Preparation And Properties Of CZTS/TiO₂ Nanotube Composites

Ti O2 nanotube array films have been extensively used in applications of gas sensor, photocatalysis and solar cells, ect. The properties of Ti O2 nanotube arrays can be improved via ions doping, noble metal depositing, narrow-band semiconductor loading. Recently, p-type semiconductor of Cu2 Zn Sn S4(CZTS), used as an absorber layers in thin film solar cells, is attracting immense interest, with the advantages of abundant element, low cost and high optical absorption coefficient. In this thesis, it is the first time that a series of CZTS/Ti O2 nanotube composites were fabricated via hydrothermal or ethanol-mediated solvothermal treatment, based on the crystallization of amorphous Ti O2 nanotube arrays prepared by anodization. The morphology, microstructures and photoelectrochemical properties of as-prepared composites were subsequently investigated.Firstly, the crystallization of amorphous Ti O2 nanotube arrays was achieved by strategies of calcination, water soaking, hydrothermal or vapor-thermal treatments. The effect of the crystallization form, especially the low-temperature crystallization, on the morphology, microstructures and photoelectric properties of the dye-sensitized solar cells(DSSCs) was comprehensively investigated. The results showed that the crystal structures of Ti O2 nanotube arrays were greatly influenced by the annealing process at different temperatures. The water soaking resulted in the crystallization of the amorphous Ti O2 on the tubular mouth, possibly owing to the limited flow behavior of water in nanoscale-tube during the water soaking process. The tubular morphologies of amorphous Ti O2 nanotube arrays were completely destroyed by hydrothermal treatment. Although only aggregated anatase particles were observed, the highest photoelectric properties of as-assembled DSSCs were obtained. It was also found that the vapor-thermal treatment, which still remain the tubular morphology, apparently give rise to the efficient crystallization of amorphous Ti O2 nanotube arrays.Secondly, by using amorphous Ti O2 nanotube arrays as the raw material, CZTS/crystalline Ti O2 nanotube composites were prepared through one step hydrothermal or ethanol-mediated solvothermal route. However, in both cases, the impurity of Cu S appeared on the sample synthesized in either low concentration of precursor solution or short reaction time. The redundant second phase would weaken the photoelectrochemical performance drastically.Finally, CZTS/Ti O2 nanotube composites with different morphologies were obtained with various crystallizing treatments of Ti O2 nanotube. In hydrothermal process, the Ti O2 nanotube with vapor-thermal crystallizing treatments remained the original morphology. The CZTS nanoparticles were found to aggregate on the surface of Ti O2 nanotube arrays. Remarkably, high photoelectrochemical properties were achieved, owing to high specific surface area of the unique structure. Furthermore, by using crystallized Ti O2 nanotube arrays pretreated with calcination as the raw material, the “leaf-like” CZTS crystals loaded on Ti O2 nanotube arrays were also prepared after a subsequent ethanol-mediated solvothermal treatment of Ti O2 nanotube arrays. Such special morphology has benefited on the CZTS inside of nanotube arrays to absorb sunlight efficiently, leading to the highest photocurrent density obtained as expected.