| The development and promotion of clean renewable energy has already been one of the effective ways to solve the increasingly serious energy shortage and environment pollution problems.Application of low cost,high efficiency solar cells can be considered as a promising direction of photovoltaics.However,people still cannot simulate photosynthesis under normal temperature or atmospheric pressure due to the limitation of recognization,and still many details cannot explain.It's true that the static equilibrium structure of the molecules has already been well known,the efficient solar cells can be designed only by exploring the detailed microcosmic steps of the conversion of solar energy into chemical energy.Ultrafast time-resolved spectroscopy is needed in order to explore the dynamics and monitor the photochemical process which leads to the change of the molecular structure in real time.However,our university have almost no person focused on this field,which seriously hinders the development of high quality and high level research projects,so it is very urgent to build our first ultrafast time-resolved laser spectroscopy platform.Porphyrin-based surface mounted metal organic frameworks?SURMOFs?may serve as a model for simulating the natural photosynthesis with highly ordered chlorophyll,i.e.,porphyrin-like chromophores.As the primary event of photosynthesis,the study of light harvesting and energy transfer are of great importance leading to improvement of photovoltaics overall performance.Perovskite solar cells based on organic-inorganic hybrid perovskite materials have aleary been the focus topic all around the world due to their excellent light absorption capacity,long carrier lifetime,high carrier mobility,good photoelectric efficiency and simple manufacturing technology.We have built the first ultrafast laser spectroscopy platform in Dalian University of Technology cooperate with professor Gagik Gurzadyan.As the first student of Prof.Gurzadyan,I was involved and responsible for the purchase,bidding,procurement,installation,training and maintenance of all the equipment and consumables of this platform.Nowdays,this platform can monitor solar cells,functional dyes,organic crystals,films,powders and nanomaterials in real time.The successful construction of this platform is the prerequisite of the beginning of my thesis,which also fills the gap in the field of ultrafast dynamics of our university,and can be used in many fields,such as physics,chemistry,biology,materials and nanoscience,and undoubtfully will further strengthens our ability in the field of ultrafast molecular dynamics.In this thesis,we have also performed a detailed study and have systematically summarized the ultrafast spectroscopic data of porphyrin SURMOFs films and organic-inorganic hybrid perovskite solar cells by using various ultrafast spectroscopic techniques,i.e.time correlated single photon counting,ultrafast fluorescence up-conversion and femtosecond pump-probe transient absorption.By analysing the fundamental photophysical processes,such as the excited state relaxation,energy and charge transfer,we can draw the flowing conclusions:1.Study of the excited state dynamics of zinc tetraphenylporphyrin?ZnTPP?SURMOF film and ZnTPP in solution demonstrate that upper excited singlet state S2 band is red shifted and spectraly broadened.Moreover,dramatic quenching of both upper excited singlet state S2 and first excited state S1 was observed.This phenomenon is?FRET?between the neighboring porphyrin moieties due to a strong spectral overlap of absorption and steady-state fluorescence spectra of porphyrins and quantum coherent energy transfer.2.In free base tetraphenylporphyrin?H2TPP?SURMOF films,by comparing with H2TPP in solution,we have observed both strong increase of quantum yield and lifetime of Soret band fluorescence?S2?S0?in SURMOFs films.Moreover,Q-band?S1?fluorescence was strongly quenched compared with its solution.Transient absorption results are in good agreement with S1 and S2 fluorescence data.These phenomena are explained in terms of alignment of the vibrational levels of the Franck-Condon active modes of the B,Qy,Qx states as well as by the coupling of these modes to the dissipative environment.Above ultrafast spectroscopic studies are useful for deep understanding of energy relaxation and transfer dynamics in SURMOFs as light harvesting devices.3.Ultrafast spectroscopic study of CH3NH3PbBr3 perovskite solar cells shows excited state dynamics with four exponentials:200 fs,30 ps,500 ps,2-10 ns.The lifetimes of fluorescence were found to be wavelength dependent.The hot fluorescence decay kinetics we explain with the following model:cooling of hot exciton and/or hot carrier in valance band and conduction band?200 fs?,relaxation of exciton after cooling in conduction band?30 ps?,collection of free carriers and relaxation to a“cold”exciton?500 ps?,recombination of free carriers?2-10 ns?.Kinetics study of CH3NH3PbBr3 films is a valuable asset for its model of carrier relaxation and transport dynamics,and undoubtfully will provide important guidance for optimizing CH3NH3PbBr3 perovskite based solar cells. |
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