Templated Synthesis of Uniform Perovskite Nanowire Arrays.

While the chemical composition of semiconducting metal halide perovskites can be precisely controlled in thin films for photovoltaic devices, the synthesis of perovskite nanostructures with tunable dimensions and composition has not been realized. Here, we describe the templated synthesis of uniform perovskite nanowires with controlled diameter (50-200 nm). Importantly, by providing three examples (CH3NH3PbI3, CH3NH3PbBr3, and Cs2SnI6), we show that this process is composition general and results in oriented nanowire arrays on transparent conductive substrates.

Solution-Dispersible Metal Nanorings with Deliberately Controllable Compositions and Architectural Parameters for Tunable Plasmonic Response.

We report a template-based technique for the preparation of solution-dispersible nanorings composed of Au, Ag, Pt, Ni, and Pd with control over outer diameter (60-400 nm), inner diameter (25-230 nm), and height (40 nm to a few microns). Systematic and independent control of these parameters enables fine-tuning of the three characteristic localized surface plasmon resonance modes of Au nanorings and the resulting solution-based extinction spectra from the visible to the near-infrared. This synthetic approach provides a new pathway for solution-based investigations of surfaces with negative curvature.

Fast Charge Extraction in Perovskite-Based Core-Shell Nanowires.

Realizing nanostructured interfaces with precise architectural control enables one to access properties unattainable using bulk materials. In particular, a nanostructured interface ( e. g., a core-shell nanowire) between two semiconductors leads to a short charge separation distance, such that photoexcited charge carriers can be more quickly and efficiently collected. While vapor-phase growth methods are used to synthesize uniform core-shell nanowire arrays of semiconductors such as Si and InP, more general strategies are required to produce related structures composed of a broader range of materials. Herein, we employ anodic aluminum oxide templates to synthesize CH3NH3PbI3 perovskite core-copper thiocyanate shell nanowire arrays employing a combination of electrodeposition and solution casting methods. Using scanning electron microscopy, powder X-ray diffraction, and time-resolved photoluminescence spectroscopy, we confirm the target structure and show that adopting a core-shell nanowire architecture accelerates the rate of charge quenching by nearly 3 orders of magnitude compared to samples with only an axial junction. Subsequently, we fit decay curves to a triexponential function to attribute fast quenching in core-shell nanowires to charge extraction by the copper thiocyanate nanotubes, as opposed to recombination within the perovskite nanowires. Dramatic improvements to charge extraction speed and efficiency result from the substantially reduced charge separation distance and increased interfacial area achieved via the core-shell nanowire array architecture.