The prediction and subsequent creation of artificially engineered metamaterials has opened the pathway to revolutionary effects in light-matter interactions. [1][2][3][4][5][6] In such materials the properties of the dielectric and magnetic permittivities, ε and μ, are not governed by the response of the individual atoms in the presence of an electromagnetic field, but are determined by the sub-wavelength structure of the material. In 1996 Pendry et al. predicted that a sparse cubic metal wire array with micrometerwide wires would have a significantly reduced plasma frequency due to the reduced average electron density and the large selfinductance of the structure.[2]A plethora of experimental work in this field has demonstrated metamaterials from GHz [7] up to yellow optical frequencies.[8] Reaching higher optical frequencies has proven problematic, as it requires the manipulation of materials on the scale of just a few tens of nanometers over macroscopic areas. While fabrication techniques such as focused ion beam lithography, direct laser writing, and atomic layer deposition [9][10][11][12][13] provide design flexibility, they are limited with regard to accessible feature sizes as well as the scalability of samples.Until now, colloidal self-organization was the only type of selfassembly used to create metamaterials.[14] These materials have feature sizes limited to above several hundreds of nanometers and to sphere-packing geometries. Block copolymers (BCPs) are unique in offering a route to creating macroscopically large samples with a variety of complex 3D architectures with features on the nanometer length scale. Unlike earlier work based on BCPs, [15] we incorporate a continuous metal phase into a BCP scaffold, [16] thereby producing the first truly optical, 3D metamaterial. As predicted by Pendry et al., [2] this material has a reduced plasmon frequency. In addition, it exhibits strongly anisotropic plasmon modes with linear dichroism and optical chirality across the visible region.BCPs are polymers that consist of two or more distinct polymer chains (blocks) joined by a covalent bond. The interplay between the energetic penalty for stretching the blocks is balanced by the chemical repulsion between the blocks, creating a range of morphologies such as spheres, cylinders, and gyroids. [17] Increasing the number of blocks leads to an increase in the number of accessible morphologies. [18] There has been previous work using BCP scaffolds with dielectrics for optical applications. [19] In this work, however, we opt to replace one of the continous nanoscale polymer networks with a metal in order to create a novel material with interesting optical properties that are very different from those of a structured dielectric. Such replication is possible because the blocks in BCPs are chemically distinct, hence we can selectively etch them and then backfill with inorganic materials to replicate self-assembled structures into materials that are not amenable to direct self-assembly in such complex morphologies.Here, w...

The ability to control and modulate the interaction of light with matter is crucial to achieve desired optical properties including reflection, transmission, and selective polarization. Photonic materials rely upon precise control over the composition and morphology to establish periodic interactions with light on the wavelength and sub-wavelength length scales. Supramolecular assembly provides a natural solution allowing the encoding of a desired 3D architecture into the chemical building blocks and assembly conditions. The compatibility with solution processing and low-overhead manufacturing is a significant advantage over more complex approaches such as lithography or colloidal assembly. Here we review recent advances on photonic architectures derived from block copolymers and highlight the influence and complexity of processing pathways. Notable examples that have emerged from this unique synthesis platform include Bragg reflectors, antireflective coatings, and chiral metamaterials. We further predict expanded photonic capabilities and limits of these approaches in light of future developments of the field.

We present a material assembly route for the manufacture of dye-sensitized solar cells, coupling a high-surface mesoporous layer to a three-dimensional photonic crystal (PC). Material synthesis aided by self-assembly on two length scales provided electrical and pore connectivity at the mesoporous and the microporous level. This construct allows effective dye sensitization, electrolyte infiltration, and charge collection from both the mesoporous and the PC layers, opening up additional parameter space for effective light management by harvesting PC-induced resonances.KEYWORDS Photonic crystal, self-assembly, photovoltaics, dye-sensitized solar cell E ver since the pioneering work of O'Regan and Grät-zel, dye-sensitized solar cells (DSCs) have attracted great interest as a promising technology for future sustainable energy generation. 1 In DSCs, charge carrier generation takes place in a chemisorbed monolayer of photoactive dye which is sandwiched between a semiconductor oxide, usually mesoscopic anatase, and an electrolyte acting as electron and hole conducting materials, respectively. Using state-of-the-art ruthenium-based inorganic dyes, efficiencies higher than 11% have been reported. [2][3][4] DSCs are generally made from cheap and nontoxic components and can be designed in a variety of different colors and transparencies, which distinguishes them as an ideal photovoltaic concept for integrated architecture. It therefore seems only a matter of time before large scale production will follow. 5 In general, improvements in the overall power conversion efficiency have been centered on increasing the photovoltage through manipulation of the oxide, improving the photocurrent with new dyes, and increasing stability by better encapsulation. 5 While record-holding liquid electrolyte DSCs already achieve maximum quantum efficiency (photon-toelectron conversion) in the spectral range around 520 nm, light harvesting in the red and near-infrared (at the tail of the absorption spectra) is still relatively low. In solid-state devices, light absorption is generally limited by the film thickness, as thick mesoporous films prove difficult to infiltrate. 6 One way to successfully enhance light harvesting is the introduction of optical elements, such as highly scattering layers. These consist of large particles, that increase the photon path length in the cell. 7,8 This ubiquitous approach has the unfortunate effect of rendering the DSC opaque thus depriving it of one of its main advantages over competing technologies. As a result, photonic band gap materials in the form of 3D inverted TiO 2 opal or porous bragg stacks have been applied to DSCs to enhance light harvesting in specific partsofthespectrumwhileretainingthecelltransparency. 9-12 Several theoretical approaches report a variety of possible effects, including the localization of heavy photons near the edges of a photonic bandgap, 13 Bragg diffraction in a periodic lattice, 14 multiple scattering at disordered regions in the photonic crystal (PC), 15 and the for...

