Let the Sun In: Inkjet Printers May Lead to Cheaper, Thinner Solar Cells
Inkjet printers could deposit thinner metallic grid lines (seen up close to the right) on silicon solar cells, thereby letting more sunlight strike the cell, among other benefits.
The next generation of cheaper, thinner and better solar cells could come courtesy of a technology found right in our homes and offices: inkjet printers.
As their name implies, inkjet printers squirt ink onto a material, such as a paper document or the silicon of a solar cell . The well-controlled, contactless deposition of inkjetting should make possible solar cells that are half as thick, yet more efficient at soaking up the sun's rays than today's industry standard.
"Inkjet is very good at putting down patterned material – anything that has a specific layout," said Maikel van Hest, a senior scientist at the National Center for Photovoltaics at the National Renewable Energy Laboratory (NREL) in Golden, Colo.
Such precision allows for the placement of thinner metallic grids on silicon solar cells that serve as collectors of sun-generated electricity . These silver "finger" strips crisscrossing solar cells measure in the 100 to 120 micrometer — or micron — range, whereas inkjet-deposited lines can be as narrow as 50 or even 20 microns, van Hest said.
The thinner contacts expose more of a solar cell's silicon to sunlight, which translates into more electricity generation. "[These lines] mean less shadows and more light onto the solar cell," said van Hest.
Using smaller portions of the expensive, electricity-capturing contact material – silver, a precious metal, being the most common – dovetails into lower overall unit costs as well.
Plus, the silver inks used in inkjets are more conductive than the pastes applied to solar cells nowadays, resulting in more efficient harvesting of electricity.
Yet another major bonus for inkjet technology is that is contactless — the printer apparatus itself never touches the brittle silicon wafer.
Conventional silicon solar cell manufacturing has relied on a comparatively rougher technique called screen printing — the same sort often used for making T-shirt designs, for example — since its early days in the 1970s.
With screen printing, fragility becomes a real issue for silicon wafers around 100 microns or less in height, van Hest said.
Given these benefits, it's surprising that inkjet printing in solar cell manufacturing has yet to be deployed commercially. But significant hurdles remain — some inherent to the technology, and others as a result of the evolution of the photovoltaic industry.
For starters, shifting to inkjet printing from screen printing will require retrofitting existing solar cell production facilities, and inkjet printing remains the more expensive process up front.
"Inkjet [printing] is always going to be more expensive than screen printing," van Hest said, "but because you use less material and get more efficiency from the solar cell, you can gain a cost advantage."
Solar panel manufacturers typically offer a 30-year warranty for their products, and for now the jury is still out on how inkjet-made components might hold up in the long run. Van Hest said NREL is doing accelerated field testing to see if there is a difference between tried-and-true manufacturing and the inkjet approach.
"Companies don’t want to risk their money going into a new technology and run into problems in the future," said van Hest.
A bright tomorrow
The continuing surge of solar cells, which as a means of electricity generation grew hundredfold last decade, according to a 2010 report by the Renewable Energy Policy Network for the 21st Century, might start changing some industry minds, however.
Slashing the amount of silicon and silver needed per solar cell is among the most direct ways of lowering the dollar per kilowatt-hour of produced power — a shared goal of the maturing solar sector.
"Inkjet will become interesting if [silicon] wafer thicknesses go below 50 microns, versus 150 microns today for 100 percent of the market, because non-touch processes will be required," said Conrad Burke, the CEO of Innovalight, a Calif.-based company that has developed an inkjettable ink currently used by screen printers.
Burke sees this inkjet era dawning in approximately six to eight years. Van Hest believes inkjet's adoption will happen alongside many other emerging photovoltaic technologies, such as thin-film solar cells , and numerous other manufacturing techniques.
"It's going to be a combination of all technologies a decade from now," van Hest told TechNewsDaily. "I think inkjet printing will be a part of mainstream production technology for solar cells . . . the industry is growing fast, so there's room for all of this."