A solution-processed bathocuproine cathode interfacial layer for high-performance bromine–iodine perovskite solar cells

Perovskite film generally has rough surface morphology due to the voids between the grain domains. Smoothed interface contact between the perovskite layer and the top electrode is critical for planar perovskite solar cells. We reported high efficiency bromine-iodine based perovskite solar cells with a flattening cathode interface by incorporating a solution-processed bathocuproine (sBCP) interfacial layer at the cathode side. Compared with vacuum evaporated bathocuproine (eBCP), sBCP demonstrated an excellent surface modification effect at the cathode side with very smaller charge transfer resistance. Accordingly, a high fill factor exceeding 85% and a power conversion efficiency exceeding 13% in CH3NH3PbI3-xBrx based perovskite solar cells were achieved. The largely improved fill factor was attributed to the smooth film morphology and full surface coverage of perovskite films modified by the solution-processed BCP layer.