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We demonstrate the viability of using ultra-thin sheets of microbially grown nanocellulose to build functional medical sensors. Microbially grown nanocellulose is an interesting alternative to plastics, as it is hydrophilic, biocompatible, porous, and hydrogen bonding, thereby allowing the potential development of new application routes. Exploiting the distinguishing properties of this material enables us to develop solution-based processes to create nanocellulose printed circuit boards, allowing a variety of electronics to be mounted onto our nanocellulose. As proofs of concept, we have demonstrated applications in medical sensing such as heart rate monitoring and temperature sensing&mdash, potential applications fitting the wide-ranging paradigm of a future where the Internet of Things is dominant.

We present the first demonstration of a fully-flexible, self-powered glucose indicator system that synergizes two flexible electronic technologies: a flexible self-powering unit in the form of a biofuel cell, with a flexible electronic device - a circuit-board decal fabricated with biocompatible microbial nanocellulose. Our proof-of-concept device, comprising an enzymatic glucose fuel cell, glucose sensor and a LED indicator, does not require additional electronic equipment for detection or verification; and the entire structure collapses into a microns-thin, self-adhering, single-centimeter-square decal, weighing less than 40 mg. The flexible glucose indicator system continuously operates a light emitting diode (LED) through a capacitive charge/discharge cycle, which is directly correlated to the glucose concentration. Our indicator was shown to operate at high sensitivity within a linear glucose concentration range of 1 mM–45 mM glucose continuously, achieving a 1.8 VDC output from a flexible indicator system that deliver sufficient power to drive an LED circuit. Importantly, the results presented provide a basis upon which further development of indicator systems with biocompatible diffusing polymers to act as buffering diffusion barriers, thereby allowing them to be potentially useful for low-cost, direct-line-of-sight applications in medicine, husbandry, agriculture, and the food and beverage industries.

We report the synthesis and characterization of highly air and temperature stable, solution-processed, n-type organic semiconductors: a perylene-diimide monomer and a perylene-diimide-based pendant polymer. When integrated into a transistor structure, both materials possess pure n-type transport with mobility as high as 10−5 cm2 V−1 s−1 for the polymer. The organic semiconductors exhibit good photoconductor properties, with photocurrent to dark current ratios of up to 103 for the monomer, despite its lower FET mobility. The differences in transistor and photoconductor properties suggest different applications for each material. Both materials can be processed in air, and their transport properties have good air stability, improving with annealing even up to 200 °C in air. It is notable that such air-stable photoconductivity and transport properties have rarely been reported for n-type organic semiconductors before, as most n-type organic semiconductors are not stable in air. Hence, these materials may have potential in a wide range of applications.

Carbon nanotube (CNT)-cellulose pellicle was developed to create a conductive CNT network on 20 μm nanostructured cellulose film. The flexible and electrically conductive film was prepared by the modification of bacterial nanocellulose pellicle with multi-walled carbon nanotubes (MWCNTs). The composite film was further modified with redox enzymes including pyroquinoline quinone glucose dehydrogenase (PQQ-GDH) and bilirubin oxidase (BODx) functioning as the anodic and cathodic catalyst, respectively with glucose as the biofuel source. The enzyme functionalized MWCNT-cellulose based glucose/O 2 biofuel cell system harnessed the biochemical energy of glucose via the oxidation of glucose and reduction of molecular oxygen to generate electrical power in the microwatt range. The biofuel cell system exhibited an open circuit voltage and power density of 470 mV and 46.25 μW/cm2, respectively, with a current density of 381 μA/cm2 in the presence of 25 mM glucose. At physiological glucose concentration, the biofuel cell exhibited an open circuit voltage and power density of 418 mV and 24.975 μW/cm2 respectively, with a current density of 293.75μA/cm2. As a result, we expect that this facile strategy to prepare flexible conductive bioelectrodes for the development of glucose biofuel cell system using synthesized bacterial nanocellulose crosslinked with MWCNTs and enzyme can be readily extended to diverse applications in enzymatic biofuel cell and biosensor technology.

