Experimental and Theoretical Investigation of High-Resolution X-ray Absorption Spectroscopy (HR-XAS) at the Cu K-Edge for Cu₂ZnSnSe₄

Energy sustainability is critical for social activities in the human world. The quaternary compound Cu₂ZnSnSe₄ (CZTSe), as a promising candidate for thin-film solar cell absorption with medium-level thermoelectric performance, is of interest for the purpose of utilizing solar energy. The defect chemistry and atomic ordering in this particular compound also triggers interests in understanding its crystallographic structure as well as defects. Hereby, high energy resolution X-ray absorption spectroscopy is employed to investigate the electronic and geometric structural complexity in pristine and cobalt-doped Cu₂ZnSnSe₄. The occupational atomic sites of Cu are found to be mixed with the Zn atoms, forming Cu_Zn anti-defects, which serve as a knob to tune local electronic structures. With proper doping, the band structure can be manipulated to improve the optical and thermoelectric properties of the CZTSe compounds.