Solar

Solar Cells

A team of researchers from the University of Toronto has created a triple-junction perovskite solar cell with record efficiency by overcoming a key limitation of previous designs.

The prototype represents a significant advance in the development of low-cost alternatives to silicon-based solar cells, which are the current industry standard.

“In addition to lower manufacturing cost, perovskites offer us the ability to stack multiple layers of light-absorbing materials on top of each other, and even on top of traditional silicon cells,” says Professor Ted Sargent, who recently joined the department of chemistry and the department of electrical and computer engineering at Northwestern University but maintains his lab at U of T’s Faculty of Applied Science & Engineering.

“In this work, we used rational design to address a critical challenge that can arise in this multi-layered paradigm, improving both efficiency and durability.”

Today’s solar cells are made from a single wafer of ultra-pure silicon, which is energy-intensive to produce. By contrast, perovskite solar cells are made using perovskite polycrystalline films that are coated onto surfaces with low-cost, solution-processing techniques similar to those used in the printing industry.

By varying the composition of the perovskite crystals within these films, each layer can be “tuned” to absorb different wavelengths of light, making efficient use of the entire solar spectrum. This is not possible with silicon, which always absorbs the same wavelengths.

Sargent’s group is among those developing new ways to unlock the potential of perovskite solar cells. Their previous work has included two-layered tandem cells, but their latest study, published in Nature, focuses on a three-layer design.

“Multi-layered cells are typically designed so that the top layer with wide-bandgap perovskites absorbs the most energetic photons, meaning high-frequency light with short wavelengths, toward the violet end of the spectrum,” says post-doctoral researcher Zaiwei Wang, one of four co-lead authors on the new paper.

“The next layer will absorb medium wavelengths and the bottom one will absorb longer wavelengths. But it’s in the top layer that we get the challenge of light-induced phase separation.”

The team used a type of perovskite material known as ABX3, which is made from a mix of different substances – including cesium, lead, tin, iodine, bromine and some small organic molecules. The top layer, in particular, is composed of mixed halide perovskites, which have a high proportion of bromine and iodine.

“What happens in light-induced phase separation of these mixed perovskites is that the bombardment of high-frequency photons causes the phases that are richer in bromine to get separated from those that are rich in iodine,” says Hao Chen, a post-doctoral researcher and co-lead author of the study.

“This leads to an increase in defects and a decrease in overall performance.”

To overcome this problem, the research team used detailed computer models to simulate the effect of altering the composition of the crystals. This work suggested two changes: removing the organic molecules for an all-inorganic perovskite structure and introducing the element rubidium.

“The introduction of rubidium suppresses the light-induced phase separation issue,” says Tong Zhu, another post-doctoral researcher and co-lead author.

“Our rubidium/cesium mixed inorganic perovskites show better light stability than [other] perovskite materials, including cesium-based inorganic perovskites and widely used organic-inorganic hybrid perovskites with similar band gaps.”

Using this knowledge, the team then designed and built a triple-junction cell with this composition. They measured its efficiency at 24.3 per cent with an open-circuit voltage of 3.21 volts. They also sent it to be independently certified by the National Renewable Energy Laboratory, which measured a quasi-steady-state efficiency of 23.3 per cent.

“In the past, triple-junction perovskite solar cells have demonstrated a maximum efficiency of around 20 per cent, so this is a big improvement. To our knowledge, this is also the first reported certification efficiency of triple-junction perovskite solar cells,” says PhD candidate Lewei Zeng, another co-lead author.

“Previous designs also tended to lose a lot of their performance in a matter of hours. By contrast, ours maintained 80 per cent of its initial efficiency even after 420 hours of operation – so that’s a big step in terms of durability as well.”

The team says that although further improvements to the performance will be needed before perovskite solar cells can compete with silicon in commercial applications, the latest study demonstrates a path forward.

“Theory tells us that perovskites have the ability to overcome a lot of the inherent limitations of silicon as a material,” Zeng says.

“But it’s not simply a matter of one displacing the other. There might be some applications better suited to perovskites, and some where silicon is better – or we could combine them both. There are a lot of exciting possibilities ahead.”

