Low Temperature Back-Surface-Field (BSF) Technology for Crystalline Silicon (c-Si) Thin Film Solar Cells Based on Heterojunctions between Boron-Doped P-Type Hydrogenated Amorphous Silicon and c-Si

We propose a low temperature back-surface field (BSF) technology for crystalline silicon (c-Si) thin film solar cells. The BSF structure has a heterojunction between a p-type c-Si substrate and a boron (B)-doped p-type hydrogenated amorphous silicon (a-Si:H) layer deposited on the back surface of the c-Si substrate at 200degC. The back-surface recombination velocity, S_b, of minority carriers can be reduced to less than 1000 cm/s in this structure, while the value of S _b is 10⁶ cm/s when a B-doped p-type layer is epitaxially grown on the c-Si substrate. We have clarified, from internal photoemission (IPE) and attenuated-total-reflection Fourier transform infrared (ATR-FTIR) spectroscopy measurements, that possible reasons for the observed low value of S_b are (1) the band lineup of the heterojunction (HJ) between B-doped p-type a-Si:H and c-Si and (2) the hydrogen passivation of defects in B-doped a-Si:H