Preparation of Organometal Halide Perovskite Photonic Crystal Films for Potential Optoelectronic Applications

Herein, a facile method for the preparation of organometal halide perovskite (OHP) thin films in photonic crystal morphology is presented. The OHP photonic crystal thin films with controllable porosity and thicknesses between 2 μm and 6 μm were prepared on glass, fluorine-doped tin oxide (FTO), and TiO₂ substrates by using a colloidal crystal of polystyrene microspheres as a template to form an inverse opal structure. The composition of OHP could be straightforwardly tuned by varying the halide anions. The obtained OHP inverse opal films possess large ordered domains with a periodic change of the refractive index, which results in pronounced photonic stop bands in the visible light range. By changing the diameter of the polystyrene microspheres, the position of the photonic stop band can be tuned through the visible spectrum. This developed methodology can be used as blueprint for the synthesis of various OHP films that could eventually be used as more effective light harvesting materials for diverse applications

Solution-processed core-shell nanowires for efficient photovoltaic cells

Semiconductor nanowires are promising for photovoltaic applications 1-11, but, so far, nanowire-based solar cells have had lower efficiencies than planar cells made from the same materials 6-10,12,13, even allowing for the generally lower light absorption of nanowires. It is not clear, therefore, if the benefits of the nanowire structure, including better charge collection and transport and the possibility of enhanced absorption through light trapping 4,15, can outweigh the reductions in performance caused by recombination at the surface of the nanowires and at p-n junctions. Here, we fabricate core-shell nanowire solar cells with open-circuit voltage and fill factor values superior to those reported for equivalent planar cells, and an energy conversion efficiency of ∼5.4%, which is comparable to that of equivalent planar cells despite low light absorption levels 16. The device is made using a low-temperature solution-based cation exchange reaction 17-21 that creates a heteroepitaxial junction between a single-crystalline CdS core and single-crystalline Cu 2S shell. We integrate multiple cells on single nanowires in both series and parallel configurations for high output voltages and currents, respectively. The ability to produce efficient nanowire-based solar cells with a solution-based process and Earth-abundant elements could significantly reduce fabrication costs relative to existing high-temperature bulk material approaches. © 2011 Macmillan Publishers Limited. All rights reserved.link_to_subscribed_fulltex

Controlling crystallization to imprint nanophotonic structures into halide perovskites using soft lithography

Halide perovskites have recently gained widespread attention for their high efficiencies in photovoltaics, and they have also been studied for applications in light emission. Both of these fields can benefit from nanophotonic patterning. Here, by controlling the crystallization of the perovskite film in contact with a nanotextured silicone polymer stamp, nanostructures are reproduced in the perovskite. Soft lithography techniques such as this imprinting are particularly useful for halide perovskites, which are incompatible with the aqueous solutions and plasmas used in conventional patterning processes. Additionally, soft lithography can pattern over defects and avoids damaging the master. By extending nanoscale soft lithography to halide perovskites, new opportunities arise in merging nanophotonics with these remarkable materials