Effects of buffer layer processing on CIGS excess carrier lifetime: application of dual-beam optical modulation to process analysis [of solar cells]

A new nondestructive contactless dual-beam optical modulation (DBOM) technique has been developed for the characterization of effective excess carrier lifetimes in CuInGaSe/sub 2/ thin-film solar cells. Developed originally for lifetime measurement of SOI wafers, the technique represents a novel tool with the capabilities of direct measurement of the lifetime effects of intermediate processing steps during device fabrication without the confounding effects that subsequent processes might have on the final device characteristics. This is demonstrated in a controlled experiment intended to elucidate the mechanisms whereby CBD CdS processes improve device performance and to compare the CBD process with an MOCVD dry process. Areal mapping of excess carrier lifetimes across the samples is used to exhibit the substantial inhomogeneity of lifetime even within very high quality sample, demonstrating another capability of DBOM applicable to quality assessment and process optimization.