Nanophotonic technology and solar cell efficiency

Fascinating research on the upper limit of light absorption by solar cells. Utilizing nanophotonic technology and thin-film solar cells, the efficiency is given an impressive boost. I keep hammering on the same point, but cost and efficiency in combination are the key to making solar a commercially viable option. Throw in some short-term government subsidies (I know, I know) and we are getting close to that sweet spot.

From the link:

But things have changed since the 1980s, not least because it is now possible to make layers of silicon much thinner than the wavelength of the light they are expected to absorb and to carve intricate patterns in these layers. How does this nanophotonic technology change the effect of light trapping?

Today, Zongfu Yu and buddies at Stanford University in California, tackle this question and say that nanophotonics dramatically changes the game.

That’s basically because light trapping works in a different way on these scales. Instead of total internal reflection, light becomes trapped on the surface of nanolayers, which act like waveguides. This increases the amount of time the photons spend in the material and so also improves the chances of absorption.

Because of the geometry of the layers, some wavelengths are trapped better than others and this gives rise to resonances at certain frequencies.

What Yu and co show is that by designing the layers in a way that traps light effectively, it is possible to beat the old limit by a substantial margin.

Also from the link:

Physicists have long known that thinner solar cells are better in a number of ways: they use less material and so are cheaper to make and the electrons they produce are easier to collect making them potentially more efficient. Now they know that light trapping is more effective in thinner layers too.

Black silicon bringing down the cost of efficient solar

The latest news in one of the two areas — cost in this case — solar needs to continue to see improvement for widespread use.

From the link:

A simple chemical treatment could replace expensive antireflective solar cell coatings, bringing down the cost of crystalline silicon panels. The treatment, a one-step dip in a chemical bath, creates a highly antireflective layer of black silicon on the surface of silicon wafers, and it would cost just pennies per watt, say researchers at the National Renewable Energy Laboratory (NREL). They’ve used it to create black silicon solar cells that match the efficiency of conventional silicon cells on the market.

Solar goes black: These two solar cells were fabricated on a silicon wafer treated to create an antireflective black silicon surface. The silvery areas around the cells are a different color because the highly absorbent black layer has been etched away.
Credit: Hao-Chih Yuan

Graphene replacing silicon — is it “when” and not “if?”

Not quite yet, but headway is being made in making graphene the successor to silicon as the semiconductor for electronics. I first blogged about graphene replacing silicon back in late March 2008 (this blog wasn’t even three months old at the time — hit the link and dig the crazy layout I was using for KurzweilAI posts).

From the first link, the latest news — both good and bad — in making graphene the semiconductor of choice:

“Graphene has been the subject of intense focus and research for a few years now,” Philip Kim tells PhysOrg.com. “There are researchers that feel that it is possible that graphene could replace silicon as a semiconductor in electronics.”

Kim is a scientist at Columbia University in New York City. He has been working with Melinda Han and Juliana Brant to try and come up with a way to make graphene a feasible replacement for silicon. Toward that end, they have been looking at ways to overcome some of the problems associated with using graphene as a semiconductor in electronic devices. They set forth some ideas for electron transport for graphene in Physical Review Letters: “Electron Transport in Disordered Graphene Nanoribbons.”

“Graphene has high mobility, and less scattering than silicon. Theoretically, it is possible to make smaller structures that are more stable at the nanolevel than those made from silicon,” Kim says. He points out that as electronics continue to shrink in size, the interest in finding viable alternatives to silicon is likely to increase. Graphene is a good candidate because of the high electron mobility it offers, its stability on such a small scale, and the possibility that one could come up with different device concepts for electronics.

And here’s a bonus fun graphene graphic from the link:

Graphene is an atomic-scale honeycomb lattice made of carbon atoms. By Dr. Thomas Szkopek, via Wikipedia

Growing graphene

It’s been a while since I’ve blogged about graphene so I was pleased to read this news at the physics arXiv blog on a method to produce the material at a substantially lower cost. The hype about graphene probably is a bit over-the-top, but it’s proving to be quite the miracle nanomaterial.

From the second link:

The world of materials science is aflutter with stories about graphene, a supermaterial that is capable of almost anything (if you believe the hype). This form of carbon chickenwire, they tell us, is stronger, faster and better than almost any other material you care to name.

But not cheaper. At least not yet. The big problem with graphene is making it. The only way to get it is to chip away at a bigger block of graphite and then hunt through the flakes looking for single layers of the stuff. That’s not a technique that’s going to revolutionise the electronics industry, regardless of how much cheap labour is available in China.

That’s why an announcement from Hirokazu Fukidome at Tohoku University in Japan and a few buddies is hugely important. These guys say they have found a way to grow graphene on a silicon substrate. To show off their technique they’ve combined it with conventional lithography to create a graphene-on-silicon field effect transistor–just the kind of device the electronics industry wants to build by the billion.

That’s a big deal for two reasons. First, being able to grow graphene from scratch is going to be a huge boost to the study of this stuff and its myriad amazing properties. Second, being able to grow it on silicon makes it compatible (in principle at least) with the vast silicon-based fabrication industry as it stands.

Quantum dots and better computers

From KurzweilAI.net— Very cool Single-atom quantum dots made of silicon. This nanotech breakthrough has very real implications in improving computer performance by reducing both size and power consumption.

Single Atom Quantum Dots Bring Real Devices Closer

PhysOrg.com, Jan. 27, 2009 Scientists at Edmonton’s National Institute for Nanotechnology have invented quantum dots less than a nanometer in diameter and containing only one atom of silicon. By controlling electrons at a smaller scale than transistors, the quantum dots could allow for silicon-based computers 1,000 times smaller in size and with a 1,000-times reduction in power consumption.   Read Original Article>>

Solar done thin, flexible and silicon

Seems like solar is a very exciting industry right now.

