The authors are most grateful to Neil Greenham and Sir Richard Friend for stimulating discussions. This material is based upon work supported at Georgia Tech in part by the National Science Foundation through the STC Program under Award Number DMR-0120967 and through grant CHE-0342321, the Office of Naval Research, and the IBM Shared University Research Program. The work in Mons is partly supported by the European Commission IST program ′STEPLED′, the Belgian Federal Services for Scientific, Technical, and Cultural Affairs (InterUniversity Attraction Pole 5/3) and the Belgian National Science Foundation (FNRS). The work in Beijing is supported by the National Science Foundation of China (Grant No. 90203015) and the Ministry of Science and Technology of China (973 programme Grant No. 2002CB613406). David Beljonne is an FNRS Senior Research Associate.
Chain-Length Dependence of Singlet and Triplet Exciton Formation Rates in Organic Light-Emitting Diodes†
Article first published online: 22 JUL 2004
Copyright © 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Advanced Functional Materials
Volume 14, Issue 7, pages 684–692, July, 2004
How to Cite
Beljonne, D., Ye, A., Shuai, Z. and Brédas, J.-L. (2004), Chain-Length Dependence of Singlet and Triplet Exciton Formation Rates in Organic Light-Emitting Diodes. Adv. Funct. Mater., 14: 684–692. doi: 10.1002/adfm.200305176
- Issue published online: 22 JUL 2004
- Article first published online: 22 JUL 2004
- Manuscript Accepted: 4 FEB 2004
- Manuscript Received: 10 DEC 2003
- Light-emitting diodes, organic
The operation and efficiencies of molecular or polymer organic light-emitting diodes depend on the nature of the excited species that are formed. The lowest singlet and triplet excitons display different characteristics that impact on the quantum yields achievable in the devices. Here, by performing correlated quantum-chemical calculations that account for both the electronic couplings and energetics of the charge-recombination process from a pair of positive and negative polarons into singlet and triplet excitons, we show that the formation rates for singlet over triplet excitons vary with chain length and favor singlet excitons in longer chains. Thus, in polymer devices, the resulting singlet/triplet fraction can significantly exceed the spin-statistical limit.