The influence of thermal cracking selenium source temperature on CIGS absorber and device performance in co-evaporation processes

Abstract

Se source cracking is reported with positive influence on CIGS absorber and device. We apply thermal cracking selenium source to co-evaporation processes, and investigate the influence of cracking Se source temperature on the CIGS absorber and device performance. The absorber films are investigated by XRF, SEM, XRD (GIXRD), SIMS, CV and Current-Voltage characterization. As the cracking temperature increase, the film topography tend to exhibit copper poor morphology, namely layered structure. The film preferred orientation was not significantly influenced by cracking temperature. For the device fabricated, we find that high thermal crack temperature decreases the open circuit voltage and fill factor. Further analysis of the IV data, we conclude that major recombination occurs in the space charge region. Though no iron material is applied in thermal cracking unit, the Fe intensity of high cracking temperature sample is still higher than those of low cracking temperature ones. Also, the cracking Se source facilitate the diffusion of Ga and In, which is similar to elevating substrate temperature. CV measurement unveiled that deep level defect concentration is higher in high cracking temperature samples. Further investigation and experiment including IVT, AS measurement and removal of material containing iron in Se source is carrying out to determine whether these defects are introduced only by impurities or by selenium activity induced atomic vacancy or substitution defects.