Simulation Of Thermal And Electrical Transport Properties In Tin-based Perovskites

The tin-based halide perovskite has many advantages such as environmental friendliness,low cost,high Seebeck coefficient,low lattice thermal conductivity,strong anisotropy,and easy low-dimensionality.However,they also inherit the significant drawback of low carrier concentration and low conductivity of perovskite materials.In order to solve the inherent shortcomings of tin-based perovskites,it is necessary to study the structure-property relationship of tin-based perovskite materials,especially the intrinsic relationship between ion transport properties and structure.In this paper,the electrical and phonon thermal transport properties of tin-based perovskites are studied based on density functional theory and Boltzmann transport equation.We selected Cs₂Sn Br₆ as the research object,and carried out research around two key issues:"The physical mechanism of the ultra-low thermal conductivity of tin-based perovskites"and"Enhancing the electrical transport properties of Cs₂Sn Br₆ through compressive strain regulation".The first-principle calculation method is mainly used for research,and the following results are obtained in the process:1.We systematically studied the thermoelectric properties and microscopic mechanism of ultra-low lattice thermal conductivity of Cs₂Sn Br₆ under atmospheric pressure using density functional theory and Boltzmann transport equation.The electronic transport properties of the material in the room temperature to medium-high temperature region are calculated under the doped carrier,and it is found that the Seebeck coefficient of Cs₂Sn Br₆ reaches 250μVK^-1 when the doped hole concentration is 5×10²⁰ cm^-3,and thermoelectric figure of merit reaches 0.55 at 450 K.2.Through iterative calculation to solve the phonon Boltzmann equation,it is found that the lattice thermal conductivity of the Cs₂Sn Br₆ is abnormally low,and the heat transfer behavior of glass appears.After analysis,it is found that the material has rattling model structure,which proves that the strong anharmonicity of the crystal is main reason for its ultra-low lattice thermal conductivity.In addition to considering the contribution of particle-like propagation to the heat transfer,we also use Wigner transport equation to calculate the thermal conductivity of the contribution of the wave-like inter-band conduction mechanism,and the lattice thermal conductivity is0.17 W m^-1k^-1 at 450 K.The results also show that the polar optical phonon scattering seriously affects the carrier lifetime.This study helps us to understand the ultra-low lattice thermal conductivity in complex crystals with strong anharmonic and proves that Cs₂Sn Br₆ is a promising thermoelectric material.At the same time,the calculated results show that the polar optical phonon scattering seriously affects the carrier lifetime.This study contributes to our understanding of ultralow lattice thermal conductivity in complex crystals with strong anharmonicity,also proves that Cs₂Sn Br₆is a promising thermoelectric material.3.Based on the Fr?hlich model of electroacoustic coupling interaction,a systematic theoretical calculation study of tin-based perovskites was carried out.We provide evidence for the effect of compressive strain on large polaritons and the scattering decay of auroral phonons.Our calculation results show that the electron mobility of Cs₂Sn Br₆ is 11 cm²V^-1s^-1 under no strain,and the electron mobility reaches about 143 cm²V^-1s^-1 after 13%compression,which is 13 times higher than that without strain.For Cs Sn Br₃ that is easy to phase change,the dynamic lone pair activity of Cs Sn Br₃ produces a larger dielectric response after applying a small compressive strain,which can enhance the dielectric shielding ability of carriers,and the carrier mobility of Cs Sn Br₃ compressed by 1%is significantly increases significantly（in the absence of a phase transition）.The enhanced carrier mobility of these two tin-based perovskites under compressive strain suggests that compressive strain can weaken the electron-phonon coupling phenomenon in polar semiconductors,thereby improving carrier transport.We demonstrate that compressive strain can tune the strength of the electron-phonon coupling effect,enhancing the carrier mobility of tin-based perovskites by tuning the large polariton radius and weakening the polar optical phonon scattering strength.