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 those of the first cells reported in 2009. MRS Bulletin presents the impact of a selection of recent advances in this burgeoning field.
A
research team led by Zachary Holman of Arizona State University and Michael McGehee of Stanford University has made tandem perovskite/silicon solar cells with a record-high efficiency of 26.3% that are also highly stable. Silicon/perovskite tandem cells typically contain perovskite layers deposited on top of crystalline silicon. They suffer from low stability as well as unwanted
b
25 — —LBSO — —TiO2
20 15 10
21.2% PCE (%)
a
Current Density (mA/cm2 )
O
ne of the biggest hurdles perovskite solar cells still face is their ability to weather moisture and ultraviolet rays. Using a novel method to synthesize a lanthanum-doped barium tin oxide (LBSO) electrode, Korean researchers have made solar cells that are highly stable under light exposure and boast the highest reported efficiency for devices made of the perovskite methylammonium lead iodide (CH3NH3PbI3). Devices reported in a recent issue of Science (doi:10.1126/science.aam6620) demonstrate an efficiency of 21.2% and were stable for 1000 hours under full sun. Efficient perovskite solar cells typically use titanium oxide as electrontransporting layers. However, titanium oxide reduces the stability of the devices under light. LBSO is an ideal replacement because it has a high electronconveying ability and crystalline structure compatible with perovskites. But the material crystallizes at temperatures
– 5 0 0.0
20 19.7% 10 0 0
0.2
– 25
50 75 Time (s)
0.4 0.6 0.8 Voltage (V)
1.0
1.2
(a) Structure of BaSnO3. Green, gray, and red spheres indicate Ba, Sn, and O ions, respectively. (b) Perovskite solar-cell performance with lanthanum-doped barium tin oxide (LBSO). Adapted with permission from Science 356, 167 (2017).
over 1000°C, making it hard to apply on glass and plastic surfaces. Sang-Il Seok, at the Ulsan National Institute of Science and Technology, and his colleagues came up with a solution-based route to prepare a LBSO electrode at temperatures below 300°C. They first made a colloidal solution of
LBSO nanoparticles by the reaction of BaCl2, SnCl2, La(NO3)3, and H2O2 in an NH4OH aqueous solution at 50°C. LBSO perovskite crystals developed from the colloidal solution, which the researchers coated on a fluorinedoped tin oxide substrate to create the electrode.
light absorption in the top window layer through which light enters the solar cell. This light absorption reduces efficiency, so the window layer needs to be highly transparent. Indium tin oxide (ITO) is the ideal transparent electrode used in displays and solar cells, but the sputtering method used to deposit it can damage perovskite layers. As reported recently in Nature Energy (doi:10.1038/nenergy.2017.9), the re-
searchers used a bottom silicon cell tuned t
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