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Researchers improve efficiency of next-generation solar cell material

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Researchers improve efficiency of next-generation solar cell material

Perovskites are a leading candidate for eventually replacing silicon as the material of choice for solar panels. They offer the potential for low-cost, low-temperature manufacturing of ultrathin, lightweight flexible cells, but so far their efficiency at converting sunlight to electricity has lagged behind that of silicon and some other alternatives.

Now, a new approach to the design of perovskite cells has pushed the material to match or exceed the efficiency of today’s typical silicon cell, which generally ranges from 20 to 22 percent, laying the groundwork for further improvements.

By adding a specially treated conductive layer of tin dioxide bonded to the perovskite material, which provides an improved path for the charge carriers in the cell, and by modifying the perovskite formula, researchers have boosted its overall efficiency as a solar cell to 25.2 percent – a near-record for such materials, which eclipses the efficiency of many existing solar panels. (Perovskites still lag significantly in longevity compared to silicon, however, a challenge being worked on by teams around the world.)

The findings are described in a paper in the journal Nature by recent MIT graduate Jason Yoo PhD ’20, professor of chemistry and Lester Wolfe Professor Moungi Bawendi, professor of electrical engineering and computer science and Fariborz Maseeh Professor in Emerging Technology Vladimir Bulovic, and 11 others at MIT, in South Korea, and in Georgia.

Perovskites are a broad class of materials defined by the fact that they have a particular kind of molecular arrangement, or lattice, that resembles that of the naturally occurring mineral perovskite. There are vast numbers of possible chemical combinations that can make perovskites, and Yoo explains that these materials have attracted worldwide interest because “at least on paper, they could be made much more cheaply than silicon or gallium arsenide,” one of the other leading contenders. That’s partly because of the much simpler processing and manufacturing processes, which for silicon or gallium arsenide requires sustained heat of over 1,000 degrees Celsius. In contrast, perovskites can be processed at less than 200 C, either in solution or by vapor deposition.

The other major advantage of perovskite over silicon or many other candidate replacements is that it forms extremely thin layers while still efficiently capturing solar energy. “Perovskite cells have the potential to be lightweight compared to silicon, by orders of magnitude,” Bawendi says.

Perovskites have a higher bandgap than silicon, which means they absorb a different part of the light spectrum and thus can complement silicon cells to provide even greater combined efficiencies. But even using only perovskite, Yoo says, “what we’re demonstrating is that even with a single active layer, we can make efficiencies that threaten silicon, and hopefully within punching distance of gallium arsenide. And both of those technologies have been around for much longer than perovskites have.”

One of the keys to the team’s improvement of the material’s efficiency, Bawendi explains, was in the precise engineering of one layer of the sandwich that makes up a perovskite solar cell – the electron transport layer. The perovskite itself is layered with a transparent conductive layer used to carry an electric current from the cell out to where it can be used. However, if the conductive layer is directly attached to the perovskite itself, the electrons and their counterparts, called holes, simply recombine on the spot and no current flows. In the researchers’ design, the perovskite and the conductive layer are separated by an improved type of intermediate layer that can let the electrons through while preventing the recombination.

This middle electron transport layer, and especially the interfaces where it connects to the layers on each side of it, tend to be where inefficiencies occur. By studying these mechanisms and designing a layer, consisting of tin oxide, that more perfectly conforms with those adjacent to it, the researchers were able to greatly reduce the losses.

The method they use is called chemical bath deposition. “It’s like slow cooking in a Crock-Pot,” Bawendi says. With a bath at 90 degrees Celsius, precursor chemicals slowly decompose to form the layer of tin dioxide in place. “The team realized that if we understood the decomposition mechanisms of these precursors, then we’d have a better understanding of how these films form. We were able to find the right window in which the electron transport layer with ideal properties can be synthesized.”

After a series of controlled experiments, they found that different mixtures of intermediate compounds would form, depending on the acidity of the precursor solution. They also identified a sweet spot of precursor compositions that allowed the reaction to produce a much more effective film.

The researchers combined these steps with an optimization of the perovskite layer itself. They used a set of additives to the perovskite recipe to improve its stability, which had been tried before but had an undesired effect on the material’s bandgap, making it a less efficient light absorber. The team found that by adding much smaller amounts of these additives – less than 1 percent – they could still get the beneficial effects without altering the bandgap.

The resulting improvement in efficiency has already driven the material to over 80 percent of the theoretical maximum efficiency that such materials could have, Yoo says.

While these high efficiencies were demonstrated in tiny lab-scale devices, Bawendi says that “the kind of insights we provide in this paper, and some of the tricks we provide, could potentially be applied to the methods that people are now developing for large-scale, manufacturable perovskite cells, and therefore boost those efficiencies.”

