•Study effects of exciton adjusting layer (EAL) to organic integrated device.•EAL specie affects hole injection and trapping, leaking current, charge separation.•EAL thickness affects optical field variation, leaking current, charge separation.•Fabricate an optimized dual functional organic integrated device.Organic optoelectronic integrated device (OID) with ultraviolet (UV) photodetective and electroluminescent (EL) properties was constructed by using four kinds of organic materials with various film thicknesses as exciton adjusting layer (EAL). The effect of EAL on the performance of OID was studied via energy level regulation, simulation of optical density distribution and charge transport analyses. Three orders of magnitude in UV-detectivity from 109 to 1012 Jones, and five folds of luminance from 5000 to 25000 cd/m2, were achieved by optimizing the species and thickness of EAL materials. We found that the energy level and thickness of EAL play important roles on the improvement of EL and UV detective properties. On one hand, the energy difference of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) between hole transport layer and active layer has a significant effect on the EL property through adjusting hole injection and passivating leaking current processes. On the other hand, the optimized EAL thickness is beneficial to enhance the distribution of optical density in the active layer, leading to more photocurrent generation for high UV detective property. Meanwhile, the EAL can trap leaking electrons to decrease the dark current for high detective performance. Moreover, both high EL and UV detective properties of OID can be simultaneously achieved by emulating calculation the carrier transport length of EAL.

Hybrid white organic light-emitting devices (OLEDs) are fabricated by employing non-doped emitting layers (EMLs), which are consisted of a blue thermally activated delayed fluorescent (TADF) emitter 9,9-dimethyl-9,10-dihydroacridine-diphenylsulfone (DMAC-DPS) and an ultrathin yellow iridium complex bis[2-(4-tertbutylphenyl)benzothiazolato-N,C2′] iridium (acetylacetonate) [(tbt)2Ir(acac)]. With thickness optimization of DMAC-DPS, a white OLED achieves maximum current efficiency, power efficiency and external quantum efficiency of 34.9 cd/A, 29.2 lm/W and 11.4%, respectively, as well as warm white emission with relatively stable electroluminescence spectra. The results suggest that, bipolar charge carrier transport property and concentration independent property of DMAC-DPS, charge carrier trapping effect of the ultrathin (tbt)2Ir(acac), and balanced self-emission process and energy transfer process between DMAC-DPS and (tbt)2Ir(acac), contribute to high device performance.

•High PCE of 4.44% with a simultaneous enhancement of JSC and FF was achieved for P3HT:Ir(piq)2acac:PC71BM ternary polymer solar cells.•Optical, electrical and morphological properties of the ternary polymer solar cells were investigated.•A 99.9% energy transfer efficiency was due to the efficient triplet-to-singlet energy transfer from Ir(piq)2acac to P3HT.•The incorporation of Ir(piq)2acac enhanced exciton harvesting and formed optimized self-organized morphology in the active layer.To study the effect of iridium complexes on performance of polymer solar cells, we report the ternary bulk heterojunction (BHJ) polymer solar cells (PSCs) by doping an iridium complex material of bis (1-phenylisoquinoline) acetylacetonate iridium(III) [Ir(piq)2acac] into the conventional active layer of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). The results show that the power conversion efficiency (PCE) of P3HT:PC71BM based ternary devices is improved from 2.99% to 4.44% by doping 1 wt% Ir(piq)2acac, which is benefited from the enhanced exciton harvesting by Förster resonance energy transfer (FRET) from Ir(piq)2acac to P3HT and optimized self-organized morphology within ternary blends.

A new type of nitrogen dioxide (NO2) gas sensor based on copper phthalocyanine (CuPc) thin film transistors (TFTs) with a simple, low-cost UV–ozone (UVO)-treated polymeric gate dielectric is reported here. The NO2 sensitivity of these TFTs with the dielectric surface UVO treatment is ≈400× greater for [NO2] = 30 ppm than for those without UVO treatment. Importantly, the sensitivity is ≈50× greater for [NO2] = 1 ppm with the UVO-treated TFTs, and a limit of detection of ≈400 ppb is achieved with this sensing platform. The morphology, microstructure, and chemical composition of the gate dielectric and CuPc films are analyzed by atomic force microscopy, grazing incident X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy, revealing that the enhanced sensing performance originates from UVO-derived hydroxylated species on the dielectric surface and not from chemical reactions between NO2 and the dielectric/semiconductor components. This work demonstrates that dielectric/semiconductor interface engineering is essential for readily manufacturable high-performance TFT-based gas sensors.

A novel hybrid cathode interlayer (CIL) consisting of reduced graphene oxide and zinc oxide (ZnO) is realized in the inverted organic solar cells (OSCs). A dual-nozzle spray coating system and facile one-step in situ thermal reduction/annealing (ITR/ITA) method are introduced to precisely control the components of the CIL, assemble ZnO with graphene oxide, and reduce graphene oxide into in situ thermal reduced graphene oxide (IT-RGO), simultaneously. The ZnO:IT-RGO hybrid CIL shows high electric conductivity, interconnecting nanostructure, and matched energy level, which leads to a significant enhancement in the power conversion efficiency from 6.16% to 8.04% for PTB7:PC71BM and from 8.02% to 9.49% for PTB7-Th:PC71BM-based OSCs, respectively. This newly developed spray-coated ZnO:IT-RGO hybrid CIL based on one-step ITR/ITA treatment has the high potential to provide a facile pathway to fabricate the large-scale, fast fabrication, and high performance OSCs.Keywords: hybrid cathode interlayer; in situ thermal annealing; in situ thermal reduction; organic solar cell; reduced graphene oxide; spray coating; zinc oxide;

•Color stable ultra-thin layer OLED was obtained by using a carrier-exciton adjusting layer.•The EQE, PE and CE of 15.0%, 36.0 l m/W and 37.2 cd/A were obtained.•The exciton recombination area and processes were elucidated in this work.Highly efficient white organic light-emitting diodes (WOLEDs) with dual ultra-thin phosphorescent blue and orange emitting layers (EMLs) were achieved in this work. The 1,3-di-9-carbazolylbenzene (mCP) was selected as a carrier-exciton adjusting layer (C-EAL), then the distribution of carriers and excitons was effectively controlled. The investigation of the relationship between C-EAL thickness and spectrum was carried out, and it concluded that the additional C-EAL was beneficial for the suppressing of charge carrier trapping and the decreasing of the direct recombination. Then the improved spectra stability to voltage was also studied. Preferably, the device based on a 4 nm C-EAL exhibits stable Commission Internationale de L'Eclairage (CIE) coordinates from (0.32, 0.40) at 124 cd/m2 to (0.30, 0.40) at 9705 cd/m2. The device structure and production process here was simplified and compatible with industrial production.Download high-res image (269KB)Download full-size image

•Architecture, function, energy transfer and exciton formation process of TOLED are introduced.•Development process and present situation of materials for emitter are reviewed.•Design of monochromatic, white and color tunable TOLED are presented.•Advantages and disadvantages of various intermediate layer in TOLEDs are reviewed.Tandem organic light-emitting diodes (TOLEDs) generally consist of two or more electroluminescent (EL) units connected electrically in series via an intermediate layer. It has been found that the current efficiency of TOLEDs is potentially several folds higher than that of single EL unit device. Based on the latest great research efforts, herein we aim to present an overview of primary principles and designation for both efficient EL unit and intermediate layer in the aspects of functional materials, energy level, device architecture and optical properties. Moreover, the design of monochromatic, white and color tunable TOLEDs, is also presented to guide the precise regulation of charge carriers in the intermediate layer and exciton distribution in distinct EL units. Finally, we end this work by presenting the challenges of TOLEDs to achieve the appealing commercial interest for information display and solid-lighting source. It can be anticipated that novel functional materials and structural construction can be devised upon suitable device engineering to achieve high performance TOLEDs.Download high-res image (320KB)Download full-size image

•Novel CNOs and ox-CNOs are firstly used to modified PEDOT:PSS as HTLs.•Conductivity, work function, surface tension of HTLs are well improved.•Acidity and hydrophily of PEDOT:PSS are suppressed by ox-CNOs.•PSC based on modified PEDOT:PSS show enhanced PCE from 11.07% to 15.26%.•PSC based on modified PEDOT:PSS exhibit dramatic improvement of stability.Poly (3,4-ethylenedioxythiophene) polystyrene sulphonate (PEDOT:PSS) is the most widely used hole transporting layer (HTL) in planar perovskite solar cells, which shows excellent optical, electrical properties and good compatibility with low temperature, solution and flexible processing. Nevertheless, the acidic and hygroscopic property of PEDOT:PSS restricts its film conductivity and leads to the degradation of device stability. Herein, for the first time, we introduce the unprecedentedly zero-dimensional dopant of carbon nano-onions (CNOs) and the functionalized oxidized carbon nano-onions (ox-CNOs) to modify the PEDOT:PSS HTL. Besides the merits of high conductivity and suitable energy level, the CNOs and ox-CNOs modified PEDOT:PSS HTLs could provide a superior perovskite crystalline film with large-scale grains and orderly grain boundaries exhibiting a high surface tension with the hydrophobic property, resulting in a significant enhancement of PCE from 11.07% to 15.26%. Moreover, by suppressing the corrosion effect of PEDOT:PSS on ITO electrode, a dramatic improvement in the device stability has also been obtained.Download high-res image (153KB)Download full-size image

Pure white organic light emitting devices (OLEDs) with high color stability have been fabricated, using a 4-aryloxy-1,8-naphthalimide derivative FluONI as a non-doped blue emitting layer (EML) combined with orange emitting exciplex at the interface of electron donor/FluONI. Three kinds of hole transport materials consisting of amino groups with stepped highest occupied molecular orbital (HOMO) levels are introduced as electron donors for the modulations of exciplex emission band and hole injection barrier. As a result, pure white emission with a standard Commission Internationale de 1'Eclairage (CIE) coordinate of (0.33, 0.33) is achieved by adopting N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4″-diamine as an electron donor with a relatively deep HOMO level and a 30 nm-thick EML. Meanwhile, excellent color stability is also observed with a slight CIE coordinates shift of (0.01, 0.01) at a luminance range from 100 to 4000 cd/m2. According to the systematic analyses on electroluminescence spectra, the pure white emission benefits from the broad emission bands of both FluONI and exciplex. The pure white emission with high color stability at different drive voltages are attributed to the sustainable equilibrium between FluONI intrinsic and exciplex emission. Our devices based on a single non-doped EML provide a simple way to realize color pure and stable white OLEDs.

