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Prototype Shows How Tiny Photodetectors Can Double Their Efficiency

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RIVERSIDE, Calif. – Physicists at the University of California, Riverside have developed a photodetector – a device that senses light – by combining two distinct inorganic materials and producing quantum mechanical processes that could revolutionize the way solar energy is collected.

Photodetectors are almost ubiquitous, found in cameras, cell phones, remote controls, solar cells, and even the panels of space shuttles. Measuring just microns across, these tiny devices convert light into electrons, whose subsequent movement generates an electronic signal. Increasing the efficiency of light-to-electricity conversion has been one of the primary aims in photodetector construction since their invention.

Lab researchers stacked two atomic layers of tungsten diselenide (WSe2) on a single atomic layer of molybdenum diselenide (MoSe2). Such stacking results in properties vastly different from those of the parent layers, allowing for customized electronic engineering at the tiniest possible scale.

Within atoms, electrons live in states that determine their energy level. When electrons move from one state to another, they either acquire or lose energy. Above a certain energy level, electrons can move freely. An electron moving into a lower energy state can transfer enough energy to knock loose another electron.

UC Riverside physicists observed that when a photon strikes the WSe2layer, it knocks loose an electron, freeing it to conduct through the WSe2. At the junction between WSe2 and MoSe2, the electron drops down into MoSe2. The energy given off then catapults a second electron from the WSe2 into the MoSe2, where both electrons become free to move and generate electricity.

“We are seeing a new phenomenon occurring,” said Nathaniel M. Gabor, an assistant professor of physics, who led the research team. “Normally, when an electron jumps between energy states, it wastes energy. In our experiment, the waste energy instead creates another electron, doubling its efficiency. Understanding such processes, together with improved designs that push beyond the theoretical efficiency limits, will have a broad significance with regard to designing new ultra-efficient photovoltaic devices.”

Study results appear today in Nature Nanotechnology.

Read more stories about Riverside solar energy.

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