FDTD modelling of nanostructured OLEDs: analysis of simulation parameters for accurate radiation patterns

Nanostructures in OLEDs allow to manipulate the radiation pattern and direct light of a specific wavelength into a specific angle in the far field by resonant light outcoupling. We present a theoretical study investigating simulation conditions for accurate radiation patterns employing the FDTD method. Radiation patterns of single dipole emitters placed in a sufficiently large simulation domain are superimposed to model the incoherent emission of a continuous emission layer. The necessary simulation domain size is derived by considering propagation length and field profile of the guided mode of a corresponding unstructured OLED. A 5 nm mesh resolution is determined as a good compromise between accuracy and simulation time. The position of an emitter with respect to the grating has a large influence on the radiation pattern. Nevertheless, we demonstrate for nine different OLED structures that the radiation pattern of a homogeneous emission layer is approximated with an amplitude error of less than 5% by superimposing only four equally spaced dipoles at positions $$\pm \,(1/8, 3/8, 5/8, 7/8) \cdot \varLambda /2$$ , which avoid points of high symmetry.