Advanced Materials

Cover image for Vol. 25 Issue 12

March 25, 2013

Volume 25, Issue 12

Pages 1657–1800

  1. Cover Picture

    1. Top of page
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    3. Inside Front Cover
    4. Back Cover
    5. Masthead
    6. Contents
    7. Review
    8. Communications
    9. Frontispiece
    10. Communications
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    12. Communications
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      Solar Cells: Effects of Impurities on Operational Mechanism of Organic Bulk Heterojunction Solar Cells (Adv. Mater. 12/2013) (page 1657)

      Loren Kaake, Xuan-Dung Dang, Wei Lin Leong, Yuan Zhang, Alan Heeger and Thuc-Quyen Nguyen

      Version of Record online: 18 MAR 2013 | DOI: 10.1002/adma.201370075

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      The front cover shows the effect of chemical impurity on the charge generation in the donor phase and the electron transport in the acceptor phase of an organic solar cell. Using photoconductive atomic force microscopy in conjunction with transient absorption spectroscopy and charge transport study, Thuc-Quyen Nguyen and co-workers investigate on page 1706 whether differing impurity shapes may lead to different loss mechanisms.

  2. Inside Front Cover

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    10. Communications
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      Force Sensors: Hybrid Mechanoresponsive Polymer Wires Under Force Activation (Adv. Mater. 12/2013) (page 1658)

      Hongbin Feng, Jin Lu, Jinghong Li, Francis Tsow, Erica Forzani and Nongjian Tao

      Version of Record online: 18 MAR 2013 | DOI: 10.1002/adma.201370076

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      Force activation is triggered in a stretched polymer wire with color changes produced as the molecules undergo structural and conformational changes. Nongjian Tao, Jinghong Li, and co-workers show on page 1729 that the hybrid mechanosensitive polymer wire can function as a micro- and nanoscale force sensor.

  3. Back Cover

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      Nanotube Arrays: In Situ Surface-Modification-Induced Superhydrophobic Patterns with Reversible Wettability and Adhesion (Adv. Mater. 12/2013) (page 1804)

      Yuekun Lai, Fei Pan, Cong Xu, Harald Fuchs and Lifeng Chi

      Version of Record online: 18 MAR 2013 | DOI: 10.1002/adma.201370077

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      A facile, in situ, ink-regulating approach is developed on page 1682 by Lifeng Chi, Yuekun Lai, and co-workers for rapidly reversible water wettability and adhesion transition, with a large degree of contrast, on superhydrophobic TiO2 nanotube array film. This finding provides new strategies in the design of siteselective, sticky superhydrophobic patterns for droplet manipulation and cell immobilization.

  4. Masthead

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      Masthead: (Adv. Mater. 12/2013)

      Version of Record online: 18 MAR 2013 | DOI: 10.1002/adma.201370078

  5. Contents

    1. Top of page
    2. Cover Picture
    3. Inside Front Cover
    4. Back Cover
    5. Masthead
    6. Contents
    7. Review
    8. Communications
    9. Frontispiece
    10. Communications
    11. Frontispiece
    12. Communications
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  6. Review

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    12. Communications
    1. Fuel Cell Electrocatalyst Using Polybenzimidazole-Modified Carbon Nanotubes As Support Materials (pages 1666–1681)

      Tsuyohiko Fujigaya and Naotoshi Nakashima

      Version of Record online: 19 FEB 2013 | DOI: 10.1002/adma.201204461

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      Polybenzimidazoles can non-covalently wrap onto the surface of carbon nanotube to introduce binding sites for the loading of Pt nanoparticles. This approach is advantageous as it helps keep the carbon nanotube structure intact and to form a triple phase boundary structure, both of which are required for electrocatalyst for fuel cells. The developed electrocatalyst is applicable both for proton-exchange and anion-exchange fuel cells.

  7. Communications

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    7. Review
    8. Communications
    9. Frontispiece
    10. Communications
    11. Frontispiece
    12. Communications
    1. In Situ Surface-Modification-Induced Superhydrophobic Patterns with Reversible Wettability and Adhesion (pages 1682–1686)

      Yuekun Lai, Fei Pan, Cong Xu, Harald Fuchs and Lifeng Chi

      Version of Record online: 3 DEC 2012 | DOI: 10.1002/adma.201203797

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      Herein is described a facile, in situ, ink-regulating approach to rapidly achieve reversible water wettability and adhesion transition, with a large degree of contrast, on superhydrophobic TiO2 nanotube array film. The ink printing and removal process allows the wettability and reversible adhesion transitions to be realized. Experimental results demonstrate the potential application of such site-selective, sticky superhydrophobic patterns for droplet manipulation by in situ surface modification.

