能源化学器件中界面势垒的高分辨原位工况研究

The interfacial energy barrier of energy chemical devices usually refers to the energy level difference that the carriers need to overcome when they across the interface. It is one of the most important factors that determines the elementary charge dynamics processes, such as dissociation, injection, transport and recombination etc. The complex interface properties of typical energy chemical devices will render the interfacial energy barrier to deviate from the original design significantly, and thus governs the energy transfer, storage, transmission and utilization. Much of the recent work focuses on interfacial layer design, which is very effective on tuning interfacial energy barrier. However, it still lacks of high-resolution imaging technique to visualize the spatial-variation and time-evolution of interfacial energy barrier, especially for operando device. In this proposal, we plan to apply the ultrahigh vacuum scanning optoelectronic probe system to in-operando visualization of device energy band alignment with high resolution better than 5 nm via in-situ cross-section preparation and tip oscillation control. We will investigate the correlation between interfacial energy barrier and properties of interfacial layer, e.g. nanostructure morphology, energy state, molecular orientation etc., typically in organic photovoltaic devices, organic photodetectors, quantum dots light-emitting diodes. In addition, more electrical and spectroscopy methods will be combined to understand the improvement in charge carrier transport and device performance by optimization of interfacial energy barrier. The proposal could contribute significantly for materials and interface design, and breakthrough device performance bottleneck.

能源化学器件的界面势垒通常指代载流子跨越界面所需克服的能级差，是载流子在界面拆分、注入和复合等过程的决定因素。然而典型器件中丰富的界面现象导致界面势垒大幅偏离预设，显著影响能源转化、存储、传输和利用。目前的研究热点在于优化设计界面修饰层可控调节界面势垒，但尚缺乏高分辨原位工况成像技术研究界面势垒随空间和时间的演化。申请人提出使用超高真空扫描光电探针系统，通过真空原位横切制样和针尖振荡动力学控制，实现器件原位工况下界面能级高分辨(优于5 nm)动态成像。申请人将通过调控界面修饰层材料特性，如微区形貌、电子能态、分子取向等，研究有机光伏器件、有机光探测器、量子点发光二极管等原型器件中界面修饰层对界面势垒的调控规律，并结合多种电学、谱学技术验证载流子传输和器件性能随界面势垒的变化行为，为材料和界面设计提供判据，推动能源的高效利用。

界面势垒是载流子跨越界面所需克服的能级差，显著影响能源转化过程中载流子的拆分、注入和复合等动力学过程，进而决定能量转化效率。界面偶极所引起的电势突变能够显著调控界面势垒和载流子传输，成为能源转化器件中广泛采用的界面调控策略之一。然而，丰富的界面效应常导致界面偶极强度偏离预设，界面势垒调控效果不如预期。本项目通过利用前期发展的定量高分辨横截面开尔文探针显微镜，实现器件工况下界面偶极对界面势垒调控效果的准确测量。进一步地，结合分子尺度的第一性原理计算，介观尺度的光谱和宏观尺度的半导体器件测试等技术手段，证实界面偶极强度不仅取决于分子电偶极矩，而且受到界面分子的排列取向，聚集情况等的显著影响。基于界面分子结构与界面偶极强度之间构效关系的准确理解，为界面偶极分子设计提供判据，从而优化界面势垒，突破能源转化效率瓶颈。