Research On Femtosecond Electron Lifetime In Au-TiO₂ Nanoparticle System

Solar energy is a new kind of energy,which is clean,abundant and widely spread,so the research on solar energy conversion devices has been a hot topic.Nowadays,traditional solar cells still have the disadvantages such as high production cost,narrow absorption range of solar energy spectrum.A new generation of solar cell based on plasmon has the characteristics of wide absorption range and large absorption cross section.It conquers the disadvantage of low conversion efficiency of traditional solar cell.But the research on plasmon solar cell is still in the preliminary stage,its photon-to-electron conversion efficiency is not so high as traditional solar cells,and a measurement of electron lifetime of materials is of vital importance to increase the photon-to-electron conversion efficiency.In this thesis,we perform an investigation on the electron transfer process in Au-TiO₂ nanoparticle system for plasmon solar cell.First,by comparing the electron yields of TiO₂ nanoparticle and Au-TiO₂ nanoparticle system under the same excitation condition,we confirmed that the process of electron transfer from Au nanoparticle to TiO₂ nanoparticle occurs in the system.We demonstrated the physical mechanism of electron transfer process by qualitatively description of the processes of electron excitation in Au nanoparticle,electron transfer from Au nanoparticle to TiO₂ nanoparticle,and electron emission from TiO₂ nanoparticles.Second,by studying the wavelength dependence of multi-photon electron emission process of Au nanoparticle and TiO₂ nanoparticle,we get the order of multi-photon electron emission of these two nanoparticles respectively,and obtained the work function of Au nanoparticle is between 4.65 eV and 4.71 eV,the minimum energy needed for multi-photon electron emission process in TiO₂ nanoparticle is between 4.59 eV and 4.65 eV.These results are necessary for measuring the electron lifetime of Au-TiO₂ nanoparticle system by femtosecond laser pump-probe technology.Finally,we combined photon emission electron microscopy and femtosecond pump-probe technology to measure electron lifetime in the experiment.Based on the electron excitation,transferring and emission processes in Au nanoparticle,TiO₂ nanoparticle and Au-TiO₂ nanoparticle system,we successfully measure the electron lifetime of Au nanoparticle,TiO₂ nanoparticle and Au-TiO₂ nanoparticle system,respectively.Experimental results indicate that there are two decay processes,a slow and a fast decay process,respectively,for the electrons on the intermediate states of Au nanoparticle,and electrons in the conduction band of TiO₂ nanoparticle as well as Au-TiO₂ nanoparticle system.Fundamental data of electron lifetime of Au nanoparticle,TiO₂ nanoparticle and Au-TiO₂ nanoparticle system are of great importance to obtain the electron transfer between Au and TiO₂,the work in this thesis is an important step towards a realization of high photon-to-electron conversion efficiency of plasmon solar cells..