Mechanisms of Triple Energy Transfer and Polaron Formation in Nanocrystals

化学系的大分子、超分子和纳米化学项目支持埃默里大学的连天全教授和他的团队研究对高效和经济的太阳能转换至关重要的纳米材料体系的能量转移过程和激发态寿命。这项研究旨在提出两种特定类型的基于量子点(小型半导体晶体)的能量转换技术。第一种技术是光子上转换。这一过程指的是将两个低能光(光子)转化为较高能量的光子，例如将不可见的红外光转化为可见光。第二种技术是使用由一种特定类别的材料制成的纳米晶体，这种材料通常被称为钙钛矿，用于太阳能电池。与传统的太阳能电池不同，钙钛矿型纳米晶提供了调整或调整太阳能电池性能的可能性。该研究对能量转换装置的设计和改进具有重要的指导意义。教育和扩大参与活动包括为亚特兰大科学博览会编写一门关于可再生能源的新课程和一个示范模块。有了这项来自高分子、超分子和纳米化学项目的奖项，连教授的团队带着三个具体的目标开展了这项研究。第一个目标是使用不同尺寸和壳层厚度的卤化铅钙钛矿和硫化镉量子点，通过考察量子点对电子耦合强度和驱动力的依赖关系来验证量子点到分子受主三重态能量转移的理论模型。第二个目的是通过考察激子精细结构与温度的关系来研究激子精细结构对从纳米晶体到分子受体的三重态能量转移速率的影响，并通过改变激子精细结构来控制这些速率。第三个目标是研究低维卤化铅钙钛矿晶体中极化子的性质(形成机理、大小和能量)，考察它们与尺寸、纳米晶体尺寸、阳离子和溶剂/配体环境的关系。这一研究结果有助于加深对低维钙钛矿纳米晶体中三重态能量从量子点到分子受主的转移以及极化子形成的理解。这些进展反过来为基于上述材料和工艺的能源转换设备的设计和改进提供了重要指导。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。

The Macromolecular, Supramolecular, and Nanochemistry Program in the Chemistry Division supports Professor Tianquan Lian and his group at Emory University to study energy transfer process and excited state lifetimes of nanomaterial systems critical to efficient and cost-effective solar energy conversion. This research is aimed at advancing two specific types of energy conversion technologies based on quantum dots (small semiconductor crystals). The first technology is photon upconversion. This process refers to converting two low energy packets of light (photons) into a higher energy photon, such as converting invisible infrared light to visible light. The second technology is the use of nanocrystals made from a specific category of materials called perovskites often used in solar cells. Unlike traditional solar cells, perovskite nanocrystals offer the possibility of tuning or adjusting the solar cell properties. This research may provide important guidance on the design and improvement of the energy conversion devices. Educational and broaden participation activities include the development of a new course on renewable energy and a demonstration module for the Atlanta Science Fair. With this award from the Macromolecular, Supramolecular, and Nanochemistry Program, Professor Lian’ group carries out the research with three specific aims. The first aim is to test the theoretical models of triplet energy transfer from quantum dots to molecular acceptors by examining its dependence on the electronic coupling strength and driving force using lead halide perovskite and cadmium chalcogenide quantum dots of different size and shell thickness. The second aim is to investigate the effect of exciton fine structure on triplet energy transfer rates from nanocrystals to molecular acceptors by examining their temperature dependence and to control these rates by changing the exciton fine structure through nanocrystal shapes. The third aim is to study the property of polarons (formation mechanism, size and energy) in low dimensional lead halide perovskite crystals, examining their dependences on the size, nanocrystal dimensionality, cations and solvent/ligand environment. The findings of this study can advance the understanding of triplet energy transfer from quantum dots to molecular acceptors and polaron formation in low dimensional perovskite nanocrystals. These advances, in turn, provide important guidance on the design and improvement of the energy conversion devices that are based on the abovementioned materials and processes.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.