Enhanced Thermal Stability in Perovskite Solar Cells via the Integration of a Nonionic Binary Compound

Abstract Phenethylammonium (PEA + ) has been extensively used for defect passivation, enhancing the photovoltaic performance of perovskite solar cells (PSCs) by forming a quasi‐2D perovskite layer atop the 3D perovskite. However, the ionic nature of PEA + renders it prone to deprotonation at elevated temperatures, generating neutral PEA 0 , which exhibits strong nucleophilicity and easily reacts with formamidinium cations (FA + ) in the 3D perovskite. This reaction accelerates perovskite degradation, thereby deteriorating photovoltaic properties and long‐term stability. Here, N , N ‐dimethylbenzenesulfonamide (DMBSA), a nonionic binary compound synthesized via a simple process, is applied as a defect passivation material. Unlike PEA + , DMBSA remains thermally stable due to strong covalent bonding and does not undergo deprotonation at elevated temperatures. Moreover, its lower nucleophilicity prevents undesirable reactions with FA + , significantly mitigating perovskite degradation. Consequently, DMBSA‐passivated PSCs maintain 96.1 ± 0.8% of their initial photoconversion efficiency (PCE) after 1500 h of thermal stress at 85 °C, compared to only 64.0 ± 0.19% for PEA + ‐passivated PSCs. Furthermore, DMBSA passivation effectively suppresses nonradiative recombination, while its dipole moment induces an electrical field, facilitating efficient hole transfer to the hole transporting layer. As a result, DMBSA‐passivated PSC achieves a PCE of 25.43% (certified 25.1%), substantially outperforming pristine PSC (22.07%).