Solar Energy

The perfect recipe for efficient perovskite solar cells

Published

3 years ago

February 24, 2021

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The perfect recipe for efficient perovskite solar cells

They have improved a process for vertically depositing a solution made from an inexpensive perovskite solute onto a moving substrate below. Not only have they discovered the crucial role played by one of the solvents used, but they have also taken a closer look at the aging and storage properties of the solution.

Solar cells made of crystalline silicon still account for the lion’s share of roof installations and solar farms. But other technologies have long since become established as well – such as those that convert sunlight into electrical energy through use of extremely thin layers of solar-cell material deposited upon a substrate. The perovskite solar cells that Prof. Eva Unger and her team at the Helmholtz-Zentrum Berlin (HZB) are researching belong to this group. “”These are the best solar cells to date that can be made using a 2D ink”, the researcher explains. “”And now their efficiencies are approaching those for cells made of crystalline silicon.””

Developing scalable methods

Many methods have been developed and used to fabricate small test cells in the laboratory, where they can be studied and improved. But industrial-scale fabrication is still a long way off. Unger knows from her own experience: “Unfortunately, processes that are optimised for fabricating small surface areas cannot always be scaled up.”

In other words: Not everything that works perfectly in the lab also necessarily works economically on the factory floor. “That’s why we are taking the next step and developing scalable methods. This means our team is focussing on processes for coating larger surfaces.” At the Hybrid Silicon Perovskite Research, Integration and Novel Technologies (HySPRINT) Innovation Lab, an infrastructure for collaboration between HZB and industry, the team is concentrating on processes that have already proven their importance in industry to start with.

“We have experimented here with slot-die coating”, she explains. In this process, the “ink”, as the thin liquid solution of perovskite precursor, solvent, and additive is known in the trade, flows from a slit-shaped nozzle and falls like a curtain onto the glass substrate being conveyed below that will later become a solar cell. After application, crystallisation begins. An ultra-thin layer of a semiconducting perovskite structure grows that gives the material group its name and the solar cell its capabilities.

Unger, together with her team members doctoral student Jinzhao Li and Dr. Janardan Dagar, have now discovered that the exact amount of an organic solvent called dimethyl sulfoxide (DMSO) in the material ink is critical for this process. Unger uses it as an additive because it has an amazing effect on the ink.

“”DMSO induces crystallisation nuclei for the perovskite”, says the researcher. Crystallisation nuclei usually are tiny grains that help jump-start a crystal and promote its growth. “”During X-ray diffraction experiments at BESSY II, we saw quite a big difference between inks with and without DMSO added”, the physical chemist explains.

It’s the amount that counts

However, as her team has found out in many experiments, the amount added plays a decisive role here. More DMSO favours crystal growth – up to a certain point. If this is exceeded, other processes come into play and the resulting microstructure reduces the performance of the solar cells. “It’s like seasoning a soup”, says Unger.

“If you add too little, it remains bland. If you add too much, it won’t taste good either. So you need to add just the right amount to make it best.” In addition to the optimal composition, the HZB team has also thoroughly investigated the ageing processes and thus the storage life of the inks. “This is an aspect that has received little attention so far”, Unger explains. “The age of a perovskite precursor ink can influence device performance. This is an important factor that must be considered when developing inks and processes.”

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Solar Energy

3D-printed microstructure forest enhances solar steam desalination

Published

3 days ago

July 24, 2024

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3D-printed microstructure forest enhances solar steam desalination

by Clarence Oxford

Los Angeles CA (SPX) Jul 24, 2024

To address the global freshwater scarcity issue, researchers in Singapore have developed advanced solar steam generators (SSGs) for seawater desalination. This method, powered by renewable energy, mimics the natural water cycle by using solar energy to evaporate and purify water, offering a potentially cost-effective solution compared to traditional, energy-intensive desalination techniques. However, current SSG technologies face limitations due to the complexity of fabricating designs that maximize surface area for optimal water evaporation.

Drawing inspiration from nature, the team utilized 3D printing to create innovative SSGs. Their findings, published in Applied Physics Reviews, highlight a novel technique for manufacturing efficient SSGs and introduce a groundbreaking method for printing functional nanocomposites using multi-jet fusion (MJF).

“We created SSGs with exceptional photothermal performance and self-cleaning properties,” said Kun Zhou, a professor of mechanical engineering at Nanyang Technological University. “Using a treelike porous structure significantly enhances water evaporation rates and ensures continuous operation by preventing salt accumulation – its performance remains relatively stable even after prolonged testing.”

