A team from the University of Toronto is researching materials that could enhance the solar-harvesting potential of silicon by absorbing wavelengths of light that silicon does not absorb. The researchers have demonstrated that perovskite crystals and quantum dots, working together, could increase the stability of solar materials. One of the challenges in the use of both perovskites and quantum dots for harvesting solar energy is maintaining their stability. At room temperature, some types of perovskites experience an adjustment in their 3D crystal structure that renders them transparent and no longer able to fully absorb solar radiation. Quantum dots must be covered in a thin layer known as a passivation layer to prevent them from sticking to each other. Temperatures above 100 °C can destroy the passivation layer, causing the quantum dots to aggregate and destroying their ability to harvest light. Researcher Mengxia Liu is the lead author on a new paper in Nature that describes a way to combine two promising solar technologies — perovskites and quantum dots — in order to enhance their stability. Courtesy of Sanyang Han. The Toronto team considered the possibility that the two materials could stabilize each other if they shared the same crystal structure. It built two types of hybrid materials. One type was primarily quantum dots with about 15% perovskites by volume, and was designed to turn light into electricity. The other type was primarily perovskites with less than 15% quantum dots by volume, and was primarily suited to turning electricity into light, as part of an LED, for example. The team was able to show that the primarily perovskite material remained stable under ambient conditions (25 °C and 30% humidity) for six months — about 10 times longer than materials composed of the same perovskite but without the addition of quantum dots. When the primarily quantum dot material was heated to 100 °C, the aggregation of the nanoparticles was five times lower than if the material had not been stabilized with perovskites. In the future, the researchers hope that their discovery will be used by solar cell manufacturers to create solution-processed solar cells that meet the same criteria as traditional silicon. Both perovskite crystals and quantum dots are amenable to solution processing. For example, said professor Ted Sargent, a “solar ink” could be printed onto flexible plastic to create low-cost, bendable solar cells. “Industrial researchers could experiment by using different chemical elements to form the perovskites or quantum dots,” said researcher Mengxia Liu. “What we have shown is that this is a promising strategy for improving stability in these kinds of structures. “Perovskite and quantum dots have distinct physical structures, and the similarities between these materials have been usually overlooked,” Liu said. “This discovery shows what can happen when we combine ideas from different fields.” The research was published in Nature (https://doi.org/10.1038/s41586-019-1239-7).
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