The biggest new word in solar these days is the littlest—nano. A host of spiffy names describe the newest achievements in creating low-cost, high power, lightweight photovoltaic panels. Quantum dots, nanowires, nanoantenna, carbon nanotubes, and multiple quantum wells, all are at the heart of this evolution in solar cells. One company has even developed spray-on photovoltaic material using nanotechnology.

Nano materials are developed on a nearly atomic scale and are visible only under electron microscopes. By developing highly efficient materials on such a small scale, scientists are able to greatly reduce the amount of materials needed to make a photovoltaic cell, hence reducing production and materials costs. Right now, many of these nearly submicroscopic materials are being tested and researched to determine if they are more cost-efficient than crystalline silicon or thin-film photovoltaics.

One company, Nanosolar, already has gone to market with their thin-film nanosolar panels. The National Renewable Energy Laboratory certified that Nanosolar’s panels are capable of capturing 15.3% of the sun’s light. And it’s all done on a thin piece of aluminum covered with what the company calls a nanoparticle ink. A video of the process shows that it is much like printing on paper. Nanosolar’s machines are capable of printing 100 feet of solar cells a minute. Their facility in California, the company claims, can produce 1 gigawatt of solar cells a year!



Nanosolar is now ramping up production of its panels. Joey Marquart, a spokesperson for the company, tells CoolerPlanet.com that it plans to be able to produce panels at 60 cents per watt and retail them for about $1.00 a watt when production is full-scale. He adds that a fully installed Nanosolar panel system would cost about $2.50 a watt.

The company already has some field tests of its products out and plans to have more out in 2010, says Marquart.

Nanoantenna arrays being developed at the U.S. Department of Energy's Idaho National Laboratory have captured up to 80% of the sun’s rays mid-infrared rays. These spiral nanoantennas are 1/25th the width of a human hair.

The lab partnered with Microcontinuum Inc. and Patrick Pinhero of the University of Missouri, to develop the material, which the lab says, could “cost pennies a yard, be imprinted on flexible materials and still draw energy after the sun has set.”

Yup, solar energy after dark! Since these arrays absorb infrared radiation, they also absorb the sun’s infrared energy reradiated by the earth after dark. Similarly, they also take in heat from industrial processes. Scientists believe the antennas could absorb waste heat and re-radiate it as electricity, this could be used to cool down buildings or even computers without air conditioning.

When developing the nanoantennas, scientists first etched the nanoantenna pattern in gold into silicon wafers. These wafers absorbed more than 80% of the infrared energy, according to the lab. As of 2008, they were embossing the tiny arrays on thin sheets of plastic and achieving similar results. Each of the gold-hued panels in the picture above contains about 260 million of the antennas. The nanoantennas are set in a type of polyethylene, which is used in plastic bags.

The little suckers are fast, too. Apparently the alternating-current (AC) electricity they produce oscillates trillions of times every second. The electricity used in homes oscillates at 60 times a second.

Appliances can’t handle the energy that comes directly from the antennas, so the electricity needs to be handled by a rectifier to convert the power to direct current. Heck, commercial rectifiers can’t handle such high frequencies. Researchers at the lab are now working to develop nanorectifiers.

"We need to design nanorectifiers that go with our nanoantennas," says researcher Dale Kotter. He explains that a nanoscale rectifier will be about 1,000 times smaller than the commercial rectifiers now available and will require new manufacturing methods. Alternatively, they may determine that developing electrical circuitry slow down the current to usable frequencies may be another way to approach the issue.

Let’s get thinner, how about 1/1,000th the width of human hair—that’s the size of silicon nanowires being made at the Lawrence Berkeley National Laboratory to generate electricity!

Chemist chemist Peidong Yang, who led the research, says, “The fabrication technique behind this extraordinary light-trapping enhancement is a relatively simple and scalable aqueous chemistry process.” He adds that “we believe our approach represents an economically viable path toward high-efficiency, low-cost thin-film solar cells.”
Yang explains that by fabricating “thin films from ordered arrays of vertical silicon nanowires we’ve been able to increase the light-trapping in our solar cells by a factor of 73.”

Every nanowire is a complete photovoltaic cell, according the lab. Each wire has a p-n junction allowing it to transmit electricity. The diagram illustrates the tiny wires, with the p-type silicon at the center surrounded by n-type silicon. The junction greatly shortens the length of transmission to electrodes and allows produced electricity to move much faster across the panel’s surface.

The conversion efficiency of these panels is about 5% to 6%, but Yang contends this efficiency was achieved without putting much effort in efficiency-increasing modifications.

He theorizes, “With further improvements, most importantly in surface passivation, we think it is possible to push the efficiency to above 10%.” The reduced amounts of silicon used in the manufacture of such cells, the ability to use lower-grade silicon and increased efficiency, the lab said, should make the technology suitable for large-scale deployment.

Well, then there’s the solar spray. New Energy Technologies, Inc. says it’s come up with a patent-pending method of spraying windows with a nano-thin photovoltaic material. In the spray application, the photovoltaic materials act as a negative polar contact to capture solar and artificial light.

The spray is an organic semitransparent photovoltaic energy converter. It was developed by the Nanostructure Optoelectronics Lab in USF in partnership with New Energy Technologies.

The company will use the process in the manufacture of its SolarWindows, to which it previously applied an nano film that was 1/1,000th the thickness of a human hair. In 2009, the company said researchers found that its super small solar cells can harness more artificial light than other solar cells “under normal office lighting conditions, without the benefit of outside natural light from windows.”

These are among the most promising photovoltaic nanotechnologies making significant headway. Research into the smallest means of producing the largest amounts of electricity from the sun is ongoing. As these technologies make it to market, even more technologically dazzling means of converting sunlight into energy are being developed.