Concurrent Nucleation of Mixed‐Halide Perovskite Phase via Balancing Solvent‐PbX 2 Interaction for Efficient Solar Cells in Air

Wide-bandgap mixed-halide perovskites generally used as front cell absorber play great importance for manufacturing high-performance tandem perovskite solar cells. However, the deviation in coordination strength between solvent molecule and lead halide always induces inhomogeneous halogen-phase crystallization and distribution, which inevitably degrades the device efficiency and durability. Herein, we propose a strategy to precisely regulate the dielectric constant (εr) and Gutmann donor number (DN) of popularly-used dimethylsulfoxide (DMSO) by incorporation of water molecule, which significantly weakens the binding energy of DMSO-PbI2, i.e., the solubility, and improves the PbBr2 counterpart. With the balance of interaction energies between DMSO and PbI2 or PbBr2, concurrent nucleation of mixed-halide perovskite phase is realized, benefiting the fabrication of high-quality wide-bandgap perovskite film with homogeneous halogen distribution. Consequently, a champion efficiency of 15.42% for all-air-processed carbon-based all-inorganic CsPbI2Br cell is achieved, one cutting-edge value among congeneric devices, with excellent reproducibility by controlling the water dosage via a hydrophobic solvent encapsulation strategy. Together with the enhanced stability, this work provides a new path for engineering perovskite solution and promoting the scalable photovoltaics in air.