(Page 2 of 2)
In previous work, Atwater and others have explored plasmonics to improve efficiency in cells made of gallium arsenide, a semiconductor material commonly used in optics; they have also tried organic materials and even amorphous silicon. However, this previous work applied the plasmonic structures to the front of thin-film amorphous silicon solar cells; in this position they tend to absorb light of certain wavelengths and convert it to heat.
"One of the things that one sees with particles on front side of solar cells is a net loss of short wavelengths due to resonant absorption in the metal itself," says Atwater. "We want to avoid that."
"It was very clever to put the metallic structures in the back contacts," says Mark Brongersma, professor of materials science and engineering at Stanford. "Now, all the incident light gets at least one pass through the cell, and the plasmonic structures can be optimized to manage a few photons with a narrower spectrum." In other words, the size and spacing of the holes can be tweaked to take advantage of the wavelengths of light that make it through the silicon to the back contact.
To make the nanopatterned holes, Atwater's group uses a stamp that is able to imprint holes over the area of an entire silicon wafer. In a series of simple steps, the array of holes is formed in a thin layer of material on the silicon wafer, which is subsequently covered with metal. The active silicon material in the cell and the top electrical contact are then deposited on top of the patterned back side. The stamp can be used for thousands of imprints before it needs to be replaced.
Brongersma, who was not involved in the work, adds that this fabrication technique is certainly amenable to high-volume manufacturing. "The work also makes a big step forward by showing that we may be able to scale plasmonic photovoltaic up to large areas."
The researchers, who will publish the work in an upcoming issue of the journal Applied Physics Letters, have run simulations to determine the optimum hole diameter and spacing. To test the performance of different types of holes, the researchers focused on the efficiency of a single wavelength of light, 660 nanometers. Their simulations indicate that by increasing the diameter and reducing the depths slightly, they can improve absorption at that wavelength from 42 percent to 54 percent, which should further improve the overall performance of the entire photovoltaic, although it's unclear by how much.
A new material, patterned at the nanoscale, absorbs a broad spectrum of light and could make thin-film solar cells more efficient.
Stanford researchers develop a trick that could help dye-sensitized solar cells trap more light.
A new tool makes etching extremely small features relatively easy and cheap.
Nanopatterns know by another name
By developing 3D patterns sometimes referred to
as holographic patterns or lensing to the resonant
frequencies of the photons increases the efficiency of the PV cell.
all points to advancements toward very inexpensive, durable and compact PV. check out: http://www.solarnetwork.net/ for an open-source application that could leverage these advancements.
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.
On Twitter
Become a Fan on Facebook
Subscribe to the Feed
flared0ne
395 Comments
There's a useful bit of info not being made quite visible enough, then.
Specifically, what portion of the total energy produced by a silicon PV cell backed by a nanopatterned electrode is actually resulting from the plasmonic mechanism -- because what it almost sounded like is that the plasmonic approach doesn't exactly really need silicon in front of it, and in terms of tweaking the conductivity and transmission/absorption characteristics to give the best plasmonic "reception", a range of other materials might improve matters. Granted, stacking multiple energy conversion processes on top of each other would seem to squeeze every possible erg out of each incident photon, but multi-factor economic break-point curve analysis doesn't reliably lend itself to "gut feel".
If a thin-film plastic membrane with a nano-patterned electrode backing can be produced significantly less expensively than the equivalent surface-area of thin-film silicon PV cells, then that 43%-as-efficient conversion rate becomes economically meaningful and may be a worthwhile target for development.
Reply