Scientists at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL), CU-Boulder and the University of Toledo have demonstrated a tin-lead perovskite cell that overcomes problems with stability and improves efficiency. The new cell, a tandem design with two layers of perovskites, reached 25.5% efficiency.
The new cell also retained 80% of its maximum efficiency after 1,500 hours of continuous operation, or more than 62 days.
“This represents an accelerated aging test in the lab,” said Kai Zhu, a senior scientist at NREL and co-author of a new paper detailing the research. “At this tandem efficiency level, the best reported stability in literature is normally several hundred hours.”
Many of the researchers in this work previously demonstrated (in a 2019 paper published in the journal Science) a tin-lead tandem perovskite cell with an efficiency measured at 23.1%. They compensated for any problems caused by tin by adding the chemical compound guanidinium thiocyanate, which resulted in marked improvements in the structural and optoelectronic properties of the cell. Solar cells create electricity when sunlight triggers the movement of electrons. A longer carrier lifetime associated with the movement improves the efficiency of the cell. The addition of guanidinium thiocyanate bolstered the carrier lifetime from less than 200 nanoseconds (each nanosecond is a billionth of a second) to 1 microsecond (or a millionth of a second).
Improving upon that earlier experiment, the scientists added phenethylammonium iodide along with guanidinium thiocyanate. The improved tin-lead perovskite saw its carrier lifetime increase to about 9 microseconds. 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.
The new cell also demonstrated an improvement in the voltage generated, at 2.1142 volts. In comparison, the best certified tandem device registered 2.048 volts.