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
- Powerful new photodetector can enable optoelectronics advanceson February 23, 2020 at 4:00 pm
Now, in a nanoscale photodetector that combines both a unique fabrication method and light-trapping structures, a team of engineers from the University at Buffalo and the University of ...
- Prefrontal parvalbumin interneurons require juvenile social experience to establish adult social behavioron February 21, 2020 at 2:21 am
Emitted light recorded from the brain through the fiber-optic cable is passed through the dichroic mirror and emission filters, and through a 0.50 N.A. microscope lens (62-561, Edmund Optics) and then ...
- Early detection of red palm weevil using distributed optical sensoron February 21, 2020 at 2:13 am
In our design, all of the optical/electronic components including the laser and photodetector are gathered within a single unit, whereas only the fiber is wound around the palm trees to form an ...
- Real-time frequency-encoded spatiotemporal focusing through scattering media using a programmable 2D ultrafine optical frequency combon February 19, 2020 at 12:59 pm
It is then combined with a single-frequency reference beam through a beam splitter (BS) and beats at a high-speed photodetector (PD). The beating signal is sent to a fast signal processing unit, ...
- Unveiling the Hot Carrier Distribution in Vertical Graphene/h-BN/Au van der Waals Heterostructures for High-Performance Photodetectoron February 18, 2020 at 11:16 am
Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Suwon 16419, Republic of Korea Article Views are the COUNTER-compliant sum of full text article downloads since November ...
- Widely tunable mid-infrared light emission in thin-film black phosphoruson February 14, 2020 at 11:30 am
Recently, a widely tunable mid-infrared photodetector with a detection limit up to 7.7 μm (34) has been demonstrated in a dual-gate hexagonal boron nitride (hBN)/BP/hBN device. Moreover, the broadband ...
- A fast light detector made of two-dimensional materialson February 13, 2020 at 5:55 am
"The possibilities are almost limitless," Flöry and Ma enthuse about their discovery. "We just picked out the photodetector as an example of what can be done with this technology." In the near future, ...
- Organic Photodetector Market 2020 Research by Business Opportunities, Top Manufacture, Industry Growth 2026on February 3, 2020 at 5:55 pm
Global ??Organic Photodetector Market Report 2020-2026 provides insightful data about business strategies, qualitative and quantitative analysis of Global Market. The report also calls for ...
- Colloidal quantum dot photodetectors see further in the infraredon February 3, 2020 at 2:07 am
This ease of manufacture makes them a cost-competitive, high-performance photodetector material that integrates readily with CMOS technologies. PbS CQDs have recently emerged as a promising basis for ...
- Maxim Highlights Techniques to Derive Reliable Sensor Data from Healthcare Wearableson January 22, 2020 at 1:15 am
When that light exits the tissue and enters a photodetector, it changes the output current. By creating a sensing system that carefully sets up a proper series of "dominos," a current sensor ...
via Google News and Bing News