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HL: Fachverband Halbleiterphysik

HL 13: Organic Electronics and Photovoltaics I: Light-Emitting Devices

HL 13.5: Vortrag

Montag, 20. März 2017, 12:00–12:15, ZEU 260

Magnetic resonance at ultra-small fields in PPV-based OLEDs — •Hermann Kraus, Viola Zeller, Sebastian Bange, and John M. Lupton — Universität Regensburg, Universitätsstraße 31, 93053 Regensburg, Deutschland

Large magnetoresistance and magnetoluminescence effects which arise, for example, due to spin-dependent recombination rates are well-known for OLEDs, although models are still under debate given that they remain hard to verify from a measurement of integrated current and luminance. At very low fields a change in the sign of magnetoresistance appears: the so called ultra-small magnetic field effect for which also several models exist.

Spin resonance of paramagnetic species enables direct manipulation of charge carrier and excitonic precursor spins but most work on spin resonance in OLEDs was done at external magnetic fields on the order of several hundred millitesla. While it is also possible to perform these experiments at fields down to a few millitesla it was believed that resonance effects disappear once the external field is of the same order of magnitude as the internal hyperfine fields. We show that electron spin resonance signals are detectable through both the current and the electroluminescence at ultra-small fields corresponding to a few MHz resonance frequency. This demonstration provides insights into the ultra-small magnetic field effect in magnetoresistance as well as testing the principles of magnetic resonance for very low Zeeman splitting.