In pursuing the research further, there are two important avenues, he says: to continue pushing the limits on better efficiency, and to focus on increasing the material’s long-term stability, which currently is measured in months, compared to decades for silicon cells. But for some purposes, Bawendi points out, longevity may not be so essential. Many electronic devices such as cellphones, for example, tend to be replaced within a few years anyway, so there may be some useful applications even for relatively short-lived solar cells.

“I don’t think we’re there yet with these cells, even for these kind of shorter-term applications,” he says. “But people are getting close, so combining our ideas in this paper with ideas that other people have with increasing stability could lead to something really interesting.”

Robert Hoye, a lecturer in materials at Imperial College London, who was not part of the study, says, “This is excellent work by an international team.” He adds, “This could lead to greater reproducibility and the excellent device efficiencies achieved in the lab translating to commercialized modules. In terms of scientific milestones, not only do they achieve an efficiency that was the certified record for perovskite solar cells for much of last year, they also achieve open-circuit voltages up to 97 percent of the radiative limit. This is an astonishing achievement for solar cells grown from solution.””

The team included researchers at the Korea Research Institute of Chemical Technology, the Korea Advanced Institute of Science and Technology, the Ulsan National Institute of Science and Technology, and Georgia Tech. The work was supported by MIT’s Institute for Soldier Nanotechnology, NASA, the Italian company Eni SpA through the MIT Energy Initiative, the National Research Foundation of Korea, and the National Research Council of Science and Technology.

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Argentina starts removing solar panels from Chilean border

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Argentina starts removing solar panels from Chilean border


Argentina starts removing solar panels from Chilean border

by AFP Staff Writers

Santiago (AFP) June 17, 2024






Argentina on Monday began removing solar panels that were installed by accident on the wrong side of its shared border with Chile, after a complaint from Chilean President Gabriel Boric.

In late April, the Argentine Navy inaugurated a maritime surveillance post on the border with Chile, in the Patagonia region of South America.

But the solar panels, which provide energy to that military unit, were set up on the Chilean side of the frontier.

In a statement, the Argentine Navy acknowledged the mistake and said it had “transferred personnel and means to begin the removal of a solar panel installed in the territory of the sister republic of Chile, north of the Island of Tierra del Fuego.”

Earlier in the day, Boric demanded that the panels be removed or Chile itself would do it.

“Borders are not something that can be ambiguous. It is a basic principle of respect between countries and therefore they must remove those solar panels as soon as possible or we are going to do it,” Boric told reporters during a visit to Paris.

Chile and Argentina share a border of about 5,000 kilometers (more than 3,000 miles).

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Chinese Premier Li targets clean energy in Australia visit

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Chinese Premier Li targets clean energy in Australia visit


Chinese Premier Li targets clean energy in Australia visit

by AFP Staff Writers

Sydney (AFP) June 18, 2024






Premier Li Qiang toured a Chinese-controlled lithium refiner in Perth on Tuesday, a sign of his country’s vast appetite for Australian “critical minerals” required for clean energy technologies.

Li ended his four-day visit to Australia with a tour of the low-carbon energy industry in resource-rich Western Australia.

His first stop was Tianqi Lithium Energy Australia, a 51-percent Chinese-owned venture comprising a mine for hard rock lithium ore, and a lithium refinery.

Along with at least a dozen other officials, China’s second most powerful man donned a white helmet during a rainy visit to the facility south of Perth.

The Chinese premier will also view a private research facility for clean energy-produced “green hydrogen” — touted as a fuel of the future to power heavy-duty items such as trucks and blast furnaces.

Australia extracts 52 percent of the world’s lithium, the vast majority of it exported as an ore to China for eventual refining and use in batteries, notably in China’s world-dominant electric vehicle industry.

But despite being a huge Australian customer, China’s involvement in the country’s critical mineral industry is sensitive because of its dominance of global supply chains.

Australia has only recently begun refining lithium rather than exporting the ore.

And the government has announced a strategic plan to develop new supply chains with friendly countries for critical minerals such as lithium, nickel and so-called rare earths.

Earlier this year, the government ordered five China-linked shareholders to sell off a combined 10 percent stake in Northern Minerals, a producer of the rare earth dysprosium.

Such foreign ownership was against Australia’s “national interests”, Treasurer Jim Chalmers said.

About 99 percent of the world’s dysprosium — used in high-performance magnets — is currently produced in China.

