Controlled positioning of metal nanoparticles in an organic light-emitting device for enhanced quantum efficiency

Abstract It is shown that there exists an optimum distance between the plane where nanoparticles (NPs) are positioned and the active layer of Au-NP-embedded organic light-emitting devices (OLEDs) for the maximum external quantum efficiency. Au NPs are precisely positioned in a specific plane in the hole-transport layer using a dry, room-temperature aerosol technique at atmospheric pressure. By controlling the position of the Au NPs and their density, we optimize the external quantum efficiency of the Au-NP-embedded OLEDs, with the maximum efficiency being 38% larger than that of the control device without Au NPs. In contrast to commonly employed methods to incorporate metal NPs in an organic layer, such as vacuum thermal evaporation or spin coating, the aerosol-deposited Au NPs do not penetrate into the underlying organic layer, not only allowing for precise control of the vertical (perpendicular to the substrate surface) position of the Au NPs, but also minimizing damage to the hole-transport organic material. Our electrical and optical characterizations show that the existence of the optimal distance occurs by the competition between the increased electron–hole recombination probability caused by the electrostatic effects of holes trapped in the Au NPs and the metal induced quenching.