Surface passivation of a Cu(In,Ga)Se2 photovoltaic absorber using a thin indium sulfide layer

Abstract

The present study demonstrates the surface passivation of Cu(In,Ga)Se2 (CIGS) photovoltaic absorbers using a thin In2S3 layer and its effect on the performance of the CIGS device. Two types of CIGS samples with different surface roughness values prepared by conventional selenization of metal precursors (2-step) and three-stage co-evaporation (3-stage) were used to determine the influence of In2S3 surface passivation on CIGS surface roughness to minimize recombination at the interface of the CIGS and buffer layers. Three types of buffer layers, i.e., In2S3, CdS single layers, and an In2S3/CdS double layer, were prepared by chemical bath deposition on bare and Mo-coated substrates as well as glass/Mo/CIGS samples. The phase formation and properties of the as-prepared buffer layers were analyzed by XRD, Raman, and UV–Vis–NIR techniques. The power conversion efficiency of the CIGS solar cells was enhanced significantly for the 2-step-processed CIGS (from 6.97% to 9.89%) and slightly for the 3-stage-processed CIGS (from 10.1% to 11.0%) when passivated with In2S3. Further, both the In2S3 surface passivated 2-step- and 3-stage-processed CIGS devices exhibited high quantum efficiencies in the wavelength range of 400–550 nm. Therefore, surface passivation with In2S3 could improve the performance of CIGS devices.