Effect of optical gap on the stability of a-SiGe solar cells

The light-induced degradation and thermal recovery behaviors of a-SiGe single-junction solar cells with i-layers having various optical gaps (E(opt)) have been investigated. The narrower E(opt) cells show slower degradation under light-soaking than the wider E(opt) cells. However, they recover by thermal annealing at 150 degrees C as fast as the wider E(opt) cells. The results indicate that the light-induced defect creation processes are suppressed in the narrower E(opt) materials, but the thermally induced process does not depend on E(opt). From a comparison among several samples, the E(opt) dependence of the light-induced processes is attributable to the difference of E(opt) itself, i.e., the band-to-band recombination energy, rather than to the difference of the compositions.