FYI,

"Pliable Solar Cells Are On a Roll"
New Scientist
http://www.newscientist.com/article.ns?id=dn6802

: Such applications could soon become a reality thanks to a light,
: flexible solar panel that is a little thicker than photographic
: film and can easily be applied to everyday fabrics. The thin, bendy
: solar panels, which could be on the market within three years, are
: the fruit of a three-nation European Union research project called
: H-Alpha Solar (H-AS).

: The new solar panels will be cheap, too, because they can be mass-
: produced in rolls that can be cut as required and wrapped around
: clothes, fabrics, furniture or even rooftops. "This technology will
: be a lot easier to handle than the old glass solar panels," claims
: Gerrit Kroesen, the physicist from Eindhoven University of
: Technology in the Netherlands who led the development team.

: Kroesen's team has made its solar cells bendy simply by making them
: thin. But this has involved a trade-off. While the best solar cells
: are now working at efficiencies above 20%, the H-AS cells are only
: about 7% efficient. The researchers think efficiency is worth
: sacrificing for a cell that is going to be more generally useful,
: though they still hope eventually to reach 10% efficiency.

: Conventional solar panels are made of pairs of sheets of
: semiconducting silicon, doped with phosphorus and boron atoms.
: Electrons in the phosphorus-doped (N-type) layer migrate across the
: boundary to occupy holes left in the boron-doped (P-type) material,
: setting up a voltage across the boundary between the two layers.
: When photons hit the silicon in a cell they knock electrons out of
: its crystal structure, generating a current that is collected by a
: mesh of metal contacts.

: The H-AS solar panels are constructed in a similar way, but they
: are made just 1 micrometre thick by depositing polymorphous silicon
: at high pressures and temperatures. "Polymorphous silicon is as
: rigid as crystalline silicon. But because it is less than a
: micrometre thick it is flexible," Kroesen says. Today's solar
: panels are typically somewhere between 4 and 10 millimetres thick.

: The process of producing H-AS films involves temperatures of up to
: 200°C, which would melt a plastic substrate. So instead of
: depositing the doped layers directly onto plastic they are first
: deposited onto aluminium foil.

: After the assembly has cooled, a plastic carrier layer is added
: underneath it and the aluminium is removed and recycled. Contacts
: are then added, followed by a protective plastic layer on top, too.
: This sequence lends itself to continuous production on rolls of
: plastic film.

: The Swedish and Dutch-owned company Akzo-Nobel, a partner in the
: H-AS research, already has a pilot plant producing rolls of silicon
: cells 40 centimetres wide. A projected full-scale manufacturing
: plant would produce panels at a cost of about 1 euro per watt. An
: A4-size panel sewn onto the back of a jacket and costing less than
: 10 euros would charge a mobile phone during a summer stroll. The
: company has not yet decided to go ahead with the plant.

: Jeremy Leggett, chief executive of the UK solar cell supplier Solar
: Century, is impressed, describing the 1 euro per watt price point
: as "breathtaking".

Mark Reiff