Characterization and numerical modeling of Cu(In,Ga)(S,Se)2 solar cells

Cu(In,Ga)(S,Se)₂ solar cells, prepared by a selenization/sulfization reaction are characterized by GD-OES, JV, and capacitance spectroscopy. A numerical model of the solar cells is used to optimize the compositional profile: the S/(S+Se) ratio at the interface, and the thickness of the S-containing layer near the surface and the Ga/(In+Ga) minimum. Device behavior is modeled using the composition profiles, and an acceptor-like defect 160-230 meV above the valence band. Comparing devices from separate processes, we found that differences in composition and defects measured with capacitance account for the differences performance. Ga/(In+Ga) at the surface determines the optimal S/(S+Se) surface ratio.