Nano Focus: Nanocones make glass invisible
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T
o make perovskite solar cells commercially, manufacturers will need to produce high-quality perovskites on large areas for a low cost. The challenge is that scaling up small laboratory devices to more than 25 cm2 can reduce the power-conversion efficiency anywhere from 10 to 20%. Researchers from Shanghai Jiao Tong University in China have come up with
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erovskites’ low stability and lead toxicity remain hurdles to commercial use. Double perovskites are an appealing alternative. Now researchers have, for the first time, made double perovskite films and built a working solar cell from the film. Conventional perovskites have the formula ABX3. Double perovskites, in which the unit cell is twice that of a conventional perovskite, have the formula AB′B″X6. The double perovskite Cs2AgBiX6 (X = Cl,
an easy route to making uniform, defectfree, large-area perovskite films in air at room temperature. The process does not require conventional solvents and a vacuum. As reported in the journal Nature (doi:10.1038/nature23877), researchers made 36 cm2 solar cells that were more than 12% efficient. The researchers placed a 1:1 mixture of the amine
complex precursors CH3NH3I3•CH3NH2 and PbI2•CH3NH2 on a substrate, applied a smooth polyimide film on top, pressed down on it for a minute with a squeezing board to spread the liquid, and then warmed the substrate at 50°C for two minutes. When they peeled off the polyimide film, a dense, uniform perovskite film had formed.
Br) is a promising material for solar cells since it is less toxic and stable. However, its precursor’s low solubility has so far hampered the fabrication of high-quality films. The team from the University of Munich, Germany, and Newcastle University, UK, found that annealing at more than 250°C was key for converting the precursors into high-quality perovskite films. They made Cs2AgBiBr6 films by dissolving BiBr3, AgBr, and
CsBr in dimethylsulfoxide; preheating the solution to 75°C, and then spin-coating it onto a substrate that was subsequently annealed at 285°C. Photovoltaic devices made with the films have a power-conversion efficiency of up to 2.43%, an open-circuit voltage of more than 1 V, and a high stability under operating conditions, the researchers reported in the Journal of Materials Chemistry A (doi:0.1039/c7ta06816f).
Nano Focus Nanocones make glass invisible
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y etching tiny nanoscale features into glass and plastic surfaces, researchers have found a way to cut their light reflection to almost zero, rendering them nearly invisible. This could be a much-needed solution to the annoying glare from phone, TV, and computer screens. Apart from making consumer displays glare-free over a wide range of viewing angles, the nanotextured glass could also make the surface water-repelling and self-cleaning. When light travels from air to glass, the abrupt change in refractive index between the materials makes around 8% of light bounce back. Manufacturers coat device displays and eyeglasses with antireflective films to reduce this unwanted reflection. Antir
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