We will describe our ongoing work on the development of sensing electronics on microns-thin bacterial nanocellulose for human monitoring applications. The porosity and hydrophobicity of nanocellulose sheets offer advantages that typical plastics cannot provide, such wicking of analytes and absorption of inks. Our first application is the detection of electrolyte concentration in a bio-fluid sample. We have developed an ultra-thin electronic decal that can simultaneously collect transmit and interrogate the bio-fluid. Our technology effectively integrated a thin-film organic electrochemical transistor (sensing component) with the nanocellulose wicking membrane (sample handling component). The nanocellulose provided robust support and physical isolation of the electronics, and efficient bio-fluid delivery to the transistor via vertical wicking, with high detection efficiencies. For our second application, we developed a printing method to form nanocellulose printed circuit boards (PCBs), and created a simple low temperature soldering process to form circuit structures using standard surfacemount components on our nanocellulose PCBs. This has been used to create nanocellulose decals that measure human body temperature and perform pulse oximetry. For both applications, the fabrication processes are solution-based and requires only ambient processing, and therefore simple, potentially low-cost, and can be aimed for a wide range of applications.

We report an ultra-thin electronic decal that can simultaneously collect, transmit and interrogate a bio-fluid. The described technology effectively integrates a thin-film organic electrochemical transistor (sensing component) with an ultrathin microbial nanocellulose wicking membrane (sample handling component). As far as we are aware, OECTs have not been integrated in thin, permeable membrane substrates for epidermal electronics. The design of the biocompatible decal allows for the physical isolation of the electronics from the human body while enabling efficient bio-fluid delivery to the transistor via vertical wicking. High currents and ON-OFF ratios were achieved, with sensitivity as low as 1 mg·L−1.

The first observation that PBBTPD, a low bandgap, ambipolar conjugated donor-acceptor (DA) polymer based on benzobisthiadiazole (BBT), possesses an open-shell singlet ground state as well as a thermally accessible triplet state is described. Similarly, interesting electronic behavior in semiconducting organic DA oligomers based on BBT is also observed. Theoretical predictions have suggested that such behavior is due to the biradicaloid character of BBT and we provide experimental evidence indicating that these predictions are correct. Furthermore, the open shell character strengthens as the conjugation length increases, as observed in the BBT-based polymer, PBBTPD. We show that this biradicaloid structure is observed in each BBT moiety along the chain and that therefore PBBTPD is in fact a polyradicaloid. This observation will most likely aid in the development of better n-type polymeric acceptors for organic semiconductor applications. (c) 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 287-293

The search for developing a deep blue long-lasting polymer light-emitting diode (PLED) has focused attention on polyfluorene (PFO) keto defect suppression with physical and chemical modifications. This study presents the synthesis and characterization of a new donor–acceptor (DA) polymer, based on naphthalene diimide (NDI) as a strong acceptor and n-phenyl-dithieno[3,2-b:2′,3′-d]pyrrole (DTP) as a strong donor. This polymer exhibits ambipolar behavior with stronger n-type properties, 0.07 cm2 V−1 s−1, versus p-type 0.006 cm2 V−1 s−1. By blending PNDIT-alt-DTP into PFO with hole and electron trapping sites, significantly enhanced electroluminescence (EL) efficiency in a simplified polymer light-emitting diode (PLED) was achieved. Further improvement is also achieved by introducing graphene oxide (GO) into the hole injection layer of PEDOT:PSS. A pure and strong long-lasting blue-color in a wide range of bias voltages can be acquired upon introducing 5.0 wt% PNDIT-alt-DTP and 0.01 wt% GO. New blend devices have lower turn-on voltages of 3.5 V, compared to 7.0–8.0 V for pure PFO PLEDs, high current efficiency up to 3.8 cd A−1 and maximum luminance exceeding 5500 cd m−2 which are at least 20 and 60 times greater than a pure PFO/0.01GO device, respectively. The enhanced efficiency can be related to improved hole injection and electron blocking nature of the GO doped PEDOT:PSS layer as well as reducing singlet exciton quenching at the interface. Additionally, the spatial confinement effect of the ambipolar polymer efficiently enhances the thermal stability of the binary blend and facilitates charge carrier balance and more efficient radiative recombination in the devices. These values are among the highest ever reported for PFO devices doped with an ambipolar polymer working in air.

