Formamidinium–caesium mixed-cation perovskites have shown better thermal stability than their methylammonium-containing counterparts but they suffer from photoinstability induced by iodide migration and phase segregation. Here we improve their photostability by adding slightly excessive AX (at a molar percentage of 0.25% to Pb²⁺ ions), where A is formamidinium or caesium and X is iodine. The excessive AX does not improve the initial solar cell efficiency. It compensates iodide vacancies and suppresses ion migration and defects generation during long-term illumination by around tenfold compared with AX-deficient devices. Consequently, generation of hole traps and phase segregation is impeded, with the former limiting solar cell efficiency after degradation. The perovskite mini-modules reached a certified stabilized efficiency of 18.6% with an aperture area of ~30 cm², corresponding to an active area efficiency of 20.2%. The mini-module maintains 93.6% of the initial efficiency after continuous operation under 1 sun illumination for >1,000 h at 50 ± 5 °C in air.

甲脒-铯混合阳离子钙钛矿比含甲基铵的钙钛矿表现出更好的热稳定性，但它们会因碘化物迁移和相分离而导致光不稳定性。在这里，我们通过添加稍微过量的 AX（摩尔百分比为 0.25% 到 Pb ²⁺离子），其中A是甲脒或铯，X是碘。过量的AX不会提高初始太阳能电池效率。与缺乏 AX 的器件相比，它可以补偿碘化物空位并在长期照明期间抑制离子迁移和缺陷产生约 10 倍。因此，空穴陷阱和相偏析的产生受到阻碍，前者限制了退化后的太阳能电池效率。钙钛矿微型模块达到了 18.6% 的经认证的稳定效率，孔径面积约为 30 cm ²，对应的有效面积效率为 20.2%。在 50 ± 5 °C 的空气中，在 1 个太阳光照下连续运行 > 1,000 小时后，微型模块可保持初始效率的 93.6%。