University of Diyala College of Science Department of Physics Synthesis and Characterization of CZTS and CZTSe Quaternary Compounds for Solar Cells Applications A Dissertation

Abstract

work. ABSTRACT Cu2ZnSnS4(CZTS) and Cu2ZnSnSe4(CZTSe), are copper zinc tin sulfide, and selenide materials. They are developing as promising new long-term light absorption materials for photovoltaic (PV) systems. The materials are abundant on the planet, non-toxic, and inexpensive. In this work, CZTS and CZTSe were synthesized by using two techniques. Firstly, copper zinc tin sulfide and selenide CZTS and CZTSe thin films have been prepared using two-step procedure. The initial step started with the preparation of Cu2ZnSnS4 and Cu2ZnSnSe4 powder using the melt quenching technique, and the second step is the fabrication of CZTS and CZTSe thin films using the thermal evaporation deposition process. The obtained films were heat-treated at annealing temperatures of 50, 150, and 300°C. UV. Vis spectroscopy, Atomic force microscopy (AFM), Field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy were used to characterize the samples. The XRD result showed that crystal structure of all of the films were polycrystalline kesterite phase. At 300 °C, CZTS film crystallite size was (9.8 nm) and for CZTSe film was (10.9 nm). The direct band gaps for CZTS and CZTSe estimated by Tauc’s equation were (1.95 and 1.89 eV); (1.90 and 1.79 eV); (1.87 and 1.71 eV) at 50, 150, and 300°C. The energy gap of CZTS and CZTSe materials is not far off the optimum value for the greatest solar cell efficiency. According to AFM findings, particle size and root-mean-square (RMS) of CZTS and CZTSe film increased with increasing annealing temperature when grain size is directly related to temperature. In addition, the surface morphological characteristics showed smooth, compact and uniform film formation at highest annealing temperature. The functional groups are analyzed by using FTIR spectroscopy. Hall measurements revealed that all of the samples were p-type. The highest carrier concentrations were found 9.75×106 cm−3 for CZTS at 300°C and 6.72×106 cm−3 for CZTSe at the same temperature. The maximum open-circuit voltage (VOC) was 0.23 mV, the highest short-current density (JSC) was 7.41 mA/cm2, and the highest efficiency (ɳ) was 14.8%, according to measurements of heterojunction for ITO/CZTS/CdS/ZnO/Al solar cell devices' (J-V) curves; as for ITO/CZTSe/CdS/ZnO/Al solar cell devices, were the highest open-circuit voltage (VOC) 0.38 mV and short-current density (JSC) 4.9 mA/ cm2, and the device highest efficiency (ɳ) was 15.6 %, therefore, both devices went through an annealing process at 300 °C Secondly CZTS and CZTSe thin films have been prepared using a two-step procedure. The initial step started with the preparation of CZTS and CZTSe powder using the hydrothermal technique which was heat-treated at annealing temperatures of 400, 600, and 800°C, whereas the second step is the fabrication of CZTS and CZTSe thin films using a spin coating process. AFM, FE-SEM, XRD, and FTIR were used to characterize the samples. The XRD result showed that the crystal structure of all films was polycrystalline kesterite phase. At 800 °C, CZTS film crystallite size was (15.47nm) and for CZTSe film was (25.4nm). The morphological properties using FE-SEM showed that the CZTS and CZTSe thin films shape were compact with more densely packed grains at the highest annealing temperature. According to AFM results, particle size and (RMS) of CZTS and CZTSe film increased with increasing annealing temperature when grain size is directly associated with 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°, the energy gap of CZTS and CZTSe materials is not far off the optimum value for 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 temperature. The maximum open-circuit voltage (VOC) was 0.39 mV, the highest short-current density (JSC) was 4.81 mA /cm2, and the highest efficiency (ɳ) was 13.3%, according to measurements of heterojunction for ITO/CZTS/CdS/ZnO/Al solar cell devices' (J-V) curves; as for ITO/CZTSe/CdS/ZnO/Al solar cell devices, were the highest open-circuit voltage (VOC) 0.42 mV and short-current density (JSC) 5.12 mA/ cm2, and the device highest efficiency (ɳ) was 15.1 %, therefore, both devices went through an annealing process at 800 °C.