The researchers have developed four and two-terminal perovskite-perovskite tandem solar cells with ideally matched bandgaps. Each cell is printed on glass, but the same technology could be used to print the cells on plastic.
They developed an infrared absorbing 1.2eV bandgap perovskite, FA0.75Cs0.25Sn0.5Pb0.5I3, that delivers 14.8% efficiency. By combining this material with a wider bandgap FA0.83Cs0.17Pb(I0.5Br0.5)3 material, a monolithic two terminal tandem cell provides efficiencies of 17.0% with over 1.65 V open-circuit voltage. The team has also mechanically stacked four terminal tandem cells and obtain 20.3% efficiency.
"Perovskite semiconductors have shown great promise for making high-efficiency solar cells at low cost," said Michael McGehee, professor of materials science and engineering at Stanford. "We have designed a robust, all-perovskite device that converts sunlight into electricity with an efficiency of 20.3 percent, a rate comparable to silicon solar cells on the market today. The efficiency of our tandem device is already far in excess of the best tandem solar cells made with other low-cost semiconductors, such as organic small molecules and microcrystalline silicon," he said.
The infrared absorbing perovskite cells exhibit excellent thermal and atmospheric stability, which is unprecedented for these perovskite materials and enable “all perovskite” thin film solar cells to reach the highest efficiencies in the long term at the lowest costs.
The all-perovskite tandem cells we have demonstrated clearly outline a roadmap for thin-film solar cells to deliver over 30 percent efficiency," said Prof Henry Snaith, professor of physics at Oxford and co-founder of startup Oxford Photovoltaic.
"The versatility of perovskites, the low cost of materials and manufacturing, now coupled with the potential to achieve very high efficiencies, will be transformative to the photovoltaic industry once manufacturability and acceptable stability are also proven," he said.