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

Journal article

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.

Authors: Hamilton, I; Chander, N; Cheetham, N; Suh, M; Dyson, M

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Chemical Society
• Journal: ACS Applied Materials Interfaces
• Volume: 10
• Issue: 13
• Pages: 11070–11082
• Publication date: 2018-03-06
• Acceptance date: 2018-03-06
• DOI: 10.1021/acsami.8b00243
• EISSN: 1944-8252
• ISSN: 1944-8244
• Pmid: 29508604
• Language: English
• Keywords: copolymers; polymer light-emitting diodes; β-phase; deep-blue; polyfluorenes