    2. Triggering Cell Adhesion, Migration or Shape Change with a Dynamic Surface Coating (pages 1687–1691)

      Stijn F. M. van Dongen, Paolo Maiuri, Emmanuelle Marie, Christophe Tribet and Matthieu Piel

      Version of Record online: 27 JAN 2013 | DOI: 10.1002/adma.201204474

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      There's an APP for that: cell-repellent APP (azido-[polylysine-g-PEG]) is used to create substrates for spatially controlled dynamic cell adhesion. The simple addition of a functional peptide to the culture medium rapidly triggers cell adhesion. This highly accessible yet powerful technique allows diverse applications, demonstrated through tissue motility assays, patterned coculturing and triggered cell shape change.

  8. Frontispiece

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    3. Inside Front Cover
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    5. Masthead
    6. Contents
    7. Review
    8. Communications
    9. Frontispiece
    10. Communications
    11. Frontispiece
    12. Communications
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      A Carbon Nanotube Synapse with Dynamic Logic and Learning (Adv. Mater. 12/2013) (page 1692)

      Kyunghyun Kim, Chia-Ling Chen, Quyen Truong, Alex M. Shen and Yong Chen

      Version of Record online: 18 MAR 2013 | DOI: 10.1002/adma.201370080

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      A carbon nanotube (CNT) electronic synapse which emulates a biological synapse with its dynamic logic, learning, and memory functions is induced by the interactions between CNTs and hydrogen ions in an electrochemical cell. Temporally correlated spikes can trigger the dynamic interactions between CNTs and hydrogen ions, resulting in spike-timing dependent plasticity (STDP) for memory and learning, as reported by Yong Chen and co-workers page 1693.

  9. Communications

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    7. Review
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    9. Frontispiece
    10. Communications
    11. Frontispiece
    12. Communications
    1. A Carbon Nanotube Synapse with Dynamic Logic and Learning (pages 1693–1698)

      Kyunghyun Kim, Chia-Ling Chen, Quyen Truong, Alex M. Shen and Yong Chen

      Version of Record online: 27 DEC 2012 | DOI: 10.1002/adma.201203116

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      A carbon nanotube (CNT) synapse emulates a biological synapse with its dynamic logic, learning, and memory functions induced by the interactions between CNTs and hydrogen ions in an electrochemical cell. A circuit of CNT synapses operates with extremely low-energy consumption and could potentially emulate the functions of the neuronal network.

    2. Decoupling Cell and Matrix Mechanics in Engineered Microtissues Using Magnetically Actuated Microcantilevers (pages 1699–1705)

      Ruogang Zhao, Thomas Boudou, Wei-Gang Wang, Christopher S. Chen and Daniel H. Reich

      Version of Record online: 28 JAN 2013 | DOI: 10.1002/adma.201203585

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      A novel bio-magnetomechanical microtissue system is described for magnetic actuation of arrays of 3D microtissues using microcantilevers. This system enables both in situ measurements of fundamental mechanical properties of engineered tissue, such as contractility and stiffness, as well as dynamic stimulation of the microtissues. Using this system, cell and extracellular matrix contributions to the tissue mechanical properties are decoupled for the first time under both static and dynamic loading conditions.

    3. Effects of Impurities on Operational Mechanism of Organic Bulk Heterojunction Solar Cells (pages 1706–1712)

      Loren Kaake, Xuan-Dung Dang, Wei Lin Leong, Yuan Zhang, Alan Heeger and Thuc-Quyen Nguyen

      Version of Record online: 20 DEC 2012 | DOI: 10.1002/adma.201203786

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      Photoconductive atomic force microscopy in conjunction with transient absorption spectroscopy and charge transport study were used to investigate the effect of impurities (TCNQ and PC84BM) on the performance of low band gap conjugated polymer and fullerene solar cells to gain insight into whether differing impurity shapes may lead to different loss mechanisms.

    4. Highly Pure Solid-State White-Light Emission from Solution-Processable Soft-Hybrids (pages 1713–1718)

      K. Venkata Rao, K. K. R. Datta, Muthusamy Eswaramoorthy and Subi J. George

      Version of Record online: 31 JAN 2013 | DOI: 10.1002/adma.201204407

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      Highly pure and solution processable white-light-emitting hybrids are presented. These soft-hybrids are designed by an organic–inorganic supramolecular co-assembly in water. White-light emission is achieved by partial energy transfer (ET) between donor and acceptor molecules anchored on the inorganic component. The unique and remarkable processability feature of these hybrids is demonstrated by painting/writing onto large glass and flexible plastic substrates.

