Solar Energy

Researchers improve efficiency of next-generation solar cell material

Published

4 years ago

February 25, 2021

sarosh

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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Solar Energy

Airbus to Provide Over 200 Sparkwing Solar Arrays for MDA AURORA Satellites

Published

2 days ago

September 17, 2024

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Airbus to Provide Over 200 Sparkwing Solar Arrays for MDA AURORA Satellites

by Clarence Oxford

Los Angeles CA (SPX) Sep 17, 2024

Airbus has been selected by MDA Space Ltd. (TSX:MDA), a global leader in advanced space technology and services, to supply solar arrays for its MDA AURORA TM software-defined satellite product line. This satellite system aims to expand communication networks across the world by enabling satellite constellations for improved global connectivity.

Under the agreement, Airbus will deliver over 200 Sparkwing solar arrays, which will be manufactured at its high-capacity facility in Leiden, the Netherlands. These solar arrays, the largest Sparkwing version to date, feature two wings with five panels each, covering a total photovoltaic area of more than 30 square meters.

MDA’s AURORA TM supply chain is designed to support Telesat’s Low Earth Orbit (LEO) satellite constellation Lightspeed, an advanced network providing enterprise-class connectivity to customers globally.

“We are delighted to be selected as the supplier of solar arrays to partner with MDA Space for Telesat Lightspeed. Our industrialised Sparkwing solar array product not only meets the demands of this ground-breaking constellation project, but is also tailored to ensure optimal performance in space. The Sparkwing solar arrays are designed for series production, ideally suited for constellations, and we will accordingly contribute to a project enabling space connectivity,” said Rob Postma, Managing Director of Airbus in the Netherlands.

MDA’s AURORA TM satellite product line is designed to address evolving technical and business needs in the satellite industry, providing unmatched flexibility and functionality. This allows operators to significantly improve the performance of satellite constellations while reducing costs and accelerating time to market.

Sparkwing is the first commercially available, off-the-shelf solar array for small satellites. Initially optimized for Low Earth Orbit missions needing power between 100W and 2000W, it offers customers various panel dimensions and configurations. The arrays can be arranged into wings with one to three panels per wing and require minimal integration effort. The product has evolved to meet the growing demands of higher power missions in LEO and beyond.

The Sparkwing product was developed by Airbus in the Netherlands with support from the Netherlands Space Office and ESA.

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Solar Energy

How solar power is keeping one California community alive as the ground shifts

Published

2 days ago

September 17, 2024

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How solar power is keeping one California community alive as the ground shifts

by Bradley Bartz

Los Angeles CA (SPX) Sep 17, 2024

The cliffs of the Palos Verdes Peninsula have always been stunning, offering sweeping views of the Pacific Ocean. But beneath the natural beauty of Portuguese Bend, a slow and terrifying force is at work. Here, in one of the most geologically unstable areas in California, the ground is in constant motion. The land is slipping into the sea at a rate of one foot per week, threatening homes and lives with every inch. The Portuguese Bend landslide, once a slow-moving anomaly, has accelerated into a full-scale disaster, and the consequences are being felt daily by the residents.

For those of us who call this place home, the landslide is not a hypothetical future threat-it’s a daily reality. The roadways buckle, driveways disappear, and utility lines fail. Southern California Edison (SCE), the local utility provider, announced a sudden shutoff of power and gas to more than 350 homes. In a cruel twist of fate, residents found themselves not only battling the land but also cut off from the essential services that tether them to modern life.

In the midst of this chaos, we at ABC Solar knew something had to be done. Our team has installed over 100 solar and battery systems in the region, but the landslide has turned this work into something more urgent, more vital. It was no longer just about helping homeowners go green-it became about survival.

Our first major site visit was at a Frank Lloyd Wright Jr. home perched above the shifting land. The house, with its futuristic design and sharp, arrow-like roofs, stood defiant against the forces below. Its driveway had become impassable, but the structure remained. We brought in Walrus Portable Battery Systems, each equipped with 30 kWh of storage, and linked them to solar panels. The owners, cut off from traditional power, now had a clean energy source that allowed them to keep the lights on, the fridge cold, and life moving forward.

And this was just the beginning.

As more homes lost power, our team worked around the clock. We deployed Walrus units to homes in the hardest-hit areas and set up temporary energy solutions. In the Sea View neighborhood, we created what nearly became a mini-grid, connecting six homes with 8 solar panels each, along with Walrus battery systems. Each day, we navigated new bumps in the road-literally. The land changed so fast that driving the same road twice meant encountering new twists and turns, fresh reminders of the ground’s instability.

The question that kept coming up wasn’t about the future of energy but the present: “Can I do my laundry today?” With each successful installation, the answer was “Yes.”

