Study Of The Ultrafast Process Of Charge Transfer In Solar Cell Systems

The application of perovskite materials and surface plasmons to the design of solar cells has become a hot spot for the rapid development of photovoltaic research internationally.The key factors affecting the photoelectric conversion efficiency of solar cell systems include performance of carrier separation and charge transfer.Femtosecond time-resolved ultrafast spectroscopy provides a very sensitive and effective experimental method to study the processes of generation,separation,migration and recombination of photo-excited carriers in photoelectric conversion materials and devices.At present,there are few studies of interfacial carrier separation and charge tranfer of all-inorganic perovskite solar cell materials,and the physical mechanisms are still unclear.Whether the plasmon effect can play a positive role in the photoelectric conversion has been controversial.Is the enhancement of photoelectric conversion efficiency due to the charge transfer caused by the thermal motion of electrons or the direct electron injection from the precious metal into the corresponding receptor?The study is of great practical significance for improving the photoelectric conversion efficiency of solar cells.The experimental method proposed in this paper is femtosecond time-resolved ultrafast spectroscopy,which is used to study the ultrafast process of charge transfer in all-inorganic perovskite CsPbBr₃ or noble metal assembled with semiconductors systems.In order to complete the above experiments,we have done the following research works:（1）All-inorganic perovskite material（CsPbBr₃）was synthesized by sintering method and assembled with different semiconductors（TiO₂,SnO₂,ZnO）.In order to further explore the separation and transmission process of photogenerated carrier in this systems,we used femtosecond time-resolved spectroscopy to detect their ultrafast spectra and ultrafast dynamics,and combined with singular value decomposition and global fitting to analyze the measured data.Four dynamic processes were obtained,which were attributed to hot carrier cooling,free exciton formation,charge transfer,and charge recombination process.By comparing of the time constants of the four dynamic processes of different systems,effects of semiconductor species on carrier separation and transport at the interface were discussed and analyzed,the charge transfer mechanism models of the CsPbBr_3/Semiconductor systems were proposed.Our work provides an effective experimental basis for a further discussion of the interfacial charge transfer mechanism of all-inorganic perovskite battery materials.（2）Semiconductor（TiO₂,SnO₂,ZnO）thin films were synthesized by the doctor blade method and then assembled with precious metal gold nanoparticles.Femtosecond time-resolved infrared transient absorption spectroscopy was used to detect their ultrafast kinetic processes.Injection of the free electrons from gold nanoparticles to the conduction bands of different semiconductors（TiO₂,SnO₂ and ZnO）were observed directly upon excitation of the plasmon band of gold nanoparticles,Furthermore,the effects of semiconductor species on electron injection efficiency and charge recombination lifetime are discussed in detail.