A study on the humidity susceptibility of thin-film CIGS absorber

The susceptibility of a thermally co-evaporated CuInGaSe₂ (CIGS) thin-film absorber to humidity and its consequence on composition, morphology, electrical and electronic properties, and device efficiency was investigated. CIGS films on Mo-coated soda lime glass were degraded either in the ambient at ~21°C and ~21% relative humidity (RH) for a period of several months or in damp heat (DH) at 85°C and 85% RH briefly for 15-30 min; then the films were processed simultaneously into devices in a batch that included an unexposed control. In addition to severe delamination on some samples of the absorber films, prolonged ambient exposure resulted in numerous ¿spot¿ formations that lost CIGS with scale-like disintegration rippling around the spots and showed a significant presence of Na. Exposure in DH for 5 h was able to reproduce the spot formations on the CIGS films. A significant to large decrease of cell efficiency was observed from 14%-16% for the unexposed control to 8%-11% for the CIGS absorber exposed in DH for 15 and 30 min and 1%-4%% for the ambient-degraded CIGS with high series resistance and very low shunt resistance.