A California company is using silicon ink patterned on top of silicon wafers to boost the efficiency of solar cells. The Sunnyvale, CA, firm Innovalight says that the inkjet process is a cheaper route to more-efficient solar power. Using this process, the company has made cells with an efficiency of 18 percent.

Innovalight has partnered with solar-cell manufacturer JA Solar, headquartered in Shanghai, which plans to integrate the inkjet printing technology into its manufacturing lines. The resulting solar cells should be on the market by next year.

It's possible to increase the efficiency of solar cells by patterning silicon in a way that improves the absorption of high-energy, short-wavelength light. But this usually requires adding several etching steps to the manufacturing process, and this type of cell architecture "costs a lot of money to make using standard procedures," says Homer Antoniadis, chief technology officer at Innovalight.

Innovalight has not disclosed the costs of adding its ink to solar cells, but if the company's process achieves such gains in efficiency at a lower cost, it could help make solar a more competitive source of electricity. The company has developed silicon inks that can be patterned using inkjet printing technology developed by OTB Solar, a company headquartered in Eindhoven, Netherlands.

Innovalight's ink is a suspension that contains silicon nanocrystals. Although the recipe is proprietary, Antoniadis says the company has good control over two key factors: the size of the nanocrystals and their printability. By making the crystals just a few nanometers in diameter, the company has lowered the temperature required to bind them to the underlying wafer. The silicon ink also contains an organic compound that helps suspend the silicon, which otherwise tends to sink to the bottom, thus making the liquid compatible with inkjet printing. Because the process requires lower temperatures and can be performed on thinner silicon wafers than those used in conventional cell manufacturing, it helps bring the price down, says Innovalight's CEO Conrad Burke.

The 18 percent average efficiency of the solar cells made in Innovalight's pilot plant in California has been independently confirmed by the National Renewable Energy Laboratory. Without using the inkjet-printing technique, the efficiency of such cells would be about 16.5 percent to 17 percent, says Antoniadis.