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 the past two years, the power conversion efficiency (PCE) of organic-inorganic hybrid perovskite solar cells has significantly increased up to 20.1%. These state-of-the-art new devices surpass other third-generation solar cells to become the most promising rival to the silicon-based solar cells. Since the morphology of the perovskite film is one of the most crucial factors to affect the performance of the device, many approaches have been developed for its improvement. This review provides a systematical summary of the methods for morphology control. Introductions and discussions on the mechanisms and relevant hotspots are also given. Understanding the growth process of perovskite crystallites has great benefits for further efficiency improvement and enlightens us to exploit new technologies for large-scale, low-cost and high-performance perovskite solar cells.

Recently, inverted planar heterojunction (PHJ) perovskite solar cells have been developed rapidly by numerous preparations and relative optimizations. Sequential solution deposition is easy to manipulate but it is difficult to control the thickness and morphology of perovskite films. In this article, we report an improved sequential deposition, named twice dipping-vapor solution deposition (TD-VSD) technology, to accurately achieve superior perovskite films. It is demonstrated that the morphology of perovskite films depended on the substrate temperatures as well as the dipping times. The resulting solar cells showed the power conversion efficiency as high as 11.77% based on the ideal thickness and morphology. This work provides a simple but effective fabrication to well control the perovskite films and enhance the power conversion efficiency for inverted PHJ solar cells.

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.