The perturbation of the current transport in aluminum tris(8-hydroxyquinoline) $\left({\text{Alq}}_3\right)$-based organic light emitting diodes has been investigated as a function of magnetic field. The change in current, or organic magnetoresistance, with applied field has been fitted using two Lorentzian functions corresponding to polaron trapping by triplets and the interaction between polarons and triplets as suggested in the triplet polaron interaction model. The model has been applied to a number of devices with ${\text{Alq}}_3$ thicknesses from 50 to 90 nm and with two different cathodes. In all cases the data could be fitted using just these two processes, the prefactors for which were found to scale linearly with the triplet population over 6 orders of magnitude. This work demonstrates that the magnitude and shape of the organic magnetoresistance can be predicted and illustrates the importance of magnetic field measurements as a tool for understanding the processes affecting current transport in organic devices.

• Received 17 September 2010

DOI:https://doi.org/10.1103/PhysRevB.82.195208