A new semiconducting polymer based on terthiophene-thienopyrrolodione alternating building blocks with a deep HOMO energy level (5.66 eV) is presented. The polymer is prepared by a direct heteroarylation polycondensation reaction, which is a low-cost and green alternative to the standard Stille coupling reaction and thus avoids any use of toxic stannyl derivatives. Integrating the polymer into bulk heterojunction solar cells with [6,6]-phenyl C71-butyric acid methyl ester ([70]PCBM) leads to a PCE of over 6% and a high open-circuit voltage of up to 0.94 V. To obtain these results a unique processing additive, 1-chloronaphthalene, is used, and a relatively low concentration of [70]PCBM is used in the blend solution.

High mobility ambipolor organic thin-film transistors based on an ultralow bandgap polymer are presented together with their morphological and optical properties. Hole and electron mobilities of this polymer are of 1.0 cm(2) V(-1) s(-1) and 0.7 cm(2) V(-1) s(-1), respectively. The inverter based on two identical ambipolar transistors exhibits a gain around 35.

We show that polybis(thienyl)thienodia-thiazolethiophene (PDDTT), a high-performance semiconducting polymer for photodetectors and field-effect transistors, has strong performance dependence on annealing temperature. An unprecedented increase of 3 orders of magnitude is observed in both transistor and photoconductive properties. XRD and AFM evidence points to increased ordering in PDDTT films with annealing. This correlation highlights the importance that order has in determining performance in PDDTT and has possible implications in the design of polymers.

Organic semiconductors based on π -delocalized conjugated polymers are under consideration for a variety of emerging optoelectronic technologies. [ 1–10 ] These materials open the possibility of solution processing and thereby manufacturing options not easily achieved with their inorganic semiconductor counterparts. However, because interchain forces arise predominantly from weak van der Waals interactions, one fi nds that not only is the molecular structure of the polymer important for determining structural, optical and electronic properties, but also the processing history. The result is that a wide performance range can be achieved for a given polymer sample depending on the choice of solvent, deposition method and thermal management history. This complexity invites research into understanding how to control supramolecular structures [ 11 ] and how charge transport can be modifi ed by the general organization of conjugated polymers in the bulk and adjacent to device interfaces. [ 12 ]

To use conducting and semiconducting polymers for electronic applications, their fundamental properties need to be understood. It is now demonstrated that the transport mechanism of poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) at high carrier densities in field-effect transmitters and electrochemically doped films match those of a one-dimensional metal. Conducting and semiconducting polymers are important materials in the development of printed, flexible, large-area electronics such as flat-panel displays and photovoltaic cells. There has been rapid progress in developing conjugated polymers with high transport mobility required for high-performance field-effect transistors (FETs), beginning1 with mobilities around 10−4 cm2 V−1 s−1 to a recent report2 of 1 cm2 V−1 s−1 for poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT). Here, the electrical properties of PBTTT are studied at high charge densities both as the semiconductor layer in FETs and in electrochemically doped films to determine the transport mechanism. We show that data obtained using a wide range of parameters (temperature, gate-induced carrier density, source–drain voltage and doping level) scale onto the universal curve predicted for transport in the Luttinger liquid description of the one-dimensional ‘metal’.

A study was conducted to investigate the effect of optically pumped lasing in a 'super yellow' film cast onto a gate dielectric and gate conducting electrode. It was observed during the study that light-emitting field-effect-transistor (LEFET) architecture with a distributed feedback (DFB) resonator structure nanoimprinted into the gain medium helped to achieve an electrically pumped plastic laser. Nanoimprint lithography was applied to obtain 1D and 2D DFB grating resonator structures in multilayer films. The study showed that the 2D DFB laser provided a lower lasing threshold compare to 1D DFB laser under same conditions. The nanoimprinted 2D DFB laser showed a lasing threshold of 32nJ/pulse and slope efficiency of 1.2%. The 1D grating provided a high degree of chain orientation for the organic semiconducting polymers in the source-drain channel.

