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Organic light-emitting diodes (OLEDs) possess many unique properties such as large-area emission, fabrication on flexible plastic films, adjustment of the emission spectrum and angular distribution by chemical and optical means, and structuring to high-density arrays with millions of pixels. While especially the latter contributed to commercialization of OLED displays in consumer electronics, the properties of OLEDs also make them highly attractive for biological applications. In this contribution, we present fluorescent blue OLEDs with electrically doped charge transport layers that reach more than 100,000 cd/m² at 5 V. We applied the light source in optogenetics to stimulate primary mouse hippocampal neurons and to evoke sensory response in Drosophila melanogaster larvae using micro-structured OLED pixels. Furthermore, by applying a distributed Bragg reflector, we narrowed the OLED spectrum down in order to enable imaging of neuronal activity using genetically encoded calcium indicators. Finally, we discuss our recent efforts on providing stable encapsulation of flexible OLEDs. These examples show how OLEDs may outperform traditional light sources applied in biophotonics by enabling conformable, bio-compatible, and bright illumination with unprecedented resolution.
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