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Energy Efficiency

Protecting Semiconductors in Solar-Field Generators from Corrosion
05/30/2014

Scientists at the California Institute of Technology have devised a new method of protecting the materials in solar-field generators from corrosion.

Solar-powered generators that can split water to yield hydrogen gas have been of significant interest in recent years as a means to create clean fuel. In order to function properly, these devices require light-absorbing materials that capture sunlight to drive the chemical reactions involved in water splitting. Semiconductors like silicon and gallium arsenide fit this requirement, as displayed by their incorporation in many solar panels; however, these materials rust when submerged in the liquid solutions found in these generators and therefore are currently not suitable. Previous research has yielded different protective layers, but these have either been too thin, allowing the solution to penetrate through and corrode the semiconductor, or too thick, preventing corrosion but also blocking the semiconductor from absorbing enough light.

Now, a new technique from researchers at Caltech’s Joint Center for Artificial Photosynthesis (JCAP) could effectively protect these semiconductors from corrosion while still allowing them to absorb light.

“For the better part of a half century, these materials have been considered off the table for this kind of use,” Nate Lewis, the George L. Argyros Professor and professor of chemistry at Caltech, and the principal investigator on the paper, said. “But we didn’t give up on developing schemes by which we could protect them, and now these technologically important semiconductors are back on the table.”

The researchers used a process known as atomic layer deposition to create a layer of “leaky” titanium dioxide (TiO2)—so-called because it leaks electricity—on single crystals of silicon, gallium arsenide or gallium phosphide. First developed in the 1990s as a material for computer chip construction but discarded because of its charge-leaking behavior, “leaky TiO2” turned out to be the ideal material to protect semiconductors in solar-fuel generators from corrosion while also allowing light to be absorbed and electrons to pass through with minimal resistance.

The TiO2 was deposited as a film ranging in thickness between 4 and 143 nanometers, with 100-nanometer thick “islands” of a nickel oxide material that successfully catalyzed the oxidation of water to form molecular oxygen placed on top.

“This is already a record in terms of both efficiency and stability for this field, but we don’t yet know whether the system fails over the long term and are trying to ensure that we make something that will last for years over large areas, as opposed to weeks,” Lewis said. “That’s the next step.”

The study, titled “Amorphous TiO2 Coatings Stabilize Si, GaAs, and GaP Photoanodes for Efficient Water Oxidation,” is published in the journal Science. The research was supported by the Office of Science of the U.S. Department of Energy through an award to JCAP, a DOE Energy Innovation Hub; the Resnick Sustainability Institute; and the Beckman Institute at Caltech. Additional coauthors on the paper include graduate students Matthew Shaner, Joseph Beardslee, and Michael Lichterman, as well as Bruce S. Brunschwig, director of the Molecular Materials Resource Center at Caltech.

 

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