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Cu2ZnSnSe4 thin films were prepared by spin-coating and chemical co-reduction with different heating modes. The phases of obtained samples were characterized by X-ray diffraction (XRD). The size and morphology of the products were observed by scanning electron microscope (SEM). Experimental results show that, the intensity of the XRD peaks of the samples was not significantly enhanced by segmented heating, but the XRD peak for (200) crystal plane appeared. The change of the reaction process in the tube furnace did not significantly improve crystallization and phase of the films. The technology with heating the precursor failed to significantly improve the film crystallinity while the effects of reaction conditions affect the morphology significantly. Introduction Cu2ZnSnSe4 (CZTSe) and Cu (In,Ga)Se2 (CIGS) have similar crystal structure and photoelectric properties, it has better prospects than CIGS since Zn and Sn elements are abundant, non-toxic and environmentally friendly. The photoelectric conversion efficiency of Cu2ZnSn (SeS)4 solar cells has exceeded 10% reported currently [1], Although which is much smaller than the theoretical value, but it has been greatly improved than the original data that less than 1 percent. Cu2ZnSnSe4 as I2-II-IV-VI4 quaternary compound has custerite crystal structure with lattice parameters of a=0.56882 nm, c=1.13378 nm. CZTSe is a P-type direct band gap semiconductor with band gap Eg about 1.5 eV and absorption coefficient α greater than 10 cm. Its thickness less than 2 μm can meet the application requirements of the solar battery. Therefore CZTSe is very suitable as the solar cell absorption layer material [2-4]。 There are many methods to prepare CZTSe thin films at present, including one-step and two-step methods according to the processes. One-step methods include evaporation, solvothermal, powder and sputtering etc. Two-step method includes preparing preset alloy layer and selenizing in a certain atmosphere, the former process may be sputtering, atomic beam sputtering, reactive magnetron sputtering, thermal evaporation, photochemical deposition, spray, sol gel or electrodeposition method [5-8]. For example, M.Ganchev et al obtained the CZTSe film by presetting two base layers of brass and bronze and selenizing [9]. Some university researchers have also provided many new ideas and methods for preparing CZTSe compounds with low cost and simple process. Cu2ZnSnSe4 thin films were prepared by spin coating and chemical reduction, the effects of heating methods on phase, crystallization and morphology of the product films were investigated in this work. Experimental details The substrates were washed in hot sulfuric acid for 30 min, and then put into acetone, ethanol respectively for ultrasonic cleaning 20 min, at last were kept in ethanol before using. The precursor solutions were prepared by dissolving raw material powders of CuCl2·2H2O, SnCl2·2H2O, ZnCl2 4th International Conference on Mechatronics, Materials, Chemistry and Computer Engineering (ICMMCCE 2015) © 2015. The authors Published by Atlantis Press 508 and SeO2 in stoichiometric proportions of Cu2ZnSnSe4 into a certain amount of solvent, such as water, alcohol. And then the precursor films with certain thickness were obtained by repeated spin coating, drying 4~8 times, and then were put into the reactor filled with 1 mL reducing agent hydrazine hydrate and heated by different technologies. The product films can be obtained after natural cooling to room temperature and the product sample was taken out and dried. The phases of product samples were characterized by X-ray diffraction (XRD) on a model of Bruker D8. The size and morphology of the products were observed by JSM6380LA electron microscope (SEM). Results and analysis Preparing CZTSe films by segmented heating (1) Heating in oven: According to segmented heating method in the reference [10], CZTSe films were prepared by segmented experiments. Fig.1 shows the XRD pattern of CZTSe film on the glass substrate. The sample was first heated at 120 C for 12 h and then at 200 C for 12h. According to the standard PDF card (No.52-0868) of Cu2ZnSnSe4, the XRD peaks at 2θ angles of 27.1 and 31.1 are corresponding to (112) and (200) crystal planes respectively. Compared with previous works, the XRD peak intensity of the samples prepared by segmented heating was not significantly enhanced. However, it appeared (200) crystal plane which almost was not found in CZTSe film samples except in the powder sample with good crystallinity. So the heating process does not obviously affect CZTSe film crystallization. Fig.1 The XRD pattern of CZTSe film on the glass substrate (2) Heating in in tube furnace: Fig.2 shows the XRD patterns of product films prepared by segmented heating in tube furnace. The reaction processes of two samples were as follows: a) 100C120C120C200C200C260C260C b) 100C120C120C 200C 200C280C280C Compared with the standard PDF card (No.52-0868), the XRD peaks at 2θ angles of 27.1 and 45.1 are corresponding to (112) and (204) crystal planes. The XRD peak intensity of the samples shows not very high. Compared with previous experimental results, the change of the reaction process in the tube furnace has not significantly improved crystallization and phase of the product films. Fig.2 XRD patterns of CZTSe films prepared by segmented heating in tube furnace Fig.3 shows the SEM images of CZTSe film sample a refered in Fig.2. Fig.3a indicates that the film surface is composed of strip sheets and small amount of polyhedral particles which may be NaCl impurities. From the scratch on the product film in Fig.3b it can be seen that it mainly consists of small particles and has about 0.7 ~ 1 μm thickness. 0 0 0 0 H-68

Cu2ZnSnSe4 Thin Films Prepared by Chemical Method with Different Heating Technologies