| (CZTS), a new emerging solar cell material that contains earth abundant elements, has optimum direct band gap energy of 1.5eV and a relatively large absorption coefficient (104cm-1). Owing to its excellent properties, CZTS is considered to be an alternative to cadmium telluride and copper indium gallium selenide for application in low cost and environment-friendly thin film solar cells. The research of CZTS semiconductor materials research is important in academic and application.In this article, CZTS powders were prepared by microwave synthesis process with reactants of zinc chloride, stannous chloride, cupric chloride and thiourea. We focus on the influence of synthesis temperature and reaction time on structure and morphology of CZTS powders. As a result:Synthesis temperature has a great impact on the structure and morphology of CZTS powders. When the temperature is below 160℃, the product also contains CuS, ZnS, Cu2SnS3 and other miscellaneous phase in addition to CZTS. The product is a mixture of spherical particles and column-like rods. When the temperature is in the range of 170℃-200℃, the synthesized product is a pure phase CZTS powder, and all product is spherical particles. When the temperature increased from 170℃ to 200℃, diameters of particle decreased from 1.5μm to 300nm, Each particle composes of nanocrystalline with the size about 10nm. The reaction time has no obvious impact on the structure and morphology of CZTS powders. Reaction time of at least 10min is essential for the growth of single kesterite CZTS. The optimum temperature for synthesis of CZTS powder ranges from 170℃ to 200℃. The optimal reaction time is at least 10min.Base on the study of synthesis of CZTS powder, CZTS thin films has growth on FTO substrate directly by microwave irradiation method. We discussed the influencing of reactants concentration on morphology, structure and optical property of the CZTS thin films. The growth mechanism of CZTS semiconductor nanocrystals films prepared by microwave irradiation were preliminary analyzed. The results are summarized as follows:The CZTS film on the FTO substrate by microwave irradiation synthesis technology has pure phase kesterite structure without ZnS, CuS, Cu2SnS3 and other miscellaneous phase. CZTS film composed of a large number of spherical particles with diameter of 400nm-900nm. Those spherial particles contain many nanocrystals in size of 6nm-13nm. Thus, the as-synthesised CZTS is called CZTS nanocrystalline. The thin film has strong absorption in a wavelength of 400nm-900nm and has the band gap of 1.27eV-1.54eV, which suitable to be used as solar cell absorber layer.The CZTS film can be grown directly on the FTO surface by microwave method without any film. CZTS growth on the glass surface on the back, indicating that the conductive, surface roughness and lattice similarity of FTO and CZTS have in favor of CZTS nucleation and growth.The optimum conditions for the synthesis of CZTS have been obtained through systematic research by microwave synthesis technology, which is described as fellow the concentration of CuCl2 is 0.08M, the concentration of ZnCl2 is 0.08M, the concentration of SnCl2 is 0.04M, the concentration of NH2CSNH2 is 0.22M, the temperature of microwave synthesis is 190℃, the reaction time is at least 90min, the amount of PVP is 1.28g.Based on experimental observations and experimental results, the growth mechanism of CZTS film can be divided into three stages. First, Cu2+, Zn2+, Sn2+and thiourea reaact into complex reaction [Cu(Tu)n(H2O)x]2+,[Zn(Tu)n(H2O)x]2+ and [Sn(Tu)n(H2O)x]4+ complex in the precursor solution. Secondly, [Cu(Tu)n(H2O)x]2+, [Zn(Tu)n(H2O)x]2+ and [Sn(Tu)n(H2O)x]4+ compound decomposed into Cu2-xS, ZnS and SnS under the action of microwave energy, then Cu2-xS adsorbed on FTO substrate, and becomes the core, which react with ZnS, SnS to start the CZTS nuclear reaction. Finally, CZTS nuclear growth by Ostwald ripening as CZTS particles on the FTO substrate grown into a film. |
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