S₈ Additive Enables CsPbI₂Br Perovskite with Reduced Defects and Improved Hydrophobicity for Inverted Solar Cells

Though prized for excellent thermal stability, inorganic perovskites are still behind organic/inorganic hybrid perovskites due to their high-density defects and poor hydrophobicity. Herein, trace hydrophobic S₈ is used as additive to optimize the solution-processed CsPbI₂Br perovskite film. A series of characterizations reveal that S₈ additive not only leads to retarded crystallization of a-CsPbI₂Br perovskite at low temperature (<150 °C) via self-formed Pb(S₈)_x²⁺ intermediate but also induces efficient grain-boundary passivation via distinctive PbS coordination interaction and reduced wettability on perovskite surface, which all point to the formation of the perovskite film with reduced defects and improved hydrophobicity. As a result, the inverted perovskite solar cells (PSCs) based on the optimized all-inorganic perovskite of CsPbI₂Br:S₈ deliver an increased power conversion efficiency (PCE) from 12.76% to 14.46% as well as remarkably enhanced device stability under thermal or ambient condition. This work thus provides a simple way as well as new insights for boosting the performance of solution-processed all-inorganic perovskite.