【作者】 王超；

【导师】 刘卫芳；

【作者基本信息】 天津大学 ， 材料科学与工程， 2022， 博士

【摘要】 有机-无机杂化钙钛矿（OIHP）材料是一类由有机分子和无机分子自组装形成的新型复合材料,其结构以无机部分为基础,有机阳离子嵌套在无机金属元素与卤族元素结合的八面体中形成具有钙钛矿结构的晶体。这种杂化材料结合了有机和无机成分的优点,既有有机成分提供的结构多样性,机械可塑性,高极化率,又有无机组分提供的热稳定性,半导体性以及磁性和介电性能。这些优异的性能使得有机-无机杂化钙钛矿材料在光伏电池,新型的存储器和光电器件等有潜在的应用前景。本论文中,我们采用第一性原理方法对于不同维度（准一维,一维,三维）有机-无机杂化钙钛矿的铁电、磁性、压电、光吸收和载流子迁移率等性质进行了探究。主要研究如下:（1）我们系统地研究了准一维OIHP（MV）AI₃Cl₂（MV=methylviologen,A=Bi,Sb）的铁电、光学和电学特性。探究了铁电性（MV）AI₃Cl₂的极化机制,发现（MV）AI₃Cl₂的铁电极化主要源自沿八面体链方向的畸变。由于准一维结构中松散耦合的铁电链,（MV）Bi I₃Cl₂和（MV）Sb I₃Cl₂在铁电极化180°反转时具有相对较低的极化转换能垒。并且,预测（MV）Bi I₃Cl₂和（MV）Sb I₃Cl₂的上限存储密度分别为14.9 Tb/cm²和15.0 Tb/cm²,有望应用于高密度铁电存储器件。（MV）AI₃Cl₂的强各向异性光吸收发生在可见光区,其最大功率转换效率>23%。（MV）AI₃Cl₂具有高的各向异性载流子迁移率促进电子-空穴对的分离。计算结果表明,（MV）AI₃Cl₂具有正压电效应。研究表明,应变工程能显著提高（MV）AI₃Cl₂的功率转换效率和载流子迁移率,从而为铁电光伏电池的实验提供了理论设计。（2）由于准一维铁电体OIHP（MV）AI₃Cl₂中含有重金属元素Bi,Sb和I元素,我们研究了其面内k_x-k_y的Rashba自旋构造。随着铁电极化的增强,Rashba常数增加。并且,Rashba常数沿着z轴方向拉伸而增加。电场和应变工程可以有效地调控（MV）AI₃Cl₂的Rashba自旋分裂,有望应用在自旋场效应晶体管和光伏电池中。（3）我们探究三维（EATMP）Pb₂X₆[EATMP=（2-aminoethyl）-trimethylphosphanium]（X=I,Br,Cl）的铁电,光电,压电等性质。（EATMP）Pb₂X₆空间群是Pc,具有双轴铁电。铁电的主要来源于有机分子EATMP旋转和无机八面体Pb₂X₆畸变。（EATMP）Pb₂X₆具有很强的光吸收各向异性和高的载流子迁移率。（EATMP）Pb₂I₆的光电转换效率高达16%。这为铁电型光伏电池提供很好的理论依据。（4）我们系统研究多轴多铁性有机-无机杂化钙钛矿材料（TMCM）TMCl₃（TMCM=trimethylchloromethylammonium,TM=V,Cr,Fe,Co,Ni）的磁性和铁电性质。（TMCM）TMCl₃具有强的铁电极化强度和反铁磁性,进一步证实了其多铁特性。其中铁电来源于有机分子转动,磁性来源于过渡金属元素3d轨道自旋劈裂。故在（TMCM）TMCl₃中若利用铁电极化来调控磁性相变实现电控磁,有望多轴多铁（TMCM）TMCl₃在信息存储的应用。更多还原

