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Film Morphology, Excess Shunt Current and Stability in Triple-Junction Cells

Published online by Cambridge University Press:  21 February 2011

T.J. McMahon  and
M.S. Bennett
T.J. McMahon
Affiliation:
NREL, Golden CO 80401
M.S. Bennett
Affiliation:
Solarex Thin Film Division, Newtown, PA 18940.
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Abstract

When a textured conductive textured oxide (CTO)-glass substrate is used for either thin single p-i-n or thin multilayer p-i-n structures, a new mode of light-induced cell degradation occurs which has been associated with enhanced shunting. In this study, triple-junction cells were examined before and after light-soaking using dark current-voltage (I-V) analysis. Two degradation mechanisms are occurring: i) The classical bulk Staebler-Wronski defect generation mechanism causes an increase in diode quality factor, ii) In cells exhibiting more as-grown shunting behavior, light-soaking greatly enhances shunting. This enhanced shunting becomes the primary mode of degradation.

Reversible incremental current steps are also seen when measuring the (I-V) characteristics on diodes with excess shunt current due to light-soaking. This is a clear indication that the increase in shunting is caused by an increase in the number of shunt pathways and not by enhancing current through existing shunts. Optical-beam-induced current (OBIC) scans show some small defect areas of reduced current responsivity that are about 5–10 urn in diameter and may not be caused by holes in the back reflector metalization. Localized accelerated light-induced degradation is measured using the OBIC scanning laser beam on small areas (5 × 10-6 cm2), and there is some evidence that these areas degrade more than areas without defects.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 258: Symposium A – Amorphous Silicon Technology – 1992 , 1992 , 941
Copyright
Copyright © Materials Research Society 1992

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References

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