Charge carrier recombination in organic bilayer electroluminescent diodes. I. Theory

A previously developed analytic model for charge carrier recombination in bilayer organic light emitting diodes D. V. Khramtchenkov, V. I. Arkhipov, and H. Bässler, J. Appl. Phys. 79, 9283 (1996) in which charge transport across the interface between anodic and cathodic cell compartments is impeded by energy barriers is extended to cells of arbitrary thickness of the constituent layers and variable energy barriers. The results indicate that the recombination yield is the result of a complicated interplay between redistribution of the electric field affecting the injection at the electrodes, internal charge accumulation, and field assisted barrier crossing. Unit charge carrier recombination efficiency is predicted to occur at moderate cell voltages and electron injection barriers less than ≈0.4 eV. At higher voltages, leakage process across the interface becomes progressively important. With increasing electron-injection barrier, that injection process becomes rate limiting.