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Organic solar cells set 'remarkable' energy record
By Matt McGrath
Chinese researchers have taken what they say is a major step
forward for the development of a new generation of solar cells.
Manufacturers have long used silicon to make solar panels
because the material was the most efficient at converting
sunlight into electricity.
But organic photovoltaics, made from carbon and plastic,
promise a cheaper way of generating electricity.
This new study shows that organics can now be just as efficient
What are organic solar cells?
The term organic relates to the fact that carbon-based
materials are at the heart of these devices, rather than
silicon. The square or rectangular solid solar panels that most
of us are familiar with, require fixed installation points
usually on roofs or in flat fields.
Organic photovoltaics (OPV) can be made of compounds that are
dissolved in ink so they can be printed on thin rolls of
plastic, they can bend or curve around structures or even be
incorporated into clothing.
What's stopped them becoming widely used?
In a word - efficiency.
This is a measure of how much of the sunlight that shines on a
panel can be turned into usable electricity.
Commercial solar photovoltaics usually covert 15-22% of
sunlight, with a world record for a silicon cell of 27.3%
reached in this summer in the UK.
Organics have long lingered at around half this rate, but this
year has seen some major leaps forward.
In April researchers were able to reach 15% in tests. Now this
new study pushes that beyond 17% with the authors saying that
up to 25% is possible.
This is important because according to estimates, with a 15%
efficiency and a 20 year lifetime, organic solar cells could
produce electricity at a cost of less than 7 cents per
In 2017, the average cost of electricity in the US was 10.5
cents per kilowatt-hour, according to the US Energy Information
So what have these researchers done differently?
One of the things that has made OPV less efficient in the past
is the fact that the organic materials have loosely bound
molecules which can trap electrons and slow down the generation
of electricity. So researchers have tried to get around this by
putting different layers of material together in a what's
termed a tandem cell approach.
"Tandem cell means you have two devices built together in the
same structure," said one of the authors, Dr Yongsheng Chen,
from Nankai University in Tianjin, China.
"We have two layers of active materials, each layer can absorb
different wavelengths of light. That means you can use sunlight
in the wider wavelengths or more efficiently and this can
generate more current."
How far are these from commercial production?
Not that far away according to the researchers. Dr Yongsheng
Chen compares the OPV to organic light-emitting diodes, or
OLED. This technology has been introduced in the past few years
and is widely used for high-end TVs.
"These are already commercial, and they use a similar material
to OPV," Dr Yongsheng Chen told BBC News.
"The physical principle is the same, just a different
direction, one is from solar to electricity, the other from
electricity to light, the device and structure are similar."
"I am very positive for OPV, and it may not need five years,"
What type of application might we expect?
Flexible, printed solar cells offer a wide range of
possibilities. They can work indoors and they can be made semi-
transparent, so they could be incorporated into windows and
generate power during daylight.
They offer huge potential for buildings as they are lightweight
so might be ideal for deploying on the roofs of houses in
developing countries where structures might not suit heavy
silicon. They could be used on the roofs of cars, and in
clothes, even in glasses to charge your phone while you are out
"Their optional semi-transparency enables their use in windows
or glass facade shading," said Dr Alexander Colsmann and expert
on organic photovoltaics from the Karlsruhe Institute of
"The very same properties render organic solar cells ideally
suited to also power mobile applications - camping gear, smart
wearables or phone chargers, just to name a few - which have
been only insufficiently addressed by classical solar cell
technologies such as silicon."
What's been the reaction of others in the field?
Other experts in this field were generally positive.
"This looks a remarkable result to me," said Dr Artem Bakulin,
from Imperial College London.
"The development of such new materials with previously
unthinkable properties allowed them to achieve the reported
record efficiency and, in general, makes OPV technology much
Dr Feng Gao from Linkцping University in Sweden also believes
the new paper is significant.
"This work is a very important contribution to organic solar
cells and will certainly inspire new developments in the
field," he said by email.
"The tandem organic solar cells with record efficiencies in
this work indicate great potential of organic solar cells for
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