China has invested in critical minerals in Latin America, Africa and Australia over the past 10-20 years, said Marina Zhang, associate professor at the University of Technology Sydney’s Australia-China Relations Institute.

Developing supply chains independent of China is “fine and dandy” but unlikely to be achieved even in the short to medium term, she said.

“We are facing a very time-pressing issue that is fighting against climate change — so that issue should be at the centre of the discourse,” Zhang said.

“But unfortunately the Western allies are taking the approach that China’s dominance across the supply chains of critical minerals is imposing national security threats,” she said.

China’s narrative, however, was that it was investing and making a contribution to sustainability and environmental protection, the analyst said.

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Rice Lab Reports Significant Advances in Perovskite Solar Cell Stability

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Rice Lab Reports Significant Advances in Perovskite Solar Cell Stability


Rice Lab Reports Significant Advances in Perovskite Solar Cell Stability

by Clarence Oxford

Los Angeles CA (SPX) Jun 18, 2024






Solar power is growing rapidly as an energy technology, recognized for its cost-effectiveness and its role in reducing greenhouse gas emissions.

A Rice University study published in Science details a method for synthesizing formamidinium lead iodide (FAPbI3) into stable, high-quality photovoltaic films. The efficiency of these FAPbI3 solar cells declined by less than 3% over more than 1,000 hours of operation at 85 degrees Celsius (185 Fahrenheit).



“Right now, we think that this is state of the art in terms of stability,” said Rice engineer Aditya Mohite. “Perovskite solar cells have the potential to revolutionize energy production, but achieving long-duration stability has been a significant challenge.”



This breakthrough represents a major step towards making perovskite photovoltaics commercially viable. The researchers added specially designed two-dimensional (2D) perovskites to the FAPbI3 precursor solution, which served as a template to enhance the stability of the crystal lattice structure.



“Perovskite crystals get broken in two ways: chemically – destroying the molecules that make up the crystal – and structurally – reordering the molecules to form a different crystal,” explained Isaac Metcalf, a Rice graduate student and a lead author on the study. “Of the various crystals that we use in solar cells, the most chemically stable are also the least structurally stable and vice versa. FAPbI3 is on the structurally unstable end of that spectrum.”



The researchers found that while 2D perovskites are more stable, they are less effective at harvesting light. By using 2D perovskites as templates, they improved the stability and efficiency of FAPbI3 films. The addition of well-matched 2D crystals facilitated the formation of high-quality FAPbI3 films, showing less internal disorder and better illumination response.



The study showed that solar cells with 2D templates retained their efficiency and durability significantly better than those without. Encapsulation layers further enhanced the stability of these solar cells, extending their operational life to timescales relevant for commercial applications.



“Perovskites are soluble in solution, so you can take an ink of a perovskite precursor and spread it across a piece of glass, then heat it up and you have the absorber layer for a solar cell,” Metcalf said. “Since you don’t need very high temperatures – perovskite films can be processed at temperatures below 150 Celsius (302 Fahrenheit) – in theory that also means perovskite solar panels can be made on plastic or even flexible substrates, which could further reduce costs.”



Silicon, the most commonly used semiconductor in photovoltaic cells, requires more resource-intensive manufacturing processes than perovskites, which have seen efficiency improvements from 3.9% in 2009 to over 26% currently.



“It should be much cheaper and less energy-intensive to make high-quality perovskite solar panels compared to high-quality silicon panels, because the processing is so much easier,” Metcalf said.



“We need to urgently transition our global energy system to an emissions-free alternative,” he added, referring to UN estimates that highlight the importance of solar energy in replacing fossil fuels.



Mohite emphasized that advancements in solar energy technologies are crucial for meeting the 2030 greenhouse gas emissions target and preventing a 1.5 degrees Celsius rise in global temperatures, essential for achieving net zero carbon emissions by 2050.



“If solar electricity doesn’t happen, none of the other processes that rely on green electrons from the grid, such as thermochemical or electrochemical processes for chemical manufacturing, will happen,” Mohite said. “Photovoltaics are absolutely critical.”



Mohite holds the title of William M. Rice Trustee Professor at Rice, is a professor of chemical and biomolecular engineering, and directs the Rice Engineering Initiative for Energy Transition and Sustainability. The study’s lead authors also include Siraj Sidhik, a Rice doctoral alumnus.



“I would like to give a lot of credit to Siraj, who started this project based on a theoretical idea by Professor Jacky Even at the University of Rennes,” Mohite said. “I would also like to thank our collaborators at the national labs and at several universities in the U.S. and abroad whose help was instrumental to this work.”



Research Report:Two-dimensional perovskite templates for durable, efficient formamidinium perovskite solar cells


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