The most important obstacle to widespread use of perovskite solar cells is their poor stability under operational stressors. Here, we systematically monitor the evolution of the photovoltaic performance of perovskite solar cells based on formamidinium-cesium lead iodide (FA_0.9Cs_0.1PbI₃) for 600 h, under a series of controlled operational stressors. Although these devices exhibit reasonable thermal stability, their stability under illumination or stabilized power output (SPO) is far from commercial demands. Synchrotron-based nanoprobe X-ray fluorescence and X-ray-beam-induced current measurements reveal that current-blocking Cs-rich phases segregate during stress tests. The decrease in performance is in line with the increasing density of the Cs-rich clusters in area upon illumination. Theoretical calculations indicate that light-generated carriers provide the thermodynamic driving force for that phase segregation. Our findings correlate device performance to microscopic behavior and atomistic mechanisms and shed light on inhibiting the cation-dependent phase segregation during device operation.

钙钛矿太阳能电池广泛使用的最重要障碍是其在工作压力下的稳定性差。在这里，我们系统地监测基于甲ami铯铯碘化铅（FA _0.9 Cs _0.1 PbI ₃的钙钛矿型太阳能电池的光伏性能的演变）600小时，在一系列受控的操作压力下。尽管这些设备表现出合理的热稳定性，但它们在照明或稳定的功率输出（SPO）下的稳定性远非商业需求。基于同步加速器的纳米探针X射线荧光和X射线束诱导的电流测量结果表明，在应力测试过程中，富电流的Cs富集相分离。性能的降低与照明后区域中富含Cs的簇的密度增加相一致。理论计算表明，光生载流子为该相分离提供了热力学驱动力。我们的发现将设备性能与微观行为和原子机理相关联，阐明了在设备运行过程中抑制依赖于阳离子的相分离。