Effective passivation for nanocrystalline Si layer/crystalline Si solar cells by use of phosphosilicate glass

We have investigated the phosphosilicate glass (PSG) passivation effect on electrical characteristics of the structure fabricated by use of the surface structure chemical transfer (SSCT) method. Cross-sectional SEM measurements show that PSG can penetrate into nano-sized pores of the nc-Si layer. For thick nc-Si layer, e.g., ∼300 nm, however, un-filled nano-sized pores remain in the deep region of the layer. It is founded that complete PSG filling of the nano-sized pores in the nc-Si layer with its thickness less than ∼160 nm greatly improves the effective minority carrier lifetime. The valence band maximum is found to shift toward the lower energy by the SSCT treatment, indicating the band-gap widening of the nc-Si layer. When pores in the nc-Si layer is completely filled with PSG, the effective minority carrier lifetime increases with the thickness of the nc-Si layer, suggesting formation of the graded band-gap structure which can suppress recombination of photo-generated electron-hole pairs.