Dual-layer solar cell sets efficiency record

Materials scientists from the University of California, Los Angeles (UCLA) have developed a highly efficient thin-film solar cell that generates more energy from sunlight than typical solar panels, thanks to its double-layer design.

Described in the journal Science, the device is made by spraying a thin layer of perovskite — an inexpensive compound of lead and iodine that has been shown to be very efficient at capturing energy from sunlight — onto a commercially available solar cell. The solar cell that forms the bottom layer of the device is made of a compound of copper, indium, gallium and selenide, or CIGS.

The CIGS base layer, which is about 2 µm thick, absorbs sunlight and generates energy at a rate of 18.7% efficiency on its own, but adding the 1 µm-thick perovskite layer improves its efficiency. The two layers are joined by a nanoscale interface that the UCLA researchers designed; the interface helps give the device higher voltage, which increases the amount of power it can export. The entire assembly sits on a glass substrate that’s about 2 mm thick.

“With our tandem solar cell design, we’re drawing energy from two distinct parts of the solar spectrum over the same device area,” said research leader Professor Yang Yang. “This increases the amount of energy generated from sunlight compared to the CIGS layer alone.”

The cell has been found to convert 22.4% of the incoming energy from the sun — a record in power conversion efficiency for a perovskite–CIGS tandem solar cell and similar to that of the polysilicon solar cells that currently dominate the photovoltaics market. This was confirmed by independent tests at the US Department of Energy’s National Renewable Energy Laboratory and easily surpassed the previous record of 10.9%, set in 2015 by a group at IBM’s Thomas J. Watson Research Center.

“Our technology boosted the existing CIGS solar cell performance by nearly 20% from its original performance,” Prof Yang said. “That means a 20% reduction in energy costs.”

Prof Yang noted that the technique of spraying on a layer of perovskite could be easily and inexpensively incorporated into existing solar-cell manufacturing processes. He added that devices using the two-layer design could eventually approach 30% power conversion efficiency, which will be his team’s next goal.

Image caption: Qifeng Han, a visiting research associate, holds the new solar cell developed by UCLA. Image credit: Oszie Tarula/UCLA.