A Startup’s Nanowire Ink Lifts Solar Cell Efficiency

Ink filled with microscopic semiconductors called nanowires could make solar power cheaper by boosting the efficiency of solar panels by 25 percent, without adding much cost to manufacturing, says Sol Voltaics, a startup that has raised $11 million, and which this week announced its intention to commercialize the ink.

The ink is based on two advances from Lund University in Sweden. Professor Lars Samuelson demonstrated that nanowires can improve the efficiency of solar cells, and he developed a new way to manufacture nanowires that could make them practical to use.

Increasing solar cell efficiency is one of the most effective ways to reduce the cost of solar power, since it can lower the cost per watt of solar panels as well as reduce installation costs, because fewer solar panels would be needed (see “Alta Devices: Finding a Solar Solution”).

Lund, Sweden-based Sol Voltaics plans to develop equipment to produce nanowire ink, and then sell it to existing manufacturers.  The ink is expected to boost efficiency by helping solar cells absorb more sunlight.

Research in making nanowires for solar photovoltaics has been going on for years, but fabricating nanowires has never been done in an economical way (see “Nanowires Suck Up Light from Around Them” and “How to Double the Power of Solar Panels”). Nanowires are usually grown on a substrate in a batch process that is too expensive for large-scale production.

The Lund University team lead by Samuelson has developed an alternative method that does away with the substrate. It starts by vaporizing gold to produce aerosol nanoparticles, which flow into a tube-shaped furnace along with two other gases. The gold serves as a seed that catalyzes a reaction with the gases to form gallium arsenide nanowires. In a paper published in Nature last December, the Lund researchers said that the process, called aerotaxy, can grow gallium arsenide nanowires 20 to 1,000 faster than batch deposition methods. By controlling temperature and reaction time, they can control the dimensions of the nanowires, which is key to optimizing their performance for solar cells.

Brian Korgel, a professor of chemical engineering at the University of Texas, says aerotaxy “has the potential to be scaled to a continuous process.” Making large volumes would overcome one of the biggest technical challenges in scaling up gas-phase nanowire production, he says.

In a separate paper in Science earlier this year, the same researchers at Lund University showed that arrays of these nanowires made with the aerotaxy method improved the efficiency of indium phosphide solar cells by 13.8 percent by trapping more light.

The next step for Sol Voltaics is to demonstrate that the effect also works on silicon solar cells, the most common type, says CEO Dave Epstein. After it does that, it intends to develop equipment to manufacture the nanowires. He estimates that the ink would add one or two cents per watt to production costs—it currently costs less than 75 cents per watt to make solar panels. “It only takes one gram of nanowires to cover a square meter of a silicon solar panel, so they only need a very small amount of material,” he says.

 “Every indication is that even if there will be an additional cost, the increased efficiency will far outweigh the cost,” says Alf Bjørseth, the founder of REC Solar and an investor in Sol Voltaics.

If the nanowire-ink-on-silicon approach is effective, the company plans to begin small-scale production in 2015. It expects to need $50 million—much less than a full-scale solar factory—to produce at commercial scale, since it’s only selling an add-on product.