In situ fabrication of Cu₂ZnSnS₄ nanoflake thin films on both rigid and flexible substrates

Cu₂ZnSnS₄ (CZTS) thin film, a highly promising and low-cost absorber layer material for solar cells, has been in situ fabricated on stainless steel and FTO glass substrates for the first time, using a one-step solvothermal treatment of CuZnSn-alloyed film with sulphur or selenium powder. The resulting products were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV-vis-NIR spectroscopy. Raman spectroscopy was used to characterize and confirm the formation of CZTS. The effects of temperature, reaction time, the ratio of Cu/Zn/Sn, and non-elemental reactants on the formation of CZTS nanocrystal films were assessed, and we found that the reaction temperature was a key factor in determining the properties of the final products. Pure CZTS phase forms at a temperature of 250 °C or higher. Our method produces CZTS thin films at 250 °C, the lowest reaction temperature that can be used in the process and the lowest temperature of any current fabrication system. We also found that flexible substrates promote the growth of CZTS nanocrystals. Using flexible substrates in the in situ fabrication of nanocrystalline thin films may make it possible to use CZTS for industrial applications.