Nav: Home

Quantum rebar: Quantum dots enhance stability of solar-harvesting perovskite crystals

May 22, 2019

University of Toronto Engineering researchers 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 Professor Ted Sargent 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 today 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.

"Research has shown the successful growth of hybrid structures that incorporated both perovskites and quantum dots," says Liu, who is now a postdoctoral fellow 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% perovskites by volume, and is designed to turn light into electricity. The other was primarily perovskites with less than 15% 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% 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 proved out our 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 improve on them even further 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."

University of Toronto Faculty of Applied Science & Engineering

Related Solar Cells Articles:

Can solar technology kill cancer cells?
Michigan State University scientists have revealed a new way to detect and attack cancer cells using technology traditionally reserved for solar power.
Solar cells with new interfaces
Scientists from NUST MISIS (Russia) and University of Rome Tor Vergata found out that a microscopic quantity of two-dimensional titanium carbide called MXene significantly improves collection of electrical charges in a perovskite solar cell, increasing the final efficiency above 20%.
Welcome indoors, solar cells
Swedish and Chinese scientists have developed organic solar cells optimised to convert ambient indoor light to electricity.
Mapping the energetic landscape of solar cells
A new spectroscopic method now makes it possible to measure and visualize the energetic landscape inside solar cells based on organic materials.
Solar energy becomes biofuel without solar cells
Soon we will be able to replace fossil fuels with a carbon-neutral product created from solar energy, carbon dioxide and water.
A good first step toward nontoxic solar cells
A team of engineers at Washington University in St. Louis has found what they believe is a more stable, less toxic semiconductor for solar applications, using a novel double mineral discovered through data analytics and quantum-mechanical calculations.
Organic solar cells will last 10 years in space
Scientists from the Skoltech Center for Energy Science and Technology, the Institute for Problems of Chemical Physics of RAS, and the Department of Chemistry of MSU presented solar cells based on conjugated polymers and fullerene derivatives, that demonstrated record-high radiation stability and withstand gamma radiation of >6,000 Gy raising hopes for their stable operation on the near-earth orbit during 10 years or even longer.
Next-gen solar cells spin in new direction
A nanomaterial made from phosphorus, known as phosphorene, is shaping up as a key ingredient for more sustainable and efficient next-generation perovskite solar cells.
Caffeine gives solar cells an energy boost
Scientists from the University of California, Los Angeles (UCLA) and Solargiga Energy in China have discovered that caffeine can help make a promising alternative to traditional solar cells more efficient at converting light to electricity.
New properties of perovskite solar cells
Perovskite solar cells are lighter and cheaper than silicon, their production is non-toxic.
More Solar Cells News and Solar Cells Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

Why do we revere risk-takers, even when their actions terrify us? Why are some better at taking risks than others? This hour, TED speakers explore the alluring, dangerous, and calculated sides of risk. Guests include professional rock climber Alex Honnold, economist Mariana Mazzucato, psychology researcher Kashfia Rahman, structural engineer and bridge designer Ian Firth, and risk intelligence expert Dylan Evans.
Now Playing: Science for the People

#541 Wayfinding
These days when we want to know where we are or how to get where we want to go, most of us will pull out a smart phone with a built-in GPS and map app. Some of us old timers might still use an old school paper map from time to time. But we didn't always used to lean so heavily on maps and technology, and in some remote places of the world some people still navigate and wayfind their way without the aid of these tools... and in some cases do better without them. This week, host Rachelle Saunders...
Now Playing: Radiolab

Dolly Parton's America: Neon Moss
Today on Radiolab, we're bringing you the fourth episode of Jad's special series, Dolly Parton's America. In this episode, Jad goes back up the mountain to visit Dolly's actual Tennessee mountain home, where she tells stories about her first trips out of the holler. Back on the mountaintop, standing under the rain by the Little Pigeon River, the trip triggers memories of Jad's first visit to his father's childhood home, and opens the gateway to dizzying stories of music and migration. Support Radiolab today at