The Shade Is Hot

Dye-sensitized solar cells (DSCs), which generate electricity from light by mimicking photosynthesis, aren’t about to replace cheap silicon photovoltaic panels on rooftops. In ambient indoor light, however, they promise to generate enough electricity at a low enough cost to displace not only silicon solar cells but also batteries. “Imagine a world in which you don’t need disposable batteries,” says Stephen Burt, chief financial officer of G24 Innovations, a Cardiff, Wales-based start-up that is among the leading manufacturers of DSCs.

Walk through G24i’s showroom, with its furnished lounge, study, and mock supermarket, and you start to sense the potential for DSCs. The coffee table houses a DSC panel that trickle-charges a cell phone from an integrated USB port. Smaller DSC strips power a wireless keyboard, TV remote control, smoke alarm, electronic pricing label, and more.

Far from being a niche market, “energy harvesting” devices enabled by DSCs and other technologies will be worth more than $9 billion in 2015, up from roughly $2 billion in 2011, according to a recent report by Pike Research, a U.S. market research firm. Of that $9 billion, about 40% is expected to be related to energy derived from ambient light; the other 60% would come from energy harvested from vibration and heat sources.

G24i’s DSC film is less than 1 mm thick. Unlike crystalline silicon, the film is flexible and can be dyed to a color specified by the customer, says Silvia Villarroya Lidon, the firm’s manager of development chemistry. Also unlike silicon, it is effective in the diffuse lighting conditions found indoors. Although the film is largely targeted at indoor uses, there is “nothing in the technology to stop its use outdoors” in applications such as backpacks, where the ability to shape DSCs can be an advantage, Burt adds.

G24i has a license to produce DSCs using a thin-film technology invented in 1988 by Michael Grätzel, a professor at Switzerland’s École Polytechnique Fédérale de Lausanne (EPFL) and a scientific adviser to G24i.

The cells are composed of two electrodes and an iodide-containing electrolyte. One electrode features dye-absorbed nanocrystalline titanium dioxide (TiO₂) deposited on an electrically conducting substrate. The dye is based on a ruthenium compound. Light that falls onto the solar cell is absorbed by the dye and excites the dye’s electrons. The electrons escape from the dye into the TiO₂ and diffuse to the second electrode to generate an electrical current. The electrons eventually return to the dye via the electrolyte.

The company tries to continually improve its cell technology. In April, it announced a new light conversion efficiency record of 26%, up from its previous record of 15%, thanks to dye and electrolyte modifications. The new cell is almost five times as powerful as an amorphous silicon cell, the company says. DSC technology competitors include Dyesol, Konarka Technologies, and Sony.

As efficiency rises, production costs are dropping, the company claims. “Three years ago we had to buy very expensive dye. Now the cost is 60% lower,” Villarroya Lidon says. A piece of G24i’s DSC material is typically more expensive than a single battery, but a device that incorporates a DSC will cost significantly less to operate over its lifetime than if it ran on batteries, she points out.

Consumer product companies are starting to buy into the concept. G24i has a commercial partnership with the computer peripherals maker Logitech. Earlier this month Logitech introduced a keyboard for Apple’s latest iPad with batteries powered by G24i cells. G24i also is selling its product to California-based Skyco Shading Systems, which uses DSCs to power motors in its hotel window blinds. G24i is in discussions with 40 other potential customers on a raft of DSC applications, Burt says.

“It has taken several years of ups and downs, but G24i is now playing to its strengths,” says Harry Zervos, technology analyst for IDTechEx, a U.K. research and analysis firm. G24i can’t compete with large-scale, low-cost silicon solar panels on performance, but its technology is suited to certain indoor applications, Zervos says. G24i competitor Dyesol is applying its DSCs to steel roofs, where they also act as an anticorrosion coating, Zervos adds.

Formed in 2004, G24i began the commercial manufacture of DSCs last year and is still ramping up. The production line in Cardiff has capacity to produce 60,000 meters of 150-mm-wide DSC film each week. Current output is at 2,000 meters each week. “Every week it increases a little bit,” Villarroya Lidon says.

The company has burned through $120 million to build the plant and bring the technology to market. In 2008, Morgan Stanley and Luxembourg-based renewable technology investment firm 4RAE each secured a 9% stake in G24i in exchange for investments of $20 million and $21 million, respectively. Founders and directors Robert Hertzberg and Edward Stevenson hold a 45% share of the firm, while Stevenson and his wife, Erin Stevenson, jointly own a further 28%. Friends, family, and smaller investors own 8%; EPFL holds 1%.

Although G24i has largely left the lab and is hitting the market, the 68-year-old Grätzel continues to play a pivotal role as its scientific adviser. “He is still the driving force” when it comes to technology development, Villarroya Lidon says. Grätzel won the 2010 Millennium Technology Grand Prize and the 2012 Albert Einstein World Award of Science, and Villarroya Lidon says that G24i’s emerging commercial presence can only boost his chances of winning further honors.