CuCl2-modified SnO2 electron transport layer for high efficiency perovskite solar cells

SnO2film is one of the most widely used electron transport layers (ETL) in perovskite solar cells (PSCs). However, the inherent surface defect states in SnO2film and mismatch of the energy level alignment with perovskite limit the photovoltaic performance of PSCs. It is of great interesting to modify SnO2ETL with additive, aiming to decrease the surface defect states and obtain well aligned energy level with perovskite. In this paper, anhydrous copper chloride (CuCl2) was employed to modify the SnO2ETL. It is found that the adding of a small amount of CuCl2into the SnO2ETL can improve the proportion of Sn4+in SnO2, passivate oxygen vacancies at the surface of SnO2nanocrystals, 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 SnO2ETLs modified with CuCl2(SnO2-CuCl2) is improved in comparison with that of the PSCs on pristine SnO2ETLs. The optimal PSC based on SnO2-CuCl2ETL exhibits a much higher PCE of 20.31% as compared to the control device (18.15%). The unencapsulated PSCs with CuCl2modification maintain 89.3% of their initial PCE after exposing for 16 d under ambient conditions with a relative humidity of 35%. Cu(NO3)2was also employed to modify the SnO2ETL and achieved a similar effect as that of CuCl2, indicating that the cation Cu2+plays the main role in SnO2ETL modification.