The utilisation of Cu 2 O photocathodes for photoelectrochemical water splitting requires their stabilisation due to photocorrosion in aqueous electrolytes. Ultrathin films of wide band gap semiconducting oxides deposited by atomic layer deposition (ALD) on top of cuprous oxide can perform the dual function of both facilitating charge extraction (through the creation of a p-n junction) and protecting the absorber material from the aqueous electrolyte, thereby suppressing corrosion in favor of hydrogen generation. The factors that determine the photocurrent performance as well as the stability of these photoelectrodes are examined. Specifically, the influence of ALD deposition temperature, electrolyte pH, electrolyte composition as well as post-deposition annealing treatments was studied. The successful development of protective overlayers must fulfil the dual requirements of favourable band alignments as well as chemical stability. At long time scales, the deactivation of the photocathodes proceeds through etching of the amorphous overlayer, accompanied by the loss of the platinum catalyst particles. Through the deposition of a semi-crystalline TiO 2 overlayer, 62% stability over 10 hours of testing has been demonstrated without re-platinization.

Colloidal quantum dots (CQDs) are promising photovoltaic (PV) materials because of their widely tunable absorption spectrum controlled by nanocrystal size. Their bandgap tunability allows not only the optimization of single-junction cells, but also the fabrication of multijunction cells that complement perovskites and silicon . Advances in surface passivation, combined with advances in device structures , have contributed to certified power conversion efficiencies (PCEs) that rose to 11% in 2016 . Further gains in performance are available if the thickness of the devices can be increased to maximize the light harvesting at a high fill factor (FF). However, at present the active layer thickness is limited to ~300 nm by the concomitant photocarrier diffusion length. To date, CQD devices thicker than this typically exhibit decreases in short-circuit current (J) and open-circuit voltage (V), as seen in previous reports. Here, we report a matrix engineering strategy for CQD solids that significantly enhances the photocarrier diffusion length. We find that a hybrid inorganic-amine coordinating complex enables us to generate a high-quality two-dimensionally (2D) confined inorganic matrix that programmes internanoparticle spacing at the atomic scale. This strategy enables the reduction of structural and energetic disorder in the solid and concurrent improvements in the CQD packing density and uniformity. Consequently, planar devices with a nearly doubled active layer thicknesses (~600 nm) and record values of J (32 mA cm) are fabricated. The V improved as the current was increased. We demonstrate CQD solar cells with a certified record efficiency of 12%.

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.

Photocathodes based on cuprous oxide (Cu2O) are promising materials for large scale and widespread solar fuel generation due to the abundance of copper, suitable bandgap, and favorable band alignments for reducing water and carbon dioxide. A protective overlayer is required to stabilize the Cu2O in aqueous media under illumination, and the interface between this overlayer and the catalyst nanoparticles was previously identified as a key source of instability. Here, the properties of the protective titanium dioxide overlayer of composite cuprous oxide photocathodes are further investigated, as well as an oxide‐based hydrogen evolution catalyst, ruthenium oxide (RuO2). The RuO2‐catalyzed photoelectrodes exhibit much improved stability versus platinum nanoparticles, with 94% stability after 8 h of light‐chopping chronoamperometry. Faradaic efficiencies of ∼100% are obtained as determined by measurement of the evolved hydrogen gas. The sustained photocurrents of close to 5 mA cm−2 obtained with this electrode during the chronoamperometry measurement (at 0 V vs. the reversible hydrogen electrode, pH 5, and simulated 1 sun illumination) would correspond to greater than 6% solar‐to‐hydrogen conversion efficiency in a tandem photoelectrochemical cell, where the bias is provided by a photovoltaic device such as a dye‐sensitized solar cell.