Researcher’s startup receives federal support to make solar-energy-control windows

siddiq22 — Thu, 16 Mar 2023 21:15:00 +0000

Researcher’s startup receives federal support to make solar-energy-control windows

siddiq22 Thu, 03/16/2023 - 17:15

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Right to left: U of T researcher Nazir Kherani co-founder of 3E Nano Inc., with chairman and cofounder Dan Shea, CEO Steve Ferrero and MP Yvan Baker after the presentation of $5 million in federal funding for the startup (photo by Shaun Mitchell)

Matthew Tierney

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Advanced Manufacturing

Entrepreneurship

Research and Innovation

Startups

U of T researcher Nazir Kherani and his collaborators at the startup 3E Nano Inc have one goal: to design the perfect window.

That includes a nano-thin window coating that can more than double the thermal protection for residential and commercial windows. That technology is now on its way to commercialization, thanks in part to $5 million in new federal funding from Sustainable Development Technology Canada.

“Windows are the weakest energy link in any building,” says Kherani, a professor in the department of material science and engineering in the Faculty of Applied Science and Engineering who is jointly appointed to the Edward S. Rogers Sr. department of electrical and computer engineering.

“Think of heat escaping in the winter months and heat entering the cool, ventilated space during the summer months," says Kherani, who co-founded 3E Nano in 2015.

Kherani explains that a window’s resistance to heat flow is measured by the R-value, which increases based on its ability to prevent heat from flowing into or escaping from a building. Currently, 3E Nano windows – in prototype as well as in pre-alpha deployment – rate R8 and higher.

"This compares remarkably to an average window whose R-value lies in a range from R1 of a single pane, to R3, a dual pane.”

How was 3E Nano able to achieve this breakthrough? In its simplest configuration, the 3E Nano coating comprises a nano-thin metallic film sandwiched between two sapphire-like nano-thin films. This three-layered stack is opaque to certain wavelengths of light, but not others. As a result, the coating can control the flow of light entering and leaving the building over three parts of the solar spectrum: the visible, the near-frequency infrared and the mid-frequency infrared.

Both near-infrared light – which accounts for almost half of the sun’s total energy – and mid-infrared light can be reflected away. This keeps the sun’s heat from penetrating indoors, but it also keeps room heat inside the building from escaping through the windows, achieving low emissivity. At the same time, natural visible light is allowed through the window to the interior, reducing the need for artificial interior lighting.

Kherani believes 3E Nano’s coating is poised to become a mainstream product. He credits the industry experience of 3E Nano’s team with a critical pivot in the research.

“Combining earth-abundant aluminum and nitrogen results in a coating material similar to sapphire in its optical and structural properties,” he says. “The stability and multi-functional character of the sapphire-like structure is suited to low-cost, high-volume manufacturing.”

The coating is applied by sputter deposition – a process which hurls argon atoms into an aluminum target in a vacuum system, knocking the aluminum atoms like billiard balls into a lightweight polymer substrate.

After adding nitrogen gas, the resulting chemical reaction forms a colourless film only tens of nanometres thick (approximately one-thousandth of the thickness of a hair strand). This combined with a nano-thin silver layer results in a robust coating that can be tuned for optical and electrical properties.

Kherani and his team envision other aspects of the perfect window as integrated functionalities ranging from metamaterial structuring to dynamic systems that maintain ideal temperatures and daylighting (the practice of placing windows so that sunlight can provide effective internal lighting) within buildings.

“In the lab, we’ve created a metamaterial that retains low emissive and solar-control properties but has high transparency in the gigahertz range critical for communication – nature-inspired with near-invisible hexagonal honeycomb patterns,” Kherani says.

“Professor Kherani has his eye on sustainability solutions that remain scalable,” says Professor Deepa Kundur, chair of the department of electrical and computer engineering. “His startup 3E Nano is a shining example of how industry can shape and direct research, and he’s given 3E Nano every chance at a positive impact in the green marketplace.”

Kundur also points out that it's because of researchers like Kherani that U of T was recently named a top-10 research institution for global innovation.

