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Optical and Physical Characterization of Cu2-xSe Thin Films for Real Time Spectroscopic Ellipsometry on Cu(In,Ga)Se2-based Photovoltaic Devices

Published online by Cambridge University Press:  31 January 2011

James D Walker
Affiliation:
james.walker@utoledo.edu, University of Toledo, Wright Center for Photovoltaics Innovation and Commercialization, Toledo, Ohio, United States
Himal Khatri
Affiliation:
Himal.Khatri@utoledo.edu, University of Toledo, Wright Center for Photovoltaics Innovation and Commercialization, Toledo, Ohio, United States
Scott Little
Affiliation:
scott.little@utoledo.edu, University of Toledo, Wright Center for Photovoltaics Innovation and Commercialization, Toledo, Ohio, United States
Vikash Ranjan
Affiliation:
Vikash.Ranjan@utoledo.edu, University of Toledo, Wright Center for Photovoltaics Innovation and Commercialization, Toledo, Ohio, United States
Robert Collins
Affiliation:
robert.collins@utoledo.edu, University of Toledo, Wright Center for Photovoltaics Innovation and Commercialization, Toledo, Ohio, United States
Sylvain Marsillac
Affiliation:
sylvain.marsillac@utoledo.edu, University of Toledo, Wright Center for Photovoltaics Innovation and Commercialization, Toledo, Ohio, United States
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Abstract

In situ, real time spectroscopic ellipsometry (RTSE) has been used to study the growth processes and optical properties of Cu2-xSe - an important binary compound in the fabrication of high efficiency copper indium gallium diselenide (CIGS) photovoltaic devices. It was found that the high surface roughness of the Cu2-xSe layers necessitated a “graded” optical model in order to extract meaningful dielectric functions at both 550 °C and room temperature. The optical model was verified at room temperature against SEM micrographs and reflectance measurements carried out ex situ. The growth temperature dielectric functions presented in this study are expected to allow for a greater level of control and understanding of the so-called 2- and 3-stage processes for CIGS fabrication in which a Cu2-xSe phase, present at the CIGS grain boundaries, acts as a fluxing agent for the growth of photovoltaic quality CIGS. Real time optical feedback via RTSE combined with the growth temperature dielectric functions presented here could play an important role in improving material fabrication on both the laboratory and industrial scales.

Type
Research Article
Copyright
Copyright © Materials Research Society 2010

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