Parameterized complex dielectric functions of CuIn _1−x Ga _x Se ₂ : applications in optical characterization of compositional non‐uniformities and depth profiles in materials and solar cells

Journal Article · Sat Apr 23 00:00:00 EDT 2016 · Progress in Photovoltaics

DOI:https://doi.org/10.1002/pip.2774· OSTI ID:1400752

Aryal, Puruswottam ^[1]; Ibdah, Abdel‐Rahman ^[1]; Pradhan, Puja ^[1]; Attygalle, Dinesh ^[1]; Koirala, Prakash ^[1]; Podraza, Nikolas J. ^[1]; Marsillac, Sylvain ^[2]; Collins, Robert W. ^[1]; Li, Jian ^[1]

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1. Center for Photovoltaics Innovation and Commercialization and Department of Physics and Astronomy University of Toledo Toledo OH 43606 USA
2. Virginia Institute of Photovoltaics and Department of Electrical and Computer Engineering Old Dominion University Norfolk VA 23695 USA

Abstract In‐situ spectroscopic ellipsometry (SE) was employed to extract the complex dielectric functions ε = ε ₁  + iε ₂ over the spectral range of 0.75–6.5 eV for a set of polycrystalline CuIn _{1− x} Ga _x Se ₂ (CIGS) thin films with different alloy compositions x  = [Ga]/{[In] + [Ga]}. For highest possible accuracy in ε for each CIGS thin film, specialized SE procedures were adopted including (i) deposition to a thickness of ~600 Å on smooth native oxide covered crystal silicon wafers, which minimizes the surface roughness on the film and thus the required corrections in data analysis, and (ii) measurement in‐situ , which minimizes ambient contamination and oxidation of the film surface. Assuming an analytical form for each of the ε spectra for these CIGS films, oscillator parameters were obtained in best fits, and these parameters were fit in turn to polynomials in x . With the resulting database of polynomial coefficients, the ε spectra for any composition of CIGS can be generated from the single parameter, x . In addition to enabling accurate contactless determination of bulk and surface roughness layer thicknesses of CIGS films by high speed multichannel SE, the database enables characterization of the composition and its profile with depth into these films, and even how the depth profile varies spatially within the plane of the films. In this study, depth profile parameters were found to correlate spatially with solar cell performance parameters. As a result, SE provides the capability of contactless compositional analysis of production‐scale CIGS photovoltaic modules at high speed. Copyright © 2016 John Wiley & Sons, Ltd.

• Sponsoring Organization: USDOE
• OSTI ID: 1400752
• Journal Information: Progress in Photovoltaics, Journal Name: Progress in Photovoltaics Vol. 24 Journal Issue: 9; ISSN 1062-7995
• Publisher: Wiley Blackwell (John Wiley & Sons)
• Country of Publication: United Kingdom
• Language: English