Preparation And Characterization Of Multilayer Transparent Conductive Films Based On D/M/D Structure

Transparent conducting oxides?TCOs?thin films exhibits high electrical conductivity as well as high transparency in the visible solar spectrum and high reflectivity in the infrared region.TCOs are widely used in opto-electronic devices,such as solar cells,and panel displays,electrochromic devices,liquid crystal displays,and so on etc.Indium tin oxide?ITO?with a high transmittance?of ⁸0%?and a low electrical resistance of?¹0-5W×cm?has been currently used as transparent conducting electrode.However,indium is rare and toxic,which limits restricts its applications.Thus,there it is an interest in of significance to searching for cheaper materials with good opto-electrical properties.Contending indium-free transparent conductors include indium-free transparent conductive oxides,graphene films,and carbon nanotubes.In recent years,the wide bandgap semiconductor ZnO materials become really hot in optoelectronic field.Especially,Al-doped transparent conductive film?AZO?and Ga-doped transparent conductive film?GZO?will gradually replace ITO films.However the crystal quality is poor when preparing AZO and GZO films by magnetron sputtering.The great influence of the substrate temperature and the annealing conditions are hard to deal with,so it is difficult to satisfy the requirements of quality transparent conductive thin film.Recently,multilayer coatings of the Dielectric/ Metal/Dielectric?D/M/D?have been investigated to develop a transparent composite electrode with the desired electrical conductivity.In comparison,the D/M/D multilayer has low sheet resistances,and high transparencies transparence.The addition of a thin metal layer in the middle will decrease reduce the effective resistivity of the multilayer without much loss in optical transmittance.The top dielectric layer can suppress the reflection from the metal layer and obtain a higher transparent effect.In this work,highly transparent indium-free composite electrodes of TiO₂/Cu/TiO₂ and ZnO/Mo/ZnO have been are deposited by electron-beam evaporation.The effect of Cu layer thickness and post-annealing on the structure,surface morphologies,optical and electrical properties of D/M/D films.Surface roughness was determined and surface images were is taken by field emission scanning electron microscope?FE-SEM?;the crystal orientation of the films was investigated by X-ray diffraction?XRD?;the sheet resistance?RS?was measured using four-point probe method;carrier concentration was measured by Hall effect measurement system;optical transmittance was measured in the a range of 300-800 nm by an ocean optics double channel spectrometer?model Lambda-1050?.The specific research contents and results are as follows:1)TiO₂/Cu/TiO₂ transparent conductive electrodes have been are prepared by electron beam vapour deposition apparatus at room temperature.The thickness influence on the structure,electrical and optical properties are studied.It indicated that the critical thickness of Cu mid-layer to form a continuous conducting layer is found to be 11 nm.The multilayer with a mid-Cu thickness of 11 nm has been is optimized to obtain a resistivity of 7.4×10-5 W×cm and an average optical transmittance of 86% in the visible spectral range.2)The TiO₂/Cu?11nm?/TiO₂ thin film was annealed at diverse temperatures in air for 0.5 hour in air.It indicated that the figure of merit of the TiO₂/Cu?11nm?/TiO₂ multilayer annealed at 150? has reached reaches a minimum resistivity of 5.9×10-5 W×cm and an average optical transmittance of 88% in the visible spectral range.3)ZnO/Mo/ZnO transparent conductive electrodes have been are prepared by electron beam vapour deposition.Composite film was annealed at diverse temperatures in air for 1 hour in air.The annealing temperature influence on the structure,electrical and optical properties are studied.The experimental results indicate that all films have strong ZnO?002?preferential orientation.With the increase of annealing temperature,the crystallization,gain size and surface roughness increase.In addition,the optical transmittance first increase and then decrease,the resistivity first decreases and then increases.The figure of merit of the ZnO/Mo/ZnO film annealed at 250? reached a minimum resistivity of 1.71×10-4 W×cm and an average optical transmittance of 80% in the visible spectral range.The experimental results indicate that ZnO/Mo/ZnO films are attractive candidates as transparent electrode for solar cell and other display application.