Spin-dependent exciton formation in π-conjugated compounds

J. S. Wilson, A. S. Dhoot, A. J A B Seeley, M. S. Khan, A. Köhler, R. H. Friend

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Abstract

The efficiency of light-emitting diodes (LEDs) made from organic semiconductors is determined by the fraction of injected electrons and holes that recombine to form emissive spin-singlet states rather than non-emissive spin-triplet states. If the process by which these states form is spin-independent, the maximum efficiency of organic LEDs will be limited to 25 per cent1. But recent reports have indicated fractions of emissive singlet states ranging from 22 to 63 per cent2-5, and the reason for this variation remains unclear. Here we determine the absolute fraction of singlet states generated in a platinum-containing conjugated polymer and its corresponding monomer. The spin-orbit coupling introduced by the platinum atom allows triplet-state emission, so optically and electrically generated luminescence from both singlet and triplet states can be compared directly. We find an average singlet generation fraction of 22 ± 1 per cent for the monomer, but 57 ± 4 per cent for the polymer. This suggests that recombination is spin-independent for the monomer, but that a spin-dependent process, favouring singlet formation, is effective in the polymer. We suggest that this process is a consequence of the exchange interaction, which will operate on overlapping electron and hole wavefunctions on the same polymer chain at their capture radius.

Original languageEnglish
Pages (from-to)828-831
Number of pages4
JournalNature
Volume413
Issue number6858
DOIs
Publication statusPublished - Oct 25 2001

ASJC Scopus subject areas

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    Wilson, J. S., Dhoot, A. S., Seeley, A. J. A. B., Khan, M. S., Köhler, A., & Friend, R. H. (2001). Spin-dependent exciton formation in π-conjugated compounds. Nature, 413(6858), 828-831. https://doi.org/10.1038/35101565