低维无铅钙钛矿及其衍生物的高压研究

HIGH PRESSURE RESEARCH ON LOW-DIMENSIONAL LEAD-FREE PEROVSKITES AND THEIR DERIVATIVES

陈忠伟

11849429

硕士

化学

权泽卫

2020-05-30

2020-07-08

哈尔滨工业大学

深圳

钙钛矿作为新型的半导体材料，被广泛应用于太阳能电池及光伏器件。而应用范围广的传统三维铅基钙钛矿有较大的毒性，低维无铅金属卤素钙钛矿及其衍生物由于其无毒、稳定等优势有望成为其替代物。另一方面，低维结构的钙钛矿具有独特的光电性质，由于其电子被限制在主体无机框架内，可能产生量子限域效应，从而引发独特的光物理现象。目前，对低维钙钛矿结构的理解不是很明确，通过高压实验方法深入研究其内在的结构-性质关系，能够为提升低维钙钛矿的性能提供策略。通过对一系列低维无铅钙钛矿及其衍生物的高压研究，本文揭示了不同组分、结构单元对材料结构性能的影响。在二维的有机-无机杂化钙钛矿(CH3NH3)3Bi2Br9中，无机[BiBr6]3-八面体的扭曲和倾斜决定了其结构相变的过程，而有机组分对结构相变的影响很小。同时揭示了八面体结构变化对光学带隙的调控规律，即八面体的压缩及结构非晶化促进了电子轨道的耦合，使得带隙值减小，而结构相变时八面体的倾斜扭曲抑制了电子轨道的相互作用，使得带隙扩张。与全无机钙钛矿Cs3Bi2Br9高压下的结构行为对比，发现杂化钙钛矿中的有机阳离子能够提升材料的柔韧性。揭示了一维铜基钙钛矿衍生物CsCu2I3中[CuI4]3-四面体结构对材料自陷态激子（STE）发光性能的影响。在常压相的CsCu2I3中，[CuI4]3-四面体扭曲程度弱，导致其STE发光很弱。在较温和的压力下，[CuI4]3-四面体间的扭曲稍微增强，使得其激子波尔半径减小，STE发光轻微地增强。在高压力范围下，结构相变使得高压相内[CuI4]3-四面体内部及面间的扭曲显著强化，导致激子自陷深度增加，脱陷能垒变高，从而引发其STE发光剧烈增强。钙钛矿衍生物CsCu2I3的四面体内部及面间的扭曲能够在不同程度上提升材料的STE发光性能，提供了压力调控低维金属卤化物STE发光的策略。在低维金属钙钛矿及其衍生物中，多面体结构单元对于调控其光学性质非常关键。

Perovskites are widely used in solar cells and photovoltaic devices, as a new type of semiconductor materials. However, the traditional three-dimensional lead-based perovskites are toxic, restricting their applications. Low-dimensional lead-free perovskites and their derivatives are expected to become substitutes because of their non-toxicity and stability. Besides, perovskites with low dimensional structure possess unique optoelectronic properties. The electrons are confined in the host's inorganic frame, resulting in quantum confinement effects, which will trigger unique photophysical phenomena. At present, the comprehending of the structure of low-dimensional perovskites is not very clear. In-depth study of their internal structure-property relationship through high-pressure experimental methods can provide strategies for improving the performance of low-dimensional perovskites. By studying the structural and property evolutions of a series of lead-free low-dimensional perovskites and their derivatives under high pressure, the effects of different components and structural units on structure and properties of materials are revealed.In the low-dimensional organic-inorganic hybrid perovskite (CH3NH3)3Bi2Br9, distortion and tilting of inorganic [BiBr6]3- octahedra determine the structural phase transition process. While the organic components have little effect on the structural phase transition. At the same time, the effects of octahedra structure on optical band gap are revealed, that is, the compression of the octahedra and the amorphous structure promote the coupling of the electron orbits, which reduces the band gap value. The tilting and distortion of the octahedra during the phase transition restrain the interaction of electron orbits, and the band gap is expanded. Compared with the structural behavior of all-inorganic perovskite Cs3Bi2Br9 under high pressure, it was found that the organic cations in the hybrid perovskites can significantly improve the flexibility of the materials.In one-dimensional copper-based perovskite-derivative CsCu2I3, the effects of the [CuI4]3- tetrahedral structure on the self-trapped excitons (STE) emission are revealed. At ambient conditions, the slight structural distortion of [CuI4]3- tetrahedra results in weak STE emission. Under milder pressure, the slight enhancement of structural distortions between [CuI4]3- tetrahedra leads to the band gap broadening and STE enhancement with a decreased Bohr radius of excitons. In the high-pressure range, the structural phase transition significantly strengthens the internal distortion of [CuI4]3- tetrahedra and obvious structural distortions between the adjoining tetrahedra within the one-dimensional chains. Consequently, inducing a higher detrapping barrier with larger activation energy, which is confirmed by the presence of a new STE emission peak at a much lower energy. Thus, the increased concentration of STEs accordingly results in the increase of radiative recombination with enhanced STE emissions.It is indicated that the structural distortions from intra- and inter-tetrahedra are revealed to enhance the STE emission with different magnitudes in CsCu2I3. This work provides a strategy for pressure regulation of STE emissions in low-dimensional metal halides.In low-dimensional perovskites and their derivatives, the polyhedral structural units are very important for regulating their optical properties.

高压 低维 钙钛矿 结构 性质 自陷态激子发光

high pressure low-dimensional perovskite structure property self-trapped excitons emission

中文

联合培养

南方科技大学

陈忠伟. 低维无铅钙钛矿及其衍生物的高压研究[D]. 深圳. 哈尔滨工业大学,2020.