Recombination Efficiency and Width in Bilayer Organic Light-emitting Devices

A bilayer model with ohmic anode contact and injection limited cathode contact has been proposed to calculate the recombination efficiency and recombination zone width of the device. The effects of the thickness of hole transport layer and the barriers of organic/organic interface on the combination efficiency and recombination width have been discussed. It is found that: (1) When the electrons are blocked fully and the holes are not blocked significantly at the organic/organic interface, for a given L_h/L, the recombination efficiency increases with increasing the applied voltage, but at a higher applied voltage, the recombination efficiency decreases with increasing L_h/L; (2) The recombination efficiency increases with increasing applied voltage and H~′_h, and when applied voltage and H~′_h exceed some value, the recombination efficiency appears as a plateau; (3) The recombination width decreases with increasing the applied voltage and L_h/L. This model might explain the relative experiment phenomena.