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Microcrystalline Silicon Tunnel Junctions for Amorphous Silicon-Based Multijunction Solar Cells

Published online by Cambridge University Press:  15 February 2011

A. S. Ferlauto ,
Joohyun Koh ,
P. I. Rovira ,
C. R. Wronski  and
R. W. Collins
A. S. Ferlauto
Affiliation:
Center for Thin Film Devices, The Pennsylvania State University, University Park, PA 16802.
Joohyun Koh
Affiliation:
Center for Thin Film Devices, The Pennsylvania State University, University Park, PA 16802.
P. I. Rovira
Affiliation:
Center for Thin Film Devices, The Pennsylvania State University, University Park, PA 16802.
C. R. Wronski
Affiliation:
Center for Thin Film Devices, The Pennsylvania State University, University Park, PA 16802.
R. W. Collins
Affiliation:
Center for Thin Film Devices, The Pennsylvania State University, University Park, PA 16802.
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Abstract

The formation of tunnel junctions for applications in amorphous silicon (a-Si:H) based multijunction n-i-p solar cells has been studied using real time optics. The junction structure investigated in detail here consists of a thin (~200 Å) layer of n-type microcrystalline silicon (μc-Si:H) on top of an equally thin layer of p-type μc-Si:H, the latter deposited on thick (~2000 Å) intrinsic a-Si:H. Such a structure has been optimized in an attempt to obtain single-phase μc-Si:H with a high crystallite packing density and large grain size for both layers of the tunnel junction. We have explored the conditions under which grain growth is continuous across the p/n junction and conditions under which renucleation of n-layer grains can be ensured at the junction. One important finding of this study is that the optimum conditions for single-phase, high-density μc-Si:H n-layers are different depending on whether the substrate is a μc-Si:H p-layer or is a H2-plasma treated or untreated a-Si:H i-layer. Thus, the top-most μc-Si:H layer of the tunnel junction must be optimized in the multijunction device configuration, rather than in single cell configurations on a-Si:H i-layers. Our observations are explained using an evolutionary phase diagram for a-Si:H and μc-Si:H film growth versus thickness and H2-dilution ratio, in which the boundary between the two phases is strongly substrate-dependent.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 557: Symposium A – Amorphous and Heterogeneous Silicon Thin Films—Fundamentals to Devices—1999 , 1999 , 579
Copyright
Copyright © Materials Research Society 1999

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