The application of polyfluorenes and related polymers in light emitting diodes

We report our progress to date in the materials and processing aspects of developing organic light emitting diode technology based on high molecular weight polymers. A portfolio of fluorene-related polymers are prepared through the coupling of 9,9-disubstituted 2,7-bis-1,3,2-dioxaborolanyl-fluorene with a variety of aromatic dibromides. In the case of fluorene homopolymers, the polyphenylene main chain provides the mechanical, electrical and electronic properties and the C-9 maintains coplanarity of the biphenylene unit and a site for property modification without altering effective conjugation. In the case of alternating polymers, the optical and electronic properties of the polymers are tailored through selective incorporation of different aromatic unit into the system. These polymers are soluble in common organic solvents and are readily processed into uniformed films of high quality by spin casting. Unlike PPV and related materials, LED devices with fluorene polymers in a conventional configuration appear to have electrons as the majority carrier and their performance is markedly improved when modified with an appropriate polymeric hole transporting layer. Bright green light with a luminance of 10000 Cd/m(2) is achieved at a very low drive voltage of <6 V attributable in part to the high hole mobility of fluorene-based polymers.