Solar Cells 2.0: in clothing, camping gear -- everywhere?

Imagine being able to charge your laptop on a two-week trek, far away from electrical outlets. That will be possible by the end of the year using organic technology, claims the plastic solar cell company Konarka. What would that mean for people in the underdeveloped world, who live far away from electricity grids?

Konarka is right now building a plant for mass production of printable electronics. The company's technology is flexible plastic photovoltaics, which converts the sunlight into electricity that can be used directly to power electrical gadgets.

It will be possible to weave these fibers into clothes – to keep you warm in the winter – or to cover electronics with them.

This new generation of organic solar cells emerged from the discovery of conductive polymers. In 2000, Professor Alan Heeger at University of California, Santa Barbara, won the Nobel prize in chemistry for this breakthrough.

Conductive polymers, or plastics that conduct electricity, can be liquified into inks and printed onto materials like plastic film. They are manufactured using nano techniques.

After his discovery, Mr. Heeger set out to commercialize the organic photovoltaics and co-founded Konarka.

Konarka is one of many companies who are working intensely on finding the right molecular structure for plastic solar cells, making them cheaper, more effective and mass producible. Konarka says it will be first to market its findings, but critics are saying that the company has raised tens of millions in venture capital and is lagging behind its time table -- and still has no products.


Plastic solar cells have been called the next generation solar technology and have many potential advantages over classical solar cells, made out of silicon wafers, as well as the thin film-approaches.

Silicon cells expensive

"The traditional solar cells are made out of big silicon crystals," says Paul Alivisatos, a pioneer in nano solar technology. "They need to be perfect and huge. You can compare them to a diamond. If you want to coat the desert with diamonds, then that is going to be hard to do."

Hard and costly. Prices for silicon have risen sharply in recent years, partly because manufacturers of the material did not anticipate the spike in demand for silicon solar cells.
“So we thought, instead of coating diamonds so big, what is the absolute smallest size we can make?” asks Mr. Alivisatos, who is a professor at the University of California at Berkeley.

He and his Berkeley research team are working on nanocrystals, both in thin film and in plastic solar cells.

Thin film cheaper but less effective

Thin film -- the other competing solar technology for home users -- mostly uses layers of copper, indium, gallium, and selenium CIGS, as a semiconductor. Thin film is not as effective at converting light into electricity as silicon solar cells, but it is cheaper. Thin film is more susceptible to moisture than silicon though, and therefore wears out more easily. On the other hand, silicon is fragile. Hail is the main reason silicon solar panels break in the field.

What Konarka is attempting to do in organic photovoltaics, companies like Global Solar and Nanosolar have already achieved with thin film technology -- the flexible solar cells. You can order Global Solar’s flexible, portable chargers for $14-15 per watt online. It comes with a plug the same as a car cigarette lighter. To charge a cell phone, you need a cable appropriate for your phone brand (i.e. Nokia) which can be plugged into a cigarette lighter.

Charging laptops is not yet possible. The portable charger lacks enough power.

Although Global solar still has a long way to go in some of its technologies, its vice president of sales and marketing, Tim Teich, is optimistic. “Thin film won’t take over the silicon industry, but we will burst the market with news in architectural- and building integrated products,” he says.

Thin film technology has the edge in maturity over plastic solar cells. But the technology is grappling with the problem of durability, just like plastic photovoltaics. A lot of the thin film companies are spreading the CIGS on glass, which is dense enough to solve the durability problem, but at the same time is the most expensive part of the solar cell.

Another problem is the rising cost of the material Indium, one part of the CIGS formula. “Some people say Indium will run out in 7 years, other say they will discover more with mining,” says Nathan Lewis, a professor of Chemistry at California Institute of Technology.

Whether the mineral is scarce or not is debatable, but researchers are trying to find substitutes for it anyway.


Efficiency solved problem

Ability to harvest the energy of the sun is the most important factor in photovoltaics. But it is not always the most relevant parameter for judging the competitiveness of the different solar technologies. “In some sense the ability of making an efficient solar cell is a solved problem," says Mr. Alivisatos. "Today we have reached even 42 percent efficiency.”

“The big problem is to make a lot" of very efficient solar cells, he continues. "This is very, very hard to do. Nobody knows how to make huge amounts of solar cells."

Instead of efficiency, solar-cell technologies are often measured in dollar per watt, or the cost of the effect they can deliver. The benchmark is one dollar per watt, which is the price for conventional energy sources like coal. Crystal silicon panels of good quality cost 3.50-4.50 dollar per watt. Thin film on the lower end has a price of 2.60-3.30 dollar per watt, according to the thin film company Global Solar.

“Cost per watt is not what matters in the end, because people are buying electricity, not capacity,” says Mr. Lewis.

In order to calculate the cost of the electricity - or energy – that the different photovoltaics deliver, two important aspects should be taken into account: their lifetime and the cost of installation. The installation costs, including hooking up the cells on the roof and attaching them to the grid, actually amounts to half of the cost for the solar cells, in traditional silicon wafers. Traditional wafers last for 30 years, but thin film and plastic solar are still far behind. In order to compensate for that, they have to be cheap to manufacture.

Finding new material

One of the research groups trying to lower the manufacturing cost of plastic solar cells is led by Michael McGehees, a professor at Stanford University's Materials Science and Engineering Department.

On a recent visit to Mr. McGehees' group, there is a buzzing sound from in the Gabelle laboratory for advanced materials, where the group conducts its experiments.

“Here are the glove boxes,” says Alex Mayer, a post-doctorate researcher who is giving a tour of the lab to a visitor.

These are six-feet tall metallic vacuum boxes, into which scientists are sticking their arms into big latex gloves in order to carry the tests. The researchers are trying to find the most effective materials for the active layer of the plastic solar cell. And they are trying to replace Indium Tinoxe, which is the most common transparent conductor that the plastic cells are being coated with.

“You see, different materials absorb different portions of the light," says Mr. Mayer. "We are stacking them onto one another in order to get the best possible effect."


The plastic solar cells that the research group is working on have huge potential, but also face big challenges. One of the toughest problems is the low efficiency, right now at 5.4 percent.

Mr. Heeger, the Santa Barbara professor, succeeded in constructing a more efficient organic cell, a so-called tandem cell. He put two light absorbing layers on top of one another, shaping the cell like a double hamburger. The construction raised the efficiency of light harvesting to 6.5 percent.

Printed electronics the future

But if some of the plastic solar cell problems could be solved, they have the potential to change the world. “Printed electronics is going to be the next wave of electronic products,” says Dan Williams, vice president of product development at Konarka. “People will use printed electronics for displays, battery technology and photovoltaic materials. It is a revolution, I think the whole area of printed electronics is going to explode within four-five years."

The flexibility, light weight and low production cost of organic photovoltaics could make them useful for a wide range of products, which are currently powered by batteries. “Just think about it," Mr. Williams says. "Today the battery is the biggest part in every product, it takes up thirty to fourty percent of the space."

“If we only had a mili part of the power, the gadgets would look differently” he continues.

Mr. Williams hopes that technology development will go hand in hand with the plastic solar cell evolution and that future products will be able to run on much less energy. They would be able to operate through sun power, like some calculators are doing today, or like newer products like for instance One laptop per child-computers.

Konarka’s R&D is today focusing on increasing the durability of the cell, which is now merely five years. The company is trying to discover new encapsulation layers that will better keep moisture out of the cell.