Researchers at The University of Toledo (UT) in Ohio (US) have developed an all-perovskite tandem solar cell that has reportedly achieved world-record conversion efficiency. The new kind of less-toxic device combines two different cells to harvest different parts of the solar spectrum, resulting in increased total electrical power generated.
“We developed a process to fabricate efficient bottom cells using mixed Sn-Pb perovskite absorbers,” says Yanfa Yan, PhD, Ohio Research Scholar chair and UT professor of physics. The fabrication of the efficient bottom cell, which he says had not been accomplished before, is what is truly innovative about this research work. “Our all-perovskite solar cells have the so-called four-terminal structure, which stacks a wide-band-gap top cell with a low-band-gap bottom cell. The current all-perovskite tandem cells are limited by the lack of efficient bottom cell.”
Breakthrough maximum power conversion efficiency <17%
In the paper “Low-bandgap mixed tin–lead iodide perovskite absorbers with long carrier lifetimes for all-perovskite tandem solar cells,” published in Nature Energy, Yan and his co-authors report efficient mixed tin-lead iodide low-band gap (∼1.25 eV) perovskite solar cells with open-circuit voltages up to 0.85 V and over 70% external quantum efficiencies in the infrared wavelength range of 700–900 nm, delivering a short-circuit current density of over 29 mA cm−2 and demonstrating suitability for bottom-cell applications in all-perovskite tandem solar cells. “Our low-band-gap perovskite solar cells achieve a maximum power conversion efficiency of 17.6% and a certified efficiency of 17.01% with a negligible current–voltage hysteresis. When mechanically stacked with a ∼1.58 eV band gap perovskite top cell, our best all-perovskite 4-terminal tandem solar cell shows a steady-state efficiency of 21.0%,” they write in the paper.
The performance of the all-perovskite tandem solar cell indeed presents a paradigm shift: “Our mixed Sn-Pb perovskite thin films exhibit very high quality, showing long carrier lifetimes and allows us to use thick enough perovskite layers to efficiently absorber photons in the long wavelength range,” confirms Yan, adding that the record-breaking technology has the potential to produce low-cost solar electricity.
Yan and his colleagues have received tremendous recognition from peers in the solar research community for this achievement. Asked what aspect he thinks astonished people the most, Yan responds: “We demonstrated that the mixed Sn-Pb perovskites can be made in high quality and are capable of producing highly efficient solar cells.”
As a result, the research success reported by The University of Toledo could indeed have significant impact on the design of the next generation of solar cells. “As the band gap is more towards the optimum band gap for single junction solar cell application, our results point to a new direct for producing ultra-high efficiency perovskite solar cells,” the expert agrees.
What lies ahead? “To further improve the performance of our bottom cell and the performance of the tandem cells, including both four-terminal and two-terminal ones,” Yan says.
Written by Sandra Henderson, Research Editor, Solar Novus Today