The Residual PbI ₂ Paradox in Perovskite Solar Cells: Harnessing Excess Phase for Synergistic Performance‐Stability Improvement

The presence of residual/excess lead iodide (PbI₂) in lead halide perovskites has been pivotal for advancing the efficiency of perovskite solar cells (PSCs), yet its chemically active nature poses severe stability challenges. Achieving optimal device performance without compromising long-term stability remains a critical hurdle in perovskite photovoltaic technologies. This review systematically analyzes the mechanistic role residual/excess PbI₂ in PSCs, elucidating its impact on both device efficiency and stability. A series of recent strategies for regulating residual/excess PbI₂ have been further summarized, including regulating the distribution of the residual PbI₂, controlling the crystallization kinetics of PbI₂, and eliminating the excess PbI₂. By providing a comprehensive roadmap for balancing efficiency and stability, this work aims to guide the rational design of high-performance and long-term stable PSCs.