Could a house or car be turned into a giant battery by coating either of them with a paint that converts light to energy?
Before you scoff at this notion as something out of “The Matrix,” consider that a few years ago, a consortium led by Swansea University in the United Kingdom and funded by the steel maker Corus Group experimented with a photovoltaic paint, made from layers of dye and electrolytes, that could be applied to steel sheets.
More recently, a research team at Notre Dame University, funded by the U.S. Department of Energy, came up with Sun-Believable, a kind of solar paint that, when applied to a transparent conducting material such as plastic or glass, creates electricity.
Don't expect to be shopping for this paint at The Home Depot tomorrow. Many issues need to be resolved before anything commercially viable emerges, says Ian Lightcap, a fifth-year Ph.D. student and one of three authors of a paper that the team published last December detailing its findings in the journal ACS Nano.
Working out of Notre Dame’s Center for Nano Science and Technology, the team, led by professor Prashant V. Kamat, has been searching for less-expensive alternatives to silicon-based solar cells. One team member, Matthew Genovese, coated nanoparticles of titanium dioxide with nanocrystals of cadmium sulfide or cadmium selenide. These compounds absorb photons, and when mixed with a water-alcohol base transform into a semiconductive yellow- or brown-colored paste. The team applied this paste to a conductive glass surface electrode, connected it to a counter-conductive electrode, exposed it to sunlight, and successfully generated a small current of energy.
How much of a breakthrough this experiment turns out to be will depend on several factors. The paper reveals that the team only achieved a light-to-energy conversion efficiency of 1 percent, compared to the 10 percent to 15 percent efficiency of silicon solar cells. (The researchers think they might be onto something if they can raise the efficiency of these “quantum dots,” as these tiny solar cells are called, to 4 percent or 5 percent.)
Second, cadmium is extremely toxic. But Lightcap notes that existing solar-panel technologies also use cadmium. “It’s all about reclamation and recycling” to minimize the risk, he explains. That said, his team is looking to replace cadmium with another substance.
The researchers are now trying different semiconductors to reduce energy losses. Lightcap thinks that a hole conductor—where electrical current travels via the flow of positively charged “holes” in the material’s electron structure—might work better.