Epitaxially Grown Ferroelectric PVDF‐TrFE Film on Shape‐Tailored Semiconducting Rubrene Single Crystal

Epitaxial crystallization of thin poly(vinylidene fluoride‐co‐trifluoroethylene) (PVDF‐TrFE) films is important for the full utilization of their ferroelectric properties. Epitaxy can offer a route for maximizing the degree of crystallinity with the effective orientation of the crystals with respect to the electric field. Despite various approaches for the epitaxial control of the crystalline structure of PVDF‐TrFE, its epitaxy on a semiconductor is yet to be accomplished. Herein, the epitaxial growth of PVDF‐TrFE crystals on a single‐crystalline organic semiconductor rubrene grown via physical vapor deposition is presented. The epitaxy results in polymer crystals globally ordered with specific crystal orientations dictated by the epitaxial relation between the polymer and rubrene crystal. The lattice matching between the c‐axis of PVDF‐TrFE crystals and the (210) plane of orthorhombic rubrene crystals develops two degenerate crystal orientations of the PVDF‐TrFE crystalline lamellae aligned nearly perpendicular to each other. Thin PVDF‐TrFE films with epitaxially grown crystals are incorporated into metal/ferroelectric polymer/metal and metal/ferroelectric polymer/semiconductor/metal capacitors, which exhibit excellent nonvolatile polarization and capacitance behavior, respectively. Furthermore, combined with a printing technique for micropatterning rubrene single crystals, the epitaxy of a PVDF‐TrFE film is formed selectively on the patterned rubrene with characteristic epitaxial crystal orientation over a large area.     

An All‐Integrated Anode via Interlinked Chemical Bonding between Double‐Shelled–Yolk‐Structured Silicon and Binder for Lithium‐Ion Batteries

The concept of an all‐integrated design with multifunctionalization is widely employed in optoelectronic devices, sensors, resonator systems, and microfluidic devices, resulting in benefits for many ongoing research projects. Here, maintaining structural/electrode stability against large volume change by means of an all‐integrated design is realized for silicon anodes. An all‐integrated silicon anode is achieved via multicomponent interlinking among carbon@void@silica@silicon (CVSS) nanospheres and cross‐linked carboxymethyl cellulose and citric acid polymer binder (c‐CMC‐CA). Due to the additional protection from the silica layer, CVSS is superior to the carbon@void@silicon (CVS) electrode in terms of long‐term cyclability. The as‐prepared all‐integrated CVSS electrode exhibits high mechanical strength, which can be ascribed to the high adhesivity and ductility of c‐CMC‐CA binder and the strong binding energy between CVSS and c‐CMC‐CA, as calculated based on density functional theory (DFT). This electrode exhibits a high reversible capacity of 1640 mA h g^?1 after 100 cycles at a current density of 1 A g^?1, high rate performance, and long‐term cycling stability with 84.6% capacity retention after 1000 cycles at 5 A g^?1.     

A Quadruple‐Hydrogen‐Bonded Supramolecular Binder for High‐Performance Silicon Anodes in Lithium‐Ion Batteries

With extremely high specific capacity, silicon has attracted enormous interest as a promising anode material for next‐generation lithium‐ion batteries. However, silicon suffers from a large volume variation during charge/discharge cycles, which leads to the pulverization of the silicon and subsequent separation from the conductive additives, eventually resulting in rapid capacity fading and poor cycle life. Here, it is shown that the utilization of a self‐healable supramolecular polymer, which is facilely synthesized by copolymerization of tert‐butyl acrylate and an ureido‐pyrimidinone monomer followed by hydrolysis, can greatly reduce the side effects caused by the volume variation of silicon particles. The obtained polymer is demonstrated to have an excellent self‐healing ability due to its quadruple‐hydrogen‐bonding dynamic interaction. An electrode using this self‐healing supramolecular polymer as binder exhibits an initial discharge capacity as high as 4194 mAh g⁻¹ and a Coulombic efficiency of 86.4%, and maintains a high capacity of 2638 mAh g⁻¹ after 110 cycles, revealing significant improvement of the electrochemical performance in comparison with that of Si anodes using conventional binders. The supramolecular binder can be further applicable for silicon/carbon anodes and therefore this supramolecular strategy may increase the choice of amendable binders to improve the cycle life and energy density of high‐capacity Li‐ion batteries.     

