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、动力学和机理(CSDM-A)计划的支持下，利哈伊大学的伊丽莎白·杨正在使用复杂的时间分辨光谱仪来研究运行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来运作，并利用这种光能来驱动化学反应。该装置的效率是一系列相互依赖的基本过程的净结果，包括光吸收、电荷分离和电荷迁移，以及可用于推动化学反应的电荷的收集。分离的电荷也可能在器件内进行无效的重组，导致效率损失。这些相互关联的过程中的每一个都严重依赖于细胞内使用的材料类型，因此有必要研究一个功能系统，而不是孤立地研究单个部件。杨博士和她的学生将使用飞秒泵浦-探测方法来研究在电位偏置和稳态照明下的光活性设备。他们的发现可能会加深我们对复杂的动力学网络的理解，这些复杂的动力学网络对于可持续化学应用所需的化学转化装置的功能至关重要。该项目还将为学生提供研究机会，从而为国家科学队伍的发展做出贡献。该项目的核心是利用瞬变吸收光谱结合电化学和光解技术来量化半导体材料堆栈中发生光致电荷转移的电荷转移动力学。该项目将利用原子层沉积合成的原子精密、极薄的吸收硫化物材料。这种材料特别适合，因为可以精细地调整层厚度和成分，以便能够在平面和纳米结构设备中进行系统研究。我们将量化外加电化学势和稳态照明(即光伏和光电化学电池最接近实际的工作条件)对载流子动力学和电荷转移动力学的影响，以确定稳态条件如何影响超快寿命和电荷转移动力学。这些工作最终将有助于深入了解光伏和光电化学电池等设备的功能和效率。这一奖项反映了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 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.