سوال ۲۰ کنکور ارشد مهندسی برق ۱۴۰۴

PASSAGE 2

Graphene could revolutionize future technologies making transparent and flexible solar panels, foldable mobile phones or ultrathin computers a reality. Now researchers from Spain, Germany, and the US think they have taken one of the first important steps along the way. Frank H.L. Koppens of the Institut de Ciéncies Fotóniques (ICFO) in Spain, along with colleagues from MIT and Harvard University have found that graphene is able to convert a single absorbed photon into multiple electrons. Graphene is currently being employed as an alternative to semiconducting materials for light-to-electricity conversion, but the finding indicates that the material could be more efficient than thought.

"In most materials, one absorbed photon generates one electron, but in the case of graphene, one absorbed photon is able to produce many excited electrons, and therefore generate larger electrical signals," explains Koppens. "We have found that this process is very efficient: more than 80% of light energy is converted." Instead of losing excess energy as heat when a photon is absorbed, graphene uses the extra to generate secondary 'hot' electrons. These 'hot' or excited electrons can drive a current, making graphene an alternative material for light harvesting photovoltaic devices or photodetection. The reason for graphene's highly efficient extraction of light energy lies in its unique physical nature. Doped graphene can be thought of as a mixture of a semiconductor, where properties are determined by the behavior of electrons and holes in the conduction and valence bands, and a metal, in which they depend upon the Fermi level.

20- The passage provides sufficient information to answer which of the following questions?

I. Who discovered graphene?

II. In which country is graphene more commonly used in the industry?

III. Does graphene's failure to extract 100% of light energy make it an inefficient material?