Reflection Electron Energy Loss Spectroscopy of Halide Perovskites
Selina Olthof a b
a University of Cologne, Luxemburger Straße, 116, Köln, Germany
b University of Wuppertal
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV25)
Roma, Italy, 2025 May 12th - 14th
Organizers: Filippo De Angelis, Francesca Brunetti and Claudia Barolo
Invited Speaker Session, Selina Olthof, presentation 056
Publication date: 17th February 2025

The analysis of fundamental properties, such as energy level positions and bandgaps, are important to enhance our understanding of semiconducting materials such as halide perovskites. Here, most commonly spectroscopic tools such as ultraviolet photoelectron spectroscopy or UV-vis measurements are exploited to measure the density of states or band-to-band transitions.

In this talk, I will show data measured by reflection electron energy loss spectroscopy (REELS), which is a measurement technique that records electrons which are inelastically scattered from a surface. The energy losses can be analyzed to give insights into a variety of surface excitations, most notable for the current study are electronic transitions from conduction to valence band states.

I will show REELS measurements obtained for a wide range of halide perovskites and compare this data to the more conventional analysis performed by UV-vis spectroscopy. The most important difference between these two techniques is the surface sensitivity. Notably, in REELS we can tune the probing depth from around 1 to 10 nm by varying the excitation energy. This allows us to investigate the effect of surface modification on the optical gap of perovskite surfaces. This is particularly interesting for the investigation of the formation of 2D perovskite films on top of 3D layers, for which I will show various examples.

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