Thermodynamics and Kinetics of Hybrid Perovskite Amino-Deliquescence and Efflorescence

在化学系化学结构、动力学和机理(CSDM-A)计划的支持下，北卡罗来纳大学教堂山分校的詹姆斯·F·卡胡恩和他的研究小组将研究潮解，这是一种盐吸收水形成液滴的现象。在这项研究中，一组类似的现象可以发生在一类被称为杂化钙钛矿的材料上。当杂化钙钛矿暴露在含氮胺中时，胺起到与水相同的作用，通过被称为氨基潮解和氨基风化的过程分别导致杂化钙钛矿材料的液化和结晶。虽然从表面上看，人们可能会认为盐已经融化了，但在微观尺度上发生的是大气中的水凝结溶解盐晶体。当湿度下降时，这种现象的反转称为风化，导致水滴中的水蒸发和盐的结晶。杂化钙钛矿是一类令人兴奋的材料，由于其可调的特性，包括强大的光吸收和发射，使其能够适应一系列潜在的技术，因此得到了广泛的研究。本项目将研究控制氨基潮解/风化过程的基本物理化学。这项研究的结果应提供可用于控制此类材料的成分和形态以使其具有特定物理特性的指导方针。这个介于物理化学和材料科学之间的项目将为高中、本科生和研究生提供全面的研究经验。混合钙钛矿，如甲基铵卤化铅，由有机和无机成分组成，已发现独特的功能，如薄膜、宏观单晶和胶体纳米晶。在本项目中，研究了混合型钙钛矿在接触胺(如甲胺、丁胺等)时的液化/结晶。在控制温度和压力的情况下，将在自制的反应堆中使用一套现场测量和显微镜对其进行定量分析。对氨基-潮解和氨基-风化相变的分析应该允许对这些过程进行详细的热力学和动力学分析，以提取这些相变的相关的热参数和熵参数。了解成核和生长动力学应该为了解和控制结晶度、取向、形态和成分提供一种手段。将使用小的和大的有机铵或二铵离子及其相应的胺或二胺来研究三维和二维层状钙钛矿。该项目预计将提供关于混合钙钛矿的一个重要的、基本的现象的信息，产生洞察力，可以促进进一步的理论研究，并帮助未来对这些系统进行化学和结构修改。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

With support from the Chemical Structure, Dynamics and Mechanisms-A (CSDM-A) Program of the Division of Chemistry, James F. Cahoon and his research group at the University of North Carolina-Chapel Hill will investigate deliquescence, the phenomenon in which a salt takes up water to form a liquid droplet. An analogous set of phenomena that can occur with a class of materials termed hybrid perovskites will be investigated in this research. When hybrid perovskites are exposed to nitrogen-containing amines, the amines play the same role as water, causing the liquefaction and crystallization of the hybrid perovskite material through processes that have been termed amino-deliquescence and amino-efflorescence, respectively. Although by appearances one may think that the salt has melted, what has occurred at a microscopic scale is the condensation of water from the atmosphere to dissolve the salt crystal. The reverse of this phenomenon, termed efflorescence, can occur when the humidity decreases, causing evaporation of water from the droplet and crystallization of the salt. Hybrid perovskites are an exciting class of materials that are being widely studied because of their tunable properties, including strong light absorption and emission, that make them amenable to a range of potential technologies. This project will examine the fundamental physical chemistry that governs the amino-deliquescence/efflorescence process. The results of this study should provide guidelines that can be used to control composition and morphology of such materials to engender them with specific physical characteristics. This project at the interface of physical chemistry and materials science will form the basis of a well-rounded research experience for the high school, undergraduate and graduate students involved.Hybrid perovskites such as methylammonium lead halide are composed of organic and inorganic constituents that have found unique functionality as thin films, macroscopic single crystals, and colloidal nanocrystals. In this project, the liquefaction/crystallization of hybrid perovskites when exposed to amines (e.g. methylamine, butylamine, etc.) at controlled temperatures and pressures will be quantitatively analyzed using a set of in situ measurements and microscopies in a home-built reactor. Analysis of amino-deliquescence and amino-efflorescence phase transitions should permit a detailed thermodynamic and kinetic analysis of the processes, to extract the relevant enthalpic and entropic parameters for these transitions. Understanding nucleation and growth kinetics should provide a means to also understand and control crystallinity, orientation, morphology, and composition. Both three-dimensional and two-dimensional layered perovskites will be studied using small and large organic ammonium or diammonium cations and their corresponding amines or diamines. The project is expected to provide information on an important, fundamental phenomenon seen with hybrid perovskites, yielding insights that could motivate further theoretical study and assist in future chemical and structural modifications of these systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.