Aerosol Jet Printed p- and n‑type Electrolyte-Gated Transistors with a Variety of Electrode Materials: Exploring Practical Routes to Printed Electronics

Printing electrically functional liquid inks is a promising approach for achieving low-cost, large-area, additive manufacturing of flexible electronic circuits. To print thin-film transistors, a basic building block of thin-film electronics, it is important to have several options for printable electrode materials that exhibit high conductivity, high stability, and low-cost. Here we report completely aerosol jet printed (AJP) p- and n-type electrolyte-gated transistors (EGTs) using a variety of different electrode materials including highly conductive metal nanoparticles (Ag), conducting polymers (polystyrenesulfonate doped poly­(3,4-ethylendedioxythiophene, PEDOT:PSS), transparent conducting oxides (indium tin oxide), and carbon-based materials (reduced graphene oxide). Using these source-drain electrode materials and a PEDOT:PSS/ion gel gate stack, we demonstrated all-printed p- and n-type EGTs in combination with poly­(3-hexythiophene) and ZnO semiconductors. All transistor components (including electrodes, semiconductors, and gate insulators) were printed by AJP. Both kinds of devices showed typical p- and n-type transistor characteristics, and exhibited both low-threshold voltages (<2 V) and high hole and electron mobilities. Our assessment suggests Ag electrodes may be the best option in terms of overall performance for both types of EGTs

Performance and Stability of Aerosol-Jet-Printed Electrolyte-Gated Transistors Based on Poly(3-hexylthiophene)

We report performance optimization and stability analysis of aerosol-jet-printed electrolyte-gated transistors (EGTs) based on the polymer semiconductor poly­(3-hexylthiophene) (P3HT). EGTs were optimized with respect to printed P3HT thickness and the completed device annealing temperature. EGTs with relatively thin P3HT films (∼50 nm) annealed at 120 °C have the best performance and display an unusual combination of metrics including sub-1-V operation, ON/OFF current ratios of 10⁶, OFF currents of <10^–10 A (<10^–6 A cm^–2), saturation hole mobilities of 1.3 cm² V^–1 s^–1, threshold voltages of −0.3 V, and subthreshold swings of 70 mV decade^–1. Furthermore, optimized EGTs printed on polyester substrates are extremely robust to bias stress and repeated mechanical bending strain. Collectively, the results suggest that optimized P3HT-based EGTs are promising devices for printed, flexible electronics

Physically Cross-Linked Homopolymer Ion Gels for High Performance Electrolyte-Gated Transistors

A new type of physically cross-linked solid polymer electrolyte was demonstrated by using a poly­(vinylidene fluoride) (PVDF) homopolymer in a room-temperature ionic liquid. The physical origins of gelation, specific capacitance, ionic conductivity, mechanical property, and capacitive charge modulation in organic thin-film electrochemical transistors were investigated systematically. Gelation occurs through bridging phase-separated homopolymer crystals by polymer chains in the composite electrolyte, thereby forming a rubbery network. The resulting homopolymer ion gels are able to accommodate both outstanding electrical (ionically conductive and capacitive) and mechanical (flexible and free-standing) characteristics of the component ionic liquid and the structuring polymer, respectively. These ion gels were successfully applied to organic thin-film transistors as high-capacitance gate dielectrics. Therefore, these results provide an effective route to generate a highly conductive rubbery polymer electrolyte that can be used in widespread electronic and electrochemical devices

Area-Controllable Stamping of Semicrystalline Copolymer Ionogels for Solid-State Electrolyte-Gated Transistors and Light-Emitting Devices

Two types of thin-film electrochemical devices (electrolyte-gated transistors and electrochemical light-emitting cells) are demonstrated using area-controllable ionogel patches generated by transfer-stamping. For the successful transfer of ionogel patches on various target substrates, thermoreversible gelation by phase-separated polymer crystals within the ionogel is essential because it allows the gel to form a conformal contact with the acceptor substrate, thereby lowering the overall Gibbs energy of the system upon transfer of the ionogel. This crystallization-mediated stamping provides a much more efficient deposition route for producing thin films of ionically conductive high-capacitance solid ionogel electrolytes. The lateral dimensions of the transferred ionogels range from 1 mm × 1 mm to 40 mm × 40 mm. These ionogel patches are incorporated in organic p-type and inorganic n-type thin-film transistors and electrochemical light-emitting devices. The resulting transistors show sub-1 V device operation with high transconductance currents, and the optoelectronic devices emit orange light through a series of electrochemical redox reactions. These results demonstrate a simple yet versatile route to employ physical ionogels for various solid-state electrochemical device applications

Continuous 1D-Metallic Microfibers Web for Flexible Organic Solar Cells

We report the use of a continuous 1D-metallic microfibers web (MFW) as transparent electrode for organic solar cells (OSCs). The MFW electrode can be produced with a process that involves simple electrospinning and wet etching of metal thin film. Au MFW exhibits a maximum optical transmittance of 90.8% (at 15 Ω/sq of the sheet resistance) and excellent mechanical flexibility. The MFW structure has an average width in the range from 4 to 6 μm and a junction-free structure, resulting in very smooth surface roughness. The OSCs with Au MFW electrode exhibited a higher power conversion efficiency (PCE) of 3.50% than the device with an indium tin oxide electrode (PCE = 3.20%). The optical modeling calculation showed that the Au MFW electrode induced light scattering and improved the light absorption in the active layer, resulting in an improved PCE in the OSCs

Solution-Processed Perovskite Gate Insulator for Sub‑2 V Electrolyte-Gated Transistors

By virtue of their semiconducting and electrolytic characteristics, hybrid organic–inorganic perovskites have received intense research attention in various applications, which include energy, electronics, and display technologies. While research studies on the semiconducting or electronic properties of perovskite materials in solar cells and light-emitting diodes have been actively investigated, studies on their electrolytic or ionic behavior have rarely been conducted. To probe the electrolyte properties of the metal halide perovskite, we have fabricated solution-processed zinc oxide (ZnO) thin-film transistors using a methylammonium lead iodide (CH₃NH₃PbI₃) perovskite thin film as a gate insulator material. The resulting perovskite film revealed ionic characteristics, with an ionic conductivity of about 10^–8 S/cm. The perovskite-gated ZnO transistors exhibited typical n-type characteristics with an average field-effect mobility of 0.047 cm²/V s at a low applied voltage below 2 V because of the electrical double layer formed by mobile I^– anions and CH₃NH₃⁺ cations in the perovskite gate dielectric. In addition, the poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS) transistors gated with the perovskite showed an abnormal increase in the channel current when applying positive gate bias, probably because of the confined ion movement inside the perovskite gate insulator