Solar Energy

Researchers improve efficiency of next-generation solar cell material

Published

4 years ago

February 25, 2021

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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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Solar Energy

Hybrid Transparent Electrodes Boost Efficiency and Lifespan of Perovskite Solar Cells

Published

5 days ago

March 6, 2025

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Hybrid Transparent Electrodes Boost Efficiency and Lifespan of Perovskite Solar Cells

by Simon Mansfield

Sydney, Australia (SPX) Feb 21, 2025

Bifacial perovskite solar cells, known for their ability to capture sunlight from both the front and rear surfaces, have taken a significant step forward thanks to researchers at the Indian Institute of Technology (IIT) Dharwad. Their development of a novel NiO/Ag/NiO (NAN) hybrid transparent electrode has led to enhancements in efficiency, durability, and infrared transparency, opening new possibilities for solar energy applications.

A recent study published in the Journal of Photonics for Energy (JPE) details how the IIT Dharwad team designed and fabricated highly transparent bifacial solar cells utilizing a three-layer NAN electrode. This innovative structure, created using a low-energy physical vapor deposition method, resulted in an electrode with extremely low electrical resistance and high transmittance of visible light.

When incorporated into the bifacial solar cells, the NAN transparent electrode delivered impressive power conversion efficiencies (PCE), achieving 9.05% and 6.54% when exposed to light from different directions. The cells also exhibited a high bifaciality factor of 72%, demonstrating their effectiveness in utilizing light from both sides.

Beyond efficiency, these solar cells displayed exceptional durability, retaining 80% of their initial performance for over 1,000 hours without the need for protective encapsulation. Additionally, their ability to transmit substantial near-infrared light makes them suitable for applications such as thermal windows and advanced optoelectronic technologies.

With a thickness of less than 40 nm, the NAN electrode is particularly advantageous for integration into building materials and tandem solar cell systems. Senior researcher Dhriti Sundar Ghosh, an associate professor of physics at IIT Dharwad, emphasized the broad implications of their work, stating, “This study offers a blueprint for designing transparent electrodes in bifacial perovskite solar cells, paving the way for advancements in tandem devices, agrivoltaics, and automotive solar technologies.”

The findings reinforce the growing potential of bifacial perovskite solar cells in renewable energy solutions, contributing to the development of more efficient and adaptable solar power technologies.

Research Report:Hybrid top transparent electrode for infrared-transparent bifacial perovskite solar cells

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Solar Energy

Bio-inspired approach creates bespoke photovoltaics

Published

5 days ago

March 6, 2025

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Bio-inspired approach creates bespoke photovoltaics

by David Nutt for Cornell Chronicle

Ithica NY (SPX) Feb 21, 2025

There is more to photovoltaic panels than the materials that comprise them: The design itself can also drive – or potentially diminish – the widespread adoption of solar technology.

Put bluntly: Most solar panels are not much to look at. And their flat, nonflexible composition means they can only be affixed to similarly flat structures. But what if photovoltaic panels were instead a hinged, lightweight fabric that was aesthetically attractive and could wrap around complex shapes, even contorting its form to better absorb sunlight?

Thus was born the idea for HelioSkin, an interdisciplinary project led by Jenny Sabin, the Arthur L. and Isabel B. Weisenberger Professor in Architecture in the College of Architecture, Art and Planning at Cornell University, in collaboration with Itai Cohen, professor of physics in the College of Arts and Sciences, and Adrienne Roeder, professor in the Section of Plant Biology in the School of Integrative Plant Science, in the College of Agriculture and Life Sciences and at the Weill Institute for Cell and Molecular Biology.

“What we’re really passionate about is how the system could not only produce energy in a passive way, but create transformational environments in urban or urban-rural settings,” Sabin said. “Sustainability is about performance and function, but equally, it’s about beauty and getting people to get excited about it, so they want to participate. The grand goal is to inspire widespread adoption of solar for societal impact.”

Sabin, the inaugural chair of the new multicollege Department of Design Tech, has made a career of collaborating with diverse disciplines and taking cues not just from architecture, but also engineering. And physics. And mathematics. And, perhaps most importantly, biology. All of her projects are united by the same question: How might buildings and their integrated material systems behave more like organisms, responding and adapting to their local environments?

