CuCl 2 -modified SnO 2 electron transport layer for high efficiency perovskite solar cells.

SnO 2 film is one of the most widely used electron transport layers (ETL) in perovskite solar cells (PSCs). However, the inherent surface defect states in SnO 2 film and mismatch of the energy level alignment with perovskite limit the photovoltaic performance of PSCs. It is of great interesting to modify SnO 2 ETL with additive, aiming to decrease the surface defect states and obtain well aligned energy level with perovskite. In this paper, anhydrous copper chloride (CuCl 2 ) was employed to modify the SnO 2 ETL. It is found that the adding of a small amount of CuCl 2 into the SnO 2 ETL can improve the proportion of Sn 4+ in SnO 2 , passivate oxygen vacancies at the surface of SnO 2 nanocrystals, improve the hydrophobicity and conductivity of ETL, and obtain a good energy level alignment with perovskite. As a result, both the photoelectric conversion efficiency (PCE) and stability of the PSCs based on SnO 2 ETLs modified with CuCl 2 (SnO 2 -CuCl 2 ) is improved in comparison with that of the PSCs on pristine SnO 2 ETLs. The optimal PSC based on SnO 2 -CuCl 2 ETL exhibits a much higher PCE of 20.31% as compared to the control device (18.15%). The unencapsulated PSCs with CuCl 2 modification maintain 89.3% of their initial PCE after exposing for 16 d under ambient conditions with a relative humidity of 35%. Cu(NO 3 ) 2 was also employed to modify the SnO 2 ETL and achieved a similar effect as that of CuCl 2 , indicating that the cation Cu 2+ plays the main role in SnO 2 ETL modification.