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The relationship between hole density and conductivity in electrochemically gated polythiophene films is examined. The films are integrated into electrolyte‐gated transistors (EGTs), so that hole accumulations can be electrochemically modulated up to ≈0.4 holes per thiophene ring (hpr). Polythiophenes include poly(3‐alkylthiophenes) (P3ATs) with four different side chain lengths – butyl (P3BT), hexyl (P3HT), octyl (P3OT), or decyl (P3DT) – and poly[2,5‐bis(3‐dodecylthiophen‐2‐yl)thieno[3,2‐b]thiophene] (PBTTT) and poly(3,3′′′‐didodecyl[2,2′:5′,2′′:5′′,2′′′‐quaterthiophene]‐5,5′′′‐diyl) (PQT). Analysis of the drain current – gate voltage (ID–VG) and gate current – gate voltage (IG–VG) characteristics of the EGTs reveals that all six polythiophene semiconductors exhibited reversible conductivity peaks at 0.12 – 0.15 hpr. Conductivity is suppressed beyond ≈0.4 hpr.The maximum carrier mobilities of the P3AT semiconductors increase, and hysteresis of the conductivity peaks decreases, with increasing alkyl side‐chain length. PBTTT and PQT with reduced side chain densities exhibit the largest hysteresis but have higher hole mobilities. The results suggest that at ≈0.4 hpr, a polaronic sub‐band is filled in all cases. Filling of the sub‐band correlates with a collapse in the hole mobility. The side‐chain dependence of the peak conductivity and hysteresis further suggests that Coulombic ion‐carrier interactions are important in these systems. Tailoring ion‐carrier correlations is likely important for further improvements in transport properties of electrochemically doped polythiophenes. [ABSTRACT FROM AUTHOR]

Recently, copper iodide (CuI) has attracted significant attention as a promising inorganic p-type semiconductor for thin-film devices, including solar cells, sensors, and thin-film transistors owing to its high carrier density, high hole mobility, and low-temperature solution processability. However, electronic devices based on CuI tend to suffer from poor operational stability and device performance, because the volatile and unstable iodine can sublime or disintegrate during thermal annealing and device operation, leading to degradation of device performance. In this study, we demonstrate a facile route to enhance the operational performance of metal halide-based p-channel transistors by anion doping. Nonvolatile bromine (Br) ions were introduced to the CuI semiconductor to suppress iodine sublimation or degradation, and Br-doped CuI composite semiconductors were solution-processed with thermal annealing at a low temperature (∼100 °C). By using Br-doped CuI semiconductors, electrolyte-gated thin-film transistors (EGTs) operating at low voltages (<1 V) were successfully fabricated and the EGTs using the 20 mol% Br-doped CuI semiconductor exhibited a high average carrier mobility of 6.3 cm2 V−1 s−1. More importantly, owing to the nonvolatile Br ions, the operational stability of the EGTs with Br-doped CuI was significantly improved compared to the EGT that utilized an undoped pristine CuI semiconductor. [ABSTRACT FROM AUTHOR]

Interest in wearable and stretchable on‐skin motion sensors has grown rapidly in recent years. To expand their applicability, the sensing element must accurately detect external stimuli; however, weak adhesiveness of the sensor to a target object has been a major challenge in developing such practical and versatile devices. In this study, freestanding, stretchable, and self‐adhesive ionogel conductors are demonstrated which are composed of an associating polymer network and ionic liquid that enable conformal contact between the sensor and skin even during dynamic movement. The network of ionogel is formed by noncovalent association of two diblock copolymers, where phase‐separated micellar clusters are interconnected via hydrogen bonds between corona blocks. The resulting ionogels exhibit superior adhesive characteristics, including a very high lift‐off force of 93.3 N m−1, as well as excellent elasticity (strain at break ≈720%), toughness (≈2479 kJ m−3), thermal stability (≈150 °C), and high ionic conductivity (≈17.8 mS cm−1 at 150 °C). These adhesive ionogels are successfully applied to stretchable on‐skin strain sensors as sensing elements. The resulting devices accurately monitor the movement of body parts such as the wrist, finger, ankle, and neck while maintaining intimate contact with the skin, which was not previously possible with conventional non‐adhesive ionogels. [ABSTRACT FROM AUTHOR]

