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Resistive Losses at c-Si/a-Si:H/ZnO Contacts for Heterojunction Solar Cells

Published online by Cambridge University Press:  01 February 2011

Florian Einsele ,
Phillip Johannes Rostan  and
Uwe Rau
Florian Einsele
Affiliation:
[email protected], Forschungszentrum Juelich, IEF-5, Photovoltaics, Jülich, 52425, Germany
Phillip Johannes Rostan
Affiliation:
[email protected], Universität Stuttgart, Institut für Physikalische Elektronik, Pfaffenwaldring 47, Stuttgart, 70569, Germany
Uwe Rau
Affiliation:
[email protected], Forschungszentrum Juelich, IEF-5, Photovoltaics, Photovoltaik, Jülich, 52425, Germany
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Abstract

We study resistive losses at (p)c-Si/(p)Si:H/(n)ZnO heterojunction back contacts for high efficiency silicon solar cells. We find that a low tunnelling resistance for the (p)a-Si:H/(n)ZnO part of the junction requires deposition of Si:H with a high hydrogen dilution RH > 40 resulting in a highly doped μc-Si:H layer. Such a μc-Si:H layer if deposited directly on a Si wafer yields a surface recombination velocity of S  180 cm/s. Using the same layer as part of a (p)c-Si/(p)Si:H/(n)ZnO back contact in a solar cell results in an open circuit voltage Voc = 640 mV and a fill factor FF = 80 %. Insertion of an (i)a-Si-layer between the μc-Si:H and the wafer leads to a further decrease of S and, for the solar cells to an increase of VOC. However, if the thickness of this intrinsic layer exceeds a threshold of 3 nm, resistive losses lead to a degradation of the fill factor of the solar cells. These resistive losses result from a valence band offset δEV between a-Si:H and c-Si of about 600 meV. The fill factor losses overcompensate the VOC gain such that there is no benefit of the (i)a-Si:H interlayer for the overall solar cell performance when using an (i)a-Si:H/(p)uc-Si:H double layer.

Keywords

Siplasma-enhanced CVD (PECVD) (deposition)photovoltaic
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 989: Symposium A – Amorphous and Polycrystalline Thin-Film Silicon Science and Technology-2007 , 2007 , 0989-A18-04
Copyright
Copyright © Materials Research Society 2007

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