Effects of free oxygen concentration in glass structures with different B/Ga ratios on the metallization of p+ emitter during laser-enhanced contact optimization

Boron-doped n-type tunnel oxide-passivated contact (n-TOPCon) solar cells are the mainstream products in the current photovoltaic market. Laser-enhanced contact optimization (LECO) technology is regarded as an effective solution for reducing contact resistance and metal-induced recombination. Herein, from the perspective of glass frits, the influence of free oxygen concentration in the glass network structure on the metallization of the p⁺ emitter during the LECO process was studied by changing the mass ratio of B₂O₃ and Ga₂O₃. The results showed that the O²⁻ provided in the glass network with a B/Ga ratio of 6 gradually transforms the [BO₃] units into [BO₄] units. The improvement of thermal stability was conducive to the uniform diffusion of molten glass on the surface of Si wafers. The high temperature melting contact angle curve exhibited a notable convergence, demonstrating the optimum high-temperature wettability. The uninterrupted glass layer facilitated the chemical reduction of Ag⁺ ions on the p⁺ emitter. Additionally, it created favorable conditions for forming Ag-Si alloys during the LECO process. The continuous glass layers reduced Ag⁺ to Ag crystals during the initial sintering process and was uniformly deposited on the surface of the emitter. The local current passed preferentially through the position of the Ag bulk, forming an effective Ag-Si alloying. Chemical reduction and LECO processes have established the optimal metallized contact between the Ag paste and the p⁺ emitter. The photoelectric conversion efficiency (PCE) of n-TOPCon solar cells had been further enhanced.