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18 June 2004 Polymer blend LEDs using polyfluorene copolymers and thermally cross-linked fluoropolymers
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The use of conjugated light emitting polymers (LEPs) blended in non-conjugated matrices offers an enhancement in electroluminescence efficiency in polymer light emitting diodes (PLEDs) since the aggregate quenching of the excited state emission is ameliorated. In such a scheme the matrix polymer may be developed in order to enhance the thermal, mechanical, and processing properties of the LEP blend as a whole. We have produced solution processable blends of polyfluorene (PF) based copolymers with thermally crosslinkable perfluoroarylether (PFAE) polymers and tested these materials' performance as a single emissive layer in the simplest PLED structure. Specifically we present results of blends consisting of red poly[{9,9-dihexyl-2,7-bis(1-cyanovinylene)fluorenyl-ene}-alt-co-{2,5-bis(N,N'-diphenylamino)-1,4-phenylene}] as the LEP and a novel PFAE which is thermally crosslinked as the matrix. The new PFAE has been specifically developed for low optical loss, high glass transition temperature (Tg), and solution process-ability. Once spun cast and thermally crosslinked, films of these polymer blends show increased solvent resistance and enhanced Tg due to the fluoropolymer matrix. Simple ITO/polymer/Al PLEDs of several concentration ratios are fabricated and tested in order to determine the efficacy of various matrix additions. The light-current density-voltage characteristics show either equivalent or enhanced efficiency depending on LEP/PFAE concentration. Blends of the PFAE and PF copolymer LEPs are patterned into 6μm waveguide structures utilizing the solvent resistance afforded by the crosslinked PFAE matrix.
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Vincenzo Casasanta, Timothy Londergan, and Raluca Dinu "Polymer blend LEDs using polyfluorene copolymers and thermally cross-linked fluoropolymers", Proc. SPIE 5351, Organic Photonic Materials and Devices VI, (18 June 2004);

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