engleski

MOLED, a simulation model for multilayer organic light-emitting diodes

We present the computational tool MOLED for simulation of OLED functioning. MOLED is available to the scientific community through the CPC Program Library (http://cpc.cs.qub.ac.uk/summaries/ADSG). It solves the transient dynamics until steady state, of electron and hole transport in multilayer OLEDs. Although the model is one-dimensional due to the planar symmetry of the OLED devices, it takes into account the discrete 3D nature of charge carrier distribution close to the electrodes. Both tunneling and thermionic mechanisms are considered for electron and hole injection at the electrodes. The charge transport inside the organic material occurs through nearest-neighbor hopping whereas the model allows choosing between different field dependent behaviour of the mobility law. The electron-hole recombination occurs when the two carriers are close enough, according to a generalized Langevin model. In fact, exciton formation originates from both drift and the diffusion current. The latter is far from being negligible at the organic-organic energy barrier. An adjustable fraction of these electron-hole pairs leads to radiative recombination. By coordinated model simulation and experiment we got valuable insights into the OLED functioning and device optimization. In particular, the simulation clarified the bias dependent charge distribution in the device and the resulting voltage drop across the different organic layers. The model also allows calculating the leakage current resulting from unrecombined carriers reaching the electrodes, which is of special interest to device optimization. In a further step dye doping related effects were addressed by adjusting the LUMO and HOMO energy levels as well as electron and hole mobility inside the doped part of the emission layer. The results show that under the special condition of selective electron trapping inside the doped region, a split of the recombination zone into two parts can be observed.

simulation; miltilayer; organic; light-emitting diode

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