Technology▼Solutions Nano-PV set to accelerate solar-energy use achieved 10% efficiency, a new record, when they used nanomaterials that combine buckyballs with electrically conducting polymers. And just this past May, researchers at the Los Alamos National Laboratory identified a way to use lead selenium nanocrystals to potentially double the energy output of a solar cell. NANOSOLAR
What innovators are calling the “next generation of photovoltaic technologies” is expected to be commercially available within the next few years, sending the traditionally high costs of solar energy spiraling down. Nanotechnology is the key to the new solarcell architecture, which promises to transform everyday polymers into flexible energy producers. The first photovoltaic (PV) devices were constructed of crystalline silicon, and the second generation relied on amorphous silicon thin-film coatings. The nano-PV technologies of the third generation rely upon coating or mixing “printable” and flexible polymer substrates with electrically conductive nanomaterials. An array of nanoscale semiconductors is now under investigation. Some predict that these cells will be produced in simple laboratory vats instead of the high-maintenance clean rooms or vacuum chambers used for current solar PV fabrication. Add rapid roll-to-roll printing and low-temperature processing capabilities that replace the energy-intensive batch manufacturing requirements of current PV devices, and the high cost of solar energy starts to come down to earth. Today’s average price of crystalline silicon PV rooftop solar modules, at $5–10 per watt for installed modules, is 4–8 times the cost of grid-fed electricity, depending on a host of local factors. “Ours will be an entire order of magnitude cheaper than current PV,” insists Martin Roscheisen, CEO of Nanosolar, a start-up company based in Palo Alto, Ca. But cost is immaterial if performance lags behind current standards. Researchers must continue to inch conversion efficiency rates upward to reach the standard 12–18% efficiency rate at which today’s conventional solar arrays convert sunlight into electricity. Earlier this year, scientists at Siemens announced that they had
New approaches to solar cells infused with nanotechnology promise to turn printed foils into flexible energy producers.
General Electric and Hitachi have also boosted efficiency rates in the laboratory using a variety of nanosized particles and flexible substrates. Yet the strongest commercialization push is coming from three well-funded start-ups: Konarka, Nanosolar, and Nanosys—all recent recipients of multimillion-dollar grants from the U.S. Defense Advanced Research Projects Agency (DARPA). Konarka, which recently purchased part of Siemens, was cofounded by Alan Heeger, a Nobel laureate in chemistry and professor of materials at the University of California, Santa Barbara. Heeger developed some of the original conducting polymers, and the company is developing a hybrid solar cell that combines nanocrystalline titanium dioxide with conducting polymers. Konarka cofounder and CEO Howard Burke reports that the company is
376A ■ ENVIRONMENTAL SCIENCE & TECHNOLOGY / OCTOBER 1, 2004
testing various product applications for consumer electronics and military devices at its pilot manufacturing facility in Lowell, Mass. However, he remains mum about specifics and whether the tests have reached the company’s stated efficiency goal of 10%. Nanosolar and Nanosys are both concentrating solely on building materials that will produce electricity. Nanosys has licensed its technology to Matsushita Electric Works, which hopes to begin selling solar rooftop tiles to the Asian construction market by 2007. Nanosolar is the only one of the three start-ups that has a target launch date and timeline for a specific product. SolarPly are 10 14-foot thin-film solar-cell modules that use a proprietary substrate coated with quantumdot-based semiconductor paint with an output of 110 volts at a conversionefficiency rate “pushing towards conventional PV,” reports Roscheisen, who declined to be more specific. Roscheisen anticipates commercial availability in 2006 at a fivefold decrease in the current cost of PV. By bringing the cost down to less than $2 per watt of electricity, Nanosolar expects that its products will be able to compete with the cost of grid-fed electricity, especially during peak loads in sunny climates where electricity rates soar from airconditioner use. Despite some promising advances, Roscheisen concedes that the biggest hurdle could be proving SolarPly’s durability and longevity to buyers who are used to 25-year guarantees on conventional rooftop PV solar cells. “We’re putting the panels through accelerated lifetime field testing, and most of the longevity data will be available next year,” says Roscheisen. In the meantime, the solar industry is growing at a breakneck pace. “Solar generation capacity has grown by an average of more than 30% annually over the past 5 years,” says Joel Makower, cofounder and principal of Clean Edge, a clean-energy research and consulting firm based in Oakland, Ca. —JEANNE TROMBLY © 2004 American Chemical Society
