Energy Focus: High-performance, long-lasting battery comes with test protocol
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n another Nature Energy article (doi: 10.1038/s41560-019-0466-3), a team lead by Hairen Tan of Nanjing University presented a different way to suppress tin oxidation in tin-lead perovskite layers. Their “simple and effective strategy” is to add metallic tin powder to the precursor solution from which perovskite films are made. In the precursor, the species Sn2+ oxidizes to Sn4+. But the metallic tin reduces
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hile most efforts on perovskite solar cells have focused on methylammonium lead trihalide perovskites, with bandgaps of 1.55 eV or higher, formamidinium-lead-iodide (FAPbI3)-based systems, with their slightly narrower bandgap, have the potential to give more efficient photovoltaic devices. The material’s drawback is that within 10 days at room temperature, it transforms from a black phase to a yellow phase— which has trigonal versus hexagonal
Energy Focus High-performance, long-lasting battery comes with test protocol
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lectric automobiles are becoming more popular and more common on the roads each year. These cars are viable because their battery banks store enough energy to facilitate daily commutes. They also deliver steady day-today performance and do not degrade rapidly. However, everyday commutes that are short and intermittent rarely tap the full capacities of these batteries. As longhaul trucks and driverless taxis transition from gasoline to electric power, their constant run time will have an adverse impact on the longevity of their batteries. Furthermore, hot and cold environments also affect the operational capabilities of electric vehicles. There is, therefore, a significant drive to deliver “beyond-lithium” cell chemistries for the next generation of batteries. The aforementioned host of dynamic variables presents a formidable challenge for these efforts: what is the most reliable
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the Sn4+ back to Sn2+, the researchers found. They filtered out the leftover metallic tin granules before making a perovskite film. “By using this strategy, we are able to reduce the Sn vacancies inside the grains and thereby achieve a long carrier-diffusion length of 3 μm in mixed Pb-Sn perovskite films,” they wrote. The resulting tin-lead perovskite films have electronic quality comparable to high-quality lead-based perovskites. This,
in turn, yielded tin-lead perovskite solar cells, with the highest reported powerconversion efficiency of 21.1%. Tandem cells made with these narrow-bandgap devices have a certified 24.8% efficiency for small-area devices (0.049 cm2) and 22.1% for large-area devices (1.05 cm2). The tandem devices retained 90% of their performance following 463 hours of operation at the maximum power point under full 1-sun illumination.
crystal symmetry, respectively—that has a wider bandgap. In a recent Science article (doi:10.1126/science.aay7044), researchers reported a method to stabilize the trigonal phase to make efficient, stable FAPbI3 solar cells. In the past, others have tried to stabilize FAPbI3 by mixing in cations and anions such as methylammonium, cesium, and bromine. But these
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