For the first time, solar cells that rely on photosensitive dyes rather than silicon to collect energy are beginning to show an energy-conversion efficiency of 10 percent in full sunlight, putting them within shooting distance of the 15 percent efficiency that’s standard for conventional silicon solar cells. (Though the standing record is 11 percent, the materials used in those high-performing dye-sensitized cells were considered too volatile to be practical.) Now researchers in China and Switzerland — and not, Mr. Next President, the U.S. — are reporting the highest efficiency yet using stable materials that could lead to a promising new genre of solar cells. Some scientists believe this avenue of research offers the best hope for making the sun a truly practical source of electricity.

The inexpensive materials and simple manufacturing processes used in the production of these new cells raise the possibility of significantly cheaper solar-collecting materials and devices. Dye-sensitive cells can use virtually any material as their base — glass, plastic, ceramic, or metal. They rely on the interactions between light and a cheap white pigment painted on titanium dioxide. One of their main benefits is that they are able to harness power from low levels of light, when ordinary silicon cells underperform. Also known as Grätzel cells (after their creator, Michael Grätzel), dye-sensitized solar cells could expand the range of conditions under which solar energy is collected inside and outside homes and businesses.

Michael Grätzel is among the authors reporting the new efficiency breakthrough. Though the light-harvesting dyes have shown promise, PV cells made with them have previously been dismissed because of their tendency to degrade from exposure to heat and ultraviolet light (which would seem to be a bare-minimum requirement for a technology meant to harness light from the sun), and because the solvents used in their assembly make them hard to protect. But the new advances suggest that researchers are moving away from the troublesome solvents and finding ways to improve their durability.

It remains to be seen whether Grätzel’s latest breakthrough will determine the path for solvent-free, stable dye-sensitized cells. For one thing, these cells are made with a new type of ruthenium-based dye, an element generally found alongside platinum ores — in other words, exceedingly rare. Low-efficiency cells worked into flexible sheets and coatings can be useful for collecting energy in sub-optimal light conditions if they are inexpensive enough, but it may take some further demonstrations to show that the ruthenium-based cells are as cheap as dye-sensitized cells need to be to compete on a commercial scale.

Story by Sandra Upson. This article originally appeared in Plenty in October 2008.

Copyright Environ Press 2008

New solar cells reach record efficiency
Solar cells that rely on photosensitive dyes to collect energy are beginning to show an energy-conversion efficiency of 10 percent in full sunlight.