Improved performance of amorphous Si thin-film solar cells on 430 stainless steel substrate by an electrochemical mechanical polishing process

Abstract

This study reports the electrochemical mechanical polishing (ECMP) technique for 430 stainless steel (SS) substrate to improve the conversion efficiency of hydrogenated amorphous silicon (a-Si:H) thin-film solar cells. The surface roughness of the untreated 430 SS substrate was ∼38nm and decreased to ∼23nm after ECMP processing of the 430 SS substrate. The average diffuse reflection rate decreased from 4.2% of the untreated 430 SS substrate to 1.1% for the ECMP processed 430 SS substrate. The analysis of chemical composition of passive layer on the ECMP processed 430 SS substrate was carried out by the X-ray photoelectron spectroscopic. The passive layer of ECMP processed 430 SS substrate is composed of Cr2O3 and Fe2O3. The SIMS result indicated that the diffusion of iron (Fe) and chromium (Cr) impurities from the 430 SS substrate into the a-Si:H solar cell can be suppressed by the passive layer which was formed by the ECMP process. In particular, the Cr impurity was effectively blocked from diffusing into a-Si:H layer of the ECMP processed 430 SS substrate. The decreased series resistance and increased shunt resistance for the a-Si:H solar cells on the ECMP processed 430 SS substrate, due to a reduction in the Cr and Fe deep-level defect density, resulted in the cell conversion efficiency increasing to 5.4%. The ECMP process provides an available surface treatment technique for achieving high conversion efficiency of a-Si:H thin-film solar cells on a 430 SS substrate.