5 August 2009

Solar organic technology steps toward viability

Organic photovoltaics use organic molecules to capture sunlight and convert it into electricity.

They start out as a kind of ink that can apply to flexible surfaces to create solar cell modules that can spread over large areas as easily as unrolling a carpet.

In this cross-section of an organic photovoltaic cell, light passes through the upper layers (from top down, glass, indium tin dioxide, and thermoplastic) and generates a photocurrent in the polymer-fullerene layer. Channels formed by polymers (tan) and fullerenes (dark blue) allow electric current to flow into the electrode at bottom. NIST research has revealed new information about how the channels form, potentially improving cell performance.

Even the best organic photovoltaics convert less than 6% of light into electricity and last only a few thousand hours.

“The industry believes that if these cells can exceed 10% efficiency and 10,000 hours of life, technology adoption will really accelerate,” said National Institute of Standards and Technology’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 beginning.”

The NIST team has advanced that understanding with their latest effort, 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 collect electrons.

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.

“We’ve identified some key parameters needed to optimize what happens at both edges of the film, which means the industry will have a strategy to optimize the cell’s overall performance,” Germack said.

For related information, go to www.isa.org/environmental.