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It’s the Holy Grail at clean energy research labs all over the world and something which could address long term energy issues domestically and beyond: more efficient photovoltaic solar. We’ve told you about scientists studying full-spectrum cells, using textured substrates, trying self-regenerating nanomaterials – we’ve even reported on an anti-reflective film inspired by a coating found in moth eyes. Now a Stanford team is claiming a breakthrough in making cheaper, more efficient panels by adding a single layer of organic molecules to solar cells.
The researchers studied this technique on a fairly new type of solar cell that uses tiny particles of semiconductors called quantum dots. Quantum dot solar cells are cheaper to produce than traditional silicon cells, but they haven’t caught on due to their relative inefficiency.
For Stacey Bent, a chemical engineering professor at Stanford, this represented something of a challenge. She knew that solar cells made of a single material have a maximum efficiency of about 31 percent, a limitation of the fixed energy level they can absorb, and that quantum dot solar cells didn’t share this limitation. “Quantum dots can be tuned to absorb a certain wavelength of light just by changing their size,” the Stanford report on her research says. “And they can be used to build more complex solar cells that have more than one size of quantum dot, allowing them to absorb multiple wavelengths of light.”
So Bent and her team coated a titanium dioxide semiconductor in their quantum dot solar cell with a very thin single layer of organic molecules. They found that just that single layer, less than a nanometer thick, was enough to triple the efficiency of the solar cells.
Even with this breakthrough, there’s still work to do: Bent said the cadmium sulfide quantum dots she’s been using aren’t ideal for solar cells, so her group plans to try other molecules for the organic layer, while also tinkering with the solar cell increase light absorption.
Her theory is, said Stanford, that once the sun’s energy creates an electron and a hole, the thin organic layer helps keep them apart, preventing them from recombining and being wasted. The group has yet to optimize the solar cells, and they have currently achieved an efficiency of, at most, 0.4 percent. But the group can tune several aspects of the cell, and once they do it is said, the threefold increase caused by the organic layer would be even more significant.
By Pete Danko