Stable high-performance perovskite solar cells based on inorganic electron transporting bi-layers

As one of the significant electron transporting materials (ETMs) in efficient planar heterojunction perovskite solar cells (PSCs), SnO2 can collect/transfer photo-generated carriers produced in perovskite active absorbers and suppress the carrier recombination at interfaces. In this study, we demonstrate that a mild solution-processed SnO2 compact layer can be an eminent ETM for planar heterojunction PSCs. Here, the device based on chemical-bath-deposited SnO2 electron transporting layer (ETL) exhibits a power conversion efficiency (PCE) of 16.10% and with obvious hysteresis effect (hysteresis index = 19.5%), owing to the accumulation and recombination of charge carriers at the SnO2/perovskite interface. In order to improve the carrier dissociation and transport process, an ultrathin TiO2 film was deposited on the top of the SnO2 ETL passivating nonradiative recombination center. The corresponding device based on the TiO2@SnO2 electron transporting bi-layer (ETBL) exhibited a high PCE (17.45%) and a negligible hysteresis effect (hysteresis index = 1.5%). These findings indicate that this facile solution-processed TiO2@SnO2 ETBL paves a scalable and inexpensive way for fabricating hysteresis-less and high-performance PSCs.