Over the last 20 years, much attention has been paid to renewable energy technology. Photovoltaic is a promising alternative to conventional fossil fuels. Dye-sensitized solar cells (DSCs) attract notable interest, not only due to their high efficiency and environmentally friendly nature, but also their easy fabrication and relatively low manufacture costs. Despite the high efficiencies, iodine/triiodine electrolytes have some disadvantages, such as the corrosion of the metallic electrodes and the sealing materials. It also absorbs visible light around 430 nm. Therefore, it is important to exploit the iodine-free redox couple in DSCs. An organic disulfide material of 2,5-dimercapto-1,3,4-thiadiazole (DMcT) is proved here to reduce and oxidize independently via homopolymerization and depolymerization. DMcT has been applied as cathode active material for lithium rechargeable batteries. Meanwhile, the self-redox property could be used as redox mediator in lieu of iodine/triiodine electrolytes. DMcT can be oxidized by self-polymerizing into PDMcT, which can be reduced by depolymerizing back to DMcT. In contrast to the conventional redox couples consisted of two different materials, DMcT can independently act as the redox mediator, which is the main difference between DMcT and the redox couples reported previously. Dye-sensitized solar cells consist of mesoporous TiO2, N719 dye, and this novel electrolyte achieved power conversion efficiency of 1.6% under 100 mW.cm(-2) simulated sunlight (AM 1.5G) and a higher efficiency of 2.6% at weak illumination (13 mW.cm(-2)), implying its promising application prospect. Although the conversion efficiency is relatively low to the iodine/triiodine-based DSCs, this novel single self-redox mediator provides a new promising way to the iodine-free dye-sensitized solar cells.

Silane derivatives with wide energy gap (approximate to 3.5 eV) containing different electron-withdrawing groups of quinoline and naphthyridine are synthesized and used as the electron transporting materials. The different electron transporting and hole/exciton blocking properties of the silane derivatives are investigated via multilayered structure of organic electrophosphorescent devices by using fac-tris(2-phenylpyridine) iridium (Ir(ppy)(3)) as the phosphorescent emitter. 15.4% of maximum external quantum efficiency (EQE) corresponding to 56.2 cd A(-1) of maximum current efficiency is obtained with a maximum power efficiency of 58.9 lm W-1 by employing di-(4-(1,8-naphthyridin-2-yl) phenyl) diphenylsilane (DNPS) as the electron transporting material, combining with 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline as the hole blocking layer, which is higher than the performance of conventional Alq(3) device. When changing naphthyridine of DNPS to the electron-withdrawing group of quinoline (di-(4-(isoquinolin-4-yl)phenyl) diphenylsilane), only 11.4% of maximum EQE with 41.4 cd A(-1) of maximum current efficiency and 32.5 lm W-1 of a maximum power efficiency is obtained. These indicate that the electron transporting ability increases while the electron-withdrawing group changes from quinoline to naphthyridine, which is also consistent with the calculated reorganization energy.

In this study, mesoscopic optical structured 2,9-dimethyl-4,7-diphenyl-1,10-phenyl-1,10-phenanthrolin (bathocuproine, BCP) film was formed to enhance the out-coupling efficiency of a top blue organic light-emitting device (OLED). Based on the refractive index matching layer of BCP on the electrode, the light can be extracted through waveguide mode. Owing to the low glass transition temperature (T-g) of BCP, which easily self-aggregates in a specific environment (controlled temperature and humidity), a mesoscopic optical structure was obtained in 3 h after film formation. Through the nano-aggregated structure, the surface plasmon polariton (SPP) mode can match the free optic field. The efficiency of the device was enhanced: the max brightness increased from 4500 to 9840 cd.m(-2) and the external quantum efficiency (EQE) increased from 0.42% to 1.14%. This leads to a 2.7-fold enhancement of top emission devices. Moreover, the EL spectra of the devices are also optimized by a blue-shift of 12 nm.

In this work, we have provided a new possible explanation for the micromechanism of electroplex. The time-resolved electroluminescent spectra of light-emitting diodes based on the blend of TAPC and TpPyPB were measured. They show that when a high bias voltage is applied on the devices, the electroplex emission gradually increases over time. After the devices worked at a high bias voltage, a strong electroplex emission can be maintained at low bias voltage, but the peaks related to the electroplex are still insignificant in photoluminescence. These results may suggest that the electroplex is a charge-transfer complex with changed conformation caused by polaron-induced molecular aggregation under electric field in essence, though further investigation is needed. Using materials with morphology stability under an electric field, electroplex was greatly reduced, which may enlarge the consideration in designing exciplex-based organic light-emitting diodes (ExOLEDs). (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

[6,6]-Phenyl-C61-butyric acid-4'-hydroxyl-azobenzene ester (PCBAb) was synthesized and used as the acceptor in the fabrication of reversible UV-VIS response bi-state polymer solar cells (PSCs) based on the photoinduced cis-trans isomerization of PCBAb. The device can be switched between ``active'' and ``sleep'' by the irradiation of UV and visible light, respectively. The active device has a PCE of 2.0%. With UV irradiation, the device goes to ``sleep'' with a lowered PCE (0.4%), and simultaneously decreased J(sc), V-oc and FF, while after visible light treatment, the device is made ``active'' again. The mechanism of the bi-state process involves the different electron mobilities of the isomers. (C) 2015 Elsevier B.V. All rights reserved.

A nonadditive hole-transporting material (HTM) of a triphenylamine derivative of N,N'-di(3-methylphenyl)-N,N'-diphenyl-4,4'-diaminobiphenyl (TPD) is used for the organic-inorganic hybrid perovskite solar cells. The power conversion efficiency (PCE) can be significantly enhanced by inserting a thin layer of 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (HAT-CN) without adding an ion additive because the hole-transporting properties improve. The short-circuit current density (J(sc)) increases from 8.5 to 13.1 mA/cm(2), the open-circuit voltage (V-oc) increases from 0.84 to 0.92 V, and the fill-factor (FF) increases from 0.45 to 0.59, which corresponds to the increase in PCE from 3.2% to 7.1%. Moreover, the PCE decreases by only 10% after approximately 1000 h without encapsulation, which suggests an alternative method to improve the stability of perovskite solar cells.