Photosystem I (PSI)/Photosystem II (PSII)‐Based Photo‐Bioelectrochemical Cells Revealing Directional Generation of Photocurrents

Layered assemblies of photosystem I, PSI, and/or photosystem II, PSII, on ITO electrodes are constructed using a layer‐by‐layer deposition process, where poly N,N′‐dibenzyl‐4,4′‐bipyridinium (poly‐benzyl viologen, PBV²⁺) is used as an inter‐protein “glue”. While the layered assembly of PSI generates an anodic photocurrent only in the presence of a sacrificial electron donor system, such as dichlorophenol indophenol (DCPIP)/ascorbate, the PSII‐modified electrode leads, upon irradiation, to the formation of an anodic photocurrent (while evolving oxygen), in the absence of any sacrificial component. The photocurrent is generated by transferring the electrons from the PSII units to the PBV²⁺ redox polymer. The charge‐separated species allow, then, the injection of the electrons to the electrode, with the concomitant evolution of O₂. A layered assembly, consisting of a PSI layer attached to a layer of PSII by the redox polymer PBV²⁺, leads to an anodic photocurrent that is 2‐fold higher, as compared to the anodic photocurrent generated by a PSII‐modified electrode. This observation is attributed to an enhanced charge separation in the two‐photosystem assembly. By the further nano‐engineering of the two photosystems on the electrode using two different redox polymers, vectorial electron transfer to the electrode is demonstrated, resulting in a ca. 6‐fold enhancement in the photocurrent. The reversed bi‐layer assembly, consisting of a PSII layer linked to a layer of PSI by the PBV²⁺ redox polymer, yields, upon irradiation, an inefficient cathodic current. This observation is attributed to a mixture of photoinduced electron transfer reactions of opposing effects on the photocurrent directions in the two‐photosystem assembly.     

Responsive Liquid‐Crystal‐Clad Fibers for Advanced Textiles and Wearable Sensors

A simple process to clad conventional monofilament fibers with low‐molecular‐weight liquid crystals (LCs) stabilized by an outer polymer sheath is demonstrated. The fibers retain the responsive properties of the LCs but in a highly flexible/drapable format. The monofilament core makes these fibers much more rugged with a magnified response to external stimuli when compared to previously reported LC‐core fibers produced by electrospinning or airbrushing. The microscopic structure and the optical properties of round and flattened fibers are reported. The sensitivity of the response of individual fibers can be tuned over a broad range by varying the composition of the LCs. Complex fabrics can be easily woven from fibers that respond to different external stimuli, such as temperature variation, chemical concentrations, and pressure. The fabrics can be fashioned into garments that can sense and report the state of health of the wearer or the status of their environment.     

Fluorescence Enhancement on Large Area Self‐Assembled Plasmonic‐3D Photonic Crystals

Discontinuous plasmonic‐3D photonic crystal hybrid structures are fabricated in order to evaluate the coupling effect of surface plasmon resonance and the photonic stop band. The nanostructures are prepared by silver sputtering deposition on top of hydrophobic 3D photonic crystals. The localized surface plasmon resonance of the nanostructure has a symbiotic relationship with the 3D photonic stop band, leading to highly tunable characteristics. Fluorescence enhancements of conjugated polymer and quantum dot based on these hybrid structures are studied. The maximum fluorescence enhancement for the conjugated polymer of poly(5‐methoxy‐2‐(3‐sulfopropoxy)‐1,4‐phenylenevinylene) potassium salt by a factor of 87 is achieved as compared with that on a glass substrate due to the enhanced near‐field from the discontinuous plasmonic structures, strong scattering effects from rough metal surface with photonic stop band, and accelerated decay rates from metal‐coupled excited state of the fluorophore. It is demonstrated that the enhancement induced by the hybrid structures has a larger effective distance (optimum thickness ≈130 nm) than conventional plasmonic systems. It is expected that this approach has tremendous potential in the field of sensors, fluorescence‐imaging, and optoelectronic applications.     

