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Crystalline Silicon Surface Passivation by Pecv-Deposited Hydrogenated Amorphous Silicon Oxide Films [a-SiOx:H]

Published online by Cambridge University Press:  01 February 2011

Thomas Mueller ,
Wolfgang Duengen ,
Reinhart Job ,
Maximilian Scherff  and
Wolfgang Fahrner
Thomas Mueller
Affiliation:
[email protected], University of Hagen, Electronic Devices, Haldener Str. 182, p.o. box 904, Hagen, 58084, Germany, +49-2331-9872200, +49-2331-987321
Wolfgang Duengen
Affiliation:
[email protected], University of Hagen, Chair of Electronic Devices, Haldener Str. 182, Hagen, 58084, Germany
Reinhart Job
Affiliation:
[email protected], University of Hagen, Chair of Electronic Devices, Haldener Str. 182, Hagen, 58084, Germany
Maximilian Scherff
Affiliation:
[email protected], University of Hagen, Chair of Electronic Devices, Haldener Str. 182, Hagen, 58084, Germany
Wolfgang Fahrner
Affiliation:
[email protected], University of Hagen, Chair of Electronic Devices, Haldener Str. 182, Hagen, 58084, Germany
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Abstract

In the research field of crystalline silicon (c-Si) solar cells, electronic surface passivation has been recognized as a crucial step to achieve high conversion efficiencies. The main issue of this article is to analyze the surface passivation properties of both, n-type and p-type crystalline silicon wafers by hydrogenated amorphous silicon sub oxide [a-SiOx:H] films the for use in hetero-junction (a-Si/c-Si) solar cells. A window layer is obtained with a certain fraction of oxygen in the a-SiOx:H layers.

The a-SiOx:H films were deposited by decomposition of silane, carbon dioxide and hydrogen as source gases using plasma enhanced chemical vapor deposition (PECVD). Films with varying deposition parameters such as gas flow ratio (oxygen fraction) and plasma frequency (13.56, 70.0 and 110.0 MHz) are compared.

To determine the passivation quality of the a-SiOx:H films, microwave-detected photo conductance decay (µ-PCD) provides a contactless measurement of the effective recombination lifetime of free carriers. The film compositions and also the changes in the microscopic structure of the amorphous network upon thermal annealing are studied using Raman spectroscopy and optical profiling techniques.

The Raman spectra reveal the generation of Si-(OH)x and Si-O-Si bonds after thermal annealing in the layers, leading to a higher effective lifetime, as it reduces the defect absorption of the sub oxides.

For n-type FZ material, lifetime values as high as 1650 µs are obtained, resulting in a surface recombination velocity Seff < 9.5 cm/s.

Keywords

passivationphotovoltaicoxide
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-A05-02
Copyright
Copyright © Materials Research Society 2007

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