A model of electroluminescence in organic double-layer light-emitting diodes

Abstract

A model has been developed for charge recombination in double-layer organic light-emitting diodes (LEDs) in which charge transport across the interface between the anodic and cathodic cell compartments is impeded by energy barriers. Current flow is assumed to be controlled by the interplay between the field-assisted injection of majority carriers (holes) and minority carriers (electrons) at the contacts and field-assisted barrier crossing, both obeying Fowler–Nordheim-type relations. Charge recombination at the internal interface is considered as the dominant source for electroluminescence. Accumulation of majority carriers at that interface causes an enhancement of the cathodic electric field giving rise to enhanced electron injection. This effect tends to compensate for imbalanced injection due to different energy barriers at the contacts and causes an increase of the luminescence yield as compared to single-layer LEDs. The model is able to predict (i) the redistribution of the electric field inside the LED, (ii) the field dependence of the cell current, (iii) the dependence of the steady state luminescence intensity, (iv) the luminescence yield as a function of the cell current, and (v) the characteristic rise time of the light output, each parametric in the cathodic and the interfacial energy barriers normalized to the energy barrier for hole injection.