At the Portuguese Bend Riding Club, a sprawling horse ranch on Narcissa Drive, the story was much the same. Power was unreliable, and gas was shut off. When we arrived with two portable solar battery generators, it was clear this wasn’t just an inconvenience-it was a matter of safety. We hooked up the systems to power the refrigerators in two apartments and set the stage for a larger, more permanent solution. Then, at noon, Southern California Edison shut off the power to the entire property. But we didn’t miss a beat-the solar batteries took over without a hitch, bringing smiles and relief to everyone on-site.

In moments like this, the gravity of our work hit home. The loud hum of gas generators was everywhere-an unsettling reminder of the fragility of the grid and the pollution that came with it. Our mission became clear: to replace those generators with clean, quiet solar power. The transition wasn’t always easy. On a 100-degree day, when air conditioning was essential for health reasons, our systems had to stretch to their limits. But the Walrus units, backed by solar panels, rose to the challenge.

But this wasn’t just about deploying technology-it was about adapting to a new way of life. Off-grid living was foreign to many, and the psychological adjustment was just as real as the technical one. We saw it at the ranch, where 4 gas generators roared, drowning out thought and peace. But as our systems took over, the noise subsided, and a new quiet emerged. Solar power didn’t just keep the lights on-it restored a sense of normalcy.

In the coming weeks, we’ll be deploying more Sol-Ark 15kW inverters and Briggs and Stratton batteries, creating long-term solutions for homes in the landslide zone. These systems will provide not just backup power but independence-450 amps of clean energy service that can scale as needed. The future we’re building is one where the land may shift, but the power stays on.

As a neighbor in this community and the founder of ABC Solar, I’ve seen firsthand how disaster brings out both the worst and the best in systems. Southern California Edison’s threats to shut down the sewer systems sparked outrage, and rightly so. Luckily, Janice Hahn stepped in, ordering the county to keep the sewers running with generators. But it shouldn’t take a political intervention to keep basic utilities functioning. This is where renewable energy can and must step in-not just in moments of calm but in the thick of crisis.

The reality is stark: the landslide won’t stop. The homes will keep shifting, and the landscape will change. But the people here are resilient. With solar panels on their roofs and batteries in their garages, they are no longer waiting for the lights to flicker out. They are taking control of their power, their future, and their peace of mind.

For now, I roll solar batteries down the street and see the look of relief on my neighbors’ faces as the lights come back on. Each installation is a small victory against forces bigger than us. In the battle between land and life, we’re learning that the key to survival is energy-clean, renewable, and ours to keep.

Bradley Bartz is the founder and president of ABC Solar Incorporated. He lives in Rancho Palos Verdes and has been working in solar energy since 2000.

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Solar Energy

Folded or cut, this lithium-sulfur battery keeps powering devices

Published

2 days ago

September 17, 2024

sarosh

Folded or cut, this lithium-sulfur battery keeps powering devices

by Clarence Oxford

Los Angeles CA (SPX) Sep 16, 2024

Most rechargeable batteries that power portable devices, such as toys, handheld vacuums and e-bikes, use lithium-ion technology. But these batteries can have short lifetimes and may catch fire when damaged. To address stability and safety issues, researchers reporting in ‘ACS Energy Letters’ have designed a lithium-sulfur (Li-S) battery that features an improved iron sulfide cathode. One prototype remains highly stable over 300 charge-discharge cycles, and another provides power even after being folded or cut.

Sulfur has been suggested as a material for lithium-ion batteries because of its low cost and potential to hold more energy than lithium-metal oxides and other materials used in traditional ion-based versions. To make Li-S batteries stable at high temperatures, researchers have previously proposed using a carbonate-based electrolyte to separate the two electrodes (an iron sulfide cathode and a lithium metal-containing anode). However, as the sulfide in the cathode dissolves into the electrolyte, it forms an impenetrable precipitate, causing the cell to quickly lose capacity. Liping Wang and colleagues wondered if they could add a layer between the cathode and electrolyte to reduce this corrosion without reducing functionality and rechargeability.

The team coated iron sulfide cathodes in different polymers and found in initial electrochemical performance tests that polyacrylic acid (PAA) performed best, retaining the electrode’s discharge capacity after 300 charge-discharge cycles. Next, the researchers incorporated a PAA-coated iron sulfide cathode into a prototype battery design, which also included a carbonate-based electrolyte, a lithium metal foil as an ion source, and a graphite-based anode. They produced and then tested both pouch cell and coin cell battery prototypes.

After more than 100 charge-discharge cycles, Wang and colleagues observed no substantial capacity decay in the pouch cell. Additional experiments showed that the pouch cell still worked after being folded and cut in half. The coin cell retained 72% of its capacity after 300 charge-discharge cycles. They next applied the polymer coating to cathodes made from other metals, creating lithium-molybdenum and lithium-vanadium batteries. These cells also had stable capacity over 300 charge-discharge cycles. Overall, the results indicate that coated cathodes could produce not only safer Li-S batteries with long lifespans, but also efficient batteries with other metal sulfides, according to Wang’s team.

Research Report:Chelating-Type Binders toward Stable Cycling and High-Safety Transition-Metal Sulfide-Based Lithium Batteries