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Details of Grant 

EPSRC Reference: GR/J43912/01
Principal Investigator: Friend, Professor Sir R
Other Investigators:
Holmes, Professor AB Bradley, Professor DD Ahmed, Professor H
Researcher Co-Investigators:
Project Partners:
Department: Physics
Organisation: University of Cambridge
Scheme: Standard Research (Pre-FEC)
Starts: 01 September 1993 Ends: 31 August 1996 Value (£): 389,354
EPSRC Research Topic Classifications:
Optoelect. Devices & Circuits
EPSRC Industrial Sector Classifications:
Related Grants:
Panel History:  
Summary on Grant Application Form
The objectives of this grant are to develop the device engineering aspects of polymer-based light-emitting diodes. This includes the optimisation of synthetic routes to the polymers most suitable for this application, such as poly(phenylene vinylene), PPV, processing and device fabrication, and measurements to establish the device physics of these structures. In addition, work is to be done to establish the scope for guided-wave devices.Progress:(i) S ynthesis of polymers to optimise processibility and electro-optical performance has progressed. PPV remains an important polymer for this project, and care with protocols for conversion from precursor to PPV now allow high luminescent efficiencies. Cyano-derivatives of PPV, which have high electron affinities, provide complementary polymers to PPV for formation of heterojunction devices. Recent progress includes the modification of the side-chains (to asymmetric, branched, alkoxy groups), which gives improved solubility in convenient solvents (toluene) and improved luminescence efficiency.(ii) Facilities for fabrication have been set up. These include RF sputtering of indium/tin oxide, for use as transparent electrodes, and a new glove-box system with insitu spin-coater and metals evaporator (thermal and electronbeam sources, with independent control from two sources). Post-deposition of indium/tin oxide onto PPV has allowed demonstration of a device formed on a non-transparent substrate (silicon wafer).(iii) Measurements of device characteristics have been augmented to include absolute efficiency determinations for electro- and photo-luminescence, using an integrating sphere. These show that the photoluminescence efficiencies of PPV and the cyano-PPVs are very much higher than had been previously considered (up to 50 per cent quantum efficiency), and demonstrate that these polymers have excellent potential for further development in LED structures (iv) The use of interference effects in microcavity structures has been demonstrated, using semitransparent gold and calcium/aluminium as electrodes and a PPV derivative as the emissive polymer layer. Control of wavelength of emission and narrowing of the emission waveband have been achieved.
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Organisation Website: http://www.cam.ac.uk