Effective Solvent‐Engineered All‐Inorganic CsPbI 2 Br Perovskite Solar Cells

All‐inorganic CsPbI 2 Br perovskite composition has attracted considerable attention in recent years due to its thermal robustness, convenience for space applications as well as for all‐perovskite triple junction applications as a top cell due to its wide‐bandgap (1.9 eV) nature. However, homogeneous film formation, perovskite α‐phase stability, poor crystallization, and solvent trapping still remain as the major challenges for this composition. Here we report a detailed analysis of solvent engineering strategy upon addition of AcN to DMSO to weaken the DMSO‐rich solvation shell as supported by DLS, FTIR, GIWAXS and device data and facilitate the residual solvent removal followed by controlled crystallization resulting in better film morphology, lower surface roughness, reduced trap‐assisted recombination and improvement in device parameters from 12.7% (untreated) to 14.0% (AcN‐treated).