Degradation effect on the magnetoresistance in organic light emitting diodes

The magnetoresistance in organic light emitting diodes (OLEDs) can be enhanced by electrical stressing of the device. In this study, magnetotransport measurements were performed on pristine and aged organic hetero-layer light emitting diodes based on small molecules with Alq3 "(tris(8-hydroxyquinoline)aluminum)" as emitter. Under pristine conditions the maximum organic magnetoresistance (OMR) was of the order of 1% at an applied magnetic field of 100 mT and a voltage of 3.5 V. After electrical stressing at a constant current density we observed an increase of the maximum OMR together with a shift towards higher voltages. The maximum OMR reached almost 6% at an applied magnetic field of 100 mT and a voltage of about 5 V. To verify the correlation between electrical aging and the magnitude of the OMR effect, we investigated OLEDs with different hole injection layers exhibiting significantly different lifetimes. (C) 2010 Elsevier B.V. All rights reserved.