Our research focuses on the exploration and exploitation of the unique optical properties offered by organic semiconductors. We embed the organic materials in high-quality optical microcavities and investigate the interactions between organic excitons and the cavity field. On the one hand, organic solids can act as active gain material and may turn the system into the regime of stimulated emission. On the other hand, when suitable resonators are used, organic semiconductors enable the observation of strong light-matter interaction effects by serving as active exciton reservoir in the strongly coupled exciton-photon system. They provide a robust platform for the investigation of polariton physics at room temperature.
Our research involves:
- Room-temperature polariton condensation in organic microcavities
- Light-matter interaction in biologically-produced materials
- Hybridization of Wannier-Mott- and Frenkel-excitons in organic-inorganic microcavities
"Organic polaritons" form in semiconductor microcavities with dielectric top and bottom mirrors and an active organic semiconductor layer when confined photons and vibrational excitations strongly interact with each other inducing a steady energy transfer between both particles. Such an organic microcavity can provide very high coupling strengths and polariton stability up to room temperature and far above. This is the result of the very high exciton binding energy in organic solids based on the strong localization of vibrational excitations (so called Frenkel-excitons). We aim at investigating the condensation properties of different types of organic solids including singlet and triplet state emitters as well as organics with long- (aggregates) and short-range interactions (monomers).
There is an increasing interest in using biologically produced structures and materials for photonic applications. Recent research impressively illustrates the broad potential of biological materials for providing optical gain. In particular, fluorescent proteins like eGFP retain a special position within the quickly growing family of biologically produced laser materials. eGFP has a barrel-like molecular structure that prevents concentration induced quenching of the fluorescence by suppressing Förster and Dexter energy transfer. This allows the use of pure solid-state fluorescent protein as efficient optical gain material. We work on the demonstration of highly efficient photon and polariton lasing in microcavities filled with recombinant eGFP in its solid state form.
Hybrid organic-inorganic systems
We aim at demonstrating the room-temperature operation of an electrically driven polariton laser that combines the outstanding properties of both inorganic and organic semiconductors. Inorganic semiconductor microcavities are commonly used for polariton experiments as a consequence of the precise control that is achieved over nearly all material parameters with modern epitaxial deposition technologies. However, main issues such as room-temperature stability of the strong coupling regime as a result of exciton dissociation remain challenging. In contrast to that, organic semiconductors provide record high exciton stability due to a strong localization of particles but lack high charge carrier concentrations as well as processability and stability during sample fabrication. A combination of both inorganic and organic semiconductors as active layers would then comprise the room-temperature operation and high radiation efficiency of specific organics and the device-applicability of inorganics. This will enable new technologies in medical imaging and quantum communication.