Berlin 2024 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 17: Organic Semiconductors
HL 17.4: Talk
Tuesday, March 19, 2024, 10:15–10:30, EW 015
Excitons in organic materials: Revisiting old concepts with new insights — •S. Anhäuser1, D. Bischof1, A.M. Valencia2, C. Cocchi2, and G. Witte1 — 1Philipps-Universität Marburg, FB Physik — 2Carl von Ossietzky Universität Oldenburg, FB Physik
The concept of excitons, originally developed for inorganic materials, is often directly transferred to organic materials, ignoring key differences in the properties of their optical excitations. Here we report a combined experiment/theory study carried out for acenes with focus on tetracene and perfluorotetracene, in order to critically examine these concepts. For this purpose we combine detailed optical spectroscopy of various states of matter ranging from solution, to poly- and single crystalline samples, and even melt, with state-of-the-art first-principles calculations, based on DFT and many-body methods on top. This integrated approach provides deep insights into the optical signatures of the organic systems and enables us to distinguish the single particle nature of excitations in isolated molecules from the collective nature of excitons in all aggregated phases. This shows that quantum mechanical interactions between similar molecules represent a critical link between these two scenarios [1]. Therefore, we propose to use the term 'exciton' only for optical excitations of aggregated molecular materials. The presented results not only provide a deeper understanding of the optical excitations in organic semiconductors, but also highlight roadmaps and potential pitfalls that need to be considered when studying these systems.
[1] A.M. Valencia et al., Electron. Struct. 2023, 5, 033003.
Keywords: Excitons; Organic Semiconductors; Optical Spectroscopy; Density Functional Theory