Multimodal Capturing of Polysulfides by Phosphorus-Doped Carbon Composites for Flexible High-Energy-Density Lithium-Sulfur Batteries.

The widespread adoption of Li-ion batteries is currently limited by their unstable electrochemical performance and high flammability under mechanical deformation conditions and a relatively low energy density. Herein, high-energy-density lithium-sulfur (Li-S) batteries are developed for applications in next-generation flexible electronics and electric vehicles with long cruising distances. Freestanding high-S-loading carbon nanotubes cathodes are assembled with a phosphorus (P)-doped carbon interlayer coated on commercial separators. Strategies for the active materials and structural design of both the electrodes and separators are highly efficient for immobilizing the lithium polysulfides via multimodal capturing effects; they significantly improve the electrochemical performance in terms of the redox kinetics and cycling stability. The foldable Li-S cells show stable specific capacities of 850 mAh g-1 over 100 cycles, achieving high gravimetric and volumetric energy densities of 387 Wh kgcell -1 and 395 Wh Lcell -1 , respectively. The Li-S cells show highly durable mechanical flexibilities under severe deformation conditions without short circuit or failure. Finally, the Li-S battery is explored as a light-weight and flexible energy storage device aboard airplane drones to ensure at least fivefold longer flight times than traditional Li-ion batteries. Nanocarbon-based S cathodes and P-doped carbon interlayers offer a promising solution for commercializing rechargeable Li-S batteries.

High Throughput Bar-Coating Processed Organic-Inorganic Hybrid Multi-Layers for Gas Barrier Thin-Films.

Herein, we demonstrate the preparation of a scalable bar-coated nanocomposite organic-inorganic hybrid film and developed robust barrier films for general purpose packaging. Using combinatory printing of polymers and nanocomposites by bar coating, a facile and effective barrier film fabrication method was developed. Based on a preliminary survey with several material combinations, a rationalized two-fold nanocomposite film was fabricated. The number of layers in the barrier film significantly modified oxygen barrier performance such that, for the 1 wt% ethylene vinyl alcohol (EVOH) intercalated film, the oxygen transmission rate (OTR) of the 5-layer sample was reduced to 31.69% of the OTR of the 3-layer sample (112.8 vs. 35.75 cc/(m² · day)). In addition, fine tuning the amount of EVOH polymer enabled further improvement of oxygen barrier performance. Intercalation of 2 wt% EVOH resulted an OTR improvement from 35.75 in the 1 wt% sample to 11.90 cc/(m² ·day), which is a 4.25-fold enhancement. Overall barrier characteristics proved that our approach could be used for large-area deposited, oxygen resistant, general purpose packaging applications.

Monolithic Graphene Trees as Anode Material for Lithium Ion Batteries with High C-Rates.

Monolithically structured reduced graphene oxide (rGO), prepared from a highly concentrated and conductive rGO paste, is introduced as an anode material for lithium ion batteries with high rate capacities. This is achieved by a mixture of rGO paste and the water-soluble polymer sodium carboxymethylcellulose (SCMC) with freeze drying. Unlike previous 3D graphene porous structures, the monolithic graphene resembles densely branched pine trees and has high mechanical stability with strong adhesion to the metal electrodes. The structures contain numerous large surface area open pores that facilitate lithium ion diffusion, while the strong hydrogen bonding between the graphene layers and SCMC provides high conductivity and reduces the volume changes that occur during cycling. Ultrafast charge/discharge rates are obtained with outstanding cycling stability and the capacities are higher than those reported for other anode materials. The fabrication process is simple and straightforward to adjust and is therefore suitable for mass production of anode electrodes for commercial applications.

One-step transfer and integration of multifunctionality in CVD graphene by TiO2/graphene oxide hybrid layer.

