Highly efficient regular polymer solar cells based on Li-TFSI doping ZnO as electron-transporting interlayers

Abstract Zinc oxide is an attractive material applied for electron-transporting interlayers of polymer solar cells. Some factors limited the efficiency and performance of the ZnO-based PSCs, such as the poor conductivity and the traps existing on ZnO film. Here, we introduce a novel approach to optimize the property of ZnO electron-transporting interlayers for the further improvement of device performance by doping bis (trifluoromethane)-sulfonimide lithium salt (Li-TFSI) in ZnO film. It is found that this way not only increased electrical conductivity and charge extraction ability of the electron-transporting interlayers but also reduced charge recombination occurred at interface that was very important for fill factor improvement. Therefore, an optimized power conversion efficiency (PCE) of 9.94% was achieved, which was observed with 13.2% enhancement (9.94% vs 8.78%) compared to that of pure ZnO-based ones. This indicates that doping Li-TFSI in ZnO film is a promising strategy to optimize the ZnO film and enhance the performance of regular polymer solar cells.