Solar Energy
Study highlights improved efficiency for hot carrier solar cells
Study highlights improved efficiency for hot carrier solar cells
by Clarence Oxford
Los Angeles CA (SPX) Sep 25, 2024
Hot carrier solar cells, first proposed decades ago, have been a key focus for surpassing the Shockley – Queisser efficiency limit in single-junction solar cells. Despite their theoretical advantages, these cells have faced significant challenges, particularly in rapidly extracting hot electrons across material interfaces.
Recent studies have investigated using satellite valleys in the conduction band to temporarily store hot electrons before extraction. However, a parasitic barrier at the interface between the absorber and extraction layers has posed a major obstacle. This barrier complicates electron transfer, which occurs in real space rather than momentum space. When the energy bands between materials aren’t perfectly aligned, electrons bypass the barrier through a tunneling process, which is affected by complex band structures.
In a new study published in the ‘Journal of Photonics for Energy (JPE)’, researchers explored evanescent states and their impact on electron tunneling using an empirical pseudopotential method. This approach helped calculate energy bands in momentum space and aligned them with experimental data, offering valuable insights into the mechanics of hot carrier extraction between valley states and across material interfaces.
The research provides a deeper understanding of tunneling processes and could lead to more efficient hot carrier solar cells, potentially breaking the efficiency limits of current solar technologies.
The study specifically highlighted that the tunneling coefficient, which measures how easily electrons move through the barrier, is exponentially large in indium-aluminum-arsenide (InAlAs) and indium-gallium-arsenide (InGaAs) structures due to mismatched energy bands. Even slight roughness at the interface-just a few atoms thick-can severely hamper electron transfer, which aligns with observed performance issues in experimental devices using these materials.
However, the situation improves with aluminum-gallium-arsenide (AlGaAs) and gallium-arsenide (GaAs) structures. In these systems, aluminum in the barrier creates degeneracy in lower energy satellite valleys, leading to better energy band alignment and more efficient electron transfer. The tunneling coefficient in AlGaAs/GaAs structures can be as high as 0.5 to 0.88, depending on the aluminum composition, suggesting a significantly more efficient transfer process.
These findings hint at the potential for valley photovoltaics, which could allow for solar cells that exceed current single bandgap efficiency limits. In high-electron mobility transistors made from AlGaAs/GaAs, electron transfer from AlGaAs to GaAs is common, but hot carriers in GaAs can also gain enough energy to transfer back to AlGaAs-a process known as real-space transfer. While usually undesirable in transistors, this process is beneficial for valley photovoltaics, where efficient hot carrier storage and transfer are crucial.
Research Report:On the use of complex band structure to study valley photovoltaics: toward efficient hot carrier extraction
Related Links
International Society for Optics and Photonics
All About Solar Energy at SolarDaily.com
Solar Energy
Bolivia announces $1 bn deal with China to build lithium plants
Bolivia announces $1 bn deal with China to build lithium plants
by AFP Staff Writers
La Paz (AFP) Nov 27, 2024
Bolivia said Tuesday it had signed a $1 billion deal with China’s CBC, a subsidiary of the world’s largest lithium battery producer CATL, to build two lithium carbonate production plants in the country’s southwest.
Bolivia’s state-owned Bolivia Lithium Deposits (YLB) said the plants — one with an annual capacity of 10,000 tons of lithium carbonate and the other of 25,000 – would be situated in the vast Uyuni salt flats.
Lithium, nicknamed “white gold,” is a key component in the production of batteries for electric vehicles and mobile phones.
Bolivia claims to have the world’s largest lithium deposits.
President Luis Arce, who presided over Tuesday’s signing ceremony, said it paved the way for Bolivia to become “a very important player in determining the international price of lithium.”
The deal follows an earlier agreement reached last year between Russia’s Uranium One Group and YLB to build a $970 million lithium extraction facility, also in Uyuni.
Both deals have yet to be approved by Bolivia’s parliament.
Arce announced that negotiations were underway with China’s Citic Guoan Group for a third contract.
“We hope to close that deal as soon as possible,” he said.
