{"id":7068,"date":"2013-12-16T12:30:26","date_gmt":"2013-12-16T17:30:26","guid":{"rendered":"https:\/\/college.unc.edu\/?p=7068"},"modified":"2024-07-02T14:28:07","modified_gmt":"2024-07-02T14:28:07","slug":"weiyou","status":"publish","type":"post","link":"https:\/\/collegearchive.unc.edu\/?p=7068","title":{"rendered":"The power of plastic"},"content":{"rendered":"
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\"Wei<\/a>
Wei You (photo by Lars Sahl)<\/figcaption><\/figure><\/p>\n

Say \u201csolar power\u201d and most of us think panels up on the roof. Those solar cells are expensive \u2014 about $15,000 for a home energy system that might take a decade to pay itself off. Rooftop panels, like the ones covering the fields of solar farms, are also big and\u00a0heavy.<\/p>\n

What will it take to bring the price of solar down to something an average U.S. homeowner can afford? And how can we tap into solar\u2019s greatest asset: its free, limitless availability anywhere the sun shines? The answers aren\u2019t far off, says UNC chemist Wei You\u2014in just a few years, we may have powerful, low-cost solar devices that will barely add weight to our\u00a0backpacks.<\/p>\n

In his office \u2014 slightly too warm on a sunny day \u2014 Wei You pulls a solar cell about the size of a CD case out of his desk. It\u2019s a silicon-based cell like the ones that make up rooftop solar panels: a thin square of dark-blue material streaked with metallic gray lines. It\u2019s also fractured into several pieces. Wei You used to take the solar cell on school visits to teach kids about solar power, he says. But silicon solar cells are brittle, and this one didn\u2019t last\u00a0long.<\/p>\n

The number-one problem with this kind of solar cell is that it\u2019s expensive. \u201cThe price has gone down in the past 10 or so years,\u201d Wei You explains. \u201cChinese manufacturers are putting lots of money into making silicon solar cells using government subsidies.\u201d Still, silicon \u2014 purified, then sliced into thin pieces \u2014 will probably never come cheap. On average, the price of powering a home with solar panels is about twice the cost of using the electrical grid, he\u00a0says.<\/p>\n

Wei You pulls out a second cell: this one looks and feels a bit like camera film that\u2019s been laminated. It isn\u2019t made from a metalloid, like silicon \u2014 it\u2019s plastic. Why? Plastic is cheap and, like silicon, it can be manipulated to convert the absorbed sunlight into electricity. The key, he says, is to figure out the right chemical configurations of polymers \u2014 long, repeating chains of molecules that make up things like plastic bags and water bottles. Polymers with certain molecular structures can gain energy from specific wavelengths of\u00a0light.<\/p>\n

\"Rene<\/a>
Rene Lopez<\/figcaption><\/figure>\n

Polymers are just one type of material scientists have tried substituting for silicon. Some other inorganic photovoltaic semiconductors are highly efficient at producing electricity, but the materials are even more expensive than silicon. UNC physicist Rene Lopez has experimented with many different solar-technology materials including polymers, dye-sensitized solar cells, and quantum dots, trying to find a technology than can match silicon\u2019s efficiency. Polymers, Lopez says, aren\u2019t the most efficient, but so far they seem like the least expensive to\u00a0mass-produce.<\/p>\n

Besides price, polymers have another advantage over silicon: they\u2019re lighter, and they won\u2019t fracture like the heavy, brittle silicon cell in Wei You\u2019s desk did. A few solar products already on the market are flexible and lightweight, but they\u2019re costly and don\u2019t put out a lot of power. The You lab wants to build solar cells that can not only roll up like posters for easy packing, but also provide enough power for anything from a camping trip to a military operation. Since the cells are semi-transparent, they could also cover the windows of buildings, gathering energy while letting in\u00a0light.<\/p>\n

