Optimization of passivation layer on the front surface of N-type tunnel oxide passivated contact solar cells

In this paper, an effective P⁺ emitter passivation scheme was proposed by continuously optimizing the passivation layer on the front surface of N-type tunnel oxide passivated contact (TOPCon) solar cells, that was using SiO_x/AlO_x/SiN_x tri-layer passivation stack. The SiO_x/AlO_x/SiN_x stack combined the benefits of the chemical passivation effect of SiO_x and the field-effect passivation of SiO_x/AlO_x stack, resulting in high-quality passivation for boron-doped emitter. Three different passivation schemes of SiN_x, AlO_x/SiN_x and SiO_x/AlO_x/SiN_x were respectively prepared on the front surface of N-type TOPCon solar cells. It was revealed that the cells with SiO_x/AlO_x/SiN_x stack had a superior conversion efficiency, while the SiO_x thickness significantly influenced the surface passivation. Through optimization of SiO_x thickness in the SiO_x/AlO_x/SiN_x stack, the optimal deposition period for SiO_x was 4 cycles by the plasma-enhanced atomic layer deposition (PEALD) process. The N-type TOPCon solar cells with SiO_x/AlO_x/SiN_x stack on the front surface exhibited the highest performances with a conversion efficiency of 24.88 % when the deposition period of SiO_x was 4 cycles. Compared with the baseline processes, the efficiency was increased by 0.11 %_abs..