Quantum Technique Increases Electrons Produced When Light Hits Metal-Dielectric Interface

Researchers have found a new technique to increase the amount of energy that can be retrieved from sunlight, which could lead to more efficient solar cells, according to a study at MIT.

The new technique uses a quantum effect that increases the number of charge carriers, known as electrons and "holes." This occurs when light with various wavelengths strike a metal surface that is coated with a type of oxide material called high-index dielectrics, according to the researchers. In their experiment, the researchers used a sheet of silver coated with an oxide. This converts light energy into the polarization of atoms at the interface.

Polarization is the process of separating opposite charges within an object. The positive charge is separated from the negative charge.

"Our study reveals a surprising fact, absorption of visible light is directly controlled by how deeply the electrons spill over the interface between the metal and the dielectric," said Nicholas Fang, researcher of the study and associate professor of mechanical engineering.

The researchers found that the composition and thickness of dielectric materials (like aluminum oxide and titanium oxide) on metal surfaces controls the amount of energy that is gathered.

"The oxide materials are exactly the kind people use for making better transistors," Fang said.

The new technique can also be used to produce better solar cells and super fast photodetectors, Kang added. He claimed that the dielectric layer is quite effective at improving the efficiency of light that is retrieved. Since the solar cells in this technique are thin, it requires less material compared to conventional silicon cells.

"We could receive or detect signals as a shorter pulse" than current photodetectors can pick up, Kang said. This could lead to new "li-fi" systems, where light can be used to send and receive high-speed data.

Kang claimed that this new technique is simple to adapt for devices, since the materials used in the process are used at an industrial level.

The findings of this study were published in the journal Physical Review Letters.

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