Electrochemical PreDaration Of Cu₂O Thin Films And Their Photoelectrochemical Properties

Generally,since Cu vacancies are present in Cu20 thin films,semiconductors often appear as p-type conductive semiconductors,while n-type Cu2O semiconductors are caused by oxygen vacancies,and are usually prepared by pulsed laser deposition,molecular beam epitaxy,solvent reduction,and the like.It is easy to obtain a p-type Cu2O film,but an n-type Cu2O semiconductor can be obtained by electrochemically adjusting parameters such as deposition voltage,solution temperature,and pH value.In this thesis,the conditions of electrochemical deposition of Cu2O semiconductor thin films are studied systematically,and their optical properties and photocatalytic mechanisms are characterized.Firstly,Cu2O thin films were prepared by electrochemical deposition method by controlling deposition voltage,deposition temperature,and solution pH value.The composition was characterized by XRD and the phase diagram of Cu2O electrochemical deposition was drawn.The electrochemical deposition of Cu,O film is first determined by cyclic voltammetry(CV),and then deposited by Au-plated silicon wafer in Cu(CH;COO)2-CH3COONa electrolyte system by constant pressure deposition.A Cu2O film was prepared.The Cu2O films prepared at different deposition voltages,deposition temperatures and solution pH values were systematically investigated.The effects of deposition temperature and photodeposition on the photoelectrochemical properties of Cu2O films were analyzed.The thesis explored the Cu2O film with different phases by adjusting the electrochemical experimental process parameters.According to the photoluminescence spectrum(PL)test,UV-vis absorption spectroscopy(UV-vis)test,photocurrent-time test(i-t)The photoelectrochemical properties of Cu2O films prepared under different conditions were analyzed by means of current-voltage test(I-V),Mott-Schottky test and alternating current impedance test(EIS).A detailed explanation is given.a)Effect of deposition temperature on Cu2O filmThe films prepared at different deposition temperatures(T=20?,40?,60?)are all Cu2o(111)phase.When the deposition temperature is 20?,the surface of Cu2O prepared is composed of irregular sheet structure.When it rises to 60?,the grain size distribution is more uniform and the film is flat and dense.PL measured Cu2O films are all n-type conductive semiconductors.Ultraviolet-visible absorption spectroscopy(UV-vis)test The optical band gap of Cu2O films prepared at different temperatures(T=20?,40?,60?)was Eg =1.7 eV,Eg 1.6 eV,Eg =2.0 eV.The photocurrent response of the Cu2O film prepared at 60 ? is the best.b)Effect of deposition voltage on Cu2O filmWhen the solution pH of 6.00 and the deposition temperature of 20?,there are three phases in the Cu20 film deposited at different voltages(V ?-0.05 V,V ?-0.10 V,V =-0.15 V.V =-0.20 V):Pure Cu-2O phase,Cu-Cu2O phase,Cu phase.PL measured Cu2O films are all n-type conductive semiconductors.Ultraviolet-visible absorption spectroscopy(UV-vis)test The Cu2O film prepared at different temperatures has a forbidden band width of 1.76 eV.c)Photoelectrocatalysis mechanism of Cu2O thin filmUnder illumination,at the n-Cu2O/electrolyte interface,electrons in the semiconductor Cu2O will transition from the valence band to the conduction band under the excitation of light,resulting in photogenerated electron-hole pairs.When a positive(negative)bias is added,it is equivalent to injecting electrons(holes)into the semiconductor,so that the width of the space charge layer is widened(narrow),and the larger the positive bias value,the larger the energy barrier difference is,the diffusion current is dominant;the larger the value of the negative bias is,the smaller the energy barrier difference is,the electron drift current is dominant,and the tunneling current is formed;when the drift current and the diffusion current in the semiconductor are balanced,positive and negative directions are added.The bias voltage causes the direction of the photocurrent to change.