Studies On The Surface Photoelectric Properties Of Zn₂SnO₄ Nanoparticles And Correlated Composites

Materials are the basis for human society to develop, especially, composites display their advantages outweighing their components. Developing and exploring novel composites are the focus in the investigation field of solar cells.Metal oxygen nanoparticles TiO₂ is a kind of photoelectric material, which is favored because of easy-obtain, cheap and stabilization. One-dimensional (1D) nanostructure TiO₂ materials such as nanotubes, nanowires have gained considerable attention for their brilliant prospects in photocalalyst, environment purification, solar cells, and gas and humidity sensor. Especially since Kasuga and his coworkers developed a simple method of hydrothermal synthesis and obtained TiO₂ nanotubes in 1998, researchers devoted more and more attention to this material. However, due to its wide bandgap (3.2 eV), TiO₂ is only sensitive to violent light, and it is easily to be eroded by light to result in short lifetime, therefore, there is need to develop new materials. Inverse-spinel Zn₂SnO₄ has high electron mobility, high electric conductivity and low visible light absorption, and it has lower rate of electron-hole recombination and longer lifetime of excited electrons than TiO₂ in dye-sensitized solar cells (DSSC), so it draws large attention to its investigation. On the other hand,α-Fe₂O₃ andα-Bi₂O₃ with narrow bandgaps (2.2 and 2.8 eV) are sensitive to visible light and have marvelous photovoltaic properties, which attract great attention to them: compounding with Zn₂SnO₄ could overcome their disadvantages and produce synergistic effect to result in enhanced photovoltaic properties.On the basis of the principle of SPS, the following is my work which is made up of three sections:In Chapter 2, three methods were employed to prepare Zn₂SnO₄ nanoparticles. X-ray diffraction spectroscopy (XRD), Raman spectroscopy, Scanning electron microscopy (SEM) and Photoluminescence (PL), Surface photovoltage spectroscopy (SPS) etc. were used to characterize the morphology and properties of samples. There is evident photovoltaic response in violent region.In Chapter 3, the composite ofα-Fe₂O₃/Zn₂SnO₄ was synthesized via a sol-gel route. Photoelectric properties are investigated by surface photovoltage spectroscopy and electric field-induced surface photovoltage spectroscopy. The photovoltaic response for the composite with the molar ratio 4:1 ofα-Fe₂O₃ to Zn₂SnO₄ without bias is similar to that for the pristineα-Fe₂O₃ under positive bias. The results show that the modification of Zn₂SnO₄ can significantly improve the surface photovoltaic response ofα-Fe₂O₃. The enhanced photogenerated charges separation could be ascribed to the good contact and energy level matching betweenα-Fe₂O₃ and Zn₂SnO₄. The high electron mobility and low rate of electron-hole recombination in Zn₂SnO₄ are also responsible for the improved photoelectric properties ofα-Fe₂O₃.In Chapter 4, tri-bandgap composites with the molar ratio 4:1 of Bi/Zn are prepared via compoundingα-Bi₂O₃ and Zn₂SnO₄ of a hydrothermal method. An evident photovoltaic response band in the wavelength range of 425-550 nm is observed for the composites, being in good agreement with the visible absorption band of the composites different from those of pristineα-Bi₂O₃ and Zn₂SnO₄. The electric-field induced surface photovoltage spectroscopy of the composites has a very strong intensity in whole absorption band. These phenomena are attributed to the small amount formation of an interfacial phase of Bi2Sn2O7 and the good contact, energy level matching among the three components. The interfacial phase results from some Bi³⁺ ions implanting the lattice of Zn₂SnO₄ to substitute Zn²⁺ ions, which is responsible for the observed green-yellow emission in photoluminescence spectrum of the composites.