How do you continue to drive down the cost of crystalline silicon solar panels?
Since material costs, especially silicon, are the dominant cost component in panels, cost reduction becomes about lowering the amount of silicon per panel, which is currently at 6 grams per watt, give or take. Manufacturers spend a great deal of time and energy fabricating blocks of polysilicon, only to see up to half of that hard-earned material turned into sawdust in the wafer production step.
Thinner silicon -- and more efficient ways of slicing silicon or fabricating silicon wafers -- are obvious paths to further lower solar module pricing. The DOE's Steve Chu has a penchant for this kind of technology.
I just spoke with Curt Vass, the CEO of Austin, Texas-based AstroWatt. Vass comes to the startup with 15 years of experience at Applied Material's silicon products division. The firm is funded with $5.0 million from Austin Ventures and NEA and $1.5 million from the DOE SunShot program.
In June of this year, AstroWatt had produced a 15-percent-efficient champion cell using AstroWatt's SOM (Semiconductor-On-Metal) technology to create litho-less local back contact (LBC) hetero-junction solar cells.
Astrowatt's process deposits 50 microns of metal onto a monocrystalline silicon wafer. The substrate is "exfoliated" using a thermal cleaving process, creating an ultra-thin ~25 um silicon metal substrate. The process reuses a one-millimeter-thick 1-0-0 silicon substrate for the multiple exfoliations. The silicon can withstand a standard texturing step despite its thinness.
So, the substrates are 25 to 50 microns thick and use just 0.22 grams per watt of silicon. Vass said that the firm has a roadmap to get to a cost of less then $0.30 per watt, compared to the current costs of $0.70 to $0.80 per watt. The company targets 22 percent to 23 percent efficiency and is starting to move toward commercialization.
The metal rear contact makes the cell easy to handle and the process can be performed with standard double heterojunction equipment from the likes of Roth & Rau and Jusung. Handling issues have been resolved on commercial tools but will have to be proven to prospective customers.
The business plan is not to add another 50 megawatts of cell production in an already over-supplied market. Instead, Vass looks to partner with a production-oriented company seeking disruptive technology in order to scale AstroWatt's technology into volume production. That would seem to point to China, where firms are suffering from slim margins and are in need of differentiation.
Long-term reliability and degradation profiles will have to meet or exceed incumbent technologies.
Other startups innovating in the thin silicon field include:
Silicon Genesis, known as SiGen, promises kerf-free wafering via an implant-and-cleave process that is still in the early stages of development but could yield wafers with thicknesses down to 20 microns.
Ampulse claims that its "c-Si thin-film technology takes advantage of HW-CVD techniques to directly deposit a very thin layer of c-Si onto a uniquely textured and flexible metal substrate."
Bandgap Engineering has developed tunable methods for nano-structuring silicon. The firm claims that the absorption of nano-silicon is enhanced by up to several orders of magnitude over bare silicon over a wide range of wavelengths. This enables nano-silicon to absorb the light in the first four microns versus the top 50 to 100 microns that bulk silicon needs to absorb most of the light. This could impact cell efficiency and direct manufacturing cost -- and make for much thinner wafers.
Crystal Solar uses a vapor deposition process for making thin crystalline silicon wafers. The firm has made wafers measuring 50 microns thick in its labs and hopes to get down to 20 microns. Oceanshore Ventures is one of the firm's investors.
1366 Technologies has a "direct wafer" technology where molten silicon is directly converted into wafers, which can then be processed into thin solar cells. 1366 is a recipient of a $150 million DOE loan guarantee.
Developing a new wafer technology and integrating it into an existing process chain is an enormous challenge. Evergreen Solar, now bankrupt, tried to revolutionize wafer technology with its string ribbon technology, but size incompatibility and insurmountable cost issues proved to be its undoing.