Study On The Surface Photovoltage Properties Of ZnFe₂O₄, CaFe₂O₄and Their Composites

The study showed that the optical and electrical properties of the composites have more advantagesthan that of a single semiconductor, which is useful for later developments in the field of solar cells andphotocatalysis. TiO₂as a metal oxygen nanoparticle is an important photoelectric material，there is a lot ofadvantages, such as easy-obtain，cheap and stabilization．One-dimensional （1D） nanostructure TiO₂materials such as nanotubes，nanowires attracted considerable attention for their brilliant prospects inphotocalalyst，environment purification, solar cells，and gas and humidity sensor．Especially, since Kasugaand his coworkers developed a simple method of hydrothermal synthesis and obtained Ti02nanotubes in1998，researchers devoted more and more attention to this material．However, due to its wide bandgap（3.2eV），Ti02is only sensitive to violent light，and it is easily to be eroded by light to result in short lifetime，therefore，The development of the new photoelectric materials is a question for study or discussion. Bandgap values of the p-CaFe₂O₄and ZnFe₂O₄are both about1.9eV, there are a large part of the absorption ofvisible light, the optical and electrical properties of the former are not very good, but the p-typesemiconductor material itself is few, so there are many people are attracted attention. The p/n typecomposite materials can significantly enhance the optical and electrical properties of the oxides; optical andelectrical properties of the latter are well, while there is no obvious improvement for the composite system,which is of a great inspiration to study the photoelectric performance of composites.The following chapters were introduced in this paper:In the second chapter, we get ZnFe₂O₄and TiO₂nanoparticles with the sol-gel method which arecharacterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, absorption spectroscopy,surface photovoltage spectroscopy （SPS） and other technology on the preparation of the morphology,structure and optoelectronic properties of the materials. The study found that ZnFe₂O₄has strong photoelectric response in the visible region, while TiO₂only has photovoltage response in the ultravioletregion, almost no response in the visible region. With the external field effect, the photovoltages ofZnFe₂O₄and TiO₂nanoparticles enhanced with the increasing of positive bias, which validated that theZnFe₂O₄and TiO₂are n-type semiconductor materials.In the third chapter, we put ZnFe₂O₄into a colloidal solution of TiO₂, to get the ZnFe₂O₄/TiO₂（1:2）composite materials, which were characterized by XRD, SEM, UV-vis and SPS tools, the results indicatethat the complexes have photovoltage response in the ultraviolet and visible region, while which are notenhanced and broaden in contrast with that of ZnFe₂O₄, which indicates that ZnFe₂O₄and TiO₂compositesdo not enhance the charge separation efficiency, but also to verify the level matching is selective.In the fourth chapter, we use the sol-gel method to get different proportions of p-CaFe₂O₄/n-WO₃composite system, and study their optical and electrical properties. p-CaFe₂O₄/n-WO₃（1:1,1:2and2:1）composite materials have a strong photovoltaic response in the wavelength range350-600nm. We study thephotoinduced charge separation mechanism with the field-induced photovoltage spectroscopy （EFISPS）,which prove that the energy level of p-CaFe₂O₄and n-WO₃can match and achieve effective electronictransfer.ZnFe₂O₄, TiO₂, ZnFe₂O₄/TiO₂, CaFe₂O₄, CaFe₂O₄/WO₃composites were synthesized by theconventional solid state reaction and the sol-gel method in this work, the X-ray diffraction （XRD）,scanning electron microscopy （SEM）, fluorescence spectrometer, UV-visible absorption spectroscopy andsurface photovoltage spectroscopy and field-induced photovoltage spectroscopy and other means of testingthe sample crystal structure, surface morphology, light absorption properties, and surface photovoltageproperties were studied.