Methylamine Gas Treatment Affords Improving Semitransparency, Efficiency, and Stability of CH₃NH₃PbBr₃-Based Perovskite Solar Cells

High bandgap semitransparent solar cells based on CH₃NH₃PbBr₃ perovskites are attractive for building integration, tandem cells, and electrochemical applications. The lack of control of the CH₃NH₃PbBr₃ perovskite growth limit the exploitation of CH₃NH₃PbBr₃-based perovskite solar cells. Herein, a post-treatment is carried out after the initial CH₃NH₃PbBr₃ crystallization based on methylamine gas that drastically enhances the perovskite quality leading to a highly crystalline film with improved average visible transmittance (AVT) close to 56%. Opaque devices showed outstanding results in terms of open-circuit voltage and power conversion efficiency (PCE) reaching 1.54 V and 9.2%, respectively. These achievements are ascribed to a film with reduced morphological defects and better interface quality and reduced nonradiative pathways. For the first time, the fabrication of semitransparent CH₃NH₃PbBr₃-based solar cells is demonstrated reaching a maximum PCE equal to 7.6%, an AVT of the full stack device of 52%, and an excellent light stability at maximum-power point tracking.