by Debra Vogler, senior technical editor, Solid State Technology
May 19, 2009 – Silicon has many advantages for solar application: it’s a well-known material with well-characterized performance data, field-proven for solar applications with high conversion efficiency and a demonstrated 30-year lifetime. Speaking at the recent SEMI PV Group luncheon (5/14 in Santa Clara, CA), NanoGram president/CEO Kieran Drain outlined his company’s focus on its 35μm multi-crystalline silicon technology (mc-Si), called SilFoil, as its chosen path to achieve grid parity. “We are not on a wafer-based paradigm,” he said; “we are a large-scale, monolithic, direct-deposition paradigm.”
With its SilFoil technology, NanoGram deposits a thin sheet of silicon that, on a morphology basis, is actually the same as slicing a cast ingot. The company has achieved a 64% reduction in silicon on prototypes at the mini-module level (150mm2), he said.
Drain described three levels of differentiation in the company’s proprietary technology that are keys to achieving high efficiency at a low cost: laser reactive deposition (LRD), high-temperature silicon deposition, and zone melt recrystallization (ZMR). The LRD process uses an optically modified CO2 laser beam whereby silane gas is split into silicon metal and hydrogen. The laser deposition process is used to create a release layer with a melt temperature well above that of silicon, followed by a silicon deposition on that release layer. The ZMR process is used to do very precise wide-format, high-cooling-rate melt re-crystallization. “We break the paradigm of how to deposit multi-crystalline silicon — we operate at extremely high temperature on ceramic substrates and we transfer the deposited silicon onto glass,” said Drain.
NanoGram’s Laser Reactive Deposition (LRD) technology. (Source: NanoGram)
As the company has moved from producing sheets of silicon into functioning solar modules, it has developed IP around both cell and module manufacturing technology. A 5MW line (pre-production devices) is slated for completion in 4Q09 (in Milpitas, CA) with a 50MW plant to follow about a year later. – D.V.