Magnetoresistance and efficiency measurements of indium tin oxide/$N,N^{\prime }$-diphenyl-$N,N^{\prime }$ bis(3-methylphenyl)-($1,1^{\prime }$-biphenyl)-$4,4^{\prime }$ diamine/aluminum tris(8-hydroxyquinoline)/cathode organic light-emitting diode structures have been made as a function of magnetic field and cathode type. It has been found that magnetoresistance occurs only when there is light emission from the devices, which suggests that the magnetoresistance is related to exciton formation. Comparison of the effects of applied field on device efficiency and magnetoresistance shows that the magnetoresistance cannot be due to the recombination current. We suggest that the effect may be due to trapping of charge carriers at triplet excitons within the device.

• Received 13 October 2006

DOI:https://doi.org/10.1103/PhysRevB.75.094423