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[tvoivozhd <tvoivozd AT infionline.net>]

Only seven percent efficient,  compared to rigid panel 20%, but at price 
and versality in use, who cares at one Euro per watt.  Forgot current 
exchange rate, think a Euro is about $1.36.



  
The World's No.1 Science & Technology News Service

Pliable solar cells are on a roll

   * 10:30 18 December 2004
   * Exclusive from New Scientist Print Edition
   * Fred Pearce, Uppsala


   * Energy Research, European Union
   * Eindhoven University of Technology
   * Akzo Nobel
   * Solar Century

Imagine wearing a jacket or rucksack that charges up your mobile phone 
while you take a walk. Or a tent whose flysheet charges batteries all 
day so campers can have light all night. Or a roll-out plastic sheet you 
can place on a car's rear window shelf to power a child's DVD player.

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.
Electron knockout

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".