Degradation Mechanism of TOPCon Solar Cells in an Ambient Acid Environment

n-Type tunnel oxide passivated contact (TOPCon) solar cells are expected to dominate the global photovoltaic market in the next decade, primarily owing to their rapidly increasing power conversion efficiency (PCE). However, acids generated from encapsulant hydrolysis under damp-heat (DH) conditions significantly impair the reliability of TOPCon solar cells. This study evaluated the degradation behavior of TOPCon solar cells under an accelerated test in an ambient acid environment. Exposure to acetic acid for 48 h resulted in the average peel force decreasing from 3.94 to 2.67 N. The study revealed significant deterioration in the contact between the silver-aluminum electrodes and silicon, as well as between the busbar and ribbon, which can be attributed to the corrosion of surface electrodes and the Pb-Sn-Bi alloy-coated ribbon in acetic acid. This deterioration led to a decrease in the front side PCE of TOPCon solar cells by 4.38% and in the rear side PCE by 2.16%, likely owing to differences in the metal contact composition on each side. As a proof-of-concept, the encapsulant was optimized by changing the additives to neutralize the acid produced during the damp-heat process. Following this modification, the PCE degradation of the glass/backsheet module after 2000 h of damp-heat (DH2000)-accelerated test was reduced from 6.49 to 1.54%. This research highlights the vulnerability of TOPCon solar cells to acetic acid exposure and emphasizes the electrochemical reactivity of metallization as a potential risk to the long-term operation of TOPCon modules. It also proposes potential improvements to the encapsulant, which are crucial for enhancing the performance and ensuring the long-term reliability of TOPCon modules.