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.
Bibliographical noteFunding Information:
This work was supported by the Global Frontier R&D Program on Center for Multiscale Energy System (Grant Nos. 2011-0031561 and 2012M3A6A7054855) and the Engineering Research Center Program (Grant No. 2009-0093428 ), both by the National Research Foundation (NRF) under the Ministry of Science, ICT, and Future Planning, Korea. The work at Yonsei was supported by the Mid-career Researcher ( 2010-0029668 ) and World Class University ( R32-2010-000-10217 ) Programs of NRF grant funded by MEST of Korea, and AFSOR/AOARD Grant ( FA2386-10-1-4080 ) (D. K.).
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Materials Chemistry
- Electrical and Electronic Engineering