In an approach that could challenge silicon as the predominant photovoltaic cell material, UW-Madison materials engineers have developed an inexpensive solar cell that exploits carbon nanotubes to absorb and convert energy from the sun. The advance could lead to solar panels just as efficient, but much less expensive to manufacture, than current panels.
The proof-of-concept carbon nanotube solar cell can convert nearly 75 percent of the light it absorbs into electricity, says Materials Science and Engineering Assistant Professor Michael Arnold (right). “We’ve made a really fundamental key step in demonstrating that it will be possible to use these new carbon nanotube materials for solar cells one day,” he says.
Silicon is abundant and an efficient solar energy gatherer, yet is expensive to process and manufacture into solar panels. As a result, researchers are studying alternative materials—among them, carbon nanotubes. The thin spaghetti-like tubes are easy and inexpensive to manufacture, stable and durable, and are both good light absorbers and electrical conductors.
Building on a half-decade of research—including foundational studies by PhD student Dominick Bindl—Arnold and PhD student Matthew Shea developed a solar cell that uses carbon nanotubes to collect light and convert it to electricity. Their proof-of-concept solar cell is an ultrathin sheet, or film, of carbon nanotubes layered atop another thin sheet of a material called buckminsterfullerene, or C60. The nanotubes absorb the bulk of the sunlight and retain the positive charge, while the C60 draws the negative charge.
In contrast with the 15-percent average efficiency of conventional silicon solar cells, the proof of concept is 1 percent efficient. The next step in boosting that efficiency already is underway. The researchers now are focusing on augmenting the thickness of the carbon nanotube thin film from a mere 5 nanometers to at least 100—which, according to their theoretical models, ultimately could put the power-conversion efficiency of their solar cells in line with that of silicon cells. “What our work shows is that you will be able to get as high efficiency as silicon eventually, and that’s why we’re excited,” says Arnold, who received funding for the research from the Army Research Office.