The Study On Preparation And Photoelectric Properties Of CdSe/TiO₂ Nanosheet Thin Films

Anatase TiO₂ nanosheet array has a huge potential in the field of photoelectric conversion because of its large specific surface area and high proportion of active facets?001?,which greatly increases its sensitivity to sunlight and improves the efficiency of electronic transmission.However,the band gap of TiO₂ is so large?3.2 eV?that it only responds to the ultraviolet light,which limits the application of TiO₂ in the field of solar cell.In this experiment,the electrochemical deposition method was used to prepare CdSe/TiO₂ nanosheet thin films in order to increase TiO₂ response under the visible light exposure and improve its photoelectric properties.?1?The TiO₂ films were prepared on the FTO conductive glass substrate by hydrothermal method.The influence of reaction time,titanium concentration,urea content and acidity on the morphology of TiO₂ nanosheets was investigated.The optimum proportion of the reaction solution is 30 mL of concentrated hydrochloric acid,30 mL of deionized water,1.5 mL of tetrabutyl titanate,0.8 g of urea and 0.8 g of ammonium hexafluorotitanate,at 180 ? hydrothermal treatment for 18 h.XRD measurement shows that the anatase TiO₂ nanosheets are of high crystallization.The UV-visible absorption spectra show that the TiO₂ nanosheet films only respond to the UV light.Their band gap is calculated as3.21 eV according to the Kubelka-Munk formula,which consists with the intrinsic band gap of anatase TiO₂.?2?CdSe/TiO₂ nanosheet thin films were prepared by depositing CdSenanoparticles on anatase TiO₂ nanosheet films with?001?facets dominated.The influence of SeO₂ concentration and deposition time on the morphology and photoelectric properties of CdSe/TiO₂ nanosheet thin films were studied.The results show the CdSe/TiO₂ nanosheet thin films achieve optimum photoelectric properties when prepared with-0.9 ^-0.3 V of electrodeposition potential vs Ag/AgCl,4 mmol·L^-1 SeO₂ and 4 cycles of voltammetry.The photocurrent density of the CdSe/TiO₂ nanosheet thin films prepared under optimum conditions is 3.14 mA·cm^-2 and the photoelectric conversion efficiency reaches2.87%.?3?Under the protection of Ar atmosphere,the CdSe/TiO₂ nanosheet thin films prepared under the optimum conditions were annealed at 150,250,350 and 450?.The influence of annealing temperature on morphology and photoelectric properties of CdSe/TiO₂ nanosheet thin films was investigated.The results show that with the increase of annealing temperature hexagonal phase CdSe nanoparticles are agglomerated and grown;the degree of crystallization is increased;the absorption spectra appears red shift and the band gap reduces from 2.52 to 2.06 eV;the photocurrent density of CdSe/TiO₂ nanosheet thin films increases from 2.92 to 6.96 mW·cm^-2,but the open circuit voltage reduces from 1.18 to 0.78 V;at the same time,the fill factor reduces from 0.83 to 0.37,which leads to photoelectric conversion efficiency decreasing from 3.12% to 2.02%.In this experimental condition,the optimum annealing temperature of CdSe/TiO₂ nanosheet films is 150 ?.The photoelectric conversion efficiency reach 3.12%.