Advanced Energy Materials

Cover image for Vol. 3 Issue 9

September, 2013

Volume 3, Issue 9

Pages 1109–1244

  1. Cover Picture

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    5. Masthead
    6. Contents
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      Solar Cells: Triazatruxene-Diketopyrrolopyrrole Dumbbell-Shaped Molecules as Photoactive Electron Donor for High-Efficiency Solution Processed Organic Solar Cells (Adv. Energy Mater. 9/2013) (page 1109)

      Thomas Bura, Nicolas Leclerc, Rony Bechara, Patrick Lévêque, Thomas Heiser and Raymond Ziessel

      Article first published online: 10 SEP 2013 | DOI: 10.1002/aenm.201370035

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      Dumbbell-shaped molecules can be created by linking functional triazatruxene platforms to highly fluorescent diketopyrrolopyrrole dyes. The association with [6,6]-phenyl-C71-butyric acid methyl ester [PC71BM] electron acceptor produces a self-supporting association capable of photon absorption over a large window and of charge separation in bulk heterojunction solar cells, giving rise to efficient photo-to-current conversion reaching 5.3%. On page 1118, Nicolas Leclerc, Raymond Ziessel, and co-workers describe how these green materials are prepared and studied within the framework of organic solar cells.

  2. Inside Front Cover

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      Fuel Cells: Electronic Activation of Cathode Superlattices at Elevated Temperatures – Source of Markedly Accelerated Oxygen Reduction Kinetics (Adv. Energy Mater. 9/2013) (page 1110)

      Yan Chen, Zhuhua Cai, Yener Kuru, Wen Ma, Harry L. Tuller and Bilge Yildiz

      Article first published online: 10 SEP 2013 | DOI: 10.1002/aenm.201370036

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      A novel combination of scanning tunneling microscopy and focus ion beam milling is developed to probe the local electronic structure near the hetero-interfaces of oxide superlattices with nanometer-scale resolution at elevated temperatures and in oxygen gas environment. On page 1221, Bilge Yildiz and co-workers use this method to reveal the mechanism behind the very high reactivity of the interface between (La,Sr)CoO3 and LaSrCoO4 layers to oxygen reduction at high temperature. The results advance the understanding of oxide hetero-interfaces at elevated temperatures and identify electronically coupled oxide structures as novel cathodes with exceptional performance for application in solid oxide fuel cells.

  3. Back Cover

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      Solar Windows: Transparent Luminescent Solar Concentrators for Large-Area Solar Windows Enabled by Massive Stokes-Shift Nanocluster Phosphors (Adv. Energy Mater. 9/2013) (page 1248)

      Yimu Zhao and Richard R. Lunt

      Article first published online: 10 SEP 2013 | DOI: 10.1002/aenm.201370037

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      Luminescent solar concentrators (LSCs) have been regaining interest for building integrated energy harvesting systems. However, the visible coloring of these systems has hindered widespread adoption, particularly in windows. On page 1143, Yimu Zhao and Richard R. Lunt demonstrate transparent LSCs based on exceptional nanocluster blends that exhibit massively down-converted emission with near-unity quantum yield and perfectly tuned absorption and emission throughout the visible spectrum. These devices present new opportunities for non-tinted and scalable solar-windows.

  4. Masthead

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      Masthead: (Adv. Energy Mater. 9/2013)

      Article first published online: 10 SEP 2013 | DOI: 10.1002/aenm.201370038

  5. Contents

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      Contents: (Adv. Energy Mater. 9/2013) (pages 1111–1117)

      Article first published online: 10 SEP 2013 | DOI: 10.1002/aenm.201370039

  6. Communications

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    1. Triazatruxene-Diketopyrrolopyrrole Dumbbell-Shaped Molecules as Photoactive Electron Donor for High-Efficiency Solution Processed Organic Solar Cells (pages 1118–1124)

      Thomas Bura, Nicolas Leclerc, Rony Bechara, Patrick Lévêque, Thomas Heiser and Raymond Ziessel

      Article first published online: 24 MAY 2013 | DOI: 10.1002/aenm.201300240

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      Stepwise construction of functional triazatruxene platforms allow linking to preorganized diketopyrrolopyrrole bearing thienyl subunits. These dyes exhibit strong absorption until 750 nm in thin films and show favorable redox activity allowing producing efficient organic solar cells when blended in solution with PC71BM. A maximum power conversion efficiency of 5.3% was obtained.

