CHARGE-CARRIER RECOMBINATION IN ORGANIC BILAYER ELECTROLUMINESCENT DIODES .1. THEORY

A previously developed analytic model for charge carrier recombination in bilayer organic light emitting diodes [D. V. Khramtchenkov, V. I. Arkhipov, and H. Bassler, J. Appl. Phys. 79, 9283 (1996)] in which cha rge transport across the interface between anodic and cathodic cell co mpartments is impeded by energy barriers is extended to cells of arbit rary 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 aff ecting 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 electr on injection barriers less than approximate to 0.4 eV. At higher volta ges, leakage process across the interface becomes progressively import ant. With increasing electron-injection barrier, that injection proces s becomes rate limiting. (C) 1997 American Institute of Physics.