11/18
DOI:10.1039/C3TC32020K
Inverted organic light-emitting diodes (IOLEDs) can effectively improve device stability because they concentrate the air-stable anode and high work function (WF) metal oxide hole-injection layer (HIL) at the top of the devices. In this work, we report a facile solution-processed ultra-thin alumina film used as an electron-injection layer in IOLEDs and present significantly improved device performance. We achieved a high current efficiency of 5.12 cd A−1 at 10 mA cm−2 and the best current efficiency approaching 5.5 cd A−1 at 40 mA cm−2 without doping of an emission layer (EML) for a single Alq3-based green fluorescent IOLED, and a high current efficiency for a green phosphorescent IOLED as well. Furthermore, the extrapolated 50% decay lifetime (t50) shows that our Alq3-based green fluorescent IOLED is about 5 times more stable than the conventional OLED.
Co-reporter:Kunyuan Lu, Jianyu Yuan, Jun Peng, Xiaodong Huang, Linsong Cui, Zuoquan Jiang, Hai-Qiao Wang and Wanli Ma
Journal of Materials Chemistry A 2013 - vol. 1(Issue 45) pp:NaN14261-14261
Publication Date(Web):2013/09/25
DOI:10.1039/C3TA12935G
Small molecules TPDA, TPDB, and TPDH, comprising the same backbone TPD (N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine) and different carboxyl side chains were designed and synthesized as hole-transporting materials in polymer solar cells. These small molecules demonstrated improved solubility in polar solvents due to the introduction of the weakly acidic carboxyl groups. The lengths of the side chains can also influence the film forming ability. Compared to conventional PEDOT:PSS, these small molecules showed higher transmittance in the visible range as revealed by UV-vis measurements. Desirable energy-level alignment for efficient hole-transporting and electron-blocking ability was indicated by their absorption and UPS spectra. Without applying any post-treatment to these buffer layers, comparable and improved device performances were achieved compared with PEDOT:PSS buffered control devices. A high power conversion efficiency of 6.51% was realized by a TPDB buffered device employing a low band gap polymer PBDTTPD as the active material, which showed ∼15% efficiency enhancement over the control devices. Equally important, better device stability was demonstrated by using TPDB as the new hole-transporting layer.
Co-reporter:Jianyu Yuan and Wanli Ma
Journal of Materials Chemistry A 2015 - vol. 3(Issue 13) pp:NaN7085-7085
Publication Date(Web):2015/02/09
DOI:10.1039/C4TA06648K
By adopting a series of donor–acceptor (D–A) polymers containing Benzo[1,2-b:4,5-b′]dithiophene (BDT) and thieno[3,4-c]pyrrole-4,6-dione (TPD) with different numbers of alkyl aromatic side-chains, we demonstrate a high optimized PCE of 4.35% for all-polymer solar cells by incorporating an n-type polymer N2200. Through systematic characterization of tapping mode atomic force microscopy (AFM), 2-dimensional grazing-incidence X-ray diffraction (2d-GIXD), photoluminescence spectra and peak force-kelvin probe force microscopy (PF-KPFM), we have shown that the introduction of alkyl aromatic side chains to the donor polymer backbone is beneficial for the intermolecular π–π stacking and hence improves the polymer crystallinity as well as hole mobility. More importantly, we discovered that conjugated side-chains and additives can work synergistically to restore the intermolecular stacking of donor–acceptor polymers in the as-cast amorphous blend film and meanwhile develop fine phase segregation for efficient exciton dissociation and transport. As a result, the donor polymer PTP8 with fully alkyl aromatic side chains demonstrated an improved short-circuit current density (Jsc), a high open-circuit voltage (Voc) of ∼1.00 V and a power conversion efficiency (PCE) of 4.35% after the addition of 0.5% DIO, which is among the highest reported efficiencies for all polymer solar cells.
Co-reporter:Wei Yue, Xiaodong Huang, Jianyu Yuan, Wanli Ma, Frederik C. Krebs and Donghong Yu
Journal of Materials Chemistry A 2013 - vol. 1(Issue 35) pp:NaN10119-10119
Publication Date(Web):2013/07/24
DOI:10.1039/C3TA12701J
A low band gap polymer PBDPDP-DTP, with alternating benzodipyrrolidone (BDP) unit and dithienopyrrole, was synthesized and characterized. A PCE of 2.60% and a Voc of up to 0.74 V were realized in PSCs, which demonstrated the strong potential of BDP as the electron deficient unit in the design of donor–acceptor conjugated polymers for PSCs.
