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

Abstract

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 Mo-coated soda lime glass substrate by annealing the metallic stack precursors prepared by radio-frequency 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.