Controlling molecular conformation for highly efficient and stable deep-blue copolymer light-emitting diodes

I. Hamilton, N. Chander, N.J. Cheetham, M. Suh, M. Dyson, X. Wang, P.N. Stavrinou, M. Cass, D.D.C. Bradley, Ji-Seon Kim

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Abstract

We report a novel approach to achieve deep-blue, high-efficiency, and long-lived solution-processed polymer light-emitting diodes (PLEDs) via a simple molecular level conformation change of an emissive conjugated polymer. We introduce rigid β-phase segments into a 95% fluorene—5% arylamine copolymer emissive layer. The arylamine moieties at low density act as efficient exciton formation sites in PLEDs, whereas the conformational change alters the nature of the dominant luminescence from a broad, charge transfer like emission to a significantly blue-shifted and highly vibronically structured excitonic emission. As a consequence, we observe a significant improvement in the Commission International de L’Eclairage (x, y) coordinates from (0.149, 0.175) to (0.145, 0.123) while maintaining high efficiency and improved stability. We achieve a peak luminous efficiency, η = 3.60 cd/A, and a luminous power efficiency, ηw = 2.44 lm/W, values that represent state-of-the-art performance for single copolymer deep-blue PLEDs. These values are 5-fold better than for otherwise-equivalent, β-phase poly(9,9-dioctylfluorene) PLEDs (0.70 cd/A and 0.38 lm/W). This report represents the first demonstration of the use of molecular conformation as a simple but effective method to control the optoelectronic properties of a fluorene copolymer; previous examples have been confined to homopolymers.
Original languageEnglish
Pages (from-to)11070-11082
Number of pages13
JournalACS Applied Materials & Interfaces
Volume10
Issue number13
DOIs
Publication statusPublished - 4 Apr 2018

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Keywords

  • deep-blue, polymer light-emitting diodes, β-phase, polyfluorenes, copolymers
  • copolymers
  • deep-blue
  • polymer light-emitting diodes
  • polyfluorenes
  • β-phase
  • beta-phase

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