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Plasma Texturing and Porous Silicon Mirrors for Epitaxial Thin Film Crystalline Silicon Solar Cells

Published online by Cambridge University Press:  01 February 2011

Izabela Jozefa Kuzma-Filipek ,
Filip Duerinckx ,
Kris Van Nieuwenhuysen ,
Guy Beaucarne  and
Jef Poortmans
Izabela Jozefa Kuzma-Filipek
Affiliation:
[email protected], IMEC, Imec, Kapeldreef 75, Leuven, N/A, Belgium
Filip Duerinckx
Affiliation:
[email protected], IMEC, Kapeldreef 75, Leuven, N/A, Belgium
Kris Van Nieuwenhuysen
Affiliation:
[email protected], IMEC, Kapeldreef 75, Leuven, N/A, Belgium
Guy Beaucarne
Affiliation:
[email protected], IMEC, Kapeldreef 75, Leuven, N/A, Belgium
Jef Poortmans
Affiliation:
[email protected], IMEC, Kapeldreef 75, Leuven, N/A, Belgium
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Abstract

Thin film silicon solar cells, consisting of an epitaxially grown active layer on a low quality highly doped silicon substrate, incorporate many attractive features usually associated with their sister cells based on bulk silicon. However, the efficiency of the current epitaxial semi-industrial screen printed cells is limited to 11-12% mainly due to optical shortcomings. This paper will give an overview of our work aimed at tackling the 2 most important problems: (i) Finding and implementing an adequate front surface texture and (ii) the simulation, fabrication and incorporation of an intermediate reflector.

The former issue has been addressed by the development of plasma texturing based on halogen species. This method allows us to fulfil the sometimes contradictory requirements for the textured surface, i.e. a uniform and reduced reflection, a strong lambertian character to scatter the light and a limited removal of silicon. It will be shown that the scattering efficiency is dependent on both the wavelength of the impinging light and on the silicon removal during the texturing process.

The second and main issue of this work is the limited absorption volume of the epitaxial layer. To resolve this drawback, an intermediate reflector is placed at the epi/substrate interface to enhance the path length of the low energy photons through the epi-layer. In practice, a multi-layer porous silicon stack is created by electrochemical anodization of the substrate. The reflection at the epi/reflector/substrate interface is a combination of several different effects including a Bragg mirror and Total Internal Reflection (TIR). Measurements of the external reflectance as well as extraction of the internal reflection parameters are used to clarify the issue. Advanced structures, including chirped porous silicon stacks, are introduced. Finally, the benefits of the reflector on the level of the epitaxial silicon solar cell are analysed. Efficiencies close to 14% are obtained for epitaxial cells incorporating an advanced porous Si reflector.

Keywords

epitaxyphotoreflectancephotovoltaic
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1101: Symposium KK – Light Management in Photovoltaic Devices–Theory and Practice , 2008 , 1101-KK04-01
Copyright
Copyright © Materials Research Society 2008

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