Enhanced efficiency of polyfluorene derivatives: Organic-inorganic hybrid polymer light-emitting diodes

Abstract

Two novel organic-inorganic hybrid polyfluorene derivatives, poly{(9,9'-dioctyl-2,7-fluorene)-co-(9,9'-di-POSS-2,7-fluorene)-co-[2,5-bis(octyloxy)-1,4-phenylene]} (PFDOPPOSS) and poly{(9,9'-dioctyl-2,7-fluorene)-co-(9,9'-di-POSS-2,7-fluorene)-co-bithiophene} (PFT2POSS), were synthesized by the Pd-catalyzed Suzuki reaction of polyhedral oligomeric silsesquioxane (POSS) appended fluorene, dioctyl phenylene, and bithiophene moieties. The synthesized polymers were characterized with H-1 NMR spectroscopy and elemental analysis. Photoluminescence (PL) studies showed that the incorporation of the POSS pendant into the polyfluorene derivatives significantly enhanced the fluorescence quantum yields of the polymer films, likely via a reduction in the degree of interchain interaction as well as keto formation. Additionally, the blue-light-emitting polyfluorene derivative PFDOPPOSS showed high thermal color stability in PL. Moreover, single-layer light-emitting diode devices of an indium tin oxide/poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate)/polymer/Ca/Al configuration fabricated with PFDOPPOSS and PFT2POSS showed much improved brightness, maximum luminescence intensity, and quantum efficiency in comparison with devices fabricated with the corresponding pristine polymers PFDOP and PFT2. In particular, the maximum external quantum efficiency of PFT2POSS was 0.13%, which was twice that of PFT2 (0.06%), and the maximum current efficiency of PFT2POSS was 0.38 cd/A, which again was twice that of PFT2 (0.19 cd/A). (c) 2006 Wiley Periodicals, Inc.