Electric‐Field‐Assisted Growth of Functionalized Poly(3,4‐ethylenedioxythiophene) Nanowires for Label‐Free Protein Detection

The construction of functionalized poly(3,4‐ethylenedioxythiophene) (PEDOT) nanowire devices for label‐free protein detection is reported. Direct growth/assembly of PEDOT nanowires with carboxylic acid side‐chain functional groups (poly(EDOT‐COOH)) across the electrode junction is achieved by using an electric‐field‐assisted method. These functionalized PEDOT nanowire devices show typical depletion‐mode p‐type field‐effect transistor (FET) properties. Upon conjugation with a protein‐binding aptamer, the PEDOT nanowire FET devices are used for label‐free electronic detection of a target protein of interest. The binding of a positively charged protein causes a substantial decrease in current flow, attributed to the specific interaction between target protein molecules and aptamer‐conjugated polymer chains.     

Approaching Intra‐ and Interchain Charge Transport of Conjugated Polymers Facilely by Topochemical Polymerized Single Crystals

Charge transport of small molecules is measured well with scanning tunneling microscopy, conducting atomic force microscopy, break junction, nanopore, and covalently bridging gaps. However, the manipulation and measurement of polymer chains remain a long‐standing fundamental issue in conjugated polymers and full of challenge since conjugated polymers are naturally disordered materials. Here, a fundamental breakthrough in generating high‐quality conjugated‐polymer nanocrystals with extended conjugation and exceptionally high degrees of order using a surface‐supported topochemical polymerization method is demonstrated. In the crystal the conjugated‐polymer chains are extended along the long axis of the crystal with the side chains perpendicular to the long axis. Devices with conducting channels along the polymer chains show efficient charge transport, nearly two orders of magnitude greater than the interchain charge transport along the π–π stacking direction. This is the first example to clarify intra‐ and interchain charge transport based on an individual single crystal of conjugated polymers, and demonstrate the importance of intrachain charge transport in plastic electronics.     

Adaptive Fabrication of a Flexible Electrode by Optically Self‐Selected Interfacial Adhesion and Its Application to Highly Transparent and Conductive Film

A novel adaptive electrode fabrication method using optically self‐selected interfacial adhesion between a laser‐processed metal layer and polymer film is introduced to fabricate cost‐effectively a high‐resolution arbitrary electrode with high conductivity. The quality is close to that from vacuum deposition on a highly heat sensitive polymer film, with active response to various design requirements. A highly conductive metal film (resistivity: 3.6 μΩ cm) below a 5 μm line width with a uniform stepwise profile and mirror surface quality (R_rms: 5–6 nm) is fabricated on a cheap polymer film with a heat resistance limit of below 100 °C. Severe durability tests are successfully completed without using any adhesion promoters. Finally, a highly transparent and conductive electrode with a transparency above 95% and sheet resistance of less than 10 Ω sq^?1 is fabricated on a polymer film and on glass by using this method. These results can help realize a potential high‐throughput, low‐cost, solution‐processable replacement for transparent conductive oxides.     

Inside Front Cover: Redox‐Tunable Defects in Colloidal Photonic Crystals (Adv. Mater. 20/2005)

The inside front cover illustrates reversible tuning of an intragap transmitting state induced by redox cycling, accomplished using a redox‐active polyferrocenylsilane polyelectrolyte multilayer planar defect embedded in a colloidal photonic crystal (CPC) synthesized by a bottom–up method combining colloidal self‐assembly and microcontact printing. In work reported on p. 2455 by Manners, Ozin, and co‐workers, the wavelength position of the defect state can be changed by changing the oxidation state of the ferrocene moieties in the polymer backbone. This could find applications in electrochemically tunable microcavities, and—if light emitters are incorporated—electrochemically tunable CPC‐based laser sources. Cover design by Ludovic Cademartiri.     

