Texas researchers look to unleash spray-on solar cell potential

If Brian Korgel’s latest research project is able to lower photovoltaic manufacturing costs, it could revolutionize the solar cell market. But for now, it’s still a research project with game-changing, paintable potential, he told the Cleantech Group today.

The University of Texas at Austin chemical engineer and his team have demonstrated proof-of-concept of a way to more cost effectively produce solar cells using tiny nanoparticle "inks" that allow them to be printed like newspaper or painted onto the sides of buildings or rooftops to absorb sunlight.

“We’re actually spray painting them on,” he said, explaining how the patent-pending process would replace the conventional copper indium gallium (di)selenide (CIGS) method where CIGS material is vapor deposited in a vacuum chamber, followed by a process that requires high temperature heating. In addition to being a costly method with multiple steps, it involves dangerous chemicals, he said.

“We’re trying to replace the vapor deposition step with this painting step, and by doing that we think we can get the manufacturing cost of the whole thing down significantly,” he said.

It would enable the solar cells to have new physical properties, including flexibility. They could be printed using a roll-to-roll process on a plastic substrate or stainless steel, as opposed to glass.

The semi-transparent inks could help realize the potential of windows that double as solar cells, which has attracted interest from potential industrial partners, Korgel said.

The idea of spray-on solar cells isn’t new. Researchers at University of California Berkeley, Massachusetts Institute of Technology, the University of Toronto and the National Renewable Energy Laboratory have been pursuing a variety of different materials other than CIGS to lower the cost of manufacturing. However, Korgel said CIGS offer advantages over silicon including requiring less material to make a solar cell.

Researchers at the Australian National University have been working on a project to develop spray-on solar panels that are more efficient and less costly than today's PV (see Aussie researchers develop spray-on solar).

And researchers at Swansea University in Wales are investigating roll-on methods for reducing solar costs (see UK researchers simplify low-light solar with paint-on PV).

For the Texas team's technology to eventually reach commercialization, it needs to be improved, Korgel said.

It must have efficiencies of at least 10 percent, rather than the team’s current solar cell prototypes that have reached 2 percent. To do that, he said the researchers have to better understand how the materials are used in the process, and how an electric charge moves through them.

“I don’t think there’s a fundamental barrier to reach 10 percent,” he said. “We haven’t hit a roadblock yet."

Korgel’s research has been funded by the National Science Foundation, the Welch Foundation, and the Air Force Research Laboratory with about $250,000 a year for the past two years from the combined agencies.

Other University of Texas at Austin collaborators include Professors Al Bard and Paul Barbara from the department of chemistry and biochemistry, and Professor Ananth Dodabalapur with the electrical and computer engineering department.

The team faces its closest competition from researchers at Purdue University, who are also researching CIGS nanocrystals. The Purdue team has reported 5 percent to 6 percent efficiencies, but requires high temperature baking of the crystalline film. Korgel said the baking step is costly and can’t be used with plastics.

Other startups that have explored ways of making paintable materials for CIGS include San Jose, Calif.-based Nanosolar and Austin, Texas-based HelioVolt.

In 2001, Korgel co-founded Sunnyvale, Calif.-based Innovalight, which is moving into production of inks using silicon, rather than CIGS, as the basis, although he’s no longer involved with the company.