Ultrafast Carrier Dynamic Of Binary Nanoparticle Superlattices Under High Pressure

Nanomaterials have been developed into many types,such as quantum dots(QDs),nanoparticles,nanofibers,nanotubes and nanofilms,etc.,which have a wide range of applications in energy,catalysts,and sensing.Due to the advantages of QDs with an adjustable bandgap,multiple exciton generation effects and strong compatibility,the photovoltaic conversion characteristics have attracted the attention of researchers.In nanomaterials,the photovoltaic conversion begins with the light-induced carriers,and then the photoelectric conversion efficiency depends on a series of dynamic processes before the charge separation.People have found a long-range carrier transport effects in the QD solids that are conducive to charge separation.This is mainly caused by the interparticle spacing in the quantum dot solid,which is far smaller than in the solution.Compared with the chemical methods,the high-pressure technology is a non-intrusive physical method for adjusting the interparticle spacing.Under the pressure,the interparticle spacing of the QD solid is reduced and the volume of QDs is compressed,which shortens the spacing and enhances the interaction between atoms,leading to the changes of the deformation potential energy.The electronic properties of materials are changed,and the electron delocalization of QDs increases with the pressure increased.Binary Nanoparticle Superlattices(BNSLs)based on QDs is a kind of QD solid material,which is conducive to long-range charge transport,resulting in improving the photoelectric conversion efficiency.In the work,the preparation conditions of BNSLs were studies.Besides,the interparticle spacing effect of CdSe/ZnS-QDs and the electron transfer process in BNSLs which consist of Au-nanoclusters(Au-NCs)and CdSe/ZnS-QDs were investigated under high pressure.The following results have been obtained:1.The experimental methods and conditions for preparing BNSLs were studies.In the experimental method,BNSLs that consisted of Au-NCs and CdSe/ZnS-QDs were prepared by the self-assembly.Some experimental factors affected the formation of BNSLs such as the evaporation rate of the solution and the size of the nanomaterials.2.The optical properties of CdSe/ZnS-QDs under high pressure dominated by the interparticle spacing effect were researched.In the pressure-dependent absorption and photoluminescence spectra,the absorption and photoluminescence peaks of CdSe/ZnSQDs appeared the blue-shift with the pressure increased,which was attributed to the quantum confinement effect of CdSe/ZnS-QDs.In the pressure-dependent photoluminescence lifetime measurement,the surface defect state of CdSe/ZnS-QDs affected the photoluminescence lifetime decay curve under different pressures.By comparing isolated and close-packed CdSe/ZnS-QDs,it is found that the interparticle spacing of CdSe/ZnS-QDs decreased with the pressure increased,which promoted the relaxation of excited state carriers through the surface states between the particles.3.The ultrafast electron transfer of BNSLs under high pressure was studied.In the steady-state pressure-dependent absorption and photoluminescence spectra,the absorption and photoluminescence peaks appeared the blue-shifted with pressure increased.Compared with the results of CdSe/ZnS-QDs,it was concluded that the optical properties of BNSLs were dominated by CdSe/ZnS-QDs.The results of the pressure-dependent ultrafast dynamic by pump-probe technology found that the defect state of CdSe/ZnS-QDs affected the electron transfer process between BNSLs,with the pressure increasing,the electron transfer process of BNSLs was accelerated.When the pressure reached 4.5 GPa,the electron transfer time showed the opposite situation with the pressure change which attributed to the defect state filled with electrons reached saturation.With the further increase of pressure,the defect states of CdSe/ZnS-QDs further increase and the electron transfer process of BNSLs further accelerates.In summary,the interparticle spacing of QDs and BNSLs can be adjusted by the pressure,which affected the electron delocalization of QDs and the electron transfer process in BNSLs.These research results are helpful to understand the carrier dynamics of the under the pressure changes or the extreme conditions.