Equivalent circuit models in organic light-emitting diodes designed using a Cole-Cole plot

Abstract

The equivalent circuit models in organic light-emitting diodes (OLEDs) consisting of indium-tin-oxide (ITO)/tris(8-hydroxyquinoline) Aluminum (Alq(3)/Aluminum (Al), ITO/Alq(3)/Lithium quinolate/Al or ITO/N,N-bis-(l-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB)/Alq(3)/Al were investigated. The relaxation times were obtained from the impedances as functions of frequencies, and the equivalent circuits in the OLEDs were designed by using the relaxation times of OLEDs determined from the impedance spectroscopies. The Cole-Cole plots calculated from the equivalent circuit models were in reasonable agreements with the experimental results. These results can help designing equivalent circuit models of multilayer OLEDs.