| Cu2ZnSnS4(CZTS) thin film has high absorption coefficient and ideal band gap (-1.5eV) close to single junction solar cell optimum band gap. CZTS consist of low-cost and non-toxic elements, and is a kind of ideal absorption layer materials of thin film solar cell. Thus, it is significant in academic and application to carry out research in the CZTS thin film materials and CZTS thin film solar cells.Magnetron sputtering method has advantages in strongly controll, good repeatability and easy prepareation of uniform film, which is suitable for the preparation of CZT metallic precursors. The preparation of CZTS films prepared by solid-state sulfurizing CZT metallic precursors can reduce the damage to equipment and less environmental pollution. It is a safe and environmental friendly way of production mode. Therefore, in this thesis we used solid-state sulfurizing the magnetron spurttered Cu-Zn-Sn(CZT) metallic precursors to prepare CZTS thin films. Micro structure, chemical composition and transmittance of CZTS films were analyzed by X-ray diffraction (XRD), Raman spectrum, scanning electron microscope (SEM), energy dispersive of X-ray (EDS), and UV-vis, respectively. The effect of metallic content of CZT precursors and sulfurization process on the mechanism of the solid-state sulfurization of CZTS thin films were investigated. We also try to make a CZTS thin film solar cell. The research content of this thesis can be summarized into the following several parts:1) Zn and Sn content in CZT metallic precursors which fabricated on soda-lime glass(SLG) influence on the properties of CZTS thin films. Increasing of Zn content can effectively reduce the Cu content which can restrain the formation of CuxS phsae. Zn/Sn ratio of precursors in between 0.21 and 0.36 can increase the grain size and crystallinity of CZTS thin film. Metallic content increases to about Cu/(Zn+Sn)=0.3 and Zn/Sn=0.24, which can effectively improve the crystallinity of the CZTS thin films. When Zn/Sn ratio is about 0.18 of metallic precursor, Sn2S3 phase will occur in CZTS films, which will reduce the quality of thin film and lead the optical band gap to decrease significantly.2) Single phase of kesterite CZTS thin film can be fabricated by solid-state sulfurizing CZT metallic precursor which Zn, Sn and Cu depositied in 92s,2173s and 221s on the SLG, respectively, sulfurized at 500℃ for 20min. The CZTS thin film show Cu-poor and Zn-rich in composition, and compact and uniform surface and good crystallinity. Its optical absorption coefficient is over 104cm-1,and optical band gap is 1.52eV.3) Sulfurization temperature is critical to the formation of CZTS thin films fabricated by solid-state sulfurized metallic precursors which deposited on Mo-coated SLG for 20min. Sulfurized at 400℃ to 450℃, CZTS films contain impurity phases, Cu2SnS3, Cu2S, CuS and Sn2S3 which surface is rough and multihole. Furthermore,it is found that sulfurizing at 500℃ is suitable to forming single phase kesterite CZTS with grain uniformly and line compactly. The adhesion strength of the Mo layer and CZTS film is poor, CZTS thin film easily peels off which sulfurized at 550℃.4) With the sulfurization time increasing, Cu and Sn content of the films increase, Zn content of the films significantly reduced. Because sulfurized at 500℃, increasing of sulfurization time accelerating the decomposition of CZTS into SnS phase, which lead the surface of the films to loose and uplift easily. The formed impurities like Cu2SnS3, Sn2S3 will decrease optical band gap of thin films. Top quality CZTS thin films were obtained by solid-state sulfurized at 500℃ for 20min.5) It is found that the annealing of as-sulfuried CZTS thin films at low temperature will optimize effectively the morphology and optical properties of the films. The results show that for CZTS thin film after annealed at 300 ℃, its grain size is about 75 nm, its surface is smooth and compact, the optical absorption coefficient is over 104 cm-1, and the optical band gap is 1.50 eV, which is suitable to be used as the absorption layer of thin film solar cell.6) A CZTS solar cell with structure of Glass/Mo/CZTS/CdS/i-ZnO/ZnO:Al/Ag was fabricated. For this cell, the short-circuit current is 0.014 mA·cm-2, open circuit voltage is 121 mV and fill factor is 0.25. |
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