基于铋、锑基有机-无机杂化分子铁电的设计及其光电性能的研究

Organic-inorganic hybrid halide perovskite materials have been extensively investigated owing to their impressive optical and electronic attributes such as an extremely low density of defects, excellent carrier transport, and strong light harvesting capability and luminescence intensity, as well as facile solution fabrication processing. In particular, the successful application of three-dimensional lead-based perovskites (APbX3, A= organic cations, X= halogen), which have recently made organic-inorganic hybrid perovskite more and more attractive as high-efficiency light absorbers in solar cells. Compared to the traditional inorganic perovskite material, the organic cations in the organic-inorganic hybrid perovskite structure are inserted into the cavity of the inorganic framework. As a potential molecular ferroelectric materials system, the dynamics of organic cations is easy to change with the temperature, which can cause ferroelectric phase transitions. By constructing various functional inorganic frameworks, the hybrid materials can combine ferroelectricity with some important properties, including semiconductor, magnetic, photoluminescence and etc. However, The impressive progress of Pb perovskite photovoltaics prompted the search for novel lead-free halide perovskite materials. Perovskites based on tin and bismuth metals have been intensively explored recently, due to these materials show promise for reduced environmental toxicity, especially for wearable and disposable devices. Additionally, the further studying for their performance of optoelectronic devices will be of great significance in promoting the industrialization of lead-free molecular ferroelectric materials.

有机－无机杂化钙钛矿材料由于其具有很低的缺陷密度、良好的传输性能、很强的吸光能力和荧光等优越的光学与电学性能，受到了广泛的研究。特别是近几年三维铅卤化物(APbX3，A=阳离子，X=卤素) 钙钛矿作为吸光层在太阳能电池领域的成功应用使得有机－无机杂化钙钛矿越来越受关注。相比于传统的无机钙钛矿材料，有机－无机杂化钙钛矿结构中的有机阳离子由于处在无机阴离子框架形成的空隙中，其动力学状态容易随着外界温度变化，可以引起铁电相变，是潜在的分子基铁电材料。通过构建不同特性的无机阴离子框架，有机－无机杂化钙钛矿能在分子水平实现铁电性质与半导体、磁性、光致发光等性质的结合。但具有毒性及其低稳定性的铅卤素基钙钛矿材料，限制了其进一步使用。因此，非铅锑、铋基杂化铁电材料，作为一种具有很好稳定性的低毒性材料，成为我们研究的主要方向。并且进一步对其器件的制作及光电性能的研究，为非铅铁电材料的运用奠定了基础。

有机-无机铅卤化钙钛矿作为新一代光电及光伏材料，由于具有显著的光电半导体特性，如：大的光子吸收系数、长的载流子扩散长度、高的载流子迁移率、以及高效光致激子解离等优点，近年来受到了广泛的关注。而铁电体具有可切换的自发电极化，可以促使其与光的耦合诱导载流子的解离。同时，载流子分离通过强烈的内部场极化，还能够实现远高于其带隙的光电压。因此铁电体与钙钛矿的结合，可以进一步拓宽铁电在光电及光伏领域的应用，促进发展廉价，便携的可再生能源材料。但目前针对钙钛矿及其铁电钙钛矿半导体的研究仍然停留在铅基材料的基础上，这类材料很不稳定，容易受湿度影响。此外，铅的毒性问题也引起了人们对环境污染和健康问题的关注。因此，如何非铅金属卤素框架中引入构型易变的结构基元，来构筑性能优异的有机-无机杂化型分子铁电材料是现在面临的一个关键科学问题。项目实施过程中我们提出了一种全新的非铅铁电设计概念，即混合阳离子铁电体的设计思路。通过调控双组份混合阳离子的搭配，不断优化其与金属卤化物之间的组装方式，开发具有优异光电性能的有机-无机杂化型分子铁电材料。基于此，我们分别设计了首例卤素双金属钙钛矿铁电体和首例一维混合阳离子钙钛矿铁电体，为设计新型铁电体拓宽了方向。同时，我们还生长大尺寸高质量的铁电单晶，探索与开发其在光电探测器，光伏，及其偏振探测器等领域的应用。实现首例一维大尺寸单晶的偏振探测器，为一维非铅铁电体提供了潜在的应用方向。并在此基础上，进一步其铁电性能，结构变化机制与光电半导体性能进行深入分析，总结铁电相变规律，自发极化与光电性能的关系等，为新颖的有机-无机杂化型分子铁电晶体的设计合成提供科学依据。