Characterization of Charge Transfer Processes Across Perylene Diimide/Electrode Interfaces for Organic Photovoltaic Devices

Persistent Link:
http://hdl.handle.net/10150/596140
Title:
Characterization of Charge Transfer Processes Across Perylene Diimide/Electrode Interfaces for Organic Photovoltaic Devices
Author:
Zheng, Yilong
Issue Date:
2016
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Embargo:
Release 08-Jan-2017
Abstract:
Charge transfer efficiency at the organic/transparent conducting oxide (TCO) interface is one of the key parameters controlling the overall efficiency of organic photovoltaics (OPVs). Modification of this interface with a redox-active organic surface modifier may further enhance the charge transfer across the interface by providing a charge-transfer pathway between the electrode and the organic active layer. Functionalized perylene diimide molecules (PDI) are useful for modifying metal oxide/acceptor interfaces for inverted solar cell devices because their LUMO energy level is close to some commonly used acceptor molecules. The effects of PDI structural parameters on the interfacial charge transfer processes across the organic/ITO interface were investigated. Six different PDI monolayers with different structural parameters were deposited on ITO surfaces to investigate the relationship between molecular orientation, linker length, aggregation and charge transfer process. The PDI orientation, degree of PDI aggregation and charge transfer process acrosses PDI/ITO interfaces were characterized by polarized ATR spectroscopy, PM-ATR spectroscopy and photoelectrochemistry. Both linker length and orientation affected the tunneling distance between PDI and ITO, therefore affecting the charge transfer rate constant across the PDI/ITO interfaces. PDI aggregation forced a more out-of-plane orientation of PDI molecules and increased the overall measured charge transfer rate constant. However, PDI aggregation also increased the excited state recombination rate which ultimately led to decrease of the charge collection efficiency. The first application of a PM-TIRF platform to characterize the electron-transfer processes of PDI monomeric films across the organic/electrode interface is presented. The PM-TIRF technique provides higher sensitivity as well as the capability to measure very fast charge transfer events, compared to other commonly used potential-modulated spectroscopy techniques. PDI-phenyl-PA monomeric films exhibited a more in-plane orientation compared with aggregated films and showed a smaller charge transfer rate constant across the PDI/ITO interfaces compared with PDI films with higher degrees of aggregation after normalizing the tunneling distance contributions.
Type:
text; Electronic Dissertation
Keywords:
Electron transfer; Organic photovoltaics; Organic semiconductors; Spectroelectrochemistry; Chemistry
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Chemistry
Degree Grantor:
University of Arizona
Advisor:
Saavedra, Steven Scott

Full metadata record

DC FieldValue Language
dc.language.isoen_USen
dc.titleCharacterization of Charge Transfer Processes Across Perylene Diimide/Electrode Interfaces for Organic Photovoltaic Devicesen_US
dc.creatorZheng, Yilongen
dc.contributor.authorZheng, Yilongen
dc.date.issued2016en
dc.publisherThe University of Arizona.en
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en
dc.description.releaseRelease 08-Jan-2017en
dc.description.abstractCharge transfer efficiency at the organic/transparent conducting oxide (TCO) interface is one of the key parameters controlling the overall efficiency of organic photovoltaics (OPVs). Modification of this interface with a redox-active organic surface modifier may further enhance the charge transfer across the interface by providing a charge-transfer pathway between the electrode and the organic active layer. Functionalized perylene diimide molecules (PDI) are useful for modifying metal oxide/acceptor interfaces for inverted solar cell devices because their LUMO energy level is close to some commonly used acceptor molecules. The effects of PDI structural parameters on the interfacial charge transfer processes across the organic/ITO interface were investigated. Six different PDI monolayers with different structural parameters were deposited on ITO surfaces to investigate the relationship between molecular orientation, linker length, aggregation and charge transfer process. The PDI orientation, degree of PDI aggregation and charge transfer process acrosses PDI/ITO interfaces were characterized by polarized ATR spectroscopy, PM-ATR spectroscopy and photoelectrochemistry. Both linker length and orientation affected the tunneling distance between PDI and ITO, therefore affecting the charge transfer rate constant across the PDI/ITO interfaces. PDI aggregation forced a more out-of-plane orientation of PDI molecules and increased the overall measured charge transfer rate constant. However, PDI aggregation also increased the excited state recombination rate which ultimately led to decrease of the charge collection efficiency. The first application of a PM-TIRF platform to characterize the electron-transfer processes of PDI monomeric films across the organic/electrode interface is presented. The PM-TIRF technique provides higher sensitivity as well as the capability to measure very fast charge transfer events, compared to other commonly used potential-modulated spectroscopy techniques. PDI-phenyl-PA monomeric films exhibited a more in-plane orientation compared with aggregated films and showed a smaller charge transfer rate constant across the PDI/ITO interfaces compared with PDI films with higher degrees of aggregation after normalizing the tunneling distance contributions.en
dc.typetexten
dc.typeElectronic Dissertationen
dc.subjectElectron transferen
dc.subjectOrganic photovoltaicsen
dc.subjectOrganic semiconductorsen
dc.subjectSpectroelectrochemistryen
dc.subjectChemistryen
thesis.degree.namePh.D.en
thesis.degree.leveldoctoralen
thesis.degree.disciplineGraduate Collegeen
thesis.degree.disciplineChemistryen
thesis.degree.grantorUniversity of Arizonaen
dc.contributor.advisorSaavedra, Steven Scotten
dc.contributor.committeememberSaavedra, Steven Scotten
dc.contributor.committeememberArmstrong, Neal R.en
dc.contributor.committeememberHeien, Michael L.en
dc.contributor.committeememberMcGrath, Dominic V.en
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