Hydrogen plasma treatment for improving bulk passivation quality of c-Si solar cells

Abstract

We have investigated the effects of radio frequency hydrogen plasma (H-plasma) treatment on bulk passivation qualities of cast poly-crystalline silicon (poly c-Si) wafers. When the hydrogen treatment was performed directly to poly c-Si wafers, the plasma damage was introduced and it was difficult to improve the minority carrier lifetime by optimizing the plasma condition. Hydrogenated amorphous silicon oxide (a-SiO x :H) films deposited by RF-PECVD using a mixture of SiH 4, H 2 and CO 2 were employed as the protection and the passivation layers. We found that the lifetime of poly c-Si substrates passivated by a RF-PECVD a-SiO x :H films with additional H-plasma treatment showed an improvement of the overall effective lifetime. Annealing up to 400 °C also enhances the further diffusion of hydrogen, and the effective lifetime of the samples with H-plasma treatment increased 20–30% compared to the samples without treatment. This result clearly indicated that the H-plasma treatment improves the bulk passivation quality of poly c-Si wafers.