Scientists at the National Institute of Standards and Technology
(NIST) in the US have recently conducted work to deepen their
understanding of the complex organic films at the heart of the new
Organic photovoltaics, which rely on organic molecules to capture
sunlight and convert it into electricity, in principle have significant
advantages over traditional rigid silicon cells.
Organic photovoltaics start out as a kind of ink that can be applied
to flexible surfaces to create solar cell modules that can be spread
over large areas as easily as unrolling a carpet.This makes them easier
to adapt to a wide variety of power applications, and considerably
cheaper to make than traditional cells.
But there are still improvements needing to be made with the
technology. Currently even the best organic photovoltaics convert less
than six per cent of light into electricity, and last only a few
“The industry believes that if these cells can exceed 10 per cent
efficiency and 10,000 hours of life, technology adoption will really
accelerate,” said NIST’s David Germack.
“But to improve them, there is critical need to identify what’s
happening in the material, and at this point, we’re only at the
The NIST team has advanced that understanding with their latest
research, which provides a powerful new measurement strategy for
organic photovoltaics that reveals ways to control how they form.
In the most common class of organic photovoltaics, the ‘ink’ is a
blend of a polymer that absorbs sunlight, enabling it to give up its
electrons, and ball-shaped carbon molecules called fullerenes that
When the ink is applied to a surface, the blend hardens into a film
that contains a haphazard network of polymers intermixed with fullerene
channels. In conventional devices, the polymer network should ideally
all reach the bottom of the film while the fullerene channels should
ideally all reach the top, so that electricity can flow in the correct
direction out of the device.
However, if barriers of fullerenes form between the polymers and the
bottom edge of the film, the cell’s efficiency will be reduced.
In their work, the team were able to change the structure at the
edges of the film by repulsing fullerenes while attracting the polymer.
This was able to reduce the accumulation of fullerenes at the bottom of
the film, and allowed the electrical current produced by the sun’s rays
more opportunities to travel to the right end of it.
Both of these changes could potentially improve the photovoltaic’s efficiency or lifetime.
“We’ve identified some key parameters needed to optimise what
happens at both edges of the film, which means the industry will have a
strategy to optimise the cell’s overall performance,” Germack said.
“Right now, we’re building on what we’ve learned about the edges to
identify what happens throughout the film. This knowledge is really
important to help industry figure out how organic cells perform and age
so that their life spans will be extended.”