Related Links
Solar Energy
The future of AI with solar-powered synaptic devices
The future of AI with solar-powered synaptic devices
by Riko Seibo
Tokyo, Japan (SPX) Nov 26, 2024
Artificial intelligence (AI) is increasingly relied upon for predicting critical events such as heart attacks, natural disasters, and infrastructure failures. These applications demand technologies capable of rapidly processing data. One such promising approach is reservoir computing, particularly physical reservoir computing (PRC), known for its efficiency in handling time-series data with minimal power consumption. Optoelectronic artificial synapses in PRC, mimicking human neural synaptic structures, are poised to enable advanced real-time data processing and recognition akin to the human visual system.
Existing self-powered optoelectronic synaptic devices, however, struggle to process time-series data across diverse timescales, which is essential for applications in environmental monitoring, infrastructure maintenance, and healthcare.
Addressing this challenge, researchers at Tokyo University of Science (TUS), led by Associate Professor Takashi Ikuno and including Hiroaki Komatsu and Norika Hosoda, have developed an innovative self-powered dye-sensitized solar cell-based optoelectronic photopolymeric human synapse. This groundbreaking device, featuring a controllable time constant based on input light intensity, represents a major advancement in the field. The study, published on October 28, 2024, in ‘ACS Applied Materials and Interfaces’, highlights the potential of this technology.
Dr. Ikuno explained, “To process time-series input optical data with various time scales, it is essential to fabricate devices according to the desired time scale. Inspired by the afterimage phenomenon of the eye, we came up with a novel optoelectronic human synaptic device that can serve as a computational framework for power-saving edge AI optical sensors.”
The new device integrates squarylium derivative-based dyes, incorporating optical input, AI computation, analog output, and power supply at the material level. It demonstrates synaptic plasticity, exhibiting features such as paired-pulse facilitation and depression in response to light intensity. The device achieves high computational performance in time-series data processing tasks while maintaining low power consumption, regardless of the input light pulse width.
Remarkably, the device achieved over 90% accuracy in classifying human movements, including bending, jumping, running, and walking, when used as the reservoir layer of PRC. Its power consumption is only 1% of that required by traditional systems, significantly reducing carbon emissions. Dr. Ikuno emphasized, “We have demonstrated for the first time in the world that the developed device can operate with very low power consumption and yet identify human motion with a high accuracy rate.”
This innovation holds significant promise for edge AI applications, including surveillance cameras, automotive sensors, and health monitoring systems. “This invention can be used as a massively popular edge AI optical sensor that can be attached to any object or person,” noted Dr. Ikuno. He further highlighted its potential to improve vehicle energy efficiency and reduce costs in standalone smartwatches and medical devices.
The novel solar cell-based device could redefine energy-efficient edge AI sensors across various applications, marking a significant leap forward in both technology and sustainability.
Research Report:Self-Powered Dye-Sensitized Solar-Cell-Based Synaptic Devices for Multi-Scale Time-Series Data Processing in Physical Reservoir Computing
Related Links
Tokyo University of Science
All About Solar Energy at SolarDaily.com
Solar Energy
Decarbonizing heavy industry with thermal batteries
Decarbonizing heavy industry with thermal batteries
by Zach Winn | MIT News
Boston MA (SPX) Nov 27, 2024
Whether you’re manufacturing cement, steel, chemicals, or paper, you need a large amount of heat. Almost without exception, manufacturers around the world create that heat by burning fossil fuels.
In an effort to clean up the industrial sector, some startups are changing manufacturing processes for specific materials. Some are even changing the materials themselves. Daniel Stack SM ’17, PhD ’21 is trying to address industrial emissions across the board by replacing the heat source.
Since coming to MIT in 2014, Stack has worked to develop thermal batteries that use electricity to heat up a conductive version of ceramic firebricks, which have been used as heat stores and insulators for centuries. In 2021, Stack co-founded Electrified Thermal Solutions, which has since demonstrated that its firebricks can store heat efficiently for hours and discharge it by heating air or gas up to 3,272 degrees Fahrenheit – hot enough to power the most demanding industrial applications.
Achieving temperatures north of 3,000 F represents a breakthrough for the electric heating industry, as it enables some of the world’s hardest-to-decarbonize sectors to utilize renewable energy for the first time. It also unlocks a new, low-cost model for using electricity when it’s at its cheapest and cleanest.
“We have a global perspective at Electrified Thermal, but in the U.S. over the last five years, we’ve seen an incredible opportunity emerge in energy prices that favors flexible offtake of electricity,” Stack says. “Throughout the middle of the country, especially in the wind belt, electricity prices in many places are negative for more than 20 percent of the year, and the trend toward decreasing electricity pricing during off-peak hours is a nationwide phenomenon. Technologies like our Joule Hive Thermal Battery will enable us to access this inexpensive, clean electricity and compete head to head with fossil fuels on price for industrial heating needs, without even factoring in the positive climate impact.”
