Scientists Detect Magnetic Fingerprints of Defects in Solar CellsA new highly sensitive method of measurement allowed physicists form Helmholtz-Zentrum Berlin for Materials and Energy to directly detect defects in solar cells with atomic resolution. This findings can be used to optimize solar cells’ efficiency and decrease production costs.HZB physicists have managed to localize defects in amorphous/crystalline silicon heterojunction solar cells. Now, for the first time ever, using computer simulations at Paderborn University, the scientists were able to determine the defects’ exact locations and assign them to certain structures within the interface between the amorphous and crystalline phases.In theory, silicon-based solar cells are capable of converting up to 30 percent of sunlight to electricity—although, in reality, the different kinds of loss mechanisms ensure that even under ideal lab conditions it does not exceed 25 %. Advanced heterojunction cells shall affront this problem: On top of the wafer’s surface, at temperatures below 200 °C, a layer of 10 nanometer disordered (amorphous) silicon is deposited. This thin film is managing to saturate to a large extent the interface defects and to conduct charge carriers out of the cell. Heterojunction solar cells have already high efficiency factors up to 24,7%—even in industrial scale. However, scientists had until now only a rough understanding of the processes at the remaining interface defects.Now, physicists at HZB’s Institute for Silicon Photovoltaics have figured out a rather clever way for detecting the remaining defects and characterizing their electronic structure. “If electrons get deposited on these defects, we are able to use their spin, that is, their small magnetic moment, as a probe to study them,” Dr. Alexander Schnegg explains. With the help of EDMR, electrically detected magnetic resonance, an ultrasensitive method of measurement, they were able to determine the local defects’ structure by detecting their magnetic fingerprint in the photo current of the solar cell under a magnetic field and microwave radiation.Theoretical physicists of Paderborn University could compare these results with quantum chemical computer simulations, thus obtaining information about the defects’ positions within the layers and the processes they are involved to decrease the cells’ efficiency. “We basically found two distinct families of defects”, says Dr. Uwe Gerstmann from Paderborn University, who collaborates with the HZB Team in a program sponsored by Deutsche Forschungsgemeinschaft (DFG priority program 1601). “Whereas in the first one, the defects are rather weakly localized within the amorphous layer, a second family of defects is found directly at the interface, but in the crystalline silicon.”For the first time ever the scientists have succeeded at directly detecting and characterizing processes with atomic resolution that compromise these solar cells’ high efficiency. The cells were manufactured and measured at the HZB; the numerical methods were developed at Paderborn University. “We can now apply these findings to other types of solar cells in order to optimize them further and to decrease production costs”, says Schnegg.George, B., Behrends, J., Schnegg, A., Schulze, T., Fehr, M., Korte, L., Rech, B., Lips, K., Rohrmüller, M., Rauls, E., Schmidt, W., & Gerstmann, U. (2013). Atomic Structure of Interface States in Silicon Heterojunction Solar Cells Physical Review Letters, 110 (13) DOI: 10.1103/PhysRevLett.110.136803If you liked this story, please consider sharing it. You can also follow us on Twitter, Facebook or Google+ to stay up to date on the breaking news and events of the energy industry.
Showing posts with label detect. Show all posts
Showing posts with label detect. Show all posts
Sunday, March 31, 2013
Scientists Detect Magnetic Fingerprints of Defects in Solar Cells
Scientists Detect Magnetic Fingerprints of Defects in Solar CellsA new highly sensitive method of measurement allowed physicists form Helmholtz-Zentrum Berlin for Materials and Energy to directly detect defects in solar cells with atomic resolution. This findings can be used to optimize solar cells’ efficiency and decrease production costs.HZB physicists have managed to localize defects in amorphous/crystalline silicon heterojunction solar cells. Now, for the first time ever, using computer simulations at Paderborn University, the scientists were able to determine the defects’ exact locations and assign them to certain structures within the interface between the amorphous and crystalline phases.In theory, silicon-based solar cells are capable of converting up to 30 percent of sunlight to electricity—although, in reality, the different kinds of loss mechanisms ensure that even under ideal lab conditions it does not exceed 25 %. Advanced heterojunction cells shall affront this problem: On top of the wafer’s surface, at temperatures below 200 °C, a layer of 10 nanometer disordered (amorphous) silicon is deposited. This thin film is managing to saturate to a large extent the interface defects and to conduct charge carriers out of the cell. Heterojunction solar cells have already high efficiency factors up to 24,7%—even in industrial scale. However, scientists had until now only a rough understanding of the processes at the remaining interface defects.Now, physicists at HZB’s Institute for Silicon Photovoltaics have figured out a rather clever way for detecting the