Improved sulfurization process for enhancing the microstructure and transport properties of spray pyrolysis-deposited Cu2ZnSnS4 films

Abstract

Cu 2 ZnSnS 4 (CZTS) is an emerging material with significant potential as an absorber layer for solar cells. Precise control over the film preparation process is crucial for attaining optimal transport, electrical, and optical properties. This study investigates the effect of sulfurization duration on the properties of CZTS films deposited onto soda lime glass substrates via spray pyrolysis, followed by annealing at 550 °C in a sulfur-rich environment under argon flow. X-ray diffraction and Raman spectroscopy confirmed the formation of monophasic CZTS, with the highest phase purity observed for films sulfurized for 5 minutes. Scanning electron microscopy demonstrated notable morphological and microstructural enhancements due to the sulfurization process, while energy-dispersive spectroscopy confirmed near-ideal stoichiometric composition (Cu:Zn:Sn:S ≈ 2:1:1:4). Optical spectroscopy determined the band gap of the films to be between 1.40 and 1.50 eV. The electrical transport properties were investigated up to 130 °C, revealing p-type conductivity, with Seebeck coefficients ranging from 30 to 70 μV K -2 and low electrical resistivity, displaying semiconductor-like behavior. The maximum power factor achieved was 0.36 μW mK -2 at 130 °C for the sample sulfurized for 5 minutes. These findings suggest that a 5-minute sulfurization time is optimal for producing single-phase CZTS films characterized by uniform morphology, accurate stoichiometric composition, and an ideal direct band gap. Given its favorable thermoelectric properties, CZTS shows significant promise as a material for thermoelectric applications, particularly in waste heat recovery systems. The results indicate that CZTS films could be further optimized for use in thermoelectric devices, and future studies could focus on enhancing their thermoelectric performance by adjusting sulfurization conditions and exploring material modifications.