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.

准2D或2D封盖是稳定有机-无机金属卤化物钙钛矿材料的有效策略，通常不利于电子传输。由于有机成分之间的有效阳离子交换，降维杂化钙钛矿层的位置和厚度很难控制。我们发现，全无机CsPbI ₃钙钛矿不能通过固态或顺序阳离子交换形成2D钙钛矿覆盖层。而是形成了一种缺陷钝化的有机阳离子封端表面，该表面改善了相稳定性和耐湿性。相应的α-CsPbI ₃钙钛矿太阳能电池显示出高再现性，冠军稳定效率达13.5％。这项工作表明，可以利用CsPbI ₃钙钛矿的高阳离子交换电阻来促进高效，稳定的钙钛矿光伏电池的开发。