Paul Stavrinou

Abstract:

We report the integration of micro-patterned polyfluorene conjugated polymers onto GaN-based ultraviolet (UV) micro-pixellated light-emitting diode arrays (micro-LEDs). The 64 × 64 element matrix-addressable AlInGaN devices have a pixel size of 20 νm diameter on a 50 νm pitch, emitting at 368 nm. Each array is covered with a 2.5 νm thick photo-curable deep-UV-transparent polymer and a 30 nm thick polyfluorene film. This polymer bi-layer is subsequently patterned into an array of 28 νm diameter discs aligned with the pixels of the micro-LED array. Polymer down-converted visible emission from these pattern-programmable organic/inorganic electroluminescent micro-arrays is achieved. © 2008 IOP Publishing Ltd.

Abstract:

The combination of efficient light emission and high charge-carrier mobility has thus far proved elusive for polymer semiconductors, with high mobility typically achieved by cofacial pi-electron system to pi-electron system interactions that quench exciton luminescence. We report a new strategy, comprising the introduction of a limited number of more effective hopping sites between otherwise relatively isolated, and thus highly luminescent, polyfluorene chains. Our approach results in polymer films with large mobility (mu approximately 3-6 x 10(-2) cm2 V-1 s-1) and simultaneously excellent light-emission characteristics. These materials are expected to be of interest for light-emitting transistors, light-emitting diode sources for optical communications and may offer renewed hope for electrically pumped laser action. In the last context, optically pumped distributed feedback lasers comprising one-dimensional etched silica grating structures coated with polymer have state-of-the-art excitation thresholds (as low as 30 W cm(-2) (0.1 nJ per pulse or 0.3 microJ cm-2) for 10 Hz, 12 ns, 390 nm excitation) and slope efficiencies (up to 11%).