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Inkjet printing solar panels: cheap and almost green

The inkjet printer researchers at Oregon State University are using to print solar panels using CIGS technology. Courtesy Oregon State University.

In the race to find renewable energy options, solar energy is one the easiest and least environmentally taxing ways to harness natural resources.  It requires minimal time and infrastructure compared to other energy sources like coal, oil or even wind.  But what continues to keep solar panels from blanketing more roofs, particularly in the U.S., is cost.

As much energy is spent researching ways to bring the cost of solar down as to create new, innovative technologies. One of the most promising trends began several years ago and has just entered a new phase of innovation — inkjet printing for solar panels. Researchers have combined the speed and low waste of using inkjet printers with newer, and much cheaper, non-silicon solar cells. It’s a move that, if it proves to be mass scalable, could reduce production waste by 90 percent, eliminate the need for ultra-pricey silicon and make even thinner solar films a viable replacement for the large and heavy traditional panels.

“I think the key contribution we’ve made is using low-cost precursors [or starting materials] and we can print them and make them into useful compounds,” said chief investigator, Dr. Chih-hung Chang, a professor in the School of Chemical, Biological and Environmental Engineering at Oregon State University in Corvallis. “Our ink is a very low-cost salt.”

This isn’t exactly the $99 inkjet printer found on a college kid’s desk, but it’s not too far from that. Using relatively small printers that can print on almost anything and low-cost starting materials can significantly cut production costs. Printing is only one part of a multi-step process, but it’s a big one. “Using this technology we should be cutting the cost about half. If we just compare this step alone, we can save 50 percent probably.”

The National Renewable Energy Laboratory in Golden, Colorado, developed similar technology two years ago, but its inkjet printers were much larger and were still using silicon solar cells. Oregon State’s process is comparatively less expensive, depositing a combination of copper, indium, gallium and selenium minerals, or CIGS, in precise patterns on a thin film. Because the minerals are excellent conductors for turning sunlight into energy, on par with silicon, Chang says CIGS technology is ideal for cost savings. “It is one of the best materials you can have in terms of [its light] absorbing characteristic.”

An added benefit, he noted, is that the chemicals that make up the solar cells are not wasted in the mist of a traditional vapor process. Therefore, with inkjet printing, manufacturers can start with a lot less product. The printers can also print onto almost anything because they don’t touch the surfaces on which they print, they essentially spray them. So, where the traditional process requires a thicker, sturdy surface, such as the standard glass-metal structures, to handle the pressure of printing, inkjet printers can print to thin films and even roofing materials, including ceramic. That bodes well for solar roof installations.

The minerals that comprise CIGS are currently much cheaper than solar cells made from silicon, which accounts for two-thirds of the cost of producing solar panels, according to the National Renewable Energy Laboratory. CIGS technology is already being mass-produced and used in commercial and residential lightweight solar panels, particularly in Europe.

But, there are questions about the sustainability of CIGS technology. Some components — indium, gallium and selenium — are rare earth minerals not mined in the U.S. Indium is the one sparking the most concern. The primary sources of indium are China, Canada and Japan, and it is primarily used in thin-film coatings of LCD screens. With the increase of televisions and devices using that technology has come a dramatic increase in indium use, according to the U.S. Geological Survey. Forbes estimates that there is roughly enough indium to last 15 years at the current rate of development, based on commodity trading supply.  Indium Corporation, the world’s top supplier, disputes that claim.

Microscopy photo of a CIGS solar cell, used instead of silicon to process light into electricity in Oregon State University's new solar film inkjet printer. Courtesy Oregon State University.

Researchers are experimenting with other substances to use as solar cell material, Chang says, but the technology isn’t there yet. He says CIGS technology is still the best option for making solar more accessible because silicon requires special attention and handling. “If you want to make a good silicon cell, you need to have very high-quality silicon,” said Chang. “It’s not easily printable. You cannot do it in the air, you have to do it in a glove box. To print enough silicon for photo efficiency is quite difficult.”

Oregon State is still working to improve the efficiency of its inkjet-printed solar films, which, according to its recent study, have a 5 percent efficiency rate, whereas commercial solar cells get about 15 percent. “We still need to achieve a higher efficiency and once we have that and we’re more confident to talk about that, then we can make it into the commercial realm,” said Chang.

But the question remains whether it’s possible to print a cheap solar cell that can be mass marketed to provide enough energy for both commercial and residential usage. While solar energy may be endlessly renewable, the technology behind it also has to be sustainable and cheap to gain traction. That’s what scientists hope this combination of simple printing and cheap materials will achieve where previous generations of solar products have failed.

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