• Login
    View Item 
    •   Home
    • UA Graduate and Undergraduate Research
    • UA Theses and Dissertations
    • Dissertations
    • View Item
    •   Home
    • UA Graduate and Undergraduate Research
    • UA Theses and Dissertations
    • Dissertations
    • View Item
    JavaScript is disabled for your browser. Some features of this site may not work without it.

    Browse

    All of UA Campus RepositoryCommunitiesTitleAuthorsIssue DateSubmit DateSubjectsPublisherJournalThis CollectionTitleAuthorsIssue DateSubmit DateSubjectsPublisherJournal

    My Account

    LoginRegister

    About

    AboutUA Faculty PublicationsUA DissertationsUA Master's ThesesUA Honors ThesesUA PressUA YearbooksUA CatalogsUA Libraries

    Statistics

    Most Popular ItemsStatistics by CountryMost Popular Authors

    Band Edge Energetics and Charge Transfer Processes in Semiconductor-Metal Heterostructured Nanorods as Photocatalysts and Metal Oxide Electrode-Organic Semiconductor Interfaces in Organic Photovoltaics

    • CSV
    • RefMan
    • EndNote
    • BibTex
    • RefWorks
    Thumbnail
    Name:
    azu_etd_14055_sip1_m.pdf
    Size:
    17.35Mb
    Format:
    PDF
    Download
    Author
    Ehamparam, Ramanan
    Issue Date
    2015
    Keywords
    Electron transfer
    Organic photovoltaics
    Semiconductor nanorods
    Spectroelectrochemistry
    Chemistry
    Band edge energies
    Advisor
    Saavedra, Steven Scott
    
    Metadata
    Show full item record
    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
    Energetics, charge selectivity and interfacial charge transfer kinetics affect the efficiency of solar electric energy conversion and solar photochemical formation of fuels. The research described herein focuses on understanding and controlling the energetics, charge selectivity, and interfacial charge transfer processes in organic photovoltaics, as well as new generation semiconductor-semiconductor and metal-semiconductor heterostructured nanorods (NRs) as photocatalysts. Waveguide and transmission based spectroelectrochemistries, photoemission spectroscopies, and impedance spectroscopy were used to characterize the frontier orbital energies, charge selectivity and interfacial charge transfer kinetics in heterostructured NRs and organic photovoltaics. CdSe NRs tipped with Au nanoparticles and CdSe seeded CdS NRs tipped with Pt nanoparticles were used to study the effect of compositional asymmetry and catalytic sites on band edge energies of NRs. We used UV photoemission spectroscopy (UPS) and waveguide and transmission-based spectroelectrochemistry of NR monolayers/multilayers on conductive substrates to estimate valence/conduction band energies. Potential-modulated attenuated total reflectance (PM-ATR) spectroscopy was utilized to measure the apparent heterogeneous rate constants of reversible electron injection into NR films on indium tin oxide (ITO). We conclude from these measurements that metal tipping, which is designed to enhance the photocatalytic activity of semiconductor NRs, altered band edge energies and enhanced electronic coupling to conductive substrates, in ways that are predicted to influence their efficiency as photoelectrocatalysts. Monolayers of functionalized phosphonic acid ruthenium phthalocyanines (RuPcPA) tethered to ITO as a model organic photovoltaic donor/electrode interface were studied to understand the aggregation and orientation dependent charge transfer kinetics and energetics of these systems. The effect of surface roughness on the orientation of RuPcPA was theoretically modeled and compared to the experimental results. Electrochemical and spectroelectrochemical studies revealed the presence of only monomeric species on ITO. Impedance spectroscopy (IS) and PM-ATR were used to measure charge transfer rate constants. Further, frontier orbital energies of RuPcPA modified ITO were measured using UPS, and the results indicated favorable energetics for hole collection at the RuPcPA/ITO interface for OPV applications. The effect of "UV-light soaking" on the performance of organic photovoltaic devices employing metal oxide (MO) electron selective interlayers (ESL) was addressed using sputtered zinc oxide (ZnO) ESL films. This study provides a coherent methodology for differentiating between the proposed origins of the s-shaped current-voltage (J-V) responses in the literature for organic photovoltaics using MO ESLs. We use IS and UPS to demonstrate that the energetic barrier for charge extraction at the ZnO/active layer interface leads to the observed s-shape response in OPVs using ZnO ESLs. Furthermore, this study provides clear guidelines for minimizing the s-shaped J-V response and the effect of UV light on the performances of OPV devices using ZnO ESLs. We have developed solution electrochemical protocols to characterize nanometer-scale porosity and electronic properties of both solution-deposited and sputtered ZnO thin films used as interlayers for electron-harvesting contacts in inverted organic solar cells on ITO substrates. These electrochemical experiments were performed in order to evaluate the hole-blocking abilities of these ZnO ESLs as well as their effective "pinhole density," thus demonstrating a strong correlation to their OPV performances. These electrochemical experiments can be used to characterize and optimize ESLs rapidly, before OPV device fabrication.
    Type
    text
    Electronic Dissertation
    Degree Name
    Ph.D.
    Degree Level
    doctoral
    Degree Program
    Graduate College
    Chemistry
    Degree Grantor
    University of Arizona
    Collections
    Dissertations

    entitlement

     
    The University of Arizona Libraries | 1510 E. University Blvd. | Tucson, AZ 85721-0055
    Tel 520-621-6442 | repository@u.library.arizona.edu
    DSpace software copyright © 2002-2017  DuraSpace
    Quick Guide | Contact Us | Send Feedback
    Open Repository is a service operated by 
    Atmire NV
     

    Export search results

    The export option will allow you to export the current search results of the entered query to a file. Different formats are available for download. To export the items, click on the button corresponding with the preferred download format.

    By default, clicking on the export buttons will result in a download of the allowed maximum amount of items.

    To select a subset of the search results, click "Selective Export" button and make a selection of the items you want to export. The amount of items that can be exported at once is similarly restricted as the full export.

    After making a selection, click one of the export format buttons. The amount of items that will be exported is indicated in the bubble next to export format.