Numerical analysis of the mechanism of carrier transport in organic light-emitting devices

The mechanism of carrier transport in organic light-emitting devices is numerically studied, on the basis of trapped-charge-limited conduction with an exponential trap distribution. The spatial distributions of the electrical potential, field and carrier density in the organic layer are calculated and analysed. Most carriers are distributed near the two electrodes, only a few of them are distributed over the remaining part of the organic layer. The carriers are accumulated near the electrodes and the remaining region is almost exhausted of carriers. When the characteristic energy of trap distribution is greater than 0.3 eV, it leads to a reduction of current density. In order to improve the device efficiency, organic materials with minor traps and low characteristic energy should be chosen. The diffusion current is the dominant component near the injection electrode, whereas the drift current dominates the remaining region of the organic layer.