Programm Photovoltaik Ausgabe 2009 ... - Bundesamt für Energie BFE

Introduction / project goal
In PV industry, crystalline silicon (single and multcrystalline) bulk material dominates the market with
over 90% market share. The difficulty in securing a feedstock supply to produce conventional waferbased
solar cells has encouraged a frenzy of industry projects related to thin-film solar cells. These
last years a lot of money have been spent to build new thin-films plants and at this pace in 2012 thin
film cells could represent about 20% of the PV technology installed worldwide. WTC, a technology
consulting company based in Munich, Germany, estimates that the market for thin-film cells is set to
explode in the next few years, reaching $1.5 billion in 2012. The High-ef European project has for aim
to provide one of the thin-film PV manufacturers, CSG Solar AG, with a novel silicon thin film material
that can be produced at competitive costs and with a efficiency > 10%.
The crystallization of a silicon thin film on a temperature sensitive cheap substrate as glass is a challenging
issue. Several methods can be used to obtain crystalline silicon thin film at maximum temperature
of 650°C that can endure the glass as for example standard solid phase crystallisation processes
in a furnace which produce grain smaller than 10�m in diameters. Laser crystallization offers the advantage
to produce large grain over several 100�m in size with very short melt duration, minimizing
the heating of the temperature sensitive glass. The laser crystallized films can be used as seeding
layer for a subsequent epitaxial growth. High-ef has for objective to develop such a combined process
of laser-crystallization of an amorphous silicon (a-Si) seed layer ( 2�m) of the seed layer by solid phase epitaxy (SPE) (Fig. 1).
High-ef is a European cooperative project involving research institutes and companies in France (Iness-CNRS
Strasbourg; Horiba Jobin Yvon), Germany (IPHT Jena; CSG Solar AG), Hungary (MFAresearch
Institute for Technical Physics and Materials Science) and Switzerland (EMPA; Bookham
Switzerland AG). The main tasks of EMPA in the project are:
� Detailed microstructure investigations of the Si thin film by electron backscatter diffraction technique
(EBSD) including grain size, grain boundaries, texture and lattice defects characterizations.
� Developing a suitable technique for strains and residual stress measurements in the polycrystalline
Si thin Film with EBSD and comparison with RAMAN measurements.
� Divers mechanical testing of the thin film and the glass substrate
Fig. 1: Schematic of the laser-SPE process which will be established to realize large grained silicon
layer on glass
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Large grained, low stress multi-crystalline silicon thin film solar cells on glass by a novel combined diode laser and solid phase crystallization process, X. Maeder, Empa
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