New approach to generating electricity from the sun

Graphene, a bizarre form of carbon consisting of carbon atoms bundled into a flat graphite plate separated at atomic size, exhibits a new reaction to light, MIT researchers found that : when exposed to the sun's energy, this Graphene sheet can produce an abnormal current. This finding could lead to improvements in photodetectors and night vision systems and could lead to a new approach to generating electricity from sunlight.

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The results of this study were published in the journal Science.

This effect was originally observed, but researchers did not determine that it was due to a photoelectric effect, says Pablo Jarillo-Herrero, associate professor of physics at MIT.

In addition, MIT researchers found that when shining light on a sheet of graphene , processed to have two areas with different conductive properties, creating temperature differences, generating alternating currents in turn. . The heat resistance of Graphene is not suitable to be illuminated by a laser, Jarillo-Herrero and colleagues found: the electrons of the material are transmitting electric current, warmed by light, but the lattice The body of carbon nuclei that forms the backbone of graphene is still cool. This is the difference in the temperature inside the material that creates the electrical current. This mechanism, called " hot - transport", "response", "is very unusual," Jarillo said.

Such difference in heat has been followed before, but only in very special cases: or at ultralow temperatures (measured in milliseconds of a degree above absolute zero), or when materials explode with energy Intense output from a high-energy laser. This reaction in graphene, on the other hand, occurs on a wide range of temperatures up to room temperature, and with light is not stronger than conventional sunlight.

Explaining this unusual heat response, Jarillo-Herrero said: Because graphene, the most durable material known. While most other materials, when there is overheating, electrons will transfer energy to the lattice around them. In the case of graphene, however, it is difficult to do this because of the strength of the material, which means it needs the impact of very high energy levels to vibrate the lattice of the carbon nucleus. Therefore, very little heat is transmitted by electrons to the lattice around them.

Because this phenomenon is new, Jarillo-Herrero said: It is difficult to know all the potential applications that can be obtained."Our work is primarily basic physics , " he said, but added that "many people believe that this graphene material can be used for a variety of different applications."

But there are also some suggestions, he said: Graphene can be a good optical detector "because it produces electric current in a different way than other materials used to detect light. Graphene It is also possible to detect light on a very large energy range, "added Jarillo-Herrero. For example, Graphene works very well in infrared light, which other detectors have difficulty processing. This advantage makes Graphene an important component of devices from night vision systems such as improved sensors of new generation telescopes.

The new work also shows that graphene can be used in detecting important biological molecules, such as: toxins, host transmissions or food contaminants, some of These elements will emit infrared light when illuminated. Graphene is made of pure and rich carbon, which may be a much cheaper detection material than currently used semiconductors, often including rare and expensive materials.

The study also shows that graphene can be a very effective material for collecting solar energy, according to Jarillo-Herrero, because it meets a variety of wavelengths, typical photovoltaic materials are: limits Specific frequency, color, light. However, more research will be needed, Jarillo-Herrero added.

"This is the absolute embryonic stage of graphene photodetectors , " Jarillo-Herrero said. "There are many factors that can make it better or faster," which will be the subject of further research.

Philip Kim, a professor of physics at Columbia University, who was not involved in the study, said the results of this study represent "extremely important progress for photovoltaic and collector's applications." energy planning " based on graphene. Philip Kim added that, thanks to the results of this study, "we now have a better understanding of the mechanism by which electrons in graphene heat up, when excited by light."

Together with Pablo Jarillo-Herrero, the lead author of the paper is an intern Dr. Nathaniel Gabor, co-author including: four MIT students, physics professor Leonid Levitov, MIT and two researchers at the National Institute of Materials Science in Tsukuba, Japan.

This study was supported by the Air Force Research Agency, along with funding from the National Science Foundation and the Packard Foundation.