Efficient α-CsPbI3 Photovoltaics with Surface Terminated Organic Cations

Quasi-2D or 2D capping is an effective strategy to stabilize organic-inorganic metal halide perovskite materials, often at a detriment to electronic transport. Due to an efficient cation exchange between organic constituents, the location and thickness of reduced-dimensional hybrid perovskite layers is difficult to control. We find that the all-inorganic CsPbI3 perovskite cannot go through either solid state or sequential cation exchange to form a 2D perovskite capping layer. Instead, a defect-passivating organic cation terminated surface is formed that improves phase stability and moisture resistance. The corresponding α-CsPbI3 perovskite solar cells exhibit high reproducibility with a champion stabilized efficiency of 13.5%. This work shows that the high cation exchange resistance of CsPbI3 perovskites can be exploited to promote the development of highly efficient and stable perovskite photovoltaics.