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The effect of gases on the electrical properties of some organic semiconductors

van Ewyk, Robert L (1978) The effect of gases on the electrical properties of some organic semiconductors. Doctor of Philosophy (PhD) thesis, University of Kent. (doi:10.22024/UniKent/01.02.94703) (KAR id:94703)

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Effects of gases (primarily NgO^, BF^, Og and NH^) on the electrical properties of molecular single crystals of donors (phthalocyanine and its Mn(ll), Co(ll), Ni(ll), Cu(ll), Zn(ll) and Ph(ll) complexes, anthracene, perylene and the bis(8-hydroxyquinoline) complexes of Cu(ll) and Pd(ll)), electron acceptor (7,7,8,8 tetraeyanoquinodimethane) and an electron donor-acceptor complex (perylene/7,7,8,8 tetracyanoquinodimethane) have been studied. Apparatus was constructed permitting measurement of semiconduction and photoconduction in vacuo and in various gas pressures, over a temperature range of 290-500K.

The conductivity of electron donor and acceptor crystals was only enhanced by electron acceptor and donor gases, respectively, whereas the donor-acceptor complexes were enhanced slightly by both types of gases. Gas effects were confined to the crystal surfaces, except for oxygen on phthalocyanines. The rate and magnitude of conductivity changes on varying the gas pressure were consistent with chemisorption involving electron transfer. Electron transfer between % delocalised orbitals (e.g. NgO^ on phthalocyanines) gave reversible adsorption and gas pressures above 10^Pa resulted in complete surface coverage, each adsorbed molecule producing one surface charge carrier. The more localised c orbitals (e.g. BF-^ on phthalo- cyanineB) resulted in stronger adsorption. Exceptionally, irreversible chemical reaction follows electron transfer (e.g. NgO^ on anthracene). Enhanced semiconduction is accompanied by significant reductions in the activation energy, to values comparable with the photoconduction activation energy. Photoconduction is more sensitive than semiconduction to low gas pressures. Changes in the photoconduction spectral response reflect the influence of adsorbed gases on the exciton dissociation process. Adsorbed NgO^ inhibits the singlet photoconduction in tetracyanoquinodimethane and perylene, but smaller low energy response, with fine structure, possibly triplet bulk photoconduction, persists. Increased surface ionized state density reduces the carrier mobility, resulting in reduced dependence of photocurrent on incident light intensity.

The implications of these findings for the design of organic semiconductor gas detectors are discussed.

Item Type: Thesis (Doctor of Philosophy (PhD))
DOI/Identification number: 10.22024/UniKent/01.02.94703
Additional information: This thesis has been digitised by EThOS, the British Library digitisation service, for purposes of preservation and dissemination. It was uploaded to KAR on 25 April 2022 in order to hold its content and record within University of Kent systems. It is available Open Access using a Creative Commons Attribution, Non-commercial, No Derivatives ( licence so that the thesis and its author, can benefit from opportunities for increased readership and citation. This was done in line with University of Kent policies ( If you feel that your rights are compromised by open access to this thesis, or if you would like more information about its availability, please contact us at and we will seriously consider your claim under the terms of our Take-Down Policy (
Uncontrolled keywords: Chemistry; physics; chemical physics
Subjects: Q Science
Divisions: Divisions > Division of Natural Sciences > Physics and Astronomy
SWORD Depositor: SWORD Copy
Depositing User: SWORD Copy
Date Deposited: 25 Nov 2022 10:58 UTC
Last Modified: 25 Nov 2022 10:58 UTC
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