Mechanical And Optical Properties Of Several Hybrid Organic-Inorganic Perovskite Materials

In recent years,hybrid organic-inorganic perovskites（HOIPs）have emerged as a class of"star"materials,which are due to their diverse chemical compositions,tunable band gaps,as well as simple synthesis.By combining both the virtues of organic and inorganic materials,HOIPs have shown abundant physical properties and broad application prospects in the field of photovoltaics,dielectrics,magnets,ferroelectrics,ferroelastics and multiferroics.In any process of industrial manufacturing,materials have to experience various stress which include compression,shearing,tensile,bending,twisting,impacting and hydrostatic pressure,however,there are very few studies about the mechanical properties of HOIPs.Therefore,it is necessary to study the fundamental mechanical properties of HOIPs.In addition,the prominent performance of HOIPs in photovoltaic and optoelectronics makes it important to study their structure-property relationships.Ruddlesden-Popper Perovskites（RPPs）,a family of two-dimensional perovskites with adjustable structures,have widely attracted researchers’attention.With the change of thickness of the inorganic layer,their photoelectric properties can be significanly tuned.In this thesis,a family of representative HOIP materials were synthesized,and their mechanical properties were characterized through experiments and first-principle calculations.The adjustable optical properties of a family of RPPs were also investigated experimentally.The main contents are as follows:（1）Two new HOIPs materials,C₆H₁₄N₂·KBr₃ and C₆H₁₄N₂·RbBr₃,were synthesized by solution method.Single crystal X-ray diffraction,elemental analysis,infrared spectral,thermogravimetric analysis were used for characterizing these two materials.Combined with first-principles calculations and nanoindentation experiments,the Young’s moduli,hardnesses,Shear moduli,Poisson’s ratios,bulk moduli and anisotropy indice of the two materials were analyzed comprehensively.The results showed that,compared with CH₃NH₃PbI₃,C₆H₁₄N₂·KBr₃ and C₆H₁₄N₂·RbBr₃ have stronger mechanical and thermal stability.In addition,by analyzing the elastic constants,the propagation law of sound velocity in both crystals were studied,the vibrations and characteristics of longitudinal waves were also further studied.（2）The crystal structures and optical properties of three RPPs with different values of n:（RNH₃）₂Cs_n-1Pb_nBr_3n+1（n=1,2,∞）were studied systematically.The spectra of ultraviolet-visible absorption and photoluminescence showed that with the increase of n,the band gaps of（RNH₃）₂Cs_n-1Pb_nBr_3n+1 decrease while the emission lifetimes strengthen.The thickness of the inorganic layer in RPPs can be controlled by changing the ratio between the organic and inorganic components,which enable the fine-tuning of the photoelectric properties.