    2. Electronic Conductivity in the Li4/3Ti5/3O4–Li7/3Ti5/3O4 System and Variation with State-of-Charge as a Li Battery Anode (pages 1125–1129)

      David Young, Alan Ransil, Ruhul Amin, Zheng Li and Yet-Ming Chiang

      Article first published online: 19 APR 2013 | DOI: 10.1002/aenm.201300134

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      The electronic conductivity of lithium titanate spinel (Li4/3Ti5/3O4) is measured as a function of lithiation and temperature. The electronic conductivity of fully lithiated spinel (Li7/3Ti5/3O4) is 2.46 S cm−1 at 300 K and is weakly thermally activated. High electronic conductivity is observed over a wide lithiation range down to x~0.04 and suggests that lithium chemical diffusion is ionically limited over most of the state of charge regime.

    3. Quantifying Bimolecular Recombination in Organic Solar Cells in Steady State (pages 1130–1134)

      Gert-Jan A. H. Wetzelaer, Niels J. Van der Kaap, L. Jan Anton Koster and Paul W. M. Blom

      Article first published online: 17 MAY 2013 | DOI: 10.1002/aenm.201300251

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      A steady-state method to probe bimolecular recombination in organic solar cells is presented. The technique is applicable to thin-film solar cells at any temperature and does not require a separate measurement setup other than conventional solar-cell testing equipment. The key element in our method is the derivation of a simple analytical expression that directly gives access to the recombination strength.

    4. Advanced Heterojunction Structure of Polymer Photovoltaic Cell Generating High Photocurrent with Internal Quantum Efficiency Approaching 100% (pages 1135–1142)

      Hui Joon Park, Jae Yong Lee, Taehwa Lee and L. Jay Guo

      Article first published online: 23 MAY 2013 | DOI: 10.1002/aenm.201300245

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      An advanced heterojunction structure is introduced for polymer photovoltaic cells that can approach almost 100% internal quantum efficiency (IQE) even with over 300 nm thick electron-donor layer for adequate light absorption. These devices show superior charge transport properties as well as non-Langevin type bimolecular recombination. The resultant short circuit current of the device is about 50% higher than that of the thermally annealed BHJ polymer PV cell.

    5. Transparent Luminescent Solar Concentrators for Large-Area Solar Windows Enabled by Massive Stokes-Shift Nanocluster Phosphors (pages 1143–1148)

      Yimu Zhao and Richard R. Lunt

      Article first published online: 25 APR 2013 | DOI: 10.1002/aenm.201300173

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      Transparent luminescent solar concentrators are a new standard for selective light harvesting allowing for non-tinted, transparent, and highly scalable solar windows. These devices are enabled by exploiting phosphorescent hexanuclear nanocrystalline-polymer blends that exhibit massive Stokes-shifts, high phosphorescent quantum yield, high stability, and perfectly tuned absorption/emission around the visible spectrum.

    6. Efficient Electro-Catalysts for Enhancing Surface Activity and Stability of SOFC Cathodes (pages 1149–1154)

      Dong Ding, Mingfei Liu, Zhangbo Liu, Xiaxi Li, Kevin Blinn, Xingbao Zhu and Meilin Liu

      Article first published online: 10 MAY 2013 | DOI: 10.1002/aenm.201200984

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      A dense, conformal, thin-film coating of Pr0.75Sr0.2MnO3−δ (PSM) and PrSrCoMnO6–δ (PSCM) on a state-of-the-art La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF)-based cathode for solid oxide fuel cells (SOFC) has drastically enhanced the electro-catalytic activity and stability of the cathode, suggesting that they are excellent electro-catalysts for surface modification of SOFC cathodes. The catalyst coating is introduced by a low-cost, one-step solution infiltration process.

