Tandem tin-lead perovskite solar cell with 25.5% efficiency

The US Department of Energy's National Renewable Energy Laboratory (NREL) has developed a tandem solar cell based on two layers of perovskite.

NREL claims the cell has better thermal stability and efficiency than other tandem devices based on perovskites. The researchers used a hole-transporting material made of phenethylammonium iodide (PEAI) and guanidinium thiocyanate to improve cell stability.

“The addition of guanidinium thiocyanate bolstered the carrier lifetime from less than 200 nanoseconds to 1 microsecond,” they said, noting that the use of the compound also resulted in marked improvements in the structural and optoelectronic properties of the device.

They noted that the formation of a quasi-two-dimensional (quasi-2D) structure from additives based on mixed bulky organic cations phenethylammonium and guanidinium enables critical defect control. They claim that this significantly improves the structural and optoelectronic properties of lead-perovskite thin films with a narrow-bandgap of 1.25 eV.

“The combined additives also reduced the defect density associated with tin oxidation to a level unprecedented for tin-lead perovskites and similar to the values for lead-only perovskites,” they said.

The solar cell achieved a power conversion efficiency of 25.5% and was able to retain 80% of its original efficiency after 1,500 hours of continuous operation, or more than 62 days.

“At this tandem efficiency level, the best reported stability in literature is normally several hundred hours,” the research group said. “The new cell also demonstrated an improvement in the voltage generated, at 2.1142 V. In comparison, the best certified tandem device registered 2.048 V.”

The scientists described the cell technology in “Carrier control in Sn–Pb perovskites via 2D cation engineering for all-perovskite tandem solar cells with improved efficiency and stability,” which was recently published in Nature Energy.