High-efficiency n-TOPCon cells ensured by an emitter preparation process without post-oxidation

Abstract

Laser-enhanced contact optimisation (LECO) technology can effectively improve the efficiency of tunnel oxide passivated contact (n-TOPCon) solar cells. Generally, the preparation of an emitter in TOPCon cells requires post-oxidation treatment at temperatures exceeding 1030 °C for over 3000 s. This high-temperature post-oxidation process results in reduced surface doping concentration, increased reflectivity of the front of the cell and elevated manufacturing costs of the junction. In this study, through process research, we reveal that the optimal profile depth of emitter (the boron doping concentration at 1 × 10¹⁸ atoms/cm³) for mass-produced LECO pastes ranges from 0.44 to 0.52 μm. Additionally, it was discovered that a boron-rich layer (BRL) thinner than 10 nm does not reduce bulk lifetime and increase contact resistivity. Based on these findings, we developed a boron-diffusion method without post-oxidation, which involves controlling the BRL thickness by adjusting the pre-oxidation layer thickness and cycle deposition. When applied to the mass production of n-TOPCon solar cells, this approach resulted in a solar cell conversion efficiency of 26.28 %. This represents an improvement of 0.03 %–0.05 % over traditional boron-diffusion processes. Furthermore, eliminating post-oxidation significantly improved the production capacity and lifespan of the boron-diffusion furnace, thereby reducing the manufacturing costs associated with the solar cells. Furthermore, eliminating post-oxidation significantly improved the production capacity and lifespan of the boron-diffusion furnace, thereby reducing the manufacturing costs associated with the solar cells.