Bipolar filed-effect transistors (BiFETs) fabricated from bulk heterojunction (BHJ) materials comprised of various ratios of the small bandgap polymer, poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT), and the soluble fullerene, [6,6]-phenyl-C71butyric acid methyl ester (PC 71 BM) are reported. We focus on the effect of the addition of small concentrations of the processing additive, 1,8-octanedithiol (ODT), on the gate-induced transport properties. Processing with the ODT additive increased the mobilities of holes (on the PCPDTBT) and electrons (on the PC 71 BM). If, however, the ODT was not completely removed from the BHJ films, the hole mobility actually decreased, implying that residual ODT functions as a hole trap.

The results of time-resolved spectroscopic studies of the structurally ordered liquid-crystalline polymer, poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene), PBTTT, and of composites of PBTTT with the soluble fullerene derivative, [6,6]-phenyl-C61 butyric acid methyl ester, PCBM are reported. These ultrafast studies focus on the photogeneration of mobile carriers in PBTTT/PCBM composites following sub-picosecond electron transfer from PBTTT to PCBM. The recombination and loss of mobile carriers at early times (approximately 200 ps following photoexcitation) were measured with different ratios of the PBTTT and PCBM components (1:1 and 1:3) by monitoring the time decay of the photoinduced absorption features associated with the charge-transferred state. The results are well-correlated with the solar-cell efficiency obtained using PBTTT/PCBM bulk heterojunction materials.

A study has reported on p-channel gate controlled light emitting diodes (LED) fabricated by spin casting an electroluminescent polymer onto high dielectric constant polyvinylidene fluoride (PVDF) with Au as the source for hole injection into the channel and Ca as the source for electrons. The study also analyzed light emission in a transistor-like configuration using a spin cast electroluminescent polymer and a bilayer of high materials (PVDF on silicon nitride) as the gate dielectric. The transistor exhibited excellent p-type electrical characteristics with a mobility of 7.4 × 10 cm Vs and current on/off ratio of 10 . The study showed that light emission was visible with brightness exceeding 310cd m at controlled quantum efficiency of 0.5%. The gate controlled bright light emission also suggests novel applications such as simplified pixels in a flat panel display and electrically driven organic lasers.

We have studied the carrier transport in poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2- b ]thiophene) field-effect transistors (FETs) at very high field-induced carrier densities (10 15 cm −2 ) using a polymer electrolyte as gate and gate dielectric. At room temperature, we find high current densities, 2 × 10 6 A/cm 2 , and high metallic conductivities, 10 4 S/cm, in the FET channel; at 4.2 K, the current density is sustained at 10 7 A/cm 2 . Thus, metallic conductivity persists to low temperatures. The carrier mobility in these devices is ≈3.5 cm 2 ·V −1 ·s −1 at 297 K, comparable with that found in fully crystalline organic devices.

A novel type of tunable organic photovoltaic (OPV) tandem device with ionic gating by in-situ ionic liquid is presented. This device is comprised of two solution-processed polymeric OPV cells connected in parallel by a dry-laminated transparent multiwall carbon nanotube (MWCNT) interlayer. The interlayer MWCNT of this 3-terminal tandem device plays a role of a common electrode with a Fermi level that can be tuned via ionic gating to turn it into a common cathode, collecting photo-generated electrons from both sub-cells. Ionic gating employs electric double layer charging of the MWCNT in order to lower the work function of the common CNT electrode and increase its n-type conductivity. This tandem device is fabricated in ambient conditions via dry-lamination of MWCNT transparent sheets The new results demonstrating the different regimes of ionic gating at low, medium, and high gating voltages Vgate are presented, showing the optimal doping of the MWCNT, then favorable doping of acceptor PCBM ([6,6]-phenyl-C...

© 2014 American Physical Society. A resurgence in the use of the donor-acceptor approach in synthesizing conjugated polymers has resulted in a family of high-mobility ambipolar systems with exceptionally narrow energy bandgaps below 1 eV. The ability to transport both electrons and holes is critical for device applications such as organic light-emitting diodes and transistors. Infrared spectroscopy offers direct access to the low-energy excitations associated with injected charge carriers. Here we use a diffraction-limited IR microscope to probe the spectroscopic signatures of electron and hole injection in the conduction channel of an organic field-effect transistor based on an ambipolar DA polymer polydiketopyrrolopyrrole-benzobisthiadiazole. We observe distinct polaronic absorptions for both electrons and holes and spatially map the carrier distribution from the source to drain electrodes for both unipolar and ambipolar biasing regimes. For ambipolar device configurations, we observe the spatial evolution of hole-induced to electron-induced polaron absorptions throughout the transport path. Our work provides a platform for combined transport and infrared studies of organic semiconductors on micron length scales relevant to functional devices.