Co-reporter:Long Hu, Weiwei Wang, Huan Liu, Jun Peng, Hefeng Cao, Gang Shao, Zhe Xia, Wanli Ma and Jiang Tang
Journal of Materials Chemistry A 2015 - vol. 3(Issue 2) pp:NaN518-518
Publication Date(Web):2014/11/24
DOI:10.1039/C4TA04272G
Here, we applied colloidal quantum dots (CQDs) as an effective p-type hole-transporting material (HTM) for planar heterojunction perovskite solar cells. By tuning the size of PbS CQDs, we engineered the energy alignment of the valence and conduction band of this new HTM with the perovskite light harvester and achieved conversion efficiencies up to 7.5%. Absorption of PbS CQDs also extends the absorption spectrum of perovskite solar cells into the infrared region.
Co-reporter:Jianyu Yuan, Michael J. Ford, Wanli Ma and Guillermo C. Bazan
Journal of Materials Chemistry A 2017 - vol. 5(Issue 19) pp:NaN8908-8908
Publication Date(Web):2017/04/18
DOI:10.1039/C7TA02510F
In comparison with many reported high-efficiency polymer solar cells, only 0.5% (v/v) additive is necessary to optimize a polymer/fullerene (PSFSiF/PC71BM) system, and the power conversion efficiency (PCE) was boosted from 2.4% to 8.0%. 2D grazing incidence wide angle X-ray scattering (GIWAXS) is utilized to understand the relevant structural features in the blend films prepared under different processing conditions, and the BHJ morphology is also examined using atomic force microscopy (AFM) and transmission electron microscopy (TEM) techniques.
Co-reporter:Jianyu Yuan, Zhichun Zhai, Jing Li, Jialing Lu, Xiaodong Huang, Zhongjie Xu and Wanli Ma
Journal of Materials Chemistry A 2013 - vol. 1(Issue 39) pp:NaN12136-12136
Publication Date(Web):2013/08/05
DOI:10.1039/C3TA12210G
A series of donor–acceptor (D–A) polymers based on furan-bridged benzodithiophene and different acceptor blocks were designed and synthesized. By incorporating various acceptors with differing electron-withdrawing abilities into the same polymer backbone, we were seeking to reveal the correlation between molecular structures and the corresponding film morphology as well as photovoltaic performance. The experimental results and theoretical calculations indicate that the selection of acceptor units has significant impacts on the polymer energy levels and backbone coplanarity, leading to differing intermolecular packing. By using atomic force microscopy and transmission electron microscopy, we also observed that the size and topology of the alkyl-chains on acceptors can tune the polymer solubility and result in different film morphology. As a result of optimized morphology, we demonstrated power conversion efficiencies over 5% for the new polymer based devices, which are among the highest efficiencies of reported furan bridged D–A polymers.
Co-reporter:Yong Li, Kunyuan Lu, Xufeng Ling, Jianyu Yuan, Guozhen Shi, Guanqun Ding, Jianxia Sun, Shaohua Shi, Xiu Gong and Wanli Ma
Journal of Materials Chemistry A 2016 - vol. 4(Issue 26) pp:NaN10134-10134
Publication Date(Web):2016/06/06
DOI:10.1039/C6TA03284B
In this contribution, we disclose the fabrication and characterization of efficient planar-heterojunction perovskite solar cells using novel amino-based fulleropyrrolidine (C60–N) as the electron transporting material (ETM). Compared to the widely spread [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), we found that C60–N can both efficiently reduce the work function of the metal cathode and passivate the trap states of the perovskite surface, further resulting in improved carrier transport, photovoltaic performance and stability. Devices using C60–N as the ETM exhibit a high power conversion efficiency (PCE) of 16.6%, significantly higher than the 12.3% of PCBM based ones. In addition, we found that C60–N can also significantly enhance the film PL lifetime and decrease the surface roughness. These findings provide insight into the selection and design of new ETMs with desirable properties.
