Paper
Abstract Chemical bath deposition (CBD) is an effective technique used to produce high‐quality SnO 2 electron transport layers (ETLs) employed in perovskite solar cells (PSCs). By optimizing the CBD process, high‐quality SnO 2 films are obtained with minimal oxygen vacancies and close energy level alignment with the perovskite layer. In addition, the 3D perovskite layers are passivated with n‐butylammonium iodide (BAI), iso‐pentylammonium iodide (PNAI), or 2‐methoxyethylammonium iodide (MOAI) to form 3D/2D heterojunctions, resulting in defect passivation, suppressing ion migration and improving charge carrier extraction. As a result of these heterojunctions, the power conversion efficiency (PCE) of the PSCs increased from 21.39% for the reference device to 23.70% for the device containing the MOAI‐passivated film. The 2D perovskite layer also provides a hydrophobic barrier, thus enhancing stability to humidity. Notably, the PNAI‐based device exhibited remarkable stability, retaining approximately 95% of its initial efficiency after undergoing 1000‐h testing in an N 2 environment at room temperature.