Low‐Temperature Stable CsPbI₂Br Perovskite for Solar Photovoltaics and Blue Photodetection

As an inorganic halide perovskite (IHP), CsPbI 2 Br has generated enormous publicity due to its suitable optical bandgap (≈1.92 eV) and thermal stability. Unfortunately, the terrible phase stability of CsPbI 2 Br film will cause a phase change in a wet environment and decelerate light response, seriously hindering the progression of IHP photovoltaics. Herein, a synergistic postmodification strategy with CsBr and MABr to achieve high‐quality CsPbI 2 Br film at a low‐temperature (≈150 °C) and positive perovskite/carbon interface is presented. Adding a small amount of MABr can promote the crystallization of perovskite. The evaporated CsBr accumulates on the grain boundaries and surface of CsPbI 2 Br and forms Br‐rich perovskite, which provides the protection of CsPbI 2 Br and segregation of water vapor. The carbon‐based perovskite solar cell (C‐PeSC) with the modified CsPbI 2 Br harvests a high power conversion efficiency (PCE) of 11.04%. Notably, the unpackaged cell maintains 81% of its original PCE after being stored for 21 days in an air atmosphere with 25–35% humidity. Flexible devices are further manufactured, whose PCE drops to 90% of the initial value during 150 bending cycles. The flexible device also exhibits excellent blue photodetection performances. The maximum responsivity and detection reach 0.68 A W −1 and 8.91 × 10 12 Jones, respectively. These findings provide broader avenues for flexible IHP in multifunctional devices.