Numerical simulations of the electrical characteristics and the efficiencies of single-layer organic light emitting diodes

We have used numerical methods to calculate the current and the efficiency of single-layer organic light emitting diodes, taking into account field-de pendent mobilities, diffusion, and thermionic injection at the metal/organi c interfaces. It is shown that when the barrier for charge injection from t he metal to the organic is lower than 0.3 eV, the contact is, for practical purposes Ohmic, supplying the bulk of the organic layer with a space charg e limited current. Determination of the carrier mobility by fitting experim ental current-voltage data is discussed and the voltage dependence of the c urrent and the efficiency are analyzed. The recombination profile is shown to evolve with voltage, shifting towards the electrode which injects the ca rrier with the lower mobility. The numerical results are compared with expe rimental data from poly[2-methoxy,5-(2-ethylhexoxy)-1,4-phenylene vinylene] (MEH-PPV) based devices. (C) 1999 American Institute of Physics. [S0021-89 79(99)06810-3].