Enhancing the efficiency of organic LEDs through spin-orbit coupling of charge-transfer states

In this thesis, the possibility of enhancing the efficiency of small molecule organic light-emitting diodes through spin-orbit effects is examined. Because only singlet spin states, statistically one quarter of the total possible states, emit fluorescent light, it has generally been thought that a maximum of 25% efficiency could be attained without the addition of an emissive phosphor. Here, we present evidence that this is not a fundamental limit. Two OLED structures have been studied, each providing evidence that the efficiency of the OLED can be enhanced by the use of a heavy-metal material to mix spin in charge-transfer states. A structure with a heavy-metal mixing layer placed beside a neat emissive layer was found to show a (2.5 ± 0.3) times enhancement in the efficiency compared with an OLED without the heavy-metal layer. However, differences in the electroluminescent emission spectra made attributing this result to spin statistics alone difficult. In a structure with the the heavy-metal mixing layer placed next to a fluorescent dye doped into a host, a (2.7 ± 0.2) times enhancement in the efficiency is measured.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Physics.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2006

Author dc:creator

• Rivoire, Kelley (Kelley E.)

Advisor dc:contributor.advisor

• Marc A. Baldo.

• Physics.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/36120

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/36120