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Expanded Beam Spectroscopic Ellipsometer for High Speed Mapping of Photovoltaic Materials

Shan, Ambalanath
http://orcid.org/0000-0002-1912-309X
http://rave.ohiolink.edu/etdc/view?acc_num=toledo1493306189501021

Abstract Details

2017, Doctor of Philosophy, University of Toledo, Electrical Engineering.
As a result of recent advances in photovoltaics technology, renewable energy generated by the sun has become a viable alternative to traditional sources of energy. Photovoltaic modules composed of thin film solar cell devices offer several advantages over standard wafer based silicon modules, including high throughput automated production and reduced materials usage and cost. Spectroscopic ellipsometry (SE) is an important measurement tool capable of aiding high throughput manufacturing processes for thin films. SE is a non-destructive measurement technique well suited to measure and track parameters critical to photovoltaic device performance such as layer thicknesses, as well as optical and electrical properties of the layer components. This dissertation seeks to extend the application of SE via an expanded-beam method to large area photovoltaic modules while retaining the high measurement speeds of single spot measurements with collimated beams. The transition of ellipsometers as laboratory instruments to ones suitable for high throughput manufacturing lines poses unique challenges. The construction of a rotating compensator ellipsometer suitable for industrial applications is addressed with an emphasis on measurement speed. Schemes are evaluated to correct SE data for the inherent misalignments present in large area measurements of full-scale panels. In particular, consideration is given to the problems of oscillations due to compensator misalignment, effects of glass stress and overlap of reflected beams in through-the-glass measurements, and off-plane corrections due to large area substrate curvature. Expanded-beam SE was developed and applied for in situ, high-speed imaging/mapping analysis of spatial uniformity over large area multilayer coated substrates used in roll-to-roll thin film photovoltaics (PV). Slower speed instrumentation available for such analysis applies a 1D detector array for spectroscopic mapping andinvolves width-wise translation of SE optics over a conveyed substrate surface, measuring point-by-point in a time-consuming process. The expanded-beam instrument instead employs a 2D detector array with no moving optics, exploiting one array index for spectroscopy and the second array index for imaging across a line on a large area sample. Thus, the instrument enables imaging width-wise and mapping length-wise for evaluation of uniformity at the high linear substrate speeds required for real-time, in-situ, and inline analysis for roll-to-roll thin film PV. In this dissertation, the expanded beam technique is employed to study the components of a hydrogenated amorphous silicon (aSi:H) thin film photovoltaic device structure in the Ag/ZnO/n-i-p substrate configuration. The layers were deposited on a flexible substrate mounted on a roll-to-roll cassette. Ellipsometric measurements were performed using an expanded beam spectroscopic ellipsometer capable of simultaneously measuring 41 locations across the width of the substrate to form a line image. Layer thicknesses and optical property maps were constructed from sets of line images generated using ellipsometric analysis techniques. These techniques apply a best fit structural model for the film stack and pertinent optical models for the constituent layers of the device structure.
Robert Collins (Advisor)
Anthony Johnson (Committee Member)
Daniel Georgiev (Committee Member)
Mohammed Niamat (Committee Member)
Nikolas Podraza (Committee Member)
210 p.
Electrical Engineering
Ellipsometry, Expanded-Beam, Device Structure

Recommended Citations

Citations

  • Shan, A. (2017). Expanded Beam Spectroscopic Ellipsometer for High Speed Mapping of Photovoltaic Materials [Doctoral dissertation, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1493306189501021

    APA Style (7th edition)

  • Shan, Ambalanath. Expanded Beam Spectroscopic Ellipsometer for High Speed Mapping of Photovoltaic Materials. 2017. University of Toledo, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=toledo1493306189501021.

    MLA Style (8th edition)

  • Shan, Ambalanath. "Expanded Beam Spectroscopic Ellipsometer for High Speed Mapping of Photovoltaic Materials." Doctoral dissertation, University of Toledo, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1493306189501021

    Chicago Manual of Style (17th edition)

toledo1493306189501021
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This open access ETD is published by University of Toledo and OhioLINK.