Effect of the i-layer optical gap on the light-induced degradation 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 cells with narrower E(opt) show slower degradation under light-soaking than the cells with wider E(opt). However, they recover upon thermal annealing at 150 degrees C as fast as the cells with wider E(opt). The results indicate that the light-induced processes are suppressed in the materials with narrower E(opt), but that the thermally induced process does not depend on E(opt). The slower light-induced processes of the cells with narrower E(opt) are attributable to the lower recombination energy, which is a driving force of light-induced defect creation. Differences in the hydrogen content, the hydrogen bonding configuration and the germanium content are less likely to cause variation in the degradation time constant.