Stable Lead Acetate-Mediated CsPbI₂Br Inorganic Perovskite Solar Cells Achieving 1.323 V Open-Circuit Voltage

All-inorganic cesium lead halide (CsPbI3–xBrx) perovskite solar cells (PSCs) have garnered significant attention due to their high-power conversion efficiency (PCE), thermally stable black perovskite phase, and strong potential for use as the top cell in tandem configurations. In this work, we successfully stabilized ambient-phase CsPbI2Br (x = 1) using a lead acetate Pb(Ac)2 additive. Pb(Ac)2 played a key role in regulating the crystallization process and stabilizing the photoactive black phase of CsPbI2Br. By incorporating 5% Pb(Ac)2 into the precursor solution, we achieved a notable enhancement in device performance, with PCE increasing from 12.33% (control CsPbI2Br device) to 16.04%. Simultaneously, the open-circuit voltage (VOC) increased from 1.231 to 1.323 V, among the highest reported for Pb(Ac)2-based inorganic perovskite solar cells. Furthermore, VOC increased up to 1.358 V for phenyltrimethylammonium chloride (PTACl) passivation. This result arises due to the reduced recombination and formation of the Pb–O surface. Moreover, the optimized 5% Pb(Ac)2-based device demonstrated excellent thermal and ambient stability, retaining over 90% of its initial performance after 100 h at 85 °C in air without encapsulation. These results highlight the effectiveness of Pb(Ac)2 in simultaneously boosting the performance and long-term stability of inorganic perovskite solar cells.