Bio Focus: Small tissue reprogramming device designed to heal damaged tissues
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team from Columbia University and the Italian Institute of Technology has provided the first direct view of an unusual phenomenon thought to be responsible for the excellent optoelectronic properties of perovskite materials. Charge carriers in lead halide perovskites last for an unusually long time and travel long distances, resulting in high efficiency despite defects in the material. Columbia’s Xiaoyang Zhu and his colleagues had proposed previously
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new method to heal defects and make them electronically less reactive in hybrid halide perovskite films could provide a path to further improve the efficiency and stability of perovskite solar cells. Perovskite surfaces and grain boundaries have a high density of ionic defects, where charges can get trapped and recombine, reducing efficiency. Oxygen or moisture can also seep into perovskite films at defects, setting off degradation,
Bio Focus Small tissue reprogramming device designed to heal damaged tissues
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he advent of cellular reprogramming technologies (those that convert one specific cell type into another) in recent years has opened the possibility for doctors to be able to use on-site, cell-based therapies to treat a range of health issues. For example, these technologies could one day be used to treat Parkinson’s disease by converting certain brain cells into nerve cells that produce the chemical messenger dopamine, which helps coordinate body movements. Approaches thus far, however, have numerous hurdles to overcome before becoming viable, such as the risky reliance on viruses to deliver genes that drive the reprogramming process. Researchers at The Ohio State University (OSU) have now developed a technology called tissue nanotransfection (TNT), which uses a nanochannel device and small electric charge to deliver
that these unique carrier properties are due to polarons—quasiparticles that represent electrons and their self-induced polarization in the lattice—that screen charge carriers and keep them from colliding with defects. But no one had been able to directly observe how, or if, they are formed. Zhu, Filippo De Angelis, and their colleagues used time-resolved optical Kerr effect spectroscopy to give a time domain view of polaron formation in CH3NH3PbBr3 and CsPbBr3 perovskites.
The results, reported in Science Advances (doi:10.1126/sciadv.1701217), revealed that deformations of the soft PbBr3– lattice are mainly responsible for the polaron formation, and having an organic cation is not essential. Polarons form more than twice as quickly in the methylammonium perovskite than the cesium one because of its higher frequency of PbBr3– vibrations. The researchers also confirmed the formation of the polarons using density functional theory calculations.
which makes devices less stable. So far, researchers have passivated charged defects in perovskites by adding molecules that act as electron donors or acceptors. But most passivation molecules only passivate one type of defect, either positively or negatively charged. University of Nebraska–Lincoln’
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