Study On Carrier Transport Kinetics Of Inorganic Perovskite

Perovskite materials especially the organic metal halide perovskite CH3NH3PbX3（X=Cl-,Br-,I-）has become a new star in the photovoltaic cell and other optoelectronic fields due to their excellent optoelectronic properties such as long carrier lifetime,high absorption coefficient,high charge mobility（or diffusion coefficient）during the last few years,which case extensive research on these materials.All-inorganic cesium lead halide perovskites（CsPbX3,X=Cl-,Br-,I-）could potentially provide comparable optoelectronic properties as a promising class of materials for photovoltaic cell（PV）,photodetector,light-emitting diode（LED）with enhanced thermal and moisture stabilities compared to organic lead halide species and are not as sensitive as organic metal halides to the moisture and oxygen in the air.Herein,we synthesize the CsPbI₃ and CsPbBr₃ microcrystalline（10 μm or so）and large-size CsPbBr₃ single crystal（average size 4 mm）through solution-based synthesis under the atmospheric environment.In addition to the characterization of the synthesized crystals for confirming that we did prepare high-quality single crystals by XRD,SEM,EDX,PL and optical imaging,we also carried out a certain molecular reaction kinetics study.We report the direct visualization and quantitative of diffusion process in single-crystal nanowires（NWs）and nanoplates（NPs）using photoluminescence（PL）-scanned imaging microscopy coupled with a time-corrected single photon counting（TCSPC）.The results are as follows:By applying the time-resolve spectroscopic technique,we determine the carrier diffusion coefficient of 0.6 to 1.2 cm-2 s-1,the intrinsic carrier lifetimes of 200 to 1300 ns,mobility of 22 46 cm2 V-1 s-1 and diffusion length of 4 to 10 μm in different individual CsPbI₃ perovskite microcrystals.The results show that the performance of this kind of inorganic metal perovskite can be close to that of organometallic perovskite.We determine the carrier diffusion coefficient of 1.27 cm2 s-1,the intrinsic carrier lifetimes of 40.46 ns and mobility of 49 cm2 V-1 s-1 in different individual CsPb Br₃ perovskite microcrystals.Simultaneously,we found that the difficulty of preparing single crystal increases with the increase of PbCl2 addition in the preparation of CsPbBr₃ microcrystals while the carrier lifetime increases first and then decreases.However,if we only use PbCl2 as raw material to prepare single crystal,the carrier life is the largest.It shows that Cl-has a great influence on the process of single crystal preparation and the performance of single crystal prepared.Compared with the experimental data,perovskite material CsPbI₃ is more suitable for photovoltaic applications.In addition,we use the femtosecond laser as a light source to stimulate large-size CsPbBr₃ crystals,so that the two-photon absorption,to detect its carrier life and other issues.We find that the large-size CsPbBr₃ crystals have the long carrier lifetime that is up to the microsecond level.The performance has a great increase compared with microcrystalline and such large-size single crystal in the laser and other devices have great potential.Our results suggest the perovskite microcrystals synthesized by solution process exhibit high quality feature and are suitable for applications in optoelectronic devices.This method should be also applicable to other optoelectronic materials.