•Effect of thickness modulation on gas sensing properties of OTFTs was studied.•All CuPc-based OTFT sensors exhibited obvious response and recovery cycles.•OTFT gas sensors with different CuPc thicknesses had different selectivities.Copper phthalocyanine (CuPc)-based organic thin film transistors (OTFTs) with various thicknesses of organic semiconductor were fabricated, and the corresponding gas sensing performance was systematically evaluated. In situ measurements of OTFTs under nitrogen dioxide (NO2) exposure showed a remarkable sensitivity enhancement from 7% to 241% by simply decreasing CuPc film thickness from 40 to 10 nm. CuPc films were analyzed by atomic force microscopy and grazing incidence X-ray diffraction. The results showed that thinner CuPc film, which enhances the interplay of CuPc film and NO2 analyte, is beneficial for NO2 diffusion and smaller CuPc grain formation, resulting in considerable sensing performance improvement.Download high-res image (221KB)Download full-size image

An organic solar cell (OSCs) containing double bulk heterojunction (BHJ) layers, namely, double-BHJ OSCs is constructed via stamp transferring of low bandgap BHJ atop of mediate bandgap active layers. Such devices allow a large gain in photocurrent to be obtained due to enhanced photoharvest, without suffering much from the fill factor drop usually seen in thick-layer-based devices. Overall, double-BHJ OSC with optimal ≈50 nm near-infrared PDPP3T:PC71BM layer atop of ≈200 nm PTB7-Th:PC71BM BHJ results in high power conversion efficiencies over 12%.

•High-performance color-tunable OLEDs controlled by bias voltage were fabricated.•Effect of four different transport materials as exciton blocking layers on color-tunable property was systematically studied.•Exciton blocking layer film thickness should be comparable to triplet exciton diffusion length to realize the color-tunable OLEDs.A series of voltage-controlled color-tunable organic light-emitting devices (OLEDs) were fabricated. Four charge transport materials with different characteristics serving as the exciton blocking layers (EBLs) were inserted between yellow and blue emissive layers, respectively, and the color-tunable properties of OLEDs were studied in detail. Carrier transport and electroluminescence (EL) mechanisms of the color-tunable devices were investigated by analyzing the EL spectra and device efficiencies. The results showed that a color-tunable range of blue, white, and yellow light had been realized by tuning the film thicknesses of EBLs. The device with 16 nm N,N′-dicarbazolyl-3,5-benzene hole transport material as the EBL could shift the color coordinates from (0.21, 0.32) to (0.38, 0.41), which exhibited the broadest color tuning range. Meanwhile, the device based on 18 nm 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene electron transport material had the opposite color-tuning sequence and slightly higher tuning voltages, comparing with other three devices. The difference of color-tunable properties in OLEDs based on various EBLs was attributed to the variation of carrier mobility and energy level of EBL materials. Moreover, to effectively harvest the excitons for color-tunable light emission, the EBL thickness should be comparable to the triplet exciton diffusion length of EBLs.

•Morphological, crystalline, electrical properties in active layer are investigated.•The light intensity distribution and exciton generation rate are analyzed.•High PCE of 9.16% is achieved in a 250 nm thick PSC.The effects of co-solvent on the morphology, crystallization and light intensity distribution of thick bulk heterojunction (BHJ) polymer solar cells (PSCs) based on polymer of [(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3000-di(2-octyldodecyl)-2,20,50,200,500,2000-quaterthiophen-5,5000-diyl)](PffBT4T-2OD):[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) are studied. By adjusting different co-solvent systems in thick BHJ layer, it is found that the polymer crystallization, fullerene absorption and PffBT4T-2OD:PC71BM BHJ morphology are optimized by using a co-solvent of chlorobenzene (CB):dichlorobenzene (DCB):1,8-diiodooctanein (DIO). The optimized BHJ thickness of 250 nm is analyzed by using transfer matrix theory, resulting in enhanced FF and PCE of 66.7% and 9.16%, respectively. This phenomenon is due to the active layer can absorb 90% of the incident light with a thickness of 250 nm, which contributes to the light intensity distribution and exciton generation rate.

•High-performance BC OTFTs based on interfacial modifying layer were fabricated.•Mechanism of OTFT performance improvement is due to lower contact resistance.•OTFTs with various interfacial modifying layers were utilized to detect NO2 gas.•Mechanism of sensitive improvement is ascribed to smaller pentacene grain size.Organic thin-film transistors (OTFTs) based on bottom-gate bottom-contact configuration were fabricated by inserting two kinds of modifying layers at the interface of source/drain electrode and organic semiconductor, while nitrogen dioxide (NO2) sensing capability was also evaluated based on the obtained OTFTs. Compared to OTFT without interfacial layer, the field-effect mobility (μ) was enhanced from 0.018 cm2/Vs to 0.15 cm2/Vs by incorporating with MoOx interfacial layer. Moreover, when exposed to 30 ppm NO2, the saturation current and μ of OTFT with MoOx interfacial layer increase 22.7% and 26.7%, respectively, while in original OTFT, the values are only 3.0% and 3.7%, respectively. The mechanism of performance improvement of OTFT sensor was systematically studied by focusing on the interface of source/drain electrode and organic semiconductor. The reduced contact resistance leads to higher μ, meanwhile, pentacene morphology modulation on MoOx contributes to better diffusion of NO2 molecules. As a result, higher μ and more diffused gas molecules enhance the gas sensing property of the transistor.Download high-res image (218KB)Download full-size image

•Thermal evaporated PTCDI-C8 is used to modify ZnO in inverted polymer solar cells.•Treatment with active layer solvent can form a smooth and dense PTCDI-C8 film.•PTCDI-C8 can promote the contact of ZnO/active layer to enhance device performance.Interfacial modification layer facilitates the preferable contact property between electron transport layer (ETL) and active layer, which is capable of enhancing the performance of inverted polymer solar cells (PSCs). In this study, we use an n-type organic small molecule of N,N-Dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) as the interfacial modification layer on the top of ZnO ETL by thermal evaporation. We demonstrate that the PTCDI-C8 layer can reduce the work function of ZnO, so that the efficiency of electron transfer is improved, and the recombination of charge carrier on the contact interface is suppressed. As a consequence, the power conversion efficiency (PCE) increases from 8.26% to 9.29%, based on the poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b]dithiophene-co-3-fluorothieno[3,4-b]-thiophene-2-carboxylate] (PTB7-Th): [6,6]-phenyl-C71-butyricacid methyl ester (PC71BM) bulk heterojunction (BHJ) active layer. The enhanced device performance is attributed to the improvement of short-circuit current (JSC), open-circuit voltage (VOC) and fill factor (FF). This work provides an effective approach to reach high performance inverted PSCs.Download high-res image (88KB)Download full-size image

The development of thick organic photovoltaics (OPV) could increase absorption in the active layer and ease manufacturing constraints in large-scale solar panel production. However, the efficiencies of most low-bandgap OPVs decrease substantially when the active layers exceed ∼100 nm in thickness (because of low crystallinity and a short exciton diffusion length). Herein, we report the use of solvent additive diphenyl ether (DPE) that facilitates the fabrication of thick (180 nm) active layers and triples the power conversion efficiency (PCE) of conventional thienothiophene-co-benzodithiophene polymer (PTB7)-based OPVs from 1.75 to 6.19%. These results demonstrate a PCE 20% higher than those of conventional (PTB7)-based OPV devices using 1,8-diiodooctane. Morphology studies reveal that DPE promotes the formation of nanofibrillar networks and ordered packing of PTB7 in the active layer that facilitate charge transport over longer distances. We further demonstrate that DPE improves the fill factor and photocurrent collection by enhancing the overall optical absorption, reducing the series resistance, and suppressing bimolecular recombination.

