Balancing crystallization rate in a mixed Sn–Pb perovskite film for efficient and stable perovskite solar cells of more than 20% efficiency

A surface treatment of PEDOT:PSS layer with [PNA]BF 4 is employed to realize vertically homogeneous distribution of Sn/Pb-containing perovskite films through balancing its crystallization rate and achieving chemical encapsulation of the acidic PEDOT:PSS substrate.