Investigating Morphology and Stability of Fac-tris (2-phenylpyridyl)iridium(III) Films for OLEDs

Authors

  • Arthur R. G. Smith,

    1. Centre for Organic Photonics and Electronics, The University of Queensland, Brisbane, QLD 4072, Australia
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  • Jeremy L. Ruggles,

    1. School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia
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  • Hamish Cavaye,

    1. Centre for Organic Photonics and Electronics, The University of Queensland, Brisbane, QLD 4072, Australia
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  • Paul E. Shaw,

    1. Centre for Organic Photonics and Electronics, The University of Queensland, Brisbane, QLD 4072, Australia
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  • Tamim A. Darwish,

    1. Bragg Institute, Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia
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  • Michael James,

    1. Bragg Institute, Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia
    2. School of Chemistry, University of New South Wales, Sydney, NSW 2052, Australia
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  • Ian R. Gentle,

    Corresponding author
    1. School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia
    • School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia.
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  • Paul L. Burn

    Corresponding author
    1. Centre for Organic Photonics and Electronics, The University of Queensland, Brisbane, QLD 4072, Australia
    • Centre for Organic Photonics and Electronics, The University of Queensland, Brisbane, QLD 4072, Australia
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Abstract

Stable film morphology is critical for long-term high performance organic light-emitting diodes (OLEDs). Neutron reflectometry (NR) is used to study the out-of-plane structure of blended thin films and multilayer structures comprising evaporated small molecules. It is found that as-prepared blended films of fac-tris(2-phenylpyridyl)iridium(III) [Ir(ppy)3] in 4,4′-bis(N-carbazolyl)biphenyl (CBP) are uniformly mixed, but the occurrence of phase separation upon thermal annealing is dependent on the blend ratio. Films comprised of the ratio of 6 wt% of Ir(ppy)3 in CBP typically used in OLEDs are found to phase separate with moderate heating while a higher weight percent mixture (12 wt%) is found to be stable. Furthermore, it is found that thermal annealing of a multilayer film comprised of typical layers found in efficient devices ([tris(4-carbazoyl-9-ylphenyl)amine (TCTA)/Ir(ppy)3:CBP/bathocuproine (BCP)]) causes the BCP layer to become mixed with the emissive blend layer, whereas the TCTA interface remains unchanged. This significant structural change causes no appreciable difference in the photo­luminescence of the stack although such a change would have a dramatic effect on the charge transport through the device, leading to changes in performance. These results demonstrate the effect of thermal stress on the delicate interplay between the chemical composition and morphology of OLED films.

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