•High PCE of 8.03% with a simultaneous enhancement of JSC and FF is achieved.•Optical, electrical and morphological properties of ternary system are investigated.•Incorporation of Rubrene increases charge transfer and energy transfer efficiency.•Rubrene increases photoconductive carriers and suppressed bimolecular recombination.In this work, through adding a fluorescent small molecule, Rubrene, in the active layer, a highly efficient ternary polymer solar cell (PSC) is obtained. By modifying the ratio of Rubrene in poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b0]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7):[6,6]-phenyl C71-butyric acidmethyl ester (PC71BM) blends, the short circuit current and fill factor are simultaneously enhanced, resulting in a 21.7% improvement in power conversion efficiency from 6.60% to 8.03%. Improved photovoltaic performance of ternary PSCs is mainly due to enhanced charge transportation by appropriate energy cascade alignment and strong Förster resonance energy transfer from Rubrene to PTB7. Moreover, the appropriate location of Rubrene in the ternary blends optimizes the blend morphology. Furthermore, the impedance spectroscopy results indicate that the incorporation of Rubrene can increase the number of photoconductive carriers and suppress the bimolecular recombination.

•A PHOLED with high efficiency and low efficiency roll-off was realized.•Emission process was studied by single-carrier devices and PL transient decay curves.•High EQE is due to the efficient utilization of triplets via RISC and FRET.•High J1/2 is ascribed to the bipolar TADF host and FRET.Phosphorescent organic light-emitting devices (PHOLEDs) with high efficiency and low efficiency roll-off were fabricated. The emissive layer was composed of a thermally activated delayed fluorescence (TADF) material 4,5-bis(carbazol-9-yl)-1,2-dicyanobenzene (2CzPN) as host and an orange iridium complex bis(4-tert-butyl-2-phenylbenzothiozolato-N,C2′)iridium(III)(acetylacetonate) [(tbt)2Ir(acac)] as dopant. At a low dopant concentration of 1 wt%, a PHOLED without light extraction optimization achieved a maximum power efficiency of 42.1 lm/W, a luminance efficiency of 77.9 cd/A and an external quantum efficiency (EQE) of 26.8%, respectively. Meanwhile, the EQE maintained 26.6% at 1000 cd/m2 and 25.8% at 5000 cd/m2, respectively. Moreover, a critical current density of 300 mA/cm2 was realized, indicating significantly improved efficiency roll-off. The efficient utilization of triplet excitons on 2CzPN for phosphorescence via reverse inter-system crossing of 2CzPN followed by Fӧrster resonance energy transfer from 2CzPN to (tbt)2Ir(acac) is responsible for the superior performance.

•High PCE of 8.09% with a simultaneous enhancement of JSC and FF was achieved.•Optical, electrical and morphological properties of ternary system were investigated.•Incorporation of TIPS-pentacene increased the mobility and lifetime of carrier.•Low thickness dependent TIPS-pentacene based ternary polymer solar cells was found.•Ternary polymer solar cells based on other systems also showed improved performance.Highly efficient ternary polymer solar cells (T-PSCs) realized by the improved mobility and lifetime of carrier in PTB7: PC71BM: TIPS-pentacene blends were fabricated. By adjusting the weight ratios of third component TIPS-pentacene in the binary PTB7: PC71BM blends, we found that the short circuit current and fill factor (FF) were simultaneously enhanced, resulting in a maximum power conversion efficiency (PCE) of 8.09% with 21.3% improvement. The improved photovoltaic performance of T-PSC was mainly due to the enhanced light absorption, energy level cascading, optimized blend morphology, and increased hole mobility. It was also found that the incorporation of TIPS-pentacene increased the average hole lifetime, ensuring efficient hole transport and collection with suppressed bimolecular recombination, contributing to the photocurrent. Additionally, the low thickness dependent row-off of FF indicates TIPS-pentacene is a promising third component for the realization of thick film T-PSC. The improved PCEs were obtained as well for other ternary donor: acceptor: TIPS-pentacene systems, demonstrating that the incorporation of TIPS-pentacene is a wide practicable methodology for the development of highly efficient T-PSCs.

High efficiency tandem organic light-emitting diodes (OLEDs) were realized using an organic bulk heterojunction (BHJ) as charge generation layer (CGL) consisted of boron subphthalocyanine chloride (SubPc) and fullerene (C60). The results showed that the SubPc:C60 based CGL is a promising connecting unit for the fabrication of high efficiency tandem OLEDs with 2.64 folds enhancement in a current efficiency of 63.6 cd/A, compare to the corresponding single-unit OLEDs. The efficiency enhancement of tandem OLEDs is attributed to better charge carrier balance derived from the optimized charge transport pathways and reduced interface energy barrier. It showed that the charge generation ability and charge transport characteristics of CGL were strongly dependent on SubPc:C60 mixing ratio and corresponding film morphology, which was verified by the charge extracting analysis. Additionally, the highest occupied molecular orbital energy level of SubPc is compatible for most of hole transporting layer to minimize the hole injection barrier and suppress the hole accumulation and charge recombination in tandem OLEDs.

•OFETs with a heterojunction structure consisting of p-type CuPc and n-type PTCDI-C8 organic semiconducting materials were fabricated.•The heterojunction OFET NO2 gas sensor exhibited 10 folds enhancement of sensitivity.•The heterojunction OFET NO2 sensor performance was strongly dependent on the active layer thickness.Organic field-effect transistors (OFETs) with a heterojunction structure, consisting of the p-type and n-type organic semiconducting materials of copper phthalocyanine (CuPc) and the dioctyl perylene tetracarboxylic diimide (PTCDI-C8), respectively, were fabricated. The heterojunction OFETs were used as the nitrogen dioxide (NO2) gas sensors, and the sensing properties were characterized with the variation of PTCDI-C8 layer thicknesses. The results showed that the OFET sensors with the optimized film thickness of 0.5 nm PTCDI-C8 and 7 nm CuPc, had one order of magnitude enhancement of sensitivity, compared to the device with single CuPc active layer. The sensitivity improvement was attributed to the intensification of the charge transfer in the heterojunction structure while introducing the oxidizing gas of NO2.

•OLEDs with exciplex interface consisting of an ultrathin rubrene were fabricated.•Energy transfer and triplet up-conversion were responsible for exciplex device.•Direct charge trapping was dominated in non-exciplex-type device.Fluorescent organic light-emitting diodes (OLEDs) with exciplex and non-exciplex forming interfaces, where an ultrathin 5,6,11,12,-tetraphenylnaphtacene (rubrene) emissive layer was sandwiched, were fabricated. The performances of 4,4′,4″-tris(N-carbazolyl)-triphenylamine (TCTA)/1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi) exciplex-type device and 4,4′-di(9H-carbazol-9-yl)biphenyl (CBP)/TPBi no-exciplex-type device were optimized in terms of the thickness of rubrene ultrathin layer. The results showed that the exciplex-type device yielded high device efficiency, attributing to the utilization of triplet excitons as the triplets of the exciplex can be up-converted into singlets via reverse intersystem crossing. The light emission process in exciplex-type device was dominated by energy transfer, while the non-exciplex type device was dominated by charge trapping emission mechanism, which was verified by the single carrier devices.

Ammonia (NH3) gas sensors based on organic field-effect transistor (OFET) using poly(3-hexylthiophene) (P3HT) blended with polystyrene (PS) as a semiconductor layer were fabricated. An optimized composition of 1.6 wt% P3HT in PS matrix exhibited the best performance to various concentrations of NH3, which is comparable to that of pure P3HT (8 wt%). The results showed the percentage responses of saturation current were 52% and 16% under 50 ppm and 5 ppm NH3, respectively. Also, it showed that there was a remarkable shift in the field-effect mobility after exposed to NH3 gas. By analyzing the morphologies of blend films and the electrical characteristics of OFET sensors, it was found that the film of P3HT blended with PS has more interface to interact with NH3, resulting in more efficient detection to NH3 even in the range of low concentration. Besides, the PS matrix would prevent the gas from diffusing into the semiconductor/dielectric interface directly, which was beneficial to the selectivity of P3HT/PS blend OFET sensor. Moreover, the sensing property was related to the solvents and molecular weight of PS. In addition, the environmental stability of OFET sensors was measured after storing the sensors under ambient atmosphere for 40 days, and the device with the blend semiconducting layer exhibited the superior stability.

•Disordered P3HT/PS blend OFETs processed with several solvents were investigated.•Disordered P3HT/PS blend has three fold higher mobility than that of pure P3HT.•Drain current on/off ratio increases almost twice than that of pure P3HT.Poly(3-hexylthiophene) (P3HT):polystyrene (PS) blends prepared from different solvents were used as the semiconducting layers in organic field-effect transistors (OFETs). The relationship between the molecular arrangement, aggregation and charge transport in P3HT:PS blends with the boil-points and solubility of different solvents were systematically analyzed. Topographic investigation by atomic force microscopy carried out on blends with various solvents revealed a lateral phase separation of the two components, which was strongly influenced by the choice of solvent. Although the blend film was highly disordered, the OFETs performed as well as that with the pristine P3HT films. Moreover, 1,2-dichlorobenzene with the high boiling temperature was found to be more desirable for achieving distinct lateral aggregation of P3HT in the blend film, which led to the superior performance of the OFET. X-ray diffraction analyses and optical absorption measurements revealed that PS matrix made the arrangement of P3HT molecules more disordered, but introduced a more efficient intermolecular coupling of P3HT molecules. This could be ascribed to that, the PS matrix made the aggregating rates of the P3HT molecules slower, inducing a uniform distribution of P3HT molecules in the blend film. This was beneficial for the efficient charge transport in the blend film, which provided a pathway between the aggregations and acted as a tie-molecule in the blend film. Consequently, the field-effect mobility of the optimized OFET (1.6 wt% P3HT) increased three times and the current on/off ratio increased two times compared to that of the pure P3HT (8 wt%). This work will fill the gap of current research about semiconductor/insulator blend transistor.

