Production and characterization of CZTS films: On the role of H2S flow rate

•CZTS films were produced to contain pure sulphide anion without any metal substitution.•Effect of flow rate on the properties of CZTS films was evaluated in detail.•Surface morphology of the films was modified by controlling the flow rate of H2S in the sulphurization stage.•Pure kesterite CZTS films without secondary phases were obtained. Kesterite CZTS films were produced to contain pure sulphide anion without any metal substitution, and optimization studies were carried out by changing the flow rate of H2S at the sulphurization stage. Effect of flow rate on the properties of CZTS films were evaluated in detail. All films were grown in polycrystalline structure with a preferential orientation through (1 1 2) plane. The intensity of the characteristic peak was higher for the samples sulphurized at high flow rates, indicating a better crystallization. Raman spectra showed no peaks indicating a second phase for any film. Optical band gap values were calculated to be between 1.43 and 1.56 eV in accordance with the literature. Especially the sample obtained at a flow rate of 40 sccm is a promising sample in terms of suitable properties which may affect the conversion efficiency in photovoltaic solar cells. At low H2S flow rates, it was determined that the surface of the films contains defects in the form of cracks/voids. This work evaluates and refers that by selecting appropriate flow rates at the sulphurization stage, CZTS films with improved characteristics for photovoltaic applications can be achieved.