Research highlights: Perovskites
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RESEARCH HIGHLIGHTS :
Perovskites
By Prachi Patel Feature Editor: Pabitra K. Nayak
Research on perovskites has progressed rapidly since the first perovskite-based solar cells with ~4% efficiency were reported in 2009. MRS Bulletin presents a selection of recent advances in this burgeoning field.
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any scientists believe that metalhalide perovskite solar cells will first see the light of day commercially in tandem form, stacked above silicon cells. This promises to boost commercial silicon module efficiency from about 20% to over 30%. But the necessary energy bandgap to realize such high-efficiency tandem cells has only been found in unstable perovskites.
Henry Snaith and his colleagues at the University of Oxford have concocted a light-stable perovskite with an ideal 1.74 eV bandgap for Si-perovskite tandem cells. The researchers substituted part of the formamidinium cations in formamidinium lead-halide perovskites with cesium. Solar cells made from the new material, [HC(NH2)2]0.83Cs0.17Pb(I0.6Br0.4)3, have a power-conversion efficiency of
17% on their own. By combining the cells with 19% efficient silicon cells, the researchers were able to make tandem cells that are over 25% efficient. “With further improvements … it is feasible that this system could deliver up to 30% efficiency,” the researchers said in their article published recently in Science (DOI: 10.1126/science. aad5845).
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esearchers at the École Polytechnique F´edérale de Lausanne, led by Wolfgang Tress, have tailored a new perovskite composition to make solar cells with a record-breaking 20.8% power-conversion efficiency. They reported the findings in a recent issue of Science Advances (DOI: 10.1126/ sciadv.1501170).
The researchers made the perovskite film in a single step from a solution of formamidinium iodide, lead iodide, methylammonium bromide, and lead bromide in a mixed solvent containing dimethyl formamide and dimethyl sulfoxide. The resulting mixed-cation, mixed-halide perovskite is rich in PbI2. The researchers reported that films with
excess PbI2 show suppressed non-radiative recombination of electrons and holes, which decreases the solar cell efficiency. The external electroluminescence quantum efficiency, a marker of good cells, of the perovskite solar cell is reported be at 0.5%, a number approaching the best silicon solar cells on the market.
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and (2) reducing the content of metallic lead atoms, which quench excitons in the film. To make the nanograin perovskite films, the researchers dripped chloroform onto the spinning MAPbBr3 layer during spin coating. To reduce lead atoms, they used excess (2–7%) MABr in the perovskite solution.
erovskites’ promise for lightemitting devices (LEDs) has been hampered so far by low luminescent efficiency. Recently, researchers from Korea and the UK, led by Tae-Woo Lee of Pohang University of Science and Technology, reported perovskite LEDs with a current efficiency (at 42.9 cd/A) competitive to that of organic LEDs in Science (DOI: 10.1126/ science.aad1818). The team achieved the high e
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