HEFOS – High Electric Fields at Organic Semiconductor Heterojunction Interfaces

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The transfer of charge carriers at heterojunctions of type II has gained an enormous attraction in the field of organic semiconductors. Related charge-transfer states at the interface are not only responsible for recombination processes in organic solar cells where they define the open circuit voltage and the charge generation but they have also been employed in so-called "exciplex" light-emiting diodes to create light with reasonable efficiency. Further, charges traversing the hetorojunction interface can absorb light. Although the cross-section for this process is relatively low, recent publications reveal that by combination with a micro-cavity, a major part of the incident light is absorbed, leading to a new generation of NIR photodetectors.Intermolecular systems can potentially be affected much stronger by an external electrical field, e.g. in contrast to intramolecular recombination and absorption processes. By that, it is likely that the properties of the interface transitions can be tuned externally. It is the aim of this project to work out device structures to apply high electric fields to the interfaces of donor and acceptor materials in order to tune the spectral range of emission and absorption. Further, it will be of interest to elaborate the operation at strong charge accumulation at such interfaces which is important for potential high excitation experiments and applications, such as an electrically driven laser. I envision to clarify the underlying physics by cooperating with several external partners who will bring in their expertise and knowledge.