The researchers say the cell has a top perovskite cell with a transparent back contact made of indium zinc oxide and a commercially established cadmium telluride bottom device. They claim the champion tandem cell has the potential to reach a 30% efficiency. A research group at the University of Toledo in the United States has designed a four-terminal (4T) tandem solar cell with a top device relying on a perovskite absorber with a tunable wide-bandgap and a bottom cell using a commercially