•OLEDs were fabricated using a charge-transfer-featured host.•Energy transfer and triplet up-conversion were responsible for the high EQE.•Direct exciton formation is involved in phosphorescent OLEDs.•The heavy doping property was elucidated by thermal and morphological analyses.Fluorescent and phosphorescent organic light-emitting diodes (OLEDs) were fabricated using a charge-transfer-featured compound, 6-{3,5-bis-[9-(4-t-butylphenyl)-9H-carbazol-3-yl]-phenoxy}-2-(4-t-butylphenyl)-benzo[de]isoquinoline-1,3-dione, as a host, and the electroluminescent (EL) characteristics of these two kinds of OLEDs were systematically studied. According to the photoluminescent quantum yields (ηpl), it was found that the external quantum efficiencies of both fluorescent and phosphorescent OLEDs were exceeding their theoretical limits. Based on the analysis of EL characteristics, the high device performance of fluorescent and phosphorescent OLEDs was attributed to both efficient energy transfer and triplet energy up-conversion, while direct exciton formation was also involved in phosphorescent OLEDs. In addition, the host film possessed high thermal and morphological stabilities due to the attachment of steric bulks on host molecule, resulting in the high doping concentration for both fluorescent and phosphorescent dyes. These results indicated that charge-transfer-featured material could be the promising host for both fluorescent and phosphorescent OLEDs.

•Physical mechanism of airbrush spray coated blend film was investigated systematically.•Surface tension and saturated vapor pressure played a significant role in film formation of airbrush spray coated blend film.•A series of ternary solvent system was proposed to control the morphology of BHJ blend film.•High performance OSC based on PTB7:PC71BM with ∼7.62% PCE fabricated by airbrush spray coating method.In this work, thieno [3,4-b] thiophene/benzodithiophene (PTB7): [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) based organic solar cell (OSC) with a new record of power conversion efficiency (PCE) of ∼7.62% has been realized using airbrush spray (AS) coating method in air ambient which can be well compatible with large-scale fabrication. By investigating the physical mechanism of AS coated blend films, a series of ternary solvent systems (TSS) are used to simultaneous optimize the surface tension and the saturated vapor pressure of solution. Therefore, different TSS further controls the morphology of PTB7:PC71BM blend films precisely and systematically. It is elucidated that the chlorobenzene (CB)/o-Xylene (o-Xy)/1, 8-diiodoctane (DIO) TSS with a ratio of 37:60:3 vol.% could lead to a homogeneous surface morphology with a decreased aggregation domain size of active layer. In addition, the high fill factor, increased PC71BM absorption and internal quantum efficiency indicate the formation of bicontinuous interpenetrating and fully percolated networks with nanostructured phase separation in BHJ blend films. Ultimately, the AS coated OSCs based on the TSS of CB/o-Xy/DIO gains a 34% enhancement in PCE, compared with the conventional CB/DIO solvent based OSCs.

Top contact organic field-effect transistors (OFETs) based on pentacene active layer, which employed the organic buffer layers of subphthalocyanine, triphenyldiamine derivative, and 4,4′,4″-tris[3-methylphenyl(phenyl)amino] triphenylamine (m-MTDATA) as the hole injection layers were fabricated. The results showed that the electrical performance of these OFETs, including the saturation current, the field-effect mobility, the on/off current ratio, and the threshold voltage, were all significantly improved by introducing the organic hole injection buffer layers. By optimizing the film thickness of these organic buffer layers to the appropriate thickness, the charge injection from gold source/drain electrodes to pentacene film could be effectively improved. Also, the interfacial properties and the contact resistance between gold source/drain electrodes and pentacene film was analyzed, and the results indicated that the interface property was significantly improved. Moreover, it was found that OFET with m-MTDATA hole injection layer exhibited the best performance compared to other two kinds of materials, and the intrinsic reason was further revealed.

A charge-transfer-featured naphthalimide derivative with a small exchange energy but a lower lying 3ππ* state than 3CT state is found to contribute to triplet harvesting through a P-type rather than an E-type delayed fluorescence, and could act as a quite promising host to achieve highly efficient OLEDs.

A novel and universal method, based on water-soluble poly(4-styrene sulfonate), was introduced into the preparation of a polymer mask. Using this mask, high-resolution, high-performance, bottom-gate, top-contact OFETs can be achieved. There is no solvent intervention in the process of manufacturing these OFETs and the mask can be recycled.

•Photodimerization of C60 leads to material degradation in organic solar cells.•Donor-acceptor blend films have reduced tendency to crystallize.•Archetype materials of SubPc/C60 used in OPVs are investigated for their photostability.•Photodegradation correlated with previously observed burn-in efficiency losses in SubPc/C60 OPVs.We investigate the photostability of organic photovoltaic (OPV) cell active layers comprised of the archetype donor, boron-subphthalocyanine chloride (SubPc), and fullerene acceptors, aged under either AM1.5G illumination or in the dark, and in either air or inert atmosphere. Under long-term exposure to light, we observe significant photobleaching and crystallization of SubPc. Mixing SubPc with C60 as is commonly done in high efficiency small molecule OPVs, the crystallite formation is inhibited and the bleaching is suppressed due to a significantly reduced exciton lifetime in the blends. Furthermore, the spectral dependence of the degradation suggests that photo-dimerization of C60 is an important factor leading to burn-in loss in efficiency previously reported in SubPc/C60 OPVs. The existence of dimerization is supported by Fourier transform infrared spectroscopy data taken both before and after exposure to light. Increasing the fraction of SubPc in a SubPc:C60 blend leads to a decrease in the rate of film degradation, providing further evidence for C60 dimerization. Due to its reduced tendency for photo-dimerization, C70 is more stable than C60 when used in small molecule OPVs.

•Spectral variation was observed from blue phosphorescent complex.•Varied intensity ratio of shoulder to peak in emission spectra of the complex.•Effects of doping ratio and solvent solution on spectral behavior were explored in solution-processed blue OLEDs.•Spectral change of the complex was studied in white OLEDs.Spectral properties of a blue phosphorescent bis[(4,6-difluorophenyl)-pyridinato-N,C2′] (picolinate) iridium(III) (FIrpic) complex were systematically investigated. The electroluminescent spectra of FIrpic in solution-processed organic light-emitting diodes (OLEDs) were focused on, and the effects of doping ratio and solvent solution on spectral characterization were explored in solution-processed blue OLEDs. The results showed that there was an unusual spectral variation between shoulder and peak intensities in the electroluminescent spectra of FIrpic, and the intensity ratio of the shoulder to the peak (the Huang-Rhys factor) was obviously increased when FIrpic was at high doping ratios and dissolved in polar solvents. The theoretical mechanism for this phenomenon was analyzed, indicating that the spectral variation was due to solvation effect induced by strong intermolecular interaction between the solvent and FIrpic molecules. Moreover, the spectral behavior of FIrpic in solution-processed white OLEDs with complementary colors was studied, providing further evidence for the spectral variation.

•Effects of polar solvents for solvent vapor annealing on the performance of polymer solar cells have been investigated.•A facile route for choosing compatible polar solvent to achieve high efficiency polymer solar cells was provided.•Hole transport mobility of polymer solar cells was studied by space-charge limited current technique.The effects of different polar solvents on the performance of solvent vapor annealing treated polymer solar cell (PSC) with a structure of ITO/ZnO/PTB7: PC71BM/MoO3/Ag was systematically investigated by applying different polar solvents, including methanol, ethanol, dimethylsulfoxide, acetone and isopropanol. By analyzing the variation of PSC performance and the morphology of active layer, we found that both the solubility parameters (Δ) and viscosity of solvent were playing an important role in controlling the morphology of PTB7: PC71BM blend. Especially, the PSC treated by methanol with high Δ and low viscosity exhibited a remarkable enhancement of power conversion efficiency from 6.55% to 8.13%. The performance improvement was mainly due to the formation of the nanoscale crystallization of PTB7: PC71BM blend and the moderated aggregation of PC71BM, resulting in efficient charge separation, balanced charge transport and suppressed charge recombination.

Efficient spray-coated inverted polymer solar cells (PSCs) based on a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transport layer (HTL) are investigated by incorporating an in situ annealing treatment. Compared to conventional annealed devices, the in situ annealed PSCs exhibited a 25.5% and 47.7% enhancement in fill factor and power conversion efficiency (PCE) respectively, as well as about a two-fold improvement in the device lifetime. The performance enhancement was attributed to the improvement of the vertical phase separation of the PEDOT:PSS HTL and the reduction of the residual humidity of the HTL. This approach significantly enhances our understanding of the application of the PEDOT:PSS HTL in inverted PSCs, and illuminates the potential of spray coating for the sustainable commercial fabrication of PSCs with high PCEs.

