UCR researchers discover new, high-efficiency photodetectors

UCR researchers this week announced a major breakthrough in microelectronics that will allow for more efficient and effective photodetector technology. A team led by Assistant Professor of Physics Nathaniel Gabor has discovered a method of layering molecules in a way that generates energy in the process of receiving photons on its surface. The findings, which have been published in Nature Nanotechnology, are predicted to have major implications for the electronics industry.

Photodetectors are microscopic parts, often a few atoms thick, which transfer light to electrons. These electrons are then used to produce an electrical signal and transmit information. Gabor and his team have invented a way of stacking the component molecules in an attempt to produce energy in the process.

Stacking two layers of tungsten diselenide (WSe2) on a single layer of molybdenum diselenide (MoSe2) results in an energy-producing chain reaction. As photons strike the upper layer of WSe2, an electron is displaced. Its motion displaces other surrounding electrons, which are “knocked free” from their position. In the electrons’ attempt to reach a lower energy level, their free motion results in electricity production.

The breakthrough of this discovery comes with the possibility of displacing more than one electron with each photon. In traditional applications, such as solar panels, this displacement knocks free only one electron. The UCR team’s findings, however, indicate that the potential uses of this technology are of a far broader scope than previously thought.

“A major source of energy loss in photovoltaics is rapid cooling of hot carriers generated by photons,” wrote Gabor in an email. “It is possible to increase the efficiency of these cells by taking advantage of the potential energy … generated by photons and converting it into kinetic energy.”

A promising factor in the discovery of this process is the relative lack of knowledge about the quantum interactions present at this minute scale. Materials with a thickness of only a few atoms often behave in strange and unpredictable ways, leaving many questions unanswered, with the potential for innovative and unexpected solutions.

“The field of atomic layer materials is one of the most exciting fields in physics,” Gabor explained, adding, “In this type of material you decrease one dimension from a bulk crystal, and enter into the quantum world, where bizarre and unintuitive behavior occurs.”

The possible applications of these findings are manyfold, with possible uses in solar energy production, home improvements and military technology. The small size of these photodetectors could result in use in wearable photovoltaics, where solar energy production is integrated into clothing. Windows in the future could also be built with nanoscale photodetectors, allowing direct sunlight exposure to generate energy to power homes.

The U.S. military is also reportedly interested in Gabor’s work, which has been partially funded by a grant from the U.S. Air Force Office of Scientific Research. “Certainly, the military will always be looking for better ways to generate power and detect light while on the move,” says Gabor. For example, “Soldiers in the field would not need to re-supply fuel before their missions but will gather it from sun while moving.”

The primary challenge to large-scale implementation of this technology lies in the difficulty of production. Gabor says, “Like the first transistor in the 20th century, the materials and processes going into our device prototype are new, and so each individual photocell is fabricated through a time-intensive process.” Fortunately, according to Gabor, “a huge effort in the engineering community is currently underway to overcome some of these challenging problems, but lab-to-commercial realization may be accelerated given the potential for high efficiency device operation.”

Gabor’s lab is currently interested in using quantum-level behavior to develop more effective energy storage. “Can energy storage be made more efficient using devices that behave quantum mechanically? Can the miniaturization of energy harvesting devices have the same profound effect that arose in the miniaturization of computing? These materials give us the ability to custom build electronic devices at the atomic scale,” Gabor explained. Such findings, Gabor added, would “allow us to answer these questions and potentially expose very new physics.”

Gabor and his team are continuing their research in streamlining photodetector technology and discovering new, potential applications.

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