We present a straightforward method for simultaneously enhancing the electrical conductivity, environmental stability, and photocatalytic properties of graphene films through one-step transfer of CVD graphene and integration by introducing TiO2/graphene oxide layer. A highly durable and flexible TiO2 layer is successfully used as a supporting layer for graphene transfer instead of the commonly used PMMA. Transferred graphene/TiO2 film is directly used for measuring the carrier transport and optoelectronic properties without an extra TiO2 removal and following deposition steps for multifunctional integration into devices because the thin TiO2 layer is optically transparent and electrically semiconducting. Moreover, the TiO2 layer induces charge screening by electrostatically interacting with the residual oxygen moieties on graphene, which are charge scattering centers, resulting in a reduced current hysteresis. Adsorption of water and other chemical molecules onto the graphene surface is also prevented by the passivating TiO2 layer, resulting in the long term environmental stability of the graphene under high temperature and humidity. In addition, the graphene/TiO2 film shows effectively enhanced photocatalytic properties because of the increase in the transport efficiency of the photogenerated electrons due to the decrease in the injection barrier formed at the interface between the F-doped tin oxide and TiO2 layers.

Synthesis of poly(p-phenylene-vinylene) derivatives containing an oxadiazole pendant group and their applications to organic electronic devices.

Poly(p-phenylene vinylene) (PPV) derivatives with 2,5-diphenyl-1,3,4-oxadiazole-diyl (OXD) as the side chain, poly[2-{4-[5-(4-(heptyloxy)phenyl)-1,3,4-oxadiazole-2-yI]phenyl-oxy}-1,4-phenylene-vinylene] (OXH-PPV), poly[2-{4-[5-(4-(heptyloxy)phenyl)-1,3,4-oxadia-zole-2-yl]phenyl-oxy}-1,4-phenylenevinylene-co-2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene] (OXH-PPV-co-MEH-PPV), and poly[2-methoxy-5-(2'-ethylhexyl-oxy)-p-phenylene vinylene] (MEH-PPV), were synthesized via a modified Gilch route. The electron-deficient oxadiazole moiety was introduced on the side chain of the polymer backbone to increase the electron-affinity of the polymers. The electroluminescent (EL) properties of the resulting polymers as an active layer, were investigated by the fabrication of single-layer LEDs and the devices using OXH-PPV-co-MEH-PPV showed better EL properties than those using pure MEH-PPV. Also, to investigate the switching properties of the resulting polymers as an active layer, OFET devices were fabricated in a top-contact/bottom-gate configuration. The resulting FETs exhibited typical p-channel characteristics, field-effect mobility of 6.5 x 10(-4) - 7.0 x 10(-5) cm2 V(-1) s(-1), and on-off ratio of about 10(4)-10(5).

Combining electron-neutral building blocks with intramolecular "conformational locks" affords stable, high-mobility p- and n-channel polymer semiconductors.

Understanding the relationship between molecular/macromolecular architecture and organic thin film transistor (TFT) performance is essential for realizing next-generation high-performance organic electronics. In this regard, planar π-conjugated, electron-neutral (i.e., neither highly electron-rich nor highly electron-deficient) building blocks represent a major goal for polymeric semiconductors, however their realization presents synthetic challenges. Here we report that an easily accessible (minimal synthetic steps), electron-neutral thienyl-vinylene (TVT)-based building block having weak intramolecular S···O "conformational locks" affords a new class of stable, structurally planar, solution-processable, high-mobility, molecular, and macromolecular semiconductors. The attraction of merging the weak TVT electron richness with supramolecular planarization is evident in the DFT-computed electronic structures, favorable MO energetics, X-ray diffraction-derived molecular structures, experimental lattice coehesion metrics, and excellent TFT performance. TVT-based polymer TFTs exhibit stable carrier mobilities in air as high as 0.5 and 0.05 cm(2)/V·s (n- and p-type, respectively). All-TVT polymer-based complementary inverter circuitry exhibiting high voltage gains (~50) and ring oscillator circuitry with high f(osc)(~1.25 kHz) is readily fabricated from these materials by simple inkjet printing.

Mass production of polyfluorene nanowires using a melt-assisted wetting method.

