The device is made by spraying a thin layer of a lead-based perovskite onto a commercially available solar cell made using a compound of copper, indium, gallium and selenide (CIGS).
The team’s cell converts 22.4 percent of the incoming energy from the sun, which is says is a record for a perovskite-CIGS tandem solar cell, confirmed by the US Department of Energy’s National Renewable Energy Laboratory. Other groups such as Ascent Solar and Oxford PV are working on boosting the performance and manufacutrability of perovskite-based tandem cells. Other tandem cells using perovskite materials on silicon substrates have shown efficiencies over 25 percent.
“With our tandem solar cell design, we’re drawing energy from two distinct parts of the solar spectrum over the same device area,” said Yang Yang, Jr. Professor of Materials Science at UCLA. “This increases the amount of energy generated from sunlight compared to the CIGS layer alone.” 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 thick, absorbs sunlight and generates energy at a rate of 18.7 percent efficiency on its own, but adding the 1 micron-thick perovskite layer improves the efficiency by converting more of the light landing on the cell. 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 percent from its original performance,” said Yang. “That means a 20 percent reduction in energy costs.”
He added that devices using the two-layer design could eventually approach 30 percent power conversion efficiency, which is the next goal for the research group.