Fabrication and Characterization of Cu(In,Ga)(S,Se)2-Based Solar Cells

We formed Cu(In,Ga)(S,Se)2 films using a three-stage process. The grain size of the films was reduced by increasing their S concentration. Judging from the phase diagrams of Cu–S and Cu–Se, a decrease in grain size with the increase in S concentration may be due to the higher the melting point of Cu2S compared to that of Cu2Se. The short circuit current density of the fabricated solar cells decreased significantly with an increase in S concentration. Secondary ion mass spectrometry showed an unsuitable compositional distribution of S and Se despite the constant S/Se flux ratio during growth. A maximum open circuit voltage of 0.83 V was obtained at a S/(S+Se) ratio of 0.80 in the fabricated solar cells in order to increase bandgap.