A MODEL OF ELECTROLUMINESCENCE IN ORGANIC DOUBLE-LAYER LIGHT-EMITTING-DIODES

A model has been developed for charge recombination in double-layer or ganic light-emitting diodes (LEDs) in which charge transport across th e interface between the anodic and cathodic cell compartments is imped ed 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-ass isted barrier crossing, both obeying Fowler-Nordheim-type relations. C harge recombination at the internal interface is considered as the dom inant source for electroluminescence. Accumulation of majority carrier s at that interface causes an enhancement of the cathodic electric fie ld giving rise to enhanced electron injection. This effect tends to co mpensate for imbalanced injection due to different energy barriers at the contacts and causes an increase of the luminescence yield as compa red to single-layer LEDs. The model is able to predict (i) the redistr ibution of the electric field inside the LED, (ii) the field dependenc e of the cell current, (iii) the dependence of the steady state lumine scence intensity, (iv) the luminescence yield as a function of the cel l current, and (v) the characteristic rise time of the light output, e ach parametric in the cathodic and the interfacial energy barriers nor malized to the energy barrier for hole injection. (C) 1996 American In stitute of Physics.