【Abstract】 Organic-inorganic hybrid perovskite（OIHP）materials are a new class of composite materials formed by the self-assembly of organic and inorganic molecules.crystals with a perovskite structure are formed in the octahedron.This hybrid material combines the advantages of organic and inorganic components,both structural diversity,mechanical plasticity,high polarizability provided by organic components,and thermal stability,semiconducting,and magnetic and dielectric properties provided by inorganic components.performance.These excellent properties make organic-inorganic hybrid perovskite materials have potential applications in photovoltaic cells,new memory and optoelectronic devices.In this paper,we investigate the ferroelectric,magnetic,piezoelectric,optical absorption and carrier mobility properties of organic-inorganic hybrid perovskites in different dimensions（quasi-one-dimensional,one-dimensional,three-dimensional）.The main researches are as follows:（1）We systematically investigated the ferroelectric,optical,and electrical properties of quasi-one-dimensional OIHP（MV）AI₃Cl₂（MV=methylviologen,A=Bi,Sb）.The polarization mechanism of ferroelectric（MV）AI₃Cl₂ was explored,and it was found that the ferroelectric polarization of（MV）AI₃Cl₂ mainly originated from the distortion along the direction of the octahedral chain.Due to the loosely coupled ferroelectric chains in the quasi-one-dimensional structure,（MV）Bi I₃Cl₂ and（MV）Sb I₃Cl₂ have relatively low energy barriers for polarization conversion when the ferroelectric polarization is reversed by 180°.The calculated results predicted that the upper storage densities of（MV）Bi I₃Cl₂ and（MV）Sb I₃Cl₂ are 14.9 Tb/cm²and 15.0Tb/cm²,respectively,which are expected to be applied in high-density ferroelectric memory devices.The strong anisotropic optical absorption of（MV）AI₃Cl₂occurs in the visible region,and its maximum power conversion efficiency is>23%.The high anisotropic carrier mobility of（MV）AI₃Cl₂ facilitates the separation of electron-hole pairs.（MV）AI₃Cl₂ has a positive piezoelectric effect.Therefore,using strain engineering to improve the power conversion efficiency and carrier mobility of（MV）AI₃Cl₂ provides a design for the experiments of ferroelectric photovoltaic cells.（2）Since the quasi-one-dimensional ferroelectric OIHP（MV）AI₃Cl₂ contains heavy metal elements Bi,Sb and I elements,we study its k_x-k_y plane Rashba spin texture.The Rashba constant increases with the enhancement of ferroelectric polarization.In addition,the Rashba constant increases along the z direction.Electric field and strain engineering can effectively tune the Rashba spin splitting of（MV）AI₃Cl₂,which is expected to be applied in spin field effect transistors and photovoltaic cells.（3）We explore the ferroelectric,optoelectronic,and piezoelectric properties of three-dimensional（EATMP）Pb₂X₆[EATMP=（2-aminoethyl）-trimethylphosphanium]（X=I,Br,Cl）.The（EATMP）Pb₂X₆ space group is Pc,with biaxial ferroelectricity.The ferroelectricity mainly originates from the organic molecular EATMP rotation and the inorganic octahedral Pb₂X₆ distortion.（EATMP）Pb₂X₆ exhibits strong light absorption anisotropy and high carrier mobility.The photoelectric conversion efficiency of（EATMP）Pb₂I₆ is as high as 16%.It has good stability in mechanical properties.This provides a good theoretical basis for ferroelectric photovoltaic cells.（4）We systematically study the magnetic and ferroelectric properties of multiaxial multiferroic organic-inorganic hybrid perovskite material（TMCM）TMCl₃（TMCM=trimethylchloromethylammonium,TM=V,Cr,Fe,Co,Ni）.（TMCM）TMCl₃ exhibits strong ferroelectric polarization and antiferromagnetism,further confirming its multiferroic properties.The ferroelectricity originates from the rotation of organic molecules,and the magnetism originates from the 3d orbital spin splitting of transition metal elements.Therefore,if the ferroelectric polarization is used to control the magnetic phase transition in（TMCM）TMCl₃ to realize the electronically controlled magnetism,it is expected that the application of multiaxial multiferroic（TMCM）TMCl₃in information storage.更多还原