Analysis of the Electronic Structure of Modified CuGaS2 with Selected Substitutional Impurities: Prospects for Intermediate-Band Thin-Film Solar Cells Based on Cu-Containing Chalcopyrites

The electronic structure of modified CuGaS2, which belongs to the family of Cu-containing chalcopyrites, has been analyzed from first principles within the density functional theory. The chalcopyrite matrix has been modified by introducing a high concentration of atomic impurities that included transition metals and elements of group IVa at substitutional sites of the lattice host. For selected cases, an intermediate band has been found that potentially fulfills the requirements as stated for intermediate-band solar cell materials. Preliminary thermochemical estimations of the stability of the Compounds proposed against eventual secondary phases in the form of binary chalcogenides have greatly simplified the general screening. Elements of groups VIIIb and IVa have been identified as interesting impurity candidates to obtain intermediate bands within the main gap of the modified ternary host. Additionally, modified chalcopyrite compounds with potential applications as magnetic semiconductors or spintronic materials have been identified. The transformation of chalcopyrite compounds as used for thin-film solar cells into intermediate-band materials could have a particular impact on the design of thin-film intermediate-band solar cells, with improved figures of energy conversion efficiency expected.