| Cu2Zn Sn S4(CZTS) is a direct p-type semiconductor. Because of the high optical absorption coefficient over 104 cm-1, suitable band gap about 1.5 e V, high theoretical conversion efficiency around 32.2%, and abundant and non-toxic raw materials, it has become one of the most promising materials for solar cells absorber layer.This article aims to explore the mechanism of thin film growth, improve the preparation process of the film, and then realize the preparation of high performance CZTS thin film. CZTS films were fabricated by sulfurizing the metal- precursor films deposited using vacuum thermal evaporation. Investigating by X-ray diffraction,Raman spectra, scanning electron microscopy, and UV spectrophotometer, we study the phase structure, morphology, optical properties of CZTS films. Specific contents are as follows:1) Several Zn/Cu/Sn stacked films were fabricated by vacuum thermal evaporation and then sulfurized into CZTS films under sulphur atmosphere(two-step method). We discuss the effect of sulfurization temperature and time on the growth of CZTS films, and deeply analyzed the transformation of structural phase and dynamic process during the formation process of CZTS films. A spot of precursor is sulfurized into CZTS phase, and the prepared films mainly consist of Sn S2, Cu S, Cu2 Sn S3 and Zn S under shorter sulfurization time and lower sulfurization temperature. Longer sulfurization time and higher sulfurization temperature can cause the decomposition of a number of CZTS phase. It is found that the optimal sulfurization temperature is500 o C and the optimal sulfurization time is 90 min. Furthermore, it is found that lower temperature at ~ 533 K easily leads to the formation of cubic-Cu2 Sn S3, but higher temperature at 823 K often causes the decomposition of CZTS phase to form Cu2 Sn S3 with tetragonal structure.2) Cu2 Zn Sn S4 thin films have been successfully prepared using three-step process: deposition of CZT metallic stacks by vacuum thermal evaporation,preparation of precursors by preheating the first samples with different temperature and synthesis of CZTS films by sulfurizing the second precursors. The preparedCZTS film by sulfurizing the preheated precursor at 300 o C presents high crystallinity, dense and uniform surface morphology, and suitable optical properties.By comparison with the optimal CZTS film formed by two-step method, we found that preheating precursor can not only improve crystal quality of CZTS films but also decline sulfurization temperature and time.3) CZTS films are fabricated using the two-step process: deposition of CZT by vacuum thermal evaporation with substrate temperature, and formed of CZTS films by sulfurizing precursors. We systematically studied the influence of substrate temperature on crystallinity and crystal quality of CZTS. The prepared CZTS film by sulfurization of metal CZT films with 50 o C substrate temperature has high crystallinity, compact and smooth surface, and suitable optical properties of 1.5 e V.Heating precursors can lead to alloy phase forming during vacuum thermal evaporation. Compared with three-step process, it is not only helpful for the synthesis of CZTS films with better crystal quality but also can make the experiment easier.
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