Donal Bradley

Abstract:

High photoluminescence (PL) efficiencies are desired to increase the brightness and operating lifetimes of organic light-emitting diodes. We present data on the transient PL-decay of PPV-type oligomers composed of 3 to 5 phenylene rings in blends and as pure films. The variation of the PL-decay with temperature, emission energy, and excitation energy is studied, and the changes in lifetime are correlated with the changes in relative efficiency. The results are compared with those of thin films of PPV. In blends the PL-decay is essentially independent of the number of phenylene rings of the oligomer. The temperature dependence of the oligomer blends is smaller than in the case of polymer films. In the oligomer blends, the PL spectrum changes with excitation energy and emission energy, indicating an inhomogeneous distribution of molecular sites.

Abstract:

Organic electroluminescence has been the subject of considerable interest in the last few years following reports from the Eastman Kodak and Kyushu University groups, and subsequently many others, on sublined films of low molecular weight dyes. We have shown that another class of organic, namely the conjugated polymers, can be used as the emissive layer in electroluminescent diodes and that these films have good stability. Combined with their ease of deposition over large areas, this makes them an attractive new category of electroluminescent material. Following our first report in 1990 on poly(p-phenylene vinylene) light emitting diodes, considerable progress has been made in enhancing device characteristics and in chemically tuning the colour of emission. In this paper I will review the status of progress in conjugated polymer electroluminescence and describe some recent results from the work ongoing in Sheffield. I will also provide a personal view of the prospects that this new area offers for lighting and display applications and highlight some of the current difficulties.