New Sideways Solar Cells Yield Greater Efficiency

Hongrui Jiang inspects the alignment of a light source to illuminate new-generation lateral solar cells. The solar cells developed by Jiang's group harvest almost three times more electricity from incoming light as compared to existing technologies. (Image courtesy of Stephanie Precourt.)

A team of engineers recently developed a unique type of solar panel that shows potential for powering personal devices. Small, efficient, and flexible, the micro-scale solar cells developed by the team greatly improve on comparable devices. Their trick? Turn the cells on their side.

Sideways Solar Cells

Solar panels mounted on rooftops generate electricity through charges that move vertically. The top-down solar cells employed in these panels are comprised of two electrodes surrounding a semiconducting material, such as silicon. Sunlight hits the top layer, excites electrons, and produces an electrical current that flows to the bottom layer.

One drawback to this method is that the top electrode must both be highly transparent as well as electrically conductive, a difficult combination for most materials. Another drawback is that the multiple layers of the top-down solar cell must be perfectly aligned on top of one another, which is a cumbersome step in the fabrication process.

Traditional solar cells (left) make use of vertically moving charges, while sideways solar cells (right) capture charge moving laterally. (Image courtesy of Hongrui Jiang.)

Both of these problems can be solved by turning solar cells on their side. These lateral solar cells are packed together in a side-by-side array of electrodes atop transparent glass. In this way, the two functions of the cell – harvesting light and conducting charge – are decoupled. Furthermore, this approach makes fabricating the cells easier by eliminating the need for precise alignment of multiple layers.

Advancements in Lateral Solar Cells

The team, led by electrical and computer engineering professor Hongrui Jiang from the University of Wisconsin-Madison, is not the first to develop lateral solar cells. However, their efforts offer significant improvements over those previously developed. More specifically, the best existing lateral cells converts 1.8 percent of sunlight into useable electricity. Jiang’s team achieved an efficiency almost three times better, maxing out at 5.2 percent.

"We easily beat all of the other lateral structures," said Jiang. "In other structures, a lot of volume goes wasted because there are no electrodes or the electrodes are mismatched. The technology we developed allows us to make very compact lateral structures that take advantage of the full volume."

The team is still working to make their cells even smaller and more efficient. If successful, their technology could be ideal for powering medical sensors or personal devices such as smartwatches. But the team has another interesting application in mind: eventually, they hope to develop solar cells that can power autofocusing contact lenses.

For more news from the world of solar energy, check out these flexible solar cells with flexible applications.