An important strategy for realizing flexible electronics is to use solution-processable materials that can be directly printed and integrated into high-performance electronic components on plastic. Although examples of functional inks based on metallic, semiconducting and insulating materials have been developed, enhanced printability and performance is still a challenge. Printable high-capacitance dielectrics that serve as gate insulators in organic thin-film transistors are a particular priority. Solid polymer electrolytes (a salt dissolved in a polymer matrix) have been investigated for this purpose, but they suffer from slow polarization response, limiting transistor speed to less than 100 Hz. Here, we demonstrate that an emerging class of polymer electrolytes known as ion gels can serve as printable, high-capacitance gate insulators in organic thin-film transistors. The specific capacitance exceeds that of conventional ceramic or polymeric gate dielectrics, enabling transistor operation at low voltages with kilohertz switching frequencies.

A new type of high performance thermoelectric material Cu2‐xS composed of non‐toxic and earth‐abundant elements Cu and S is reported. Cu2‐xS surprisingly has lower thermal conductivity and more strikingly reduced specific heat compared to the heavier Cu2Se, leading to an increased zT to 1.7.

Four amphiphilic poly((1,2-butadiene)-block-ethylene oxide) (PB-PEO) diblock copolymers were shown to aggregate strongly and form micelles in an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF(6)]). The universal micellar structures (spherical micelle, wormlike micelle, and bilayered vesicle) were all accessed by varying the length of the corona block while holding the core block constant. The nanostructures of the PB-PEO micelles formed in an ionic liquid were directly visualized by cryogenic transmission electron microscopy (cryo-TEM). Detailed micelle structural information was extracted from both cryo-TEM and dynamic light scattering measurements, with excellent agreement between the two techniques. Compared to aqueous solutions of the same copolymers, [BMIM][PF(6)] solutions exhibit some distinct features, such as temperature-independent micellar morphologies between 25 and 100 degrees C. As in aqueous solutions, significant nonergodicity effects were also observed. This work demonstrates the flexibility of amphiphilic block copolymers for controlling nanostructure in an ionic liquid, with potential applications in many arenas.

We demonstrate the fabrication of polymer thin-film transistors gated with an ion gel electrolyte made of the blend of an ionic liquid and a polymerised ionic liquid. The ion gel exhibits a high stability and ionic conductivity, combined with facile processing by simple drop-casting from solution. In order to avoid parasitic effects such as high hysteresis, high off-currents and slow switching, a fluorinated photoresist is employed in order to enable high-resolution orthogonal patterning of the polymer semiconductor over an area that precisely defines the transistor channel. The resulting devices exhibit excellent characteristics, with an on/off ratio of 10 6 , low hysteresis and a very large transconductance of 3 mS. We show that this high transconductance value is mostly the result of ions penetrating the polymer film and doping the entire volume of the semiconductor, yielding an effective capacitance per unit area of about 200 µF cm −2 , one order of magnitude higher than the double layer capacitance of the ion gel. This results in channel currents larger than 1 mA at an applied gate bias of only-1 V. We also investigate the dynamic performance of the devices and obtain a switching time of 20 ms, which is mostly limited by the overlap capacitance between the ion gel and the source and drain contacts. Electrolyte-gated organic thin-film transistors (OTFTs) have received a lot of attention over the past years, thanks to their ability to operate at very low voltages (< |1| V), 1-3 which makes them particularly attractive for use in portable devices powered by low supply voltage sources such as thin-film batteries, and interfacing with conventional Si CMOS electronics. If an electrolyte is placed in contact with two electrodes, to which a small voltage is applied, ionic species within the electrolyte migrate towards the electrode of opposite polarity, forming ultra-thin electrical double layers at both electrolyte/electrode interfaces. When one of these electrodes is the channel of a transistor, large charge densities arise within the semiconductor, as a result of the ionic accumulation within a small volume close to the interface or within the bulk of the semiconductor, depending on the mode of operation of the device. In the case where ionic charges are contained at the interface with the semiconductor, for example by using a polyelectrolyte in which the ionic charges are covalently linked to the polymer chains 4 or a crystalline semiconductor impermeable to ion penetration, 5 the device operates much like a field-effect transistor. On the other hand, when ions penetrate inside the bulk of a polymer semiconductor, the capacitance must be considered as a volumetric parameter and the doping process is electrochemical in nature, 6-8 resulting in very large currents flowing through the whole channel volume. As a) Electronic mail: alasdair.campbell@imperial.ac.uk a consequence, large transconductances surpassing that of silicon-based TFTs can be obtained, 9 even in OTFTs employing polymer semiconductors with modest ...

Iodine-doped Cu2 Se shows a significantly improved thermoelectric performance during phase transitions by electron and phonon critical scattering, leading to a dramatic increase in zT by a factor of 3-7 times culminating in zT values of 2.3 at 400 K.