Kherani is encouraged by 3ENano's progress and optimistic about the company’s ability to help transform the building sector, which ranks a close second to transportation in energy-related carbon dioxide emissions.

“Although the shortest distance from point A to point B is a straight line, finding that straight line is not a simple matter," he notes. "On the other hand, we are in a promising place today, and we can clearly see where we need to be.”

U of T, international researchers develop more efficient two-sided solar cells

geoff.vendeville — Tue, 12 Jan 2021 16:42:41 +0000

U of T, international researchers develop more efficient two-sided solar cells

geoff.vendeville Tue, 01/12/2021 - 11:42

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A bifacial perovskite/silicon solar cell prototype is field-tested at King Abdullah University of Science and Technology in Saudi Arabia (photo courtesy of Michele De Bastiani)

Nicholas G. Demille

Topic

Breaking Research

Global

Research & Innovation

Ted Sargent

To increase the performance of solar panels, a team of researchers based in Saudi Arabia, Italy, Germany and Canada has created a bifacial, or two-sided, tandem solar cell. The prototypes bring together the best of two separate technologies: silicon and perovskites.

Out in the field, light primarily comes directly from the sun. Conventional tandem solar cells already convert this light into electricity more efficiently compared to traditional silicon-only solar cells by absorbing additional wavelengths of light.

Now, researchers at the University of Toronto's Faculty of Applied Science & Engineering – with colleagues at King Abdullah University of Science and Technology (KAUST), the University of Bologna and the Karlsruhe Institute of Technology – have realized that even more energy can be gathered using a two-sided tandem configuration. Light reflected and scattered from the ground – known as “albedo” – can also be collected to significantly increase the current of a tandem solar cell.

The research, published this week in the journal Nature Energy, outlines how the team engineered the perovskite/silicon device to exceed the currently accepted performance limits for the tandem configuration. The study’s authors include University Professor Ted Sargent, in the Edward S. Rogers Sr. department of electrical and computer engineering, and post-doctoral researcher Yi Hou.

“By exploiting the albedo, we can now generate currents higher than in conventional tandems, without increasing the manufacturing costs at all,” said Michele De Bastiani of KAUST, co-lead author of this study.

The potential for capturing indirect sunlight has been studied in the past, but without experimental verification. The researchers collaborated to solve the scientific and engineering challenges required to include indirect sunlight in the energy gathering capacity of their modules.

With this knowledge, they tested the bifacial tandem solar cell in outdoor conditions, achieving efficiencies beyond any commercial silicon solar panel.

“Bifacial silicon-only solar cells have rapidly taken an increasing share in the photovoltaics market, as they can lead to a performance gain of 20 per cent relative,” said Stefaan De Wolf, an associate professor of material science and engineering at KAUST. “Exploiting this concept in perovskite/silicon tandems now opens opportunities for ultra-high power generation at affordable cost.”

U of T student creates renewable energy information hub for Canadians

Christopher.Sorensen — Thu, 16 Jan 2020 18:02:05 +0000

U of T student creates renewable energy information hub for Canadians

Christopher.Sorensen Thu, 01/16/2020 - 13:02

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Rylan Urban, who is doing a master's degree in sustainability management at U of T Mississauga, launched Energyhub.org a year ago (photo by Drew Lesiuczok)

Topic

A University of Toronto student is bringing together homeowners and solar panel installers in an attempt to increase the use of sustainable energy systems in residential homes across Canada.

Rylan Urban, a second-year student in the Master of Science in Sustainability Management program, launched Energyhub.org a year ago and has since helped broker over $1 million in residential solar sales across five provinces.

Urban got the idea for the website after noting a lack of accessible information for Canadian homeowners interested in sustainable energy systems. He decided to bridge that knowledge gap with the creation of a comprehensive, information source that homeowners would find useful.

Urban began by answering questions he would have as a homeowner interested in installing a solar power system. That included information on the cost of solar systems, where to get them installed, what the installation process looks like, how effective they are when there’s snow, timelines and rebate programs.

