On the properties of Cu2ZnSn(S,Se)4 thin films prepared by selenization of binary precursors using rapid thermal processing

Cu2ZnSn(S,Se)(4) thin films were grown on molybdenum coated glass substrates by selenization of stacked precursor layers of zinc, tin disulfide and copper sulfide. Selenization was performed using a rapid thermal processor at maximum temperatures in the range of 400 degrees C to 550 degrees C and at heating rates of 1 degrees C/s and 2 degrees C/s. The compositional, morphological and structural characterization of the films was carried out using energy dispersive x-ray spectroscopy, scanning electron microscopy, x-ray diffraction and Raman spectroscopy. X-ray diffraction and Raman scattering analysis suggests the formation of Cu2ZnSn(S,Se)(4) only at lower temperatures, whereas Cu2ZnSnSe4 was formed at higher temperatures regardless of the heating rate used. Compositional analysis revealed that the films were Zn-poor and Sn-rich. However, the samples approach a near stoichiometric composition due to the loss of tin at a selenization temperature and heating rate of 550 degrees C and 2 degrees C/s, respectively. Large grains with an average lateral dimension of 4.5 mu m were observed for films prepared at these conditions which are very desirable for an absorber for solar cells.