【作者】 赵广辉；

【导师】 刘韩星； 郭丽玲；

【作者基本信息】 武汉理工大学 ， 材料物理与化学， 2012， 博士

【摘要】 层状类钙钛矿杂合物是有机、无机组分在分子尺度上复合而成的一类天然量子阱材料。通过在分子尺度上对其进行结构剪裁,可以实现性能的精确设计和控制,因而具有巨大的应用潜力。系统地研究层状类钙钛矿杂合物的组成-结构-能带-性能之间的内在关系,对精确设计及控制这类材料的微观结构、能带结构和电子学性能具有重要理论意义与实际应用价值。本文对结构式为(C4H9NH3)2MI4(M=Ge,Sn,Pb)、(NH3C6H12NH3)MI4(M=Ge,Sn,Pb)、(RNH3)2(CH3NH3)n-1MnI3n+1(M=Sn,Pb; n=1,2,3)、(C6H5C2H4NH3)2-MI4(M=Ge,Sn,Pb)、(CnH2n+1NH3)2PbI4(n=4～10,12,14,16,18)、(NH3C8H14NH3)PbI4(CH3C6H4CH2NH3)2PbI4、(CnH2n-1NH3)2PbI4(n=3,4,5)和(C6H5CH(CH3)NH3)2PbI4等一系列具有层状结构的有机-无机类钙钛矿杂合物晶体进行第一性原理计算,系统研究金属种类、无机层数目及有机元对杂合物材料电子学性能的影响,在电子结构的层面上寻找该系列材料组成和微观结构对电子学性能的影响及规律。本文的研究工作包括：(1)建立不同系列的结构模型,采用第一性原理计算方法,获得各杂合物材料体系的电子态密度、Mulliken电荷、能带结构、键级及费米能级；(2)利用半导体能带模型计算不同系列杂合体系的载流子浓度；(3)系统分析各杂合物材料体系在电子态密度、Mulliken电荷、能带结构及载流子浓度等方面的差异,对差异产生的组成和结构原因进行详细分析,系统研究杂合物的组成-结构-能带-性能之间的内在关系。研究发现：费米面附近的能带均来自无机元的原子轨道,无机元中金属的种类和无机元层数对材料的带隙有着直接影响。当含有相同的有机元时,锗、锡、铅的碘化物基杂合物体系中碘化亚锡基杂合物的带隙最小,为1.080eV；载流子浓度最大,为4.389×109cm-3；同时,随无机层数目增加,带隙减小,碘化亚锡基杂合物电性能由半导性向金属性转变,载流子浓度也随之提高,当无机层数为3时,载流子浓度可达3.479x1015cm-3。费米面附近的价带顶和导带底由无机元的原子轨道构成,有机元的原子轨道对带隙附近的能带没有贡献,有机元并不直接对带隙产生影响。但是,有机元对无机层的结构有模板作用,有机元与无机元之间的氢键强弱影响了无机层金属离子和碘离子之间的键长键角,对带隙具有间接微调作用,从而影响了体系的载流子浓度。关于无机层微观结构与能带结构及带隙之间的关系的研究结果表明,对二维方向上共顶连接的八面体[M16]2-无机层来说,由于与有机元的氢键作用,M-I-M键的键角会产生面内和面外弯曲,桥位和端位碘离子与金属离子之间的键长也会发生变化。一个普遍的规律是：M-I-M键角偏离180°越大,M-I键长越短,八面体发生的畸变越大,带隙越大。对于以饱和脂肪胺为有机元的Pbca碘化铅杂合体系,碳链长度增加,有机链之间的叠置程度变大,相互作用增强,胺基头与无机层间氢键作用强度发生变化。当碳原子数大于10时,氢键作用较碳原子小于10时更强,导致无机层八面体畸变增大,因而带隙增大。对于含芳环的杂合物,芳环上支链数目、位置及支链上碳原子数的不同会引起芳环空间排列变化,同时胺基头接近无机层的角度和深度也发生改变,引起带隙变化。对于含环烷基的体系,由于环间存在较大的作用力,其推动环烷基胺向无机层方向移动,环上碳原子数越多,胺基头伸入无机层越深,引起无机层形变越少,从而导致带隙变小,载流子浓度变大。改变无机元的种类、无机元层数、有机元的结构,可以调控有机-无机钙钛矿杂合体系的带隙和载流子浓度,可望设计一类具有低带隙、高载流子浓度,同时兼具优异成膜性能的层状类钙钛矿有机-无机杂合材料。更多还原

【Abstract】 Layered perovskite-type hybrids, assembling with organic and inorganic components at the molecular scale, are a family of natural quantum well materials. Due to their unique tunable structure and controlled property, such materials have a great potential in many practical applications. By building the related structural models, detailed and systematic electronic property of the resulting structures has been carried out to gain fundamental insight into key relations between component-structure-bands-properties.Based on the ab inito concentration functional theory, a serial of hybrid perovskite structures, such as (C4H9NH3)2MI4(M=Ge,Sn,Pb),(NH3C6H12NH3)MI4(M=Ge,Sn,Pb),(RNH3)2(CH3NH3)n.1MnI3n+1(M=Sn,Pb;n=1,2,3),(CnH2n-1NH3)2PbI4(n=3,4,5),(C6H5C2H4NH3)2MI4(M=Ge,Sn,Pb),(CnH2n+iNH3)2PbI4(n=4-10,12,14,16,18),(CH3C6H4CH2NH3)2PbI4,(C6H5CH(CH3)NH3)2Pbl4,(NH3C6H12-NH3)PbI4and (NH3CgH14NH3)PbI4were built, and the relationship among electronic properties, organic and inorganic layers, metallic elements were systematically investigated.Our work mainly focus on:(1) the electronic concentration of states, Mulliken charge, energy band structure, bond energy of organic-inorganic layered perovskite-type hybrids were calculated based on first principles calculation method;(2) the carrier concentration of layered perovskite-type hybrids was calculated by energy band of semiconductor model;(3) the difference of the physical properties (e.g. DOS, Mulliken charge, the carrier concentration, band structure) of the organic-inorganic hybrids and the physics origin of them were analyzed. The influencing factors on the carrier concentration with the sort of the inorganic and organic layers have been established.In this paper, it can be found that the band gap nearby Fermi surface comes from inorganic types and layers. Comparing with germanium iodide and lead iodide system, the tin iodide was found that it can increase the carrier concentration of the metal into semiconductor. Based on the same organic unit, the band gap of tin iodide-based hybrids is the lowest than those of lead-based and germanium-based hybrids. In this case, the band gap is up to1.080eV while their carrier concentration reach4.389x109cm-3. Increasing the number of inorganic layers, the hybrids transition from semiconductor to metal. When the inorganic layers are up to3, the carrier concentration of layered perovskite-type hybrids can reach3.479×1015cm-3.The organic species have no the direct influence to the band gap of any hybrids. However, the organic units play a key role owing to the interaction between inorganic metal and organic unites. The hydrogen bond between organic and inorganic components have an effect on the inorganic layer to deviate from the ideal cubic perovskite framework, leading to the inorganic layer in the M-I bond lengths and M-I-M bond angle changes, causing the octahedral structure distorted, and increasing the inorganic layer band gap, and changing carrier concentration. Generally, layered perovskite-type hybrids, integrated inorganic metal and organic unites would be exhibit desirable physics properties by tuning their components and structure which aim to develop an effective approach towards excellent and flexible semiconductor materials.更多还原