Mitigating contaminant-induced surface degradation in TOPCon solar cells: Mechanisms, impacts, and mitigation

The tunnel oxide passivated contact (TOPCon) solar cell has become the dominant technology for high-efficiency silicon photovoltaics. Despite its success, TOPCon solar cells face significant reliability challenges under environmental stresses such as damp heat (DH) exposure. In this study, we investigate the degradation mechanisms affecting TOPCon cells, particularly focusing on contamination-induced surface passivation loss, which varies between the front and rear surfaces. Our results show that the rear side of TOPCon cells, in particular the silicon nitride (SiN_x) layer, is prone to chemical degradation under exposure to sodium-based salts, resulting in a significant loss of open-circuit voltage (V_oc). Sodium acetate and sodium chloride are found to accelerate surface passivation degradation through enhanced surface oxidation and diffusion of contaminants. We propose a novel approach utilizing a 10 nm aluminum oxide (AlO_x) barrier layer, deposited through atomic layer deposition (ALD), to mitigate these degradation pathways effectively. Accelerated DH testing demonstrates that this barrier improves the long-term stability of TOPCon solar cells, reducing degradation and maintaining performance over extended periods. This study highlights the importance of surface protection to enhance the durability and operational lifetime of TOPCon solar cells in harsh environments.