Improved structural and optical properties of Cu2ZnSnS4 thin films via optimized potential in single bath electrodeposition

• We investigate the role of deposition potential over compositional, structural and optical properties of the CZTS films.
• A single bath electrodeposition process for Cu2ZnSnS4 thin film deposition has been used.
• We demonstrate an experimental methodology to control the defects, structural and optical properties of the CZTS film.

Here we report on the preparation of high quality Cu2ZnSnS4 thin films using single bath electrodeposition process via an optimized deposition potential. X-ray diffraction and Raman analysis validated the formation of kesterite phase of CZTS without any secondary phases at an optimized deposition potential of -1.4 V vs. Ag/AgCl. As a signature of highly pure crystalline films of CZTS kesterite phase, we observed a characteristic Raman peak at 338 cm−1 that corresponds to the vibration of sulfur atoms. Elemental analysis using energy dispersion analysis of X-rays (EDX) reveals a near ideal composition ratio of 2:1:1:4 for these films, and indicates the formation of the ideal stoichiometric compound. Furthermore, X-ray photoelectron spectroscopy analysis of the grown films illustrates an appropriate chemical composition and valence states of the constituent elements without a trace of free sulfur. Using the chrono- amperometry data and the Scharifker and Hill model we found that the nucleation mechanism for CZTS thin film is instantaneous. Optical properties demonstrated the optimum band gap of 1.5 eV for kesterite CZTS film prepared from a precursor electrodeposited at -1.4 V vs. Ag/AgCl. Mott-Schottky electrical measurements confirm the p-type nature of the film with a carrier concentration of 1017 cm−3, a flat band potential of VFB = 0.7 V and space charge region width of 0.2 μm.