Plasmon‐Enhanced Spectroscopies with Shell‐Isolated Nanoparticles

Shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS), due to its versatility, has been able to break the long‐term limitations of the material‐ and substrate‐specific generalities in the traditional field of surface‐enhanced Raman spectroscopy. With a shell‐isolated work principle, this method provides an opportunity to investigate successfully in surface, biological systems, energetic materials, and environmental sciences. Both the shell material and core morphology are being improved continuously to meet the requirements in diverse systems, such as the electrochemical studies at single crystal electrode surfaces, in situ monitoring of photoinduced reaction processes, practical applications in energy conversion and storage, inspections in food safety, and the surface‐enhanced fluorescence. Predictably, the concept of shell‐isolated nanoparticle‐enhancement could be expanded to the wider range for the performance of plasmon‐enhanced spectral modifications.     

High‐Performance All‐Polymer Solar Cells Enabled by an n‐Type Polymer Based on a Fluorinated Imide‐Functionalized Arene

A novel imide‐functionalized arene, di(fluorothienyl)thienothiophene diimide (f‐FBTI2), featuring a fused backbone functionalized with electron‐withdrawing F atoms, is designed, and the synthetic challenges associated with highly electron‐deficient fluorinated imide are overcome. The incorporation of f‐FBTI2 into polymer affords a high‐performance n‐type semiconductor f‐FBTI2‐T, which shows a reduced bandgap and lower‐lying lowest unoccupied molecular orbital (LUMO) energy level than the polymer analog without F or with F‐functionalization on the donor moiety. These optoelectronic properties reflect the distinctive advantages of fluorination of electron‐deficient acceptors, yielding “stronger acceptors,” which are desirable for n‐type polymers. When used as a polymer acceptor in all‐polymer solar cells, an excellent power conversion efficiency of 8.1% is achieved without any solvent additive or thermal treatment, which is the highest value reported for all‐polymer solar cells except well‐studied naphthalene diimide and perylene diimide‐based n‐type polymers. In addition, the solar cells show an energy loss of 0.53 eV, the smallest value reported to date for all‐polymer solar cells with efficiency > 8%. These results demonstrate that fluorination of imide‐functionalized arenes offers an effective approach for developing new electron‐deficient building blocks with improved optoelectronic properties, and the emergence of f‐FBTI2 will change the scenario in terms of developing n‐type polymers for high‐performance all‐polymer solar cells.     

Inside Front Cover: Aromatic Carbonyl Derivative Polymers as High‐Performance Li‐Ion Storage Materials (Adv. Mater. 12/2007)

Molecular simulation of a PTCDA sulfide polymer crystal, in which a layered structure can be clearly observed. As reported on p. 1616 by Taolei Sun, Jutang Sun, and co‐workers, this is a new class of promising organic positive‐electrode materials for Li‐ion batteries. The excellent electrochemical performance of these materials, which is comparable or even superior to conventional inorganic materials, as well as their high safety, environmental friendliness, molecular design flexibility and diversity, and low cost, endow them with broad application and market potential.     

Inside Front Cover: Experimental Evidence for Superprism Effects in Three‐Dimensional Polymer Photonic Crystals (Adv. Mater. 2/2006)

The inside cover illustrates the highly dispersive propagation of light in a three‐dimensional polymer photonic crystal. White light is coupled into a woodpile structure and split into its wavelength components due to the frequency‐dependent dispersion properties of the structure. This superprism effect is orders of magnitudes higher than in a conventional glass prism and is caused by the strong anisotropy of the dispersion surface at frequencies slightly above the photonic bandgap. In work reported on p. 221, Serbin and Gu fabricated these woodpile structures operating in the near‐infrared wavelength range by means of two‐photon polymerization and give theoretical and experimental evidence for the superprism effect in these low‐index photonic‐crystal structures.     

