Performance Boost of Organic Light-Emitting Diodes with Plasmonic Nanostars

The performance of organic light-emitting diodes (OLEDs) is boosted by adding star-shaped plasmonic particles, so called nanostars. For this purpose, silver-enhanced gold nanostars coated with a thin silica shell, which tightly follow the nanostar morphology, are synthesized. An optimal spectral overlap between the multiple plasmon resonances of the nanostars and the luminescence of the emitting polymers is one key for the substantial increase of the electroluminescence. The second key ingredient is the star-shaped morphology. Experiments quantifying the photoluminescence, electroluminescence, and the current-voltage characteristics reveal that the physical origins of the improved performance are twofold; first, a plasmon mediated increase of the radiative recombination of excitons, and second, an improved outcoupling of light otherwise trapped inside the OLEDs. The thin silica shell apparently minimizes exciton quenching via energy transfer and prevents the nanostars from short-cutting the active layer.