Sustainable p-type copper selenide solar material with ultra-large absorption coefficient.

Earth-abundant solar absorber materials with large optical absorption coefficients in the visible enable the fabrication of low-cost high-efficiency single and multi-junction thin-film solar cells. Here, we report a new p-type semiconductor, CuTiSe (CTSe), featuring indirect (1.15 eV) and direct (1.34 eV) band gaps in the optimal range for solar absorber materials. CTSe crystallizes in a new noncentrosymmetric cubic structure (space group 4[combining macron]3) in which CuSe tetrahedra share edges and corners to form octahedral anionic clusters, [CuSe], which in turn share corners to build the three-dimensional framework, with Ti ions located at tetrahedral interstices within the channels. The unique crystal structure and the Ti 3d orbital character of the conduction band of CTSe give rise to near-optimal band gap values and ultra-large absorption coefficients (larger than 10 cm) throughout the visible range, which are promising for scalable low-cost high-efficiency CTSe-based thin-film solar cells.