Herein is a description of the mass production of poly(9, 9-dioctylfluorene-co-benthiadiazole) (F8BT) and poly(9, 9-dioctylfluorene) (PFO) nanowires (NWs) using a melt-assisted wetting method with an anodic alumina membrane. The conjugated polymer NWs had a uniform shape (D = 250-300 nm/L = 10-30 microm) and a defect-free smooth surface. Optical properties were investigated by UV-vis, photoluminescent spectroscope, and fluorescent optical microscope. Individual F8BT and PFO NWs had a bright yellow (lambda = 541 nm) andblue (lambda = 442 nm) luminescence, respectively, under UV light irradiation.

Effect of curing temperature on nano-silver paste ink for organic thin-film transistors.

Silver (Ag) metal electrode having 20 microm channel length was printed by reverse offset printing (ROP) using nano-silver paste ink for the source/drain of organic thin-film transistors (OTFT). Specific resistance and surface roughness of printed Ag electrodes with increasing curing temperature were investigated, and surface morphology and grain growth mechanism were systematically verified using a scanning electron microscope (SEM) and atomic force microscope (AFM) in order to obtain an optimized ROP Ag electrode. The Ag electrode was applied to fabricate top-gate/bottom-contact poly(3-hexylthiophene) OTFT devices, which showed reproducible OTFT characteristics such as the field-effect mobility, threshold voltage, and an on/off-current ratio of -10(-3) cm2/Vs, 0.36 V, and -10(2), respectively.

Versatile Solution-Processed Reductive Interface Layer for Contact Engineering of Staggered Organic Field-Effect Transistors.

Efficient charge injection/extraction from/to contact electrodes is essential to realize organic electronic and optoelectronic devices with optimum characteristics for many applications. Herein, we studied a versatile reductive interlayer based on sodium borohydride (NaBH4) to control the contact properties of the staggered organic field-effect transistors (OFETs) either by doping and/or by regulating the contribution of charge carriers. The versatile functionalities of the NaBH4 layer are mainly determined by the alignment of frontier molecular orbitals of donor-acceptor (D-A) type copolymer semiconductors and the work function of the contact electrode. After incorporating the NaBH4 layer, the work function of the bottom-contact gold electrode can be decreased significantly by 1.0 eV, which makes it favorable to efficient electron injection. An Ohmic contact is achieved by the spontaneous injection of electrons to the n-type organic semiconductors with high electron affinity while converting the OFET operation mode to n-type characteristics by blocking the counter-charge carriers for the other types of ambipolar and p-type semiconductors. The solution-processed reducing agent can be a valuable approach to develop high-performance printed and flexible electronic devices through careful engineering to obtain proper contributions of charge carriers either as electrons or holes in various D-A copolymer semiconductors.

Bithiophene-imide-based polymeric semiconductors for field-effect transistors: synthesis, structure-property correlations, charge carrier polarity, and device stability.

Developing new high-mobility polymeric semiconductors with good processability and excellent device environmental stability is essential for organic electronics. We report the synthesis, characterization, manipulation of charge carrier polarity, and device air stability of a new series of bithiophene-imide (BTI)-based polymers for organic field-effect transistors (OFETs). By increasing the conjugation length of the donor comonomer unit from monothiophene (P1) to bithiophene (P2) to tetrathiophene (P3), the electron transport capacity decreases while the hole transport capacity increases. Compared to the BTI homopolymer P(BTimR) having an electron mobility of 10(-2) cm(2) V(-1) s(-1), copolymer P1 is ambipolar with balanced hole and electron mobilities of ∼10(-4) cm(2) V(-1) s(-1), while P2 and P3 exhibit hole mobilities of ∼10(-3) and ∼10(-2) cm(2) V(-1) s(-1), respectively. The influence of P(BTimR) homopolymer M(n) on film morphology and device performance was also investigated. The high M(n) batch P(BTimR)-H affords more crystalline film microstructures; hence, 3× increased electron mobility (0.038 cm(2) V(-1) s(-1)) over the low M(n) one P(BTimR)-L (0.011 cm(2) V(-1) s(-1)). In a top-gate/bottom-contact OFET architecture, P(BTimR)-H achieves a high electron mobility of 0.14 cm(2) V(-1) s(-1), only slightly lower than that of state-of-the-art n-type polymer semiconductors. However, the high-lying P(BTimR)-H LUMO results in minimal electron transport on exposure to ambient. Copolymer P3 exhibits a hole mobility approaching 0.1 cm(2) V(-1) s(-1) in top-gate OFETs, comparable to or slightly lower than current state-of-the-art p-type polymer semiconductors (0.1-0.6 cm(2) V(-1) s(-1)). Although BTI building block incorporation does not enable air-stable n-type OFET performance for P(BTimR) or P1, it significantly increases the OFET air stability for p-type P2 and P3. Bottom-gate/top-contact and top-gate/bottom-contact P2 and P3 OFETs exhibit excellent stability in the ambient. Thus, P2 and P3 OFET hole mobilities are almost unchanged after 200 days under ambient, which is attributed to their low-lying HOMOs (>0.2 eV lower than that of P3HT), induced by the strong BTI electron-withdrawing capacity. Complementary inverters were fabricated by inkjet patterning of P(BTimR)-H (n-type) and P3b (p-type).