Metallosupramolecular Photonic Elastomers with Self‐Healing Capability and Angle‐Independent Color

Photonic elastomers that can change colors like a chameleon have shown great promise in various applications. However, it still remains a challenge to produce artificial photonic elastomers with desired optical and mechanical properties. Here, the generation of metallosupramolecular polymer‐based photonic elastomers with tunable mechanical strength, angle‐independent structural color, and self‐healing capability is reported. The photonic elastomers are prepared by incorporating isotropically arranged monodispersed SiO₂ nanoparticles within a supramolecular elastomeric matrix based on metal coordination interaction between amino‐terminated poly(dimethylsiloxane) and cerium trichloride. The photonic elastomers exhibit angle‐independent structural colors, while Young's modulus and elongation at break of the as‐formed photonic elastomers reach 0.24 MPa and 150%, respectively. The superior elasticity of photonic elastomers enables their chameleon‐skin‐like mechanochromic capability. Moreover, the photonic elastomers are capable of healing scratches or cuts to ensure sustainable optical and mechanical properties, which is crucial to their applications in wearable devices, optical coating, and visualized force sensing.     

Mineral‐Templated 3D Graphene Architectures for Energy‐Efficient Electrodes

3D graphene networks have shown extraordinary promise for high‐performance electrochemical devices. Herein, the chemical vapor deposition synthesis of a highly porous 3D graphene foam (3D‐GF) using naturally abundant calcined Iceland crystal as the template is reported. Intriguingly, the Iceland crystal transforms to CaO monolith with evenly distributed micro/meso/macropores through the releasing of CO₂ at high temperature. Meanwhile, the hierarchical structure of the calcined template could be easily tuned under different calcination conditions. By precisely inheriting fine structure from the templates, the as‐prepared 3D‐GF possesses a tunable hierarchical porosity and low density. Thus, the hierarchical pores offer space for guest hybridization and provide an efficient pathway for ion/charge transport in typical energy conversion/storage systems. The 3D‐GF skeleton electrode hybridized with Ni(OH)₂/Co(OH)₂ through an optimal electrodeposition condition exhibits a high specific capacitance of 2922.2 F g⁻¹ at a scan rate of 10 mV s⁻¹, and 2138.4 F g⁻¹ at a discharge current density of 3.1 A g⁻¹. The hybrid 3D‐GF symmetry supercapacitor shows a high energy density of 83.0 Wh kg⁻¹ at a power density of 1011.3 W kg⁻¹ and 31.4 Wh kg⁻¹ at a high power density of 18 845.2 W kg⁻¹. The facile fabrication process enables the mass production of hierarchical porous 3D‐GF for high‐performance supercapacitors.     

Double‐Layer Polymer Electrolyte for High‐Voltage All‐Solid‐State Rechargeable Batteries

No single polymer or liquid electrolyte has a large enough energy gap between the empty and occupied electronic states for both dendrite‐free plating of a lithium‐metal anode and a Li⁺ extraction from an oxide host cathode without electrolyte oxidation in a high‐voltage cell during the charge process. Therefore, a double‐layer polymer electrolyte is investigated, in which one polymer provides dendrite‐free plating of a Li‐metal anode and the other allows a Li⁺ extraction from an oxide host cathode without oxidation of the electrolyte in a 4 V cell over a stable charge/discharge cycling at 65 °C; a poly(ethylene oxide) polymer contacts the lithium‐metal anode and a poly(N‐methyl‐malonic amide) contacts the cathode. All interfaces of the flexible, plastic electrolyte remain stable with no visible reduction of the Li⁺ conductivity on crossing the polymer/polymer interface.     

