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Tejas Prabhakar MS Thesis.pdf (52.36 MB)

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Study of Earth Abundant TCO and Absorber Materials for Photovoltaic Applications

Prabhakar, Tejas
http://rave.ohiolink.edu/etdc/view?acc_num=toledo1382269621

Abstract Details

2013, Master of Science, University of Toledo, Physics.
In order to make photovoltaic power generation a sustainable venture, it is necessary to use cost-effective materials in the manufacture of solar cells. In this regard, AZO (Aluminum doped Zinc Oxide) and CZTS (Copper Zinc Tin Sulfide) have been studied for their application in thin film solar cells. While AZO is a transparent conducting oxide, CZTS is a photovoltaic absorber. Both AZO and CZTS consist of earth abundant elements and are non-toxic in nature. Highly transparent and conductive AZO thin films were grown using RF sputtering. The influence of deposition parameters such as working pressure, RF power, substrate temperature and flow rate on the film characteristics was investigated. The as-grown films had a high degree of preferred orientation along the (002) direction which enhanced at lower working pressures, higher RF powers and lower substrate temperatures. Williamson-Hall analysis on the films revealed that as the working pressure was increased, the nature of stress and strain gradually changed from being compressive to tensile. The fall in optical transmission of the films was a consequence of free carrier absorption resulting from enhanced carrier density due to incorporation of Al atoms or oxygen vacancies. The optical and electrical properties of the films were described well by the Burstein-Moss effect. CZTS absorber layers were grown using ultrasonic spray pyrolysis at a deposition temperature of 350 C and subsequently annealed in a sulfurization furnace. Measurements from XRD and Raman spectra confirmed the presence of pure single phase Cu2ZnSnS4 . Texture analysis of as-deposited and annealed CZTS films indicated that the (112) plane which is characteristic of the kesterite phase was preferred. The grain size increased from 50 nm to 100 nm on conducting post-deposition annealing. CZTS films with stoichiometric composition yielded a band gap of 1.5 eV, which is optimal for solar energy conversion. The variation of tin in the film changed its resistivity by several orders of magnitude and subsequently the tin free ternary chalcogenide Cu2ZnS2 having very low resistivity was obtained. By carefully optimization of concentrations of tin, zinc and copper, a zinc-rich/tin-rich/copper-poor composition was found to be most suitable for solar cell applications. Etching of CZTS films using KCN solution reduced their resistivity, possibly due to the elimination of binary copper sulfide phases. CZTS solar cells were fabricated both in the substrate and superstrate configurations.
Yanfa Yan (Committee Chair)
Victor Karpov (Committee Co-Chair)
Alvin Compaan (Committee Co-Chair)
187 p.
Condensed Matter Physics; Electrical Engineering; Energy; Engineering; Experiments; Materials Science; Morphology; Nanotechnology; Physics; Plasma Physics; Solid State Physics; Sustainability; Technology; Theoretical Physics
Solar cells; Photovoltaic; CZTS; Thin films; Materials Science; TCO; Transparent conducting oxide; ZnO; AZO; Zinc oxide; Sputtering; Spray pyrolysis; Williamson-Hall; Stress; lattice strain; Argon flow rate; Working pressure; Earth abundant

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Citations

  • Prabhakar, T. (2013). Study of Earth Abundant TCO and Absorber Materials for Photovoltaic Applications [Master's thesis, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1382269621

    APA Style (7th edition)

  • Prabhakar, Tejas. Study of Earth Abundant TCO and Absorber Materials for Photovoltaic Applications. 2013. University of Toledo, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=toledo1382269621.

    MLA Style (8th edition)

  • Prabhakar, Tejas. "Study of Earth Abundant TCO and Absorber Materials for Photovoltaic Applications." Master's thesis, University of Toledo, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1382269621

    Chicago Manual of Style (17th edition)

toledo1382269621
361
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This open access ETD is published by University of Toledo and OhioLINK.
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