    7. Carbon-Nanotube-Decorated Nano-LiFePO4 @C Cathode Material with Superior High-Rate and Low-Temperature Performances for Lithium-Ion Batteries (pages 1155–1160)

      Xing-Long Wu, Yu-Guo Guo, Jing Su, Jun-Wei Xiong, Ya-Li Zhang and Li-Jun Wan

      Article first published online: 17 MAY 2013 | DOI: 10.1002/aenm.201300159

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      A novel LiFePO4 cathode material (LFP@C/CNT) is demonstrated, whereby the LiFePO4 nanoparticles are decorated with both an amorphous carbon coating and conducting carbon nanotubes. This material exhibits much improved electrochemical properties in terms of specific capacity, rate capability, cycling, and low-temperature performances benefiting from the enhanced electronic and ionic conductivities, stabilized interface and lower charge polarization compared to pristine LFP and other carbon-decorated LFP materials.

    8. Enhanced Efficiency Parameters of Solution-Processable Small-Molecule Solar Cells Depending on ITO Sheet Resistance (pages 1161–1165)

      Dong Hwan Wang, Aung Ko Ko Kyaw, Vinay Gupta, Guillermo C. Bazan and Alan J. Heeger

      Article first published online: 2 MAY 2013 | DOI: 10.1002/aenm.201300277

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      Enhanced efficiency parameters of solution-processable small-molecule bulk-heterojunction solar cells are successfully achieved using ITO substrate with a sheet resistance of 5 Ω/□. The PCE of the device with a 5 Ω/□-ITO shows 8.24% with enhanced JSC of 14.74 mA/cm2, and fill factor of 72.4%. Furthermore, the PCE and FF values are optimized and reproducible due to an improved shunt resistance and a reduced series resistance of the small molecule solar cells.

    9. A Solution-Processable Small Molecule Based on Benzodithiophene and Diketopyrrolopyrrole for High-Performance Organic Solar Cells (pages 1166–1170)

      Yuze Lin, Lanchao Ma, Yongfang Li, Yunqi Liu, Daoben Zhu and Xiaowei Zhan

      Article first published online: 8 MAY 2013 | DOI: 10.1002/aenm.201300181

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      A linear solution-processable small molecule (BDT-2DPP) based on 5-alkylthiophene-2-yl-substituted benzodithiophene and diketopyrrolopyrrole is designed and synthesized. BDT-2DPP exhibits strong and broad absorption with low band gap, low lying energy levels matching with PC61BM and high hole mobility. Solution-processed organic solar cells based on BDT-2DPP:PC61BM blend showed power conversion efficiencies as high as 5.79%.

    10. Leaf-Like V2O5 Nanosheets Fabricated by a Facile Green Approach as High Energy Cathode Material for Lithium-Ion Batteries (pages 1171–1175)

      Yanwei Li, Jinhuan Yao, Evan Uchaker, Jianwen Yang, Yunxia Huang, Ming Zhang and Guozhong Cao

      Article first published online: 17 MAY 2013 | DOI: 10.1002/aenm.201300188

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      Leaf-like V2O5 nanosheets are fabricated by a facile green approach. Used as cathode material for lithium-ion batteries, this nano-structured material exhibits superior performance, i.e., high rate capability and good capacity retention upon cycling. Thus, the leaf-like V2O5 Nanosheets are promising as a cathode material for high power lithium batteries.

