Enhancement of electroluminescence through a two-dimensional corrugated metal film by grating-induced surface-plasmon cross coupling.

We report enhancement of electroluminescence through opaque-topped metal cathodes in organic light-emitting devices (OLEDs), which are periodically corrugated in two dimensions. The enhancement is caused by grating-induced cross coupling and outcoupling of surface plasmons. The emission intensity observed at normal direction is enhanced by a factor of 4 compared with that of OLEDs with one-dimensionally corrugated metal cathodes and is higher than that observed from the transparent substrate side in uncorrugated OLEDs. We attribute the enhancement to the fact that the surface plasmons propagating in all lateral directions are coupled out into free space by the two-dimensional corrugated structure of the OLEDs. In addition, the emission from the transparent substrate side is also much enhanced owing to the efficient coupling out of the waveguide modes trapped in the emissive layer.