In our information-rich world, it is becoming increasingly important to develop technologies capable of displaying dynamic and changeable data, for reasons ranging from valueadded advertising to environmental sustainability. There is an intense drive at the moment towards paper-like displays, devices having a high reflectivity and contrast to provide viewability in a variety of environments, particularly in sunlight where emissive or backlit devices perform very poorly. The list of possible technologies is extensive, including electrophoretic, cholesteric liquid crystalline, electrochromic, electrodewetting, interferometric and more. Despite tremendous advances, the key drawback of all these existing display options relates to colour. As soon as an RGB (red, green and blue) colour filter or spatially modulated colour scheme is implemented, substantial light losses are inevitable even if the intrinsic reflectivity of the material is very good.We describe a reflective flat-panel display technology based on the electrical actuation of photonic crystals. These materials display non-bleachable structural colour, reflecting narrow bands of wavelengths tuned throughout the entire visible spectrum by expansion and contraction of the photonic-crystal lattice. The material is inherently bright in high-light environments, has electrical bistability, low operational voltage, can be integrated onto flexible substrates, and is unique among all display technologies in that a continuous range of colours can be accessed without the need for colour filters or optical elements.Photonic crystals (PCs) 1,2 , materials with a periodic modulation in refractive index, can be sources of exceptionally bright and brilliant reflected colours arising from coherent Bragg optical diffraction 3 . Exemplified by gemstone opals, threedimensional PCs are readily available by means of colloidal selfassembly, making them a fertile test-bed for investigating concepts based on tunable structural colour. Synthetic preparations for silica or polymer microspheres with low dispersity (,2%) are well-developed, and their self-assembly into a close-packed ordered structure leaves a void volume of 26% available for further material infiltration or modification 4,5 . Tuning of colloidal PC optical properties has been effected by the infilling of metals, insulators, semiconductors and polymers of all types, and by the inversion of such constructs through removal of the template spheres.Given their bright colours with potential tunability, it seems obvious at first glance to use PCs as the active materials in refreshable full-colour digital displays. The fact that this has not yet been achieved highlights the difficult set of requirements that must be met by any potential candidate, including electrical tunability, access to thin and homogeneous oriented films, large tuning range, relatively rapid response time, mechanical and cycling stability, low voltage/current requirements, and obviously the ability to implement the material into a feasible, practical, sca...

In organic light-emitting diodes (OLEDs), a stack of multiple organic layers facilitates charge flow from the low work function [~4.7 electron volts (eV)] of the transparent electrode (tin-doped indium oxide, ITO) to the deep energy levels (~6 eV) of the active light-emitting organic materials. We demonstrate a chlorinated ITO transparent electrode with a work function of >6.1 eV that provides a direct match to the energy levels of the active light-emitting materials in state-of-the art OLEDs. A highly simplified green OLED with a maximum external quantum efficiency (EQE) of 54% and power efficiency of 230 lumens per watt using outcoupling enhancement was demonstrated, as were EQE of 50% and power efficiency of 110 lumens per watt at 10,000 candelas per square meter.

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Photonic crystals (PCs) [1,2] made by bottom-up self-assembly and top-down nanofabrication approaches have been receiving increasing attention across the science and engineering disciplines in academia and industry. They have been envisioned for a range of applications including optical transistors and waveguides, [3,4] light-emitting diodes and lasers, [5,6] chemical and biochemical sensors, [7,8] and data storage media.[9] A challenge in the field has been the realization of PCs for full-color reflective displays which could be used for electronic books, billboards, shelf-edge labels, and state-of-health fuel gauges for batteries. To reduce this objective to practice requires an active PC whose refractive index contrast and/or lattice dimension can be continuously, reversibly, and rapidly altered by an electrical, optical, or magnetic stimulus, and that can be prepared with high structural and optical quality, and on a large scale at low cost.There have been a few early attempts at achieving these objectives. One involves an electrically tuned liquid crystal imbibed within the void spaces of an inverse silica opal; however, this device is limited as it is able to switch between just two colors corresponding to random and aligned director fields.[10] Another involves magnetic tuning of the spacing between an ordered dispersion of superparamagnetic iron oxide microspheres; however, while full-color magnetic tuning was demonstrated, it is difficult to envision how this dispersion can be made into a practical display.[11] The first demonstration of full-color tuning of a PC was based on an electroactive polymer-gel/silica opal composite, the reflected color of which can be electrically tuned through reversible expansion and contraction of its photonic lattice.[12] The problem with this system relates to the difficulty of electrolyte permeating through a contiguous space-filling opal lattice made of close-packed silica spheres embedded within a polymer-gel matrix. This construct impedes electron and ion charge transport, slows switching times, and increases the drive voltage needed to power the device, all together negating the overall performance of the device.Herein we describe the first example of a high-performance electroactive inverse polymer-gel opal in which electrolyte freely infuses the nanoporous lattice. The positive outcome is the reduction in electron and ion diffusion lengths, the increase in switching speed, and the decrease in the driving voltage, with unprecedented tuning of the wavelength and brightness of Bragg diffracted light continuously from the invisible ultraviolet through the visible to the invisible near infrared.The structures of the polymers chosen for the inverse polymer-gel opal in this study are shown in Figure 1 b. They comprise the polyferrocenylsilane (PFS) derivatives polyferrocenylmethylvinylsilane (PFMVS) and polyferrocenyldivinylsilane (PFDVS); narrow polydispersity index (PDI < 1.1) and molecular weight control are achieved through anionic ring-opening polymerization from the...

The self-assembly paradigm in chemistry, physics and biology has matured scientifically over the past two-decades to a point of sophistication that one can begin to exploit its numerous attributes in nanofabrication. In what follows we will take a brief look at current thinking about self-ssembly and with some recent examples taken from our own work examine how nanofabrication has benefited from self-assembly

One-dimensional photonic structures, known as Bragg stacks reflectors or Bragg mirrors, represent a well-developed subject in the field of optical science. However, because of a lack of dynamic tunablity and their dependence on complex top-down techniques for their fabrication, they have received little attention from the materials science community present recent and ongoing developments on the way to fun dimensional photonic structures obtained from simple botton-up techniques. We focus on the versatility of this new approach, which allows the incorporation of a wide range of materials into photonic structures

“Smelling” chemicals and bacteria by using structural color: the photonic nose is a novel platform for the identification of volatile chemicals based on color changes of porous Bragg stack arrays with potential for applications in chemical sensing and bacteria identification.

We herein demonstrate visible electroluminescence from colloidal silicon in the form of a hybrid silicon quantum dot-organic light emitting diode. The silicon quantum dot emission arises from quantum confinement, and thus nanocrystal size tunable visible electroluminescence from our devices is highlighted. An external quantum efficiency of 0.7% was obtained at a drive voltage where device electroluminescence is dominated by silicon quantum dot emission. The characteristics of our devices depend strongly on the organic transport layers employed as well as on the choice of solvent from which the Si quantum dots are cast.