Organic field-effect transistors (OFETs) promise for printed intelligence embedded into, and coated onto many different items that previously have been considered impossible to make electronically active. It is crucial that this technology is driven at low voltage and power. Also, we need to obtain solid understanding of the charge transport in organic semiconductors. Different materials [1] and architectures have been utilized as the probe to reveal the nature of charge transport along the transistor channel and to achieve low-voltage switching. In transistors operating according to field-effect or electrochemical principles, respectively, vacuum, air, [2] oxides, [3] high-permittivity dielectrics, [4] organic mono-layers, [5] and electrolytes [6] have successfully served as the medium to electronically separate the gate from the transistor channel, of which the latter three allow low-voltage operation. In particular electrolytes have attracted much attention lately since they generate very high electric fields at the organic transistor channel/electrolyte interface already at very low voltages, i.e., below 1 V. One issue with those devices is that electrochemical switching and field-effect modulation of the organic channel often coexist, [7] which result in transistors that are typically slow and that exhibit a great degree of hysteresis. Here, we report OFETs gated via pure water that operates entirely in the field-effect mode of operation. Our findings shed new light on low-voltage operating OFETs, their charge transport characteristics under exposure to water [8] and opens for sensor applications using water-gated OFETs as transducers in aqueous media.[9] Because of the simplicity and readiness of its production, it could also reveal a very helpful tool for rapid testing of new organic semiconductor compounds.Electrolyte (insulator)/semiconductor interfaces have attracted much attention during the last decades, in part driven by an interest to achieve high-performing sensors operating in water, to reach low-voltage operation for OFETs and to study the fundamentals of charge transport in semiconducting solids. In ion-sensitive field-effect transistors (ISFETs), the electrical potential at the electrolyte/insulator interface is translated into a modulation of the transistor output characteristics.[10] Actually, the modulation originates from that the threshold voltage (V T ) is sensitive to the ion concentration. The high electric field that is possible to establish at electrolyte/solid interfaces becomes a powerful tool for probing various features of the transport and accumulation of charges inside solids. Electrostatic field-operated transistors and switches, including for instance silicon, carbon nanotubes, [11] rubrene, [12] or manganites [13] as the active material, have been extensively studied in the past. In all those cases pure field-effect operation, without any parasitic electrochemical reactions of the bulk of the solid, is achieved simply because the materials included in the devices are known ...

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Organic field-effect transistors (OFETs) are currently being developed for low-cost, large-area, and flexible electronic applications. Many of these potential applications, e.g., in radio frequency identification (RFID) tags and addressing backplanes in displays, put requirements on the switching speed and the current throughput of the OFETs. Ideally, the switching time and the drain current (I D ) are proportional to L 2 /m and m/L, respectively, where L is the channel length and m is the charge carrier mobility. [1,2] Major efforts have been devoted to improve the charge-carrier field-effect mobility in the organic polymers and a mobility of 0.1-0.6 cm 2 V À1

Electrolyte-gated organic thin-film transistors (OTFTs) can offer a feasible platform for future flexible, large-area and low-cost electronic applications. These transistors can be divided into two groups on the basis of their operation mechanism: (i) field-effect transistors that switch fast but carry much less current than (ii) the electrochemical transistors which, on the contrary, switch slowly. An attractive approach would be to combine the benefits of the field-effect and the electrochemical transistors into one transistor that would both switch fast and carry high current densities. Here we report the development of a polyelectrolyte-gated OTFT based on conjugated polyelectrolytes, and we demonstrate that the OTFTs can be controllably operated either in the field-effect or the electrochemical regime. Moreover, we show that the extent of electrochemical doping can be restricted to a few monolayers of the conjugated polyelectrolyte film, which allows both high current densities and fast switching speeds at the same time. We propose an operation mechanism based on self-doping of the conjugated polyelectrolyte backbone by its ionic side groups.conducting polymers | organic electronics