Here’s the latest from Technology Review:

Conventional solar cells are bulky and rigid, but building lightweight, flexible cells has come with trade-offs in efficiency and robustness. A new method for making flexible arrays of tiny silicon solar cells could produce devices that don’t suffer these trade-offs. Arrays of these microcells are as efficient as conventional solar panels and may be cheaper to manufacture because they use significantly less silicon. The tiny solar cells could be incorporated into, among other applications, window tinting, and they might be used to power a car’s air conditioner and GPS.

Nanowire circuits and tracking asteroids

From KurzweilAI.net, the House passed a bill to begin tracking potential Earth-strike asteroids, and a new low-cost, high-volume method of integrating nanowires onto silicon has been developed.

House passes bill mandating a plan for asteroid warning and deflection

KurzweilAI.net, June 27, 2008 In recently passed H.R.6063, The U.S. House of Representatives would direct the NASA Administrator to develop plans for a low-cost spacemission to rendezvous with the Apophis asteroid and attach a tracking device (subject to Senate approval). The Apophis is expected to pass at a distance from Earth that is closer than geostationary satellites in 2029. The bill would also require the Director of the White House’s Office of Science and TechnologyPolicy (OSTP) to develop a policy within two years for notifying Federal agencies and relevant emergency response institutions of an impending near-Earth objectthreat. And the OSTP would be required to recommend a Federal agency (or agencies) to be responsible for protecting the Nation from any near-Earth object anticipated to collide with Earth, and for implementing a deflection campaign.

 

Researchers develop new technique for fabricating nanowire circuits

Nanowerk News, June 26, 2008 Scientists at Harvard University and German universities of Jena, Gottingen, and Bremen have developed a reproducible, high-volume, low-cost fabrication methodfor integrating nanowire devices directly onto silicon. The method incorporates spin-on glass technology, used in silicon integrated circuits manufacturing, and photolithography, transferring a circuit pattern onto a substrate with light. These devices can then function as light-emitting diodes, with the color of light determined by the type of semiconductor nanowire used. Because nanowires can be made of materials commonly used in electronics and photonics, they hold great promise for integrating efficient light emitters, and could lead to the development of a completely new class of integrated circuits, such as large arrays of ultra-small nanoscale lasers that could be designed as high-density optical interconnects or used for on-chip chemical sensing.   Read Original Article>>

Nano, solar and other KurzweilAI.net news

Different format today for the KurzweilAI.net newsletter highlights. There is so much good stuff I’m dropping bits directly from the newsletter. Today features solar, stretchy silicon, quantum computing news, self assembly, electricity producing nanotubes, and a possible successor to silicon — graphene.

Do follow the links.

From the newsletter:

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More-Powerful Solar Cells
Technology Review Mar. 27, 2008
*************************
An MIT researcher has found a way
to improve the efficiency of
multicrystalline silicon solar cells
by 27 percent without raising costs,
making them as efficient as the more
expensive single-crystal cells. The
first cells incorporating the new
technology are predicted to cost
$1.65 per watt, compared to $2.10
per watt today….
http://www.kurzweilai.net/email/newsRedirect.html?newsID=8278&m=39667

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Stretchy circuits promise elastic
gadgets
NewScientist.com news service Mar. 27, 2008
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University of Illinois at
Urbana-Champaign researchers have
made stretchable and flexible
silicon and plastic integrated
circuits that are just one
crystal–1.5 microns–thick. The
circuits are designed so that the
plastic, not the silicon, absorbs
most of the stress when the chips
are bent. Until now, integrated
circuits have been limited by…
http://www.kurzweilai.net/email/newsRedirect.html?newsID=8277&m=39667

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Silicon chips for optical quantum
technologies
KurzweilAI.net Mar. 28, 2008
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Bristol University researchers have
demonstrated the world’s smallest
optical controlled NOT gate–the
building block of a quantum
computer–fabricated from silica
wave-guides on a silicon chip. The
team generated pairs of photons,
each encoding a quantum bit or qubit
of information. They coupled these
photons into and out of the…
http://www.kurzweilai.net/email/newsRedirect.html?newsID=8276&m=39667

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Nanomaterial turns radiation
directly into electricity
NewScientist.com news service Mar. 27, 2008
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Two researchers–a former Los
Alamos National Laboratory engineer
and an Alabama A&M University
researcher–have developed highly
efficient nanotube-based tile
materials that can convert
radiation, not heat, from nuclear
materials into electricity. The
tiles are made of carbon nanotubes
packed with gold and surrounded by
lithium hydride….
http://www.kurzweilai.net/email/newsRedirect.html?newsID=8275&m=39667

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Self-Assembled Materials Form Mini
Stem Cell Lab
KurzweilAI.net Mar. 28, 2008
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Northwestern University researchers
have built self-assembling thin-film
sacs able to hold human stem cells
for four weeks in culture, keeping
the cells separated while allowing
proteins to cross the membrane. This
new mode of self-assembly from a mix
of peptide amphiphiles and
biopolymers also can produce thin
films whose size and shape can be…
http://www.kurzweilai.net/email/newsRedirect.html?newsID=8273&m=39667

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Is Graphene the New Silicon?
KurzweilAI.net Mar. 28, 2008
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University of Maryland physicists
have found that graphene conducts
electricity at room temperature with
less intrinsic resistance than any
other known material. Graphene, a
new material that combines aspects
of semiconductors and metals, is one
of the materials being considered as
a potential replacement for silicon
for future computing. The…
http://www.kurzweilai.net/email/newsRedirect.html?newsID=8271&m=39667