Showing papers by "Anvar A. Zakhidov published in 2011"

Biscrolling nanotube sheets and functional guests into yarns.

Abstract: Multifunctional applications of textiles have been limited by the inability to spin important materials into yarns. Generically applicable methods are demonstrated for producing weavable yarns comprising up to 95 weight percent of otherwise unspinnable particulate or nanofiber powders that remain highly functional. Scrolled 50-nanometer-thick carbon nanotube sheets confine these powders in the galleries of irregular scroll sacks whose observed complex structures are related to twist-dependent extension of Archimedean spirals, Fermat spirals, or spiral pairs into scrolls. The strength and electronic connectivity of a small weight fraction of scrolled carbon nanotube sheet enables yarn weaving, sewing, knotting, braiding, and charge collection. This technology is used to make yarns of superconductors, lithium-ion battery materials, graphene ribbons, catalytic nanofibers for fuel cells, and titanium dioxide for photocatalysis.

Structural model for dry-drawing of sheets and yarns from carbon nanotube forests.

Abstract: A structural model is developed for describing the solid-state transformation of a vertically oriented carbon multiwall nanotube (MWNT) forest to a horizontally oriented MWNT sheet or yarn. The key element of our model is a network of individual carbon nanotubes or small bundles interconnecting the array of main large-diameter MWNT bundles of the forest. The dry-draw self-assembly mechanism for MWNT sheet formation involves two principal processes that reconfigure the interconnection network: (1) unzipping by preferentially peeling off interconnections between the bundles in the forest and (2) self-strengthening of these interconnections by densification at the top and bottom of the forest during draw-induced reorientation of the bundles. It is shown that interconnection density is a key parameter that determines the ability of a MWNT forest to be dry-drawable into sheets and yarns. This model describes the principal mechanism of solid-state draw (confirmed by dynamic in situ scanning electron microscopy)...

Monolithic parallel multijunction oled with independent tunable color emission

Abstract: A tandem organic light emitting diode (OLED) device comprised of multiple stacked single OLEDs electrically connected in parallel via transparent interlayer is recited herein. Transparent interlayers are coated by charge injection layers in order to enhance the charge injection efficiency and decrease the operation voltage. Transparent nanomaterials, such as carbon nanotube sheets (or graphene, graphene ribbons and similar conductive transparent nano-carbon forms) are used as Interlayers or outer electrodes. Furthermore, functionalization of carbon nanotubes inter layers by n-doping (or p-doping) converts them into common cathode (or common anode), further decreasing operation voltage of tandem. The development of these alternative interconnecting layers comprised of nanomaterials simplifies the process and may be combined with traditional OLED devices. In addition, novel architectures are enabled that allow the parallel connection of the stacked OLEDs into monolithic multi-junction OLED tandems.

Nanoimprint of dehydrated PEDOT:PSS for organic photovoltaics

Abstract: We demonstrate the fabrication of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) nanogratings by a dehydration-assisted nanoimprint lithographic technique. Dehydration of PEDOT:PSS increases its cohesion to protect the nanostructures formed by nanoimprinting during demolding, resulting in the formation of high quality nanogratings of 60 nm in height, 70 nm in width and 70 nm in spacing (aspect ratio of 0.86). PEDOT:PSS nanogratings are used as hole transport and an electron blocking layer in blended poly(3-hexylthiophene-2,5-diyl) (P3HT):[6,6]-penyl-C61-butyric-acid-methyl-ester (PCBM) organic photovoltaic devices (OPV), showing enhancement of photocurrent and power efficiency in comparison to OPV devices with non-patterned PEDOT:PSS films.

