Preparation, Microstructure And Photoelectrical Properties Of New Ag-ITO Composite Films

Due to their unique photoelectrical properties, transflective and highly conductive composite films, composed of highly reflective and conductive metal and transparent conductive materials, could be widely studied for both theoretical and practical significance. A new type of transflective technology, which employs this kind of composite films as a lower-electrode material, will be indispensable in modern LCD industry.In this investigation, Ag-ITO composite films of different thicknesses were prepared. The microstructure, composition, photoelectrical properties of the films and their relationship were studied both experimentally and theoretically. In addition, a new criterion, based on efficiency factor and light splitting ratio, has been established for evaluating photoelectrical properties of transflective conductive films. The aim of the investigation is to explore novel photoelectrical functional films with transflective and conductive performance and to promote the application of Ag-ITO composite films in modern LCD industry.The main contents of the investigation are as follows:1. To design and characterize Ag-ITO composite film system, it is necessary to understand the microstructure and photoelectrical properties of the component materials in a state of low dimension. Therefore, Ag films of different thicknesses were prepared by DC magnetron sputtering. The microstructure, thickness and photoelectrical properties of prepared Ag films were studied by employing X-ray diffraction (XRD), stylus profiler, ultraviolet-visible spectroscopy and four-probe technique.2. ITO films were prepared by DC magnetron sputtering. The microstructure, chemical composite, thickness and photoelectrical properties of un/annealed ITO films were investigated by making use of X-ray diffraction, X-ray photoelectron spectroscopy (XPS), stylus profiler, ultraviolet-visible spectroscopy and four-probe technique.3. The DC magnetron sputtering method for preparing Ag-ITO composite films was explored, and Ag-ITO composite films of different Ag-layer thicknesses were prepared by the method. ITO content in the composite films, based on XRD results, keeps In₂O₃ crystal structure (bcc). With Ag-layer thickness increasing, the intensity of ITO (222) diffraction peak increases while (400) diffraction peak decreases as a whole. And only (111) diffraction peak (2θ=38°) of Ag can be observed.4. The photoelectrical properties of Ag-ITO composite films were studied by employing ultraviolet-visible spectroscopy and four-probe technique. As suggested by the results, the microstructure and thickness of Ag are vital to the photoelectrical behaviours of the composite films. With increasing Ag thickness, Ag transforms from granular to continuous state; the average transmittance and reflectance over visible range of the composite films increase, while average absorptance decreases; the electrical resistivity of the composite films decreases. Compared to that of the single-layer ITO film, the electrical resistivity of the composite film with 12.5-nm-thick Ag layer decreases by one order. The unique photoelectrical behaviours have been interpreted qualitatively by employing multi-beam transflectance and parallel electrical resistance theoretical model.5. Based on efficiency factor and light splitting ratio, a new criterion has been established for evaluating photoelectrical properties of Ag-ITO composite films and other transflective conductive films.The main innovations of the investigation are as follows:â—†A new type of transflective and highly conductive Ag-ITO composite films, composed of highly reflective and conductive Ag and transparent conductive ITO, have been prepared successfully. And their transflective and conductive performance can be controlled by altering the amount of Ag content. This kind of composite films could be applied in novel transflective LCD device as a lower-electrode material.â—†Employing Film Wizard and 1stOpt software, a new method for obtaining film thickness and optical constants has been raised by fitting transmittance spectra with multi-beam transflectance model.â—†A new criterion, based on efficiency factor and light splitting ratio, has been established for evaluating photoelectrical properties of Ag-ITO composite films and other transflective conductive films.