Threshold voltage shift and formation of charge traps induced by light irradiation during the fabrication of organic light-emitting diodes

We examined the effects of ambient light on the device properties of an organic light-emitting diode, indium tin oxide/4,4′-bis[N-(1-naphthyl)-N-phenylamino]-biphenyl (α-NPD)/tris-(8-hydroxyquinolate) aluminum (Alq3)∕Al, during fabrication using displacement current measurement. Light irradiation induces a shift in the threshold voltage for hole injection and results in the formation of charge traps in the Alq3 layer. The voltage shift implies a reduction in charge density at the α-NPD∕Alq3 interface. The origin of the interfacial charge can be attributed to dipole moment ordering in the Alq3 layer.