UCLA researchers have recently reported a highly efficient thin-film solar cell with a double-layer design that converts 22.4% of the incoming energy from the sun. The device is made by spraying a thin layer of perovskite 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 performance was reportedly confirmed in independent tests at the U.S. Department of Energy’s National Renewable Energy Laboratory. The UCLA device’s efficiency rate is similar to that of the poly-silicon solar cells that currently dominate the photovoltaics market.

“With our tandem solar cell design, we’re drawing energy from two distinct parts of the solar spectrum over the same device area,” the team said. “This increases the amount of energy generated from sunlight compared to the CIGS layer alone.” They added that the technique of spraying on a layer of perovskite could be easily and inexpensively incorporated into existing solar-cell manufacturing processes.

The cell’s CIGS base layer, which is about 2 microns (or two-thousandths of a millimeter) thick, absorbs sunlight and generates energy at a rate of 18.7% efficiency on its own, but adding the 1 micron-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 millimeters thick.

“Our technology boosted the existing CIGS solar cell performance by nearly 20% from its original performance,” the researchers said. “That means a 20% reduction in energy costs.” They added that devices using the two-layer design could eventually approach 30% power conversion efficiency. That will be the research group’s next goal.