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Validity of the Einstein relation in disordered organic semiconductors
G A H Wetzelaer1, L J A Koster, P W M Blom
1Molecular Electronics, Zernike Institute for Advanced Materials, University of Groningen, The Netherlands.
Physical Review Letters
|September 10, 2011
Summary
The Einstein relation in disordered semiconductors is not violated in thermal equilibrium. Deeply trapped carriers cause violations only under nonequilibrium conditions, proven by recombination experiments.
Area of Science:
- Solid-state physics
- Materials science
- Organic electronics
Background:
- The classical Einstein relation connects diffusion and mobility in semiconductors.
- Its validity in disordered materials, especially under thermal equilibrium, remains debated.
- Deeply trapped carriers are suspected to influence charge transport properties.
Purpose of the Study:
- To investigate the conditions under which the Einstein relation is violated in disordered semiconductors.
- To determine the role of deeply trapped carriers in potential violations.
- To clarify the validity of the Einstein relation in thermal (quasi)equilibrium.
Main Methods:
- Utilizing diffusion-driven current measurements in organic single-carrier diodes.
- Inducing and monitoring carrier recombination processes.
- Analyzing charge transport under both equilibrium and nonequilibrium conditions.
Main Results:
- The Einstein relation is demonstrably violated specifically under nonequilibrium conditions.
- Deeply trapped carriers were identified as the cause of these nonequilibrium violations.
- Recombination of trapped carriers confirmed the Einstein relation's validity in thermal (quasi)equilibrium.
Conclusions:
- The classical Einstein relation holds true for disordered semiconductors in thermal (quasi)equilibrium.
- Violations are exclusively linked to nonequilibrium states induced by deeply trapped carriers.
- Understanding carrier trapping and recombination is crucial for accurate semiconductor transport modeling.
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