“Nature is not efficient,” Sabin said. “It’s resilient, and biology is in it for the long game, over much longer time scales. Additionally, it has been demonstrated that plants that track the sun exhibit a photosynthetic advantage. And we think that’s a pretty powerful way to think about sustainability and resiliency in architecture.”

Sabin’s design interests address a very real need. The primary convergent problem is that 40% of total greenhouse gas emissions in the United States comes from buildings, according to the International Energy Agency.

“By developing a new solar skin product that can scale, we aim to turn the needle by getting homeowners and businesses to adopt solar to reduce the 28% of CO2 that comes from the heating, lighting and cooling of buildings,” Sabin said.

HelioSkin originated in a partnership between Sabin and Mariana Bertoni, an energy engineer at Arizona State University, who is also a member of the HelioSkin team. Together they combined computational design, digital fabrication and 3D printing to create customized filters and photovoltaic panel assemblies – what Sabin calls “nonstandard angularity” – that could simultaneously boost light absorption and architectural beauty. The key to that effort was looking at the mechanics of heliotropism – how sunflowers track sunlight.

For HelioSkin, that research foundation expanded to include Roeder’s expertise in heliotropism and cellular morphogenesis – i.e., how plant cells grow to bend the plant toward the sun – and Cohen’s specialization in using geometric methods such as origami and kirigami to improve the mechanical performance of metamaterials, increasing their flexibility while expending very little energy.

The flowering Arabidopsis plant is an ideal model for HelioSkin because, as “the fruit fly of the plant world” according to Roeder, it’s easy to study at the cellular level. Those cells play a vital role in changing the curvature of the plant’s stem as it angles toward the sunlight, with the Arabidopsis’ hormones causing the cells on its sunless side to expand by 25%, bending the stem 90 degrees.

“We’ve already figured out how to translate our plant cells’ tracking mechanism into Jenny’s architectural software,” Roeder said. “Now we have to start figuring out how to make that transition in HelioSkin.”

‘The human-centered design process’

The ultimate goal is to generate a mechanically tracking solar-collection skin for retractable roofs, stadiums and skyscrapers, but to get there, the team is launching a three-year pilot project whereby they create small solar canopies for backyards, which can then be scaled up for urban parks.

Bringing that vision to market not only involves scientific innovation and smart design, but requires industry partnerships, capital and a marketing plan.

The project was launched through the National Science Foundation’s Convergence Accelerator program, which last year awarded the team $650,000 in phase I funding. The team has applied for the next phase of funding – $5 million over three years.

The industry partners include E Ink and Rainier Industries, which are helping integrate photovoltaics and ePaper onto lightweight, stretchable architectural fabric. SunFlex, a company that uses laser-welded back contact module technology for photovoltaics manufacturing, is onboard to help refine the HelioSkin prototypes in phase 2 – the sensing, the wiring, the arrangement of the panels, plus the geometry and substrate.

By the pilot project’s second year, the team plans to have a full-scale backyard canopy prototype that can potentially provide light and power outdoor appliances; by the third year, they aim to be in the early stages of commercialization.

As part of their commercialization plan, the team conducted extensive marketing analysis and interviews that showed HelioSkin’s gross cost, the cost-per-watt and system capacity were competitive with existing PV products.

“This was a really encouraging and exciting process to go through, to see how we compare to existing products and the potential that we have to then scale,” Sabin said. “The human-centered design process, including engaging people in many different industries, from end users to potential stakeholders to people that work for the energy grid and the state or the region – that’s been a big part of our process, and it’s been really helpful.”

The analysis revealed niche applications that the team hadn’t initially considered, such as “big box” commercial businesses that want to pursue solar to attain net-zero emissions but are also interested in display advertising or colorful pattern change for aesthetic applications. To that end, the team is working with E Ink to create a HelioSkin with electrically powered responsive display features, so solar skins can be placed on retail structures and stadiums and function as ever-changing billboards.

“This was something that came out of interviews,” Sabin said. “We had never thought about these types of applications.”

One of the virtues of working with E Ink is the company uses roll-to-roll printing to mass produce photovoltaic sheets – the same method that makes the low-cost manufacturing of perovskite photovoltaics feasible.