Co-reporter:Guidong Ge, Jinan Gu, Jiangsheng Yu, Enwei Zhu, Jiefeng Hai, Linyi Bian, Fujun Zhang, Zhongsheng Xu, Wanli Ma and Weihua Tang
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 12) pp:NaN7856-7856
Publication Date(Web):2015/02/12
DOI:10.1039/C5CP00349K
Three dialkylthio benzo[1,2-b:4,5-b′]dithiophene (S-BDT) based polymers have been developed using different accepting units to tune their bandgaps. The polymer:PC71BM solar cells achieved the highest power conversion efficiency (PCE) of 4.51% without any post-treatment (such as annealing and solvent additive) in conventional single-cell devices. Joint photophysical, electrical and computational studies on the polymer based solar cells revealed the considerable impact of molecular planarity on polymer design. The polymer:PC71BM devices processed with 1,8-diiodooctane for improving their morphology afforded an improved PCE value of 5.63%, with a Voc of 0.83, a Jsc of 10.24 mA cm−2 and a FF of 66.3%.
Co-reporter:Jianyu Yuan, Aidan Gallagher, Zeke Liu, Yaxiang Sun and Wanli Ma
Journal of Materials Chemistry A 2015 - vol. 3(Issue 6) pp:NaN2579-2579
Publication Date(Web):2014/09/24
DOI:10.1039/C4TA03995E
Solution-processed hybrid solar cells (HSCs), composed of conjugated polymers and semiconducting PbS nanocrystals, are promising candidates for the next-generation photovoltaic devices. Through deliberate molecular design, a series of new organic donor–acceptor polymers bearing varying optical band-gaps (1.25–1.65 eV) and suitable HOMO (highest occupied molecular orbital) energy levels (∼5.0 eV) were synthesized. Due to improved device architecture, we achieved the highest power conversion efficiency (PCE) of 4.23% to date for polymer–PbS based HSCs. Furthermore, the correlation between the polymer molecular structure and hybrid blend morphologies was systematically investigated using 2-dimensional grazing incidence X-ray diffraction, atomic force microscopy and scanning transmission electron microscopy. We believe our findings can be beneficial to the future molecular design toward highly efficient polymer–PbS HSCs.
Co-reporter:Jianyu Yuan, Xiaodong Huang, Fengjiao Zhang, Jialing Lu, Zhichun Zhai, Chongan Di, Zuoquan Jiang and Wanli Ma
Journal of Materials Chemistry A 2012 - vol. 22(Issue 42) pp:NaN22742-22742
Publication Date(Web):2012/09/11
DOI:10.1039/C2JM34004F
Three low-band-gap donor–acceptor (D–A) copolymers containing benzo(1,2-b:4,5-b′)dithiophene (BDT), 3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (TDP) or 3,6-di(furan-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (FDP) were designed and synthesized. Their thermal stability, optical and electrochemical properties, device performances for organic field effect transistors (OFETs) and polymer solar cells were systematically investigated. The device performances were significantly enhanced by the introduction of conjugated alkylthienyl side chains to the BDT core and the substitution of thiophene with furan moieties in polymer backbone. Compared to alkoxy side chains, conjugated alkylthienyl chains resulted in higher coplanarity, increased thermal stability (Td increased from 364 °C to 417 °C) and a lower HOMO level (from −5.10 eV to −5.24 eV). The incorporation of furan evidently improved the polymer solubility, leading to a finer phase separation morphology as proved by atomic force microscopy and transmission electron microscopy. After optimization, the designed polymer showed excellent performance in both OFETs and PSCs with an optimal hole mobility of 0.16 cm2 V−1 s−1 and a high power conversion efficiency of 5.54%.
