ABSTRACT Heterojunction technology (HJT) silicon solar cells have garnered significant attention owing to their high solar power conversion efficiency. However, despite their promise, HJT solar cells still confront challenges related to long‐term stability and reliability, primarily attributed to factors such as corrosion by acids and thermal damage. In this study, we investigated the specific conditions leading to acid leakage using commercially available encapsulants, including ethylene vinyl acetate (EVA), polyolefin elastomer (POE), and a sandwich‐structured encapsulant known as EPE (EVA‐POE‐EVA). Various combinations of temperature and duration were examined to identify conditions triggering encapsulant decomposition and subsequent acid generation. Additionally, the mechanism by which acetic acid contributes to indium tin oxide (ITO) corrosion was explored. Our findings reveal that acidic conditions with a pH below 3 initiate ITO corrosion, with the extent of corrosion influenced by the crystal structure of the ITO. Corrosion of the ITO layer leads to an increase in resistivity, as observed through four‐probe method and electroluminescence testing. These results provide valuable insights for researchers in both industry and academia, facilitating a better understanding of the effects of acid corrosion. Future research endeavors will focus on developing strategies to mitigate HJT degradation resulting from corrosion.