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Site: http://www.rdmag.com/rss-feeds/all/rss.xml/all

Solar energy is on the rise. Many technical advances have made solar cells quite efficient and affordable in recent years. A big disadvantage remains in the fact that solar cells produce no power when it's raining. This may change, however: In the journal Angewandte Chemie, Chinese researchers have now introduced a new approach for making an all-weather solar cell that is triggered by both sunlight and raindrops. For the conversion of solar energy to electricity, the team from the Ocean University of China (Qingdao) and Yunnan Normal University (Kunming, China) developed a highly efficient dye-sensitized solar cell. In order to allow rain to produce electricity as well, they coated this cell with a whisper-thin film of graphene. Graphene is a two-dimensional form of carbon in which the atoms are bonded into a honeycomb arrangement. It can readily be prepared by the oxidation, exfoliation, and subsequent reduction of graphite. Graphene is characterized by its unusual electronic properties: It conducts electricity and is rich in electrons that can move freely across the entire layer (delocalized). In aqueous solution, graphene can bind positively charged ions with its electrons (Lewis acid-base interaction). This property is used in graphene-based processes to remove lead ions and organic dyes from solutions. This phenomenon inspired researchers working with Qunwei Tang to use graphene electrodes to obtain power from the impact of raindrops. Raindrops are not pure water. They contain salts that dissociate into positive and negative ions. The positively charged ions, including sodium, calcium, and ammonium ions, can bind to the graphene surface. At the point of contact between the raindrop and the graphene, the water becomes enriched in positive ions and the graphene becomes enriched in delocalized electrons. This results in a double-layer made of electrons and positively charged ions, a feature known as a pseudocapacitor. The difference in potential associated with this phenomenon is sufficient to produce a voltage and current.


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Site: http://phys.org/nanotech-news/

Solar energy is on the rise. Many technical advances have made solar cells quite efficient and affordable in recent years. A big disadvantage remains in the fact that solar cells produce no power when it's raining. This may change, however: In the journal Angewandte Chemie, Chinese researchers have now introduced a new approach for making an all-weather solar cell that is triggered by both sunlight and raindrops. For the conversion of solar energy to electricity, the team from the Ocean University of China (Qingdao) and Yunnan Normal University (Kunming, China) developed a highly efficient dye-sensitized solar cell. In order to allow rain to produce electricity as well, they coated this cell with a whisper-thin film of graphene. Graphene is a two-dimensional form of carbon in which the atoms are bonded into a honeycomb arrangement. It can readily be prepared by the oxidation, exfoliation, and subsequent reduction of graphite. Graphene is characterized by its unusual electronic properties: It conducts electricity and is rich in electrons that can move freely across the entire layer (delocalized). In aqueous solution, graphene can bind positively charged ions with its electrons (Lewis acid-base interaction). This property is used in graphene-based processes to remove lead ions and organic dyes from solutions. This phenomenon inspired researchers working with Qunwei Tang to use graphene electrodes to obtain power from the impact of raindrops. Raindrops are not pure water. They contain salts that dissociate into positive and negative ions. The positively charged ions, including sodium, calcium, and ammonium ions, can bind to the graphene surface. At the point of contact between the raindrop and the graphene, the water becomes enriched in positive ions and the graphene becomes enriched in delocalized electrons. This results in a double-layer made of electrons and positively charged ions, a feature known as a pseudocapacitor. The difference in potential associated with this phenomenon is sufficient to produce a voltage and current.


« BMW Connected North America makes its world debut at Microsoft Build 2016; powered by Azure | Main | Uno-X Hydrogen to build 1st hydrogen refueling station w/ hydrogen produced by surplus renewable energy from neighboring building » While many technical advances have made solar cells more efficient and affordable, a disadvantage remains in the fact that solar cells produce no power when it’s raining. Now, however, researchers from the Ocean University of China (Qingdao) and Yunnan Normal University (Kunming, China) have developed an all-weather solar cell that is triggered by both sunlight and raindrops by combining an electron-enriched graphene electrode with a dye-sensitized solar cell. The new solar cell can be excited by incident light on sunny days and raindrops on rainy days, yielding an optimal solar-to-electric conversion efficiency of 6.53% under AM 1.5 irradiation and current over microamps as well as a voltage of hundreds of microvolts by simulated raindrops. Their work is published as a “Very Important Paper” in the journal Angewandte Chemie. Graphene is a two-dimensional form of carbon in which the atoms are bonded into a honeycomb arrangement. It can readily be prepared by the oxidation, exfoliation, and subsequent reduction of graphite. Graphene is characterized by its unusual electronic properties: it conducts electricity and is rich in electrons that can move freely across the entire layer (delocalized). In aqueous solution, graphene can bind positively charged ions with its electrons (Lewis acid-base interaction). This property is used in graphene-based processes to remove lead ions and organic dyes from solutions. This phenomenon inspired researchers working with Qunwei Tang to use graphene electrodes to obtain power from the impact of raindrops. Raindrops are not pure water; they contain salts that dissociate into positive and negative ions. The positively charged ions, including sodium, calcium, and ammonium ions, can bind to the graphene surface. At the point of contact between the raindrop and the graphene, the water becomes enriched in positive ions and the graphene becomes enriched in delocalized electrons. This results in a double-layer made of electrons and positively charged ions, a feature known as a pseudocapacitor. The difference in potential associated with this phenomenon is sufficient to produce a voltage and current. On rainy days, the new solar cells can be reversed with rGO film upward, creating current and voltage outputs under he persistent dropping of raindrops (NaCl aqueous solution with concentration of 0.6m, 1m, or 2m is used as simulated rain). … Moreover, each droplet can yield voltage and output power of 152.6 mV and 7.17 pW for 9.46 mm, 54.7 mV and 20.7 pW for 7.58 mm, and 25.1 mV and 84.7 pW for 4.52 mm. … When dropping onto a rGO surface, simulated raindrops will quickly spread to the periphery. In this fashion, the cations are adsorbed at the front end, advancing the pseudocapacitor forward and drawing electrons in the rGO. The migration of drawing electrons creates current. Subsequently, the cations are desorbed at the rear end of the droplets during the shrinking process due to a hydrophobic rGO surface … discharging the pseudocapacitor and releasing the p-electrons to rGO. This discharging process results in a reduced current. The research team suggested that the work opens a viable concept of developing all-weather solar cells that can persistently generate electricity.


