Platinum Binuclear Complexes as Phosphorescent Dopants for Monochromatic and White Organic Light-Emitting Diodes

Authors

  • B. Ma,

    1. Department of Chemical Engineering and Materials Science, and Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA
    2. Current address: Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
    Search for more papers by this author
  • P. I. Djurovich,

    1. Department of Chemical Engineering and Materials Science, and Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA
    Search for more papers by this author
  • S. Garon,

    1. Department of Chemical Engineering and Materials Science, and Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA
    Search for more papers by this author
  • B. Alleyne,

    1. Department of Chemical Engineering and Materials Science, and Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA
    2. Current address: Universal Display Corporation, Ewing, NJ 08618, USA
    Search for more papers by this author
  • M. E. Thompson

    1. Department of Chemical Engineering and Materials Science, and Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA
    Search for more papers by this author

  • We thank the Universal Display Corporation and the Department of Energy for financial support of this work. Supporting Information is available online from Wiley InterScience or from the author.

Abstract

Efficient blue-, green-, and red-light-emitting organic diodes are fabricated using binuclear platinum complexes as phosphorescent dopants. The series of complexes used here have pyrazolate bridging ligands and the general formula CNPt(μ-pz)2PtCN (where CN = 2-(4′,6′-difluorophenyl)pyridinato-N,C2′, pz = pyrazole (1), 3-methyl-5-tert-butylpyrazole (2), and 3,5-bis(tert-butyl)pyrazole (3)). The Pt–Pt distance in the complexes, which decreases in the order 1 > 2 > 3, solely determines the electroluminescence color of the organic light-emitting diodes (OLEDs). Blue OLEDs fabricated using 8 % 1 doped into a 3,5-bis(N-carbazolyl)benzene (mCP) host have a quantum efficiency of 4.3 % at 120 Cd m–2, a brightness of 3900 Cd m–2 at 12 V, and Commission Internationale de L'Eclairage (CIE) coordinates of (0.11, 0.24). Green and red OLEDs fabricated with 2 and 3, respectively, also give high quantum efficiencies (∼ 6.7 %), with CIE coordinates of (0.31, 0.63) and (0.59, 0.46), respectively. The current-density–voltage characteristics of devices made using dopants 2 and 3 indicate that hole trapping is enhanced by short Pt–Pt distances (< 3.1 Å). Blue electrophosphorescence is achieved by taking advantage of the binuclear molecular geometry in order to suppress dopant intermolecular interactions. No evidence of low-energy emission from aggregate states is observed in OLEDs made with 50 % 1 doped into mCP. OLEDs made using 100 % 1 as an emissive layer display red luminescence, which is believed to originate from distorted complexes with compressed Pt–Pt separations located in defect sites within the neat film. White OLEDs are fabricated using 1 and 3 in three different device architectures, either with one or two dopants in dual emissive layers or both dopants in a single emissive layer. All the white OLEDs have high quantum efficiency (∼ 5 %) and brightness (∼ 600 Cd m–2 at 10 V).

Ancillary