“I went through the very long and laborious process of answering those questions, specific to every single province and territory in Canada,” Urban says, explaining a lot of the information was scattered across utility, government, regulatory and individual company websites.

“There was no real central place that brought it all together. I’ve tried to make it really easy for someone who is interested in sustainable energy systems to find everything they need in one place.”

The site now gets more than 15,000 visitors a month who are looking for information on how to tap into the sustainable energy market.

Urban also acts as a facilitator, connecting customers with installation companies and earning a small fee in the process. The project also helped land him an internship, which has already led to a full-time position as an energy consultant after he graduates.

The big motivation behind the project, though, is promoting sustainability.

“Climate change and, more generally, systemic sustainability issues are important to me,” Urban says. “I think that these are very important issues that humanity is going to have to solve in the next 10 to 50 years if we want the planet to continue operating the same way it does today.”

Urban plans to expand the focus of Energyhub.org to include other products and services, including wind and geothermal systems. He says he would also like to add information about general efficiency and smart home technologies.

U of T study finds success in combining two emerging technologies for next-generation solar power

noreen.rasbach — Mon, 12 Aug 2019 04:00:00 +0000

U of T study finds success in combining two emerging technologies for next-generation solar power

noreen.rasbach Mon, 08/12/2019 - 00:00

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Mengxia Liu is the lead author of a recent paper in Nature that describes a way to combine two promising solar technologies in order to enhance their stability (photo by Sanyang Han)

Tyler Irving

Topic

Our Community

Global

Research & Innovation

Ted Sargent

Researchers at the University of Toronto's Faculty of Applied Science & Engineering have combined two emerging technologies for next-generation solar power – and discovered that each one helps stabilize the other. The resulting hybrid material is a major step toward reducing the cost of solar power while multiplying the ways it can be used.

Today virtually all solar cells are made of high-purity silicon. It’s a well-established technology, and in recent years the manufacturing cost has dropped significantly due to economies of scale. Nevertheless, silicon has an upper limit to its efficiency. A team led by Ted Sargent, a professor in the department of electrical and computer engineering, is pursuing complementary materials that can enhance the solar-harvesting potential of silicon by absorbing wavelengths of light that silicon does not.

“Two of the technologies we pursue in our lab are perovskite crystals and quantum dots,” says Sargent. “Both of these are amenable to solution processing. Imagine a ‘solar ink’ that could be printed onto flexible plastic to create low-cost, bendable solar cells. We can also combine them in front of, or behind, silicon solar cells to further enhance their efficiency.”

One of the key challenges facing both perovskites and quantum dots is stability. At room temperature, some types of perovskites experience an adjustment in their 3D crystal structure that renders them transparent – they no longer fully absorb solar radiation.

For their part, quantum dots must be covered in a thin layer known as a passivation layer. This layer – only a single molecule thick – prevents the quantum dots from sticking to each other. But temperatures above 100 C can destroy the passivation layer, causing the quantum dots to aggregate or clump together, wrecking their ability to harvest light.

In a paper published recently in Nature, a team of researchers from Sargent’s lab report a way to combine perovskites and quantum dots that stabilizes both.

“Before we did this, people usually tried to address the two challenges separately,” says Mengxia Liu, the paper’s lead author who received her PhD at U of T in 2018.

“Research has shown the successful growth of hybrid structures that incorporated both perovskites and quantum dots,” says Liu, who is now a postdoctoral researcher at Cambridge University. “This inspired us to consider the possibility that the two materials could stabilize each other if they share the same crystal structure.”

Liu and the team built two types of hybrid materials. One was primarily quantum dots with about 15 per cent perovskites by volume, and is designed to turn light into electricity. The other was primarily perovskites with less than 15 per cent quantum dots by volume, and is better suited to turning electricity into light, for example, as part of a light emitting diode (LED).

The team was able to show that the perovskite-rich material remained stable under ambient conditions (25 C and 30 per cent humidity) for six months, about ten times longer than materials composed of the same perovskite alone. As for the quantum dot material, when heated to 100 C, the aggregation of the nanoparticles was five times lower than if they hadn’t been stabilized with perovskites.

