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.
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he biggest hurdle to the commercialization of perovskite solar cells is that organic–inorganic metal-halide perovskites tend to decompose into their consitutents in the presence of humidity and at high temperatures. Researchers have now made the devices more stable at high temperatures by adding an impermeable tin oxide and an aluminumdoped zinc oxide layer to a conventional perovskite cell architecture. Typical perovskite solar cells employ an inverted cell architecture, in which positive charge carriers, or holes, are extracted from a PEDOT layer that is deposited on the transparent electrode. Electrons are extracted from the other electrode, which is a metal. Thomas Riedl of the University of Wuppertal in Germany and his colleagues added a 20-nm-thick tin oxide (SnOx ) layer followed by a 100-nm-thick
aluminumdoped zinc oxide (AZO) layer between the perovskite and the top metal electrode. The – – AZO is an excellent electron conductor, and the SnO x layer is crucial for blocking moisture. Cells with the protective bi- Credit: Nature Communications. layer lasted for more than 350 hours at 60°C, while those without the hours in ambient air with 50% humidtin degraded within 100 hours. The work ity, whereas those without the SnOx layer degraded within tens of hours. The is reported in Nature Communications bilayer cells also lasted more than 1000 (doi:10.1038/ncomms13938).
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of the paper in Nature Communications (doi:10.1038/ncomms13941). This method could eventually improve power-conversion efficiencies in light-emitting diodes as well as solar cells. Photon recycling involves light-generated electrons and holes recombining to produce a photon, and the process of charge separation and recombination continuing until the charges are extracted at the electrical contacts or the photons escape the film. The more photons that escape the film, the better the performance of the light-emitting devices or solar cells.
ast summer, physicists at the University of Cambridge discovered that perovskites can reuse photons multiple times. By depositing thin perovskite films on textured surfaces, the Cambridge team, led by Felix Deschler and Richard Friend, has now been able to extract these recycled photons and boost the external photoluminescent quantum efficiency of devices. “We were surprised at the high gains in photoluminescence quantum efficiency we could achieve with our simple texturing approach, from 20% to almost 60%,” says Johannes Richter, lead author
To increase every photon’s chance to leave the film at the film–air interface, the researchers trapped the photons in the perovskite layer. They achieved this by depositing the perovskite film on a randomly textured glass substrate with
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