Solar Energy

Scientists develop perovskite solar modules with greater size, power and stability

Published

3 years ago

February 8, 2021

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Scientists develop perovskite solar modules with greater size, power and stability

Researchers from the Okinawa Institute of Science and Technology Graduate University (OIST) have created perovskite solar modules with improved stability and efficiency by using a new fabrication technique that reduced defects. Their findings were published on the 25th January in Advanced Energy Materials.

Perovskites are one of the most promising materials for the next-generation of solar technology, soaring from efficiencies of 3.8% to 25.5% in slightly over a decade. Perovskite solar cells are cheap to produce and have the potential to be flexible, increasing their versatility. But two obstacles still block the way to commercialization: their lack of long-term stability and difficulties with upscaling.

“Perovskite material is fragile and prone to decomposition, which means the solar cells struggle to maintain high efficiency over a long time,” said first author Dr. Guoqing Tong, a postdoctoral scholar in the OIST Energy Materials and Surface Sciences Unit, led by Professor Yabing Qi. “And although small-sized perovskite solar cells have a high efficiency and perform almost as well as their silicon counterparts, once scaled up to larger solar modules, the efficiency drops.”

In a functional solar device, the perovskite layer lies in the center, sandwiched between two transport layers and two electrodes. As the active perovskite layer absorbs sunlight, it generates charge carriers which then flow to the electrodes via the transport layers and produce a current.

However, pinholes in the perovskite layer and defects at the boundaries between individual perovskite grains can disrupt the flow of charge carriers from the perovskite layer to the transport layers, reducing efficiency. Humidity and oxygen can also start to degrade the perovskite layer at these defect sites, shortening the lifespan of the device.

“Scaling up is challenging because as the modules increase in size, it’s harder to produce a uniform layer of perovskite, and these defects become more pronounced,” explained Dr. Tong. “We wanted to find a way of fabricating large modules that addressed these problems.”

Currently, most solar cells produced have a thin perovskite layer – only 500 nanometers in thickness. In theory, a thin perovskite layer improves efficiency, as the charge carriers have less distance to travel to reach the transport layers above and below. But when fabricating larger modules, the researchers found that a thin film often developed more defects and pinholes.

The researchers therefore opted to make 5 x 5 cm2 and 10 x 10 cm2 solar modules that contained perovskite films with double the thickness.

However, making thicker perovskite films came with its own set of challenges. Perovskites are a class of materials that are usually formed by reacting many compounds together as a solution and then allowing them to crystallize.

However, the scientists struggled to dissolve a high enough concentration of lead iodine – one of the precursor materials used to form perovskite – that was needed for the thicker films. They also found that the crystallization step was fast and uncontrollable, so the thick films contained many small grains, with more grain boundaries.

The researchers therefore added ammonium chloride to increase the solubility of lead iodine. This also allowed lead iodine to be more evenly dissolved in the organic solvent, resulting in a more uniform perovskite film with much larger grains and fewer defects. Ammonia was later removed from the perovskite solution, lowering the level of impurities within the perovskite film.

Overall, the solar modules sized 5 x 5 cm2 showed an efficiency of 14.55%, up from 13.06% in modules made without ammonium chloride, and were able to work for 1600 hours – over two months – at more than 80% of this efficiency.

The larger 10 x 10 cm2 modules had an efficiency of 10.25% and remained at high levels of efficiency for over 1100 hours, or almost 46 days.

“This is the first time that a lifespan measurement has been reported for perovskite solar modules of this size, which is really exciting,” said Dr. Tong.

This work was supported by the OIST Technology Development and Innovation Center’s Proof-of-Concept Program. These results are a promising step forward in the quest to produce commercial-sized solar modules with efficiency and stability to match their silicon counterparts.

In the next stage of their research, the team plans to optimize their technique further by fabricating the perovskite solar modules using vapor-based methods, rather than by using solution, and are now trying to scale up to 15 x 15 cm2 modules.

