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Light-Emitting Diodes Based on Conjugated Polymers: Control of Colour and Efficiency

Published online by Cambridge University Press:  25 February 2011

Paul L. Burn ,
A. B. Holmes ,
A. Kraft ,
A. R. Brown ,
D. D. C. Bradley  and
R. H. Friend
Paul L. Burn
Affiliation:
University Chemical Laboratory, Lensfield Road, Cambridge, CB2 1EW, United Kingdom
A. B. Holmes
Affiliation:
University Chemical Laboratory, Lensfield Road, Cambridge, CB2 1EW, United Kingdom
A. Kraft
Affiliation:
University Chemical Laboratory, Lensfield Road, Cambridge, CB2 1EW, United Kingdom
A. R. Brown
Affiliation:
Cavendish Laboratory, Madingley Road, Cambridge, CB3 OHE, United Kingdom
D. D. C. Bradley
Affiliation:
Cavendish Laboratory, Madingley Road, Cambridge, CB3 OHE, United Kingdom
R. H. Friend
Affiliation:
Cavendish Laboratory, Madingley Road, Cambridge, CB3 OHE, United Kingdom
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Abstract

Studies of the effect of different electrode combinations on the device characteristics of simple three layer light-emitting diodes (LEDs) prepared with poly(ρ-phenylenevinylene) (PPV) as the emissive layer sandwiched between two metal contacts have shown that it is generally more difficult to inject electrons than holes. In order to improve the efficiency of such devices it is, therefore, necessary to develop methods to enhance the injection of electrons and we illustrate here one example where we have successfully achieved this by the introduction of a further, electron transport, layer. The result is an eight fold increase in efficiency over our best three layer PPV devices. The efficiency is also dependent on the details of the polymer electronic structure and using a family of copolymers we have been able to produce enhancements in efficiency to values of up to 30 times that of the corresponding PPV devices. Variations in the polymer electronic structure also affect the colour of emission and the same family of copolymers allow control of emission colour from blue/green to orange/red. Supramolecular control of the copolymer electronic structure can be achieved by lithographic patterning and we show that it is possible to produce regions within a single polymer film that possess different π-π* energy gaps.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 247: Symposium N – Electrical, Optical, and Magnetic Properties of Organic Solid State Materials , 1992 , 647
Copyright
Copyright © Materials Research Society 1992

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References

REFERENCES

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