Synthesis and study of microstructural, optical and electrical properties of Na-doped Cu2ZnSnS4 thin films via thermal evaporation

Non-doped and sodium-doped Cu 2 ZnSnS 4 (CZTS) thin films deposited on heated glass substrates at 100 °C have been successfully fabricated by the thermal evaporation technique, after what all layers were annealed under sulfur atmosphere at 400 °C. The structural properties of all layers were analyzed using X-ray diffraction and Raman spectroscopy methods. These analysis reveals a polycrystalline with kesterite structure and preferential orientation along the (112) plane for all samples. The surface morphology of all samples was investigated using atomic force microscopy (AFM). The obtained topographies show an improvement of the crystalline quality of post-sulfurized Na-doped CZTS films. Further, the optical measurement recorded by UV–Vis spectroscopy reveals that the direct band gap energy of post-sulfurized Na-doped CZTS films were in the range of 1.56 eV and 1.61 eV. Electrically, all films show p-type electrical conductivity, measured by the hot probe method. In addition, Hall Effect measurements show that Na-doped CZTS thin films exhibit lower resistivity and mobility, as well as higher carrier concentration, than Non-doped films. We can conclude that doping CZTS with Na makes it a better photovoltaic material, and that it is suitable as an absorber layer.