The secret to producing thin-film solar cells comes in part from the snack food industry, says Ascent Solar.
The Littleton, Colo.-based company says it will deploy high-speed thermal evaporators--the same equipment used to seal Doritos bags--to produce copper-indium-gallium-selenide (CIGS) solar cells.
Here's how it works. Ascent will spray the active CIGS material onto a polymer sheet rolling from one spool to another. The evaporating equipment will rapidly heat up the coated polymer sheet to eliminate liquid carriers and fix the CIGS material in place.
Ascent will then cut up the sheets and integrate the solar cells into roof tiles, building materials or traditional solar panels.
"You can do rapid thermal evaporation. The CIGS is what slows it down," said CEO Matt Foster. Some of the evaporation equipment comes from General Vacuum of Manchester, England.
In a sense, Ascent is mixing early and new ideas from the CIGS industry. Laboratory scientists have demonstrated how to produce CIGS cells through evaporation. Evaporation, however, can be a slow process.
Several start-ups, and even some established solar manufacturers, have tried to get around the slow pace of evaporation by applying the active CIGS materials in a different way and combining roll-to-roll manufacturing. Miasole is trying to sputter the material onto metal or polymer substrate in a roll-to-roll process. Nanosolar wants to print CIGS onto rolls of materials. Solopower is trying to combine electroplating with roll-to-roll processes. HelioVolt has developed what it calls the FASST process.
To date, no one has perfected an alternate method to evaporation. Rather than fight the status quo, Ascent is essentially trying to marry the proven process with roll-to-roll manufacturing.
"CIGS is hard enough to do without a proven process," Foster said.
Tucson'sis taking a similar, but even less fancy, tack with CIGS. It is using evaporation but applying CIGS cells to sheets of glass, rather than plastic. Glass costs more than polymer and it costs more to ship. But Global's chief technology officer, Jeffrey Britt, points out that it is also really simple to spray stuff onto glass. First Solar, one of the more successful solar companies in recent years, sells cadmium telluride solar cells on glass.
CIGS solar cells cannot convert as much sunlight into electricity as silicon solar cells. CIGS manufacturers are now producing cells on their in-development manufacturing lines that can convert between 4 percent and 10 percent of the light that hits them into electricity. Efficiency is expected to rise to around 16 percent. By contrast, commercial silicon solar cells can now hit 22 percent efficiency. But CIGS cells are expected to cost less. Conceptually, a contractor could shrink wrap the roof of a Wal-Mart and turn the massive surface into a solar generator.
Ascent has a ways to go. It will receive equipment and start to build a prototyping plant next month. It hopes that this plant will be running by the first quarter of next year.