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Polycrystalline silicon passivated tunneling contacts for high efficiency silicon solar cells

Published online by Cambridge University Press:  23 March 2016

Bill Nemeth ,
David L. Young ,
Matthew R. Page ,
Vincenzo LaSalvia ,
Steve Johnston ,
Robert Reedy  and
Paul Stradins
Bill Nemeth*
Affiliation:
National Renewable Energy Laboratory, Golden, Colorado 80401, USA
David L. Young
Affiliation:
National Renewable Energy Laboratory, Golden, Colorado 80401, USA
Matthew R. Page
Affiliation:
National Renewable Energy Laboratory, Golden, Colorado 80401, USA
Vincenzo LaSalvia
Affiliation:
National Renewable Energy Laboratory, Golden, Colorado 80401, USA
Steve Johnston
Affiliation:
National Renewable Energy Laboratory, Golden, Colorado 80401, USA
Robert Reedy
Affiliation:
National Renewable Energy Laboratory, Golden, Colorado 80401, USA
Paul Stradins
Affiliation:
National Renewable Energy Laboratory, Golden, Colorado 80401, USA
*
a)Address all correspondence to this author. e-mail: William.Nemeth@nrel.gov
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Abstract

We apply n- and p-type polycrystalline silicon (poly-Si) films on tunneling SiOx to form passivated contacts to n-type Si wafers. The resulting induced emitter and n+/n back surface field junctions of high carrier selectivity and low contact resistivity enable high efficiency Si solar cells. This work addresses the materials science of their performance governed by the properties of the individual layers (poly-Si, tunneling oxide) and more importantly, by the process history of the cell as a whole. Tunneling SiOx layers (<2 nm) are grown thermally or chemically, followed by a plasma enhanced chemical vapor deposition growth of p+ or n+ doped a-Si:H. The latter is thermally crystallized into poly-Si, resulting in grain nucleation and growth as well as dopant diffusion within the poly-Si and penetration through the tunneling oxide into the Si base wafer. The cell process is designed to improve the passivation of both oxide interfaces and tunneling transport through the oxide. A novel passivation technique involves coating of the passivated contact and whole cell with atomic layer deposited Al2O3 and activating them at 400 °C. The resulting excellent passivation persists after subsequent chemical removal of the Al2O3. The preceding cell process steps must be carefully tailored to avoid structural and morphological defects, as well as to maintain or improve passivation, and carrier selective transport. Furthermore, passivated contact metallization presents significant challenges, often resulting in passivation loss. Suggested remedies include improved Si cell wafer surface morphology (without micropyramids) and postdeposited a-Si:H capping layers over the poly-Si.

Keywords

photovoltaicpassivationthin film
Type
Invited Feature Paper
Information
Journal of Materials Research , Volume 31 , Issue 6 , 28 March 2016 , pp. 671 - 681
Copyright
Copyright © Materials Research Society 2016 

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References

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