Formation of Quaternary Czt(S,Se) Compounds Using Hydrothermal Synthesis and Spin Coating Technique

Abstract

Cu2ZnSn(Se,S)4 or CZT(S,Se) composed of copper, zinc, tin, sulfur, or selenium are developing as promising new long-term light absorption materials for photovoltaic (PV) systems. The materials are abundant, non-toxic, and inexpensive. CZT(S,Se) thin films have been prepared using a two-step procedure. The initial step started with the preparation of CZT(S,Se) powder using the hydrothermal technique which was heat-treated at annealing temperatures of 400°C, 600°C, and 800°C, whereas the second step is the fabrication of CZT(S,Se) thin films using a spin coating process. The XRD result showed that the crystal structure of all films was polycrystalline kesterite phase. At 800 °C, CZTS and CZTSe thin films crystallite size was 15.47 nm and 25.4 nm respectively. According to AFM results, particle size and (RMS) of CZT(S,Se) film increased with increasing annealing temperature when the grain size is directly associated with temperature. The morphological properties using FE-SEM showed that the CZT(S,Se) thin films were compact with more densely packed grains at the highest annealing temperature. The direct band gaps for CZTS and CZTSe estimated by Tauc’s equation were (1.73 and 1.68) eV; (1.66 and 1.59) eV; (1.56 and 1.53) eV at 400 °C, 600 °C, and 800 °C respectively. The energy gap of CZT(S,Se) materials is not far off the optimum value for the greatest solar cell efficiency. Hall measurements revealed that all of the samples were p-type. The lowest value of resistivity was found to be 0.031 Ω.cm for CZTS at 800°C and 0.0191 Ω.cm for CZTSe at the same annealing temperature.

Keywords

• CZT(S,Se); Hydrothermal synthesis; Spin coating technique; Thermal annealing