Efficient planar heterojunction perovskite solar cells with enhanced FTO/SnO2 interface electronic coupling

Ultrathin and compact SnOx amorphous layers derived from SnCl4 were introduced at the interface of electron transport layer (ETL)/perovskite or FTO/ETL to enhance the electron coupling between layers, passivate the trapping defects and optimize the energy level alignment. As results of the increased interface electron collection and reduced interface recombination, the planer perovskite solar cell (PSC) with SnO2 nanocrystal (NC) ETL pre-treated by SnCl4 (Cl-SnO2) shows the power conversion efficiency (PCE) enhancement from 16.3% to 18.6%, and the device hysteresis has also been significantly restrained. In comparison, the planer PSCs with traditional SnCl4 (SnO2-Cl) post-treated SnO2 NC ETL makes the PCE increased from 16.3% to 17.3%. These results indicate that both two kinds of treated ways could improve the performance of the PSCs but compared with the post-treatment process, the devices based on Cl-SnO2 pre-treated ETL present superior performance, which is attributed to the closer contact and enhanced electron coupling between FTO and SnO2 NC ETL with Cl-SnO2 in between.