News Article
Site: http://www.nanotech-now.com/

Abstract: Thin films of crystalline materials called perovskites provide a promising new way of making inexpensive and efficient solar cells. Now, an international team of researchers has shown a way of flipping a chemical switch that converts one type of perovskite into another -- a type that has better thermal stability and is a better light absorber. The study, by researchers from Brown University, the National Renewable Energy Laboratory (NREL) and the Chinese Academy of Sciences' Qingdao Institute of Bioenergy and Bioprocess Technology published in the Journal of the American Chemical Society, could be one more step toward bringing perovskite solar cells to the mass market. "We've demonstrated a new procedure for making solar cells that can be more stable at moderate temperatures than the perovskite solar cells that most people are making currently," said Nitin Padture, professor in Brown's School of Engineering, director of Brown's Institute for Molecular and Nanoscale Innovation, and the senior co-author of the new paper. "The technique is simple and has the potential to be scaled up, which overcomes a real bottleneck in perovskite research at the moment." Perovskites have emerged in recent years as a hot topic in the solar energy world. The efficiency with which they convert sunlight into electricity rivals that of traditional silicon solar cells, but perovskites are potentially much cheaper to produce. These new solar cells can also be made partially transparent for use in windows and skylights that can produce electricity, or to boost the efficiency of silicon solar cells by using the two in tandem. Despite the promise, perovskite technology has several hurdles to clear -- one of which deals with thermal stability. Most of the perovskite solar cells produced today are made with of a type of perovskite called methylammonium lead triiodide (MAPbI3). The problem is that MAPbI3 tends to degrade at moderate temperatures. "Solar cells need to operate at temperatures up to 85 degrees Celsius," said Yuanyuan Zhou, a graduate student at Brown who led the new research. "MAPbI3 degrades quite easily at those temperatures." That's not ideal for solar panels that must last for many years. As a result, there's a growing interest in solar cells that use a type of perovskite called formamidinium lead triiodide (FAPbI3) instead. Research suggests that solar cells based on FAPbI3 can be more efficient and more thermally stable than MAPbI3. However, thin films of FAPbI3 perovskites are harder to make than MAPbI3 even at laboratory scale, Padture says, let alone making them large enough for commercial applications. Part of the problem is that formamidinium has a different molecular shape than methylammonium. So as FAPbI3 crystals grow, they often lose the perovskite structure that is critical to absorbing light efficiently. This latest research shows a simple way around that problem. The team started by making high-quality MAPbI3 thin films using techniques they had developed previously. They then exposed those MAPbI3 thin films to formamidine gas at 150 degrees Celsius. The material instantly converted from MAPbI3 to FAPbI3 while preserving the all-important microstructure and morphology of the original thin film. "It's like flipping a switch," Padture said. "The gas pulls out the methylammonium from the crystal structure and stuffs in the formamidinium, and it does so without changing the morphology. We're taking advantage of a lot of experience in making excellent quality MAPbI3 thin films and simply converting them to FAPbI3 thin films while maintaining that excellent quality." This latest research builds on the work this international team of researchers has been doing over the past year using gas-based techniques to make perovskites. The gas-based methods have the potential of improving the quality of the solar cells when scaled up to commercial proportions. The ability to switch from MAPbI3 to FAPbI3 marks another potentially useful step toward commercialization, the researchers say. "The simplicity and the potential scalability of this method was inspired by our previous work on gas-based processing of MAPbI3 thin films, and now we can make high-efficiency FAPbI3-based perovskite solar cells that can be thermally more stable," Zhou said. "That's important for bringing perovskite solar cells to the market." Laboratory scale perovskite solar cells made using this new method showed efficiency of around 18 percent -- not far off the 20 to 25 percent achieved by silicon solar cells. "We plan to continue to work with the method in order to further improve the efficiency of the cells," said Kai Zhu, senior scientist at NREL and co-author of the new paper. "But this initial work demonstrates a promising new fabrication route." ### Other authors on the paper were Mengjin Yang from NREL and Shuping Pang from CAS Qingdao Institute of Bioenergy and Bioprocess Technology. The work was supported by the National Science Foundation (DMR-1305913, OIA-1538893) and the Department of Energy (DE-FOA-0000990). For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


News Article | April 12, 2016
Site: http://www.topix.com/energy/alt-energy

Researchers from two Chinese universities have developed a solar cell that can produce electricity from light and water, enabling a solar panel that works in the sun or rain. The scientists from Ocean University of China in Qingdao and Yunnan Normal University in Kunming developed a highly efficient and flexible dye-sensitized solar cell and then coated that cell with a one atom-thick layer of electron-enriched graphene.

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