A method of fabricating organic photovoltaic (OPV) tandems that requires no vacuum processing is presented. These devices are comprised of two solution-processed polymeric cells connected in parallel by a transparent carbon nanotubes (CNT) interlayer. This structure includes improvements in fabrication techniques for tandem OPV devices. First the need for ambient-processed cathodes is considered. The CNT anode in the tandem device is tuned via ionic gating to become a common cathode. Ionic gating employs electric double layer charging to lower the work function of the CNT electrode. Secondly, the difficulty of sequentially stacking tandem layers by solution-processing is addressed. The devices are fabricated via solution and dry-lamination in ambient conditions with parallel processing steps. The method of fabricating the individual polymeric cells, the steps needed to laminate them together with a common CNT cathode, and then provide some representative results are described. These results demonstrate ionic gating of the CNT electrode to create a common cathode and addition of current and efficiency as a result of the lamination procedure.

Praseodymium doped CaFe2As2 (122 structure) and CaFeAs2 (112 structure) are characterized by modulated Low Magnetic Field Microwave Absorption (LFMA) spectroscopy. In both (Pr,Ca)122 and (Pr,Ca)112 structures, a strong hysteretic LFMA is found, with a TcH of ∼30 K and ∼26 K, respectively. However, in (Pr,Ca)122, measurements also show an unusual Narrow Peak (NP) LFMA signal appearing at higher temperatures, above the lower TcH superconducting state until a TcNP of 49 K. We associate this NP LFMA with interfacial superconductivity, which has been found previously by highly anisotropic magnetization measurements. Furthermore, the absence of NP in (Pr,Ca)112 correlates with the absence of an interfacial phase. These results give useful information about the microwave signature of interfacial superconductivity present in the (Pr,Ca)122 system, and may form a roadmap towards a stabilized high temperature superconducting phase in pnictides.

An "XOR" gate built using label-free, dual-analyte electrochemical sensors and the activation of this logic gate via changing concentrations of cocaine and the relevant cDNA as inputs are described.

Substituted N-alkyldinaphthocarbazoles were synthesized using a key double Diels-Alder reaction. The angular nature of the dinaphthocarbazole system allows for increased stability of the conjugated system relative to linear analogues. The N-alkyldinaphthocarbazoles were characterized by UV-vis absorption and fluorescence spectroscopy as well as cyclic voltammetry. X-ray structure analysis based on synchrotron X-ray powder diffraction revealed that the N-dodecyl-substituted compound was oriented in an intimate herringbone packing motif, which allowed for p-type mobilities of 0.055 cm(2) V(-1) s(-1) from solution-processed organic field-effect transistors.

We have fabricated electric double-layer field-effect devices to electrostatically dope our active materials, either $x$=0.015 Ga$_{1-x}$Mn$_x$As or $x$=3.2$\times10^{-4}$ Ga$_{1-x}$Be$_x$As. The devices are tailored for interrogation of electric field induced changes to the frequency dependent conductivity in the accumulation or depletions layers of the active material via infrared (IR) spectroscopy. The spectra of the (Ga,Be)As-based device reveal electric field induced changes to the IR conductivity consistent with an enhancement or reduction of the Drude response in the accumulation and depletion polarities, respectively. The spectroscopic features of this device are all indicative of metallic conduction within the GaAs host valence band (VB). For the (Ga,Mn)As-based device, the spectra show enhancement of the far-IR itinerant carrier response and broad mid-IR resonance upon hole accumulation, with a decrease of these features in the depletion polarity. These later spectral features demonstrate that conduction in ferromagnetic (FM) Ga$_{1-x}$Mn$_x$As is distinct from genuine metallic behavior due to extended states in the host VB. Furthermore, these data support the notion that a Mn-induced impurity band plays a vital role in the electron dynamics of FM Ga$_{1-x}$Mn$_x$As. We add, a sum-rule analysis of the spectra of our devices suggests that the Mn or Be doping does not lead to a substantial renormalization of the GaAs host VB.