Photoinduced Optical Transparency in Dye-Sensitized Solar Cells Containing Graphene Nanoribbons

Abstract: We describe the use of few-layer graphene nanoribbons, either attached to counter electrodes or dispersed into electrolyte, to induce optical transparency of an iodide/triiodide redox couple in a dye-sensitized solar cell (DSSC). We then evaluate the effect of reversible bleaching of the electrolyte on the DSSC performance. This bleaching effect is related to an energy transfer from photoexcited quantum-dot-like regions to the triiodide (I3–) radical ions in the electrolyte, saturating their absorption in the visible optical range. DSSC power conversion efficiency using few-layer graphene nanoribbons at the counter electrode (5.8%) did not deteriorate when the electrolyte became optically transparent. The increased transparency of the electrolyte resulted in a decreased photocurrent density (from 17.6 to 14.2 mA/cm2), an unchanged open circuit voltage of 750 mV, and a slightly increased fill factor (from 0.45 to 0.55). When the few-layer graphene nanoribbons were introduced into the electrolyte directly b...

Multijunction hybrid solar cell with parallel connection and nanomaterial charge collecting interlayers

Abstract: A tandem (or multijunction) hybrid photovoltaic device (PV) device comprised of multiple stacked single PVs connected in parallel with each other is described herein. Furthermore, nanomaterials are used as transparent charge collecting electrodes that allow both parallel connection via anode interlayer and also "inverted parallel" connection via cathode type interlayer of different types of solar cells. Carbon nanotube sheets are used as a convenient example for the charge collecting electrodes. The development of these alternative interconnecting layers simplifies the process and may be also used for combined organic PVs with traditional inorganic PVs and Dye Sensitized Solar Cells (DSSC). In addition, novel architectures are enabled that allow the parallel connection of the stacked PVs into monolithic multi-junction PV tandems. This new monolithic parallel connection architecture enables enhanced absorption of the solar spectrum and results in increased power conversions efficiency. Moreover, architectures where cells are stacked monolithically using a series connection can be coupled with cells to create mixed series and parallel connected tandem cells.

Diamond direct and inverse opal matrices produced by chemical vapor deposition

Abstract: Diamond structures with inverse and direct three-dimensional opal lattices with period of 250–530 nm were grown by microwave plasma deposition in methane-hydrogen mixtures using porous SiO2 opal matrix and its Si replica as templates, respectively. The Si templates can be filled with diamond to the depth as large as 80 layers of the spheres.

SYNTHESIS OF PbS NANOCRYSTAL/FUNCTIONALIZED CONDUCTING POLYMERS FOR PLASTIC SOLAR CELLS

Abstract: Lead-based nanocrystals (NCs) are promising materials for high-efficiency solar cells since they are able to generate multiexcitons with high efficiency. One complication of utilizing these NCs is the insulating ligands capping their surfaces. In this paper, we have successfully developed and characterized a phosphonate-functionalized poly-3-hexylthiophene (POP3HT-50) and used it in the direct synthesis of PbS NCs within the polymeric host matrix without extraneous ligands. Devices made of POP3HT-50/PbS nanocomposites show an order of magnitude improvement in η when compared to that reported for a P3HT/PbS device (η = 0.011% versus 0.001%). The improved performance is consistent with better electronic contact between PbS NCs and POP3HT-50.

Light propagation in liquid crystal infiltrated two-dimensional photonic crystal at a High-Order photonic band

Abstract: Light propagation into a photonic crystal infiltrated with a nematic liquid crystal is numerically investigated. At a high-order photonic band, photonic crystals generally exhibit interesting characteristics such as a negative refraction and a superprism effect. Our numerical results show that the sign of an effective refractive index of the tunable photonic crystal can be controlled at a certain frequency by changing molecular orientation. Furthermore, using a combination of positive and negative index photonic crystals, a light could be redirected 90° without a waveguide structure.

Ionic Plasma Screening and Long-Range Electron Correlations in Quasi-One-Dimensional Conductors

Abstract: In quasi-one-dimensional systems with the intercalation-type doping, the dynamical response of dopant ions can substantially affect the interplay of density-wave and superconducting instabilities. A generic model system of Coulombically coupled Luttinger-liquid chains augmented by the interaction with the ion displacements is exactly solved in the forward-scattering channel providing for the resulting system excitations and electron correlations. For a jellium-like ion response, the effect of the bare electron–electron repulsion is essentially canceled by the ions. Superconducting correlations can then be developed due to a non-polarizational interaction with an additional phonon mode.