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Studies on Backside Al-Contact Formation in Si Solar Cells: Fundamental Mechanisms

Published online by Cambridge University Press:  21 March 2011

Bhushan Sopori ,
Vishal Mehta ,
Przemyslaw Rupnowski ,
Helio Moutinho ,
Aziz Shaikh ,
Chandra Khadilkar ,
Murray Bennett  and
Dave Carlson
Bhushan Sopori
Affiliation:
National Renewable Energy Laboratory, Golden, CO 80401, USA
Vishal Mehta
Affiliation:
National Renewable Energy Laboratory, Golden, CO 80401, USA
Przemyslaw Rupnowski
Affiliation:
National Renewable Energy Laboratory, Golden, CO 80401, USA
Helio Moutinho
Affiliation:
National Renewable Energy Laboratory, Golden, CO 80401, USA
Aziz Shaikh
Affiliation:
Ferro Electronic Materials, Vista, CA 92083, USA
Chandra Khadilkar
Affiliation:
Ferro Electronic Materials, Vista, CA 92083, USA
Murray Bennett
Affiliation:
BP Solar, Frederick, MD 21703, USA
Dave Carlson
Affiliation:
BP Solar, Frederick, MD 21703, USA
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Abstract

We have studied mechanisms of back-contact formation in screen-printed Si solar cells by a fire-through process. An optimum firing temperature profile leads to the formation of a P-Si/P+- Si/ Si-Al eutectic/agglomerated Al at the back contact of a Si solar cell. Variations in the interface properties were found to arise from Al-Si melt instabilities. Experiments were performed to study melt formation. We show that this process is strongly controlled by diffusion of Si into Al. During the ramp-up, a melt is initiated at the Si-Al interface, which subsequently expands into Al and Si. During the ramp-down, the melt freezes, which causes the doped region to grow epitaxially on Si, followed by solidification of the Si-Al eutectic. Any agglomerated (or sintered) Al particles are dispersed with Si. Implications on the performance of the cell are described.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1123: Symposium P – Photovoltaic Materials and Manufacturing Issues , 2008 , 1123-P07-11
Copyright
Copyright © Materials Research Society 2009

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