A Novel Strategy to Overcome the Hurdle for Commercial All-Solid-State Batteries via Low-Cost Synthesis of Sulfide Solid Electrolytes.

Unlike commercial lithium-ion batteries, the high cost and low ionic conductivity of solid electrolytes (SEs) continues to be a big hurdle in commercially available all-solid-state batteries (ASSBs). Rather than the conventional dry-process and high-energy ball milling processes, the productive solution synthesis of bulk-type SEs is the most crucial issue in the successful application of high-energy-density ASSBs. In this study, the way is paved to overcome the hurdle for commercial lithium phosphorus sulfide chloride (LPSCl) SEs via a readily processable bulk-type solution-based synthesis without acquiring any high-energy ball-milling processes. By incorporating an elemental sulfur additive during the preparation process, Li2 S and S form a polysulfide, and P2 S5 is induced to react readily to provide LPSCl with excellent ion conductivity as high as 1.8 mS cm-1 . Surprisingly, the purity of bulk type precursors does not affect the final composition and ionic conductivity of sulfide electrolytes, which show the same electrochemical characteristics of ASSB cells with a high discharge capacity of 185.6 mA h g-1 . The study offers a promising strategy for saving the production cost of sulfide SEs, possibly up to 92%, and their commercial ASSBs are expected to be achieving a competitive cost per energy density of ≈0.46 $ W-1 .

Facile fabrication of solution-processed solid-electrolytes for high-energy-density all-solid-state-batteries by enhanced interfacial contact.

Instead of commercial lithium-ion batteries (LIBs) using organic liquid electrolytes, all-solid-state lithium-ion batteries (ASSBs) employing solid electrolytes (SEs) are promising for applications in high-energy-density power applications and electric vehicles due to their potential for improving safety and achieving high capacity. Although remarkable progress in SEs has been achieved and has resulted in high ionic conductivity, which now reaches values comparable to those of liquid electrolytes, the typical use of a slurry process for the fabrication of conventional ASSBs inevitably causes harmful reactions between sulfide materials and polar solvents. Here, we studied the efficient infiltration process of SE slurry into conventional composite LIB electrodes (NCM622) for achieving high-energy-density ASSBs via a scalable solution-based fabrication process. Two methods are proposed to ensure that SE materials are evenly distributed and sufficiently infiltrated into the porous structures of LIB electrodes. The LPSCl SE solutions were effectively infiltrated into the electrodes at higher processing temperatures and the temperature was subsequently optimized at above the boiling point of the ethanol solvent due to the dynamic motion of SE molecules via a convective flow during solvent vaporization. Moreover, the porous LIB composite electrodes with a mixture of active materials of different particle sizes formed and filled capillary pores resulting in a high electrode density. The LPSCl SE-infiltrated NCM622 electrodes that used this strategy could remarkably improve the initial discharge capacity of ASSBs to as high as 177 mAh/g. These ASSBs also showed excellent performance even at high loading values (about 17 mg/cm2), making them competitive with LIBs using conventional liquid electrolytes.

