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.”
Learn more: Prototype Shows How Tiny Photodetectors Can Double Their Efficiency
The Latest on: Photodetector
[google_news title=”” keyword=”photodetector” num_posts=”10″ blurb_length=”0″ show_thumb=”left”]
- Coros' Vertix 2S may be the most accurate, longest-lasting sports watch I've seen yeton April 25, 2024 at 10:09 am
When you buy a Coros watch, you can trust it will be updated for years. The latest feature update, currently in beta, will bring screen mirroring, a virtual pacer, and more.
- Scientists reveal working mechanism of multilayer MoS₂ photodetector with broad spectral range and multiband responseon April 24, 2024 at 9:27 am
A research team from the school of Electronic Science and Engineering of Southeast University has developed wideband MoS2 photodetector, covering a range from 410 to 1550 nm. Through a series of ...
- Multilayer MoS2 photodetector with broad spectral range and multiband responseon April 23, 2024 at 5:00 pm
As a typical two-dimensional material, MoS 2 exhibits unique optical and electrical properties due to its atomic thickness in the vertical dimension, making it a research hotspot in the field of ...
- MIT Technology Reviewon April 23, 2024 at 2:00 pm
Electrical engineer Nili Persits, PhD ’24, has developed low-cost Raman spectroscopy systems that allow instant chemical analysis.
- Novel method developed for phosphorescent multi-color carbon dotson April 15, 2024 at 5:00 pm
A research team has devised a novel method to prepare carbonized polymer nanodots capable of emitting multi-color ultra-long room-temperature phosphorescence (RTP) from blue to green. "These ...
- PhotonWear develops new wearable sensorson April 4, 2024 at 1:03 pm
A black silicon photodetector can demonstrate up to 50 percent higher sensitivity compared to untreated material, according to the PhotonWear developers. "The black silicon developed by ElFys enables ...
- OURA partners in PhotonWear to develop more accurate wearable sensorson April 1, 2024 at 5:00 pm
Photonic optical sensors contain a new kind of photodetector, which can be 50% more sensitive compared to traditional technology. That's according to ElFys, one of the PhotonWear hardware partners.
- Autocollimators Informationon February 11, 2018 at 7:08 am
Visual autocollimators rely on the operator’s eye as the photodetector. This can result in varying resolution among operators, but most visual autocollimators can resolve from 3-to-5 arc-seconds.
- Lux Meters (Light Meters) Informationon February 11, 2018 at 7:08 am
Total power output is measured as radiant flux. Most lux meters register brightness with an integrated photodetector. The photodetector is positioned perpendicular to the light source for optimal ...
- Are optical transistors the logical next step?on January 1, 2010 at 4:00 am
In optical lines there is no need to charge the line to the signal voltage; essentially, we only need to transmit enough energy to charge the photodetector at the receiving end. This benefit ...
via Google News and Bing News