![Stannane, 1,1'-(4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2,6-diyl)bis[1,1,1-trimethyl-](/data/chemimg/3781900/920503-98-6.png)
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![Stannane, 1,1'-[4,8-bis(4,5-didecyl-2-thienyl)benzo[1,2-b:4,5-b']dithiophene-2,6-diyl]bis[1,1,1-trimethyl-](/data/chemimg/3781900/1307899-54-2.png)
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![Benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetrone, 4,9-dibromo-2,7-bis(2-hexyldecyl)-](/data/chemimg/3730400/1459168-68-3.png)
![Benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetrone, 4,9-dibromo-2,7-bis(2-hexyldecyl)-](/data/chemimg/3730400/1459168-68-3_b.png)
![2,1,3-Benzothiadiazole, 4,7-bis[6-bromo-4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b']dithien-2-yl]-5,6-difluoro-](/data/chemimg/3730500/1432791-00-8.png)
![2,1,3-Benzothiadiazole, 4,7-bis[6-bromo-4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b']dithien-2-yl]-5,6-difluoro-](/data/chemimg/3730500/1432791-00-8_b.png)
![2,1,3-Benzothiadiazole, 4,7-bis(4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b']dithien-2-yl)-](/data/chemimg/3781900/1262552-69-1.png)
![2,1,3-Benzothiadiazole, 4,7-bis(4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b']dithien-2-yl)-](/data/chemimg/3781900/1262552-69-1_b.png)
![2,1,3-Benzothiadiazole, 4,4'-[4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b']dithiophene-2,6-diyl]bis[7-bromo-6-fluoro-](/data/chemimg/3781900/1589072-33-2.png)
![2,1,3-Benzothiadiazole, 4,4'-[4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b']dithiophene-2,6-diyl]bis[7-bromo-6-fluoro-](/data/chemimg/3781900/1589072-33-2_b.png)
![Benzo[1'',2'':4,5;4'',5'':4',5']bissilolo[3,2-b:3',2'-b']dithiophene, 4,4,9,9-tetrahexyl-4,9-dihydro-2,7-bis(trimethylstannyl)-](/data/chemimg/3781900/1569453-45-7.png)
![Benzo[1'',2'':4,5;4'',5'':4',5']bissilolo[3,2-b:3',2'-b']dithiophene, 4,4,9,9-tetrahexyl-4,9-dihydro-2,7-bis(trimethylstannyl)-](/data/chemimg/3781900/1569453-45-7_b.png)
![9H-Carbazole, 9-[3,5-bis(dodecyloxy)phenyl]-2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-](/data/chemimg/3781900/1872371-66-8.png)
![9H-Carbazole, 9-[3,5-bis(dodecyloxy)phenyl]-2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-](/data/chemimg/3781900/1872371-66-8_b.png)
![2,1,3-Benzothiadiazole, 4,4'-[4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b']dithiophene-2,6-diyl]bis[7-bromo-](/data/chemimg/164900/1401032-28-7.png)
![2,1,3-Benzothiadiazole, 4,4'-[4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b']dithiophene-2,6-diyl]bis[7-bromo-](/data/chemimg/164900/1401032-28-7_b.png)
![Stannane, 1,1'-[4,8-bis[5-(2-ethylhexyl)-2-thienyl]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl]bis[1,1,1-trimethyl-](/data/chemimg/139400/1352642-37-5.png)
![Stannane, 1,1'-[4,8-bis[5-(2-ethylhexyl)-2-thienyl]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl]bis[1,1,1-trimethyl-](/data/chemimg/139400/1352642-37-5_b.png)
![4H-Silolo[3,2-b:4,5-b']dithiophene, 4,4-bis(2-ethylhexyl)-2-(trimethylstannyl)-](/data/chemimg/164900/1228237-08-8.png)
![4H-Silolo[3,2-b:4,5-b']dithiophene, 4,4-bis(2-ethylhexyl)-2-(trimethylstannyl)-](/data/chemimg/164900/1228237-08-8_b.png)
![4H-Silolo[3,2-b:4,5-b']dithiophene, 4,4-bis(2-ethylhexyl)-](/data/chemimg/164900/1207627-85-7.png)
![4H-Silolo[3,2-b:4,5-b']dithiophene, 4,4-bis(2-ethylhexyl)-](/data/chemimg/164900/1207627-85-7_b.png)
![Benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetrone, 4,9-dibromo-2,7-bis(2-octyldodecyl)-](/data/chemimg/139000/1100243-35-3.png)
![Benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetrone, 4,9-dibromo-2,7-bis(2-octyldodecyl)-](/data/chemimg/139000/1100243-35-3_b.png)
![Benzo[1,2-b:4,5-b']diselenophene](http://img.cochemist.com/ccimg/700400/700373-48-4.png)
![Benzo[1,2-b:4,5-b']diselenophene](http://img.cochemist.com/ccimg/700400/700373-48-4_b.png)
![Stannane, 1,1'-[2,2'-biselenophene]-5,5'-diylbis[1,1,1-trimethyl-](/data/chemimg/105500/220770-51-4.png)
![Stannane, 1,1'-[2,2'-biselenophene]-5,5'-diylbis[1,1,1-trimethyl-](/data/chemimg/105500/220770-51-4_b.png)
![Benzo[1,2-b:4,5-b']dithiophene](/data/chemimg/477000/267-65-2.png)
![Benzo[1,2-b:4,5-b']dithiophene](/data/chemimg/477000/267-65-2_b.png)
