Transparent conducting electrodes are essential components for numerous flexible optoelectronic devices, including touch screens and interactive electronics. Thin films of indium tin oxide-the prototypical transparent electrode material-demonstrate excellent electronic performances, but film brittleness, low infrared transmittance and low abundance limit suitability for certain industrial applications. Alternatives to indium tin oxide have recently been reported and include conducting polymers, carbon nanotubes and graphene. However, although flexibility is greatly improved, the optoelectronic performance of these carbon-based materials is limited by low conductivity. Other examples include metal nanowire-based electrodes, which can achieve sheet resistances of less than 10Ω □(-1) at 90% transmission because of the high conductivity of the metals. To achieve these performances, however, metal nanowires must be defect-free, have conductivities close to their values in bulk, be as long as possible to minimize the number of wire-to-wire junctions, and exhibit small junction resistance. Here, we present a facile fabrication process that allows us to satisfy all these requirements and fabricate a new kind of transparent conducting electrode that exhibits both superior optoelectronic performances (sheet resistance of ~2Ω □(-1) at 90% transmission) and remarkable mechanical flexibility under both stretching and bending stresses. The electrode is composed of a free-standing metallic nanotrough network and is produced with a process involving electrospinning and metal deposition. We demonstrate the practical suitability of our transparent conducting electrode by fabricating a flexible touch-screen device and a transparent conducting tape.

We provide a theoretical discussion of the scattering cross section of individual subwavelength structures. We show that, in principle, an arbitrarily large total cross section can be achieved, provided that one maximizes contributions from a sufficiently large number of channels. As a numerical demonstration, we present a subwavelength nanorod with a plasmonic-dielectric-plasmonic layer structure, where the scattering cross section far exceeds the single-channel limit, even in the presence of loss.

Here we report on a novel substrate, nanopaper, made of cellulose nanofibrils, an earth abundant material.Compared with regular paper substrates, nanopaper shows superior optical properties. We have carried out the first study on the optical properties of nanopaper substrates. Since the size of the nanofibrils is much less than the wavelength of visible light, nanopaper is highly transparent with large light scattering in the forward direction. Successful depositions of transparent and conductive materials including tin-doped indium oxide, carbon nanotubes and silver nanowires have been achieved on nanopaper substrates, opening up a wide range of applications in optoelectronics such as displays, touch screens and interactive paper. We have also successfully demonstrated an organic solar cell on the novel substrate. Broader contextWood ber cellulose has been used for more than 2000 years as an ingredient for making paper. The cellulose paper that we see in our everyday lives consists of bers with diameters of tens of micrometers. Using chemical or enzymatic pretreatments followed by high-pressure homogenization, the micrometer-sized cellulose bers can be disintegrated into nanobrillated cellulose (NFC) with a diameter of around 10-20 nm and a length of 2 mm. By compressing the NFC pulp with the right composition in a sheet-former, highly transparent nanocellulose paper can be produced. The nanocellulose paper has large light scattering in the forward direction, which is very useful for solar cell applications. The nanocellulose paper can be coated with a wide variety of conductive materials, such as carbon nanotubes, silver nanowires and tin-doped indium oxide (ITO), to produce transparent conductive paper. By depositing a thin layer of ITO, the conductive nanocellulose paper can be used as a substrate for making organic solar cells.

A cylindrical wave expansion method is developed to obtain the scattering field for an ideal two-dimensional cylindrical invisibility cloak. A near-ideal model of the invisibility cloak is set up to solve the boundary problem at the inner boundary of the cloak shell. We confirm that a cloak with the ideal material parameters is a perfect invisibility cloak by systematically studying the change of the scattering coefficients from the near-ideal case to the ideal one. However, due to the slow convergence of the zero th order scattering coefficients, a tiny perturbation on the cloak would induce a noticeable field scattering and penetration. * These authors contributed equally to this work.† Corresponding author. Electronic address: min@kth.se.