A quantitative numerical model of multilayer vapor-deposited organic lightemitting diodes

A one-dimensional numerical model for the quantitative simulation of multil ayer organic light emitting diodes (OLEDs) is presented. It encompasses bip olar charge carrier drift with field-dependent mobilities and space charge effects, charge carrier diffusion, trapping, bulk and interface recombinati on, singlet exciton diffusion and quenching effects. Using field-dependent mobility data measured on unipolar single layer devices, reported energetic levels of highest occupied and lowest unoccupied molecular orbitals, and r ealistic assumptions for experimentally not direct accessible parameters, c urrent density and luminance of state-of-the-art undoped vapor-deposited tw o- and three-layer OLEDs with maximum luminance exceeding 10000 cd/m(2) wer e successfully simulated over 4 orders of magnitude. For an adequate descri ption of these multilayer OLEDs with energetic barriers at interfaces betwe en two adjacent organic layers, the model also includes a simple theory of charge carrier barrier crossing and recombination at organic-organic interf aces. The discrete nature of amorphous molecular organic solids is reflecte d in the model by a spatial discretization according to actual molecule mon olayers, with hopping processes for charge carrier and energy transport bet ween neighboring monolayers. (C) 1999 American Institute of Physics. [S0021 -8979(99)02218-5].