| In recent years, the solar energy continues to be a kind of clean and renewable energy due to solar photovoltaic power generation has no serious selectivity to apparatus and environment, and its highly respected advantages of nearby power supply. But there is still a big gap to compete with traditional power generation technology, at the same time, high cost and environmental pollution problems exist in some solar cell preparation process hindered the large-scale application of solar photovoltaic power generation system. Therefore, exploring and developing high efficiency, low cost and environmentally friendly solar photovoltaic absorption material and devices are of great significance.ZnO is an n-type and II-VI family direct bandgap semiconducting oxide, the band gap of 3.37 eV, the exciton binding energy of about 60 meV, with high chemical and thermal stability. Due to its good optical performance, ZnO has been widely applied in many fields such as ultraviolet lasers, light emitting diodes, gas sensors, solar cells, etc. Meanwhile, the existence of intrinsic vacancy type defects in the ZnO crystal lattice leads to the difficulties of the preparation of p-type ZnO. While Gu2O is a direct band gap p-type semiconductor materials, with optical band gap of about 2.0eV, abundant in nature, high exciton energy and high absorption coefficient, which is an ideal material for solar spectrum absorbtion. The main obstacles is hard to obtain n-type Cu2O for homogeneous junction solar cells. In this thesis, on the ZnO nanorod arrays, Cu2O was deposited onto it to form n-ZnO/p-Cu2O heterojunction solar cell and its performance was investigated.Cu2ZnSnS4(CZTS), a quaternary chalcogenide-based compound semiconductor, attracted much interest in applications on absorber layers of thin film solar cells, due to its direct band-gap, large optical absorption coefficient in the order of 104cm-1, and medium band gap of about 1.5eV matched solar spectrum. And also elements of CZTS is abundant reserves and non-toxic. We adopted the non-vacuum process, and prepared CZTS films by both single-step electrochemical deposition method and sol-gel method. The structure, morphology, composition and optical properties of the films were analyzed by XRD, Raman, SEM, EDS, UV-visable spectra, respectively. The thesis includes the following five parts:The first part is an introduction, which introduces solar cell pricinples, structure and classcification; emphatically introduces CZTS basic properties, its preparation methods and research progress.The second part research on ZnO/Cu2O heterojunction solar cells. First, ZnO nanorods arrays was prepared by chemical bath deposition, at 85℃, the average nanorod diameter of 100-150 nm, length of 1.5 μm, distributed evenly with wurtzite structure, preferential growth along the c-axis direction. Secondly, Gu2O was prepared by electrodeposition method. The influence of the morphology, crystal structure, etc. by deposition voltage, pH value and deposition time, electrolyte temperature and other growth conditions was investigated in detail. Thirdly, ZnO/Cu2O heterojunction was obtained by growth Cu2O on top of the ZnO nanorod arrays, the gap between the ZnO nanorod arrays were filled. Finally, Au/Cu2O/ZnO/ITO heterojunction solar cells was assembled with good p-n junction characteristics, the photoelectric conversion efficiency of up to 1.2% was achieved, the corresponding open circuit voltage, current density was 250 mv,7.551 mA/cm2, respectively.The third part mainly deals with deposition of CZTS thin film on ITO or Mo substrate by single-step electrochemical deposition. Two kinds of electrolyte solutions with different concentration were studied. Experimental results show that, the best condition was 0.02MCuSO4,0.01MZnSO4,0.01MSnCl2,0.01MNa2S2O3,0.2M trisodium citrate,0.1M tartaric acid electrolytic solution at a constant voltage of-1.2V, deposition time 20min, and finally through annealing under N2 500℃ for 1h. The thus obiained films has compact surface, although there are some defects in the layer. The element ratio deviates from the ideal stoichiometric ratio, but the band gap was 1.5eV which confirms kesterite structure of CZTS thin film, thus can be used in the solar cell absorbent layer.The fourth part focused on sol-gel method combined with spin coating technique and heat treatment process to obtain CZTS thin films. CZTS film properties depend on different annealing temperature was investigated, the experimental results show that under N2 atmosphere and 450℃, diffraction peaks of XRD pattern corresponding to kesterite structure of CZTS (112) (200) (220) and (312) crystal surface. The surface of the film was rough and closely packed, although with some voids. The band gap of 1.49eV was deduced from UV-VIS spectra, confirms its good quality.The fifth part is summary and prospect, mainly summarize current work, and made the planning for the future work. |
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