Work Function Engineering of Electrohydrodynamic-Jet-Printed PEDOT:PSS Electrodes for High-Performance Printed Electronics

The Multifaceted Role of 3D Printed Conducting Polymers in Next-Generation Energy Devices: A Critical Perspective

The increasing human population is leading to growing consumption of energy sources which requires development in energy devices. The modern iterations of these devices fail to offer sustainable and environmentally friendly answers since they require costly equipment and produce a lot of waste. Three-dimensional (3D) printing has spurred incredible innovation over the years in a variety of fields and is clearly an attractive option because technology can create unique geometric items quickly, cheaply, and with little waste. Conducting polymers (CPs) are a significant family of functional materials that have garnered interest in the research community because of their high conductivity, outstanding sustainability, and economic significance. They have an extensive number of applications involving supercapacitors, power sources, electrochromic gadgets, electrostatic components, conducting pastes, sensors, and biological devices thanks to their special physical and electrical attributes, ease of synthesis, and appropriate frameworks for functional attachment. The use of three-dimensional printing has become popular as an exact way to enhance prepared networks. Rapid technological advancements are reproducing patterns and building structures that enable automated deposition of polymers for intricate structures. Different composites have been created using oxides of metals and carbon to improve the efficiency of the CPs. Such composites have been actively investigated as exceptional energy producers for low-power electronic techniques, and by increasing the range of applications, they have verified increasing surface area, electronic conductivity, and remarkable electrochemical behavior. The hybridization with such materials has produced a range of equipment, such as gathering energy, sensors, protective gadgets, and storage facilities. A few possible uses for these CPs such as sensors and energy storage devices are discussed in this perspective. We also provide an overview of the key strategies for scientific and industrial applications with an eye on potential improvements for a sustainable future.

Wafer-Scale Vertical 1D GaN Nanorods/2D MoS2/PEDOT:PSS for Piezophototronic Effect-Enhanced Self-Powered Flexible Photodetectors

van der Waals (vdW) heterostructures constructed by low-dimensional (0D, 1D, and 2D) materials are emerging as one of the most appealing systems in next-generation flexible photodetection. Currently, hand-stacked vdW-type photodetectors are not compatible with large-area-array fabrication and show unimpressive performance in self-powered mode. Herein, vertical 1D GaN nanorods arrays (NRAs)/2D MoS2/PEDOT:PSS in wafer scale have been proposed for self-powered flexible photodetectors arrays firstly. The as-integrated device without external bias under weak UV illumination exhibits a competitive responsivity of 1.47 A W-1 and a high detectivity of 1.2 × 1011 Jones, as well as a fast response speed of 54/71 µs, thanks to the strong light absorption of GaN NRAs and the efficient photogenerated carrier separation in type-II heterojunction. Notably, the strain-tunable photodetection performances of device have been demonstrated. Impressively, the device at - 0.78% strain and zero bias reveals a significantly enhanced photoresponse with a responsivity of 2.47 A W-1, a detectivity of 2.6 × 1011 Jones, and response times of 40/45 µs, which are superior to the state-of-the-art self-powered flexible photodetectors. This work presents a valuable avenue to prepare tunable vdWs heterostructures for self-powered flexible photodetection, which performs well in flexible sensors.

Photolithography-Free, Solution-Processable Perovskite Electrodes for High-Performance Organic Transistors

Solution-processable electrodes are promising for next-generation electronics due to their simplicity, cost-effectiveness, and potential for large-area fabrication. However, current solution-processable electrodes based on conductive polymers, carbon-based compounds, and metal nanowires face challenges related to stability, patterning, and production scalability. Here we introduce a novel approach using 3D tin halide perovskites (THPs) combined with a photolithography-free solution patterning technique to fabricate solution-processed electrodes. We demonstrate the preparation of highly conductive CsSnI3 films (234.9 S cm-1) and the fabrication of patterned 35 × 35 perovskite electrode arrays on a 4-in. silicon wafer. These electrodes, used as source/drain electrodes in organic transistors, resulted in devices showing high uniformity and stability. This electrode fabrication strategy is also applicable to other 3D THPs like FASnI3 and MASnI3, showcasing versatility for diverse applications. The results highlight the feasibility and advantages of using 3D THPs as solution-processable electrodes, providing a new material system for the advancement of solution-processed electronics.

Conductive PEDOT-Dominant Surface of Transparent Electrode Patch via Selective Phase Transfer for Efficient Flexible Photoelectronic Devices

In this study, a conductive patch for a flexible organic optoelectronic device is proposed and implemented using a poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) polymer electrode based on a transfer process to achieve its high conductivity with an efficient conductive pathway. This PEDOT-dominant surface is induced by phase inversion during the transfer process owing to the solvent affinity of the PSS phase. The PEDOT:PSS patch formed by the transfer process minimizes the power loss in a flexible optoelectronic device due to the improved charge collection and suppressed leakage current responses. In addition, the bending stability of the flexible photoelectronic device is also enhanced by maintaining performance for 1000 bending cycles. Therefore, in the fabrication of a transparent flexible conductive PEDOT:PSS patch, the transfer process of a conducting polymer constitutes an effective strategy that can improve conductivity and embellished morphology.

