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."
