Quantum dots improve the stability of solar recovery perovskite crystals

The University of Toronto's engineering researchers combined two emerging technologies for next-generation solar energy and discovered that each one helped stabilize the other. The hybrid material that results is a major step in reducing the cost of solar energy while increasing the potential uses.

Today, almost all solar cells are made of high purity silicon. It is 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 studying complementary materials that can improve the silicon solar capture potential by absorbing different wavelengths of light than silicon.

"Two of the technologies we use in our lab are perovskite crystals and quantum dots," said Sargent. "These two solutions are compatible with solution processing, imagine a" solar ink "that can be printed on flexible plastic to create flexible and cost-effective solar cells, or we can combine them in front of or behind silicon solar cells to improve their performance. efficiency. "

One of the main challenges for both perovskites and quantum dots is stability. At room temperature, some types of perovskites undergo an adjustment of the 3D crystalline structure that makes them transparent – they no longer absorb solar radiation completely.

For their part, the quantum dots must be covered with a thin layer called the passivation layer. This layer – a single molecule of thickness – prevents quantum dots from sticking to each other. But temperatures above 100 ° C can destroy the passivation layer, causing aggregation or agglutination of quantum dots, reducing their ability to capture light.

In an article published today in Nature, a team of researchers from the Sargent laboratory has described a way to combine perovskites and quantum dots that stabilizes them.

"Before that, people usually tried to treat both problems separately," said Mengxia Liu, the newspaper's chief author.

"Research has shown the successful growth of hybrid structures incorporating both perovskites and quantum dots," said Liu, currently a postdoctoral fellow at the University of Cambridge. "This has prompted us to consider the possibility that both materials will stabilize if they share the same crystalline structure."

Liu and the team have built two types of hybrid materials. One was mainly composed of quantum dots containing about 15% perovskites by volume and is designed to turn light into electricity. The other was mainly perovskites with less than 15% of quantum dots in volume and is better suited for the transformation of electricity into light, for example in the context 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. As for the quantum dot, when it is heated to 100 ° C, the aggregation of nanoparticles is five times lower than if they had not been stabilized with perovskites.

"This proved our hypothesis remarkably well," says Liu. "It was an impressive result beyond our expectations."

The new document provides a proof of concept for the idea that these types of hybrid materials can improve stability. In the future, Liu hopes that solar cell manufacturers will build on his ideas and further improve them to create solution-treated solar cells that meet all the same criteria as traditional silicon.

"Industrial researchers could experiment using different chemical elements to form perovskites or quantum dots," says Liu. "What we have shown is that it is a promising strategy to improve stability in this type of structures."

"Perovskites have shown tremendous potential as solar materials, but fundamental solutions are needed to turn them into stable, robust materials that can meet the high demands of the renewable energy sector." says Jeffrey C. Grossman, Professor Morton and Claire Goulder and his family, Environmental Systems Specialist, and Professor in the Materials Science and Engineering Department of the Massachusetts Institute of Technology, who did not participate in the study. "The Toronto study shows an exciting new way to advance the understanding and realization of stable perovskite crystalline phases."

Liu attributes this discovery in part to the team's collaborative environment, which included researchers from many disciplines, including chemistry, physics, and his own field of materials science.

"Quantum and perovskite dots have distinct physical structures and the similarities between these materials have generally been overlooked," she says. "This discovery shows what can happen when we combine ideas from different fields."