The fabrication of electronic devices based on organic materials, known as 'printed electronics', is an emerging technology due to its unprecedented advantages involving fl exibility, light weight, and portability, which will ultimately lead to future ubiquitous applications. [ 1 ] The solution processability of semiconducting and metallic polymers enables the cost-effective fabrication of optoelectronic devices via high-throughput printing techniques. [ 2 ] These techniques require high-performance fl exible and transparent electrodes (FTEs) fabricated on plastic substrates, but currently, they depend on indium tin oxide (ITO) coated on plastic substrates. However, its intrinsic mechanical brittleness and inferior physical properties arising from lowtemperature ( T ) processing below the melting T of the plastic substrates (i.e., typically below 150 °C) have increased the demand for alternative FTE materials. [ 3 ] Conducting polymers (CPs) have been considered a promising candidate for FTEs due to their mechanical fl exibility and solution processability. The high transparency of CPs originates from the charge carrier density ( n ) of approximately 10 21 cm −3 because both the refl ectance and absorption are confi ned in the IR region below the plasma frequency ( ω P , ω P 2 = 4 π e 2 n / m * where m * is the effective mass of the charge carrier) at approximately hω P ≈ 1 eV. [ 2 ] A complex of poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(4-styrenesulfonate) (PSS), in which PSS acts as both a counter-ion and a soluble template for PEDOT, is a successful CP due to its high electrical conductivity ( σ dc ) and excellent transparency in the visible range. [ 4 ] The conducting fi lms, which were coated from PEDOT:PSS solution in an aqueous dispersion, consist of hydrophobic and conducting PEDOT-rich grains encapsulated by hydrophilic and insulating PSS-rich shells. [ 5 ] These morphological features involve an excess amount of PSS as well as low chain alignment, resulting in a low σ dc of approximately 1 S cm −1 . Over the past decade, pre-and/or post-treatment with various organic solvents, surfactants, salts, and acids have been found to enhance the σ dc of PEDOT:PSS by two to three orders of magnitude. [6][7][8] Recently, the high σ dc (≈3065 S cm −1 ) was achieved using a treatment of dropping a 1.0 M H 2 SO 4 solution onto the PEDOT:PSS fi lms. [ 8 ] Although numerous studies suggested that the σ dc enhancement could be attributed to morphological changes in the PEDOT:PSS complex, such as grain growth, polymer chain expansion, and phase separation, a clear understanding of the mechanism of the σ dc enhancement is still required for both the basic material studies on CPs and developing high-performance FTEs. [6][7][8] Herein, we report the solution-processed crystalline formation in PEDOT:PSS via H 2 SO 4 post-treatment. By rigorously controlling the post-treatment conditions (i.e., the H 2 SO 4 concentration, treatment T , and processing details), we obtained insight into how the H 2 SO 4 solution proce...

We investigated the charge dynamics of the conductivity enhancement from 2 to 1000 S/cm in poly(3, 4-ethylenedioxythiophene):poly(styrenesulfonate) as induced by structural changes through the addition of a polar solvent and the following solvent bath treatment. Our results indicate that the addition of a polar solvent selectively enhanced the π-π coupling of the polymer chains, resulting in the reduction of disorder and tremendously increasing the charge carrier mobility, which yielded an insulator-to-metal transition. In contrast, the following solvent bath treatment selectively enhanced the intergrain coupling, which did not affect the disorder or the mobility but increased the charge carrier density. Therefore, we demonstrate that the conduction-character defining disorder in this conducting polymer system is determined by the extent of interchain coupling.

Graphene is a promising next-generation conducting material with the potential to replace traditional electrode materials such as indium tin oxide in electrical and optical devices. It combines several advantageous characteristics including low sheet resistance, high optical transparency and excellent mechanical properties. Recent research has coincided with increased interest in the application of graphene as an electrode material in transistors, light-emitting diodes, solar cells and flexible devices. However, for more practical applications, the performance of devices should be further improved by the engineering of graphene films, such as through their synthesis, transfer and doping. This article reviews several applications of graphene films as electrodes in electrical and optical devices and discusses the essential requirements for applications of graphene films as electrodes.

This work demonstrates a large-scale batch fabrication of GaN light-emitting diodes (LEDs) with patterned multi-layer graphene (MLG) as transparent conducting electrodes. MLG films were synthesized using a chemical vapor deposition (CVD) technique on nickel films and showed typical CVD-synthesized MLG film properties, possessing a sheet resistance of [Formula: see text] with a transparency of more than 85% in the 400-800 nm wavelength range. The MLG was applied as the transparent conducting electrodes of GaN-based blue LEDs, and the light output performance was compared to that of conventional GaN LEDs with indium tin oxide electrodes. Our results present a potential development toward future practical application of graphene electrodes in optoelectronic devices.

A highly flexible and transparent transistor is developed based on an exfoliated MoS2 channel and CVD-grown graphene source/drain electrodes. Introducing the 2D nanomaterials provides a high mechanical flexibility, optical transmittance (∼74%), and current on/off ratio (>10(4)) with an average field effect mobility of ∼4.7 cm(2) V(-1) s(-1), all of which cannot be achieved by other transistors consisting of a MoS2 active channel/metal electrodes or graphene channel/graphene electrodes. In particular, a low Schottky barrier (∼22 meV) forms at the MoS2 /graphene interface, which is comparable to the MoS2 /metal interface. The high stability in electronic performance of the devices upon bending up to ±2.2 mm in compressive and tensile modes, and the ability to recover electrical properties after degradation upon annealing, reveal the efficacy of using 2D materials for creating highly flexible and transparent devices.

Organic memory: Our three‐dimensionally (3D) stacked 8 × 8 cross‐bar array organic resistive memory devices showed non‐volatile memory switching behavior, in which individual memory cells in the different layers can be independently controlled and monitored. The 3D stackable organic memory devices will enable achieving highly integrable organic memory devices and other organic‐based electronics with much increased cell density.

Organic nonvolatile memory devices fabricated on flexible substrates showed rewritable and nearly consistent switching characteristics, regardless of the bending circumstances. This stable memory performance with bending stress is a promising property for the practical memory devices in future flexible electronics.

Pentacene organic field‐effect transistors with multilayer graphene electrodes exhibit a lower contact resistance and lower charge‐injection barrier height than those with conventional Au electrodes. This enhancement in performance is related to the favorable dipole layer formation at the graphene/pentacene interface.