Study On Preparation And Photoelectron Characteristics Of Cu Doped ZnSe QDs-sensitized Nano-TiO₂ Film

In this paper,La doped mesoporous TiO₂ nanocrystals are prepared by sol-gel method,and the corresponding mesoporous TiO₂ films are obtained with knife coating process.Then,Cu-doped ZnSe QDs was synthesized by aqueous phase synthesis at room temperature.A series of QDs was made by changing the molar ratio of Se and Cu as 10:1,20:1,30:1,40:1,and 50:1;the doping time after the reaction of Zn and Se precursor for0min,30min,60min,90min,120min and 160min;and different capping ligand as L-cysteine?L-cys?,mercaptoethylamine?CA?,glutathione?GSH?,and mercaptoethanol?ME?,respectively.And the photoelectron properties of quantum dots are studied,then,the main factors affecting their photoelectric properties are discussed,and the methods are optimized.On the base of these,quantum dots sensitized mesoporous TiO₂ heterostructure films are fabricated by chemical bath deposition.The photoelectric characteristics of the as-prepared samples are characterized by means of stationary surface photovoltage method,and the dynamic information about the separation,transmission and recombination of photoinduced charges are investigated through transient photovoltaic technology.The morphology,microstructure,phase composition and optical absorption properties are probed via X-ray diffraction,nitrogen adsorption-desorption isotherms,energy dispersive spectrometer,Fourier transform infrared and ultraviolet-visible absorption spectra.The experimental results show that the TiO₂ nanocrystals have a large specific surface area and a mesoporous structure with uniform pore size due to the introduction of La.In Cu-doped ZnSe quantum dots,the impurity energy levels exist as the acceptor shallow energy levels,which leads to the obvious quantum limiting effect and the weakening of the n-type photovoltaic properties of the quantum dots.The photogenerated free carrier lifetime and diffusion length of Cu doped ZnSe QDs are all imporoved as those of ZnSe QDs.The surface photovoltaic response of quantum dot sensitized thin films covers the wavelength range of 300-800nm.The sensitized films exhibit n-type photovoltaic properties,and the lifetime of photogenerated carriers increases by two orders of magnitude.The separation rate and diffusion length of photogenerated electron-hole pairs increase obviously.In addition,the specific surface area of TiO₂ thin films sensitized by Cu doped ZnSe QDs decreases,the photovoltaic response intensity is higher,and the maximum separation time is late,which indicates that the doping of Cu can prolong the carrier life of quantum dots.It also contributes to the deposition of quantum dots and thus increases the efficiency of photoelectron implantation into mesoporous nano-TiO₂ films.