Though prices of photovoltaic (PV) panels have been dropping like a stone the past few years, they still aren't cheap. Part of the reason for that is that a few of the semiconducting ingredients used in making the newer generation of thin-film solar cells are somewhat rare. The tellurium in cadmium telluride thin-film cells is about as rare as platinum, and the indium and gallium used in copper indium gallium selenide (CIGS) PV cells aren't exactly thick on the ground either. In order for PV panels to become cheap enough to shingle your roof with them, scientists are going to have to find a way to build them out of elements that are far more common.
According to Caltech physicist Harry Atwater, that work is well underway.
Atwater gave a presentation this week at the 244th National Meeting & Exposition of the American Chemical Society (ACS) in Philadelphia in which he unveiled some startling advances in efficiency in solar cells made out of what he calls "earth-abundant" materials. These more abundant materials are cheaper and less likely to become the subject of politically restricted markets, as has happened with the Chinese rare earths industry.
Speaking at the ACS meeting with Dow Chemical physicist James C. Stevens, Atwater described advances in photovoltaic cells relying on zinc phosphide and copper oxide as semiconductors. Both substances have been examined for their PV potential for decades, and both have stymied efforts to use them to generate power due to very low efficiency, converting around 1% of the solar energy that hits them to electricity. But advances in fabrication technology, including nanotechnological techniques, have allowed increases in that efficiency; in theory, copper oxide and zinc phosphide semiconductors ought to be able to reach between 8%-12% efficiency, not much lower than current commercially available cadmium telluride solar cells.
Atwater expects that advances in designing photovoltaic cells with earth-abundant elements will bring the cost of their power down to parity with coal-fired power within 20 years. "Sustainability involves developing technology that can be productive over the long-term, using resources in ways that meet today's needs without jeopardizing the ability of future generations to meet their needs," Atwater said. "That's exactly what we are doing with these new solar-energy conversion devices."
"The United States alone has about 69 billion square feet of appropriate residential rooftops that could be generating electricity from the sun," added Stevens, who worked on Dow's development team for its PowerHouse Solar Shingle, introduced last October . "The sunlight falling on those roofs could generate at least 50 percent of the nation's electricity, and some estimates put that number closer to 100 percent. With earth-abundant technology, that energy could be harvested, at an enormous benefit to consumers and the environment."