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, Sb, 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 Sb 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
Improvement of crystalline silicon surface passivation by hydrogen plasma treatment
A completely dry low-temperature process has been developed to passivate 3.3 Ω cm p-type crystalline silicon surface with excellent results. Particularly, we have investigated the use of a hydrogen plasma treatment, just before hydrogenated amorphous silicon carbide (a-SiCx:H) deposition, without breaking the vacuum. We measured effective lifetime, τeff, through a quasi-steady-state photoconductance technique. Experimental results show that hydrogen plasma treatment improves surface passivation compared to classical HF dip. Seff values lower than 19 cm s−1 were achieved using a hydrogen plasma treatment and an a-SiCx:H film deposited at 300 °C.
Analysis of a flowing silane dc discharge in the presence of a hot surface
We have measured the rates for the depletion of silane and the formation of solid material, disilane, trisilane, and hydrogen under steady‐state conditions in a flowing dc silane discharge in the presence of a heated substrate. The depletion rate of silane depends linearly on discharge current whereas the film yield and hydrogen yield increase superlinearly and the disilane and trisilane yields increase sublinearly with current. The yield of disilane is reduced in the presence of a hot substrate which we interpret as evidence that a significant fraction of disilane is produced by surface combination of SiH3 radicals. We also find that the optical emission intensity of the Balmer Hα line is proportional to the partial pressure of H2, and the intensity of the SiH 414‐nm band is unrelated to the film deposition rate.