    5. Graded Doping for Enhanced Colloidal Quantum Dot Photovoltaics (pages 1719–1723)

      Zhijun Ning, David Zhitomirsky, Valerio Adinolfi, Brandon Sutherland, Jixian Xu, Oleksandr Voznyy, Pouya Maraghechi, Xinzheng Lan, Sjoerd Hoogland, Yuan Ren and Edward H. Sargent

      Version of Record online: 5 FEB 2013 | DOI: 10.1002/adma.201204502

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      A novel approach to improving all-inorganic colloidal quantum dot (CQD) homojunction solar cells by engineering the doping spatial profile to produce a doping gradient within the n-type absorber is presented. The doping gradient greatly improves carrier collection and enhances the voltages attainable by the device, leading to a 1 power point power conversion efficiency (PCE) improvement over previous inorganic CQD solar cells.

    6. Ultralow Reflection from a-Si Nanograss/Si Nanofrustum Double Layers (pages 1724–1728)

      Srikanth Ravipati, Jiann Shieh, Fu-Hsiang Ko, Chen-Chieh Yu and Hsuen-Li Chen

      Version of Record online: 5 FEB 2013 | DOI: 10.1002/adma.201204235

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      A double-layer nanostructure comprising amorphous Si nanograss on top of Si nanofrustums (NFs) with a total height of 680 nm exhibits ultralow reflection. Almost near-unity absorption and near-zero reflectance result in this layered nanostructure, over a broad range of wavelengths and a wide range of angles of incidence, due to the low packing density of a-Si and the smooth transition of the refractive index from the air to the Si substrate across both the nanograss and NF layers.

    7. Hybrid Mechanoresponsive Polymer Wires Under Force Activation (pages 1729–1733)

      Hongbin Feng, Jin Lu, Jinghong Li, Francis Tsow, Erica Forzani and Nongjian Tao

      Version of Record online: 20 DEC 2012 | DOI: 10.1002/adma.201204105

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      Force activation is triggered in a stretched polymer wire with color changes produced as a consequence of the molecules undergoing structural and conformational changes. A markedly increased efficiency of force activation is achieved by decreasing the diameter of the wires. The hybrid mechanosensitive polymer wire can function as micro- and nanoscale force sensor.

    8. Aromatic Polythiourea Dielectrics with Ultrahigh Breakdown Field Strength, Low Dielectric Loss, and High Electric Energy Density (pages 1734–1738)

      Shan Wu, Weiping Li, Minren Lin, Quinn Burlingame, Qin Chen, Andrew Payzant, Kai Xiao and Q. M. Zhang

      Version of Record online: 14 JAN 2013 | DOI: 10.1002/adma.201204072

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      The promise of aromatic, amorphous, polar polymers containing high dipolar moments with very low defect levels is demonstrated for future dielectric materials with ultrahigh electric-energy density, low loss at high applied fields, and ultrahigh breakdown strengths. Specifically, aromatic polythiourea films exhibit an ultrahigh breakdown field (>1 GV m−1), which results in an energy density of ≈22 J cm−3, as well as a low loss.

    9. Crosslinking Using Rapid Thermal Processing for the Fabrication of Efficient Solution-Processed Phosphorescent Organic Light-Emitting Diodes (pages 1739–1744)

      Carlos A. Zuniga, Jassem Abdallah, Wojciech Haske, Yadong Zhang, Igor Coropceanu, Stephen Barlow, Bernard Kippelen and Seth R. Marder

      Version of Record online: 29 JAN 2013 | DOI: 10.1002/adma.201204518

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      Copolymers with a triscarbazole hole-transport group and an oxetane or benzocyclobutene crosslinkable group can be readily thermally crosslinked on timescales of 30 min or less, with rapid thermal processing (RTP) being highly effective for this purpose. Devices with RTP-crosslinked hole-transport layers and spin-coated emissive layers exhibit high external quantum efficiencies of up to 15%.

    10. Nano-electromanipulation of Spin Crossover Nanorods: Towards Switchable Nanoelectronic Devices (pages 1745–1749)

      Aurelian Rotaru, Julien Dugay, Reasmey P. Tan, Ilya A. Guralskiy, Lionel Salmon, Philippe Demont, Julian Carrey, Gábor Molnár, Marc Respaud and Azzedine Bousseksou

      Version of Record online: 27 JAN 2013 | DOI: 10.1002/adma.201203020

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      The nanoscale manipulation and charge transport properties of the [Fe(Htrz)2(trz)](BF4) spin-crossover compound is demonstrated. Such 1D spin-crossover nanostructures are attractive building blocks for nanoelectronic switching and memory devices.

