Sweating the small stuff Home

Solar-Cell Rollout

By Peter Fairley

Breakthroughs in nanotech are making it possible to churn out cheap, flexible solar cells by the meter. Soon your cell phone may be powered by the sun.

On the test benches of Konarka Technologies in Lowell, MA, a new kind of solar cell is being put through its paces. Strips of flexible plastic all but indistinguishable from photographic film bask under high-intensity lights. These strips, about 10 centimeters long and five centimeters wide, are converting the light into electricity. Wire a few of them together, and they generate enough power to run a small fan.

Solar cells, of course, are nothing new. But until now, solar power has required expensive silicon-based panels that have relegated it, largely, to niche applications like satellites and high-end homes. What's remarkable about Konarka's power-producing films is that they are cheap and easy to make, using a production line of coating machines and rollers. The process is more akin to the quick-and-dirty workings of a modern printing press than to the arcane rituals performed in the clean rooms of silicon solar-panel manufacturing. The company literally has rolls of the stuff; its engineers plan to cut off usable sheets as if it were saran wrap.

Konarka's technology is just one example of a new type of printable solar cell, or photovoltaic, that promises to go almost anywhere, paving the way for affordable and ubiquitous solar power. Not only are the cells inexpensive to produce--less than half the cost of conventional panels, for the same amount of power--but they're also lightweight and flexible, so they can be built into all sorts of surfaces. Flexible films laminated onto laptops and cell phones could provide a steady trickle of electricity, reducing the need to plug in for power. Solar cells mixed into automotive paint could allow the sun to charge the batteries of hybrid cars, reducing their need for fuel. Eventually, such solar cells could even cover buildings, providing power for the electricity grid.

A growing number of startups, like Konarka, and big corporations, such as General Electric, Siemens, and chip maker STMicroelectronics, are vying to realize this vision (see "Printable-Solar Revolution," sidebar). Konarka hopes to start selling its solar films next year for use in consumer electronics and defense applications. And this winter, Siemens announced that it had boosted the power output of its own prototype plastic-based solar cell to new heights--an achievement that could finally make the technology viable for widespread use.

What's making all this possible is recent breakthroughs in materials science, including advances in nanomaterials. Some of the most promising solar devices are made from conducting plastics and nano-based particles, far too small for the eye to see, that are mixed in a solution. This solution can then be printed, in a process similar to ink-jet printing, onto a surface; there the nanomaterials assemble themselves into structures within the plastic, forming the basis of a solar cell. And all this is done with little human intervention. "The fabulous notion here is that we may be able to put this active agent in some spreadable medium and basically print these things," says Rice University chemist Richard Smalley, who shared the 1996 Nobel Prize in chemistry for the discovery of soccer-ball-shaped carbon molecules known as buckyballs, a key ingredient in many nano solar cells.

Making these cells efficient enough to compete with coal, wind, and nuclear power remains an ambitious goal, but it's one that experts say is attainable. Though mainstream applications are early-stage, "the way has been opened," says Serdar Sariciftci, a materials physicist at Johannes Kepler University in Linz, Austria, and a Konarka advisor. "The avalanche has started."

Printable-Solar Revolution

General Electric, Schenectady, NY
Adapting methods developed for printable lighting panels to make solar cells; pushing for 10 percent energy efficiency in a practical cell

Konarka Technologies, Lowell, MA
Manufacturing solar cells made of semiconductor particles; plans to market 5 percent efficient cells by 2005

Nanosolar, Palo Alto, CA
Testing titanium compounds and conductive plastic that can be sprayed on surfaces to form solar cells; seeking 10 percent efficiency by late 2005

Nanosys, Palo Alto, CA
Developing self-orienting nanoparticles in conductive plastic for photovoltaic coatings; plans to incorporate them into commercial roofing tiles in a few years

Siemens, Erlangen, Germany
Researching buckyballs and conductive plastic for solar cells and photodetectors; seeks practical flexible cells by 2005

STMicroelectronics, Geneva, Switzerland
Blending buckyballs with carbon-based molecules containing copper atoms to make solar cells; conducting research into efficiency and feasibility