Minimizing Solvent Residues in CsPbI 1.5 Br 1.5 Perovskite Films for Efficient Ultra‐Wide Bandgap Solar Cells

ABSTRACT As an intermediate composition between CsPbI 2 Br and CsPbIBr 2 , the inorganic perovskite material CsPbI 1.5 Br 1.5 is expected to exhibit both high efficiency and enhanced stability, attracting significant attention. However, as a Br‐rich perovskite, CsPbI 1.5 Br 1.5 suffers from poor film quality, primarily due to the substantial disparity in solvent evaporation rates and nucleation growth kinetics of the precursor films. This leads to severe non‐radiative recombination, closely related to the larger open‐circuit voltage loss ( V OC loss) and lower efficiencies compared to mainstream inorganic perovskites (e.g., CsPbI 3 and CsPbI 2 Br). To address these issues, we employed a Sequential Extraction Vacuum Method (SEVM), which integrates antisolvent extraction with vacuum treatment, to minimize solvent residues in perovskite films. This approach promotes grain densification, mitigates pinhole formation, and enhances film coverage, thereby significantly inhibiting non‐radiative recombination. Following SEVM treatment, the champion device achieved a power conversion efficiency (PCE) of 14.29% and a V OC of 1.336 V, representing the highest PCE and smallest V OC loss for ultra‐wide bandgap (> 1.95 eV) inorganic perovskite solar cells (PSCs). Furthermore, the SEVM‐based PSCs retained 90% of their initial PCE after 500 h of unencapsulated storage.