    11. Transparent Conductive Gas-Permeation Barriers on Plastics by Atomic Layer Deposition (pages 1750–1754)

      Chun-Ting Chou, Pei-Wei Yu, Ming-Hung Tseng, Che-Chen Hsu, Jing-Jong Shyue, Ching-Chiun Wang and Feng-Yu Tsai

      Version of Record online: 6 FEB 2013 | DOI: 10.1002/adma.201204358

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      A mixed-deposition atomic layer deposition process produces Hf:ZnO films with uniform dopant distribution and high electrical conductivity (resistivity = 4.5 × 10−4 W cm), optical transparency (>85% from 400–1800 nm), and moisture-barrier property (water vapor transmission rate = 6.3 × 10−6 g m−2 day−1).

    12. A High-Performance Room-Temperature NO2 Sensor Based on An Ultrathin Heterojunction Film (pages 1755–1760)

      Shiliang Ji, Haibo Wang, Tong Wang and Donghang Yan

      Version of Record online: 5 FEB 2013 | DOI: 10.1002/adma.201204134

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      A heterojunction device which has good transport characteristics and low sensitivity is obtained through two kinds of organic molecules inert to NO2. Using the heterojunction device, constructing more-sensitive double-heterojunction devices can obtain better room-temperature detection characteristics.

    13. Unexpected Crystal and Domain Structures and Properties in Compositionally Graded PbZr1-xTixO3 Thin Films (pages 1761–1767)

      R. V. K. Mangalam, J. Karthik, Anoop R. Damodaran, Joshua C. Agar and Lane W. Martin

      Version of Record online: 29 JAN 2013 | DOI: 10.1002/adma.201204240

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      Synthesis of compositionally graded versions of PbZr1-xTixO3 thin films results in unprecedented strains (as large as ≈4.5 × 105 m−1) and correspondingly unexpected crystal structures, ferroelectric domain structures, and properties. This includes the observation of built-in electric fields in films as large as 200 kV/cm. Compositional and strain gradients could represent a new direction of strain-control of materials.

  10. Frontispiece

    1. Top of page
    2. Cover Picture
    3. Inside Front Cover
    4. Back Cover
    5. Masthead
    6. Contents
    7. Review
    8. Communications
    9. Frontispiece
    10. Communications
    11. Frontispiece
    12. Communications
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      Self-Assembled, Nanowire Network Electrodes for Depleted Bulk Heterojunction Solar Cells (Adv. Mater. 12/2013) (page 1768)

      Xinzheng Lan, Jing Bai, Silvia Masala, Susanna M. Thon, Yuan Ren, Illan J. Kramer, Sjoerd Hoogland, Arash Simchi, Ghada I. Koleilat, Daniel Paz-Soldan, Zhijun Ning, André J. Labelle, Jin Young Kim, Ghassan Jabbour and Edward H. Sargent

      Version of Record online: 18 MAR 2013 | DOI: 10.1002/adma.201370081

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      A solution-processed, bottom-up nanowire network electrode is developed and employed in a bulk heterojunction colloidal quantum dot solar cell. The electrode features a ZnO template which is converted into locally connected, infiltratable TiO2 nanowires. The new electrode allows the application of a thicker light absorbing film without compromising the charge extraction, as reported by Edward H. Sargent, Ghassan Jabbour, and co-workers on page 1769. The frontispiece shows schematically the electrode shape and the resultant device architecture.

  11. Communications

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    12. Communications
    1. Self-Assembled, Nanowire Network Electrodes for Depleted Bulk Heterojunction Solar Cells (pages 1769–1773)

      Xinzheng Lan, Jing Bai, Silvia Masala, Susanna M. Thon, Yuan Ren, Illan J. Kramer, Sjoerd Hoogland, Arash Simchi, Ghada I. Koleilat, Daniel Paz-Soldan, Zhijun Ning, André J. Labelle, Jin Young Kim, Ghassan Jabbour and Edward H. Sargent

      Version of Record online: 6 JAN 2013 | DOI: 10.1002/adma.201203759

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      Herein, a solution-processed, bottom-up-fabricated, nanowire network electrode is developed. This electrode features a ZnO template which is converted into locally connected, infiltratable, TiO2 nanowires. This new electrode is used to build a depleted bulk heterojunction solar cell employing hybrid-passivated colloidal quantum dots. The new electrode allows the application of a thicker, and thus more light-absorbing, colloidal quantum dot active layer, from which charge extraction of an efficiency comparable to that obtained from a thinner, planar device could be obtained.

