Tuning Resistivity And Transmittance Of TCO Films Through Varying Oxygen Vacancy

The transparent conductive oxide film（TCOs mainly includes three basic systems of indium oxide In₂O₃,tin oxide SnO₂ and zinc oxide ZnO）is an optoelectronic material capable of perfectly combining optical transparency and electrical conductivity.Due to its optical and electrical characteristics,it is widely used in many fields,such as touch screen,photocatalysis,pressure sensitive devices,gas sensors,solar cells and so on.Therefore,it is the pursuit of the researcher and manufacturer to adjust the light transmittance and resistivity to achieve the required performance.Zinc oxide films,aluminum-doped zinc oxide（AZO）films and indium trioxide（In2O3）films were prepared on a glass substrate by RF magnetron sputtering powder target at room temperature.The photoelectric properties of the films were regulated by controlling the preparing oxygen partial pressure,deposition voltage,annealing oxygen partial pressure,annealing temperature,pH value in electrolysis,and construction of three-dimensional systems.The micro-structure and photoelectric properties of the films were characterized by Scanning Electron Microscopy,X-ray Diffractometry,Raman Spectroscopy,UV-visible Spectrophotometer and Hall Effect Meter.The main results are as follows:（1）The AZO film annealed in the given oxygen partial pressure still has a c-axis preferred orientation of the hexagonal wurtzite structure,and the surface of the film is dense and smooth.With the decrease of the oxygen partial pressure in the annealing process,the particle size of the film surface gradually decreases,and the light transmittance and the resistivity decreases gradually.As the annealing temperature increases,the surface morphology of the film does not change significantly,and the light transmittance decreases slightly,and the resistivity gradually decreases.When annealed at 450℃,the carrier concentration of AZO film increases to 1.86×10²⁰/cm³,and the resistivity of AZO film decreases to 1.42×10^-2Ω·cm.（2）Oxygen Vacancy in AZO film used as the cathode material of the electrolytic cell is regulated by hydrogen evolution during water electrolysis.The optical and electrical properties of the AZO film depend on the electrolyzing voltage,electrolyzing time,and electrolyzing temperature under the deionized water electrolysis.As the pH of the electrolytic Zn（NO₃）₂ solution decreases,the transmittance and the resistivity of AZO film change significantly.When pH is 5,the photoelectric properties of AZO film are the most excellent,with the light transmittance reduced from 91.3%of the original AZO film to90.1%,and the resistivity reduced from the original 7.1×10^-1Ω·cm to 3.7×10^-3Ω·cm.As the electrodepositing voltage increases in zinc chloride solution,the increasing zinc deposited on the surface of the film leads to the light transmittance reduction from 92.8%to 77.9%,and the resistivity reduction from 3.3×10^-2Ω·cm to 2.9×10^-3Ω·cm.（3）Both the transmittance and the resistivity of In₂O₃ film with a rough surface deposited in the pure Ar are lower than that of In₂O₃ film deposited in the O₂:Ar of 1:10.After annealing,In₂O₃ film deposited in the pure Ar has a higher degree of crystallinity,which makes the transmittance increase from 84.31%to 87.349%and the resistivity increase from 7.15×10^-4Ω.cm to 9.75×10^-3Ω.cm.Under the same oxygen partial pressure conditions,the annealed In₂O₃ film has the higher transmittance and lower resistivity than the as-prepared In2O3 film.The comprehensive photoelectric performance of In2O3 film could be optimized by the electrodeposition of nano-sized Sn layer in SnCl₄ solution with the deposition voltage of 2 V.The light transmittance of the film changes lightly while the resistivity decreases significantly.Oxidation annealing after deposition of Sn could improve the light transmittance of the composite film with the increasing resistivity.（4）A three-dimensional ZnO photo-electrode structure with two-dimensional nano-film and one-dimensional nano-pillars was constructed.The increase of sputtering power of the film layer results in a decrease in optical band gap;The Al with an effective doping in the nano-pillars could reduce the width of band gap;Co-annealing the aluminum-doped ZnO nano-pillars on AZO film could reduce the width of band gap of three-dimensional ZnO more effectively and achieve a good match between the two-dimensional current-collected layer and the one-dimensional photo-activated layer.