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Metastability

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Amorphous and Microcrystalline Silicon Solar Cells: Modeling, Materials and Device Technology

Part of the book series: Electronic Materials: Science & Technology ((EMST,volume 5))

Abstract

The light-induced metastability of hydrogenated amorphous silicon was discovered in 1977 (Staebler and Wronski, 1977). The thin films deposited with the equipment available in those days were slightly n-type, and the light-induced change, later called the Staebler-Wronski effect (SWE), manifested itself in these materials as a shift of the Fermi level towards mid-gap accompanied by a reduction of the dark conductivity and the photoconductivity. In 1980, it was established that the SWE is a bulk effect rather than a surface band bending effect (Staebler and Wronski, 1980). Since then, all experimental data have shown evidence that exposure of hydrogenated amorphous silicon to light increases the density of neutral silicon dangling bonds. The excess defects, which are metastable as they can be removed in 1 – 3 hours by thermal annealing above 150 °C, have a roughly one order of magnitude higher concentration than the as-deposited dangling bonds that are initially present in device-quality material, and thus significantly reduce the lifetime of free carriers. The vast body of experiments carried out during the last 20 years by numerous laboratories suggests that the creation of metastable dangling bonds is the result of recombination events between carriers created by light absorption or by injection in the dark. Although it takes 10 – 100 million recombination events to create only a single metastable dangling bond, the concentration of ≈ 1017 cm-3 defects at which the SWE saturates does impose a limitation to the maximum obtainable conversion efficiency in amorphous silicon based solar cells and is still an important drawback for this technology.

I honestly can’t remember the moment when I realized that there was something funny going on, but Chris remembers I accused him (jokingly I’m sure) that he couldn’t measure these samples right. —David L. Staebler, April 3, 1997

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Authors and Affiliations

  1. Utrecht University, Debye Institute, Netherlands

    Ruud E. I. Schropp

  2. Delft University of Technology, Netherlands

    Miro Zeman

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  1. Ruud E. I. Schropp
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  2. Miro Zeman
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© 1998 Springer Science+Business Media New York

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Schropp, R.E.I., Zeman, M. (1998). Metastability. In: Amorphous and Microcrystalline Silicon Solar Cells: Modeling, Materials and Device Technology. Electronic Materials: Science & Technology, vol 5. Springer, Boston, MA. https://doi.org/10.1007/978-1-4615-5631-2_5

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  • DOI: https://doi.org/10.1007/978-1-4615-5631-2_5

  • Publisher Name: Springer, Boston, MA

  • Print ISBN: 978-0-7923-8317-8

  • Online ISBN: 978-1-4615-5631-2

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