nacre is a technologically remarkable organic-inorganic composite biomaterial. It consists of an ordered multilayer structure of crystalline calcium carbonate platelets separated by porous organic layers. This microstructure exhibits both optical iridescence and mechanical toughness, which transcend those of its constituent components. Replication of nacre is essential for understanding this complex biomineral, and paves the way for tough coatings fabricated from cheap abundant materials. Fabricating a calcitic nacre imitation with biologically similar optical and mechanical properties will likely require following all steps taken in biogenic nacre synthesis. Here we present a route to artificial nacre that mimics the natural layer-bylayer approach to fabricate a hierarchical crystalline multilayer material. Its structure-function relationship was confirmed by nacre-like mechanical properties and striking optical iridescence. our biomimetic route uses the interplay of polymer-mediated mineral growth, combined with layer-by-layer deposition of porous organic films. This is the first successful attempt to replicate nacre, using CaCo 3 .

Low-cost antireflection coatings (ARCs) on large optical surfaces are an ingredient-technology for high-performance solar cells. While nanoporous thin films that meet the zero-reflectance conditions on transparent substrates can be cheaply manufactured, their suitability for outdoor applications is limited by the lack of robustness and cleanability.Here, we present a simple method for the manufacture of robust selfcleaning ARCs. Our strategy relies on the self-assembly of a blockcopolymer in combination with silica-based sol−gel chemistry and preformed TiO 2 nanocrystals. The spontaneous dense packing of copolymer micelles followed by a condensation reaction results in an inverse opal-type silica morphology that is loaded with TiO 2 photocatalytic hot-spots. The very low volume fraction of the inorganic network allows the optimization of the antireflecting properties of the porous ARC despite the high refractive index of the embedded photocatalytic TiO 2 nanocrystals. The resulting ARCs combine high optical and self-cleaning performance and can be deposited onto flexible plastic substrates.

Hybrid dye-sensitized solar cells are typically composed of mesoporous titania (TiO 2 ), light harvesting dyes and organic molecular hole-transporters. Correctly matching the electronic properties of the materials is critical to ensure efficient device operation. In this study we synthesize TiO 2 in a well defined morphological confinement that arises from the self-assembly of a diblock copolymer -poly(isoprene-b-ethylene oxide) (PI-b-PEO). We show that the crystallization environment, tuned by the inorganic (TiO 2 mass) to organic (polymer) ratio, is a decisive factor in determining the distribution of sub band gap electronic states and the associated electronic function in solid-state dyesensitized solar cells. Interestingly, the tuning of the sub band gap states does not appear 2 2 to strongly influence the charge transport and recombination in the devices. However, increasing the depth and breadth of the density of sub band gap states correlates well with an increase in photocurrent generation, suggesting that a high density of these sub band gap states is critical for efficient photo-induced electron transfer and charge separation.

The field of solution‐processed photovoltaic cells is currently in its second spring. The dye‐sensitized solar cell is a widely studied and longstanding candidate for future energy generation. Recently, inorganic absorber‐based devices have reached new record efficiencies, with the benefits of all‐solid‐state devices. In this rapidly changing environment, this review sheds light on recent developments in all‐solid‐state solar cells in terms of electrode architecture, alternative sensitizers, and hole‐transporting materials. These concepts are of general applicability to many next‐generation device platforms.

Anatase TiO 2 is typically a central component in high performance dye-sensitised solar cells (DSCs). This study demonstrates the benefits of high temperature synthesised mesoporous titania for the performance of solid-state DSCs. In contrast to earlier methods, the high temperature stability of mesoporous titania is enabled by the self-assembly of the amphiphilic block copolymer polyisoprene-block-polyethylene oxide (PI-b-PEO) which compartmentalises TiO 2 crystallisation, preventing the collapse of porosity at temperatures up to 700 • C. The systematic study of the temperature dependence on DSC performance reveals a parameter trade-off: while high temperature annealed anatase consisted of larger crystallites and had a higher conductivity, this came at the expense of a reduced specific surface area.While the reduction in specific surface areas was found to be detrimental for liquid-electrolyte DSC performance, solid-state DSCs benefitted from the increased anatase conductivity and exhibited a performance increase by a factor of three.