“Going from lab-sized solar cells to 5 x 5 cm2 solar modules was hard. Jumping up to solar modules that were 10 x 10 cm2 was even harder. And going to 15 x 15 cm2 solar modules will be harder still,” said Dr. Tong. “But the team is looking forward to the challenge.”

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Solar Energy

Research team achieves significant solar cell efficiency milestone

Published

3 days ago

May 26, 2024

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Research team achieves significant solar cell efficiency milestone

by Simon Mansfield

Sydney, Australia (SPX) May 26, 2024

A research team has created a tandem solar cell using antimony selenide as the bottom cell material and a hybrid perovskite material as the top cell, achieving over 20 percent power conversion efficiency. This advancement highlights antimony selenide’s potential for bottom cell applications.

Photovoltaic technology converts sunlight into electricity, offering a clean energy source. Scientists aim to enhance the efficiency of solar cells, achieving over 20 percent in conventional single-junction cells. Surpassing the Shockley-Queisser limit in these cells would be costly, but tandem solar cells can overcome this limit by stacking materials.

The team focused on antimony selenide for tandem cells, traditionally used in single-junction cells. “Antimony selenide is a suitable bottom cell material for tandem solar cells. However, because of the rarity of reported tandem solar cells using it as a bottom cell, little attention has been paid to its application. We assembled a tandem solar cell with high conversion efficiency using it as the bottom cell to demonstrate the potential of this material,” said Tao Chen, professor of Materials Science and Engineering at the University of Science and Technology of China.

Tandem cells absorb more sunlight than single-junction cells, converting more light into electricity. The team created perovskite/antimony selenide tandem cells with a transparent conducting electrode, optimizing the spectral response and achieving over 17 percent efficiency. By optimizing the antimony selenide bottom cell, they reached 7.58 percent efficiency.

The assembled four-terminal tandem cell achieved 20.58 percent efficiency, higher than independent subcells. The tandem cell is stable and uses nontoxic elements. “This work provides a new tandem device structure and demonstrates that antimony selenide is a promising absorber material for bottom cell applications in tandem solar cells,” said Chen.

The team aims to develop an integrated two-terminal tandem cell and further improve performance. “The high stability of antimony selenide provides great convenience for the preparation of two-terminal tandem solar cell, which means that it may have good results when paired with quite a few different types of top cell materials.”

Research Report:Sb2Se3 as a bottom cell material for efficient perovskite/Sb2Se3 tandem solar cells

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Solar Energy

Flower or power? Campaigners fear lithium mine could kill rare plant

Published

4 days ago

May 24, 2024

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Flower or power? Campaigners fear lithium mine could kill rare plant

By Romain FONSEGRIVES

Rhyolite Ridge, United States (AFP) May 23, 2024

Delicate pink buds sway in the desert breeze, pregnant with yellow pompoms whose explosion will carpet the dusty corner of Nevada that is the only place on Earth where they exist.

Under their roots lie vast reserves of lithium, vital for the rechargeable electric car batteries that will reduce planet-heating pollution.

But campaigners fear the extraction of the precious metal could destroy the flower’s tiny habitat.

“This mine is going to cause extinction,” says Patrick Donnelly, an environmentalist who works at the Center for Biological Diversity, a non-governmental organization.

“They somehow claim that they’re not harming the (plant). But can you imagine if someone built an open-pit mine 200 feet from your house? Wouldn’t that affect your life profoundly?”

The plant in question is Tiehm’s buckwheat.

There are only around 20,000 known specimens, growing in a few very specific places on a total surface area equivalent to around five soccer fields.

In 2022, the wildflower was classified as endangered by US federal authorities, with mining cited as a major threat to its survival.

The plant and the lithium reserve on which it grows embody one of the key challenges and contradictions of the global climate struggle: how much damage can we inflict on the natural world as we seek to halt or reverse the problems we have already created?

– ‘Coexist’ –

Bernard Rowe, boss of Australian miner Ioneer, which holds the mineral rights to the area, says the lithium produced at Rhyolite Ridge “will be sufficient to provide batteries for about 370,000 vehicles” a year.

“We’ll do that year-on-year for 26 years,” he said.

