Scientists at the Department of Energy’s Sandia National Laboratories are using nanowires to strengthen a promising solar material known as indium gallium nitride to expand a photovoltaic device’s ability to absorb wavelengths of light. .

Most photovoltaic material can only absorb one or two wavelengths of light from the solar spectrum. The most common ones can harness visible light but not others, such as ultraviolet and infrared light.   Scientists believe that increasing the variety of wavelengths a solar cell can absorb will increase its efficiency.

Indium gallium nitride is a photovoltaic material that is easily “tweaked” to absorb different parts of the solar spectrum. Changing the concentration of indium changes which wavelengths of light it responds to.

By controlling the amount of indium, scientists can design a cell that can absorb more of the solar spectrum. However, structural deficiencies are hampering the commercial use of indium gallium nitride.

Indium gallium nitride is typically gown on thin films of gallium nitride. The atomic layers of gallium nitride have different crystal lattice spacing from indium gallium nitride atomic layers and the mismatch leads to structural strain that limits the layer thickness and percentage of indium that can be added.

In order to get around this weakness, Sandia National Laboratory scientists Jonathan Wiere Jr. and George Wang grew their indium mixture on a phalanx of nanowires, rather than a thin film.

They found that the small surface areas of the nanowires allow the indium layer to “relax,” easing strain.  This allowed them to create a nanowire solar cell with indium percentages of roughly 33 percent, higher than any other reported attempt.

While the initial attempt also resulted in lower power conversion efficiencies of 0.3 percent, the scientists believe that refinements would lead to higher efficiencies.

The research was funded by the Department of Energy’s Office of Science through the Solid State Lighting Science Energy Frontier Research Center and Sandia’s Laboratory Directed Research and Development Program. – K.R. Jalbuena

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