Determination Of Localized-State Distributions In Organic Light-Emitting Diodes By Impedance Spectroscopy

A method for determining localized-state distributions in organic light-emitting diodes by impedance spectroscopy is proposed on the basis of a theory for single-injection space-charge-limited current. The method is sensitive and has high energy resolution. The applicability of the method is demonstrated in polyfluorene-based Green K (Sumation (TM)) light-emitting polymer; the localized-state distributions in this polymer are mapped out in the energy range of 0.3-0.8 eV, both below the conduction-band mobility edge and above the valence-band mobility edge.