Despite rapid advancements in the photovoltaic efficiencies of perovskite solar cells (PSCs), their operational stability remains a significant challenge for commercialization. This instability mainly arises from light‐induced halide ion migration and subsequent oxidation into iodine (I2). The situation is exacerbated when considering the heat effects at elevated temperatures, leading to the volatilization of I2 and resulting in irreversible device degradation. Mercaptoethylammonium iodide (ESAI) is thus incorporated into perovskite as an additive to inhibit the oxidation of iodide anion (I−) and  the light‐induced degradation pathway of FAPbI3→FAI+PbI2. Additionally, the formation of a thiol‐disulfide/I−‐I2 redox pair within the perovskite film provides a dynamic mechanism for the continuous reduction of I2 under light and thermal stresses, facilitating the healing of iodine‐induced degradations. This approach significantly enhances the operational stability of PSCs. Under the ISOS‐L‐3 testing protocol (maximum power point (MPP) tracking in an environment with relative humidity of ≈50% at ≈65 °C), the treated PSCs maintain 97% of their original power conversion efficieney (PCE) after 300 h of aging. In contrast, control devices exhibit almost complete degradation, primarily due to rapid thermal‐induced I2 volatilization. These results demonstrate a promising strategy to overcome critical stability challenges in PSCs, particularly in scenarios involving thermal effects. Mercaptoethylammonium iodide (ESAI) is incorporated into perovskite as an additive to inhibit the oxidation of I−, which provides a dynamic mechanism for the continuous reduction of I2 under light and thermal stresses, facilitating the healing of iodine‐induced degradations. Under ISOS‐L‐3 conditions, the device with ESAI retained 97% of the original power conversion efficiency (PCE) after 300 h.