Spin-dependent exciton formation rates in π-conjugated materials

M Wohlgenannt; Z. V Vardeny

doi:10.1088/0953-8984/15/3/202

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Spin-dependent exciton formation rates in π-conjugated materials

Journal article

Peer reviewed

Spin-dependent exciton formation rates in π-conjugated materials

M Wohlgenannt and Z. V Vardeny

Journal of physics. Condensed matter, Vol.15(3), pp.R83-R107

01/29/2003

DOI: 10.1088/0953-8984/15/3/202

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Abstract

π-conjugated compounds have been intensively studied for their use in 'plastic electronics', an alternative to inorganic semiconductor devices. In particular, research in the use of π-conjugated compounds as the active layer in electroluminescent devices has advanced rapidly: potential applications include e.g. flat, flexible display panels. In organic electroluminescent devices the annihilation of positive and negative charge carriers to the ground state proceeds via two fundamental steps: (i) formation of a neutral exciton, either spin singlet or spin triplet, and (ii) the radiative or non-radiative decay of the exciton. In most π-conjugated materials only the spin singlet exciton is emissive, and this is why the spin statistics of step (i) determines the maximum achievable electroluminescent efficiency. A number of recent studies indicate that exciton formation is spin dependent and that more singlets form in organic electroluminescent devices than what is expected from spin degeneracy. We review recent experimental and (to a lesser degree) theoretical results. In particular we focus on our own recent work, where we have measured the ratio, r = σS/σT, of the spin-dependent formation cross section, σ, of singlet (S) and triplet (T) excitons in π-conjugated oligomer and polymer films, using a spectroscopic/magnetic resonance technique. The experimental results reveal a distinct difference between exciton formation in molecular devices compared to polymer devices.

Physics

Condensed matter: electronic structure, electrical, magnetic, and optical properties

Electroluminescence

Electron states

Exact sciences and technology

Excitons and related phenomena

Intrinsic properties of excitons; optical absorption spectra

Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation

Other luminescence and radiative recombination

Details

Title: Subtitle: Spin-dependent exciton formation rates in π-conjugated materials
Creators: M Wohlgenannt - University of Iowa
Z. V Vardeny - University of Utah
Resource Type: Journal article
Publication Details: Journal of physics. Condensed matter, Vol.15(3), pp.R83-R107
Publisher: Institute of Physics
DOI: 10.1088/0953-8984/15/3/202
ISSN: 0953-8984
eISSN: 1361-648X
Language: English
Date published: 01/29/2003
Academic Unit: Physics and Astronomy
Record Identifier: 9984428807602771

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