MIT: “A fundamentally new kind of photovoltaic cell”

Photovoltaic solar is already competitive with traditional sources of power, especially during times of peak usage.

We’re just getting started.

MIT:

About 40 percent of the solar energy reaching Earth’s surface lies in the near-infrared region of the spectrum — energy that conventional silicon-based solar cells are unable to harness. But a new kind of all-carbon solar cell developed by MIT researchers could tap into that unused energy, opening up the possibility of combination solar cells — incorporating both traditional silicon-based cells and the new all-carbon cells — that could make use of almost the entire range of sunlight’s energy.

“It’s a fundamentally new kind of photovoltaic cell,” says Michael Strano, the Charles and Hilda Roddey Professor of Chemical Engineering at MIT and senior author of a paper describing the new device that was published this week in the journal Advanced Materials.

The new cell is made of two exotic forms of carbon: carbon nanotubes and C60, otherwise known as buckyballs. “This is the first all-carbon photovoltaic cell,” Strano says — a feat made possible by new developments in the large-scale production of purified carbon nanotubes. “It has only been within the last few years or so that it has been possible to hand someone a vial of just one type of carbon nanotube,” he says. In order for the new solar cells to work, the nanotubes have to be very pure, and of a uniform type: single-walled, and all of just one of nanotubes’ two possible symmetrical configurations.

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But Strano points out that since the near-infrared part of the solar spectrum is currently entirely unused by typical solar cells, even a low-efficiency cell that works in that region could be worthwhile as long as its cost is low. “If you could harness even a portion of the near-infrared spectrum, it adds value,” he says.

Strano adds that one of the paper’s anonymous peer reviewers commented that the achievement of an infrared-absorbing carbon-based photovoltaic cell without polymer layers is the realization of “a dream for the field.”

Michael Arnold, an assistant professor of materials science and engineering at the University of Wisconsin at Madison who was not involved in this research, says, “Carbon nanotubes offer tantalizing possibilities for increasing the efficiency of solar cells and are kind of like photovoltaic polymers on steroids.” This work, he says, “is exciting because it demonstrates photovoltaic power conversion using an active layer that is entirely made from carbon.” He adds, “This seems like a very promising direction that will eventually allow for nanotubes’ promise to be more fully harnessed.”