Co-Etching Process for Boron-Rich and Phosphorus-Rich Layers in Crystalline Silicon Solar Cells
The boron-rich layer (BRL) and phosphorus-rich layer (PRL) formed during thermal diffusion in crystalline silicon solar cells are detrimental to carrier lifetime and conversion efficiency. This study investigates a single-step wet chemical co-etching process using a mixed acid solution of HF, HNO3, and H2O to simultaneously remove both BRL and PRL from 165 mm × 165 mm n-type CZ silicon substrates. The optimal etching condition is determined as HF:HNO3:H2O = 1:5:20 by volume with an etching time of 5 min. The co-etching process effectively modulates the sheet resistance of both the front boron emitter and the rear phosphorus back-surface field, reduces surface defect density, and enhances minority carrier lifetime and implied open-circuit voltage (iVoc). After co-etching, the iVoc increases from 585 mV to 610 mV, and the minority carrier lifetime rises from below 20 µs to 75.7 µs. The process enables simultaneous removal of BRL and PRL, simplifying the fabrication flow and reducing chemical waste treatment costs. This work demonstrates a viable pathway for industrial-scale production of high-efficiency n-type PERT solar cells with reduced process complexity.