Templated assembly of metal nanoparticles in nanoimprinted patterns for metal nanowire fabrication.

We have developed a new method that combines nanoimprint lithography and metal nanoparticle solution processing for fabricating metal nanowires. A polymer template with nanoscale features, fabricated by nanoimprint lithography, provided physical reservoirs which were filled with a silver nanoparticle solution during the spin-coating. After the lift-off process, the defined silver nanoparticle patterns were annealed to enhance the conductivity for use as electrodes. Silver nanowire patterns (500 nm linewidth with a 300 nm gap) were fabricated without using an expensive high-vacuum system for metal deposition. This method demonstrated pattern resolution enhancement compared with ink-jet printing which inherently suffers from ink spreading on the substrate surface. By using this method, organic thin film transistors composed of the solution-processed silver source/drain electrodes with a channel length of 300 nm were fabricated and showed comparable behaviors to those with vacuum-deposited electrodes.

Solution-Processed Nonvolatile Organic Transistor Memory Based on Semiconductor Blends.

Solution-processed nonvolatile organic transistor memory devices are fabricated by employing semiconductor blends of p-channel 6,13-bis(triisopropylsilylethynyl)pentacene and n-channel poly{[ N, N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]- alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-2T); N2200) on polystyrene-brush as a polymer electret. Electret-based memory characteristics are significantly changed depending on the frontier molecular orbitals of the active semiconductors because the charge-trapping efficiency is mainly determined by the energy barrier to transfer electrons and holes from the active channel to the electret layer. A semiconductor mixture with an optimized blending ratio results in an efficient programming and erasing process. Thus, we obtained a remarkably high ratio of ON/OFF current (memory ratio) about 107 and a large amount of shifts in the threshold voltage (memory window) between the programmed and erased states of 55 V, while single-component N2200 showed only writing-once-read-many (WORM)-type memory. Especially, the programmed data can be stably retained more than 10 years with a sufficient memory ratio of 103. Furthermore, our semiconductor blend system leads to preferable vertical phase separation, which affords good reliability under a sequential memory operation condition as well as stability in ambient air. It is expected that our memory devices can be applied for versatile data storage in printed and flexible electronic applications.

Organic nano-floating-gate transistor memory with metal nanoparticles.

Organic non-volatile memory is advanced topics for various soft electronics applications as lightweight, low-cost, flexible, and printable solid-state data storage media. As a key building block, organic field-effect transistors (OFETs) with a nano-floating gate are widely used and promising structures to store digital information stably in a memory cell. Different types of nano-floating-gates and their various synthesis methods have been developed and applied to fabricate nanoparticle-based non-volatile memory devices. In this review, recent advances in the classes of nano-floating-gate OFET memory devices using metal nanoparticles as charge-trapping sites are briefly reviewed. Details of device fabrication, characterization, and operation mechanisms are reported based on recent research activities reported in the literature.

Large Enhancement of Carrier Transport in Solution-Processed Field-Effect Transistors by Fluorinated Dielectric Engineering.

The universal role of high-k fluorinated dielectrics in assisting the carrier transport in transistors for a broad range of printable semiconductors is explored. These results present general rules for how to design dielectric materials and achieve devices with a high carrier concentration, low disorder, reliable operation, and robust properties.

Ultrafast Heating for Intrinsic Properties of Atomically Thin Two-Dimensional Materials on Plastic Substrates.

Despite recent progress in producing flexible and stretchable electronics based on two-dimensional (2D) nanosheets, their intrinsic properties are often degraded by the presence of polymeric residues that remain attached to the 2D nanosheet surfaces following fabrication. Further breakthroughs are therefore keenly awaited to obtain clean surfaces compatible with flexible applications. Here, we report a method that allows the 2D nanosheets to be intrinsically integrated onto flexible substrates. The method involves thermal decomposition of polymeric residues by microwave-induced ultrafast heating of the surface without affecting the underlying flexible substrate. Mapping the C═O stretching mode by Fourier-transform infrared spectroscopy in combination with atomic force microscopy confirms elimination of the polymeric residues from the 2D nanosheet surface. Flexible devices prepared using microwave-cleaned 2D nanosheets show enhanced electrical, optical, and electrothermal performances. This simple technique is applicable to a wide range of 2D nanomaterials and represents an important advance in the field of flexible devices.

