Comparative study of the structural and optical properties of Cu₂SnX₃ and Cu₂ZnSnX₄ (X=S, Se) thin films and optoelectronic devices

The structural and optical properties of Cu₂SnX₃ (CTX, X=S, Se) and Cu₂ZnSnX₄ (CZTX, X=S, Se) thin films have been investigated experimentally. CTX and CZTX thin films were grown on a Mocoated soda lime glass substrate by annealing the metallic stack precursors prepared by radiofrequency magnetron sputtering. The similar structure of CTX and CZTX causes overlap of the diffraction peaks in the X-ray diffraction (XRD) pattern. Additionally, selenization annealing is an easier procedure than sulfurization annealing. The results of Raman scattering spectroscopy and Fourier transform infrared spectroscopy provide evidence regarding structure and phase identification to complement the information obtained from XRD. Optical characterization demonstrates that CTX has a narrower band gap than CZTX, attributed to band gap evolution from ternary to quaternary compounds with cation occupation. A photoelectric detector and thin film solar cell (TFSC) were prepared with the eco-friendly compounds Cu₂SnS₃ (CTS) and Cu₂ZnSnS₄(CZTS). Device performance for both photoelectric detector and TFSC is improved by integrating CZTS thin film rather than CTS thin film. The simpler structure of a photoelectric detector provides an easy way to detect the quality of the thin film before it is applied to fabricate the whole TFSC structure.