Enhanced Near-infrared Amplified Spontaneous Emission In Solution-processed Perovskite Films Via Employing Polymer And Gold Nanorods

In recent years,metal halide perovskites have attracted attention from academics as its excellent photoelectric properties,including high extinction coefficient,long and balance of exciton diffusion distance,high and balance electron-hole mobility,low density of defects,high tolerance for defects,tunable band gap,tunable nanostructure,processing technology diversification,etc.In addition,considerable progress has been made in the study of perovskite materials.However,there are several aspects need to be considered to realize the commercialization based on perovskite materials,including thermal stability and photostability,lead toxicity problems,inside charge recombination kinetics,nanostructure refer to its photoelectric performance.Until now,as a kind of high extinction coefficient material,the precondition for the occurrence of lasing,the lasing properties of perovskite thin films have been rarely reported.Therefore,in this article,we aim to combine the properties of the high extinction coefficient of perovskite materials with the effect of polymer/metal nanoparticles on the photoelectric properties of perovskite materials to research inside charges recombination kinetics.The lasing behavior of MAPbI₃ perovskite films,how to enhance its lasing properties,and the inside free carrier recombination kinetics related to its lasing behavior are investigated,which fills in the blank of perovskite materials in laser applications and further deepens people's understanding of the photoelectric properties of perovskite materials.Specifically:In the third chapter,we prepared MAPbI₃ perovskite thin films with lasing properties by"two-step"fabrication method and then enhanced the lasing properties by employing PMMA and Au-NRs which means to reduce the lasing threshold and to improve the lasing intensity.By utilizing PMMA,the surface defects of MAPbI₃ perovskite films could be passivated through the interaction between C=0 and I-,as well as the filling of I vacancy by C=0,so as to reduce the non-radiation recombination inside the MAPbI₃ perovskite films and dissipate more excited energy in the form of radiation transition.The lasing intensity of MAPbI₃ perovskite film was increased by 5.8 times after PMMA modification.In addition,PMMA acted as an insulating layer,effectively blocking water and oxygen,preventing the erosion of MAPbI₃ perovskite film by atmospheric water and oxygen,greatly improving the stability of MAPbI₃ perovskite film in humidity environment?30.5%?.By using gold nanorods,both excitation efficiency and emission efficiency could be enhanced since the local surface plasma resonance?LSPR?effects of gold nanorods,which results from the coupling between longitudinal LSPR peaks?775 nm?and the fluorescence peaks?770 nm?of MAPbI₃,together with the high overlap between lateral LSPR peak?520 nm?and the absorption spectrum of MAPbI₃ perovskite.As a result,the lasing threshold could be reduced from 26.5 to 16.9 and the lasing intensity of MAPbI₃ perovskite films could be improved 13.9 times.In the fourth chapter,by employing time-resolved photoluminescence?TRPL?transient absorption test?TA?and pump-probe,we investigated the free carrier recombination kinetics inside MAPbI₃ perovskite films under excitation before and after lasing threshold and also the free carrier recombination kinetics with and without PMMA and gold nanorods modification.Finding that 1)the free carrier recombination was dependent on excitation power,indicating that the fluorescence emission of MAPbI₃ perovskite film was consistent with the free carrier recombination model.2)the excited state accumulation of MAPbI₃ perovskite films decreased from 14.9ps under excitation lower than lasing threshold to 300fs under excitation greater than the lasing threshold,indicating that when the excitation power greater than the lasing threshold value,the faster free carrier accumulation and less optical loss happened inside the MAPbI₃perovskite films,which was the direct evidence of the avalanche effect of electrons.3)with the modification from PMMA,the life of free carriers became longer,from 2.26 ns to 2.78 ns,which was the direct evidence of the passivation of PMMA so as to reduce the non-radiative recombination inside MAPbI₃ perovskite film.4)with the assistance from gold nanorods,the PL lifetime of MAPbI₃ perovskite film decreased from 6.8ns to 6.3ns,indicating that gold nanorods improved the radiative transition rate of MAPbI₃ perovskite film due to its unique local surface plasmon resonance effect,and thus enhanced the lasing intensity of MAPbI₃perovskite film.