Fabrication of selective boron emitters for TOPCon solar cells using boron-doped amorphous silicon as diffusion source

Abstract

The fabrication of selective boron emitters (BSEs) plays a pivotal role in improving the efficiency of tunnel oxide passivated contact (TOPCon) solar cells. This study presents a novel approach for BSE fabrication, which involves depositing boron-doped amorphous silicon (a-Si(B)) via magnetron sputtering, followed by defining heavily doped regions using a continuous wave infrared laser. The final step is a one-step thermal oxidation process that converts a-Si(B) into borosilicate glass (BSG). The single-sided deposition process effectively reduces chemical consumption and simplifies processing steps, while the high laser energy utilization efficiency of a-Si significantly decreases energy expenditure during laser treatment. By changing the nitrogen and oxygen ratio of the thermal process atmosphere, the sheet resistance in the lightly doped region can be adjusted over a wide range. While, the distribution of boron atoms in the heavily doped region is mainly controlled by the boron content in a-Si (B) and the laser power, and is less affected by the thermal process atmosphere. Our experimental results demonstrate that this approach allows for precise adjustment of dopant concentrations in both lightly and heavily doped regions, resulting in improved passivation quality and contact performance. The study highlights the potential of this method to meet diverse design requirements and enhance the efficiency of TOPCon solar cells.