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

Abstract

ABSTRACT 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 ( ε r ) and Gutmann donor number ( D N ) of popularly‐used dimethylsulfoxide (DMSO) by incorporation of water molecule, which significantly weakens the binding energy of DMSO‐PbI 2 , i.e., the solubility, and improves the PbBr 2 counterpart. With the balance of interaction energies between DMSO and PbI 2 or PbBr 2 , 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 CsPbI 2 Br 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.