Efficient post-treatment of CsPbBr3 film with enhanced photovoltaic performance

All-bromide inorganic perovskite CsPbBr 3 has attracted enormous attention due to its excellent stability against thermal and high humidity environmental conditions. The wide bandgap of CsPbBr 3 (2.3 eV) makes it a promising material for tandem and semitransparent solar cells. However, cesium based inorganic perovskite solar cells (PSCs) usually suffer from low device performance because of their imperfect film quality and mismatched energy levels with respect to charge transport materials. Herein, we describe a post-treatment strategy for CsPbBr 3 films using formamidinium bromide (FABr). With this protocol, FA + can partially substitute Cs + in the bulk phase of CsPbBr 3 , improving energy level alignment and enhancing charge extraction. Meanwhile, grain boundaries could be effectively passivated by a second phase (FA y Cs 4−y PbBr 6 ) generated in the ion exchange reaction . As a result, FABr-treated PSC exhibits a champion power conversion efficiency (PCE) of 8.25%, much higher than the pristine device with PCE of 6.74%. This work provides a feasible method to improve device performance of CsPbBr 3 PSCs while maintaining their outstanding stability.