New nanomaterials technique bends light, pushing the limit of thin-film absorption in solar and water-splitting applications.

A silicon solar cell harvests the energy of the sun as light travels down through light-absorbent silicon. To reduce weight and cost, solar cells are thin, and while silicon absorbs visible light well, it captures less than half of the light in the near-infrared spectrum, which makes up one-third of the sun’s energy. The depth of the material limits absorption. But what if light within the cell could be channeled horizontally so that silicon could absorb its energy along the width of the cell rather than its depth?

With such an advance in mind, Shawn-Yu Lin, professor of physics, applied physics, and astronomy, has built a nanostructure whose crystal lattice bends light as it enters the material and directs it in a path parallel to the surface, known as “parallel to interface refraction.” The structure is built of overlapping nanotubes and resembles a three-dimensional grid made of Lincoln Logs. Photonic nanocrystals built using his process enable extreme “light trapping” and could have applications from thin-film solar cells to photo-chemical functions like sensing and water splitting.