Study On Structure Characterization And Photoelectric Properties Of ZnO And Cu₂O Films Synthesized By Electrochemical Deposition

As an n-type and Ⅱ-Ⅵ family semiconducting oxide, zinc oxide(ZnO) has been applied in many fields such as solar cells, sensors, filed emission displays, varistors and transparent electrodes, due to its excellent piezoelectric, catalytic and optical properties. Besides, the size and morphology of materials have major influence on the property of various devices, therefore the preparation of different sizes and shapes of ZnO materials by a controlled way has important practical significance. Meanwhile, the existence of oxygen vacancy and interstitial zinc atom make massive donor type intrinsic defects appear in the ZnO crystal lattice, which leads to the difficulties of the preparation of p-type ZnO. So it is hard to obtain the homogeneous p-n junction of ZnO. In order to realize the application of ZnO in photovoltaic filed, especially the practical application in light-emitting diodes and laser device, this project commit to study ZnO heterojunction.Cu2O is a kind of typical p-type semiconductor material. Due to the big absorption coefficient of visible light range and the high rate of energy transformation, Cu2O is the potential material for preparation of solar cell. Cu2O chosen as the material for preparing ZnO heterojunction has two reasons:On the one hand, Cu2O with the narrow bandgap has strong visible light response to improve the use efficiency of ZnO thin film for visible light, so that light absorption range of the composite film will be expanded; On the other hand, heterojunction formed in the interface between ZnO and Cu2O, is in favor of improving the separation efficiency of photoinduced electron and electron hole, which realize the enhancement of the photoelectric conversion efficiency of composite film.In this dissertation, the microstructure and photoelectric performance of ZnO thin film and Cu2O/ZnO composite film by electrochemical deposition have been systematically synthesized and investigated. The main results are as follows:1. Different morphology of ZnO thin films have been electrodeposited from an aqueous solution of Zn(NO3)2as electrolyte on ITO glass substrate by cathodic reduction method without any surfactants. ZnO thin films have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-Vis spectrometer. The results indicate that the morphology of ZnO films can be controlled by adjusting the concentrations of Zn(NO3)2solution, current density and solution temperature; ZnO thin films have strong light absorption in the range of UV band and show the quantum dimension effect at room temperature.2. Cu2O/ZnO composite thin film has been prepared on ITO glass substrate by two-step electrochemical deposition method, and its morphology, crystal structure and photoelectric properties have been characterized by using X-ray energy spectrum, X-ray diffraction (XRD), scanning electron microscope(SEM), UV-Vis absorbtion and electrochemical workstation. The results indicate that flaky ZnO and nanoparticles Cu2O can be composited well by electrochemical deposition at room temperature. Increasing current density can make Cu2O particles become larger and more, and changing solution temperature can alter the structure of Cu2O. Cu2O/ZnO composite films not only effectively broaden the range of visible light absorption, but also enhance the absorption intensity of ultraviolet light. When Cu2O is deposited by pulse deposition with current density of0.1mA/cm2, Cu2O/ZnO composite film has the largest photocurrent.