How Efficient Can Solar Photovoltaics Become?

Cesar ClaveroCosts for some solar photovoltaics (PV) have dropped sharply over the past few years, but efficiency has not necessarily followed suit. The search for PV modules that are both low-cost and highly efficient continues at government research labs.

Plasmonic energy conversion, which generates “hot” (highly energetic) electrons in plasmonic nanostructures through the electromagnetic decay of surface plasmons, is one promising solution. It offers potentially high conversion efficiencies (greater than 22 percent) while keeping fabrication costs low, given the right materials, architectures, and fabrication methods.

César Clavero, an Environmental Energy Technologies Division researcher at Lawrence Berkeley National Laboratory, surveyed the current state of the technology. The resulting paper, “Plasmon-induced hot electron generation in nanoparticle/metal oxide interfaces for photovoltaic and photocatalytic devices,” was published in the January 30 issue of Nature Photonics.

The review found that two key factors promote high conversion efficiencies: fast hot-electron injection before recombination and optimum carrier regeneration. The research also suggests that by combining multiple metals and conducting oxides, the devices will be able to generate electricity from more spectrums of solar radiation, thereby increasing electricity production.

Clavero found that material, size, and shape of the plasmonic nanostructures are the most important design factors affecting the localized surface plasmon resonance (LSPR) electron-generation processes. Plasmonic energy conversion could solve the problem of efficiency decreases at higher temperatures, which affects conventional PV cells, because the efficiency with plasmonic structures actually increases with temperature.

While titanium dioxide has been the most-used semiconductor for plasmonic energy conversion, Clavero suggests that the valence bands of zinc oxide, cerium oxide, and silver bromide could also make them efficient electron acceptors. Further studies will need to determine the most efficient semiconductor material.

This work was supported by the Department of Energy’s Office of Energy Efficiency and Renewable Energy, Office of Building Technology.

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