High-mobility organic thin film transistors based on a benzobisthiadiazole-containing polymer are presented together with their morphological and optical properties. A very tight packing pattern of "edge-on" orientated polymer chains is observed in their thin films after annealing, and the hole mobility of this polymer is up to 2.5 cm(2) V(-1) s(-1) .

The split-gate light emitting field effect transistors (SG-LEFETs) demonstrate a new strategy for ambipolar LEFETs to achieve high brightness and efficiency simultaneously. The SG architecture forces largest quantity of opposite charges on Gate 1 and Gate 2 area to meet in the center of the channel. By actively and independently controlling current injection from separated gate electrodes within transporting channel, high brightness can be obtained in the largest injection current regime with highest efficiency.

A family of four new DA polymers, in which the acceptor moiety benzobisthiadiazole was paired with four different donor moieties, has been synthesized. Surpri-singly, all members of the family exhibit balanced ambipolar behavior, despite polymer to polymer mobilities varying from 10(-4) cm(2) V(-1) s(-1) to 10(-1) cm(2) V(-1) s(-1). Applications in single component CMOS integrated circuits are envisioned.

We report on infrared (IR) absorption and dc electrical measurements of thin films of poly(3-hexylthiophene) (P3HT) that have been modified by a fluoroalkyl trichlorosilane (FTS). Spectra for FTS-treated films were compared to data for electrostatically-doped P3HT in an organic field-effect transistor (OFET). The appearance of a prominent polaron band in mid-IR absorption data for FTS-treated P3HT supports the assertion of hole doping via a charge-transfer process between FTS molecules and P3HT. In highly-doped films with a significantly enhanced polaron band, we find a monotonic Drude-like absorption in the far-IR, signifying delocalized states. Utilizing a simple capacitor model of an OFET, we extracted a carrier density for FTS-treated P3HT from the spectroscopic data. With carrier densities reaching 10$^{14}$ holes/cm$^2$, our results demonstrate that FTS doping provides a unique way to study the metal-insulator transition in polythiophenes.

The optoelectronic gate light-emitting field-effect transistor (OEG LEFET) containing alternate SiO2 and SiNx dielectric stacks allows enhanced light emission for a designed spectrum range and provides reliable strength for a wide operating voltage. The device can improve the emission efficiency by 4.5 times in comparison to a reference LEFET with a SiNx gate dielectric and can reach a brightness as high as 4500 cd/m2.

A split-gate field effect transistor containing four electrodes, source, drain, two gates allows enhanced transport for specific carrier species and separate control of carrier polarity over two gate regimes. The device can be operated as a transistor or a diode by controlling gate biases.

We have demonstrated a novel sensing strategy employing single-stranded probe DNA, unmodified gold nanoparticles, and a positively charged, water-soluble conjugated polyelectrolyte to detect a broad range of targets including nucleic acid (DNA) sequences, proteins, small molecules, and inorganic ions. This nearly “universal” biosensor approach is based on the observation that, while the conjugated polyelectrolyte specifically inhibits the ability of single-stranded DNA to prevent the aggregation of gold-nanoparticles, no such inhibition is observed with double-stranded or otherwise “folded” DNA structures. Colorimetric assays employing this mechanism for the detection of hybridization are sensitive and convenient—picomolar concentrations of target DNA are readily detected with the naked eye, and the sensor works even when challenged with complex sample matrices such as blood serum. Likewise, by employing the binding-induced folding or association of aptamers we have generalized the approach to the specific and convenient detection of proteins, small molecules, and inorganic ions. Finally, this new biosensor approach is quite straightforward and can be completed in minutes without significant equipment or training overhead.

