CAS-SC: Uncovering Mechanistic Details of Photo-Induced Charge Transfer in Thin Films of Photoactive Materials with In situ and Operando Transient Absorption Spectroscopy

在化学系化学结构，动力学和机制-A（CSDM-A）计划的支持下，利哈伊大学的Elizabeth Young正在使用复杂的时间分辨光谱来研究操作条件下的光活性化学转化装置。光化学电池通过吸收来自太阳的光并使用该光能来驱动化学反应来工作。器件的效率是一系列相互依赖的基本过程的最终结果，包括光吸收、电荷分离和电荷迁移，以及可用于驱动化学反应的电荷的收集。分离的电荷也可能在器件内经历非生产性的复合，导致效率损失。这些相互关联的过程中的每一个都在很大程度上取决于细胞内使用的材料类型，因此有必要研究功能系统，而不是孤立的单个部分。 杨博士和她的学生将使用飞秒泵浦探测方法研究潜在偏压和稳态照明下的光敏器件。他们的发现可以进一步加深我们对复杂动力学网络的理解，这些网络是可持续化学应用所需的化学转化装置的核心功能。该项目还将为学生提供研究机会，从而促进国家科学劳动力的发展。该项目的中心是使用瞬态吸收光谱与电化学和光解技术相结合，以量化经历光诱导电荷转移的半导体材料堆叠中的电荷转移动态。该项目将利用原子层沉积合成的原子级精确、极薄的吸收硫属化物材料。这种材料特别适合，因为层的厚度和组成可以微调，使系统的研究在平面和纳米结构的设备。施加的电化学电势和稳态照明（即，光致发光和光电化学电池的最现实的操作条件）对电荷载流子动力学和电荷转移动力学的影响将被量化，以确定稳态条件如何影响超快寿命和电荷转移动力学。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值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 in the Division of Chemistry, Elizabeth Young of Lehigh University is using sophisticated time-resolved spectroscopies to study photoactive chemical conversion devices under operational conditions. Photochemical cells operate by absorbing light from the sun and use that light energy to drive chemical reactions. The efficiency of the device is the net result of a series of interdependent fundamental processes, including light absorption, charge separation, and charge migration, as well as the collection of charges that can be used to drive chemical reactions. The separated charges can also undergo unproductive recombination within the device, resulting in loss of efficiency. Each of these interconnected processes depends heavily on the types of materials used within the cell, making it necessary to study a functional system rather than the individual parts in isolation. Dr. Young and her students will use femtosecond pump-probe methods to study photoactive devices under potential bias and steady-state illumination. Their discoveries could further our understanding of the complex kinetic networks that are central to the functioning of the chemical conversion devices needed for sustainable chemistry applications. The project will also provide research opportunities for students, thus contributing to the development of the Nation's scientific workforce. This project centers on the use of transient absorption spectroscopy coupled with electrochemical and photolysis techniques to quantify charge transfer dynamics in semiconductor material stacks that undergo photo-induced charge transfer. The project will utilize atomically precise, extremely thin absorbing chalcogenide materials synthesized using atomic layer deposition. Such materials are particularly well suited because layer thicknesses and compositions can be finely tuned to enable systematic study in both planar and nanostructured devices. The influence of an applied electrochemical potential and steady-state illumination (i.e., the most realistic operating conditions for photovoltaics and photoelectrical chemical cells) on charge-carrier dynamics and charge transfer kinetics will be quantified to determine how steady-state conditions influence ultrafast lifetimes and charge transfer kinetics. Such work could ultimately provide insight into the function and efficiency of devices such as photovoltaic and photoelectrochemical cells.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.