Those nearly 10 million vehicles will go a long way towards meeting the goal President Joe Biden has set of cutting down the nation’s fleet of gas-guzzlers as a way to slash US production of planet-warming pollutants.

So-called zero-emission cars make up around 7.5 percent of new vehicle sales in the United States today — more than double the percentage just a few years earlier.

In California, the figure is more than 20 percent.

And while expansion in the sector has slowed, the category remains the fastest-growing, according to Kelley Blue Book.

And it’s not only in the United States: Global demand for lithium will increase five to seven times by 2030, according to the International Energy Agency.

The difficulty for US manufacturers is that much of the world’s lithium supply is dominated by strategic rival China, as well as Australia and Chile.

“The United States has very, very little domestic production,” said Rowe.

“So it’s important to develop a domestic supply chain to allow for that energy transition, and Rhyolite Ridge will be an integral part of that.”

Ioneer’s plans show that over the years the mine is in operation — it is projected to start producing lithium in late 2027 — around a fifth of the plant’s habitat will be directly affected.

But the company, which has spent $2.5 million researching the plant, says mining will not affect its survival; it is already growing well in greenhouses and biologists think it can be replanted.

“We’re very confident that the mine and Tiehm’s buckwheat can coexist,” Rowe said.

– ‘Greenwashing’ –

Donnelly counters that Ioneer is “basically greenwashing extinction.”

“They’re saying. ‘We’re going to save this plant,’ when actually they are going to send it to its doom,” he said.

Under the company’s plans, the strip mine will use hundreds of trucks, which Donnelly says will raise clouds of dust that will affect photosynthesis and harm the insects that pollinate the plants.

Ioneer says it has already planned mitigation methods, like dust curtains, and keeping the roads wet.

Still, Donnelly says, why not just move the mine? But Rowe counters that it’s not as simple as just digging somewhere else.

Ioneer has invested $170 million since 2016 to demonstrate the feasibility of this site, which it believes is one of the best around.

“Many of these other deposits haven’t had that amount of work, so they’re not viable alternatives to a project like this,” he said.

The US Department of Energy has offered Ioneer a $700 million loan for the project, if the Bureau of Land Management signs off on an operating permit.

Donnelly insists the issue is not just the future of one obscure wildflower, but rather just one example of large-scale biodiversity loss that is threatening millions of plants and animals.

“If we solve the climate crisis, but we drive everything extinct while we do it, we’re still going to lose our world,” he said.

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Solar Energy

Tesla breaks ground on huge Shanghai battery plant

Published

4 days ago

May 24, 2024

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Tesla breaks ground on huge Shanghai battery plant

by AFP Staff Writers

Shanghai (AFP) May 23, 2024

Tesla broke ground on a massive battery factory in Shanghai on Thursday, Chinese state media reported, making it the US electric car giant’s second plant in the financial hub.

The project was announced last April after boss Elon Musk presented a vague but ambitious plan to investors to turbocharge growth.

However, the company last month reported a 55 percent drop in quarterly earnings, reflecting a decline in EV sales in an intensively competitive market.

The new Shanghai factory should make 10,000 units per year of Tesla’s Megapack batteries, state news agency Xinhua said.

Tesla says Megapacks are intended to store energy and stabilise supply for power grids, with each unit able to store more than three megawatt-hours of power.

The factory is expected to start mass production in 2025, state media said in May.

“I believe the new plant is a milestone for both Shanghai and Tesla,” the company’s vice president Tao Lin told Xinhua.

“In a more open environment, we can… supply the global market with large-scale energy-storage batteries manufactured in China.”

Musk has extensive business interests in China and is a fairly frequent visitor.

In April, he met Chinese Premier Li Qiang, and received a key security clearance for Tesla’s locally produced EVs.

Musk’s interests in China have long raised eyebrows in Washington — President Joe Biden has said in the past that his links to foreign countries were “worthy” of scrutiny.

The battery plant will be Tesla’s second in the Chinese city after its enormous Shanghai Gigafactory, which broke ground in 2019.

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