Enhanced Stability through Efficient Suppression of Iodine Oxidation Pathways in CsFAMA Perovskite Solar Cells via Thiourea‐Based Molecule

Perovskite solar cells (PSCs) exhibit remarkable efficiency but face serious stability challenges due to defects and environmental stresses such as oxygen and moisture. This study introduces enhancing the stability and performance of triple‐cation CsFAMA‐based PSCs through 4‐(Carbamothioylamino)phenylthiourea (CPTU), which is a thiourea derivative with diverse functional groups. CPTU's sulfur and amino groups passivate surface and bulk defects, suppress iodide oxidation, and mitigate superoxidation‐induced degradation, thus improving the passivation mechanism and reducing photodegradation. In this work, CPTU is incorporated into the perovskite active layer via additive engineering. Compared to control devices (without CPTU), the CPTU‐treated PSCs showed improved photovoltaic performance, with power conversion efficiency (PCE) increasing from 20.74% to 22.97%. Long‐term stability tests under continuous illumination (45 °C) demonstrated that CPTU‐based devices retained 92% of their initial PCE after 500 h (vs. 69% for control devices) and 84% after 1000 h. These results highlight CPTU's role in defect passivation and oxidation suppression.