Quantum dots, a Ghostbuster backpack & the future of solar technology

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Sometimes, it just takes a Google search to overcome a big technical hurdle in a lab. OK, so it didn’t quite happen that way, but for Illan Kramer, a University of Toronto researcher and IBM employee, a simple search turned up the right tool that helped him make a working solar cell out of quantum dots, with are ultra tiny semiconductor bits.

Kramer’s efforts have now demonstrated how to spray a coating of quantum dots using a nozzle that Japanese company, Ikeuchi, developed for steel makers to cool steel with a fine mist of water. Previously, quantum dot solar cell research was mostly focused on using spin-coating, where the semiconductor compound is applied on a substrate that spins to spread the materials. But that process is slow, which means it’d be an expensive way to mass produce solar cells because the equipment cannot coat a large area quickly.

By contrast, silicon solar cells, which dominate the market today, are made by melting and shaping the semiconductor material into rods that are then sliced into wafers. Those wafers then undergo chemical treatment before being assembled into panels.

I caught up with Kramer, a post-doc fellow, because I wanted to learn more about what his research could mean for the future of solar technology. The breakthrough create the ability to quickly print solar materials on a variety of surfaces, including those that are currently unsuitable for placing the thicker and more brittle silicon solar cells. IBM doesn’t make solar cells, but it’s run a solar research lab for years and works on finding manufacturing partners that can license its technology.

U. of Toronto IBM solar quantum dots Illam Kramer

To motivate himself to achieve the next research milestone, Kramer said he conjured up a futuristic image of men with Ghostbusters-style backpacks spraying solar materials onto home roofs. “If only you could one day buy a (solar) spray can at Home Depot the way you can do with a can of paint. But that’s a really long way off,” said Kramer, laughing over the phone during an interview. More likely, a first-generation product would involve a thin layer of quantum dots sprayed onto glass or a flexible material on an assemble line that would then be installed on a building.

I love that Ghostbuster backpack idea, too. After writing about solar technology for six years and witnessing the death of many startups attempting to bring to market ultra-thin and flexible solar cells with all sorts of non-silicon materials, I wonder how solar technology will evolve in the next few decades. Will we mostly see increasingly efficient and thinner silicon cells, which would increase energy production while reducing the material cost? Will there be more color choices for cells beyond blue and black? And do solar panels always have to be rectangular?

Not that there’s been a dearth of research in academic and company labs around making cells that look quite different than what’s available to consumers today. But efforts to commercialize these types of cells haven’t been very successful, mostly because the technology hasn’t been nearly as cheap or efficient as the silicon version.

Konarka Technologies tried to make money from printing an organic compound onto plastic but filed for bankruptcy in 2012. And, yes, there was the spectacular demise of Solyndra, whose novel design of lining copper-indium-gallium-selenide cells inside tubes drew huge crowds at trade shows.

There’s still a lot of cool solar technology research underway that may one day make a market debut, such as using silicon or other materials to build nanowires to improve a cell’s efficiency. Research into producing perovskites, a class of solar compounds with a particular crystalline structure, appears very promising at creating efficient and cheap solar cells that can be tuned into different colors.

U. of Toronto IBM solar quantum dots spray coating

Quantum dots make for an intriguing area of solar research because the tiny size and shape of these nanocrystals make it possible to engineer them to be able to absorb different parts of the light spectrum. The way silicon is created today doesn’t allow it to offer that flexibility.

Kramer is using lead sulfite, which has been shown to work well for creating quantum dots, to make solar cells measuring 1 inch by 1 inch. The best cell that his team has made with the spay-painting method can covert just over 7 percent of the sunlight. That is lower than the 9.24 percent efficiency, a world record for quantum dots, that his fellow researchers at the same lab recently created using spin coating, he noted.

The goal, of course, is to not only to exceed the spin-coating method but to chase after the efficiencies of silicon solar cells, which are mostly in the mid- to high teens. Kramer also wants to develop equipment that could produce cells more cheaply by printing quantum dots, which are suspended in a liquid, on rolls of substrates that could range from glass to plastic. Once the solvent in the liquid evaporates, the nanoparticles are left and then will undergo further chemical treatment to activate their ability to produce electricity by absorbing light.

The path to designing equipment and a process that can mass produce quantum dots is still a long way off. It will likely take 5 to 10 years, Kramer noted.

But there is still cause for optimism. “We are really excited about this process of making nanoparticle ink and using a printing process. You don’t need a billion dollar foundry,” to do it, he said.

Images courtesy of University of Toronto and IBM

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