Conducting and semiconducting polymers are important materials in the development of printed, flexible, large area electronics such as flat panel displays and photovoltaic cells. There has been rapid progress in developing conjugated polymers with high transport mobility required for high performance field effect transistors (FETs), beginning with mobilities around 10-5cm2/Vs to a recent report of 1cm2/Vs for poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno [3,2-b]thiophene) (PBTTT). In this work, the electrical properties of PBTTT are studied at high charge densities both as the semiconductor layer in FETs and in electrochemically doped films to determine the transport mechanism. We show that data obtained using a wide range of parameters (temperature, gate-induced carrier density, source-drain voltage and doping level) scale onto the universal curve predicted for transport in the Luttinger Liquid description of the onedimensional "metal", where fermions along the 1D chain collectively behave as bosons, and where charge and spin are decoupled.

Two criteria for processing additives introduced to control the morphology of bulk heterojunction (BHJ) materials for use in solar cells have been identified: (i) selective (differential) solubility of the fullerene component and (ii) higher boiling point than the host solvent. Using these criteria, we have investigated the class of 1,8-di(R)octanes with various functional groups (R) as processing additives for BHJ solar cells. Control of the BHJ morphology by selective solubility of the fullerene component is demonstrated using these high boiling point processing additives. The best results are obtained with R = Iodine (I). Using 1,8-diiodooctane as the processing additive, the efficiency of the BHJ solar cells was improved from 3.4% (for the reference device) to 5.1%.

By comparing the changes in pi-pi* absorption with the transconductance in PEO-LiClO4 electrolyte-gated FETs, we have demonstrated that the high channel currents obtained at low gate voltages result from reversible electrochemical doping of the semiconducting polymer film. At low temperatures, the conductivity of the electrochemically doped poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene), PBTTT-C14, is nonlinear with a crossover from dsigma(T)/dT0 to dsigma(T)/dT approximately 0 as a function of the source-drain voltage. High current densities, up to 10(6) A/cm2 at 4.2 K, can be sustained in the electrochemically doped PBTTT-C14 films.

Polymer field-effect transistors with a field-effect mobility of μ ≈0.3 cm 2 /V . s have been demonstrated using regioregular poly(3-hexylthiophene) (rr-P3HT). Devices were fabricated by dip-coating the semiconducting polymer followed by annealing at 150°C for 10 minutes. The heat annealed devices exhibit an increased field-effect mobility compared with the as-prepared devices. Morphology studies and analysis of the channel resistance demonstrate that the annealing process increases the crystallinity of rr-P3HT and improves the contact between the electrodes and the P3HT films, thereby increasing the field effect mobility of the films. Based on the results obtained from unipolar FETs using rr- P3HT, we have also applied postproduction heat treatment to ambipolar polymer FETs fabricated with rr-P3HT and C 61 - butyric acid methyl ester (PCBM). Devices were fabricated using aluminum (Al) source and drain electrodes to achieve an equivalent injection for the both holes and electrons. As the case of P3HT unipolar FETs, the thermal annealing method also improves the film morphology, crystallinity, and the contact properties between Al and active layer, thereby resulting in excellent ambipolar characteristics with the hole mobility of 1.7×10 -3 cm 2 /V . s and the electron mobility of 2.0×10 -3 cm 2 /V . s.

We demonstrate an organic photovoltaic (OPV) device with an electrochemically gated carbon nanotube (CNT) charge collector. Bias voltages applied to the gate electrode reconfigure the common CNT electrode from an anode into a cathode which effectively collects photogenerated electrons, dramatically increasing all solar cell parameters to achieve a power conversion efficiency of ∼3%. This device requires very little current to initially charge and the leakage current is negligible compared to the photocurrent. This device can also be viewed as a hybrid tandem OPV-supercapacitor with a common CNT electrode. Other regimes of operation are briefly discussed.

Recent progress in the development of conjugated semiconducting polymers for thin film transistor applications has yielded materials with mobilities consistently exceeding 0.1 cm2 V−1 s−1. Even more significant are recent reports of polymers with TFT mobilities surpassing 1 cm2 V−1 s−1. With performance comparable to those of amorphous silicon TFTs, and with improved material stability, one can realistically envision promising future applications of these polymers. In reviewing the development of conjugated semiconducting polymers, two particularly interesting and significant observations are made. First, most of these high-performance materials are donor–acceptor polymers; and second, high mobilities of above 1 cm2 V−1 s−1 generally involve donor–acceptor polymers with strongly electron accepting moieties. The present perspective covers these latter polymers. We will cover the features that are common among these high-performance polymers and discuss unresolved issues that may determine their performance.