Stretchability and sensitivity are essential properties of wearable electronics for effective motion monitoring. In general, increasing the sensitivity of strain sensors based on ionic conductors trades off elasticity, which results in low sensitivity of the strain sensors at large mechanical deformations. To address this, ion‐permeable conducting polymer electrodes with low contact resistance are utilized in ionic gel‐based strain sensors. Using a rectangular‐shaped ionic gel and ion‐permeable electrodes significantly increase the gauge factor of the strain sensor, similar to the theoretical value at a given strain. To further increase the sensitivity of the strain sensor, the ionic gel is patterned with zigzagged tracks that gap apart as the gel stretches, and the gaps close as the gel contracts, leading to a large variation in the relative resistance upon stretching. By combining the zigzagged ionic gel and the ion‐permeable electrodes, highly sensitive stretchable sensors are realized with a record‐high gauge factor of 173, compared to existing ionic conductor‐based stretchable strain sensors. The zigzag‐patterned ionic sensor can successfully monitor various motions when attached to the human body. These results are expected to afford promising strategies for developing highly sensitive, stretchable sensing systems for E‐skin sensors and soft robotics. [ABSTRACT FROM AUTHOR]

Electrochemiluminescence (ECL) is a self‐emission of light from electrochemically excited luminophores via a series of redox reactions. Over the past decade, light‐emitting devices based on gel‐phase ECL active materials, i.e., gel electrolyte composites (referred to as ECL gels) containing an ECL luminophore, electrolyte, and network matrix, have attracted considerable attention as a complementary device platform to conventional electroluminescent devices for low‐cost printable displays and solid‐state light sources. Although the ECL phenomenon is extensively exploited in analytical diagnostics and sensing, the development of printable and fast‐response gel‐type luminescent materials may further expand the potential application of ECL in solid‐state flexible, bendable, and stretchable light‐emitting devices. This review summarizes the operation mechanisms of ECL‐based light‐emitting devices, ECL emitters and electrolytes, engineering strategies for obtaining printable high‐strength/high‐conductivity ECL gels, and emerging applications of gel‐type ECL devices. [ABSTRACT FROM AUTHOR]

Ionic liquids (ILs) or solidified ionic liquids, known as ionogels, have been actively employed in supercapacitors (SCs) owing to their superior electrochemical stabilities to aqueous and organic electrolytes. However, initial efforts of using ILs and ionogels in SCs were not successful because bulky and sluggish ions cannot effectively access tiny pores of conventional microporous carbons. To address this, a strategy is developed to optimize the electrochemically active surfaces of carbonaceous electrodes and thus to improve the energy storage performance by incorporating 3D ordered/interconnected large mesoporous carbons with ionogel electrolytes. Precisely designed large mesopores interconnected via windows promote mass transport of the electrolyte ions within the solid ionogel electrolytes and effectively utilize the surface of the carbon electrodes for capacitive energy storage, giving rise to record‐high energy storage performance that surpasses the upper bound of the Ragone plots of the current state‐of‐the‐art SCs. In addition, all‐solid‐state SCs with outstanding bending/folding durability are successfully demonstrated. Overall, these results provide critical insight into surface utilization of carbon electrodes as well as capacitive energy storage, when viscous and bulky ILs or ionogels are used as electrolytes. [ABSTRACT FROM AUTHOR]

Single-walled carbon nanotube (SWCNT)-based hybrid gel electrodes were fabricated for fully printed stretchable thin-film transistors and inverters operating at very small voltages (below 1 V). Printable and stretchable electrodes were fabricated by supplementing electrically conductive SWCNTs in rubbery polymer electrolytes, known as ionic gels. To fabricate stretchable electronic circuits, SWCNT-based stretchable source and drain electrodes as well as semiconductors, gate dielectrics, gate electrodes (either conducting polymer or SWCNT-based hybrid electrode) and load resistors were directly deposited by spray printing at low temperatures (≤130 °C). Fully printed electrolyte-gated transistors (EGTs) based on SWCNT hybrid electrodes turned on and off at low operation voltages below 1 V and the devices showed low hysteresis with reasonably high on/off current ratios on polymer and paper substrates. In addition, stretchable side-gated coplanar transistors were successfully demonstrated on a rubber substrate, which exhibited reliable electrical characteristics even at a strain of 100%. An array of resistor-loaded stretchable inverters was also fabricated by spray-printing EGTs and CNT-based resistors. The resulting inverters exhibited appropriate voltage-inverting characteristics at different tensile strains and the shift in inversion voltage was in a very small Vin range of 0.1 V. These results demonstrate that the hybrid gel-type electrodes are promising for the fabrication of low-voltage stretchable all-printed transistors and electronic circuits. [ABSTRACT FROM AUTHOR]

