the international year of chemistry, James Mitchell Crow looks back at some
of the discoveries and developments made by chemists over the past six
2000s: thin film solar cells
alternative energy rose inexorably up the political agenda throughout the
2000s, so rose the performance of a new breed of cheap, efficient solar
cells that could fill that gap - if the price is right.
cells are all about cost,' says Ali Javey, who studies light-harvesting
nanomaterials at the University of California, Berkeley, US. 'Back in the
1950s, the first cells cost around $1,700 (£1,060 at today's exchange rates)
per watt. Today we're at about $3 per watt, and it's continuing to fall.'
government, which invested heavily in solar technology research as part of
its economic stimulus package, predicts that solar energy could reach grid
parity with fossil fuel generated electricity by 2015. Subsequent
improvements should see the costs fall still further.
developments are in no small part the result of emerging thin film
technologies, which in 2009 dropped below the cost of traditional silicon
panels for the first time. 'Today, the installed cost of a crystalline
silicon solar panel is $5 per peak watt. For thin film cadmium telluride it
is $4.50,' says Javey.
breakthrough for cadmium telluride cells has been finding ways to grow them
uniformly, reliably and reproducibly over large areas at low cost. The US
firm First Solar, for example, has developed a solution-based process for
large scale manufacture of these cells.
Thin film solar cells are now beginning to compete with silicon in
efficiency and cost
© US DEPARTMENT OF ENERGY/ SCIENCE PHOTO LIBRARY
thin film technologies aren't far behind. Amorphous silicon, organic dye-sensitised
cells, and copper indium gallium selenide (CIS or CIGS), are also beginning
to be commercialised. In some cases the first products might be rather
niche, but that's just the beginning, says Udo Bach, who researches dye-sensitised
solar cells at Monash University in Melbourne, Australia.
me who work in this area wouldn't put in all the effort if they thought that
all we could make is a solar-powered backpack that could charge a mobile
phone. We have something much bigger in mind, and I definitely see the
potential for these organic solar cells to be applied in large scale solar
farms,' says Bach.
also looking ahead. 'We're trying to grow single crystal materials using a
cheap process on low cost substrates,' he says. 'We start with a cheap
aluminium foil, and anodise it, which generates an array of pores in the
surface. We use these pores like little test tubes to grow single crystals
in. The test tube confines the growth of the crystal, so acts as a
template.' The resulting material is an array of light-absorbing nanopillars,
all single crystals.
very difficult to say which technology will make it in 10 or 20 years' time
- which is why we have to work on all of them,' says Bach. 'That's why it's
such an exciting area to work in,' says Javey. 'One major technological
advance could change the story completely.'
1 E De
Clercq, Rev. Med.
2009, 19, 287