UC Riverside research invokes quantum mechanical processes that occur when two atomically thin materials are stacked together
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.
“The electron in WSe2 that is initially energized by the photon has an energy that is low with respect to WSe2,” said Fatemeh Barati, a graduate student in Gabor’s Quantum Materials Optoelectronics lab and the co-first author of the research paper. “With the application of a small electric field, it transfers to MoSe2, where its energy, with respect to this new material, is high. Meaning, it can now lose energy. This energy is dissipated as kinetic energy that dislodges the additional electron from WSe2.”
In existing solar panels models, one photon can at most generate one electron. In the prototype the researchers developed, one photon can generate two electrons or more through a process called electron multiplication.
The researchers explained that in ultrasmall materials, electrons behave like waves. Though it is unintuitive at large scales, the process of generating two electrons from one photon is perfectly allowable at extremely small length scales. When a material, such as WSe2 or MoSe2, gets thinned down to dimensions nearing the electron’s wavelength, the material’s properties begin to change in inexplicable, unpredictable, and mysterious ways.
“It’s like a wave stuck between walls closing in,” Gabor said. “Quantum mechanically, this changes all the scales. The combination of two different ultra small materials gives rise to an entirely new multiplication process. Two plus two equals five.”
“Ideally, in a solar cell we would want light coming in to turn into several electrons,” said Max Grossnickle, also a graduate student in Gabor’s lab and the research paper’s co-first author. “Our paper shows that this is possible.”
Barati noted that more electrons could be generated also by increasing the temperature of the device.
“We saw a doubling of electrons in our device at 340 degrees Kelvin (150 F), which is slightly above room temperature,” she said. “Few materials show this phenomenon around room temperature. As we increase this temperature, we should see more than a doubling of electrons.”
Electron multiplication in conventional photocell devices typically requires applied voltages of 10-100 volts. To observe the doubling of electrons, the researchers used only 1.2 volts, the typical voltage supplied by an AA battery.
“Such low voltage operation, and therefore low power consumption, may herald a revolutionary direction in photodetector and solar cell material design,” Grossnickle said.
He explained that the efficiency of a photovoltaic device is governed by a simple competition: light energy is either converted into waste heat or useful electronic power.
“Ultrathin materials may tip the balance in this competition by simultaneously limiting heat generation, while increasing electronic power,” he said.
Gabor explained that the quantum mechanical phenomenon his team observed in their device is similar to what occurs when cosmic rays, coming into contact with the Earth’s atmosphere with high kinetic energy, produce an array of new particles.
He speculated that the team’s findings could find applications in unforeseen ways.
“These materials, being only an atom thick, are nearly transparent,” he said. “It’s conceivable that one day we might see them included in paint or in solar cells incorporated into windows. Because these materials are flexible, we can envision their application in wearable photovoltaics, with the materials being integrated into the fabric. We could have, say, a suit that generates power – energy-harvesting technology that would be essentially invisible.”
The Latest on: Photodetector
Perovskite Sandwich Generates Energy
on April 13, 2018 at 3:40 am
KAUST researchers develop self-powered photodetector by coupling silicone-based polymers with an organometallic halide perovskite Autonomy is a much-anticipated feature of next-generation microsystems, such as remote sensors, wearable electronic gadgets ... […]
Nanotechnology wearable self-charging power units
on April 12, 2018 at 6:54 am
The researchers have developed a self-powered photodetector by coupling the silicone-based polymer polydimethylsiloxane (PDMS) as a TENG with a material called organometallic halide perovskite¹. The lead-halide-based material features optoelectronic ... […]
Using Graphene as a Photodetector
on April 11, 2018 at 2:34 am
First, let’s define a photodetector. Photodetectors are a type of sensor that detects wavelengths of light or electromagnetic waves. Photodetectors then convert this optical detection into electrical current using a semiconducting p-n junction. […]
Comparing Optical Sensors: Understanding D-Star
on April 5, 2018 at 9:31 pm
In many applications, the performance of a photodetector is not particularly important. A photodiode-based proximity sensor, for example, may be designed so that the light source is either very intense or completely obstructed. In such cases it is not ... […]
High Speed Photodetector Market: Segmented by Applications and Geography Trends, Growth and Forecasts 2022
on March 22, 2018 at 4:52 am
The High Speed Photodetector Market report offers a detailed Outlook and future prospects of the High Speed Photodetector Industry. The High Speed Photodetector Market report analyses major information that helps Industry experts, analysts and business ... […]
POET Technologies Demonstrates Functionality of PIN Photodetector Targeting 100G to 400G Optical Transceivers
on January 29, 2018 at 4:00 pm
SAN JOSE, Calif., Jan. 30, 2018 (GLOBE NEWSWIRE) -- POET Technologies Inc. (“POET”) (POETF) (TSX Venture:PTK), a designer, developer and manufacturer of optoelectronic devices, including light sources, passive wave guides and Photonic Integrated ... […]
Global Organic Photodetector Market Revenue Status and Outlook (2012-2022)
on November 22, 2017 at 1:00 am
Global Organic Photodetector Market Research Report 2017 contains historic data that spans 2012 to 2016, and then continues to forecast to 2022. That makes this report so invaluable, resources, for the leaders as well as the new entrants in the Industry ... […]
First Graphene Photodetector To Operate in the Microwave
on November 30, 2016 at 1:00 am
While graphene may be losing its luster in the field of digital electronics because of its lack of an inherent band gap, in the world of optoelectronics graphene’s gapless band structure seems to be winning a new set of acolytes. This is seen no more ... […]
Self-powered UV photodetector charges energy storage devices
on October 14, 2016 at 8:15 pm
In a novel approach, researchers from the Indian Institute of Science (IISc), Bangalore, have developed a cost-effective, high-performance, self-powered UV photodetector that can use the harvested optical energy for direct self-charging of energy storage ... […]
via Google News and Bing News