Rethinking the Role of Excess/Residual Lead Iodide in Perovskite Solar Cells

Abstract It is widely believed that excess/residual lead iodide (PbI 2 ) can affect the performance of perovskite solar cells . Moderate PbI 2 can enhance efficiency by passivating defects, while extremely active PbI 2 leads to non‐negligible hysteresis effects and reduces device stability. Although several efforts are made to investigate the role of excess PbI 2 , its impact is still underestimated. Recent advances further demonstrate the extraordinary potential of modifying excess PbI 2 ; however, a comprehensive study is required to obtain a deeper understanding. Herein, the important breakthroughs regarding excess PbI 2 are reviewed and the mechanism of excess PbI 2 in terms of efficiency and stability is rethought. In addition, the origins, verification, and regulation of residual PbI 2 are summarized.