The technology works by converting light to thermal energy, where SSGs absorb solar energy and convert it to heat to evaporate water. The porous structure of the SSGs aids in self-cleaning by removing accumulated salt, ensuring sustained desalination performance.

“By using an effective photothermal fusing agent, MJF printing technology can rapidly create parts with intricate designs,” Zhou added. “To improve the photothermal conversion efficiency of fusing agents and printed parts, we developed a novel type of fusing agent derived from metal-organic frameworks.”

The SSGs feature miniature tree-shaped microstructures that mimic plant transpiration, forming an efficient, heat-distributing forest.

“Our bioinspired design increases the surface area of the SSG,” Zhou explained. “Using a treelike design increases the surface area of the SSG, which enhances the water transport and boosts evaporation efficiency.”

In both simulated environments and field trials, the SSGs exhibited a high rate of water evaporation. The desalinated water consistently met drinking water standards, even after extended testing.

“This demonstrates the practicality and efficiency of our approach,” Zhou said. “And it can be quickly and easily mass-produced via MJF commercial printers.”

The team’s work shows significant potential for tackling freshwater scarcity.

“Our SSGs can be used in regions with limited access to freshwater to provide a sustainable and efficient desalination solution,” said Zhou. “Beyond desalination, it can be adapted for other applications that require efficient solar energy conversion and water purification.”

Research Report:3D printing of bio-inspired porous polymeric solar steam generators for efficient and sustainable desalination

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Solar Energy

Renewables overproduction turns electricity prices negative

Published

3 days ago

July 24, 2024

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Renewables overproduction turns electricity prices negative

By Nathalie Alonso and Catherine Hours

Paris (AFP) July 24, 2024

With the proliferation of solar panels and wind turbines an unusual phenomenon is becoming more and more frequent: wholesale electricity prices turn negative.

While that may brighten the mood of consumers whose power bills have surged in recent years, it could undermine the further development of renewables, a key element in the fight against global warming.

The increasingly frequent phenomenon is “extremely problematic” for the wind and solar sector, said Mattias Vandenbulcke, strategy director of the renewables industry group France Renouvelables.

“It allows some to have harmful, even dangerous rhetoric which says ‘renewables are useless’,” Vandenbulcke said.

In southern Australia, wholesale electricity prices have been negative some 20 percent of the time since last year, according to the International Energy Agency.

The share of negatively priced hours in southern California was above 20 percent in the first half of the year, more than triple from the same period in 2023, the IEA said.

In the first six months of the year in France, there were negative prices around five percent of the time, beating the record set last year, according to the electricity grid operator RTE.

In Switzerland the price tumbled as far as -400 euros (-$436) per megawatt hour on July 14. The lowest prices are usually recorded around midday during the summer when solar production is at its peak.

– ‘A warning signal’ –

The trend has been accelerating for the past three years as demand in Europe has unexpectedly dropped since the Covid pandemic and the war in Ukraine.

Prices turn negative on the spot wholesale electricity market when production is strong while demand is weak.

Around a fifth of the total is traded on this market, where electricity is bought for the following day.

Negative prices help reduce the bills of consumers, said Rebecca Aron, head of electricity markets at French renewables firm Valorem, but the impact is delayed and difficult to discern among the other factors that send prices higher and lower.

Large, industrial consumers that can shift production to times when prices are negative and buy on wholesale markets can reap the biggest rewards.

Negative prices are “a warning signal that there is way too much production on the electrical grid”, said energy analyst Nicolas Goldberg at Colombus Consulting.

Electricity grids need to be kept constantly in balance. Too much can lead to the electricity to increase in frequency beyond norms for some equipment. Too little can lead to some or all customers losing power.

There are currently few options to stock surplus electricity production so producers have to reduce output.

Many renewable producers stop their output when prices are set to turn negative. It takes one minute to stop output at a solar park, two to three minutes for a wind turbine.

But not all stop their production.

– Tripling renewables –

“Renewable energy can be controlled, but depending on production contracts, there might not necessarily be an incentive to stop,” said Mathieu Pierzo at French grid operator RTE, which has the responsibility for balancing the electricity load.

Some producers are paid a fixed price under their contract or are compensated by the state if prices fall below a certain level.

