solar cells made entirely of carbon--Printed Solar Panels, Lithium-Ion Power

Low-cost solar cell for everyday use

Typical solar cells use expensive rare earth minerals. Researchers at Stanford University have come up with an alternative method of creating solar cells made entirely of carbon

Mirror Bureau

Posted On Saturday, November 03, 2012 at 08:39:51 AM

Stanford University scientists have built the first solar cell made entirely of carbon, a promising alternative to the expensive materials used in photovoltaic devices today. The results are published in the journal ACS Nano. “Carbon has the potential to deliver high performance at a low cost,” said study senior author Zhenan Bao. “To the best of our knowledge, this is the first demonstration of a working solar cell that has all of the components made of carbon.” Unlike rigid silicon solar panels that adorn many rooftops, Stanford’s thin film prototype is made of carbon materials that can be coated from solution. “Perhaps in the future we can look at alternative markets where flexible carbon solar cells are coated on the surface of buildings, on windows or on cars to generate electricity,” Bao said. The coating technique also has the potential to reduce manufacturing costs, said student Michael Vosgueritchian, co-lead author of the study with Marc Ramuz. “Processing silicon-based solar cells requires a lot of steps,” Vosgueritchian explained. “But our entire device can be built using simple coating methods that don’t require expensive tools and machines.” Carbon nanomaterials The Bao group’s experimental solar cell consists of a photoactive layer, which absorbs sunlight, sandwiched between two electrodes. In a typical thin film solar cell, the electrodes are made of conductive metals and indium tin oxide (ITO). “Materials like indium are scarce and becoming more expensive as the demand for solar cells, touchscreen panels and other electronic devices grows,” Bao said. “Carbon, on the other hand, is low cost and Earth-abundant.” For the study, Bao and her colleagues replaced the silver and ITO used in conventional electrodes with graphene – sheets of carbon that are one atom thick and single-walled carbon nanotubes that are 10,000 times narrower than a human hair. “Carbon nanotubes have extraordinary electrical conductivity and light-absorption properties,” Bao said. For the active layer, the scientists used material made of carbon nanotubes and “buckyballs” – soccer ball-shaped carbon molecules just one nanometer in diameter. The research team recently filed a patent for the entire device. “Every component in our solar cell, from top to bottom, is made of carbon materials,” Vosgueritchian said. “Other groups have reported making all-carbon solar cells, but they were referring to just the active layer in the middle, not the electrodes.” One drawback of the all-carbon prototype is that it primarily absorbs near-infrared wavelengths of light, contributing to a laboratory efficiency of less than 1 per cent – much lower than commercially available solar cells. “We clearly have a long way to go on efficiency,” Bao said. “But with better materials and better processing techniques, we expect that the efficiency will go up quite dramatically.”  [[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[ A century ago, The University of Texas was built on energy. Some sources may have changed, but as these brilliant innovations prove, UT is still charging ahead. 1. Spray solar panels on. The sun pours enough energy onto the Earth in an hour to supply all our energy needs in a year, if we could harvest it. Silicon-based solar cells are still pricey, largely because manufacturing them eats up a lot of energy. For energy users on a budget—and that would be most of us—the numbers still favor fossil fuels. But what will future solar panels, or photovoltaics, be like? Think ink on a plastic sheet. Brian Korgel, professor of chemical engineering and a nanotechnology expert, is among a group of scientists who are reimagining photovoltaics. Steering away from silicon in favor of copper, indium, gallium, and selenium (a combo he calls CIGS), Korgel is using extremely small crystals of these elements to form a liquid that can collect solar energy. This “nanocrystal ink” can be used to make photovoltaics at far lower temperatures than silicon requires, and low temperatures in turn allow for more delicate and multilayered devices. Much like traditional ink, it can be printed or even sprayed onto flexible surfaces. “We’re trying to create a process like a printing press for making solar cells,” Korgel says. “One thing that I think could be possible would be to have a solar panel that’s almost like a carpet you unfurl on the top of your roof.” There are many alternatives to silicon, and lightweight CIGS-based photovoltaics aren’t new. But Korgel hopes that painting with nanocrystals will allow solar cells to be mass-produced quickly and cheaply while remaining efficient enough to compete with other energy sources. How efficient do newfangled photovoltaics need to be? To succeed on the market, the magic number is 10 percent. A few years ago, Korgel’s group proved that CIGS inks could work at 1 percent efficiency; they have since pushed that to 3 percent with low-heat and 7 percent for high-heat manufacturing methods. (By comparison, silicon solar panels are about 15-20 percent efficient.) “There’s no reason to believe you couldn’t get to 10 percent,” Korgel says. “It’s just a challenge of figuring out how to do it.” While Korgel says his group is one of many around the world working on more cost-effective solar cells, he’s optimistic that somebody will invent photovoltaics that hit “grid parity,” meeting or beating the cost of grid power, in the next decade. “The pace and progress in the area of photovoltaics has been really, really impressive in the last four or five years,” he says. “It’s the kind of problem that if you solved it would really change the world.” —Jenny Blair 2. Develop the next generation of lithium-ion batteries. UT scientists have repeatedly pushed boundaries when it comes to batteries. In the 1970s, Cockrell School professor John Goodenough pioneered lithium-ion technology to power the vast array of small electronics we rely on today. Now his colleague Arumugam Manthiram, director of UT’s Texas Materials Institute and the Materials Science and Engineering Program, has taken Goodenough’s discoveries to the next level. Manthiram is innovating how to use lithium-ion technology to power cars and store electricity produced by renewable sources. Cost, cycle life, safety, energy, and power are major barriers. Manthiram is developing safe, nano-engineered alloy anodes to replace the unsafe graphite anodes now used, in addition to new high-energy cathode materials. To bring these ideas to market, Manthiram partnered with Cleantech entrepreneur Bill Ott. They co-founded ActaCell, a company that got early support from the Austin Technology Incubator’s Clean Energy division and seed funding from the Texas Emerging Technology Fund. ActaCell is now developing high-power lithium-ion batteries based on the technology developed in Manthiram’s lab. —Maria Arrellaga Read the next great ideas on energy here. Top, Illustration by Dan Page. Bottom, John Goodenough. Photo by Marc Brown.