Accelerating solar power: Twin Creeks’ Hyperion 3 is an ion accelerator that bombards plates of silicon with hydrogen ions to produce very thin solar wafers for solar cells. The silicon plates are arranged around the outside of the spoke structure, which spins as the wafers are hit with ions.
The process begins in a vacuum chamber, where a high-energy beam of hydrogen ions bombards three-millimeter-thick disks of crystalline silicon. The ions accumulate at a precise depth of 20 micrometers, which is controlled by the voltage of the beam. Once enough ions accumulate, a robotic arm quickly removes the wafers, which are then placed inside a furnace, where the ions in the silicon form microscopic bubbles of hydrogen gas that expand, creating tiny fractures within the silicon wafer and causing a 20-micrometer-thick layer of silicon to flake off. The company then applies a metal backing to the thin silicon. (The proprietary process it uses sets it apart from another company, Astrowatt, which makes wafers that are similarly thin. But Astrowatt’s wafers are slightly curved, which could make them difficult to handle in conventional production equipment.)
The Twin Creeks wafers are compatible with conventional solar-cell production equipment, and with processes now being used to make advanced solar-cell designs, such as heterojunction cells. Sivaram says the hydrogen-ion process works with single-crystal materials other than silicon, including gallium arsenide, a semiconductor that has been used to produce world-record efficiency solar cells.
Using an ion beam to create thin wafers of crystalline silicon has been considered before, but it was far too expensive to be a practical manufacturing method. It required a particle accelerator that could produce ion beams that are both very high current and very high energy, and “such a beast did not exist,” Sivaram says. To make the technology viable, Twin Creeks developed an ion accelerator that is “10 times more powerful” than any commercially available accelerator, he says.
While the company emphasizes that the technology is compatible with existing production lines, it does require at least one change. Ordinarily, wafers are treated to create a rough surface texture that helps them absorb light rather than reflect it. The texture is made of pyramids that are about as tall as the Twin Creeks wafers are thick, so it isn’t practical to use with the new wafers. Sivaram says the company has implemented an alternative anti-reflection technology that allows its solar cells to perform as well as ones made with the conventional process.