Growth And Properties Of Perovskite CH₃NH₃PbX₃（X=I,Br） Photoelectric Crystals

Organic-inorganic hybrid perovskite materials CH3NH3PbX3(X=I,Br,Cl)have the advantages such as excellent photoelectric conversion properties,long carrier lifetime,long hole and electron transmission distance,easy preparation at low temperature,simple deposition operation and low cost properties etc,therefore,the researches on these materials have become a hotspot in the fields of solar cell,light-emitting diodes and related optoelectronic devices.In recent years,in order to deeply explore the photoelectric properties of these materials and their application in the semiconductor field,the research work on their basic properties are of great significance.In this thesis,single crystals of CH3NH3PbX3(X=I,Br)were grown and their structures,microstructures,optical and thermal properties were studied.The main results are as follows:Crystal growth process study:CH3NH3PbX3(X = I,Br)single crystals were grown by inversion temperature crystallization and solvent-assisted crystallization.The effects of temperature heating/cooling rate,temperature field,solvent,etc.on the quality of the crystals were investigated.High-quality,large-size single crystals were obtained by optimizing the process parameters.Crystal structure and microstructure study:The crystal phases were identified by powder X-ray diffraction(XRD),and the vibration peaks of the infrared spectrum(FT-IR)were identified;scanning electron microscopy(SEM)and high-resolution transmission electron microscopy(HRTEM)were used to study the microscopic morphology and the results showed that the solvent has significant effects on the crystal’s morphology.Study on the crystals’ optical properties:The band gaps of the crystals were measured by ultraviolet-visible-infrared absorption spectroscopy absorption spectra(UV-vis-IR).The luminescence mechanism of the crystals was explored by comparing the UV-vis-IR absorption spectra and photoluminescence(PL)spectra,which showed that the CH3NH3PbI3 crystal is a direct-indirect bandgap material and the CH3NH3PbI3 crystal is a direct bandgap material.Study on the crystals’ thermal properties:Thermal analysis(TG/DTA/DSC)showed that the thermal decomposition of CH3NH3PbI3 and CH3NH3PbBr3 crystals occurs at about 230 ℃and 310 ℃,respectively,and the thermal decomposition mechanism was studied.The above research results show that the inversion method is very useful for the growth of CH3NH3PbX3 single crystals with high quality,and the studies on their structural,optical and thermal properties can provide theoretical basis for optimizing the performance of perovskite solar cells.