Reaction routes for the formation of a Cu2ZnSnS4 absorber material from homogenous ethanol-based solution

Abstract

Solution-based deposition processes have taken a leading role in producing high efficiency devices from Cu₂ZnSnS₄ (CZTS) systems. The Cu₂ZnSn(S,Se)₄ (CZTSSe) films deposited from our ethanol-based process currently provide a high reported efficiency for this material system at 5.36%. In this paper, we report a detailed study of the ethanol-based solution deposition route from the chemistry occurring in the precursor solution to the transformation from solid state framework to the CZTS phase during a subsequent annealing treatment. The homogenous CZTS precursor solution is a mixture of three different metal–thioacetamide (TAA) complexes, which has been proven by the analysis of UV-vis-near-IR absorption spectra and FT-IR absorption spectra. X-ray diffraction (XRD) and Raman spectroscopy have been employed to track every stage of the reaction route. It is found that the complexes build up an ordered framework upon drying and transform to a CuSn_3.75S₈ phase and finally to the CZTS phase after subsequent annealing treatments. The relative simplicity of this formation mechanism is beneficial for the performance of the CZTS based solar cells.