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Electron-Transfer Boost For Solar Cells

Molecular Electronics: Researchers report 24-fold improvement in the efficiency of metal-to-semiconductor electron transfer

by Stu Borman
August 17, 2015 | A version of this story appeared in Volume 93, Issue 32

Credit: Science
These TEM images show CdSe nanorods with tips made from spherical gold nanoparticles.
Micrograph of gold-tipped cadmium slenide nanorods.
Credit: Science
These TEM images show CdSe nanorods with tips made from spherical gold nanoparticles.

A study reports significant improvement in the efficiency of a physical process that has been one hurdle for creating combination metal-semiconductor solar cells. Solar cells typically rely on semiconductors to generate electrons from light. Some scientists would like to use metal nanoparticles for this step because they’re up to 100 times as efficient as semiconductors. But light-induced electrons in metals don’t last long. They recombine with electron vacancies, called holes, so quickly that less than 1% of them ever reach the adjacent semiconductor layer, a step needed to complete a circuit. Tianquan (Tim) Lian of Emory University and coworkers experimented with different combinations of materials and found that they could get 24% of the electrons generated by gold nanoparticle surface plasmons—photoinduced electron oscillations that occur at the air-nanoparticle surface—to relocate to a cadmium selenide semiconductor (Science 2015, DOI: 10.1126/science.aac5443). The improvement in efficiency is attributed to a newfound mechanism called plasmon-induced interfacial charge-transfer transition (PICTT), which the researchers believe may work with electrons in other materials.

Photon stringing a nanorod and creating electrons.
Credit: Science/Courtesy of Phillip Christopher
Light generates electrons through surface plasmons (red squiggles) on a gold nanoparticle (left). These electrons travel to a cadmium selenide nanorod (right) by a direct charge-transfer mechanism that is much more efficient than the conventional indirect route (bottom); e = electron and h+ = hole.


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