光电响应的二维多层钙钛矿分子铁电材料的设计合成、结构调控及性能研究

Organic-inorganic hybrid perovskites, most notably CH3NH3PbX3, have emerged as a significant class of photoelectric functional materials. In the case of these compounds, ferroelectricity is considered as an important element for the improvement of their optoelectric performances. However, three-dimensional (3D) perovskite motifs can only be achieved from a quite narrow selection of small-size organic cations, due to the strict restriction of tolerance factor concept. In this context, it is a great challenge to rationally design the hybrid perovskite-type ferroelectrics and to modulate their bulk properties, which are highly-dependent on the structural compatibility. This project mainly focuses on the design of new two-dimensional multilayered perovskite-type ferroelectrics with photoelectric responses. Experimentally, we will introduce the secondary organic ligand (Aʹ) into the 3D perovskite template of CH3NH3PbX3 framework, which favors the assembly of perovskite motifs containing the “mixed organic cations”. This is a promising design strategy to design two-dimensional multilayered perovskite-type ferroelectrics with the formula of (Aʹ)2(CH3NH3)n-1PbnX3n+1. Single-crystal X-ray diffraction, nonlinear optical, pyroelectric, dielectric and piezoelectric measurements will be performed to study the relevant parameter changes in the vicinity of ferroelectric-paraelectric phase transition temperature. Such results will provide the solid evidence for the presence of the ferroelectricity. Subsequently, we will modulate the size of secondary organic ligands and number of inorganic layers (i.e. n value) to improve their ferroelectric and optoelectric properties. The target of our project is to obtain 3~5 examples of ferroelectrics with large spontaneous polarization and notable carrier mobility. Finally, we will grow high-quality ferroelectric single crystals to assemble the crystal-based optoelectric devices, which will establish the solid foundations for further exploration and application of ferroelectric materials in the field of photovoltaics and photodetection.

有机-无机杂化钙钛矿已发展为一类重要的功能材料，其中铁电效应被认为是提升光电性能的重要因素。但是三维钙钛矿对有机阳离子有着严苛的尺寸要求,只有极少数配体能够形成稳定结构。如何提高结构兼容性、实现杂化钙钛矿铁电体的结构设计与性能调控是当前所面临的一个科学难题。本项目聚焦光电响应的二维多层钙钛矿分子铁电体，以CH3NH3PbX3为模板骨架，通过“化学嵌入”第二有机配体(Aʹ)形成混合阳离子，设计结构新颖的钙钛矿铁电体(Aʹ)2(CH3NH3)n-1PbnX3n+1；利用单晶衍射、非线性光学、热释电、介电和压电等测试方法研究材料的铁电-顺电相变，确定其铁电性；优化第二有机配体和无机层数目(n值)，提升材料的极化与光电性能，获得3~5例具有大自发极化和显著载流子迁移率的光电响应型铁电体；立足高质量的晶体，开展光电器件的组装和性能表征，为推动此类材料在铁电光伏、光电探测等领域的应用及器件化打下基础。

有机-无机杂化钙钛矿已经逐渐成为一类重要的功能材料，铁电效应被认为是提升光电性能的潜在因素之一。典型的三维钙钛矿受到结构容忍因子制约，只有极少数有机基元能够形成稳定结构。如何提高结构兼容性、实现钙钛矿分子铁电体的设计合成与性能调控是本项目拟解决的关键科学问题。我们将二维多层钙钛矿体系作为研究对象， 以实现光电响应分子铁电体的结构设计、可控合成与性能调控为主要目标，在项目执行期间严格按照计划完成既定的研究内容和工作任务，并进一步对研究工作的特色进行凝练与提升，顺利实现了预期目标，取得了主要成果包括：(a)以金属卤素配位的钙钛矿骨架为模板，利用“化学嵌入”有机阳离子的结构设计策略，发展了二维钙钛矿分子铁电体家族(Aʹ)2(A)n-1MnX3n+1，初步实现分子铁电化合物的可控制备；(b) 立足该二维材料体系较强的结构兼容性和性能可调控性，优化有机阳离子和无机配位骨架的组装方式，实现铁电自发极化和半导体光电特性的共存，获得了兼具铁电性和优良光电响应特性的分子铁电体材料，为组装光电器件提供了物质支撑；(c)发挥铁电材料极化形成的内置电场对载流子输运的促进作用，构筑了高性能的晶体光电器件，探索了光电响应的铁电材料在自驱动光电探测、偏振光及辐射检测等方面的应用潜力，拓展了铁电材料的应用方向。在本项目资助下，相关研究结果发表学术研究论文55篇，包括J. Am. Chem. Soc.、Angew. Chem. Int. Ed.、Nature Commun.、Adv. Mater.、Adv. Funct. Mater. 和 Matter等国内外知名学术期刊，申请国家发明专利3件，在项目执行期间培养/联合培养硕士毕业生6名，博士毕业研究生2名，在站的博士后工作人员2名，为无机功能晶体材料化学的发展注入了年轻后备力量。