The magnetic field effect on the transport and efficiency of group III tris(8-hydroxyquinoline) organic light emitting diodes

Magnetoresistance and efficiency measurements of organic light emitting diode structures based on the group III hydroxyquinolates (Mq(3)) have been made as a function of magnetic field and Mq(3) thickness, where M=Al, Ga, and In. For all quinolates, independent of thickness, we observed very similar behavior for the efficiency of the devices, with large increases in efficiency occurring at low values of applied field, which rapidly saturate as the field is increased. The current through these devices is found to be a strong function of both the device thickness and the metal ion. For Alq(3) based devices, the current changes appear to correlate strongly with the triplet population in the devices. For Gaq(3) and Inq(3) devices, the magnetoresistance is found not to correlate with the triplet concentration and this may be evidence that there is little energetic barrier for carrier trapping in these materials. For all materials, a further dependence of the magnetoresistance on applied field was observed, which needs closer investigation. (C) 2008 American Institute of Physics.