It is widely believed that excess/residual lead iodide (PbI2) can affect the performance of perovskite solar cells . Moderate PbI2 can enhance efficiency by passivating defects, while extremely active PbI2 leads to non‐negligible hysteresis effects and reduces device stability. Although several efforts are made to investigate the role of excess PbI2, its impact is still underestimated. Recent advances further demonstrate the extraordinary potential of modifying excess PbI2; however, a comprehensive study is required to obtain a deeper understanding. Herein, the important breakthroughs regarding excess PbI2 are reviewed and the mechanism of excess PbI2 in terms of efficiency and stability is rethought. In addition, the origins, verification, and regulation of residual PbI2 are summarized.

In perovskite solar cells, the formation of residual/excess lead iodide (PbI2) in the perovskite film is detrimental to device stability. However, the understanding of the effect of residual/excess PbI2 and...