title: Effects of Gold-Nanoparticle Surface and Vertical Coverage by Conducting Polymer between Indium Tin Oxide and the Hole Transport Layer on Organic Light-Emitting Diodes.
abstract: The effect of varying degrees of surface and vertical coverage of gold nanoparticles (Au-NPs) by poly(styrenesulfonate)-doped poly(3,4-ethylenedioxythiophene) (
  PSS), which was used as a capping layer between indium tin oxide (ITO) and a hole transport layer (HTL) on small-molecule fluorescent organic light-emitting diodes (OLEDs), was systemically investigated. With respect to the Au-NP loading amount and size, the resultant current densities influenced the charge balance and, therefore, the OLED device performance. When the capping layer consisted of ITO/Au-NPs/
  PSS+Au-NPs, superior device performance was obtained with 10-nm Au-NPs through increased surface coverage in comparison to other Au-NP PEDOT:PSS coverage conditions. Furthermore, the Au-NP size determined the vertical coverage of the capping layer. The current densities of OLEDs containing small Au-NPs (less than 30 nm, small vertical coverage) covered by
  PSS decreased because of the suppression of the hole carriers by the Au-NP trapping sites. However, the current densities of the devices with large Au-NPs (over 30 nm, large vertical coverage) increased. The increased electromagnetic fields observed around relatively large Au-NPs under electrical bias were attributed to increased current densities in the OLEDs, as confirmed by the finite-difference time-domain simulation. These results show that the coverage conditions of the Au-NPs by the
  PSS clearly influenced the OLED current density and efficiency.
authors.affiliation: †Department of Chemistry, College of Natural Sciences, Seoul National University, Seoul 151-747, Republic of Korea.
authors.forename: Sung Hyun
authors.initials: SH
authors.lastname: Kim
authors.forename: Tae-Sung
authors.initials: TS
authors.lastname: Bae
authors.affiliation: §Department of Chemistry, Pohang University of Science and Technology (POSTECH), 77 Cheongam-Ro, Nam-Gu, Pohang, Gyeongbuk 790-784, Republic of Korea.
authors.forename: Wooseok
authors.initials: W
authors.lastname: Heo
authors.affiliation: §Department of Chemistry, Pohang University of Science and Technology (POSTECH), 77 Cheongam-Ro, Nam-Gu, Pohang, Gyeongbuk 790-784, Republic of Korea.
authors.forename: Taiha
authors.initials: T
authors.lastname: Joo
authors.affiliation: ∥Department of Physics, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul, 136-701, Republic of Korea.
authors.forename: Kyung-Deok
authors.initials: KD
authors.lastname: Song
authors.affiliation: ∥Department of Physics, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul, 136-701, Republic of Korea.
authors.forename: Hong-Gyu
authors.initials: HG
authors.lastname: Park
authors.forename: Seung yoon
authors.initials: Sy
authors.lastname: Ryu
keywords: charge balance; conducting polymer; gold nanoparticles; organic light-emitting diodes; surface and vertical coverage; surface plasmonic resonance effect