Inactive Secondary Phase Stabilizes Perovskite for Efficient Solar Cells

In halide perovskite solar cells, the formation of a secondary phase of excess lead iodide has little effect on power conversion efficiencies (PCEs), but can be detrimental to device stability and lead to large hysteresis effects in voltage sweeps. We converted lead iodide into inactive secondary phase, which effectively stabilizes the perovskite. We obtained a certified PCE of 25.6% for FAPbI₃ perovskite solar cells based on this strategy. Devices retained 96% of their original PCE values after 1000 hours shelf storage and 80% after 500 hours of thermal stability testing at 85 Celsius .