The lab also wants to make their new solar cell the first one that comes with a built-in battery. \u201cWhen you have solar energy, you want to store it to use when the sun is down,\u201d Wei You says. \u201cOne way is to inject the electricity into the power grid \u2014 that\u2019s what solar farms do. The most effective and direct way to do that is a battery.\u201d Such a device, he says, could provide an off-grid, round-the-clock power supply. To make this solar-cell\/battery hybrid, they\u2019re working with engineers and chemists at Duke University who design supercapacitors \u2014 high-power storage devices that, for the flexible solar cells, must be ultrathin and\u00a0lightweight.<\/p>\n

Wei You plans for the active part of the solar cell \u2014 layers of energy-capturing polymers plus the supercapacitor \u2014 to be less than 500 nanometers thick. That\u2019s one-twentieth of one millimeter. The polymer solar cell he holds in his hand is a little bit thicker than a piece of paper \u2014 the new device, he says, will be just slightly thicker than\u00a0that.<\/p>\n

One big advantage of the new device, he says, will be that the polymers are processed in a liquid \u2014 this opens up the possibility to cheaply mass-produce solar cells by printing them onto plastic, much like printing a design on a T-shirt. Wei You\u2019s lab is full of little tubes of liquid polymers, ranging in color from bright red to deepest blue. Each color absorbs different wavelengths of light, and the broader the spectrum of light a solar cell captures, the more electricity it can\u00a0produce.<\/p>\n

The idea sounds good enough to get the attention of Solarmer Energy, an organic-photovoltaics company that has the technology to print these types of cells. The company will collaborate with the UNC and Duke labs to make sure the new cell design can be mass-produced with Solarmer\u2019s\u00a0technology.<\/p>\n

Wei You\u2019s main task is to pack more efficiency into a thin, flexible cell with inexpensive materials. It\u2019s a tall order, but it\u2019s not so different from what his lab has already done. All solar cells lose a lot of energy in the form of heat, but the lab has helped raised the maximum efficiency of polymer solar technology from 2 percent to about 10 percent by experimenting with new polymer designs and improving the solar-cell\u00a0structures.<\/p>\n

On the market, a much lower purchase price might make up for polymers\u2019 having lower efficiency than silicon, which has an efficiency of about 15-20 percent. But purchasing solar cells isn\u2019t the only cost a customer incurs. \u201cYou also pay for permits, regulatory fees, insurance, electrical equipment, the guy who goes on your roof, etc.,\u201d Lopez says. According to the Department of Energy, these nonhardware or \u201csoft\u201d costs are about 50 percent of the price of using solar power at\u00a0home.<\/p>\n

\u201cDifferent people are working on different pieces of the problem,\u201d Lopez says. Some scientists and engineers are investigating how to make electricity generated from solar power less costly to convert to the frequency and voltage used in homes. Other advocates for solar power are looking for ways to make the permitting and inspection process less expensive (it can cost about $2,500<\/a>). Polymer or other thin, lightweight solar cells might be part of the answer: they\u2019d be a lot easier to haul up to the\u00a0roof.\u00a0<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

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Wei You is an associate professor of chemistry, and Rene Lopez is an associate professor of physics, both in the College of Arts and Sciences. You\u2019s lab just began a $1.5 million grant from the National Science Foundation to create the thin-film solar cell and supercapacitor in partnership with Duke University and Solarmer Energy, Inc.<\/a>\u00a0He was also awarded a 2013 Phillip and Ruth Hettleman Prize for Artistic and Scholarly Achievement by Young Faculty.\u00a0 Lopez\u2019s solar research is funded by the Department of Energy, the National Science Foundation, and the Research Corporation for Science\u00a0Advancement.<\/em><\/p>\n

[ Story by Susan Hardy, <\/em>Endeavors magazine<\/em><\/a> ]<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"

What might make solar technology more affordable? Trading silicon for plastic. Chemist Wei You and physicist Rene Lopez in the College of Arts and Sciences are studying the 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