Why adding holograms to solar cells could lead to massive performance boost

Holograms could hold the secret to solving a common problem with solar cell designs, allowing solar cells to capture sunlight that would normally be wasted and boosting electricity yields by as much as five per cent.

The research, recently published in the Journal of Photonics for Energy, was led by scientists from the University of Arizona who have proposed the use of ‘holographic light collectors’ to steer light that would normally be wasted towards parts of a solar cell that can convert the sunlight into useful electricity.

The problem the researchers were trying to solve is how to utilise parts of solar cells that are usually blocked from receiving sunlight due to the way solar cells are designed.

For example, the surfaces of solar PV cells are usually patterned with a metal grid, made from copper coated with silver or aluminium and called bus bars or ‘fingers’, on their surface. This metal grid is key to collecting the useful electricity produced in solar cells – but these ‘fingers’ also cover up parts of a solar cell that could otherwise be used to convert more sunlight into electricity.

Solar cell designers have long juggled the need to optimise the number and thickness of these metal gridlines, which can increase the amount of electricity collected from a solar cell, with the need to maximise the amount of uncovered solar cell surface area that can be directly exposed to sunlight to boost production.

In commercially available solar cells, as much as five to ten per cent of a solar cell’s service could be covered up and rendered inactive as a result of these design considerations.

To solve this problem, University of Arizona PhD student Jianbo Zhao developed a holographic light collector that can be incorporated into solar cell designs that allows light that would otherwise go unused to be redirected to parts of a solar cell that are not encumbered by the metal grid contacts on their surface.

Zhao worked under the supervision of professor of electrical and computer engineering and optical sciences, Raymond K. Kostuk, and collaborated with a fellow PhD student, Benjamin Chrysler. The researchers found that by adding the holographic light collector to solar cell designs, the overall energy yield of a solar cell could be improved by as much as five per cent.

The special holograms allow sunlight to be split up across different wavelengths, and through the use of a light diffuser, the light can then be directed towards parts of a solar cell to be converted into electricity.

Editor-in-chief of the Journal of Photonics for Energy, Sean Shaheen from the University of Colorado Boulder, said that the solution proposed by Zhao was noteworthy because it was a low cost and easily scalable design technique that produced a significant improvement in energy yield.

“The enhancement of approximately five per cent in annual yield of solar energy enabled by this technique could have large impact when scaled to even a small fraction of the 100s of gigawatts of photovoltaics being installed globally,” Shaheen said.

“Professor Kostuk’s team has demonstrated their holographic approach with a low-cost material based on gelatin, which is readily manufactured in large quantity. And while gelatin is normally derived from animal collagen, progress in lab-derived versions has made it likely that synthetic alternatives could be used at scale.”

The researchers found that the addition of the holographic materials had the greatest impact on solar panel performance when the solar panels were combined with a sun tracking system, but notable improvements in performance could still be achieved for stationary panels.