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Modelling charge transport in organic semiconductors
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McMahon, David Paul (2011) Modelling charge transport in organic semiconductors. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b2491804~S15
Abstract
Modelling of the charge transport in different types of organic semiconductors
(molecular crystals and semicrystalline polymers) is undertaken using a number of
different methods.
Using a polarisable force field we have determined the extent of the external
reorganisation energy for hole transport in molecular crystals. We have found that
this key parameter is very small for naphthalene, anthracene, tetracene, pentacene
and rubrene and discussed the implications of this finding in the context of charge
transport modelling.
Charge trapping in organic crystals due to defect states is studied by
computation of the rate of escape of a trapped charge carrier using non-adiabatic rate
theory. Two cases are considered, the first is hopping between separate identical
defect states and the second is hopping from a defect state into the bulk (delocalised)
states. This latter process is determined as the more likely to occur for a realistic
defect concentration. The necessity of the inclusion of an effective quantum mode of
vibration for the accurate computation of the rate is also demonstrated.
A linear scaling method based on the definition of a localised molecular
orbital set is devised for the computation of the electronic structure of a conjugated
polymer (poly(3-hexylthiophene) (P3HT)). Utilising a combined classical and
quantum chemical approach we show that charge carriers are localised in
correspondence with long-lived traps which are also present in the crystalline phase
of the polymer. The regio-regularity of P3HT is shown to have little impact on the
shape and tail of the density of states; we compute the 2D localised trap density as
~3.1×1013 cm-2, a value which is not found to significantly change with the regioregularity.
The states in the tail of the density of states are found to be
predominantly localised but energetically close to delocalised "quasi-band" states
which are accessible under device operation.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QC Physics Q Science > QD Chemistry |
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Library of Congress Subject Headings (LCSH): | Organic semiconductors -- Analysis | ||||
Official Date: | February 2011 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Department of Chemistry | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Troisi, Alessandro | ||||
Sponsors: | Engineering and Physical Sciences Research Council (EPSRC) ; European Research Council (ERC) | ||||
Extent: | 157 leaves : ill., charts | ||||
Language: | eng |
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