We developed a new high performance amorphous donor–acceptor conjugated copolymer consisting of a dithienylcylclopentadienone subunit as an electron acceptor and carbazole derivative as an electron donor. X-Ray diffraction analysis shows no scattering patterns, indicating that a disordered amorphous solid is formed. Atomic force microscopy (AFM) images show an amorphous surface mophology regardless of the annealing temperature. A high on/off current ratio of approximately 106 and high field effect mobility of 2.2 × 10−2 cm2 V−1 s−1 were obtained with stable output characteristics. The high performance of the amorphous copolymer is ascribed to the relatively low activation energy and low characteristic temperature obtained from a low temperature transport analysis, reflecting that localization of the charge carrier is not substantial in the film.

Films of Cytop™, a perfluorinated polymer, are spin cast as a single barrier layer for evaluation of barrier properties on organic light-emitting devices and on Ca thin films. Cytop™ is water repellant, resulting in encapsulated organic light-emitting field effect transistors and organic light-emitting diodes (OLEDs), which remain active even after immersion into water or exposure to water droplets on the Cytop™ surface. OLEDs encapsulated with Cytop™ exhibit up to five times longer continuous operation under identical environmental and driving conditions compared with devices that are not encapsulated with Cytop™.

Solution processed light emitting field-effect transistors (LEFETs) with peak brightness exceeding 2500cd∕m2 and external quantum efficiency of 0.15% are demonstrated. The devices utilized a bilayer film comprising a hole transporting polymer, poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b] thiophene) and a light emitting polymer, Super Yellow, a polyphenylenevinylene derivative. The LEFETs were fabricated in the bottom gate architecture with top-contact Ca∕Ag as source/drain electrodes. Light emission was controlled by the gate voltage which controls the hole current. These results indicate that high brightness LEFETs can be made by using the bilayer film (hole transporting layer and a light emitting polymer).

Field-effect transistors comprising a layer of regioregular poly(3-hexylthiophene) (rr-P3HT) separated from a parallel layer of the soluble fullerene,[6,6]-phenyl C61-butyric acid methyl ester (PCBM) by a layer of titanium suboxide (TiOx), are fabricated by solution processing. Because the TiOx is an electron transporting material and a hole blocking material, this multilayer architecture operates either in the p-channel mode with holes in the rr-P3HT layer or in the n-channel mode with electrons in the PCBM layer.

Light emitting field-effect transistors (LEFETs) were fabricated with a low work function metal (calcium) and a high work function metal (gold) as the source and drain electrodes. The gold electrode serves as the source for holes into the π band and the drain for electrons from the π* band; the calcium electrode serves as the source for electrons into the π* band and the drain for holes from the π band. For 65V

An organic multifunctional device, which can function as an ambipolar field-effect transistor (FET) and a photovoltaic (PV) cell, has been demonstrated using a phase separated mixture of poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester. The gold (Au) electrode used for hole injection in the FET mode (source) acts as the anode in PV cell mode, and the aluminum (Al) electrode for electron injection in the FET mode (drain) acts as the cathode in PV cell mode. The device exhibits clear PV phenomena under illumination at zero gate bias with a power conversion efficiency of 0.6% as well as the properties of an ambipolar FET when the gate bias is applied.

A thermally cross-linkable perfluorocyclobutane (PFCB) polymer was synthesized and examined for use as the gate dielectric in organic thin film transistors (OTFTs). The PFCB polymer showed good solvent and process resistance during the photolithographic patterning of the electrodes. Bottom contact OTFTs were fabricated with poly(3-hexylthiophene)-2,5-diyl (P3HT) as the semiconductor, either spin cast or dip coated, on the PFCB gate dielectric. OTFTs fabricated with dip-coated P3HT showed a field effect mobility of 1.8×10−3cm2∕Vs and a high on/off current ratio of 8.3×106 in the saturation regime, with a source-drain voltage of VD=−50V.