Dissociation of organic molecules is one critical factor leading to degradation of perovskite solar cells. The much-improved thermal stability of formamidinium (FA) can significantly reduce molecular dissociation; however, FA-based perovskite suffers from high defect density, which affects efficiency and long-term stability. In this work, based on a precise ion-exchange reaction at the grain surface, we fabricate a Cs_0.15FA_0.85PbI₃/Cs_xFA_1-xPbI₃ heterostructure with a Cs-rich Cs_xFA_1-xPbI₃ quasi-shell structure. The Cs-rich inorganic structure on the perovskite surface increases defect formation energy and reduces defect density, leading to a power conversion efficiency of 20.7%. The encapsulated device maintains 95% of its initial efficiency after 1,000 h of continuous operation, corresponding to a calculated lifetime approaching 2 years. The device can operate at 60°C for 250 h and at 85°C for over 3,000 min, which is one of the best operational stabilities for Cs_xFA_1-xPbI₃-based devices.

有机分子的解离是导致钙钛矿太阳能电池降解的一个关键因素。大大提高的甲）（FA）的热稳定性可以显着减少分子解离。然而，基于FA的钙钛矿的缺陷密度高，这会影响效率和长期稳定性。在这项工作中，基于晶粒表面的精确离子交换反应，我们制备了Cs _0.15 FA _0.85 PbI ₃ / Cs _x FA _1-x PbI ₃异质结构和富Cs的Cs _x FA _1-x PbI ₃准壳结构。钙钛矿表面上富含Cs的无机结构增加了缺陷形成能并降低了缺陷密度，从而导致功率转换效率为20.7％。连续运行1,000小时后，封装的设备可保持其95％的初始效率，相当于2年的计算寿命。该器件可以在60°C下运行250小时，在85°C下运行超过3,000分钟，这是基于Cs _x FA _1-x PbI ₃的器件的最佳运行稳定性之一。