Synergistic High Charge-Storage Capacity for Multi-level Flexible Organic Flash Memory.

Electret and organic floating-gate memories are next-generation flash storage mediums for printed organic complementary circuits. While each flash memory can be easily fabricated using solution processes on flexible plastic substrates, promising their potential for on-chip memory organization is limited by unreliable bit operation and high write loads. We here report that new architecture could improve the overall performance of organic memory, and especially meet high storage for multi-level operation. Our concept depends on synergistic effect of electrical characterization in combination with a polymer electret (poly(2-vinyl naphthalene) (PVN)) and metal nanoparticles (Copper). It is distinguished from mostly organic nano-floating-gate memories by using the electret dielectric instead of general tunneling dielectric for additional charge storage. The uniform stacking of organic layers including various dielectrics and poly(3-hexylthiophene) (P3HT) as an organic semiconductor, followed by thin-film coating using orthogonal solvents, greatly improve device precision despite easy and fast manufacture. Poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] as high-k blocking dielectric also allows reduction of programming voltage. The reported synergistic organic memory devices represent low power consumption, high cycle endurance, high thermal stability and suitable retention time, compared to electret and organic nano-floating-gate memory devices.

Chemically doped three-dimensional porous graphene monoliths for high-performance flexible field emitters.

Despite the recent progress in the fabrication of field emitters based on graphene nanosheets, their morphological and electrical properties, which affect their degree of field enhancement as well as the electron tunnelling barrier height, should be controlled to allow for better field-emission properties. Here we report a method that allows the synthesis of graphene-based emitters with a high field-enhancement factor and a low work function. The method involves forming monolithic three-dimensional (3D) graphene structures by freeze-drying of a highly concentrated graphene paste and subsequent work-function engineering by chemical doping. Graphene structures with vertically aligned edges were successfully fabricated by the freeze-drying process. Furthermore, their number density could be controlled by varying the composition of the graphene paste. Al- and Au-doped 3D graphene emitters were fabricated by introducing the corresponding dopant solutions into the graphene sheets. The resulting field-emission characteristics of the resulting emitters are discussed. The synthesized 3D graphene emitters were highly flexible, maintaining their field-emission properties even when bent at large angles. This is attributed to the high crystallinity and emitter density and good chemical stability of the 3D graphene emitters, as well as to the strong interactions between the 3D graphene emitters and the substrate.

Rearrangement of 1D conducting nanomaterials towards highly electrically conducting nanocomposite fibres for electronic textiles.

Nanocarbon-based conducting fibres have been produced using solution- or dry-spinning techniques. Highly conductive polymer-composite fibres containing large amounts of conducting nanomaterials have not been produced without dispersants, however, because of the severe aggregation of conducting materials in high-concentration colloidal solutions. Here we show that highly conductive (electrical conductivity ~1.5 × 10(5) S m(-1)) polymer-composite fibres containing carbon nanotubes and silver nanowires can be fabricated via a conventional solution-spinning process without any other treatment. Spinning dopes were fabricated by a simple mixing of a polyvinyl alcohol solution in dimethylsulfoxide with a paste of long multi-walled carbon nanotubes dispersed in organic solvents, assisted by quadruple hydrogen-bonding networks and an aqueous silver nanowire dispersion. The high electrical conductivity of the fibre was achieved by rearrangement of silver nanowires towards the fibre skin during coagulation because of the selective favourable interaction between the silver nanowires and coagulation solvents. The prepared conducting fibres provide applications in electronic textiles such as a textile interconnector of light emitting diodes, flexible textile heaters, and touch gloves for capacitive touch sensors.