Charge Transfer Processes across Organic/Electrode Interfaces in Organic Photovoltaics

Persistent Link:
http://hdl.handle.net/10150/312512
Title:
Charge Transfer Processes across Organic/Electrode Interfaces in Organic Photovoltaics
Author:
Lin, Hsiao-Chu
Issue Date:
2013
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.
Abstract:
Charge transfer efficiency at organic/electrode interfaces affects the performance organic photovoltaics (OPVs). It is hypothesized that the charge collection efficiency at organic/electrode interfaces is influenced by the structure of the first molecular layer adjacent to the electrode surface. Two differently oriented monolayers composed of two phosphonic acid (PA) functionalized zinc phthalocyanine (ZnPc) molecules, one with four PAs attached peripherally (ZnPcPA₄), one at each quadrant, and another that is functionalized with one PA (ZnPcPA), were tethered to indium tin oxide (ITO) surfaces as models for the donor/transparent conducting oxide (TCO) interface in OPVs to address the relationship between molecular orientation and electron transfer kinetics across the organic/ITO interface. The electron transfer rate constants across the monolayer/ITO interface were measured using potential modulated attenuated total reflectance (PM-ATR) spectroscopy in TE and TM polarizations, which allows rate constants to be determined for subpopulations of molecules that are oriented predominately in-plane and out-of-plane, respectively. The templating effect of the tethered monolayer on sequential layers of donor material for ZnPcPA and ZnPcPA₄ monolayers was assessed by depositing a few layers of CuPc on ZnPcPA- and ZnPcPA₄-modified ITO. The performance of OPV devices fabricated on ITO modified with these two monolayers was compared and correlated to their orientation and energy alignments with other layers in the devices. The dependence of kinetics of electron transfer on overpotential was studied using monolayer-tethered ZnPcPA on ITO. Measurements of apparent heterogeneous electron transfer rate constants (kapp) as a function of applied potential across the ZnPcPA/ITO interface were acquired using PM-ATR at various dc biases (Edc). With varying Edc imposed on the electrode, the fraction of adsorbed molecules in reduced or oxidized states is changed, and both the energetics and kinetics of the electrode reaction are affected. The results were discussed and compared to theoretical predictions. The photoinduced charge harvesting and photocurrent generation were assessed using a clicked ZnPc-perylene diimide (PDI) donor-acceptor assembly tethered to ITO via a PA anchoring group. This ZnPc-PDI donor-acceptor assembly was used to investigate the mechanism of photoinduced charge transfer and hole-capture by ITO in the presence of a solution phase redox mediator.
Type:
text; Electronic Dissertation
Keywords:
Chemistry
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Chemistry
Degree Grantor:
University of Arizona
Advisor:
Saavedra, S. Scott

Full metadata record

DC FieldValue Language
dc.language.isoen_USen
dc.titleCharge Transfer Processes across Organic/Electrode Interfaces in Organic Photovoltaicsen_US
dc.creatorLin, Hsiao-Chuen_US
dc.contributor.authorLin, Hsiao-Chuen_US
dc.date.issued2013-
dc.publisherThe University of Arizona.en_US
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_US
dc.description.abstractCharge transfer efficiency at organic/electrode interfaces affects the performance organic photovoltaics (OPVs). It is hypothesized that the charge collection efficiency at organic/electrode interfaces is influenced by the structure of the first molecular layer adjacent to the electrode surface. Two differently oriented monolayers composed of two phosphonic acid (PA) functionalized zinc phthalocyanine (ZnPc) molecules, one with four PAs attached peripherally (ZnPcPA₄), one at each quadrant, and another that is functionalized with one PA (ZnPcPA), were tethered to indium tin oxide (ITO) surfaces as models for the donor/transparent conducting oxide (TCO) interface in OPVs to address the relationship between molecular orientation and electron transfer kinetics across the organic/ITO interface. The electron transfer rate constants across the monolayer/ITO interface were measured using potential modulated attenuated total reflectance (PM-ATR) spectroscopy in TE and TM polarizations, which allows rate constants to be determined for subpopulations of molecules that are oriented predominately in-plane and out-of-plane, respectively. The templating effect of the tethered monolayer on sequential layers of donor material for ZnPcPA and ZnPcPA₄ monolayers was assessed by depositing a few layers of CuPc on ZnPcPA- and ZnPcPA₄-modified ITO. The performance of OPV devices fabricated on ITO modified with these two monolayers was compared and correlated to their orientation and energy alignments with other layers in the devices. The dependence of kinetics of electron transfer on overpotential was studied using monolayer-tethered ZnPcPA on ITO. Measurements of apparent heterogeneous electron transfer rate constants (kapp) as a function of applied potential across the ZnPcPA/ITO interface were acquired using PM-ATR at various dc biases (Edc). With varying Edc imposed on the electrode, the fraction of adsorbed molecules in reduced or oxidized states is changed, and both the energetics and kinetics of the electrode reaction are affected. The results were discussed and compared to theoretical predictions. The photoinduced charge harvesting and photocurrent generation were assessed using a clicked ZnPc-perylene diimide (PDI) donor-acceptor assembly tethered to ITO via a PA anchoring group. This ZnPc-PDI donor-acceptor assembly was used to investigate the mechanism of photoinduced charge transfer and hole-capture by ITO in the presence of a solution phase redox mediator.en_US
dc.typetexten
dc.typeElectronic Dissertationen
dc.subjectChemistryen_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineChemistryen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorSaavedra, S. Scotten_US
dc.contributor.committeememberSaavedra, S. Scotten_US
dc.contributor.committeememberArmstrong, Neil R.en_US
dc.contributor.committeememberMcGrath, Dominic V.en_US
dc.contributor.committeememberPemberton, Jeanne E.en_US
dc.contributor.committeememberRatcliff, Erin L.en_US
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