Surface p-type band bending and energy level alignment minimizes voltage loss in perovskite solar cells

Abstract

Due to the significant energy level mismatch and contact energy loss between the perovskite absorber layer and p-type hole-transporting layer (HTL), there exists a large hole transport barrier between the perovskite absorber layer and HTL, which hinders hole transport and leads to lower open circuit voltage (VOC) in perovskite devices. Therefore, the surface contact process between the perovskite film and the hole-transporting layer becomes particularly important. Here, we doped cesium silver bismuth bromide (Cs2AgBiBr6) quantum dots (QDs) into ethyl acetate (EA) as an anti-solvent to achieve the formation of a bulk heterojunction structure with quantum dot solution on the surface of the MAPbI3 perovskite film. The perovskite film exhibits appropriate band edge bending and forms a p-type semiconductor. This facilitates the directed transport of photo-induced charge carriers to the hole-transporting layer, reducing carrier recombination losses and enhancing the collection efficiency of holes by the HTL. Through characterization experiments, we have found that this method significantly improves the VOC and photovoltaic conversion efficiency (PCE) of perovskite solar cells. The perovskite solar cells fabricated using this method show a better PCE with a VOC of 1.06 V.