Application of polycrystalline silicon carbide thin films as the passivating contacts for silicon solar cells

Abstract

In this paper, silicon rich polycrystalline silicon carbide (poly-SiCx) thin films were prepared for passivating contact of silicon solar cells. The effect of different carbon doping ratios R [methane flow (sccm)/silane flow (sccm)] and the annealing temperatures on the passivation quality was investigated. The lifetime test showed that, given a lower annealing temperature, the passivation quality of poly-SiCx thin films was very poor at R over 0.2, and it can be improved by elevating the annealing temperature. The effective lifetime of over 1.8 ms can be obtained with implied open-circuit voltages (iVoc) of 715 mV and saturated dark current (J0) of 18 fA/cm2. The microstructure and optical property of poly-SiCx films was studied by Raman spectra, X-ray photoelectron spectroscopy and UV-VIS spectrophotometer. The results showed that the incorporation of carbon lowered the crystalline fraction of poly-SiCx and a higher annealing temperature was needed to achieve high crystallinity. The optical band gap of poly-SiCx was widened with increase in R, and got up to 2.3eV when R was 0.4. A proof-of-concept top/rear TOPCon solar cells, featuring a N+-poly-SiCx (R = 0.2) front contact, was fabricated to demonstrate the potential of this SiCx passivation contact. The decrease in the parasitic absorption of light at the front side resulted in higher photogenerated current. And the conversion efficiency of 20.17% was achieved.