A series of polymers containing benzo[1,2‐b:4,5‐b′]dithiophene and N‐alkylthieno[3,4‐c]pyrrole‐4,6‐dione are designed. By incorporating different alkylthienyl side chains, the fill factor (FF) and open circuit voltage (Voc) of the copolymers are further improved. The experimental results and theoretical calculations show that the size and topology of the side chains can influence the polymer solubility, energy levels, and intermolecular packing by altering the molecular coplanarity. As a result of improved morphology and fine‐tuned energy levels, an increased FF and a high Voc of 1.00 V are achieved, as well as a power conversion efficiency of 6.17%, which is the highest efficiency ever reported for polymer solar cells with a Voc over 1 V.

By application of thermal annealing and UV ozone simultaneously, a solution‐processed NiOx film can achieve a work function of approximately –5.1 eV at a temperature below 150 °C, which allows the processing of NiOx that is compatible with fabrication of polymer solar cells (PSCs) on plastic substrates. The low processing temperature, which is greatly reduced from 250–400 °C to 150 °C, is attributed to the high concentration of NiOOH species on the film surface. This concentration will result in a large surface dipole and lead to increased work function. The pretreated NiOx is demonstrated to be an efficient buffer layer in PSCs based on polymers with different highest occupied molecular orbital energy levels. Compared with conventional poly(3,4‐ethylenedioxy‐thiophene):poly(styrenesulfonate)‐buffered PSCs, the NiOx‐buffered PSCs achieve similar or improved device performance as well as enhanced device stability.

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In this work, we have reported for the first time a facile route for developing solution-processed Al2O3 film at a greatly reduced processing temperature and studied its applications in producing inverted polymer solar cells (PSCs). These PSCs using Al2O3 thin film as the electron-extraction layer demonstrated improved diode characteristics and achieved a 20% higher power conversion efficiency than devices using the conventional ZnO buffer layer. Furthermore, the low temperature processing of the Al2O3 film makes it compatible with fabrication of flexible organic electronic devices based on plastic substrates.

A series of donor-acceptor (D-A) polymers based on furan-bridged benzodithiophene and different acceptor blocks were designed and synthesized. By incorporating various acceptors with differing electron-withdrawing abilities into the same polymer backbone, we were seeking to reveal the correlation between molecular structures and the corresponding film morphology as well as photovoltaic performance. The experimental results and theoretical calculations indicate that the selection of acceptor units has significant impacts on the polymer energy levels and backbone coplanarity, leading to differing intermolecular packing. By using atomic force microscopy and transmission electron microscopy, we also observed that the size and topology of the alkyl-chains on acceptors can tune the polymer solubility and result in different film morphology. As a result of optimized morphology, we demonstrated power conversion efficiencies over 5% for the new polymer based devices, which are among the highest efficiencies of reported furan bridged D-A polymers.