Koen Vandewal

Koen Vandewal Research Professor
Institut für Angewandte Photophysik
Technische Universität Dresden
01062 Dresden, Germany

Organic small molecule optoelectronic devices

This talk will give a brief introduction to organic optoelectronic devices, highlighting fundamental and technical challenges in the field. Organic light emitting diodes based on vacuum deposited small molecules are a commercial product nowadays and several approaches to reach near unity electron-to-photon conversion exist. However, out-coupling of photons from the emissive layer remains a challenge. Organic solar cells based on interfaces between electron donor and electron acceptor molecules are currently still in the research phase but incident-photon-to-extracted-charge conversion yields of over 85%, and absorbed photon-to-extracted-charge conversion yields of 90-100% have been achieved. The main challenge is their low operating voltage, as compared to the optical gap of the main absorber material, indicating large energy losses per absorbed photon. We explore possibilities for increasing the operating voltage and discuss the influence of the donor-acceptor interfacial area, electronic coupling and molecular reorganization. Furthermore the role of charge transfer (CT) states at organic and hybrid organic-inorganic interfaces will be discussed. Finally, a new device architecture for narrow band, near-IR photodetectors based on direct CT state absorption with enhanced light in-coupling will be presented. This new type of photodetector competes in the near-infrared wavelength range with standard organic photodetectors but extends their detection range to longer wavelengths.


Dr. Koen Vandewal received his MSc in photonics engineering from Ghent University (Belgium) in 2004 and his PhD in Physics from Hasselt University (Belgium) in 2009. Subsequently, he spent 2 years as a postdoctoral researcher in the Biomolecular and Organic Electronics group at Linkoping University (Sweden), followed by a 2 year postdoc at Stanford University (USA), investigating charge carrier generation and recombination processes in organic optoelectronic devices. Since 2014 he holds the endowed chair for Organic Photovoltaics at the Institut für Angewandte Photophysik (IAPP) of the Technische Universität Dresden (Germany).