Effect of selenization and sulfurization on the structure and performance of CIGS solar cell

Abstract

This study prepares a Cu (In, Ga) Se2 (CIGS) thin film by sputtering metal precursors and subsequent selenization/sulfurization. The quality of the Mo bilayers/CIGS samples that are selenized at 550 °C is confirmed by SEM. The XRD patterns for the CIGS absorber film show a chalcopyrite crystal structure with a preferred orientation of (112), (204)/(220) and (312)/(116). The Raman scattering results for the CIGS thin films show a mean peak at ~ 174 cm−1 and weak signals at ~ 215 cm−1. The high resolution TEM micrograph shows the corresponding (112) peak for the chalcopyrite structure, which is in agreement with the XRD and Raman results. Sulfurization uses sulfur powder (without toxic H2S gas) in a tube type resistance furnace. After sulfurization, S atoms substitute Se atoms to form a Cu (In, Ga) (Se,S)2 (CIGSS) mixed crystal at the surface regions and an additional CIGSS diffraction peak appears at 2θ ~ 27.40°. The SEM images show that the films’ surface becomes smooth and densely uniform. The main structure of the CIGS films remains unchanged and the grain size increases slightly after sulfurization. The SIMS scan shows that S atoms diffuse into the surface regions of the CIGS layer to a depth of ~ 300 nm, after sulfurization at 530 °C for 5 min. The CIGS solar cell devices that are prepared using sulfurization exhibit improved photo-conversion efficiency.