Effects of disorder on the current density and recombination profile in organic light-emitting diodes

In this paper the effects of energetic disorder on the current density and recombination profile of single-layer organic light-emitting diodes (OLEDs) with Gaussian shapes of the electron and hole densities of states are studied. Gaussian disorder is found to give rise to a strong enhancement of the double carrier current density as compared to the sum of the single-carrier current densities and, in symmetric OLEDs, to a strong confinement of the recombination profile to the center of the device. The study is made using a OLED device model which makes use of a one-dimensional master-equation method within which hopping takes place in between discrete sites at physically meaningful intersite distances and within which the intersite hopping rates are consistent with the carrier density dependence of the mobility as obtained by Pasveer [Phys. Rev. Lett. 94, 206601 (2005)]. The model is shown to provide physically transparent descriptions of the dependence of the mobility and the recombination rate on the electric field, based on results from three-dimensional modeling. An outlook is given on applications to multilayer OLEDs.