Excitonic band structure and transport of organic films and crystals with ultrastrong coupling

• Applicants: Professor Dr. Martin Knupfer; Professor Dr. Karl Leo
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 568086748

In this project, we plan to investigate organic films and crystals by means of electron energy-loss spectroscopy in conjunction with optical spectroscopy, photoemission spectroscopy, and transport. In particular, we will study materials such as the recently discovered merocyanines with a quinoid structure, which show very unusual photophysical properties: e.g an extremely large blue shift of the main absorption peaks of the thin film as compared to the solution, indicating H-aggregation with very large coupling. These properties make the materials immediately interesting as infrared absorbers, but also point towards very unusual transport properties. We plan to study the general properties of these and related new materials and fully understand the band structure of excitons of these materials. We will extend the studies to single crystals and will investigate the influence of doping, up to high-doping blends representing charge transfer salts. Furthermore, we wish to investigate the effects ofthis ultrastrong coupling on the transport and charge carrier generation properties of these materials: Is there a path to much higher mobilities using these materials?

• DFG Programme: Research Grants