Layered perovskites with the formula (R-NH)PbI have excellent environmental stability but poor photovoltaic function due to the preferential orientation of the semiconducting layer parallel to the substrate and the typically insulating nature of the R-NH cation. Here, we report a series of these n = 1 layered perovskites with the form (aromatic- O-linker-NH)PbI where the aromatic moiety is naphthalene, pyrene, or perylene and the linker is ethyl, propyl, or butyl. These materials achieve enhanced conductivity perpendicular to the inorganic layers due to better energy level matching between the inorganic layers and organic galleries. The enhanced conductivity and visible absorption of these materials led to a champion power conversion efficiency of 1.38%, which is the highest value reported for any n = 1 layered perovskite, and it is an order of magnitude higher efficiency than any other n = 1 layered perovskite oriented with layers parallel to the substrate. These findings demonstrate the importance of leveraging the electronic character of the organic cation to improve optoelectronic properties and thus the photovoltaic performance of these chemically stable low n layered perovskites.
The design of soft matter in which internal fuels or an external energy input can generate locomotion and shape transformations observed in living organisms is a key challenge. Such materials could assist in productive functions that may range from robotics to smart management of chemical reactions and communication with cells. In this context, hydrated matter that can function in aqueous media would be of great interest. Here, we report the design of hydrogels containing a scaffold of high–aspect ratio ferromagnetic nanowires with nematic order dispersed in a polymer network that change shape in response to light and experience torques in rotating magnetic fields. The synergistic response enables fast walking motion of macroscopic objects in water on either flat or inclined surfaces and also guides delivery of cargo through rolling motion and light-driven shape changes. The theoretical description of the response to the external energy input allowed us to program specific trajectories of hydrogel objects that were verified experimentally.
Iron-incorporated nickel-based materials show promise as catalysts for the oxygen evolution reaction (OER) halfreaction of water electrolysis. Nickel has also exhibited high catalytic activity for methanol oxidation, particularly when in the form of a bimetallic catalyst. In this work, bimetallic iron−nickel nanoparticles were synthesized using a multistep procedure in water under ambient conditions. When compared to monometallic iron and nickel nanoparticles, Fe−Ni nanoparticles show enhanced catalytic activity for both OER and methanol oxidation under alkaline conditions. At 1 mA/cm 2 , the overpotential for monometallic iron and nickel nanoparticles was 421 and 476 mV, respectively, while the bimetallic Fe−Ni nanoparticles had a greatly reduced overpotential of 256 mV. At 10 mA/cm 2 , bimetallic Fe−Ni nanoparticles had an overpotential of 311 mV. Spectroscopy characterization suggests that the primary phase of nickel in Fe−Ni nanoparticles is the more disordered alpha phase of nickel hydroxide.
Skeletal muscle provides inspiration on how to achieve reversible, macroscopic, anisotropic motion in soft materials. Here we report on the bottom-up design of macroscopic tubes that exhibit anisotropic actuation driven by a thermal stimulus. The tube is built from a hydrogel in which extremely long supramolecular nanofibers are aligned using weak shear forces, followed by radial growth of thermoresponsive polymers from their surfaces. The hierarchically ordered tube exhibits reversible anisotropic actuation with changes in temperature, with much greater contraction perpendicular to the direction of nanofiber alignment. We identify two critical factors for the anisotropic actuation, macroscopic alignment of the supramolecular scaffold and its covalent bonding to polymer chains. Using finite element analysis and molecular calculations, we conclude polymer chain confinement and mechanical reinforcement by rigid supramolecular nanofibers are responsible for the anisotropic actuation. The work reported suggests strategies to create soft active matter with molecularly encoded capacity to perform complex tasks.
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