    11. Oxidation Stability of Nanographite Materials (pages 1176–1179)

      Huaiguang Li, Niancai Cheng, Yao Zheng, Xiao Zhang, Haifeng Lv, Daping He, Mu Pan, Freddy Kleitz, Shi Zhang Qiao and Shichun Mu

      Article first published online: 21 MAY 2013 | DOI: 10.1002/aenm.201300177

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      The oxidation stabilities of nanographite materials (NGMs) including single/double-walled carbon nanotubes and graphene are investigated. The key factors that influence the oxidation behavior of NGMs such as double layer capacitance, electrical conductivity, and specific surface area is clarified. A facile and effective solution to increase resistance to oxidation is developed.

  7. Full Papers

    1. Top of page
    2. Cover Picture
    3. Inside Front Cover
    4. Back Cover
    5. Masthead
    6. Contents
    7. Communications
    8. Full Papers
    1. Imidazolium-Substituted Polythiophenes as Efficient Electron Transport Materials Improving Photovoltaic Performance (pages 1180–1185)

      Jurgen Kesters, Toon Ghoos, Huguette Penxten, Jeroen Drijkoningen, Tim Vangerven, Dani M. Lyons, Bregt Verreet, Tom Aernouts, Laurence Lutsen, Dirk Vanderzande, Jean Manca and Wouter Maes

      Article first published online: 19 APR 2013 | DOI: 10.1002/aenm.201300049

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      An alcohol-soluble imidazolium-substituted polythiophene is fabricated to enhance the photovoltaic performance of polymer solar cells. The conjugated polyelectrolyte is used as an additional electron transport layer, boosting the inherent IV characteristics of the resulting devices. The ionic polythiophene interlayer is compared with known electron transport materials and shows improved power conversion efficiencies.

    2. Sodium Storage and Transport Properties in Layered Na2Ti3O7 for Room-Temperature Sodium-Ion Batteries (pages 1186–1194)

      Huilin Pan, Xia Lu, Xiqian Yu, Yong-Sheng Hu, Hong Li, Xiao-Qing Yang and Liquan Chen

      Article first published online: 13 MAY 2013 | DOI: 10.1002/aenm.201300139

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      The sodium storage properties of layered Na2Ti3O7, as a potential anode material for sodium-ion batteries, are elaborated from thermodynamic and kinetic aspects. An interesting zero-current overpotential related to thermodynamic factors in Na2Ti3O7 is studied. The electronic structure and sodium transport properties are experimentally investigated, combined with first-principles calculations.

    3. Thermoelectric Property Study of Nanostructured p-Type Half-Heuslers (Hf, Zr, Ti)CoSb0.8Sn0.2 (pages 1195–1200)

      Xiao Yan, Weishu Liu, Shuo Chen, Hui Wang, Qian Zhang, Gang Chen and Zhifeng Ren

      Article first published online: 10 MAY 2013 | DOI: 10.1002/aenm.201200973

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      A good combination!: Based on the previous best binary compositions, thermoelectric figures-of-merit (ZT) of 0.97 at 700 °C and ≥1 at 800 °C were achieved in Hf0.44Zr0.44Ti0.12CoSb0.8Sn0.2. This composition has two advantages over the previous two best compositions: higher ZT than Hf0.5Zr0.5CoSb0.8Sn0.2 and less of the most expensive component, Hf, than in Hf0.8Ti0.2CoSb0.8Sn0.2.

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      Relating Recombination, Density of States, and Device Performance in an Efficient Polymer:Fullerene Organic Solar Cell Blend (pages 1201–1209)

      Steven A. Hawks, Florent Deledalle, Jizhong Yao, Dylan G. Rebois, Gang Li, Jenny Nelson, Yang Yang, Thomas Kirchartz and James R. Durrant

      Article first published online: 12 JUN 2013 | DOI: 10.1002/aenm.201300194

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      The high performance PBDTTT-C:PC71BM BHJ system is limited by recombination of a nongeminate and non-Langevin origin. Both the mobility and carrier lifetime are increased with higher PC71BM content around the optimal range of 50–67 wt.% PC71BM. The likely origin of this observation is a significant shift in density of states with increased PC71BM concentration.

