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Spin-conserving carrier recombination in conjugated polymers

Spin-conserving carrier recombination in conjugated polymers
Spin-conserving carrier recombination in conjugated polymers
The ultimate efficiency of polymer light-emitting diodes is limited by the fraction of charges recombining in the molecular singlet manifold. We address the question of whether this fraction can principally exceed the fundamental limit set down by spin statistics, which requires the possibility of spin changes during exciton formation. Sensitized phosphorescence at 4?300 K enables a direct quantification of spin conversion in coulombically bound electron?hole pairs, the precursors to exciton formation. These are stabilized in external electric fields over times relevant to carrier transport, capture and recombination in devices. No interconversion of exciton intermediates between singlet and triplet configurations is observed. Static magnetic fields are equally unable to induce spin mixing in electroluminescence. Our observations imply substantial exchange splitting at all times during carrier capture. Prior statements regarding increased singlet yields above 25% merely on the basis of higher singlet than triplet formation rates should therefore be re-examined.
1476-1122
340-346
Reufer, Martin
9003a4cb-a048-4ec5-9a09-6b321fbf7606
Walter, Manfred J.
13fc080a-c86e-4e8f-8c8d-5c3ad9f5e118
Lagoudakis, Pavlos G.
ea50c228-f006-4edf-8459-60015d961bbf
Hummel, Anne Beate
a659b614-e556-47c9-a652-c5bb39bfd136
Kolb, Johanna S.
68b8a2db-08fc-4835-9f72-61b36787436f
Roskos, Hartmut G.
276d0de0-3e92-4601-8800-b452669bf3ce
Scherf, Ullrich
2cae67b6-723f-4cb8-ae65-2e70d5858dd8
Lupton, John M.
ae46a2f5-a0dd-4964-a85b-fb73b8b25e73
Reufer, Martin
9003a4cb-a048-4ec5-9a09-6b321fbf7606
Walter, Manfred J.
13fc080a-c86e-4e8f-8c8d-5c3ad9f5e118
Lagoudakis, Pavlos G.
ea50c228-f006-4edf-8459-60015d961bbf
Hummel, Anne Beate
a659b614-e556-47c9-a652-c5bb39bfd136
Kolb, Johanna S.
68b8a2db-08fc-4835-9f72-61b36787436f
Roskos, Hartmut G.
276d0de0-3e92-4601-8800-b452669bf3ce
Scherf, Ullrich
2cae67b6-723f-4cb8-ae65-2e70d5858dd8
Lupton, John M.
ae46a2f5-a0dd-4964-a85b-fb73b8b25e73

Reufer, Martin, Walter, Manfred J., Lagoudakis, Pavlos G., Hummel, Anne Beate, Kolb, Johanna S., Roskos, Hartmut G., Scherf, Ullrich and Lupton, John M. (2005) Spin-conserving carrier recombination in conjugated polymers. Nature Materials, 4 (4), 340-346. (doi:10.1038/nmat1354).

Record type: Article

Abstract

The ultimate efficiency of polymer light-emitting diodes is limited by the fraction of charges recombining in the molecular singlet manifold. We address the question of whether this fraction can principally exceed the fundamental limit set down by spin statistics, which requires the possibility of spin changes during exciton formation. Sensitized phosphorescence at 4?300 K enables a direct quantification of spin conversion in coulombically bound electron?hole pairs, the precursors to exciton formation. These are stabilized in external electric fields over times relevant to carrier transport, capture and recombination in devices. No interconversion of exciton intermediates between singlet and triplet configurations is observed. Static magnetic fields are equally unable to induce spin mixing in electroluminescence. Our observations imply substantial exchange splitting at all times during carrier capture. Prior statements regarding increased singlet yields above 25% merely on the basis of higher singlet than triplet formation rates should therefore be re-examined.

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Published date: April 2005

Identifiers

Local EPrints ID: 19267
URI: http://eprints.soton.ac.uk/id/eprint/19267
ISSN: 1476-1122
PURE UUID: 4ade5785-9e68-4237-adf7-d87837a9da5f

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Date deposited: 30 Jan 2006
Last modified: 09 Dec 2019 19:12

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