Issue
EPL
Volume 87, Number 5, September 2009
Article Number 57008
Number of page(s) 5
Section Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties
DOI http://dx.doi.org/10.1209/0295-5075/87/57008
Published online 23 September 2009
EPL, 87 (2009) 57008
DOI: 10.1209/0295-5075/87/57008

The role of triplet states in the emission mechanism of polymer light-emitting diodes

M. Arif1, S. Mukhopadhyay2, S. Ramasesha2 and S. Guha1

1   Department of Physics and Astronomy, University of Missouri - Columbia, MO 65211, USA
2   Solid State and Structural Chemistry Unit, Indian Institute of Science - Bangalore 560012, India

ramasesh@sscu.iisc.ernet.in
guhas@missouri.edu

received 17 July 2009; accepted in final form 27 August 2009; published September 2009
published online 23 September 2009

Abstract
The blue emission of polyfluorene (PF)-based light-emitting diodes (LEDs) is known to degrade due to a low-energy green emission, which hitherto has been attributed to oxidative defects. By studying the electroluminescence (EL) from ethyl-hexyl substituted PF LEDs in the presence of oxygen and in an inert atmosphere, and by using trace quantities of paramagnetic impurities (PM) in the polymer, we show that the triplet states play a major role in the low-energy emission mechanism. Our time-dependent many-body studies show a large cross-section for the triplet formation in the EL process in the presence of PM, primarily due to electron-hole recombination processes.

PACS
78.55.Kz - Solid organic materials.
78.60.Fi - Electroluminescence.
71.10.Li - Excited states and pairing interactions in model systems.

© EPLA 2009