Efficiency and stability enhancement of polymer solar cells using multi-stacks of C60/LiF as cathode buffer layer

Abstract

We report on the improved performance and stability of bulk heterojunction (BHJ) polymer solar cells using five stacks of C60/LiF as cathode buffer layer, which was prepared by alternating deposition of C60 and LiF layers. The five-stacked C60/LiF film, even with a large thickness ratio of LiF to C60, exhibits good electrical conductivity. The devices with five stacks of C60/LiF buffer layer show a peak power conversion efficiency (PCE) which is 19% higher than that of the conventional devices with only LiF interlayer, primarily due to the improvement in fill factor (FF) of the device. Moreover, the high efficiency of five-stacked C60/LiF based devices is insensitive to changes in the thickness ratio between C60 and LiF layers. Since much thicker LiF can be used in five-stacked C60/LiF film, these devices also show superior air stability as compared to the devices with only LiF interlayer. Therefore, five-stacked C60/LiF is a promising alternative to pristine LiF as a cathode buffer layer in polymer solar cells.