remaining defects and characterizing their electronic structure. “If electrons get deposited on these defects, we are able to use their spin, that is, their small magnetic moment, as a probe to study them,” Dr. Alexander Schnegg explains. With the help of EDMR, electrically detected magnetic resonance, an ultrasensitive method of measurement, they were able to determine the local defects’ structure by detecting their magnetic fingerprint in the photo current of the solar cell under a magnetic field and microwave radiation.Theoretical physicists of Paderborn University could compare these results with quantum chemical computer simulations, thus obtaining information about the defects’ positions within the layers and the processes they are involved to decrease the cells’ efficiency. “We basically found two distinct families of defects”, says Dr. Uwe Gerstmann from Paderborn University, who collaborates with the HZB Team in a program sponsored by Deutsche Forschungsgemeinschaft (DFG priority program 1601). “Whereas in the first one, the defects are rather weakly localized within the amorphous layer, a second family of defects is found directly at the interface, but in the crystalline silicon.”For the first time ever the scientists have succeeded at directly detecting and characterizing processes with atomic resolution that compromise these solar cells’ high efficiency. The cells were manufactured and measured at the HZB; the numerical methods were developed at Paderborn University. “We can now apply these findings to other types of solar cells in order to optimize them further and to decrease production costs”, says Schnegg.George, B., Behrends, J., Schnegg, A., Schulze, T., Fehr, M., Korte, L., Rech, B., Lips, K., Rohrmüller, M., Rauls, E., Schmidt, W., & Gerstmann, U. (2013). Atomic Structure of Interface States in Silicon Heterojunction Solar Cells Physical Review Letters, 110 (13) DOI: 10.1103/PhysRevLett.110.136803If you liked this story, please consider sharing it. You can also follow us on Twitter, Facebook or Google+ to stay up to date on the breaking news and events of the energy industry.
Monday, October 29, 2012
Computers get a better way to detect threats
ScienceDaily (Sep. 20, 2012) — UT Dallas computer scientists have developed a technique to automatically allow one computer in a virtual network to monitor another for intrusions, viruses or anything else that could cause a computer to malfunction.
The technique has been dubbed "space travel" because it sends computer data to a world outside its home, and bridges the gap between computer hardware and software systems.
"Space travel might change the daily practice for many services offered virtually for cloud providers and data centers today, and as this technology becomes more popular in a few years, for the user at home on their desktop," said Dr. Zhiquian Lin, the research team's leader and an assistant professor of computer science in the Erik Jonsson School of Engineering and Computer Science.
As cloud computing is becoming more popular, new techniques to protect the systems must be developed. Since this type of computing is Internet-based, skilled computer specialists can control the main part of the system virtually -- using software to emulate hardware.
Lin and his team programmed space travel to use existing code to gather information in a computer's memory and automatically transfer it to a secure virtual machine -- one that is isolated and protected from outside interference.
"You have an exact copy of the operating system of the computer inside the secure virtual machine that a hacker can't compromise," Lin said. "Using this machine, then the user or antivirus software can understand what's happening with the space traveled computer setting off red flags if there is any intrusion.
Previously, software developer had to manually write such tools.
"With our technique, the tools already being used on the computer become part of the defense process," he said.
The gap between virtualized computer hardware and software operating on top of it was first characterized by Drs. Peter Chen and Brian Noble, faculty members from the University of Michigan.
"The ability to leverage existing code goes a long way in solving the gap problem inherent to many types of virtual machine services," said Chen, Arthur F. Thurnau Professor of Electrical Engineering and Computer Science, who first proposed the gap in 2001. "Fu and Lin have developed an interesting way to take existing code from a trusted system and automatically use it to detect intrusions."
Lin said the space travel technique will help the FBI understand what is happening inside a suspect's computer even if they are physically miles away, instead of having to buy expensive software.
Space travel was presented at the most recent IEEE Symposium on Security and Privacy. Lin developed this with Yangchun Fu, a research assistant in computer science.
"This is the top conference in cybersecurity, said Bhavani Thuraisingham, executive director of the UT Dallas Cyber Security Research and Education Center and a Louis A. Beecherl Jr. Distinguished Professor in the Jonsson School. "It is a major breakthrough that virtual developers no longer need to write any code to bridge the gap by using the technology invented by Dr. Lin and Mr. Fu. This research has given us tremendous visibility among the cybersecurity research community around the world."
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