A new approach to an old technology
Stack’s research plans changed quickly when he joined MIT’s Department of Nuclear Science and Engineering as a master’s student in 2014.
“I went to MIT excited to work on the next generation of nuclear reactors, but what I focused on almost from day one was how to heat up bricks,” Stack says. “It wasn’t what I expected, but when I talked to my advisor, [Principal Research Scientist] Charles Forsberg, about energy storage and why it was valuable to not just nuclear power but the entire energy transition, I realized there was no project I would rather work on.”
Firebricks are ubiquitous, inexpensive clay bricks that have been used for millennia in fireplaces and ovens. In 2017, Forsberg and Stack co-authored a paper showing firebricks’ potential to store heat from renewable resources, but the system still used electric resistance heaters – like the metal coils in toasters and space heaters – which limited its temperature output.
For his doctoral work, Stack worked with Forsberg to make firebricks that were electrically conductive, replacing the resistance heaters so the bricks produced the heat directly.
“Electric heaters are your biggest limiter: They burn out too fast, they break down, they don’t get hot enough,” Stack explains. “The idea was to skip the heaters because firebricks themselves are really cheap, abundant materials that can go to flame-like temperatures and hang out there for days.”
Forsberg and Stacks were able to create conductive firebricks by tweaking the chemical composition of traditional firebricks. Electrified Thermal’s bricks are 98 percent similar to existing firebricks and are produced using the same processes, allowing existing manufacturers to make them inexpensively.
Toward the end of his PhD program, Stack realized the invention could be commercialized. He started taking classes at the MIT Sloan School of Management and spending time at the Martin Trust Center for MIT Entrepreneurship. He also entered the StartMIT program and the I-Corps program, and received support from the U.S. Department of Energy and MIT’s Venture Mentoring Service (VMS).
“Through the Boston ecosystem, the MIT ecosystem, and with help from the Department of Energy, we were able to launch this from the lab at MIT,” Stack says. “What we spun out was an electrically conductive firebrick, or what we refer to as an e-Brick.”
Electrified Thermal contains its firebrick arrays in insulated, off-the-shelf metal boxes. Although the system is highly configurable depending on the end use, the company’s standard system can collect and release about 5 megawatts of energy and store about 25 megawatt-hours.
The company has demonstrated its system’s ability to produce high temperatures and has been cycling its system at its headquarters in Medford, Massachusetts. That work has collectively earned Electrified Thermal $40 million from various the Department of Energy offices to scale the technology and work with manufacturers.
“Compared to other electric heating, we can run hotter and last longer than any other solution on the market,” Stack says. “That means replacing fossil fuels at a lot of industrial sites that couldn’t otherwise decarbonize.”
Scaling to solve a global problem
Electrified Thermal is engaging with hundreds of industrial companies, including manufacturers of cement, steel, glass, basic and specialty chemicals, food and beverage, and pulp and paper.
“The industrial heating challenge affects everyone under the sun,” Stack says. “They all have fundamentally the same problem, which is getting their heat in a way that is affordable and zero carbon for the energy transition.”
The company is currently building a megawatt-scale commercial version of its system, which it expects to be operational in the next seven months.
“Next year will be a huge proof point to the industry,” Stack says. “We’ll be using the commercial system to showcase a variety of operating points that customers need to see, and we’re hoping to be running systems on customer sites by the end of the year. It’ll be a huge achievement and a first for electric heating because no other solution in the market can put out the kind of temperatures that we can put out.”
By working with manufacturers to produce its firebricks and casings, Electrified Thermal hopes to be able to deploy its systems rapidly and at low cost across a massive industry.
“From the very beginning, we engineered these e-bricks to be rapidly scalable and rapidly producible within existing supply chains and manufacturing processes,” Stack says. “If you want to decarbonize heavy industry, there will be no cheaper way than turning electricity into heat from zero-carbon electricity assets. We’re seeking to be the premier technology that unlocks those capabilities, with double digit percentages of global energy flowing through our system as we accomplish the energy transition.”
Related Links
Electrified Thermal Solutions
Powering The World in the 21st Century at Energy-Daily.com
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