Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Modified quantum dots capture more energy from light and lose less to heat

08.10.2019

Los Alamos National Laboratory researchers discover a new approach for capturing energy from light-generated, 'hot' electrons, avoiding wasteful heat loss

Los Alamos National Laboratory scientists have synthesized magnetically-doped quantum dots that capture the kinetic energy of electrons created by ultraviolet light before it's wasted as heat.


Doping a quantum dot with magnesium (right half of graphic) speeds the capture of energy from a hot electron to 0.15 picoseconds, outpacing losses to phonons in the crystal lattice.

Credit: Los Alamos National Laboratory

"This discovery can potentially enable novel, highly-efficient solar cells, light detectors, photocathodes and light-driven chemical reactions," said Victor Klimov, lead researcher on the Laboratory's quantum dot project.

In standard solar cells, a large amount of sunlight energy is wasted as heat. This waste occurs due to the lack of effective approaches for capturing kinetic energy of 'hot' electrons generated by photons in the green to ultraviolet portion of the sun's light spectrum. The problem is that hot electrons lose their energy very quickly due to interactions with crystal lattice that the devices are made of, leading to vibrations known as phonons. This process typically occurs in a few picoseconds (trillionths of a second).

Previous efforts to capture hot-carrier energy have exploited the transfer of kinetic energy from the energetic hot electron to an immobile, low-energy electron exciting it to a current-conducting state. This effect, known as carrier multiplication, doubles the number of electrons contributing to the photocurrent which can be used for boosting the performance of solar cells. In most conventional materials, however, the energy losses to phonons outpace the energy gains of carrier multiplication.

In their study published today in Nature Nanotechnology, researchers demonstrate that incorporating magnetic ions into quantum dots can greatly enhance useful, energy-producing interactions so as they become faster than wasteful phonon scattering.

To implement these ideas, the researchers prepared manganese-doped quantum dots based on cadmium selenide. "The photon absorbed by the cadmium selenide quantum dot creates an electron-hole pair, or an exciton," said Klimov."This exciton is quickly trapped by the dopant creating an excited state that stores energy much like a compressed spring. When the second photon is absorbed by the quantum dot, the stored energy is released and transferred to the newly created exciton promoting it to a higher-energy state. The energy release by the manganese ion is accompanied by the flip of its magnetic moment, known as spin. Hence this process is termed spin-exchange Auger energy transfer."

An intriguing observation of LANL scientists was the extremely short time scale of the spin-exchange Auger interactions - around one tenth of a picosecond. To their surprise, these interactions were quicker than phonon emissions, which were generally believed to be the fastest process in semiconductor materials. To prove that the new effect could beat phonon-assisted cooling, Los Alamos researchers demonstrated that properly designed magnetically doped quantum dots allowed them to extract a hot electron created by an ultraviolet photon before it loses its energy to heating the crystal lattice.

These paradigm-shifting findings open exciting opportunities for exploiting spin-exchange Auger processes in advanced schemes for boosting the performance of solar cells or driving unusual photochemical reactions. Interesting opportunities are also envisioned in areas of high-sensitivity, high-speed light detection and new types of light-driven electron sources.

###

Publication: Hot-Electron Dynamics in Quantum Dots Manipulated by Spin-Exchange Auger Interactions, Nature Nanomaterials, DOI- For Klimov's paper: https://doi.org/10.1038/s41565-019-0548-1

Funding: This work was supported by the Solar Photochemistry Program of the Chemical Sciences, Biosciences and Geosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.

About Los Alamos National Laboratory

Los Alamos National Laboratory, a multidisciplinary research institution engaged in strategic science on behalf of national security, is operated by Triad, a public service oriented, national security science organization equally owned by its three founding members: Battelle Memorial Institute (Battelle), the Texas A&M University System (TAMUS), and the Regents of the University of California (UC) for the Department of Energy's National Nuclear Security Administration.