Fossil fuel and nuclear power plants can adjust their production to some extent, but halting and restarting output is costly.

In the future, solar and wind will also have to “participate more in balancing the electricity system”, Pierzo said.

Solar and wind production is set to rise further as nations agreed at the COP28 climate conference last year to triple renewable energy capacity by 2030 as part of efforts to limit warming to 1.5 degrees Celsius compared with pre-industrial levels.

“Rising frequency of negative prices sends an urgent signal that greater flexibility of supply and demand is needed,” the Paris-based IEA warned last week.

“The appropriate regulatory frameworks and market designs will be important to allow for an uptake in flexibility solutions such as demand response and storage,” it said.

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Solar Energy

NREL explores long-term strategies for sustainable perovskite solar panels

Published

3 days ago

July 24, 2024

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NREL explores long-term strategies for sustainable perovskite solar panels

by Clarence Oxford

Los Angeles CA (SPX) Jul 24, 2024

Researchers at the National Renewable Energy Laboratory (NREL) are examining the future of perovskite solar panels, focusing on scaling, deploying, and designing panels to be recyclable.

Perovskite solar panels could play a key role in global efforts to reduce greenhouse gas emissions. With the technology still in its developmental stages, researchers are emphasizing the importance of designing these panels to minimize environmental impact.

“When you have a technology in its very early stages, you have the ability to design it better. It’s a cleaner slate,” said Joey Luther, a senior research fellow at the U.S. Department of Energy’s (DOE’s) National Renewable Energy Laboratory (NREL) and coauthor of the newly published article in the journal Nature Materials. “Pushing perovskite PV toward enhanced sustainability makes more sense at this stage. We’re thinking about how we can make sure we have a sustainable product now rather than dealing with sustainability issues toward the end of its practical life.”

The article highlights the PV research community’s influential position to prioritize remanufacturing, recycling, and reliability efforts, aiming to make perovskite PV one of the most sustainable energy sources available.

“Perovskites could unlock the next evolution of high-efficiency PV, and it is our responsibility to assure they are manufactured, used, and recycled sustainably,” said the lead author of the study, Kevin Prince, a former graduate researcher at NREL who now researches perovskites at Helmholtz Zentrum Berlin in Germany.

While silicon solar panels dominate the industry and cadmium telluride (CdTe) panels have established recycling programs, perovskites are at a critical point where sustainability issues can be addressed from the start.

The most effective circular economy begins at the design stage, considering materials sourcing, product lifetime, and end-of-life management. Researchers suggest assessing environmental impacts by looking at carbon emissions during production, embodied energy, sustainable material sourcing, and module circularity.

The journal article identifies critical sustainability concerns for each component of a perovskite solar panel. For instance, lead can be diluted with metals like tin to reduce lead content, though this may affect PV efficiency and durability. Expensive precious metals such as silver and gold could be replaced with cheaper alternatives like aluminum, copper, or nickel. Fluorine-tin oxide is recommended over the scarcer indium-tin oxide for front electrodes.

“We want to have the lowest amount of embodied energy in the fabrication,” Luther said. “We want to have the lowest amount of emissions in the fabrication. At this stage, now is the chance to look at those components. I don’t think we have to change anything. It’s more a matter of what decisions should be made, and these arguments should certainly be discussed.”

The authors discuss various ways to improve the circularity of perovskite panels. Remanufacturing involves reusing parts from old modules to make new ones, while recycling converts waste materials into raw materials for reuse. Attention is needed for the specialized glass used in perovskite modules, which is crucial for structural support and protection while allowing maximum sunlight penetration. Establishing a recycling pathway for this glass will be essential as PV deployment increases.

Silvana Ovaitt, a PV researcher and coauthor of the paper, noted that cleaner electricity grids will lead to cleaner manufacturing processes, further reducing emissions.

“Another concern is the transportation of the final modules and the raw glass because those are the heaviest items,” Ovaitt said. “Local manufacturing will be a great way to reduce those carbon impacts.”

The researchers explain that increasing the durability of PV modules, thereby extending their useful life, is a more effective approach to reducing net energy, energy payback, and carbon emissions than designing for circularity alone. A longer lifespan means panels won’t need to be recycled as often.

“Ultimately, we want to make them as durable as possible,” Luther said. “But we also want to consider the aspects of whenever that time does come. We want to be deliberate about how to take them apart and to reuse the critical components.”

Research Report:Sustainability pathways for perovskite photovoltaics