SusChEM: Atomic Structure and Dynamic Behaviors of Extended Defects in Earth-Abundant Solar-Cell Materials

非技术描述：太阳能电池材料CZTS由低成本、富含稀土的元素铜、锌、锡、S和硒制成。高效CZTS太阳能电池发展面临的挑战包括杂质和缺陷的控制。本项目的目的是利用最先进的透射电子显微镜和原理研究实验室开发的新的原位电子显微镜方法，对CZTS中缺陷在电和光激励下的原子结构和局域性质有一个基本的了解。这些新技术将使我们能够直接探测单个缺陷的原子结构，以及这些缺陷对外加电场和/或光照明的响应，从而确定单个缺陷的原子尺度结构-性质关系。其结果将是优化材料微结构和成分所需的知识，推动低成本和可持续材料的开发，并提高太阳能技术的性能。此外，该项目还为当今工业和学术研究所需的本科生和研究生的跨学科教育和培训提供了广泛的机会。技术描述：该SusChEM项目结合先进的像差校正的透射电子显微镜和新的原位电子显微镜技术，研究地球上丰富的太阳能电池材料的结构和动态行为。本论文主要研究的是取代Cu(In，Ga)Se_2(CIGS)的候选材料开斯特型Cu2ZnSn(S，Se)_4(CZTS)薄膜。由于CZTS薄膜的多晶性和多个杂质相的共存，了解缺陷和界面在控制CZTS薄膜电学性能和太阳能转换效率方面的作用是至关重要的，但也是非常具有挑战性的。在这个项目中，PI结合了最先进的像差校正的透射电子显微镜成像、光谱学和他的实验室最近开发的新的原位技术来研究CZTS材料中单个缺陷、晶界和界面的原子结构和动力学行为。空间分辨阴极发光和扫描隧道显微镜光学激发结合全息术和电子能量损失谱(EELS)被用来识别缺陷的活跃和非活跃区域(晶界、界面、第二相界等)，而相同区域的原子结构、化学成分和局域电子性质则通过透射电子显微镜成像和原子分辨光谱来确定。结合从同一材料测量的光电性能，可以理解缺陷在控制材料性能中的作用。

Nontechnical Description: The solar-cell material CZTS is made of the low-cost, Earth-abundant elements Cu, Zn, Sn, S, and Se. Challenges to the development of high-efficiency CZTS solar cells include control of impurities and defects. This project is designed to gain a fundamental understanding of the atomic structure and local properties of defects in CZTS under electrical and optical excitations, using state-of-the-art transmission electron microscopy (TEM) in combination with novel in-situ TEM methods developed in the Principle Investigator's lab. These new techniques will allow us to directly probe the atomic structure of individual defects and the responses of those defects to an applied electric field and/or light illumination providing for the determination of the atomic scale structure-property relationships of individual defects. The result will be knowledge needed for the optimization of the material's microstructure and composition, advancing the development of low-cost and sustainable materials with improved properties for solar energy technology. In addition, this project provides a wide range of opportunities for the interdisciplinary education and training of undergraduate and graduate students needed in both industry and academic research today.Technical Description: This SusChEM project is to study the structure and dynamic behaviors of Earth-abundant solar-cell materials using a combination of advanced aberration-corrected transmission electron microscopy (TEM) and novel in-situ TEM techniques. The research primarily focuses on thin films of kesterite Cu2ZnSn(S,Se)4 (CZTS), a candidate material to replace Cu(In,Ga)Se2 (CIGS). Because of the polycrystalline nature and the co-existence of multiple impurity phases in CZTS thin films, it is critical, but very challenging to understand the role of defects and interfaces in controlling the electrical properties and solar conversion efficiency. In this project, the PI combines the state-of-the-art aberration-corrected TEM imaging, spectroscopy, and the novel in-situ techniques recently developed in his lab to study the atomic structure and dynamic behaviors of individual defects, grain boundaries, and interfaces in CZTS materials. Spatially resolved cathode-luminescence and scanning tunneling microscopy holders with optical excitation, combined with holography and electron energy-loss spectroscopy (EELS), are used to identify the active and inactive regions of defects (grain boundaries, interfaces, secondary phase boundaries, etc.), while the atomic structure, chemical composition and local electronic properties of the same regions are determined by TEM imaging and spectroscopy with atomic resolution. In combination with the optoelectronic properties measured from the same material, the role of defects in controlling the materials properties can be understood.