Chen Weijie

The all-inorganic perovskite-based solar cells have attracted much attention. Unfortunately, the all-inorganic perovskite CsPbI₃ with suitable band gap faces a critical challenge of low phase stability and sensitivity to moisture. Interestingly, the Cs⁺ cation in the CsPbI₃ crystal lattice is highly stable and would not cation exchange with organic cations to form a 2D perovskite layer, while the organic cation in organic-inorganic hybrid perovskite can easily cation exchange with other organic cations. We then demonstrate a simple surface organic cation termination instead of a 2D perovskite capping layer to stabilize and passivate the CsPbI₃. This novel strategy of organic cation surface termination on all-inorganic perovskite could be a promising strategy for developing high-efficiency and stable perovskite photovoltaics.

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.