(Page 2 of 2)
Researchers at SiOnyx and Harvard are still investigating why black silicon produces much more current than does normal silicon when exposed to the same light. The theory is that this happens because of a mechanism called photoconductive gain. In regular silicon, each photon will knock loose only one electron to contribute to electric current. But in the new material, each photon sends multiple electrons cruising through the circuit, boosting the current 200 to 300 times. "We believe this is really the first time photonic gain has been seen in silicon," Saylor says.
The material's potential for photovoltaic solar cells remains to be seen. In a light detector, an external voltage is applied to the silicon. When a photon hits the material, it knocks loose an electron. The voltage sweeps the electron out into an external electric circuit to produce current. But photovoltaic materials have to create a voltage in response to light. It is not clear if black silicon can be coaxed into doing that efficiently, says MIT mechanical-engineering professor Tonio Buonassisi.
Buonassisi is now exploring the material for photovoltaic applications. He and his group are trying to understand the atomic structure of the material so that they can harness it to make a solar cell. The material's high absorbance makes it a promising candidate. "This is a very interesting material, and it certainly is intriguing for solar cells . . . although a lot of the mysteries have yet to be unraveled," Buonassisi says.
SiOnyx, meanwhile, is developing a black-silicon fabrication process. Saylor says that the company wants to develop a scalable way to make uniform black-silicon wafers. Then it plans to license the manufacturing method to companies that make silicon light detectors and solar cells.
A one-step process creates a highly antireflective layer for photovoltaics.
A new form of silicon could create cheaper photo detectors that are easier to make in bulk.
On reflection to what I just read this is the solution that can be effected now.
Stack a normal "clear" silicon cell on top of the black silicon. If visual light in not utilized by the black and the clear silicon utilizes all forms of light other then IR and higher, it seems pretty strait forward what to do. Layer the cells and to uses exsisting tech; one clear, one black, a true 100% cell
The hype here is rather extravagantly outreaching the actual physics. I notice that these people do not claim to have made a solar cell from their material, and for good reason.
In a good silicon cell manufactured with today's technology, the absorption of light in the wavelength band usable by silicon is already well above 90%. You cannot possibly produce "hundreds of times more current" in a solar cell; this is physically nonsensical.
It is true that silicon solar cells do not respond to infrared longer than about 1.1 microns wavelength. This portion of the solar spectrum contains about a third of the energy in sunlight. However, these infrared photons have too little energy to create electron/hole pairs. Increasing the absorption of these photons by the silicon isn't going to help; silicon can not make use of the energy of the photons because its bandgap is too wide. If you narrow the bandgap, you can absorb these photons-- but at the price of decreasing the available voltage. (And, in any case, you couldn't increase the current by "hundreds of times" even if you drop the output voltage to zero.)
hey, it has been a while since you wrote your comment but only now i started to show interest in the technology.
i would love if you can send me a reference to solar cell that uses well over 90% of the light.
as far as i know the commercial solar cells are abou 10-20% and the highest any one got is about 60% with a very expencive technology in one of the US univercities. (i also know that in weitzman Institute in IL they got about 40% few years ago.
since my research is about solar cells implemintation i would love to get a refernce to these cells you mentioned.
thanks in advance,
gil.
Manufacturing in the United States is in trouble. That's bad news not just for the country's economy but for the future of innovation.
Our list of the 50 most innovative companies, including the following:
On Twitter
Become a Fan on Facebook
Subscribe to the Feed
Ed_E
2 Comments
Black Silicon
This material sounds promising, and could possibly approach a true black body absorber. For example electrical tape absorbs infrared quite well, no matter the visible color. Cavities absorb infraed even better but not the visible spectrum unless they are the correct size corresponding to whe wavelength. The conical nature of the cavities formed by this material should make it a broad band absorber. By electricaly isolating the cavites so formed one from another, an efficient broad band photo-detector or photo cell is produced depending on the way they are reconnected or scanned.
Reply