Graphene boosts efficiency of next-gen solar cells

Graphene, a two-dimensional honeycomb of carbon atoms, is a rising star in the materials community for its radical properties. One of those properties is electrical conductivity, which could make it a key ingredient in the next generation of photovoltaic cells, says Yun Hang Hu, a professor of materials science and engineering.

Dye-sensitized solar cells don't rely on rare or expensive materials, so they could be more cost-effective than cells based on silicon and thin-film technologies. But they are not as good at converting light into electricity.

In dye-sensitized solar cells, photons knock electrons from the dye into a thin layer of titanium dioxide, which relays them to the anode. Hu's group found that adding graphene to the titanium dioxide increased its conductivity, bringing 52.4 percent more current into the circuit.

"The excellent electrical conductivity of graphene sheets allows them to act as bridges, accelerating electron transfer from the titanium dioxide to the photoelectrode," Hu said.

The team also developed a comparably foolproof method for creating sheets of titanium dioxide embedded with graphene. It first made graphite oxide powder, then mixed it with titanium dioxide to form a paste, spread it on a substrate (such as glass) and then baked it a high temperatures.

"It's low-cost and very easy to prepare," said Hu. But not just any recipe will do. "If you use too much graphene, it will absorb the light in the solar cell and reduce its efficiency," he said.

Hu presented a talk on their work, "Graphene for Solar Cells," at the US-Egypt Joint Workshop on Solar Energy Systems, held March 12-14 in Cairo. It was funded by the American Chemical Society Petroleum Research Fund and the National Science Foundation.