High voltage Cu(In,Ga)Se/sub 2/ devices with Ga-profiling fabricated using co-evaporation

The influence of bandgap profiling of Cu(In,Ga)Se/sub 2/ absorbers for thin film solar cells has been investigated. Profiles have been obtained by depositing CuGaSe/sub 2/ back surface layers in the beginning of the Cu(ln,Ga)Se/sub 2/ growth process. Two different concentrations of Ga was used for the nongraded part of the Cu(ln,Ga)Se/sub 2/ film corresponding to Ga/(Ga+In) ratios of 0.2 and 0.5. The interdiffusion of Ga and In was studied and it was found that, although substantial interdiffusion occurred, a back surface layer with a high Ga content remained as analyzed with SIMS and XRD. The main influence on the solar cell parameters, by widening of the bandgap towards the back contact using this Ga-rich back surface layer, was found to be an enhancement of the efficiency by improved voltage.