Synthesis And Photo-physical Properties Of Halide Perovskite Nanocrystals Under Weak Quantum Confinement Effect

With the rapid development of material science,perovskite material（structural formula:ABX₃）,has come into view and has achieved excellent performance in optoelectronic applications owing to the excellent photon capture ability,high defect tolerance,high photoluminescence quantum yield（PLQY）and tunable band gap.For example,the efficiency of perovskite-based solar cells has reached 25.7%,and the external quantum efficiency（EQE）of perovskite-based light emitting diodes has already reached 19.3%.In addition,in the field of photodetectors,lasers,communications,etc.,perovskite material has also attracted extensive research interest.In recent years,perovskite materials have developed rapidly,and have developed various morphologies of perovskite material such as nanocrystals,nanoplates,nanowires,nanorods.In addition to morphology,nanocrystal size is an important factor affecting the properties of perovskite material,for example,as the size of nanocrystal decreases,the quantum confined effect gradually appears,which in turn affects their photophysical properties and further influences their applications.In this paper,we have conducted the following studies:1.CsPbBr₃ nanocrystals with three different sizes are synthesized by controlling the reaction temperature using the hot injection method,and the obtained samples are characterized using transmission electron microscopy（TEM）technique and X-ray diffraction（XRD）technique.Through the TEM images the samples are found to be homogeneous in size,with sizes of 10.7,9.2 and 7.1 nm,respectively.The structure of the three samples is cubic phase in compare with standard card.2.The carrier dynamics of the three samples is studied by transient absorption spectroscopy,and it is found that the hot carrier cooling rate accelerated with decreasing size.Combined with the analyses of temperature-dependent PL spectra,it is found that the longitudinal optical phonons might affect the energy dissipation and thus affect the exciton activity.3.By changing the environmental pressure,the bandgap evolution of the three samples is studied under different pressure,and it is found that with the increase of pressure,the phase transition occurred in all three samples,and the phase transition pressure points are 1.22,1.09 and 0.97 GPa,respectively.4.The optical waveguide effect of the three samples in optical fiber is investigated by changing the excitation position on the fiber,and the result shows that the self-absorption and conventional optical waveguide effects can significantly affect the propagation of photoluminescence.