Effect of air annealing on the electronic properties of CdS/Cu(In,Ga)Se-2 solar cells

The effect of air annealing on state-of-the-art, solar-cell-quality CdS/Cu(In,Ga)Se-2 heterojunctions has been studied using contact potential difference and surface photovoltage measurements. The annealing treatment is shown to have no significant effect on the band lineup of the heterojunction. However, the surface photovoltage spectral response increases markedly upon air annealing. These results can be reconciled if air annealing of the junctions leads mainly to elimination of recombination centers, rather than to changes in the built-in voltage or in the band lineup. We also show that ZnO deposition has an effect on the surface photovoltage that is similar to that of air annealing.