Interfacial Passivation Toward Photostable Wide‐Bandgap Perovskites for Efficient Semitransparent Solar Cells

Light‐induced halide demixing constrains the photovoltaic performance and stability of wide bandgap perovskite solar cells and tandem cells. Previous studies have demonstrated defects induced ionic migration is the primary reason for the halide demixing. Herein, we develop a generic buried interface passivation approach to mitigate the halide demixing of wide bandgap perovskite (1.70 eV) by using sodium formate (NaFo). Systematic molecular level characterizations disclose that NaFo can form strong interactions with Pb 2+ and FA + , which enable perovskite films with larger grain sizes and less residual PbI 2 . As a result, perovskite films with lower defect density and longer carrier lifetime have been obtained. The halide demixing activation energy is significantly increased from 8.5 ± 0.5 to 43.8 ± 2.1 kJ mol −1 . These advantages enable the fabrication of opaque and semi‐transparent solar cells based on the wide bandgap perovskite with efficiencies of 22.2% and 20.0% (stabilized power output of 21.4% and 19.5%), respectively. Moreover, the semi‐transparent PSCs retain more than 80% of their initial performance after 500 h continuous operation.