New Methods Produce Cheaper, Thinner Solar Building Materials

But to become commercially successful, thin film manufacturing costs must be cut.

Now, the National Renewable Energy Lab in Golden has installed a unique platform that enables NREL scientists to work directly with industry partners to test novel designs and manufacturing methods using precise digital printing technologies under controlled conditions.

Called an Atmospheric Processing Platform, it allows the scientists to print prototypes of less costly thin film solar cells from inks and other solutions.

The new platform allows collaborative research teams to isolate important steps in the thin film manufacturing process and look for ways to refine or accelerate those steps to reduce the cost of the finished solar cell.

At 6.2 x 6.2 inches, the thin film PV samples the platform produces are much larger than what is used in typical laboratory experiments, so the results can be more rapidly commercialized.

"There is no other laboratory platform quite like it in the world, and we're already running real samples through some of its chambers," said senior scientist Maikel van Hest. "We should be running samples continuously by the end of the summer."

NREL scientist Maikel van Hest holds a substrate sample used for making thin film solar cells in the Atmospheric Processing Platform. (Photo by Joe Verrengia courtesy NREL)

Traditionally, solar cells are made using intensive processes such as depositing metal contacts and absorber layers. These processes typically require high temperatures and vacuum deposition, which contribute to making solar electricity more expensive than electricity from other sources.

To find ways of reducing these costs, the new platform consists of several large glove boxes that are connected both by internal portals and a linear transport train that runs beneath the boxes. The system allows researchers to work with samples under controlled conditions inside the glove boxes.

The heart of the platform, says van Hest, is a pair of glove boxes fitted with a variety of solution deposition techniques that can be used for different aspects of thin film manufacturing at ambient pressures.

The thin films are made from inks and other solutions made of material precursors and nanoparticles. They can be deposited on common substrates such as glass, plastic and metal and closely examined — one layer at a time.

The deposition techniques themselves are commercially available units, but the platform can use them in unconventional ways.

Three techniques are possible with the new platform. Ink jet printers can replicate complex and specific images, and offer advantages for precisely adding patterns of metal contacts from solutions such as nickel and silver inks.

Aerosol jets provide a very fine mist to write a specific pattern, moving back and forth much like a plotter.

Ultrasonic sprayers can be used to deposit homogenous layers of conducting, semiconducting or dielectric materials

All three methods use very small amounts of ink in precise patterns to improve manufacturing efficiencies. Because the solution deposition tools do not make direct contact with the samples, losses from breakage and blemishes are reduced.

"There are significant cost savings especially as you scale up," van Hest said.

The platform also includes work stations that allow researchers to assess prototype photovoltaic cells under the same controlled conditions, including X-ray fluorescence for compositional analysis and X-ray diffraction for structural analysis.

Prototype thin film cells move through the platform in about a minute. At the industrial scale, thin film cells need to be manufactured in a few seconds or less.

"But speed is not our main concern — this isn't a factory," van Hest said. "Doing this in a minute is sufficient to develop new materials, new contacts and new processing approaches. We know these deposition techniques can be sped up to industrial speeds"

"If you can do it faster, it's always better — and it will get faster," he said. "But what this system really lets us do is go back and forth between the glove boxes and develop new concepts and materials."

The Atmospheric Processing Platform is located in the Process and Development Integration Laboratory at NREL, a unique collaborative facility that allows government and industry scientists to work together towards commercialization of next-generation photovoltaics.

Copyright Environment News Service, ENS, 2009. All rights reserved.