| (CZTS) thin film solar cells have become one of the hot spots in the research of solar cells because of its advantages such as environmental protection, low cost and high photoelectric conversion efficiency. CZTS semiconductor thin films plays an important role in the quality and performance of CZTS thin film solar cells as the absorption layer of CZTS thin film solar cells. Therefore, the research on CZTS semiconductor thin film is of great significance and value.CZTS semiconductor thin films were directly grown on the transparent conductive fluorine-doped tin oxide (FTO) substrates by solvothermal method. In the solvothermal fabrication process, precursors of ethanol, copper (Ⅱ) chloride dihydrate, tin (Ⅱ) chloride dehydrate, zinc (Ⅱ) chloride, thiourea, oxalic acid and hexadecyl trimethyl ammonium bromide were used. The effect of reaction temperature, copper (Ⅱ) chloride concentration, zinc (Ⅱ) chloride concentration and reaction time on the structure, morphology and optical property of CZTS thin films have been studied using X-ray diffraction (XRD), Energy dispersive spectrum (EDS), Raman spectrum, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and UV-Vis spectroscopy, respectively. The research content of this thesis can be summarized into the following several parts:CZTS thin films are in kesterite phase at different temperature. With reaction temperature increasing from 140℃ to 230℃, the average nanocrystallite size increase from 4.25nm to 13.17nm, the values of the optical band gap decrease from 1.76eV to 1.53 eV. For CZTS thin films prepared at low temperature, they are composed of a large number of uniform sphere-like particles with an average diameter of about 450nm, however, for CZTS thin films prepared at high temperature, they are composed of a large number of nanosheets which interconnect with each other to form an entangled network-like architecture.Concentration of copper chloride has great impact on the purity of the CZTS thin films. When the copper chloride concentration is lower than 0.025M, CZTS thin film is pure phase, when the copper chloride concentration is greater than 0.0375M, Cu7S4 impurity phase appears in the film. The copper chloride concentration is 0.025M, the crystallinity of CZTS films is the best, they are composed of a large number of nanosheets which interconnect with each other to form an entangled network-like architecture, the film is uniform and compact. When the concentration of copper chloride is other values, CZTS thin films are composed of massive irregular particles of different sizes, thin film is not very dense, and it is not uniform on the substrate; With copper chloride concentration gradually increased, the band gap of CZTS films decreases gradually.Cu2ZnSnS4 thin films are in kesterite phase prepared at different zinc chloride concentration; Zinc chloride concentration has little effect on the morphology of CZTS thin films. The CZTS thin films are composed of mutually wrapped nano sheets at different zinc chloride concentration, They are evenly distributed on the FTO substrate; When the concentration of zinc chloride is lower than 0.0625M, The transmittance of the prepared CZTS thin film samples was lower than 20% in the UV and visible bands. The band gap of CZTS thin films prepared is close to the best band gap of solar cells under different concentrations of zinc chloride.Cu2ZnSnS4 thin films are in kesterite phase prepared at different reaction time. With the reaction time increased, the crystallinity of the thin films and the average nanocrystallite size increased. The reaction time has little effect on the morphology of CZTS thin films, they are composed of a large number of nanosheets which interconnect with each other to form an entangled network-like architecture. As time increases, CZTS thin films become more and more uniform and compact; CZTS thin films were prepared at 5h, 10h,15h,20h, respectively. The corresponding band gap of CZTS films were 1.89eV,1.81eV,1.71eV, 1.83eV. |
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