Nitrogen‐Induced Surface Area and Conductivity Modulation of Carbon Nanohorn and Its Function as an Efficient Metal‐Free Oxygen Reduction Electrocatalyst for Anion‐Exchange Membrane Fuel Cells

Nitrogen‐doped carbon morphologies have been proven to be better alternatives to Pt in polymer‐electrolyte membrane (PEM) fuel cells. However, efficient modulation of the active sites by the simultaneous escalation of the porosity and nitrogen doping, without affecting the intrinsic electrical conductivity, still remains to be solved. Here, a simple strategy is reported to solve this issue by treating single‐walled carbon nanohorn (SWCNH) with urea at 800 °C. The resulting nitrogen‐doped carbon nanohorn shows a high surface area of 1836 m² g^?1 along with an increased electron conductivity, which are the pre‐requisites of an electrocatalyst. The nitrogen‐doped nanohorn annealed at 800 °C (N‐800) also shows a high oxygen reduction activity (ORR). Because of the high weight percentage of pyridinic nitrogen coordination in N‐800, the present catalyst shows a clear 4‐electron reduction pathway at only 50 mV overpotential and 16 mV negative shift in the half‐wave potential for ORR compared to Pt/C along with a high fuel selectivity and electrochemical stability. More importantly, a membrane electrode assembly (MEA) based on N‐800 provides a maximum power density of 30 mW cm^?2 under anion‐exchange membrane fuel cell (AEMFC) testing conditions. Thus, with its remarkable set of physical and electrochemical properties, this material has the potential to perform as an efficient Pt‐free electrode for AEMFCs.     

Electron Transfer Mediated by Surface‐Tethered Redox Groups in Nanofluidic Devices

Electrochemistry provides a powerful sensor transduction and amplification mechanism that is highly suited for use in integrated, massively parallelized assays. Here, the cyclic voltammetric detection of flexible, linear poly(ethylene glycol) polymers is demonstrated, which have been functionalized with redox‐active ferrocene (Fc) moieties and surface‐tethered inside a nanofluidic device consisting of two microscale electrodes separated by a gap of <100 nm. Diffusion of the surface‐bound polymer chains in the aqueous electrolyte allows the redox groups to repeatedly shuttle electrons from one electrode to the other, resulting in a greatly amplified steady‐state electrical current. Variation of the polymer length provides control over the current, as the activity per Fc moiety appears to depend on the extent to which the polymer layers of the opposing electrodes can interpenetrate each other and thus exchange electrons. These results outline the design rules for sensing devices that are based on changing the polymer length, flexibility, and/or diffusivity by binding an analyte to the polymer chain. Such a nanofluidic enabled configuration provides an amplified and highly sensitive alternative to other electrochemical detection mechanisms.     

Hierarchical and Heterogeneous Bioinspired Composites—Merging Molecular Self‐Assembly with Additive Manufacturing

Biological composites display exceptional mechanical properties owing to a highly organized, heterogeneous architecture spanning several length scales. It is challenging to translate this ordered and multiscale structural organization in synthetic, bulk composites. Herein, a combination of top‐down and bottom‐up approach is demonstrated, to form a polymer‐ceramic composite by macroscopically aligning the self‐assembled nanostructure of polymerizable lyotropic liquid crystals via 3D printing. The polymer matrix is then uniformly reinforced with bone‐like apatite via in situ biomimetic mineralization. The combinatorial method enables the formation of macrosized, heterogeneous composites where the nanostructure and chemical composition is locally tuned over microscopic distances. This enables precise control over the mechanics in specific directions and regions, with a unique intrinsic–extrinsic toughening mechanism. As a proof‐of‐concept, the method is used to form large‐scale composites mimicking the local nanostructure, compositional gradients and directional mechanical properties of heterogeneous tissues like the bone‐cartilage interface, for mechanically stable osteochondral plugs. This work demonstrates the possibility to create hierarchical and complex structured composites using weak starting components, thus opening new routes for efficient synthesis of high‐performance materials ranging from biomaterials to structural nanocomposites.