•Inverted polymer UV-PDs with high detectivity was fabricated.•The influence of active layer thickness and thermal annealing treatment was systematically investigated.•Both photocurrent and dark current were affected by modifying polymer active layer.•Detailed analysis of atomic force microscope measurement, charge carrier mobility were carried out.Organic ultraviolet photodetectors (UV-PDs) consisting of a polymer active layer of poly(N-vinyl carbazole):[6,6]-phenyl-C71-butyric acid methyl ester were fabricated, and the properties of UV-PDs were systematically investigated by optimizing the thickness of active layer and temperature of thermal annealing. The result showed that, under an illumination of 350 nm ultraviolet light with an intensity of 0.6 mW/cm2, the device exhibited a high detectivity of 1.07 × 1012 Jones, which is among the highest detectivity of the reported inverted UV-PDs. Through the UV–Vis absorption spectra and atomic force microscopy measurement, along with charge carrier mobility analysis, the high performance of UV-PDs was attributed to the improved UV absorption, preferred morphology and effective charge transport of polymer active layer.

Two bis(ethylenedioxythiophene)naphthalene monomers 1,4-bis(2-(3,4-ethylenedioxythiophene))-naphthalene (M1) and 2,6-bis(2-(3,4-ethylenedioxythiophene))-naphthalene (M2) were synthesized, and corresponding polymer poly(1,4-bis(2-(3,4-ethylenedioxythiophene))-naphthalene) (P1) and poly(2,6-bis(2-(3,4-ethylenedioxythiophene))-naphthalene) (P2) were electrochemically synthesized and characterized. Characterizations of the resulting polymers were performed by cyclic voltammetry, UV–vis spectroscopy and scanning electron microscopy. The oxidation potential of monomer M2 was lower than that of the M1, and the conjugation lengths of both the M2 and P2 were longer than the corresponding M1 and P1, respectively. Spectroelectrochemical analysis revealed that both the polymer films had good electrochromic properties and exhibited multi-electrochromic behaviors. Besides, the corresponding devices P1/Poly(3,4-ethylenedioxythiophene) (PEDOT) device and P2/PEDOT device showed satisfactory optical contrast (ΔT%), fast response time and excellent cyclic voltammetry stability. The electrochromic properties of two EDOT-naphthalene-EDOT style polymers are dependent on the position of substitution.Graphical abstractThis figure shows electrochromic properties of the polymers were greatly influenced by the different substituted position.Highlights► Two bis(ethylenedioxythiophene)naphthalene monomers are synthesized and their polymers are electrochemically synthesized. ► The polymer films display satisfactory electrochromic properties. ► The electrochromic properties of two polymer films are dependent on the position of substitution.

Polymer solar cell (PSC) with a structure of ITO/PEDOT:PSS/P3HT:PCBM/Bphen/Ag was fabricated using spray coating method, and the influence of in situ annealing treatment on the PSC performance was studied. Comparing the performance of in situ annealed PSC with that of conventional post-annealed cell, the results showed that the in situ annealing treatment at low temperature not only corresponding to 12% enhancement of fill factor, but also resulting in 13% increase of open circuit voltage. The interpenetrating networks of P3HT:PCBM film were characterized by X-ray diffraction, and surface morphologies have been studied by atomic force microscope. The performance enhancement of PSC was attributed to the improved hole mobility of P3HT:PCBM blend and the increased interaction of active layer.Highlights► We introduce the in situ annealing treatment to spray coating PSCs process. ► By optimizing the spray parameters, we successfully obtain a relatively high performance of PSCs. ► We detailed analysis the performance of in situ annealing treated PSCs. ► We give the main reason for the enhancement or limitation of PSCs performance. ► Comparing the time of one fabrication cycle of two annealing treatment.

•OFET based ammonia gas sensors with various polymer dielectrics are fabricated.•PS based OFET exhibits reliable recovery property and detect limitation of 1 ppm.•Preferable surface property of PS is responsible for the high-performance.Ammonia (NH3) gas sensors based on pentacene organic field-effect transistors (OFETs) are fabricated using polymers as the dielectric. Compared with those incorporating poly(vinyl alcohol), poly(4-vinylphenol) or poly(methyl methacrylate) dielectric, a low detect limitation of 1 ppm and enhanced recovery property are obtained for OFETs with polystyrene (PS) as gate dielectric. By analyzing the morphologies of pentacene and electrical characteristics of the OFETs under various concentrations of NH3, the variations of the sensing properties of different dielectrics based OFET-sensors are proved to be mainly caused by the diversities of dielectric/pentacene interfacial properties. Furthermore, low surface trap density and the absence of polar groups in PS dielectric are ascribed to be responsible for the high performance of NH3 sensors.Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slide

The performance of n-type organic field-effect transistors (OFETs) based on C60 active layer was investigated by focusing on the role of 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene (TPBi), bathocuproine (BCP) and bathophenanthroline (Bphen) as buffer layers. It was found that the OFETs with the organic buffer layers exhibited significant improved electrical characteristics, such as saturation current, threshold voltage, field-effect mobility and current on/off ratio. Moreover, by optimizing the film thicknesses of these buffer layers, we also found that the buffer layers with appropriate film thickness can effectively improve charge carrier injection from Ag source/drain electrodes to C60 films. Also, the interface properties and the contact resistance between Ag source/drain electrodes and C60 films have been analyzed.Graphical abstractHighlights► Different organic buffer layers in n-channel OFETs were investigated. ► The film thickness of these buffer layers were optimized. ► High performance of n-type OFETs has been obtained. ► The contact resistance was studied.

Phosphorescent white organic light-emitting devices (WOLEDs) with a structure of ITO/TAPC/δ-EML1/mCP:FIrpic/δ-EML2/Bphen/Mg:Ag were fabricated, wherein two ultrathin and host-free emitting layers (EMLs) were formed by using yellow bis[2-(4-tertbutylphenyl)benzothiazolato-N,C2′] iridium (acetylacetonate) [(tbt)2Ir(acac)] and referred to as delta-EMLs (δ-EML1 and δ-EML2). By adjusting the thicknesses of δ-EMLs, a maximum current efficiency of 27.6 cd/A, an external quantum efficiency (EQE) of 10%, together with low efficiency roll-off at high luminance were achieved. The results showed that δ-EML1 played a dominant role on charge carrier trapping, while δ-EML2 had major impact on yellow light emission, which were highly sensitive to the location of δ-EMLs. Furthermore, by introducing 5-nm Au as anode modifying layer, high device efficiency was maintained along with excellent color stability of warm white emission, displaying color coordinates of (0.38, 0.42) and color temperature of 4348 K at a luminance of 7000 cd/m2. Importantly, explanation and analysis for the influence of both ultrathin δ-EMLs and anode modifying layer on device performance were proposed.Highlights► Phosphorescent WOLEDs with two yellow delta-emitting layers (δ-EMLs). ► The ultrathin δ-EMLs were formed by host-free (tbt)2Ir(acac). ► Effects of the δ-EMLs show a dependence on their location in the devices. ► A layer of 5-nm gold was employed as anode modifying layer. ► High device efficiency together with excellent color stability was achieved.

•Small molecule dye of rubrene was doped into P3HT:PCBM heterojunction solar cells.•Rubrene increased the absorption and charge separation of active layers.•Short current circuit and power conversion efficiency of solar cells were enhanced.•Photocurrent of solar cells was simulated using Onsager–Braun theory.•Rubrene doping improved the charge transfer generation and dissociation.Poly(3-hexylthiphene) (P3HT):[6,6]-phenyl C60-butyric acid methyl ester (PCBM) bulk heterojunction solar cells doped with a small molecule dye of rubrene were fabricated. The effect of different doping concentration on the performance of solar cells was investigated. The results showed that by doping 3.5 wt% rubrene, the short circuit current and the power conversion efficiency (PCE) of the cell were improved by 23.1% and 23.4%, respectively. The increased light absorption and effective charge separation of blend films contributed to the enhancement of PCE in doping devices. Moreover, by simulating the photocurrent of solar cells using Onsager–Braun theory, it was found that doping rubrene was responsible for the enhancement of charge transfer generation and dissociation, thereby improving the performance of P3HT:PCBM solar cells.

Polyisoprene (PIp)/single-walled carbon nanotube (SWNT) composites were prepared by grafting PIp from the surface of SWNTs via in situ anionic polymerization using sec-butyllithium as an initiator. The anionic initiator molecules were covalently attached to the SWNTs to form SWNTs-bearing carbanions, as confirmed by Fourier transform infrared analysis and Raman spectra. Scanning electron microscopy (SEM) and transmission electron microscope (TEM) were used to image the PIp-g-SWNT composites; the results show a relatively uniform polymer phase present on the surface of individual, debundled nanotubes. The carbanions on the SWNT surface help separate the nanotubes in solution and lead to the development of homogeneous PIp rubber composites with well-dispersed nanotubes. Compared with pure PIp, the PIp/SWNT nanocomposites showed a significant improvement in thermal properties.

Highly efficient white organic light-emitting devices (WOLEDs) with a four-layer structure were realized by utilizing phosphorescent blue and yellow emitters. The key concept of device construction is to combine host–guest doping system of the blue emitting layer (EML) and the host-free system of yellow EML. Two kinds of WOLEDs incorporated with distinct host materials, namely N,N'-dicarbazolyl-3,5-benzene (mCP) and p-bis(triphenylsilyly)benzene (UGH2), were fabricated. Without using light out-coupling technology, a maximum current efficiency (ηC) of 58.8 cd/A and a maximum external quantum efficiency (ηEQE) of 18.77% were obtained for the mCP-based WOLED; while a maximum ηC of 65.3 cd/A and a maximum ηEQE of 19.04% were achieved for the UGH2-based WOLED. Meanwhile, both WOLEDs presented higher performance than that of conventionally full-doping WOLEDs. Furthermore, systematic studies of the high-efficiency WOLEDs were progressed.Highlights► Efficient WOLEDs by combining two systems. ► Host–guest doping system for blue emitting layer. ► Host-free system for yellow emitting layer. ► Maximum current efficiency of 65.3 cd/A and external quantum efficiency of 19.04%.

