A high-efficiency tandem perovskite solar cell could be ready for use in full-sized solar panels in the consumer market in the near future, said scientists at the University of Toledo, who are collaborating with the U.S. Department of Energy’s National Renewable Energy Lab to improve the material. The researchers used guanidinium thiocyanate (GuaSCN) to fine-tune the mix of tin and lead in the perovskite films and improve their structural and optoelectronic properties. The mixed tin-lead organic-inorganic perovskite material, which contains a small fraction of GuaSCN, has demonstrated a low bandgap, long charge-carrier lifetime. Professor Zhaoning Song holds a perovskite solar cell mini-module he developed with professor Yanfa Yan. The higher-efficiency, lower-cost solar cell technology could revolutionize the way that energy is generated. Courtesy of Daniel Miller, University of Toledo. The enhanced perovskite films have defect densities that are lower by a factor of 10, leading to carrier lifetimes of greater than 1 μs and diffusion lengths of 2.5 μm. These advances enabled the team to demonstrate low-bandgap perovskite solar cells with greater than 20% efficiency. When combined with wider-bandgap perovskite solar cells, the team achieved 23.1% efficiency in the tandem solar cells. In comparison, silicon solar panels have around an 18% efficiency rating. The all-perovskite tandem solar cell brings together two different solar cells to increase the total electrical power generated by using two different parts of the sun’s spectrum. “Our tandem solar cells with two layers of perovskites deliver high-power conversion efficiency and have the potential to bring down production costs of solar panels, which is an important advance in photovoltaics,” said professor Zhaoning Song. While the team has improved the quality of the materials and the process to manufacture them at a low cost, more progress needs to be made. “The material cost is low and the fabrication cost is low, but the lifetime of the material is still an unknown,” Song said. “We need to continue to increase efficiency and stability.” “Also, lead is considered a toxic substance,” said professor Yanfa Yan. “I am determined to work with the solar industry to ensure solar panels made of this material can be recycled so they don’t cause harm to the environment.” In April 2019, the U.S. Department of Energy awarded Yan a $1.1 million grant to continue his research. The research was published in Science (https://doi.org/10.1126/science.aav7911).