“The basic idea is to try to print things in 2D, which is cheap, and then morph it into 3D, allowing it to curve around structures,” Cohen said. “You can’t just take a normal sheet of paper and wrap something. It’s going to have all sorts of creases to it. Like if you try to wrap an orange, you get all these crinkles. One of the innovations that we came up with was to cut the paper into a pattern of panels and hinges that allows it to locally stretch around these round objects. A second strategy we came up with is to use fabric as a way to make the hinge. Fabric is floppy enough to give you that hinge-like behavior.”

In her experimental architecture practice, Sabin has spent more than 15 years developing large urban-scale canopies and architectural installations, experience that has served her well in launching a product.

“There’s a strong focus on commercialization and developing IP management plans. As a designer, I have a practice, and so I find this really interesting,” Sabin said. “But it’s also completely new for most of my collaborators. They don’t necessarily think about this level of application and spinning out a product. So the learning curve around that is pretty steep for all of us.”

The ability to collaborate across disciplines is what initially drew Sabin to Cornell in 2011. It’s a place where “everybody has their door open,” she said. The excitement, and the opportunities for impact, are palpable.

“Bottom line, we are in New York’s mecca for solar,” she said. “So there’s a lot going on, both in terms of innovative research, but also applied systems, in farming and agrivoltaics, solar farms, etc. So that dynamic community of people actively working on a common set of goals and questions and problems is super exciting for us, too.”

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Solar Energy

China aims to add 200 GW in renewables

Published

7 days ago

March 4, 2025

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China aims to add 200 GW in renewables

by Simon Mansfield

Sydney, Australia (SPX) Mar 04, 2025

China is poised to make another substantial push in renewable energy expansion this year, targeting the addition of more than 200 gigawatts of renewable capacity. According to the National Energy Administration (NEA), this will contribute to an overall power generation capacity of approximately 10.6 trillion kilowatt-hours in 2025.

The nation’s total installed power capacity is expected to exceed 3.6 billion kilowatts by the end of the year, as outlined in the NEA’s newly released energy work guidelines. China is also advancing efforts to establish a unified national power market, with non-fossil fuel power generation projected to make up around 60 percent of total installed capacity. Additionally, non-fossil energy is anticipated to constitute about 20 percent of total energy consumption.

Industry analysts indicate that while new market-based pricing mechanisms for renewable energy grid connections introduce some uncertainty, the 200 GW target, though moderate, still provides ample opportunities for stakeholders in the renewable energy sector.

“The 200 GW installation goal for this year accounts for just 56 percent of the total wind and solar capacity added in 2024, but it underscores China’s continued commitment to renewable energy,” noted Zhu Yicong, vice-president of renewables and power research at Rystad Energy.

Zhu also acknowledged concerns raised following the NEA’s latest directive requiring renewable energy producers to fully integrate into power markets and adhere to market-based electricity pricing from June. “Although a vast number of renewable projects are either under development or nearing construction across various provinces, uncertainties regarding future financial returns could lead to delays in project implementation,” she said.

To enhance the market value of renewable energy and align prices with supply-demand dynamics, the National Development and Reform Commission and the NEA recently issued a notice emphasizing competitive market mechanisms for electricity pricing.

Industry projections suggest that renewable electricity prices could decline under the new pricing system, given the low variable costs associated with sources such as solar power, particularly during peak daylight hours. This price decline could introduce hesitation among investors assessing new projects.

Despite a relatively modest target for new installations this year, the industry sees this as a strategic approach, allowing developers time to adapt to evolving market conditions. “The moderate goal enables market participants to refine sustainable strategies without facing excessive pressure for rapid installation,” Zhu added.

Experts recommend that renewable energy developers navigate the transition to market-driven pricing by securing power purchase agreements, integrating battery storage solutions, and optimizing energy output for competitiveness.

China continues to prioritize renewable energy as a fundamental component of its green economy and dual-carbon objectives. In 2024, newly installed renewable capacity accounted for 86 percent of the nation’s total new power installations. The cumulative share of renewables in the country’s total installed capacity reached a record 56 percent, according to NEA data.

While renewable energy development surges, China’s overall energy production is set to maintain steady growth. Coal production will remain stable with some planned expansion, while crude oil output is expected to stay above 200 million metric tons. The country also plans to bolster its oil and gas reserves to enhance energy security.

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