Top contact pentacene field-effect transistors (OFETs) with or without MoO3 source/drain (S/D) electrodes buffer layers were fabricated by utilizing different deposition rates of Au S/D electrodes. The results showed that the characteristics of these OFETs have a strong dependence on the deposition rate of Au S/D electrodes. More importantly, single pentacene layer OFETs with optimized Au deposition process exhibits significantly improved performance, which is almost equal to the OFETs with MoO3 buffer layers. The high performance of OFETs with optimized Au deposition process was attributed to an improved contact of Au and pentacene caused by ordered dipole arrangement at the interface, leading to a nearly non-injection barrier of charge carriers from Au electrodes to pentacene.Highlights► Effect of various Au electrodes deposition rates on OFETs performance was studied. ► High performance OFETs with the optimized Au deposition rate were obtained. ► Contact resistance of the OFETs was investigated.

Planar heterojunction organic solar cells using wide bandgap phosphorescent material bis[2-(4-tertbutylphenyl)benzothiazolato-N,C2'] iridium (acetylacetonate) [(t-bt)2Ir(acac)] as electron donor and fullerene (C60) as electron acceptor were fabricated. A large open circuit voltage of 0.94 V was achieved due to low highest occupied molecular orbital level of (t-bt)2Ir(acac). The effect of different hole transport layers and substrate heating were investigated to improve fill factor. It is shown that the open circuit voltage is strongly influenced by the interface energy barrier, whereas the fill factor is mainly limited by the charge carrier transport properties in active materials. The fill factor was significantly improved by either using hole transport layer with high carrier mobility or increasing the hole mobility of (t-bt)2Ir(acac). A power conversion efficiency of 2.10% under AM 1.5 solar illumination at an intensity of 100 mW/cm2 was achieved by heating the substrate during the deposition of active materials.Highlights► Organic solar cells based on wide bandgap phosphorescent material were fabricated. ► A relatively high open circuit voltage about 0.94 V was achieved. ► The fill factor (FF) is mainly limited by the charge transport properties. ► The FF can be improved by using hole transport layers with high mobility. ► Increasing the mobility of active materials can also enhance the FF.

The open circuit voltage (VOC) of smallmolecule organic solar cells (OSCs) could be improved by doping suitable fluorescent dyes into the donor layers. In this paper, 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) was used as a dopant, and the performance of the OSCs with different DCJTB concentration in copper phthalocyanine (CuPc) was studied. The results showed that the VOC of the OSC with 50% of DCJTB in CuPc increased by 15%, compared with that of the standard CuPc/fullerene (C60) device. The enhancement of the VOC was attributed to the lower highest occupied molecular orbital (HOMO) level in the DCJTB than that in the CuPc. Also, the light absorption intensity is enhanced between 400 and 550 nm, where CuPc and C60 have low absorbance, leading to a broad absorption spectrum.

Organic photovoltaic (OPV) cells using a medium-bandgap phosphorescent material of bis(1,2-dipheny1-1H-benzoimidazole) iridium (acetylacetonate) [(pbi)2Ir(acac)] as an electron-donating layer were fabricated. An S-shaped kink was observed in the current–voltage curves with the increase in (pbi)2Ir(acac) thickness. Two ways of using different hole transport layers to reduce interfacial energy step and doping to improve charge carrier mobility were used to investigate the origin of the kink. The results showed that this anomalous feature is due to the presence of large interfacial energy step between the anode/donor-interface and the low hole mobility of (pbi)2Ir(acac). An improved power conversion efficiency of 2.23% under AM 1.5 solar illumination at an intensity of 100 mW/cm2 was obtained using N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine to minimize the energy barrier for charge injection.

Organic thin-film transistors (OTFTs) with high crystallization copper phthalocyanine (CuPc) active layers were fabricated by inserting an ultrathin pentacene buffer layer between the dielectric and CuPc layers. Comparing with the OTFTs without a pentacene buffer layer, the charge carrier mobility of the OTFT with a buffer layer presented a much higher value of ~ 0.20 cm2/V s. Meanwhile, by investigating the morphology of the CuPc active layer with an ultrathin pentacene buffer layer through scanning electron microscopy and X-ray diffraction, the high crystallization of the CuPc film with a larger grain size and less grain boundaries can be observed. As a result, the resistance of the conducting channel was decreased, leading to a performance improvement of the OTFTs.Highlights► Pentacene was inserted between dielectric and copper phthalocyanine (CuPc) films. ► High performance devices were obtained. ► Crystallization enhancement of CuPc was observed by scanning electron microscopy.

Highly efficient phosphorescent white organic light-emitting devices (PHWOLEDs) with a simple structure of ITO/TAPC (40 nm)/mCP:FIrpic (20 nm, x wt.%)/bis[2-(4-tertbutylphenyl)benzothiazolato-N,C2′] iridium (acetylacetonate) (tbt)2Ir(acac) (y nm)/Bphen (30 nm)/Mg:Ag (200 nm) have been developed, by inserting a thin layer of non-doped yellow phosphorescent (tbt)2Ir(acac) between doped blue emitting layer (EML) and electron transporting layer. By changing the doping concentration of the blue EML and the thickness of the non-doped yellow EML, a PHWOLED comprised of higher blue doping concentration and thinner yellow EML achieves a high current efficiency of 31.7 cd/A and Commission Internationale de l'Eclairage coordinates of (0.33, 0.41) at a luminance of 3000 cd/m2 could be observed.Highlights► We introduce a simplified architecture for phosphorescent white organic light-emitting device. ► The key concept of device fabrication is combination of doped blue emissive layer (EML) with non-doped ultra-thin yellow EML. ► Doping concentration of the blue EML and thickness of the yellow EML are sequentially adjusted. ► High device performance is achieved due to improved charge carrier balance as well as two parallel emission mechanisms in the EMLs.

Two iridium complexes bearing benzothiazole cyclometallate ligands, bis[2-(3′,5′-di-tert-butylbiphenyl-4-yl)benzothiazolato-N,C2′]iridium(III)(acetylacetonate) [(tbpbt)2Ir(acac)] and bis[2-(9,9-dimethyl-9H-fluoren-2-yl)benzothiazolato-N,C2′]iridium(III)(acetylacetonate) [(fbt)2Ir(acac)], have been evaluated as orange and red electrophosphorescent materials. Both X-ray crystallographic analysis and photophysical results indicate that they possess alleviated self-quenching characteristics due to the existence of steric bulky ligands. As a result, phosphorescent organic light-emitting diodes (PhOLEDs) based on them show high performance even in heavily-doped level (≥ 15 wt.%). The (tbpbt)2Ir(acac)-based PhOLED gives efficient orange emission with peak current efficiency of 26.9 cd/A (1280 cd/m2) at doping ratio of 15 wt.%, while the 15 wt.% (fbt)2Ir(acac)-doped device emits efficient red light with Commission Internationale de l'Eclairage coordinates of (0.63, 0.36), and peak current and external quantum efficiency of 28.5 cd/A (1210 cd/m2) and 15.6%, respectively. Moreover, all these heavily-doped PhOLEDs exhibit low efficiency roll-off at relatively high current density.Highlights► Two iridium complexes with bulky ligands are developed as orange/red emitter. ► Organic light-emitting diodes using these phosphors show low efficiency roll-off. ► High performance devices could be achieved under high doping ratio of ≥ 15 wt.%. ► The high device efficiencies arise from the reduced self-quenching of the phosphors.

In this study, syndiotactic-rich poly(methyl methacrylate) (PMMA) is obtained by using a soluble nickle acetylacetonate [Ni(acac)2] and modified methylaluminoxane (MMAO-3A) catalyst system under modest polymerization conditions. The main purpose of this work is concerned with the study of previous conflicting stereospecificity data. Types of MAO, temperature of polymerization, MAO/Ni(acac)2 (Al/Ni) mole ratio, and various solvents have been investigated in the MMA polymerization. Particularly, high syndiotactic PMMA [(rr) > 91 %] has been obtained when MMAO-3A is used as cocatalyst with Al/Ni ratio of ca. 50 or polymerization temperature ca. 0 °C. As expected, the prepared syndiotacticity-rich PMMA has a higher glass transition temperature (Tg) within 120 ~ 127 °C. The details of the polymerization mechanism, especially in relation to the stereoregularity problems are under investigation.

