3D printed architectures impart additional control over reactive materials
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n solar cells, energy is lost due to the cooling of electrons (hot carriers) excited by supra-bandgap photons. The rate at which the hot carriers cool determines whether they can be used to boost the solar-cell efficiency or not. A few groups have used transient absorption (TA) spectroscopy to examine chargecarrier cooling properties of perovskites. In a recent Nature Communications article (DOI: 10.1038/ncomms9420), a team of researchers led by Felix Deschler at
the University of Cambridge observed a phonon bottleneck phenomenon. In this phenomenon, phonons (heat-carrying quasi-particles) that are formed while the charge carriers cool cannot decay quickly enough. Instead, they re-heat the charge carriers, slowing down their cooling rates. Matthew Beard and his colleagues at the National Renewable Energy Laboratory also observed this bottleneck in lead iodide perovskites, suggesting
that the material could have a theoretical efficiency limit much higher than that of current solar-cell technologies. They found that the phonon bottleneck slowed down charge-carrier cooling by three to four orders of magnitude. So the carriers retain their initial energy for much longer periods of time. This extra energy could potentially be tapped in what is called a hot-carrier solar cell. The results were published recently in Nature Photonics (DOI: 10.1038/nphoton.2015.213).
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which the researchers grew directly from solution, had well-defined square shape and large size. The materials exhibited efficient photoluminescence, and the researchers were able to tune the emission color by changing sheet thickness
and material composition. Peidong Yang and his colleagues from the University of California–Berkeley, and ShanghaiTech University in China reported the advance in a recent issue of Science (DOI: 10.1126/science.aac7660).
n a promising advance for nanoscale optoelectronic devices, researchers made atomically thin two-dimensional (2D) sheets of organic–inorganic hybrid perovskites. The high-quality singlecrystalline 2D (C4H9NH3)2PbBr4 sheets,
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3D printed architectures impart additional control over reactive materials
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eactive materials (RMs) are a class of composite materials that, when ignited, produce a sudden release of energy in the form of heat and pressure. Their performance, which can vary based on the choice of constituent materials, is typically midway between that of a propellant and an explosive. This makes them ideal for use in applications that rely on a quick, precise burst of energy such as ejector seats and airbags—situations where fractions of a second can make a world of difference. Recent advances in RM technology have largely focused on improving formulations, for example by altering the size, morphology, assembly, and ratios of the reactive particles. However, while effective in tailoring reactivity, many of these practices are limited by processing constraints or by diminishing returns in performance. Christopher M. Spadaccini at Lawrence Livermore National Laboratory, Jennifer A. Lewis at H
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