Ionic liquid-based solid polymer electrolytes, or ion gels, have attracted great research attention recently as nonvolatile electrolytes for thin film electronic/electrochemical devices due to their outstanding electrochemical properties, such as thermal/electrochemical stability, ionic conductivity, and specific capacitance. Although the polymer host provides solid-state mechanical integrity to the liquid electrolytes, it simultaneously causes sluggish ion transport and ion polarization, which leads to slow response of the ion gel-based devices to an applied bias. To address this issue and enhance the ion motion in the ion gels, we blended the aprotic solvent propylene carbonate (PC) with the ion gels and investigated the effect of the blend composition on the electrical, thermal, and mechanical properties of the solid electrolytes. Both the ionic conductivity and specific capacitance of the blended ion gels were significantly increased compared to the neat ion gel, exhibiting maximum values of ∼6 mS cm−1 and ∼15 μF cm−2, respectively, at a PC mole fraction of 81%. When these mixed ion gels were applied in transistor gating experiments, the mixed ion gel-gated devices showed superior device performance to the neat ion gel without added PC, namely, larger channel current and smaller subthreshold swing. These results demonstrate that the solvent-blending strategy provides an effective pathway to improve ion transport and also the operational performance of ion gel-based thin-film devices. [ABSTRACT FROM AUTHOR]

Ionogels: Optimizing Electrochemically Active Surfaces of Carbonaceous Electrodes for Ionogel Based Supercapacitors (Adv. Funct. Keywords: electrochemically active surfaces; facilitated ion transport; flexible supercapacitors; ionogels; large mesoporous carbons EN electrochemically active surfaces facilitated ion transport flexible supercapacitors ionogels large mesoporous carbons 1 1 1 07/25/20 20200723 NES 200723 In article number 2002053, Keun Hyung Lee, Won Cheol Yoo, and co-workers present a facile strategy to effectively utilize the surface of carbonaceous electrodes using 3D ordered/interconnected large mesoporous carbons and solidified ionic liquid electrolytes, known as ionogels. Electrochemically active surfaces, facilitated ion transport, flexible supercapacitors, ionogels, large mesoporous carbons. [Extracted from the article]

Semiconducting copper(I) thiocyanate (CuSCN) is actively studied for electronic and optoelectronic applications. Although various kinds of CuSCN‐based transistors are reported, these devices suffer from low charge carrier mobility of about 0.01–0.1 cm2 V−1 s−1. Here, ion gel electrolyte consisting of network polymer and ionic liquid is used as a high capacitance gate insulator to achieve high performance CuSCN‐based electrolyte‐gated transistors (CuSCN‐EGTs) with low operation voltage below 1 V. 30 nm thick CuSCN semiconductor film can be formed by a simple solution process with a low processing temperature (≈100 °C) that is directly applicable to flexible plastic substrates. By doping copper iodide to the CuSCN semiconductor, device performance including drain current and charge carrier mobility of the CuSCN EGT can be improved significantly. The measured charge carrier mobility of ≈0.3 cm2 V−1 s−1 is the highest among the reported CuSCN transistors using various gate insulators. These CuSCN‐EGTs also display good operation stability under continuous quasistatic external gate voltage sweeps. Such superior electrical performance and versatile processability of ion gel–gated CuSCN transistors make them suitable for use in complimentary circuits and large‐area flexible electronics. [ABSTRACT FROM AUTHOR]

Organic/inorganic hybrid complementary inverters operating at low voltages (1 V or less) were fabricated by transfer-stamping organic p-type poly(3-hexylthiophene) (P3HT) and inorganic n-type zinc oxide (ZnO) electrolyte-gated transistors (EGTs). A semicrystalline homopolymer-based gel electrolyte, or an ionogel, was also transfer-stamped on the semiconductors for use as a high-capacitance gate insulator. For the ionogel stamping, the thermoreversible crystallization of phase-separated homopolymer crystals, which act as network cross-links, was employed to improve the contact between the gel and the semiconductor channel. The homopolymer ionogel-gated P3HT transistor exhibited a high hole mobility of 2.81 cm 2 /(V s), and the ionogel-gated n-type ZnO transistors also showed a high electron mobility of 2.06 cm 2 /(V s). The transfer-stamped hybrid complementary inverter based on the P3HT and ZnO EGTs showed a low-voltage operation with appropriate inversion characteristics including a high voltage gain of ∼18. These results demonstrate that the transfer-stamping strategy provides a facile and reliable processing route for fabricating electrolyte-gated transistors and logic circuits.