Scientists create cells that can harness sun's rays

Scientists create cells that can harness sun's rays Posted by: Earth on http://PEJ.org Monday, January 10, 2005 - 10:18 PM

Scientists create cells that can harness sun's rays Sarah Staples CanWest News Service - Van Sun

;http://www.canada.com/vancouver/vancouversun/news/story.html?id=1751c381-ec3b-48ac-8264-bef1d95f3ab1

Canadian scientists have made a discovery that could become a catalyst for new generations of "battery-less" consumer electronic devices and the long-awaited solar-hydrogen economy. They have created paintable plastic solar cells that are the first to harness the sun's invisible, infrared rays, and could deliver up to five times the power of the most advanced photovoltaic cells today.

The plastic solar cells would be exponentially cheaper and easier to manufacture than similar material made of traditional semi-conductors like silicon, and more efficient than previous plastic solar cells that until now had managed to capture only the visible portion of the spectrum.

The material dissolves into a liquid without losing any of its performance, and may be painted onto walls or windows, sprayed on clothing, or printed onto rolls of paper.

Hydrogen-powered automobiles coated with solar cells, for example, could covert enough energy into electricity to continually recharge a car battery so it could run longer, said Ted Sargent, a University of Toronto physicist and holder of a Canada Research Chair in Emerging Technologies, who was one of the inventors.

Devices from PDAs and iPods to cellphones coated with the solar cell plastic would automatically recharge themselves, eliminating electrical chords and battery packs.

"The one thing that's not wireless about all the wireless devices we have, is the way we power them; solar energy is literally wireless power," said Josh Wolfe, a managing partner at the venture capital firm Lux Capital, in New York. "Everything you can think of will be different; from batteries to electricity bills, to the way devices themselves are manufactured."

The invention solves a basic problem of energy efficiency that is the last important barrier to mass commercialization of solar energy.

Photovoltaic cells have traditionally been made from silicon crystal wafers that need to be individually cut and smoothed into shape -- an expensive, time-consuming process relegating them to niche purposes, such as powering space vehicles.

Plastic cells were first designed in the 1990s and companies since have been refining methods of manufacturing them cheaply by printing them onto large rolls, like newsprint.

But normal plastic absorbs only visible rays within the blue-red range 400 to 700 nanometres -- billionths of a metre -- in wavelength, a region that accounts for only half of the energy in sunlight.

The Canadian version is the first to cull power from the visible spectrum plus the invisible infrared, a deep garnet region some 700 nanometres to 10 microns in wavelength.

With minor fine-tuning, the new plastic is expected to convert 30 per cent of solar energy into electricity -- a five-fold improvement over current nano-engineered solar cells.

The material is an electricity-conducting polymer mixed with nano-sized crystal particles called "quantum dots." The mix was painted onto glass, plied with electrodes and blasted with infrared light -- methods that allowed electrons to escape from the quantum dots and then be harvested almost instantaneously.

Peter Peumans, a professor of electrical engineering at Stanford University in California, called it, "a very important demonstration" that will yield solar cells "on order of magnitude cheaper than silicon, with the same or better performance as [current] plastic," within a decade.

The plastic is also adaptable for medical use. A characteristic of infrared light is that it penetrates up to 10 centimetres inside human flesh, so one option would be to coat digital-camera chips with the plastic in order to create a low-cost, portable diagnostic scanner for detecting cancer, said Peumans.

By mid-century, "solar farms" consisting of photoconductive plastic rolled across unpopulated expanses of desert could conceivably generate enough low-cost, "clean" energy to supply the entire planet's power needs, said Sargent.

But to affordably replace coal-fired or nuclear-generating stations, the average cost of converting sunlight into power must drop to six cents US per kilowatt-hour, from 25 to 50 cents US per kilowatt hour, according to Michael Rogol, an expert in solar power economics from the Massachusetts Institute of Technology.

Products nearest to market will be the most consumer-oriented items, such as energy-saving plastic sheeting that could be unfurled onto a rooftop to supply heating needs, or solar cell window coatings that could let in enough infrared light to power home appliances, Rogol said.

The discovery was reported Sunday in the prestigious nanotechnology journal Nature Materials.