Phosphorescent white organic light-emitting devices (PhWOLEDs) were fabricated by doping with the blue and yellow phosphors of iridium (III) bis (4,6-(di-fluorophenyl)-pyridinato-N, C2′) picolinate and [2-(4-tertbutylphenyl) benzothiazolato-N, C2′] iridium (acetylacetonate), respectively. The influence of interlayer on the performance of PhWOLEDs was studied with the assistance of three different interlayers consisting of 4,7-diphenyl-1,10-phenanthroline (BPhen), BPhen mixing N,N′-dicarbazolyl-3,5-benzene (mCP), and mCP inserted between the blue and yellow emitting layers. The results showed that the characteristics of PhWOLEDs were significantly dependent on the selection of interlayers, which tailored charge carrier transport and exciton distribution. Compared with the device without interlayer, the insertion of BPhen interlayer was detrimental to device performance, while the introduction of BPhen: mCP and mCP interlayers was beneficial to the performance. The PhWOLED with mCP interlayer had the highest performance, exhibiting stable white emission with slight Commission Internationale del’Eclairage coordinates variation at a wide luminance range, with a maximum luminance of 46,714 cd/m2, current efficiency of 35.4 cd/A, and power efficiency of 14.5 lm/W. Moreover, the efficiency roll-off was much lower, which was only one third of the device without interlayer.Highlights► Different interlayers used in phosphorescent white organic light-emitting devices. ► Interlayer adjusts the distribution of charge carriers and excitons. ► The insert of BPhen interlayer is detrimental to the performance. ► The introduction of BPhen:mCP and mCP interlayers is beneficial to the performance. ► Device with mCP interlayer performances best for balanced charge carriers.

Electroluminescent (EL) spectra was employed to probe the triplet exciton diffusion length (LT) of a commonly used host material of N,N′-dicarbazolyl-3,5-benzene (mCP) in phosphorescent organic light-emitting devices (OLEDs). By varying the film thickness of bis [2-(4-tertbutylphenyl) benzothiazolato-N,C2], iridium (acetylacetonate) [(t-bt)2Ir(acac)] phosphor doped layer within 30 nm thick mCP layer, a series of devices were fabricated to investigate the EL characteristics. The results showed that with the increasing doped layer thickness (d), both (t-bt)2Ir(acac) emission peaks at 562 nm and mCP emission centered at 403 nm were observed. Moreover, the relationship between mCP EL intensity and d was detected. The LT was induced by an abrupt decrease in variation of mCP EL intensity when d is increased from 10 to 15 nm, and the reason to cause this phenomenon was investigated. The LT of mCP approximately to 15 nm was perfectly consistent to the result of 16±1 nm, which was calculated by the traditional steady-state diffusion model.Highlights► EL spectra were employed to probe triplet exciton diffusion length (LT). ► The relationship between mCP EL intensity and doped layer thickness was studied. ► The LT (∼15 nm) was induced by an abrupt decrease in variation of mCP EL intensity.

Study on the diffusion of triplet excitons from light emitting layer (EML) in organic light-emitting devices doped with yellow phosphorescent material to the adjacent hole transporting layer (HTL) is carried out, in which a non-doped red phosphorescent ultra-thin layer as an exciton-sensing layer is set in various position of HTL. A diffusion length of triplet exciton between 3 nm and 5 nm is inferred from the observed and disappeared red light emission in electroluminescent spectra. For further device optimization, either 5 nm 4,4′,4″-tri(N-carbazolyl)triphenylamine (TCTA) or 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) as a exciton blocking layer is introduced to block the exciton diffusion. The maximum current efficiency and power efficiency of the optimized device are reached to 24.6 cd/A and 16.3 lm/W, respectively. The high performance is ascribed to confined diffusion of triplet excitons from light-emitting zone and higher radiation efficiency of the triplet exciton.Highlights► Diffusion of triplet excitons from light emitting layer is studied. ► A non-doped red phosphorescent ultra-thin layer is used as exciton-sensing layer. ► A diffusion length of triplet exciton between 3 nm and 5 nm is inferred. ► Further device optimization is obtained by introducing 5 nm exciton blocking layer.

Well-aligned ZnO nanorod arrays (ZNAs) with various growth time were fabricated on indium tin oxide (ITO) coated glass substrate using hydrothermal method. The average diameter of the ZnO nanorods ranged from 35 to 100 nm with elongating growth time from 0.5 to 3 h. The ZNAs had wurtzite-structured (hexagonal) ZnO and preferred growth along (0001) direction. When growth time was less than 2 h, the ZNAs showed very high optical transmission (>80%) in visible light region. The formation of Ohmic contact between ZNAs and the substrates was also observed. Furthermore, solar cells consisted of ZNAs/polymer hybrid were fabricated, and a highest power conversion efficiency (PCE) of 1.11% from these devices was achieved. Moreover, The PCE of this device almost remained constant for long time when exposed to ambient atmosphere.

Organic light-emitting devices (OLEDs) were constructed with a structure of indium tin oxide (ITO)/N,N’-bis(naphthalen-1-yl)-N,N’-bis(phenyl)-benzidine (NPB) (50 − x nm)/bis[2-(4-tertbutylphenyl)benzothiazolato-N,C2’] iridium (acetylacetonate) [(t-bt)2Ir(acac)] (dnm)/NPB (x nm)/2,2’,2"(1,3,5-benzenetriyl)tris-(1-phenyl-1H-benzimidazole) (TPBI) (30 nm)/Mg:Ag (200 nm). A thin blue emission material of NPB was used as a separating layer, and the (t-bt)2Ir(acac) yellow phosphorescent dye was acted as an ultrathin light-emitting layer. TPBI acted as both hole-blocking and electron-transporting layer. By changing the location (x) and the thickness (d) of the phosphor dye, the variation of device performance were investigated. The results showed that all the devices had a turn-on voltage of 2.8 V. In the case of d = 0.2 nm and x = 5 nm, the OLED had a maximum luminance of 18367 cd/m2 and a maximum power efficiency of 5.3 lm/W. The high performance is attributed to both direct charge carrier trapping of iridium phosphor dye and the thin NPB separation layer, which effectively confines the recombination zone of charge carriers.

We present the current-voltage characteristics of organic solar cells based on single and double heterojunction of copper phthalocyanine (CuPc) and C60 by introducing a constant JP instead of photo-current density Jph to represent the density of polaron-pairs generated from excitons at D/A interface. A diode Dext models polaron-pair dissociation, and a diode Drec stands for loss due to polaron-pair recombination. The photovoltaic response under AM 1.5 solar illumination at an intensity of 100 mW/cm2 is parameterized and modeled using the improved equivalent circuit model developed for inorganic pn-junction solar cells. The instinct mechanisms including dissociation, recombination of polaron-pairs and charge carrier collection process are explained by introducing Jph/JP as the dissociation rate of polaron-pairs and |J|/Jph as charge carrier application efficiency ηCA. Especially, we reveal the optimization mechanism for the fill factor FF and series resistance RS of organic solar cells.

High performance polymer light-emitting diodes (PLEDs) based on a phosphor of noble metal complex bis(1,2-dipheny1-1H-benzoimidazole) iridium (acetylacetonate) [(pbi)2Ir(acac)] doped in poly(N-vinylcarbazole) (PVK) host with various concentration were demonstrated. The photoluminescence (PL) and electroluminescence (EL) spectra of the PLEDs exhibited an emission intensity decrease of PVK and a gradually enhanced feature of (pbi)2Ir(acac) with increased doping concentration. The device with a 5 wt% (pbi)2Ir(acac) doped PVK system showed a high power efficiency of 3.84 lm/W and a luminance of 26,006 cd/m2. The results indicated that both energy transfer and charge trapping have a significant influence on the performance of PLEDs. The devices have a broadened EL spectrum of full-width at half-maximum (FWHM) more than 100 nm, which can be realized for WOLEDs.

High-performance undoped white organic light-emitting diode (OLED) has been fabricated using an ultrathin yellow-emitting layer of 5,6,11,12-tetraphenylnaphthacene (rubrene) inserted at two sides of interface between two N,N′-bis-(1-naphthyl)-N,N′- biphenyl-1,1′-biphenyl-4,4′- diamine (NPB) layers as a hole transporting and blue emissive layer, respectively. The results showed that a maximum luminance of the device reached to as high as 21,500 cd/m2 at 15 V. The power efficiencies of 2.5 and 1.6 lm/W at a luminance of 1000 and 10000 cd/m2, respectively, were obtained. The peaks of electroluminescent (EL) spectra locate at 429 and 560 nm corresponding to the Commissions Internationale De L’Eclairage (CIE) coordinates of (0.32, 0.33), which is independent of bias voltage. The performance enhancement of the device may result from direct charge carrier trapping in rubrene. Energy transfer mechanism was also found in the EL process.

Double-layer and triple-layer organic light-emitting diodes (OLEDs) were fabricated using a novel star-shaped hexafluorenylbenzene organic material, 1,2,3,4,5,6-hexakis(9,9-diethyl-9H-fluoren-2-yl)benzene (HKEthFLYPh) as an energy transfer layer, N, N′-bis-(1-naphthyl)-N, N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) as a hole-transport layer (HTL) and blue emissive layer (EML), and tris(8-hydroxyquinoline)aluminum (Alq3) as an electron-transport layer (ETL) and green light-emitting layer. Bright white light was obtained with a triple-layer device structure of indium-tin-oxide (ITO)/NPB (40 nm)/HKEthFLYPh (10 nm)/Alq3 (50 nm)/Mg:Ag (200 nm). A maximum luminance of 8523 cd·m−2 at 15 V and a power efficiency of 1.0 lm·W−1 at 5.5 V were achieved. The Commissions Internationale de L′Eclairage (CIE) coordinates of the device were (0.29, 0.34) at 9 V, which located in white light region. With increasing film thickness of HKEthFLYPh, light emission intensity from NPB increased compared to that of Alq3.

