Emission characteristics of OLEDs on planar and non-planar substrates

We report on light extraction experiments with polyfluorene based organic light emitting diodes (OLEDs). The intensity distribution of emission within the substrate and within air is determined experimentally. For the devices investigated in this study, we find that the external quantum efficiency can be increased by a factor of 1.82, in the case of complete suppression of waveguiding within the substrate. The experimental data is in good agreement with modeling results based on dipole emission within a multilayer system. As a consequence of these findings, we modified the device topology by introducing light extraction structures between glass substrate and indium tin oxide anode. This results in redirection of photon trajectories and thus in a higher probability to extract waveguided radiation. At a luminance of 100 cd/m(2), the photometric efficiency for emission in forward direction is enhanced by a factor of 1.45 to 8.9 cd/A.