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Sunlight to Fuel Hydrogen Future By John Gartner
Story location: http://www.wired.com/news/technology/0,1282,65936,00.html

02:00 AM Dec. 07, 2004 PT

The photovoltaic cell is old news. The latest way to exploit the sun is through tiny materials that can directly convert sunlight into large amounts of hydrogen.

Hydrogen Solar of Guilford, England, and Altair Nanotechnologies are building a hydrogen-generation system that captures sunlight and uses the energy to break water molecules into hydrogen and oxygen. The company's current project is a fuel station in Las Vegas that will soon be dispensing hydrogen fuel.

Hydrogen Solar CEO David Auty said his company's Tandem Cell technology uses two solar cells that together capture sunlight from every part of the ultraviolet spectrum. The interaction of photons with a semiconductor material causes a photoelectrochemical reaction that excites electrons and causes water molecules to break up into hydrogen and oxygen, according to Auty.

Auty said Tandem Cells are coated with a layer containing metal oxide particles that are less than 30 nanometers thick and can convert sunlight energy into hydrogen with 8 percent efficiency. Auty said that while other researchers view 10 percent efficiency as cost-competitive with fossil fuels, his technology can compete today.

Auty hopes to have a working demonstration system in early 2005. He said they are currently able to produce a few kilograms of hydrogen per day at the Hydrogen Solar laboratory using cells that are approximately 10 square inches.

Hydrogen Solar is creating consumer and industrial applications that extend research performed by the Swiss Federal Institute of Technology and the University of Geneva, according to Auty. He said a system on a home's garage roof that is 10 percent efficient could provide enough hydrogen for a fuel-cell car to drive 11,000 miles per year. "The market will have a niche in the home, as people will be able to install their own systems and run their vehicles using the hydrogen produced during daylight hours," he said.

Auty is not assuming that the United States will shift from fossil fuels to the hydrogen economy by 2020, as touted by the Bush administration, California Gov. Arnold Schwarzenegger and many scientists. "You can't put all of your eggs in one basket," Auty said, so his company is developing products that will compete in the current industrial hydrogen market.

Hydrogen Solar is one of several organizations pursuing photoelectrochemical hydrogen production. In October, the Department of Energy awarded (.pdf) $10 million in research grants to four groups also working on producing hydrogen from sunlight -- GE Global Research, the University of California at Santa Barbara, MVSystems and Midwest Optoelectronics.

Caltech University professor of chemistry Nathan Lewis, who is working with GE on hydrogen research, said integrated systems that convert solar energy photoelectrochemically are more efficient than splitting water through the more extensively researched electrolysis technique. Lewis said electrolysis requires two stages. Photovoltaic, nuclear, wind or coal energy systems generate electricity, and then a metal-based catalyst uses the electricity to split the water into hydrogen and oxygen.

Electrolysis requires using "very expensive materials such as platinum and palladium that won't scale at current costs," according to Lewis. Nanotech-based photoelectrochemical materials could lower the cost of hydrogen production "somewhere between a factor of 4 and 10," Lewis said.

Lewis is researching metal oxide materials that can be applied to tarps or roofs in very thin coatings. He said covering an area 57,600 square miles in the sunny southwest United States with such thin materials that convert sunlight with 10 percent efficiency could provide all of the domestic energy needs for buildings and transportation. While that number may not sound large (just 1.7 percent of the U.S. surface area), it is 10 times the size of all the rooftops in the country, he said.

"Visible light has enough energy to split water," said John Turner, a principal scientist at the National Renewable Energy Lab who is working on identifying and developing nanomaterials for photoelectrochemically creating hydrogen. Turner's group is using computer modeling to identify materials with the necessary properties for efficiently capturing light across the entire spectrum while remaining stable.

Photoelectrochemical reactions require the materials to be continually immersed in water, so they are susceptible to corrosion, Turner said. Some of the early materials Turner's team tested were effective for less than one day because of corrosion. "It's a question of stability" in selecting the optimal materials, he said. The researchers are testing metal oxides as well as organic compounds, according to Turner.

Turner said it's important to turn up the heat on hydrogen research now. "In 2030 we're not going to have enough oil, natural gas and coal to meet our energy needs ... and hydrogen is the best carrier" for an alternative fuel.

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