Developing Nonlinear Time-of-Flight Spectroscopies for Studies of Transport Mechanisms in Layered Perovskite Solar Cells

在化学系化学测量和成像（CMI）计划的支持下，北卡罗来纳州大学查佩尔山的Andrew Moran教授正在开发光谱工具和飞行时间技术来测量钙钛矿中的电子运动。几十年来，单脉冲飞行时间技术一直用于测量二维材料（如太阳能电池）中的电子速度;然而，收集信号所需的时间传统上受到用于信号检测的电子设备的限制。Moran教授和他的团队将构建一种仪器，通过检测多个激光脉冲诱导的光电流来减少这一时间。然后将同时测量钙钛矿太阳能电池内光激发物质的漂移和扩散。他们的发现可以更好地理解层状钙钛矿材料中的电子传输机制。参与该项目的学生将发展涉及激光，光学和电子的技术技能。能够解开光伏电池中的并行能量和电荷泛函过程的多维作用光谱将用于测量自发过程，例如由设备产生的光电流和荧光。这种自发过程的直接检测澄清了测量与设备功能的相关性，并最大限度地减少了传统光谱方法中固有的模糊性。为了充分表征光伏电池有源层中发生的并行过程，Moran教授和他的团队将开发一种瞬态光栅光电流光谱仪，在该光谱仪中，漂移和扩散在器件有源层内的正交方向上同时测量。此外，将纳入单独的检测通道，以区分涉及激子（荧光）和自由电荷载流子（光电流）的传输过程。漂移速度分散将通过飞行时间测量来表征，其中一个脉冲启动漂移，第二个脉冲的颜色被调整以探测有源层中不同深度的光激发载流子。该奖项反映了NSF的法定使命，并被认为值得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来支持。

With support from the Chemical Measurement and Imaging (CMI) Program in the Division of Chemistry, Professor Andrew Moran of the University of North Carolina, Chapel Hill is developing spectroscopic tools and time-of-flight techniques to measure electron movement in perovskites. Single pulse, time-of-flight techniques have been used to measure electron velocities in two-dimensional materials such as solar cells for many decades; however, the time required to collect the signal is traditionally limited by the electronics employed for signal detection. Professor Moran and his group will construct an instrument to reduce this time by detecting the photocurrent induced with multiple laser pulses. Both drift and diffusion of photoexcited species within perovskite solar cells will then be simultaneously measured. Their discoveries could lead to a better understanding of electron transport mechanisms in layered perovskite materials. Students involved in this project will develop technical skills involving lasers, optics, and electronics. Multidimensional action spectroscopies capable of disentangling parallel energy and charge funneling processes in photovoltaic cells will be used to measure spontaneous processes such as the photocurrent and fluorescence produced by a device. Direct detection of such spontaneous processes clarifies the relevance of a measurement to the function of a device and minimizes the ambiguities inherent in conventional spectroscopic approaches. To fully characterize the parallel processes occurring in the active layers of photovoltaic cells, Professor Moran and his group will develop a transient grating photocurrent spectrometer in which drift and diffusion are simultaneously measured in orthogonal directions within the active layers of the devices. In addition, separate detection channels will be incorporated to distinguish transport processes involving excitons (fluorescence) and free charge carriers (photocurrent). Drift velocity dispersion will be characterized with time-of-flight measurements in which one pulse initiates drift and the color of a second pulse is tuned to probe photoexcited carriers at various depths in the active layer.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.