We report a new way of developing ion gels through the self-assembly of a triblock copolymer in a room-temperature ionic liquid. Transparent ion gels were achieved by gelation of a poly(styrene-block-ethylene oxide-block-styrene) (SOS) triblock copolymer in 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) with as low as 5 wt % SOS triblock copolymer. The gelation behavior, ionic conductivity, rheological properties, and microstructure of the ion gels were investigated. The ionic conductivity of the ion gels is only modestly affected by the triblock copolymer network. Its temperature dependence nearly tracks that of the bulk ionic liquid viscosity. The ion gels are thermally stable up to at least 100 degrees C and possess significant mechanical strength. The results presented here suggest that triblock copolymer gelation is a promising way to develop highly conductive ion gels and provides many advantages in terms of variety and processing.

The development of new gate dielectric materials that offer both low-temperature processability and high capacitance is an important goal for organic electronics in order to facilitate the fabrication of low-voltage circuitry on plastic substrates. [1][2][3][4] Marks, Facchetti, and colleagues, for example, have recently demonstrated that ultra-thin (∼10 nm) crosslinked polymer blend films [5,6] and self-assembled siloxane layers [7] can be used as gate insulators in organic thin-film transistors (OTFTs), providing turn-on potentials of a few volts with gate leakage current densities < 10 -8 A cm -2 . Likewise, Berggren and colleagues have demonstrated polyelectrolyte proton conductors as solution-processable, high-capacitance gate dielectrics for low-voltage OTFT operation. [8,9] In an alternative strategy, we and others have shown that a solid state polymer electrolyte consisting of a Li salt (LiClO 4 or Li bis(trifluoromethylsulfonyl)imide (LiTFSI)) dissolved in poly(ethylene oxide) (PEO) can also serve as a high-capacitance gate insulator in OTFTs. [10][11][12][13][14][15][16][17][18][19][20][21] The specific capacitance for LiClO 4 /PEO is exceptionally large (>10 lF cm -2 ), providing both low-voltage operation and very high ON-currents for OTFTs. Low voltage, LiClO 4 /PEO gated transistors based on polythiophene, [10] poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene), [11] pentacene, [12] perylene diimides, [13] and organic single crystals [14][15][16] have been demonstrated.However, the switching speed of these devices is determined by the polarization response time of the LiClO 4 /PEO, and not by the carrier mobility in the semiconductor channel, as is usually the case. [22] The slow polarization response of LiClO 4 / PEO limits transistor switching speed to a few hertz at room temperature, which is a major disadvantage for applications.In order to decrease the polarization response time while maintaining a large specific capacitance, we have investigated ion gels (Fig. 1) as novel gate dielectric materials. Ion gels comprise a polymer network swollen with an ionic liquid. [23] In this work, we have gelled ionic liquids by self-assembly of a triblock copolymer, PS-PEO-PS (Fig. 1), where the polystyrene (PS) endblocks are insoluble in the ionic liquid. [24] The ion gels contain a modest amount of polymer (as little as 4 wt %) producing sufficient mechanical integrity without appreciable change in the ionic conductivity. The room-temperature ionic conductivity is more than 10 -3 S cm -1, much larger than in the PEO/LiClO 4 or PEO/LiTFSI systems (10 -5 S cm -1 at 25°C), which dramatically decreases the polarization response time. In this Communication, we demonstrate that high-capacitance (∼ 40 lF cm -2 ) ion gel-gated OTFTs (GEL-OTFTs) can operate at frequencies up to 1 kHz. This represents a nearly 1000-fold improvement over PEO-gated transistors and a 10-fold improvement over our initial report on ion gel-gated polymer TFTs.[25] Moreover, we have surveyed the behavior of gels made from thr...

Miscible blends of perdeuteriopoly(ethylene oxide) (d4PEO) and poly(methyl methacrylate) (PMMA) were studied using deuterium NMR over the concentration range of 0.5−30% d4PEO using 2−4 Larmor frequencies ranging from 31 to 76 MHz. Spin−lattice relaxation times and line widths were measured from 300 to 475 K. Over this range PEO is liquidlike or rubbery in terms of its dynamics even though many of the measurements are below the blend glass transition temperature. There is no indication of the DSC glass transition in terms of a jump in either the spin−lattice relaxation times or the line widths. A model suitable for a rubber solid was used to interpret the spin−lattice relaxation times in terms of segmental motion and backbone libration. Segmental correlation times for d4PEO fall in the nanosecond range with a very broad distribution of correlation times described by a KWW β of about 0.27. The segmental dynamics of d4PEO are 12 orders of magnitude faster than PMMA segmental dynamics for a 3% d4PEO blend near the blend T g. Over the temperature range studied, d4PEO segmental dynamics are nearly independent of composition for blends from 0.5% to 30% d4PEO. At the lowest concentration studied, d4PEO is in the dilute solution range; this eliminates intermolecular concentration fluctuations as an explanation of the rapid d4PEO dynamics. These observations are unusual for miscible polymer blends and cannot be described by current models.