Post-Grant Reports


Characterization of a Back Contact Barrier in Solar Cells

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Condensed Matter Physics | Materials Science and Engineering


Recent solar cell technology, in striving for lowest cost, results in materials with many imperfections. Capacitance measurements are a common, nondestructive method to identify defects which compromise the device performance. These techniques assume that the device includes a single blocking contact, or “top” contact; however, these imperfect devices often also have a non- ideal “back” contact which significantly influences the sample response but is neglected in standard data interpretation. In this project, Cu(In,Ga)Se2 solar cell samples were obtained from collaborators at the University of Oregon and the University of Delaware. One of these samples was grown with non-ideal conditions and expected to have a poor back contact. The other was grown in more standard conditions, and expected to have a high quality back contact. We found evidence of non-ideal back contacts in both samples, and have been studying their temperature response and other characteristics. Research is on-going, although these preliminary results are intriguing, and suggest that our interpretation of capacitance results in such samples—even in ‘good’ samples—needs careful revision. This work lays the foundation for further study of the characterization techniques commonly used to understand solar cell materials, as well as study of the properties of Cu(In,Ga)Se2 solar cells themselves, including contact properties, the barrier height, relationship to bulk and interface defects in the film, and the dependence on sample preparation and stoichiometry. This work also addresses a topic of significant debate in the Cu(In,Ga)Se2 solar cell research community. Results were presented at the 2014 Murdock Trust conference in Vancouver WA, and will be presented on March 4 at the American Physical Society March Meeting in San Antonio, TX, as well as at the Linfield Student Scholarship symposium in May.


This research was conducted as part of a Linfield College Student-Faculty Collaborative Research Grant in 2014-2015, funded by the Office of Academic Affairs.

Student collaborators were Justin Davis and Thaddeus Cox.

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