Methylamine Gas Treatment Affords Improving Semitransparency, Efficiency, and Stability of CH 3 NH 3 PbBr 3 ‐Based Perovskite Solar Cells

High bandgap semitransparent solar cells based on CH 3 NH 3 PbBr 3 perovskites are attractive for building integration, tandem cells, and electrochemical applications. The lack of control of the CH 3 NH 3 PbBr 3 perovskite growth limit the exploitation of CH 3 NH 3 PbBr 3 ‐based perovskite solar cells. Herein, a post‐treatment is carried out after the initial CH 3 NH 3 PbBr 3 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 CH 3 NH 3 PbBr 3 ‐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.