The UV-Vis absorption and photoluminescence (PL) spectra of 2,3-bis(9,9-dihexyl-9H-fluoren-2-yl) quinoxaline (Py), 2,3-bis(9,9-dihexyl-9H-fluoren-2-yl)-6,7-difluoroquinoxaline (F2Py) and 2,3-bis(9,9-dihexyl-9H-fluoren-2-yl)-5,6,7,8-tetrafluoroquinoxaline (F4Py), which are fluorene molecular derivatives with conjugated structure, were investigated. For further investigation of the influences of fluorine auxochrome in fluorene molecular electroluminescent material on optoelectronic property, the electroluminescence (EL) characteristics of materials were studied by double-layer organic light-emitting diodes (OLEDs) using N,N′-Di-[(1-naphthalenyl)-N,N′-diphenyl]-(1,1′-biphenyl)-4,4′-diamine (NPB) as a hole transporting layer (HTL) with the conventional vacuum deposition method. The results showed that the absorption and PL spectra of materials in film state red shifted with fluorine substituents increased in molecule configuration. The performance of OLEDs is as follows: at a bias voltage of 5 V, Py emitted a blue-green light at 508 nm with the Commission Internationale d’Eclairage (CIE) coordinates of (0.23, 0.43) and full width at half maximum (FWHM) of 100 nm. The device had a turn-on voltage (defined as the drive voltage at the luminance of 1 cd/m2) of 4.8 V, a luminance of 129 cd/m2 with a current density of 59 mA/cm2 at 10 V, and a maximum luminous efficiency of 0.18 lm/W at 5.4 V. F2Py and F4Py emitted a green light peaking at 544 nm and a yellow light at 570 nm at 5 V, with the CIE coordinates of (0.38, 0.56) and (0.44, 0.49), and FWHM of 103 and 117 nm, respectively. The F2Py and F4Py devices had a turn-on voltage of 4 and 2 V, a luminance of 557 and 3300 cd/m2 with a current density of 100 and 880 mA/cm2 at 10 V, and a maximum luminous efficiency of 0.22 lm/W at 7.6 V and 0.53 lm/W at 2 V, respectively.

Both single-layer and double-layer organic light-emitting devices based on tris-(8-hydroxylquinoline)-aluminum (Alq3) as emitter are fabricated by thermal vacuum deposition. The electroluminescent characteristics of these devices at various temperatures are measured, and the temperature characteristics of device performance are studied. The effect of temperature on device current conduction regime is analyzed in detail. The results show that the current-voltage (I-V) characteristics of devices are in good agreement with the theoretical prediction of trapped charge limited current (TCLC). In addition, both the charge carrier mobility and charge carrier concentration in the organic layer increase with the rise of temperature, which results in the monotonous increase of Alq3 device current. The current conduction mechanisms of two devices at different temperatures are identical, but the exponent m in current-voltage equation changes randomly with temperature. The device luminance increases slightly and the efficiency decreases monotonously due to the aging of Alq3 luminescent properties caused by high temperature. A tiny blue shift can be observed in the electroluminescent (EL) spectra as the temperature increases, and the reduction of device monochromaticity is caused by the intrinsic characteristics of organic semiconductor energy levels.

Conventional fluorescent dyes, i.e., 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB), 5,12-dihydro-5,12-dimethylquino [2,3-b]acridine-7,14-dione (DMQA) and 5,6,11,12-tetraphenylnaphthacene (Rubrene), were used to investigate the performance of organic light-emitting diodes (OLEDs) based on indium tin oxide (ITO)/N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB)/tris-(8-hydroxyquinolate)-aluminum (Alq3)/MgAg. The dyes were either inserted into devices as an ultra-thin film at the NPB/Alq3 interface by sequential evaporation, or doped into the Alq3 emission layer by co-evaporation with the doping ratio about 2%. Electroluminescence (EL) spectra of devices indicated that concentration quenching effect (CQE) of the dye-dopant was slightly bigger in the former than in the latter, while the degrees of CQE for three dopants are in the order of DMQA > DCJTB > Rubrene suggested by the difference in EL spectra and performances of devices. In addition, EL process of device with an ultra-thin layer of dopant is dominated by direct carrier trapping (DCT) process due to almost no holes recombine with electrons in Alq3-host layer.

The self-assembly of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) nanoparticles at an air/water interface was achieved by means of the electrostatic force between an octadecylamine (ODA) monolayer and PEDOT-PSS nanoparticles. A surface pressure (π)–area (A) isotherm and X-ray photoelectron spectroscopy of the composite film were used to confirm the electrostatic force between the SO3− group of PSS and the NH4+ group of aliphatic amines. Monolayer and multilayer composite films of ODA/PEDOT-PSS and ODA-stearic acid (SA)/PEDOT-PSS were fabricated. These solid Langmuir–Blodgett films were investigated by the UV–Vis spectrum, atomic force microscopy, and X-ray diffraction method. It is observed that ODA-SA/PEDOT-PSS films had a higher film-forming capability than ODA/PEDOT-PSS films and an ordered multilayer structure was developed. The conductive properties of ODA-SA/PEDOT-PSS LB films were investigated in detail. Factors influencing the film conductivity such as the layer number and surface pressure were discussed and the conductive mechanism was also studied.

We used various treatment methods such as ethanol treatment, sodium hydroxide solution treatment, sulfur acid treatment, and oxygen plasma treatment to modify the surface of indium–tin oxide (ITO) substrates for organic light-emitting devices (OLEDs). The surface properties of the treated ITO substrates were characterized by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), contact angle, surface energy measurements, four-point probe, X-ray Diffraction (XRD) and ultraviolet-visible spectrophotometer. The results showed that the ITO surface properties were closely related to the treatment methods, and the oxygen plasma is more efficient than other treatments as it leads to smoother surface, better surface stoichiometry, higher work function and surface energy, lower sheet resistance, and higher transmission of the ITO substrates. Moreover, small molecular organic light-emitting devices (SMOLEDs) using different treated ITO substrates as anodes were fabricated and investigated. It was found that surface treatment of ITO substrates has influence upon the injection current, the turn-on voltages of light emission, luminance, efficiency and lifetime. Oxygen plasma treatment on the ITO substrate yields the highest performance of SMOLEDs due to the improvement of interface formation and electrical contact of the ITO substrate with the small molecular material blend in the SMOLEDs.

•The photovoltaic effect on the performance of OLEDs was studied.•The device performance with different planar heterojunctions was investigated.•The mechanism relies on the overlap of electroluminescence and absorption spectrum.Organic light-emitting diodes (OLEDs) with planar heterojunction (PHJ) architecture consisting of photovoltaic organic materials of fullerene carbon 60 (C60) and copper (II) phthalocyanine (CuPc) inserted between emitting unit and cathode were constructed, and the photovoltaic effect on OLEDs performance was studied. The electroluminescent (EL) characteristics and mechanism of device performance variation without and with different PHJs (herein including C60/CuPc, CuPc/C60 and CuPc) were systematically investigated in red, green and blue OLEDs. Of the three combinations, OLEDs with C60/CuPc showed the highest efficiency. It is revealed that the photovoltaic C60/CuPc PHJ can absorb part of photons, which are radiated from emission zone, then form excitons, and dissociated into free charges. Consequently, the high device efficiency of OLEDs performance improvement was acquired. This research demonstrates that PHJ consisting of two n- and p-type photovoltaic organic materials could be a promising methodology for high performance OLEDs.

•Hybrid WOLEDs with excellent color stability and high efficiency were obtained.•WOLEDs were based on heavily doped TADF and ultrathin non-doped phosphorescence EMLs.•Good color stability was ascribed to the orange EML dominated by Förster energy transfer.•High efficiency was attributed to alleviated triplet energy loss in blue EMLs.Blue/orange complementary fluorescence/phosphorescence hybrid white organic light-emitting devices with excellent color stability and high efficiency have been fabricated, which are based on an easily fabricated multiple emissive layer (EML) configuration with an ultrathin non-doped orange phosphorescence EML selectively inserted between heavily doped blue thermally activated delayed fluorescence (TADF) EMLs. Through systematic investigation and improvement on luminance-dependent color shift and efficiency deterioration, a slight Commission Internationale de 1′Eclairage coordinates shift of (0.008, 0.003) at a practical luminance range from 1000 to 10000 cd/m2, a maximum power efficiency of 45.8 lm/W, a maximum external quantum efficiency (EQE) of 15.7% and an EQE above 12% at 1000 cd/m2 have been achieved. The heavily doped blue TADF emitters which act as the main charge transport channels and recombination sites in the host with high-lying lowest triplet excited state, take advantage of the bipolar transport ability to broaden the major charge recombination region, which alleviates triplet energy loss. The selectively inserted ultrathin non-doped orange EML makes its emission mechanism dominated by Förster energy transfer, which is effective to keep color stable under different drive voltages.Download high-res image (196KB)Download full-size image

A charge-transfer-featured naphthalimide derivative with a small exchange energy but a lower lying 3ππ* state than 3CT state is found to contribute to triplet harvesting through a P-type rather than an E-type delayed fluorescence, and could act as a quite promising host to achieve highly efficient OLEDs.

A novel and universal method, based on water-soluble poly(4-styrene sulfonate), was introduced into the preparation of a polymer mask. Using this mask, high-resolution, high-performance, bottom-gate, top-contact OFETs can be achieved. There is no solvent intervention in the process of manufacturing these OFETs and the mask can be recycled.