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Applied Physics Letters / Volume 93 / Issue 12 / ORGANIC ELECTRONICS AND PHOTONICS
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Appl. Phys. Lett. 93, 123312 (2008); http://dx.doi.org/10.1063/1.2988273 (3 pages)

Spin injection effects on exciton formation in organic semiconductors

M. Yunus1, P. P. Ruden1, and D. L. Smith2

1University of Minnesota, Minneapolis, Minnesota 55455, USA
2Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA

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(Received 18 June 2008; accepted 30 August 2008; published online 25 September 2008)

The effects of spin-polarized electron and hole injection from ferromagnetic contacts on the formation and distribution of singlet and triplet excitons in a conjugated organic semiconductor are modeled. Electron and hole transport in the semiconductor are described by spin-dependent device equations for a structure resembling an organic light emitting diode. The formation of electron-hole pairs at a given site is modeled as a Langevin process, and the subsequent local relaxation into the lowest energy exciton states is described by rate equations. Once formed, excitons may recombine in the semiconductor or diffuse through the material and recombine at the contact interfaces. The model calculations yield steady-state spatial profiles for singlet and triplet excitons. It is shown that spin-polarized injection increases the formation of singlet excitons, and that the diffusion of excitons has significant effects on the triplet exciton profile.

© 2008 American Institute of Physics

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KEYWORDS and PACS

Keywords

excitons, ferromagnetic materials, organic semiconductors, spin polarised transport

PACS

  • 72.25.Dc

    Spin polarized transport in semiconductors

  • 72.25.Hg

    Electrical injection of spin polarized carriers

  • 72.80.Le

    Polymers; organic compounds (including organic semiconductors)

  • 71.35.-y

    Excitons and related phenomena

ARTICLE DATA

Digital Object Identifier
http://dx.doi.org/10.1063/1.2988273

PUBLICATION DATA

ISSN

0003-6951 (print)  
1077-3118 (online)

Publisher

$abstract.society.value is a Member of CrossRef American Institute of Physics

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Figures (4) Tables (1)

Figures (click on thumbnails to view enlargements)

FIG.1
A schematic representation of singlet and triplet exciton formation, recombination, and diffusion.

FIG.1 Download High Resolution Image (.zip file) | Export Figure to PowerPoint

FIG.2
AP and P pair generation rates as a function of position inside the organic semiconductor for different carrier mobilities. Solid lines are for unpolarized cases and dashed lines are for CP of 0.99 (μp = μn) and 0.964 (μp = 100μn).

FIG.2 Download High Resolution Image (.zip file) | Export Figure to PowerPoint

FIG.3
Profiles of the singlet exciton fraction, χS, inside the organic semiconductor for the different cases shown in Fig. 2.

FIG.3 Download High Resolution Image (.zip file) | Export Figure to PowerPoint

FIG.4
Steady-state profiles of singlet (solid) and triplet (dashed) exciton densities inside the organic semiconductor for different carrier mobilities.

FIG.4 Download High Resolution Image (.zip file) | Export Figure to PowerPoint

Tables

Table I. Model transport parameters of the half metal and the organic semiconductor.

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