Research highlights: Perovskites
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RESEARCH HIGHLIGHTS :
Perovskites
By Prachi Patel Feature Editor: Pabitra K. Nayak
Research on perovskites has progressed rapidly, with solar-cell efficiencies now at 22%, five times higher than first cells reported in 2009. MRS Bulletin presents the impact of a selection of recent advances in this burgeoning field.
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Current Density (mA/cm2 )
aterials scientists a b at the University 0 of Oxford and Stanford –5 University report highperformance perovskite– –10 perovskite tandem cells using efficient and sta–15 ble lead- and tin-based –10 1.2 eV Cell perovskites. 1.8 eV Cell So far, researchers –25 2T Tandem have made tandem cells –30 by putting perovskite 0.0 0.5 1.0 1.5 Voltage (V) cells, which have a wide energy bandgap, on top of low-bandgap silicon cells. (a) Scanning electron micrograph of the two-terminal (2T) all-perovskite solar cell with the schematic for the monolithic Perovskite-only tandem tandem cell operation; (b) current–voltage curves for the single junction and tandem solar cells. Credit: Pabitra Nayak. cells would cost less and be easier to produce. The research team perovskite. By coupling solar cells made efficiency of 17% and a four-termiled by Henry Snaith (Oxford) and with these two materials, the researchnal all-perovskite solar cell with an Michael McGehee (Stanford) used ers demonstrated a monolithic two-terefficiency of 20.3%. The researchFA 0.75Cs 0.25Pb 0.5Sn 0.5I 3 as the lowbandgap (1.22 eV) and FA0.83Cs0.17Pb minal all-perovskite tandem solar cell ers reported their findings in Science (I0.5Br0.5)3 (1.8 eV) as the high-bandgap (see Figure) with a power-conversion (doi:10.1126/science.aaf9717).
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hin films of lead halide perovskites are remarkably efficient at converting light to electricity, even when they have defects. A research group has now uncovered the secret behind this trait. Charge carriers in hybrid organic–inorganic perovskites, they argue, acquire a dynamic cloaking screen that allows them to travel through the material without colliding with defects.
Researchers led by Xiaoyang Zhu of Columbia University compared charge dynamics in lead bromide perovskites with three different cations: organic methylammonium and formamidinium, and inorganic cesium. They made single-crystal samples of the materials and conducted time-resolved photoluminescence and time-resolved optical Kerr effect spectroscopy measurements.
Organic cations in the hybrid perovskites are dipoles that rotate freely as in a liquid. The dynamic reorientation of these dipoles creates an effective cloaking fi eld for charged particles, keeping them from scattering by defect centers or optical phonon modes. The researchers report their work in Science (doi:10.1126/science. aaf9570).
Prachi Patel, [email protected] Pabitra K. Nayak, [email protected]
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