Interpretation of electron diffusion coefficient in organic and inorganic semiconductors with broad distributions of states
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comunitat-uji-handle2:10234/2507
comunitat-uji-handle3:10234/6973
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Title
Interpretation of electron diffusion coefficient in organic and inorganic semiconductors with broad distributions of statesAuthor (s)
Date
2008Publisher
Royal Society of ChemistryISSN
14639076Type
info:eu-repo/semantics/articleVersion
info:eu-repo/semantics/acceptedVersionAbstract
The carrier transport properties in nanocrystalline semiconductors and organic materials play a
key role for modern organic/inorganic devices such as dye-sensitized (DSC) and organic solar
cells, organic and hybrid ... [+]
The carrier transport properties in nanocrystalline semiconductors and organic materials play a
key role for modern organic/inorganic devices such as dye-sensitized (DSC) and organic solar
cells, organic and hybrid light-emitting diodes (OLEDs), organic field-effect transistors, and
electrochemical sensors and displays. Carrier transport in these materials usually occurs by
transitions in a broad distribution of localized states. As a result the transport is dominated by
thermal activation to a band of extended states (multiple trapping), or if these do not exist, by
hopping via localized states. We provide a general view of the physical interpretation of the
variations of carrier transport coefficients (diffusion coefficient and mobility) with respect to the
carrier concentration, or Fermi level, examining in detail models for carrier transport in
nanocrystalline semiconductors and organic materials with the following distributions: single and
two-level systems, exponential and Gaussian density of states. We treat both the multiple
trapping models and the hopping model in the transport energy approximation. The analysis is
simplified by thermodynamic properties: the chemical capacitance, Cm, and the thermodynamic
factor, wn, that allow us to derive many properties of the chemical diffusion coefficient, Dn, used
in Fick’s law. The formulation of the generalized Einstein relation for the mobility to diffusion
ratio shows that the carrier mobility is proportional to the jump diffusion coefficient, DJ, that is
derived from single particle random walk. Characteristic experimental data for nanocrystalline
TiO2 in DSC and electrochemically doped conducting polymers are discussed in the light of
these models [-]
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