FME Talk by Dr. Chittaranjan Das - Bridging materials and devices: Surface science insights from photoelectron spectroscopy

Materials are interestingly distinct, showcasing a wide range of behaviors and applications closely tied to their elemental composition and how those elements are chemically bonded. For example, it forms soft, combustible coal, slippery graphite, and the incredibly hard diamond – all of which are purely carbon but arranged differently. To truly understand a material and how it performs in applications, we need to know its precise chemical and elemental fingerprint, especially at its surface. X-ray Photoelectron Spectroscopy (XPS), a technique that leverages the photoelectric effect. By bombarding a material's surface with X-rays, we eject electrons, and these electrons carry information about the elements present, their chemical states, and the electronic structure of the surface. Essentially, XPS enables us to visualize the chemical composition of a material's surface.[1]
This powerful tool opens doors to fundamental materials science and practical applications. We will explore how XPS is used to track the intricate interaction of molecules during thin film growth, particularly in the atomic layer deposition of metal oxides, revealing the secrets of their early formation. We will explore how XPS can elucidate the fundamental properties of materials, such as perovskites, offering critical insights into their behavior and potential. Finally, we will also examine its role in unraveling the electronic properties at the interfaces of perovskite solar cells, helping us understand how these devices convert sunlight into electricity.[2,3]

[1] Klein, A.; Mayer, T.; Thissen, A.; Jaegermann, W. Photo electron Spectroscopy in Materials Science and Physical Chemistry. Sci. Phys. Chem.Bunsen- Magazin 2008, 124−139.
[2] Wussler, M. et al., Tapered Cross-Section Photoelectron Spectroscopy of State-of-the-Art Mixed Ion Perovskite Solar Cells: Band Bending Profile in the Dark, Photopotential Profile Under Open Circuit Illu-mination, and Band Diagram. Adv. Fun. Mat. 2020, 30, 1910679. 
[3] Das, C. et al., Surface, Interface, and Bulk Electronic and Chemical Properties of Complete Perovskite Solar Cells: Tapered Cross-Section Photoelectron Spectroscopy, a Novel Solution. ACS App. Mat. & Int. 2020, 12, 40949.

Chittaranjan Das earned his Ph.D. in Applied Physics from Brandenburg Technical University Cottbus-Senftenberg, Germany, in 2015. He has been working at different institutes like TU Darmsatd, KIT, Forcshungszentrum Jülich, and University of Stuttgart in Germany at senior researcher level. His research focuses on advancing thin-film technology for various applications in renewable energy generation, conversion, and storage. In addition to his core work in thin-film technology, Chittaranjan's research also delves into the role of surface and interface physicochemical properties of devices. He employs cutting-edge surface analysis techniques such as X-ray Photoelectron Spectroscopy (XPS), X-ray Absorption Spectroscopy (XAS), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), and Atomic Force Microscopy (AFM) to gain valuable insights into the behaviour of materials at the atomic and molecular level. Currently, Chittaranjan's primary research area centers around perovskite photovoltaics and flexible thin-film solar cells, where he strives to develop innovative solutions for efficiently harnessing solar energy.