Solar Energy

Study highlights improved efficiency for hot carrier solar cells

Published

2 months ago

September 25, 2024

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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

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Solar Energy

Record efficiency achieved with perovskite and organic tandem solar cells

Published

1 hour ago

December 4, 2024

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Record efficiency achieved with perovskite and organic tandem solar cells

by Robert Schreiber

Berlin, Germany (SPX) Dec 04, 2024

Researchers at the University of Potsdam have unveiled a tandem solar cell combining perovskite and organic materials that sets a new efficiency benchmark of 25.7%. This advancement leverages low-temperature processing methods to reduce the carbon footprint while maximizing energy absorption across the solar spectrum.

The new solar cell employs two materials that absorb distinct parts of sunlight: perovskites capture blue and green wavelengths, while a novel organic layer targets red and infrared wavelengths. These tandem designs optimize the use of sunlight for higher efficiency compared to traditional technologies like silicon or copper indium gallium selenide (CIGS), which require high-temperature processing and have a greater environmental impact.

Felix Lang, a lead researcher on the project, explained that achieving this efficiency required two key innovations. “This was only possible by combining two major breakthroughs,” Lang said. The first was the development of an organic solar cell by Meng and Li, which extended infrared absorption capabilities. “Still, tandem solar cells were limited by the perovskite layer, which shows strong efficiency losses if adjusted to absorb only blue/green parts of the sun spectrum,” Lang explained.

To overcome this, the team applied a novel passivation layer to the perovskite. This isomeric diammonium passivation layer addresses material defects, significantly enhancing the overall performance of the tandem cell.

The study, titled “Isomeric diammonium passivation for perovskite-organic tandem solar cells,” is now published in *Nature*.

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Solar Energy

Bolivia announces $1 bn deal with China to build lithium plants

Published

7 days ago

November 27, 2024

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Bolivia announces 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.

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Solar Energy

The future of AI with solar-powered synaptic devices

Published

7 days ago

November 27, 2024

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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