Solar Cell technology

Breakthrough: IBM Makes a Solar Cell Out of Inexpensive "Earth Abundant" Materials

by Michael Graham Richard, Ottawa, Canada

Photo: IBM
And It's Pretty Efficient Too!
IBM researchers have recently published a paper in the journal Advanced Materials about a very promising breakthrough in solar technology. How is it different from existing solar technologies such as silicon-based solar cells, or CIGS thin film? The main thing is that it's made from earth abundant materials that can be found in large quantities relatively inexpensively (not quite dirt cheap, but cheaper than what we have now), making it easier to scale up and drive prices down.

Magnified view of a cross section of the compound Cu2ZnSn(S,Se)4 Image: IBM
The layer that absorbs sunlight to convert it into electricity is made with Copper (Cu), Tin (Sn), Zinc (Zn), Sulfur (S) and/or Selenium (Se). This is pretty abundant compared to the Copper (Cu), Indium (In), Gallium (Ga), and Selenium (Se) that GIGS thin film cells use.
The beauty is that it has a "conversion efficiency of 9.6 percent, which is 40 percent higher than previous attempts to create a solar cell made of similar materials." But this is just a start. More improvements to power conversion should be possible.
IBM says that it "does not plan to manufacture solar technologies, but is open to partnering with solar cell manufacturers to demonstrate the technology." Let's hope that this can be moved out of the lab quickly.
Now how about working on cheaper and efficient ways to store large quantities of energy? That's the missing half of the puzzle that would make solar power more practical on the very large scale.

IBM Releases Cheaper,

40% More Efficient Thin-Film Solar Cell

IBM has announced the development of a thin film solar cell with an efficiency of 9.6% – a whopping 40% increase from its previous prototypes. An efficiency of 9.6% isn’t terribly impressive compared to the 18% previously achieved by NREL in the laboratory, but IBM’s thin film is a completely different type. What makes IBM’s thin film unique is that it is made up of cheaper and more common materials – not the expensive stuff traditionally used in making solar cells.  IBM’s progress, which they claim as a record for this more affordable cell, could significantly bring down the cost of thin film solar power.

New Solar Cell is 98% Plastic and Catches a Record-Breaking 96% of Incident Light

by Michael Graham Richard, Ottawa, Canada 

Photo: Caltech
The Return of the Hairy Solar Panel
The big brains at the California Institute of Technology (every time I hear about Caltech I think of Richard Feynman...) have figured out a way to create solar panels that have at least three very desirable characteristics: 1) They are very good at absorbing light, 2) they are mostly made of cheap plastic and only use a very small amount of expensive semiconductors, and 3) they are flexible. How do they do that?

Photo: Caltech
At the microscopic scale, the surface of the solar cells resemble the "hairy" nanowire-based solar panels that we've covered in the past, except that instead of making the wires with exotic materials like "indium gallium phosphide", they make them mostly out of plastic with a bit of silicon (2% silicon, 98% is polymer).
This structure is very good at absorbing light (it has a huge surface area to catch photons):

"These solar cells have, for the first time, surpassed the conventional light-trapping limit for absorbing materials," says Harry Atwater, Howard Hughes Professor, professor of applied physics and materials science [...] The light-trapping limit of a material refers to how much sunlight it is able to absorb. The silicon-wire arrays absorb up to 96 percent of incident sunlight at a single wavelength and 85 percent of total collectible sunlight. "We've surpassed previous optical microstructures developed to trap light," he says.

Part of the reason why so much light is absorbed is shown on the image above. Each of the silicon wires (30 and 100 microns in length and only 1 micron in diameter) is a good solar cell on its own, and the light that isn't absorbed is scattered and then hits other wires.
The flexibility of the panels is also important because it means that they can be manufactured using roll-to-roll processes, reducing production costs compared to non-flexible panels.
Next Step: Scaling Up
So far only a few square centimeters of cells have been made, but the Caltech team is already working on making new demonstration panels that are as big as regular solar panels and that have higher operating voltage.
Maybe one day I'll have a hairy solar panel on my rooftop...

Cheap Carbon-Based Solar Cells Could Replace Silicon Cells

Forget silicon — the next major light-absorbing material in solar cells could be carbon. Chemists at Indiana University Bloomington have figured out how to effectively create big sheets of carbon that collect light — a discovery that could lead to cheap, non-toxic solar cells.

Carbon used in the chemists’ solar cells appears in the form of graphene (similar to graphite found in pencil lead), which can absorb a wide range of light frequencies. In the past, scientists have found large sheets of graphene to be too unwieldy to work with. That’s because larger sheets become sticky and often attach to other sheets. But the IU researchers figured out how to make ultra-stable non-sticky graphene sheets by “attaching a semi-rigid, semi-flexible, three-dimensional sidegroup to the sides of the graphene.”
Now that the IU chemists have managed to collect energy using carbon, they have to figure out how to turn it into electricity. Eventually, the discovery could lead to carbon becoming an important light-absorbing material for the solar industry — potentially as an alternative to expensive silicon and ruthenium, which is as rare as platinum.

Canadian Researchers Move Closer to Affordable, Efficient Solar Power

by Cameron Scott, 04/22/10

Enough solar energy hits the Earth in an hour to meet global power demand for an entire year: the trick is catching it, and doing it with equipment cheap enough to allow it to compete with fossil fuels. Researchers at the University of Quebec in Montreal have made progress on both those fronts by improving on the promising technology of dye-sensitized solar cells. This type of solar cell is easier to manufacture and has a lower cost per watt of energy than the photovoltaic array you might see on your neighbor’s roof. It’s also – at least theoretically – more versatile.

The trouble is that dye-sensitized cells rely on cathodes that are covered in platinum — which, as your credit card company will tell you, ain’t cheap. Others have tried and failed to find a functional substitute for platinum, but the Canadian researchers, led by Benoît Marsan, have found that cobalt sulfide is not only cheaper but also more efficient at converting sunlight into electricity. Marsan’s team also looked to improve the dye – another major focus of solar R&D. They were able to substitute a transparent gel which, they say, is more efficient and longer-lasting.

In the big picture, all of these improvements move toward a single goal: making it affordable for average Joes and Janes to install and use solar arrays.

Flexible & Lightweight Solar Fabric by FTL Solar

by Bridgette Meinhold, 04/30/10

FTL Solar has created a lightweight tensile fabric with integrated thin film solar panels that is capable of shading your deck while powering your home. Originally designed as easily deployable canopies for military applications, FTL’s solar products are now available now for solar parking lot shades, rooftop building installations, and small and large solar tent structures. The solar fabric could even act as a shading for your sunny deck, and since it’s a fabric it’s easy to install without any heavy duty mounting hardware

FTL has two main solar products – the Powermod 285 and the Powermod 1200, which are rated at 285 W and 1200 W, respectively. Each version of the solar fabric can be utilized in a number of situations — as a sun shade in your backyard, on top of a pop-up festival tent, or they can even be strung together for an even larger shade for parking lots and other large spaces. The fabric can basically be installed in the same ways you would utilize a tarp. The Powermod 285 can easily produce enough power to run phones, computers, fans, power tools, lights, signs, projectors, gadgets, appliances, and back-lit signage, and the Powermod 1200 can generate about 4.5 kWh a day.
The benefits of this type of solar installation are numerous. They are lightweight, flexible, easily deployed, portable, movable, can be hooked up to battery storage, they don’t require heavy or complicated mountings, and you certainly don’t need a permit to install one. Now if only they could develop a “plug and play” installation so individuals could do it themselves, these could easily be on the shelves of Walmart or Ikea and selling like hotcakes.