    5. Effect of Hf Concentration on Thermoelectric Properties of Nanostructured N-Type Half-Heusler Materials HfxZr1–xNiSn0.99Sb0.01 (pages 1210–1214)

      Shuo Chen, Kevin C. Lukas, Weishu Liu, Cyril P. Opeil, Gang Chen and Zhifeng Ren

      Article first published online: 24 MAY 2013 | DOI: 10.1002/aenm.201300336

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      Half-Heusler n-type thermoelectric materials MNiSn (M = Hf, Zr) exhibit peak thermoelectric figure-of-merit (ZT) of ∼1.0 at 600–700 °C with a composition of Hf0.75Zr0.25NiSn0.99Sb0.01. This work achieves the same ZT by reducing the concentration of the most expensive component Hf to one third of the previously reported best composition, i.e., Hf0.25Zr0.75NiSn0.99Sb0.01, which corresponds to an overall 50% reduction on material cost.

    6. Nanoporous Polytetrafluoroethylene/Silica Composite Separator as a High-Performance All-Vanadium Redox Flow Battery Membrane (pages 1215–1220)

      Xiaoliang Wei, Zimin Nie, Qingtao Luo, Bin Li, Baowei Chen, Kevin Simmons, Vincent Sprenkle and Wei Wang

      Article first published online: 2 MAY 2013 | DOI: 10.1002/aenm.201201112

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      A nanoporous polytetrafluoroethylene (PTFE)/silica composite separator has been successfully developed for all-vanadium redox flow battery (VRB). The new separator has demonstrated an excellent combination of chemical stability, conductivity, capacity retention, and cost for VRB application, offering great promise as a substitute for the Nafion membrane.

    7. Electronic Activation of Cathode Superlattices at Elevated Temperatures – Source of Markedly Accelerated Oxygen Reduction Kinetics (pages 1221–1229)

      Yan Chen, Zhuhua Cai, Yener Kuru, Wen Ma, Harry L. Tuller and Bilge Yildiz

      Article first published online: 8 MAY 2013 | DOI: 10.1002/aenm.201300025

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      A novel in situ approach is developed to probe the electronic structure across the interface of nanoscale multilayer systems at high temperature and in oxygen environment. Using this approach, the (La0.5Sr0.5)2CoO4/La0.8Sr0.2CoO3 (LSC214/113) multilayer is investigated, and the electronic activation of LSC214 at high temperature by LSC113 is discovered, which leads to the ultra-high oxygen reduction activity near the LSC113/214 interface.

    8. Inkjet Printing of Back Electrodes for Inverted Polymer Solar Cells (pages 1230–1237)

      Dechan Angmo, Jorgen Sweelssen, Ronn Andriessen, Yulia Galagan and Frederik C. Krebs

      Article first published online: 12 JUN 2013 | DOI: 10.1002/aenm.201201050

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      Inkjet printing is explored as an ambient technique for processing of silver back electrodes in inverted polymer solar cells with the structure: ITO/ZnO/P3HT:PCBM/PEDOT:PSS/Ag. Comparison is made with evaporation and the commonly used ambient processing technique – screen printing. Inkjet printing is found to be an effective ambient processing technique in the processing of back electrodes with devices exhibiting photovoltaic properties similar to those with evaporated back electrodes.

    9. Low Electron Scattering Potentials in High Performance Mg2Si0.45Sn0.55 Based Thermoelectric Solid Solutions with Band Convergence (pages 1238–1244)

      Xiaohua Liu, Tiejun Zhu, Heng Wang, Lipeng Hu, Hanhui Xie, Guangyu Jiang, G. Jeffrey Snyder and Xinbing Zhao

      Article first published online: 30 APR 2013 | DOI: 10.1002/aenm.201300174

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      Both the acoustic phonon scattering and alloy scattering contribute to the carrier transport in the Sb doped Mg2Si0.45Sn0.55 solid solutions. A low deformation potential and a low alloy scattering potential have been derived by modeling of thermoelectric transport properties, which are believed to be intrinsic features contributing to the high thermoelectric performance of the solid solutions.

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