Minimizing Solvent Residues in CsPbI1.5Br1.5 Perovskite Films for Efficient Ultra-Wide Bandgap Solar Cells

As an intermediate composition between CsPbI₂Br and CsPbIBr₂, the inorganic perovskite material CsPbI_1.5Br_1.5 is expected to exhibit both high efficiency and enhanced stability, attracting significant attention. However, as a Br-rich perovskite, CsPbI_1.5Br_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., CsPbI₃ and CsPbI₂Br). 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.