Electronic textiles (e-textile) are an emerging field [1] that can open new possibilities in a number of different areas. The concept of embedding a large number of components in fabrics is today subject of design analysis and simulation. [2,3] Some e-textile manufacturing schemes comprise the integration of conventional off-the-shelf electronic components by attaching these directly onto clothes. However, a key step for the integration of truly mass-produced e-textiles is to completely integrate electronic production with textile production. The integration of components directly onto the textile fibers requires functional materials and methods of using these. Conducting polymers are materials that fulfill the necessary requirements for e-textiles, and have previously been used for the construction of organic field-effect transistors (OFETs) directly on fibers. [4][5][6] These fiber OFETs are constructed on single fibers in four-layered structures, including an insulating dielectric material between channel and gate. Such structures, however, suffer from a number of drawbacks, including complexity of manufacturing, due to the necessity of adding four layers on the same fiber, very high operation voltages, and poor stability during mechanical stress on the fibers. We have previously demonstrated a way to circumvent some of these problems, by presenting an electrochemical transistor (ECT) [7] based on poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) implemented directly on textile fibers. [8] These fiber ECTs present a number of advantages, such as high channel currents and ease of fabrication; a weakness is, however, the mode of operation, being restricted to only depletion mode, which complicates the design of logic circuits. Moreover, the electrochemical doping mechanism defining the principle of operation of this device, where the entire bulk of the channel has to be doped/undoped in order to switch the transistor, should put more limitations on the maximum switching speed. Another class of electrolyte-gated transistors comprises electric doublelayer capacitor-gated OFETs (EDLC-OFETs). In contrast to ECTs, it is believed that only the conductivity of the semiconductor at its interface with the electrolyte is modulated by the electric field induced by the electrolyte polarization upon gate bias, leading to higher operation speeds. These types of transistors have been demonstrated on planar substrates that offer low driving voltages ( 1 V), yielding high current densities and, recently, high switching speeds, surpassing 1 kHz in microdevices. [9][10][11] Here, a fiber-based organic electrolyte-gated thin-film transistor (TFT) based on poly(3-hexylthiophene) (P3HT) and imidazolium ionic liquids is demonstrated. The demonstrated fiber TFTs are shown to operate in both field-effect and electrochemical operation modes, thus enabling both delivery of large currents or high speeds at low voltages. The transistors are further presented in a design scheme that is compatible with textile-production m...

A polyanionic proton conductor, named poly(styrenesulfonic acid) (PSSH), is used to gate an organic field-effect transistor (OFET) based on poly(3-hexylthiophene) (P3HT). Upon applying a gate bias, large electric double layer capacitors (EDLCs) are formed quickly at the gate-PSSH and P3HT-PSSH interfaces due to proton migration in the polyelectrolyte. This type of robust transistor, called an EDLC-OFET, displays fast response (<1ms) and operates at low voltages (<1V). The results presented are relevant for low-cost printed polymer electronics.

Low-voltage organic field-effect transistors (OFETs) promise for low power consumption logic circuits. To enhance the efficiency of the logic circuits, the control of the threshold voltage of the transistors are based on is crucial. We report the systematic control of the threshold voltage of electrolyte-gated OFETs by using various gate metals. The influence of the work function of the metal is investigated in metal-electrolyte-organic semiconductor diodes and electrolyte-gated OFETs. A good correlation is found between the flat-band potential and the threshold voltage. The possibility to tune the threshold voltage over half the potential range applied and to obtain depletion-like (positive threshold voltage) and enhancement (negative threshold voltage) transistors is of great interest when integrating these transistors in logic circuits. The combination of a depletion-like and enhancement transistor leads to a clear improvement of the noise margins in depleted-load unipolar inverters.organic electronics | polyelectrolytes | thin-film transistors | gate electrode material T he possibility to process organic electronic materials from solution allows for printing electronic systems on a wide variety of large area and flexible substrates thus enabling new applications and ultralow cost electronics (1-3). The transistor is a corner stone in modern electronics. The OFETs are promising devices for applications that require medium-speed operation such as driving circuits for displays (4) and sensors (5, 6); however, to enable their integration in portable devices or electronic labels, i.e., distributed systems typically driven by printed batteries (7) or solar cells (8), the OFETs should operate at low voltage and power. A low driving voltage can be achieved by employing a gate dielectric composed of a ultrathin, cross-linked polymer (9), a self-assembled monolayer in combination with a thin metal oxide layer (10), or high-permittivity dielectrics (11); however, high-quality inorganic dielectrics or ultrathin organic dielectrics are normally difficult to combine with common printing technologies. Recently, various electrolytes have successfully been explored as the gate insulator in low-voltage operating OFETs (12-17). In this case, the formation of the gate capacitance includes polarization of electronic and ionic charges. Indeed, if we consider a p-channel OFET, applying a negative voltage to the gate attracts cations from the solution towards the electrolyte/gate interface while anions are repelled towards the electrolyte/semiconductor interface. Such ion redistribution results in the formation of electrical double layers (EDLs) at the two interfaces. These two EDLs can be assimilated to two capacitors in series in which the redistributed ions in the electrolyte are balanced by oppositely charged electronic charge carriers at the gate electrode and in the semiconductor, respectively (Fig. 1A). The ionic and electronic charges within these EDLs are separated by only a few Å resulting in a very high capacitance (typi...

Scalable circuits of organic logic and memory are realized using all-additive printing processes. A 3-bit organic complementary decoder is fabricated and used to read and write non-volatile, rewritable ferroelectric memory. The decoder-memory array is patterned by inkjet and gravure printing on flexible plastics. Simulation models for the organic transistors are developed, enabling circuit designs tolerant of the variations in printed devices. We explain the key design rules in fabrication of complex printed circuits and elucidate the performance requirements of materials and devices for reliable organic digital logic.