“It provedour hypothesis remarkably well,” says Liu. “It was an impressive outcome beyond our expectations.”

The new paper provides proof-of-concept for the idea that these kinds of hybrid materials can enhance stability. In the future, Liu hopes that solar cell manufacturers will take her ideas and build on them to create solution-processed solar cells that meet all the same criteria as traditional silicon.

“Industrial researchers could experiment by using different chemical elements to form the perovskites or quantum dots,” says Liu. “What we have shown is that this is a promising strategy for improving stability in these kinds of structures.”

“Perovskites have shown tremendous potential as solar materials; but fundamental solutions are needed to turn them into stable and robust materials that can meet the demanding requirements of the renewable energy sector.” says Jeffrey C. Grossman, the Morton and Claire Goulder and Family Professor in Environmental Systems and a professor in the department of materials science and engineering at the Massachusetts Institute of Technology, who was not involved in the study. “The Toronto study shows one exciting new avenue to advancing the understanding, and the achievement, of stable perovskite crystal phases.”

Liu credits the discovery in part to the collaborative environment in the team, which included researchers from many disciplines, including chemistry, physics and her own field of materials science.

“Perovskite and quantum dots have distinct physical structures, and the similarities between these materials have been usually overlooked,” she says. “This discovery shows what can happen when we combine ideas from different fields.”

U of T startup QD Solar secures international financing

lanthierj — Tue, 14 Feb 2017 13:17:43 +0000

U of T startup QD Solar secures international financing

lanthierj Tue, 02/14/2017 - 08:17

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Ted Sargent (photo by Roberta Baker, courtesy Faculty of Applied Science & Engineering)

Topic

Global Lens

Research and Innovation

Nanotechnology

QD Solar, a Canadian startup co-founded by U of T researchers Ted Sargent and Sjoerd Hoogland, has received a big boost in funding and an important international nod to help bring its solar technology to market.

On Monday, the company announced it had closed its first significant round of venture capital financing led by DSM Venturing, based in the Netherlands, with participation from existing investors, KAUST Innovation Fund and MaRS Innovation.

Coupled with the $2.55 million the company received from Sustainable Development Technology Canada last March, QD Solar “has the resources to advance, develop, test and de-risk our solar technology, while concurrently developing the manufacturing processes needed to bring this technology to market,” said Dan Shea, CEO of QD Solar and a former senior executive with Celestica and BlackBerry, in a news release.

QD Solar’s quantum dot-based solar cells use nano-engineered, low-cost materials that can absorb otherwise wasted infrared light. Solar panels with this technology can boost their overall power generation by 20 per cent, the company says.

In the future, QD Solar says, it intends to develop quantum dot-based solar material that can be applied to any flexible surface to generate energy.

The technology was developed in labs at U of T by Sargent, a University Professor in the Edward S. Rogers Sr. Department of Electrical and Computer Engineering at U of T and Canada Research Chair in Nanotechnology, and Hoogland, director of research, technology and innovation at the Sargent Group.

“We’re delighted to see QD Solar and this novel technology created at the University of Toronto receive this substantial investment from Canadian and international sources to advance their bold vision for a new clean energy product,” said Derek Newton, U of T’s assistant vice–president of innovation, partnerships and entrepreneurship.

The startup was supported by MaRS Innovation and U of T’s Innovations & Partnership Office, which provided seed funding, patent protection and helped the company meet international industry partners and investors.

Since 2011, U of T researchers have created more than 830 inventions, founded more than 90 research-based startups and generated $49 million from licensing revenues.

The next generation of solar pioneers: U of T alumni are electrifying the Democratic Republic of Congo

ullahnor — Fri, 09 Dec 2016 22:12:17 +0000

The next generation of solar pioneers: U of T alumni are electrifying the Democratic Republic of Congo

ullahnor Fri, 12/09/2016 - 17:12

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The Virunga landscape in the Democratic Republic of Congo (photo by flöschen via Flickr)

Kevin Soobrian

Author legacy

Kevin Soobrian

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Research & Innovation