Luminescence Dynamics Study Of Perovskite Micro-crystals

In recent years,due to low-cost fabrications and outstanding optoelectronic properties,perovskites with direct band gaps have attracted extensive attentions from researches of photovoltaic and luminescence.However,the solution-fabricated perovskite crystals usually contain abundant lattice defects because of low crystal nucleus formation energy.These defects tend to form carriers trap states in momentum space.The carrier trap states caused by lattice defects could heavily dissipate energies of photocarriers into heat through non-radiative recombinations,which is a serious problem for photovoltaic and luminescence applications of perovskites.On basis of understanding the formation mechanism of lattice defects,revealing the mediation mechanism of trap states and their spatial distributions imposed on the photocarrier recombination dynamics is fundamentally important.Such efforts will significantly contribute to constructing physical models of perovskite-based photovoltaic devices as well as improving their performances,which can even provide theoretical and experimental supports for developing novel functionalities beyond.To reveal the spatiotemporal mediation mechanism of carrier trap states imposed on photocarrier dynamics,we comprehensively employed steady photo-luminescence（PL）,micro-absorptance spectroscopy,time-resolved PL and pump-probe spectroscopy techniques.Comparing with electrical methods,our spectroscopy techniques not only possess unique advantages such as non-invasive,fast and non-contact,but also undertake high temporal and spatial resolutions.Based on construction of optical spectroscopy systems and fabrications of defect-rich perovskite micro-cystals via solution methods,we study and elucidate trap-state-mediated ultrafast photocarrier dynamics.Meanwhile,we investigate the all-optically active control of photocarrier dynamics through collective interactions between localized surface plasmon of Au nanoparticles and trap states of perovskite surface regions.Then,we develop a new all-optical technique,which is named as spatiotemporal sectioning of two-photon fluorescence ellipsoid with a perovskite nanosheet.In specific,original researches of this dissertation include the following contents:1.Constructing optical spectroscopy systems for luminescence dynamics study of perovskites,that are micro-PL,micro-absorption,time-resolved micro-PL and femtosecond laser pump-probe systems.2.Studying spatial distribution of carrier trap states and trap-state-mediated photocarrier dynamics in perovskite microplates.Firstly,by using time-resolved PL（TRPL）spectra technique,it shows that the long and short lifetimes originate from unequal trap densities in bulk and surface regions,respectively.Besides,trap state densities in surface region are one order of magnitude higher than that in bulk region.Furthermore,with TRPL and femtosecond laser transient absorption spectra,dynamical competition processes of photocarrier dynamics between bulk and surface regions are elucidated.Results have shown that hot carrier energy can transfer from surface to bulk region within 20 ps when carrier trap states in surface region are completely filled,resulting in an enhanced PL emission in bulk region of perovskite microplates.3.Actively controlling luminescence dynamics in surface region of perovskite micro-crystal by localized surface plasmon.To achieve this propose,we constructed the Au-Cs Pb Br₃interface,regulating the carrier dynamics process in surface region of perovskite micro-crystal.Results have shown that,Au nanoparticles can regulate the carrier dynamics process in surface region of perovskite micro-crystal by physical channel of plsmon-induced hot carrier transfer and plsmon-induced resonant energy transfer,which can modulate photocarrier lifetimes and PL intensities of perovskite micro-crystal.4.Developing a new spatiotemporal sectioning technique with perovskite nanosheets.Utilizing a Cs Pb Br₃ nanosheet,nanoscale spatial scanning and picosecond resoltion of time-resolved TPF spectra are simutaneously achived.So we are able to reconstruct the spatiotemporal evolution of TPF ellipsoid along axial direction.Not limited to perovskite,such technique can be applied to other TPF materials,and set a solid foundation for spatiotemporal sensing and imaging applications.In conclusion,we employ steady-PL,time-resolved PL and transient absorption techniques to study trap-state-mediated luminescence dynamics in perovskite crystal;investigate the active control of luminescence processes via surface plasmon.Last but not the least,a spatiotemporal sectiong technique demonstrated by a perovskite nanosheet is developed.These original work spatiotempoally elaborate the mediation mechanism of carrier trap states imposed on photocarrier dynamics.Our researches can not only provide theoretical and experimental backups for improving perovskite-based devices,but also establish a general approach to quantitatively investigating fluoresence processes mediated by trap states for semiconductors.