Passivation Improvement of Poly-SiOx Based TOPCon Contacts by Thermal Annealing in a Water Vapor Atmosphere: Mechanism Exploration and Application Research

Post-treatment techniques of tunnel oxide passivated contact (TOPCon) structure are universally implemented via executing an additional hydrogenation process to optimize the passivation performance. However, the underlying physical mechanism and which method is most applicable are still being investigated. Herein, the effectiveness of thermal annealing in water vapor and N₂ atmosphere is studied, which is both environmentally friendly and easy to operate. It is demonstrated that compared to other common hydrogenation techniques, the wet N₂ outperforms in improving the passivation performance, which can be attributed to the neutralization of internal defects in poly-Si and the optimization of structural densities, and interestingly, this gain effect is amplified when this contact is doped with oxygen impurity. A power conversion efficiency of 22.62% is achieved using this technology which verifies its reliability and applicability. A loss analysis based on numerical simulations, outlining ways to achieve higher conversion efficiency and highlighting the great potential of this technology is also provided. Extensive experiments and first-principles calculations based on density-functional theory are conducted to clarify the underlying dynamics, including the surface adsorption process and the potentiation mechanisms, revealing that passivation and neutralization of hydrogen atoms couple with the compactness optimization of the structure.