Los Alamos enhances national security by ensuring the safety and reliability of the U.S. nuclear stockpile, developing technologies to reduce threats from weapons of mass destruction, and solving problems related to energy, environment, infrastructure, health, and global security concerns.

Media Contact

James Riordon
riordon@lanl.gov
505-667-3272

 @LosAlamosNatLab

http://www.lanl.gov 

James Riordon | EurekAlert!
Further information:
http://dx.doi.org/10.1038/s41565-019-0548-1

Further reports about: Electrons crystal lattice kinetic energy quantum dot solar cells

More articles from Physics and Astronomy:

nachricht Time-resolved measurement in a memory device
19.02.2020 | ETH Zurich

nachricht Studying electrons, bridging two realms of physics: connecting solids and soft matter
18.02.2020 | Tokyo University of Science

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: A step towards controlling spin-dependent petahertz electronics by material defects

The operational speed of semiconductors in various electronic and optoelectronic devices is limited to several gigahertz (a billion oscillations per second). This constrains the upper limit of the operational speed of computing. Now researchers from the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg, Germany, and the Indian Institute of Technology in Bombay have explained how these processes can be sped up through the use of light waves and defected solid materials.

Light waves perform several hundred trillion oscillations per second. Hence, it is natural to envision employing light oscillations to drive the electronic...

Im Focus: Freiburg researcher investigate the origins of surface texture

Most natural and artificial surfaces are rough: metals and even glasses that appear smooth to the naked eye can look like jagged mountain ranges under the microscope. There is currently no uniform theory about the origin of this roughness despite it being observed on all scales, from the atomic to the tectonic. Scientists suspect that the rough surface is formed by irreversible plastic deformation that occurs in many processes of mechanical machining of components such as milling.

Prof. Dr. Lars Pastewka from the Simulation group at the Department of Microsystems Engineering at the University of Freiburg and his team have simulated such...

Im Focus: Skyrmions like it hot: Spin structures are controllable even at high temperatures

Investigation of the temperature dependence of the skyrmion Hall effect reveals further insights into possible new data storage devices

The joint research project of Johannes Gutenberg University Mainz (JGU) and the Massachusetts Institute of Technology (MIT) that had previously demonstrated...

Im Focus: Making the internet more energy efficient through systemic optimization

Researchers at Chalmers University of Technology, Sweden, recently completed a 5-year research project looking at how to make fibre optic communications systems more energy efficient. Among their proposals are smart, error-correcting data chip circuits, which they refined to be 10 times less energy consumptive. The project has yielded several scientific articles, in publications including Nature Communications.

Streaming films and music, scrolling through social media, and using cloud-based storage services are everyday activities now.

Im Focus: New synthesis methods enhance 3D chemical space for drug discovery

After helping develop a new approach for organic synthesis -- carbon-hydrogen functionalization -- scientists at Emory University are now showing how this approach may apply to drug discovery. Nature Catalysis published their most recent work -- a streamlined process for making a three-dimensional scaffold of keen interest to the pharmaceutical industry.

"Our tools open up whole new chemical space for potential drug targets," says Huw Davies, Emory professor of organic chemistry and senior author of the paper.

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

70th Lindau Nobel Laureate Meeting: Around 70 Laureates set to meet with young scientists from approx. 100 countries

12.02.2020 | Event News

11th Advanced Battery Power Conference, March 24-25, 2020 in Münster/Germany

16.01.2020 | Event News

Laser Colloquium Hydrogen LKH2: fast and reliable fuel cell manufacturing

15.01.2020 | Event News

 
Latest News

Sweet beaks: What Galapagos finches and marine bacteria have in common

20.02.2020 | Life Sciences

Social networks reveal dating in blue tits

20.02.2020 | Life Sciences

More focus and comfort at telephone workstations

20.02.2020 | Communications Media

VideoLinks
Science & Research
Overview of more VideoLinks >>>