The Regulation Of Luminescence And Investigation Of Microcavity Lasing From All-inorganic Halide Perovskite Single Crystals

Optoelectronic technology is one of the standards to judge the comprehensive strength of a country and a region.The development of new optoelectronic information materials and devices is an important means to promote national informatization construction.In recent years,metal halide perovskites have become one of the most potential optoelectronic materials due to their excellent optoelectronic properties.Their ionic crystal properties and easy composition control have brought changes to many optoelectronic fields including photodetectors,lasers,solar cells,and light-emitting diodes.Nevertheless,there are still a series of problems in inorganic halide perovskite materials that limit their further application in optoelectronic devices.For example,halide perovskite samples prepared by solution methods such as hot injection method are prone to residual corresponding organic ligands,and polycrystalline films prepared by spin coating method have adverse effects on the stability of halide perovskite due to the existence of grain boundaries.It will also affect the study of basic photophysical properties such as ion migration in crystals.Therefore,in order to deeply study the intrinsic properties of inorganic halide perovskite semiconductors,it is necessary to use single crystal materials with low defect density,high crystal quality and smooth crystal surface.This thesis uses chemical vapor deposition（CVD）to prepare high quality inorganic halide perovskite single crystals on different substrates.Furthermore,we investigate the variations in the photoelectric properties of the samples under different field conditions.The effects of different field conditions on crystal ion migration were investigated.At the same time,the application of inorganic halide perovskite single crystal prepared by CVD method in laser and light-emitting diode is studied.The main findings are summarized as follows:（1）Transferable high-quality CsPbBr₃ single crystals were fabricated on highly oriented pyrolytic graphite（HOPG）substrates by van der Waals heteroepitaxy.The bonding properties between the CsPbBr₃ micro-nano single crystal and the HOPG interface were investigated by first-principles calculations,and the van der Waals epitaxial growth process of perovskite on HOPG substrates was explained by semi-quantitative kinetic analysis based on classical nucleation theory.Importantly,the extremely weak van der Waals interaction between the perovskite and HOPG not only enables the high quality of the crystals but also endows them with the facile transferability to metals,flexible electrodes and quartz glass substrates by the mechanical exfoliation technique.Based on the successful fabrication of low-threshold micro-nano lasers(～45.5μJ cm^-2)and monolithic LED devices at room temperature represents an important step toward the fabrication of advanced integrated optoelectronic devices based on inorganic halide perovskite single crystals.（2）CsPbBr_xI_（3-x）micro-nano single crystal was successfully prepared by one-step chemical vapor deposition method,and the fluorescence color change caused by real-time ion migration,as well as the change of its luminescence spectrum peak position and intensity were observed.We propose that the electric field generated by the trapping of photogenerated carriers is the driving force for the phase separation phenomenon caused by ion migration.It is found that the reduction of the luminescence intensity of the bromine-rich phase decreases from 91%to 51%under the laser irradiation of the samples spin-coated with the polymethyl methacrylate（PMMA）layer.The ratio of the luminescence intensity decreased from 2.38 to 0.45.It was concluded that the main path of ion migration was the vacancy defects on the surface of the sample,and the surface spin coating of PMMA was an effective way to alleviate the ion migration.The programmable fabrication of perovskite surface patterning using light-induced ion migration lays the foundation for understanding and controlling the phase separation induced by ion migration in all-inorganic perovskites under light field.（3）The reversible and giant（>13 times）enhancement of the photoluminescence from inorganic halide perovskite nanoplatelets by electric-field is demonstrated.The regulation of photoluminescence is attributed to the electric field-induced ion migration and the dynamic surface healing effect caused by redistribution.The temperature-dependent luminescence spectroscopy analysis of the electric field proves that the electric field regulates the luminescence intensity of the crystal at a reversal temperature of～190 K.Moreover,the activation energy of 142.8±31.1 meV was obtained,which confirmed that the migration of Br^-in the perovskite crystal under the electric field filled the vacancy and dominated the trap healing process.Based on the above results,a three-stage defect passivation model of the vertical configuration is established.By constructing an asymmetric structure,the synergistic effect of charge injection and ion migration on the optical properties of perovskites is studied,which provides a new idea for exploring the photophysical properties of halide perovskites,which is conducive to the in-depth development of on-chip optical circuits and systems in the future.（4）Using a precisely controlled two-step atmospheric pressure chemical vapor deposition process,the perovskite lateral heterostructures in forms of microplates and microwires were fabricated.Comprehensive spectroscopic analysis demonstrated that the"funnel-shaped"type-I energy band arrangement at the interface promote an efficient energy transfer process.As for the different refractive indices of the two regions increase the confinement of photons.The synergistic effect achieved a high quality factor（Q～3400）and low threshold(≈3.5μJ cm^-2)lasing in a single heterostructure.The distinctive optical waveguides with propagation length independent output spectra and low threshold(≈9.9μJ cm^-2)Fabry–Pérot mode lasing from the microwire heterostructure are realized.These results demonstrate the possibility of developing novel functional optoelectronic devices by designing perovskite heterostructures.