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Spin-Dependent Recombination in PPV and Polyfluorene LEDs

Published online by Cambridge University Press:  01 February 2011

Anoop S. Dhoot  and
Neil C. Greenham
Anoop S. Dhoot
Affiliation:
Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE, United Kingdom
Neil C. Greenham
Affiliation:
Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE, United Kingdom
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Abstract

In a polymer light-emitting diode, the fraction of excitons formed as singlets is of crucial importance in determining the quantum efficiency. We have shown that it is possible to measure excited state absorptions due to triplet excitons and polarons in working polymer LEDs, and we are able to quantify the triplet generation rate by measuring the strength of the triplet absorption. Here, we show that by careful study of singlet emission and triplet absorption in an LED based on a poly(p-phenylenevinylene) derivative we can obtain an accurate value of 83±7% for the singlet formation probability, significantly higher than the value of 25% predicted by simple spin statistics. We extend these measurements to devices based on poly(dioctyl-fluorene), where we find similarly high values for the singlet formation probability. In devices using the polyfluorene copolymer F8BT, we find that the triplet absorption is extremely small, consistent with even higher singlet formation probabilities.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 725: Symposium P – Organic and Polymeric Materials and Devices-Optical, Electrical, and Optoelectronic Properties , 2002 , P8.2
Copyright
Copyright © Materials Research Society 2002

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