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Toward understanding the degradation without light soaking in hot-wire a-Si:H thin films and solar cells

Published online by Cambridge University Press:  01 February 2011

Qi Wang ,
Keda Wang  and
Daxing Han
Qi Wang
Affiliation:
National Center of Photovoltaic, National Renewable Energy Laboratory, Golden, CO 80401-3305, U.S.A.
Keda Wang
Affiliation:
Department of Physics & Astronomy, Univ. of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3255, U.S.A.
Daxing Han
Affiliation:
Department of Physics & Astronomy, Univ. of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3255, U.S.A.
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Abstract

The non-reversible degradation without light soaking has been observed in both thin films and solar cells fabricated using the hot-wire CVD technique. For solar cells, a 9.8% initial efficiency became 9.2% when measured after a few weeks of being stored in the dark. For the intrinsic layers, the conductivity increased in the air but remained steady in vacuum up to 700 hours. Also, the conductivity increased and activation energy decreases from an initial ∼0.95 eV to ~∼0.85 eV after several thermal cycles, even in a vacuum. We suggest that the degradation in both materials and solar cells come from the same origin: the upward shift of the Fermi-energy position from its initial value. In other words, the as-grown material is slightly p-type and gradually became slightly n-type after sitting in the air or after thermal annealing cycles in a vacuum. The shift in the Fermi-energy made the fill factor of the solar cell decrease and changes in the electronic properties of the i-layer. It is likely that adsorption of oxygen from water vapor is driving this degradation.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 762: Symposium A – Amorphous and Nanocrystalline Silicon-Based Films – 2003 , 2003 , A7.10
Copyright
Copyright © Materials Research Society 2003

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