Research On The Mechanism Of Photophysics Properties Regulation Of Halide Perovskite Materials

The continuous development of human civilization is inseparable from the utilization of energy.Now,the depletion of fossil energy is imminent,and the development and efficient utilization of clean energy has become the focus of research.As a kind of clean energy,the solar energy,how to effectively be transformed into energy that can be directly used by human beings has become a breakthrough to effectively solve energy problems.So far,it is an effective form of human utilization of solar energy converting solar energy into electrical energy through solar cells.Therefore,it is an important research topic today finding suitable materials for solar cells to realize high-efficiency photoelectric conversion.As an emerging semiconductor material,perovskite material is rapidly rising into popular research object in the field of solar cells due to its rich composition,simple preparation method,strong light absorption capacity,long carrier lifetime and diffusion length,etc.At the same time,the perovskite also shows strong development potential at other optoelectronic devices,including LEDs,semiconductor lasers,and photodetectors.However,the instability of perovskite materials in the atmospheric environment seriously hinders the commercial application.B-site cation doping and construction of quasi-two-dimensional perovskite materials are two commonly used methods to enhance the stability of perovskite materials.It is particularly important to study the stability improvement strategies of perovskite materials,which will promote the further commercial application.This paper mainly focuses on the two methods of constructing quasi-two-dimensional perovskite and B-site cation doping.The two methods have been studied to effectively study the physical mechanism of improving the photophysical properties of perovskite materials.The main research contents are as follows:1.The photophysical properties of perovskite are dependent on the number of layers of the quasi-two-dimensional perovskite film material.We have prepared quasi-two-dimensional PBA₂（MAPbBr₃）_n-1PbBr₄ perovskite films with different layers.The dependence of physical properties（including luminescent properties,amplified spontaneous emission properties）and photoelectric response properties on the number of layers n was studied.The number of layers of quasi-two-dimensional perovskite films can control the luminescence properties of the materials by adjusting the exciton binding energy and carrier phonon coupling.Meanwhile,the competition between radiation and non-radiation recombination processes determines the fluorescence quantum yield of the samples.We use temperature-dependent amplified spontaneous radiation（ASE）spectroscopy to scan the ASE threshold of the sample film.The ASE threshold of perovskite thin films decreased from 29.91μJ cm^-2（3D）to 19.23μJ cm^-2（n=3）due to the rapid radiation recombination rate and the effective formation of optical resonator,which showed the potential application in semiconductor laser.At the same time,the large exciton binding energy,multiple quantum well structure and carrier-carrier annihilation phenomenon of quasi-two-dimensional perovskite will hinder its photoelectric performance.2.We systematically investigated the photophysics properties of Cd alloy CsPbBr₃nanocrystals(CsPb_1-xCd_xBr₃ NCs).With the incorporation of Cd element,the crystal structure transforms from cubic phase（x=0.0）to hexagonal phase（x=0.95）.The linear absorption cross section at 400 nm decreases monotonically with increasing x,while the two-photon absorption cross section at 800 nm increases to a maximum of 5.7×10⁵GM at x=0.10.Meanwhile,the thermal activation model is used to explain that the photocurrent and photoresponsivity of the CsPb_1-xCd_xBr₃ NCs photodetectors reach the maximum value at x=0.27.Finally,the corresponding flexible photodetectors show perfect stability.Our results provide insight into the strategy of alloying Cd elements into perovskite nanocrystals,which will promote its effective application in nonlinear optics and photoelectric detection.3.We investigated the dynamics of photogenerated carriers in Cd-doped CsPbBr₃perovskite nanocrystals by using transient absorption spectroscopy.It is found that doping of Cd elements can limit monomolecular recombination by optimizing structure and passivating defects and improve the probability of bimolecular radiation recombination.In addition,it can effectively improve the heating effect of charge carriers in perovskite nanocrystals and keep them at high temperature for a long time,which will be helpful for their application in hot carrier solar cells.