    2. A Low Energy Oxide-Based Electronic Synaptic Device for Neuromorphic Visual Systems with Tolerance to Device Variation (pages 1774–1779)

      Shimeng Yu, Bin Gao, Zheng Fang, Hongyu Yu, Jinfeng Kang and H.-S. Philip Wong

      Version of Record online: 27 JAN 2013 | DOI: 10.1002/adma.201203680

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      Neuromorphic computing is an emerging computing paradigm beyond the conventional digital von Neumann computation. An oxide-based resistive switching memory is engineered to emulate synaptic devices. At the device level, the gradual resistance modulation is characterized by hundreds of identical pulses, achieving a low energy consumption of less than 1 pJ per spike. Furthermore, a stochastic compact model is developed to quantify the device switching dynamics and variation. At system level, the performance of an artificial visual system on the image orientation or edge detection with 16 348 oxide-based synaptic devices is simulated, successfully demonstrating a key feature of neuromorphic computing: tolerance to device variation.

    3. Well-Defined Multibranched Gold with Surface Plasmon Resonance in Near-Infrared Region from Seeding Growth Approach Using Gyroid Block Copolymer Template (pages 1780–1786)

      Han-Yu Hsueh, Hung-Ying Chen, Yu-Chueh Hung, Yi-Chun Ling, Shangjr Gwo and Rong-Ming Ho

      Version of Record online: 29 JAN 2013 | DOI: 10.1002/adma.201204631

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      Well-defined multibranched gold (Au) in polymers, both as bulk or continuous thin films, can be fabricated by using a nanoporous polymer with gyroid nanochannels as a template. The nanoporous polymer template is obtained from the self-assembly of a degradable block copolymer, polystyrene-b-poly (L-lactide) (PS-PLLA), followed by the hydrolysis of PLLA blocks. Templated seeding growth approach can be conducted to create precisely controlled nanostructured Au giving remarkable surface plasmon resonance (SPR) in (branched Au with uniform distribution in PS matrix) near-infrared (NIR) region. Controlled growth conditions allow the fabrication of three-dimensionally ordered nanoporous Au particles that possess NIR SPR. Double gyroid Au with dual networks in the PS matrix is obtained after completing the seeding growth at which the NIR SPR diminishes resulting from the reduction in the density of nanostructured edge.

    4. Liquid-Crystalline Elastomer-Nanoparticle Hybrids with Reversible Switch of Magnetic Memory (pages 1787–1791)

      Johannes M. Haberl, Antoni Sánchez-Ferrer, Adriana M. Mihut, Hervé Dietsch, Ann M. Hirt and Raffaele Mezzenga

      Version of Record online: 29 JAN 2013 | DOI: 10.1002/adma.201204406

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      A stimuli-responsive material is synthesized that combines the actuation potential of liquid-crystalline elastomers with the anisotropic magnetic properties of ellipsoidal iron oxide nanoparticles. The resulting nanocomposite exhibits unique shape-memory features with magnetic information, which can be reversibly stored and erased via parameters typical of soft materials, such as high deformations, low stresses, and liquid-crystalline smectic-isotropic transition temperatures.

    5. Electrospun TiO2 Nanorods with Carbon Nanotubes for Efficient Electron Collection in Dye-Sensitized Solar Cells (pages 1792–1795)

      Lijun Yang and Wallace Woon-Fong Leung

      Version of Record online: 28 JAN 2013 | DOI: 10.1002/adma.201204256

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      A high power conversion efficiency of 10.24% can be obtained in a dye-sensitized solar cell by incorporating multiwall carbon nanotubes inside a TiO2 nanorod photoanode. The multiwall carbon nanotubes in the nanorod can effectively collect and transport photogenerated electrons reducing the recombination as well as improving efficiency of the device.

    6. Fast, Reversible, and General Photomechanical Motion in Single Crystals of Various Azo Compounds Using Visible Light (pages 1796–1800)

      Oleksandr S. Bushuyev, Thomas A. Singleton and Christopher J. Barrett

      Version of Record online: 18 JAN 2013 | DOI: 10.1002/adma.201204831

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      Pseudostilbene-type single crystals exhibit ubiquitous, fast, and reversible photomechanical motion under visible-light irradiation. Push-pull substituents impart extremely rapid switching using just one wavelength of light by shortening the lifetime of the cis-form. This results in a bending motion in the microsecond regime. The influence of crystal density, thickness, and molecular orientation on optimization of the photomechanical effect is investigated.

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