Transfer-Printing of Insoluble Conducting Polymer for Soft 3D Conformal All-Organic Transistors

The development of high-precision insoluble conducting polymer patterns for soft electronics is extremely challenging, mainly because of the incompatibility of the synthesis process with the underlying layers. In this study, a novel transfer-printing method is designed that enables the fabrication of photolithographic insoluble conducting polypyrrole (PPy) electrode patterns on soft substrates with high precision, demonstrating compatibility with various soft organic functional layers. Excellent mechanical stability, good biocompatibility, ultra-smooth surface, and outstanding conformability are observed. The photolithographic PPy electrode patterns, combined with an elastic organic semiconductor and dielectric, produce conformal all-organic transistors with mobility of 1.8 cm2 V-1 s-1. This study paves the way to use insoluble conducting polymers to develop complex, high-density flexible patterns and offers a promising organic electrode for the new-generation soft all-organic electronics.

Stepwise Aggregation Control of PEDOT:PSS Enabled High-Conductivity, High-Resolution Printing of Polymer Electrodes for Transparent Organic Phototransistors

Electrohydrodynamic (EHD) jet printing is a widely employed technology to create high-resolution patterns and thus has enormous potential for circuit production. However, achieving both high conductivity and high resolution in printed polymer electrodes is a challenging task. Here, by modulating the aggregation state of the conducting polymer in the solution and solid phases, a stable and continuous jetting of PEDOT:PSS is realized, and high-conductivity electrode arrays are prepared. The line width reaches less than 5 μm with a record-high conductivity of 1250 S/cm. Organic field-effect transistors (OFETs) are further developed by combining printed source/drain electrodes with ultrathin organic semiconductor crystals. These OFETs show great light sensitivity, with a specific detectivity (D*) value of 2.86 × 1014 Jones. In addition, a proof-of-concept fully transparent phototransistor is demonstrated, which opens up new pathways to multidimensional optical imaging.

Fabrication of SU-8 polymer micro/nanoscale nozzle by hot embossing method

Electrohydrodynamic-jet printing (E-jet printing) is a direct-writing technology for manufacturing micro-nano devices. To further reduce the inner diameter of the nozzle to improve the printing resolution, a large-scale manufacturing method of SU-8 polymer micro/nanoscale nozzle by means of a process combining UV exposure and hot embossing was proposed. To improve the adhesive strength between the UV mask and SU-8, the influence of the oxygen plasma treatment parameters on the water contact angles of the UV mask was analyzed. The effect of hot embossing time and temperature on the replication precision was studied. The influence of UV exposure parameters and thermal bonding parameters on the micro and nanochannel pattern was investigated. The SU-8 polymer nozzles with 188 ± 3 nm wide and 104 ± 2 nm deep nanochannels were successfully fabricated, and the replication precision can reach to 98.5%. The proposed manufacturing method of SU-8 polymer nozzles in this study will significantly advance the research on the transport properties of nanoscale channels in E-jet nozzles and facilitate further advancements in E-jet based applications.

Fast and versatile electrostatic disc microprinting for piezoelectric elements

Nanoparticles, films, and patterns are three critical piezoelectric elements with widespread applications in sensing, actuations, catalysis and energy harvesting. High productivity and large-area fabrication of these functional elements is still a significant challenge, let alone the control of their structures and feature sizes on various substrates. Here, we report a fast and versatile electrostatic disc microprinting, enabled by triggering the instability of liquid-air interface of inks. The printing process allows for fabricating lead zirconate titanate free-standing nanoparticles, films, and micro-patterns. The as-fabricated lead zirconate titanate films exhibit a high piezoelectric strain constant of 560 pm V-1, one to two times higher than the state-of-the-art. The multiplexed tip jetting mode and the large layer-by-layer depositing area can translate into depositing speeds up to 109 μm3 s-1, one order of magnitude faster than current techniques. Printing diversified functional materials, ranging from suspensions of dielectric ceramic and metal nanoparticles, to insulating polymers, to solutions of biological molecules, demonstrates the great potential of the electrostatic disc microprinting in electronics, biotechnology and beyond.

Direct Writing of Silver Nanowire Patterns with Line Width down to 50 μm and Ultrahigh Conductivity

Direct writing of one-dimensional nanomaterials with large aspect ratios into customized, highly conductive, and high-resolution patterns is a challenging task. In this work, thin silver nanowires (AgNWs) with a length-to-diameter ratio of 730 are employed as a representative example to demonstrate a potent direct ink writing (DIW) strategy, in which aqueous inks using a natural polymer, sodium alginate, as the thickening agent can be easily patterned with arbitrary geometries and controllable structural features on a variety of planar substrates. With the aid of a quick spray-and-dry postprinting treatment at room temperature, the electrical conductivity and substrate adhesion of the written AgNWs-patterns improve simultaneously. This simple, environment benign, and low-temperature DIW strategy is effective for depositing AgNWs into patterns that are high-resolution (with line width down to 50 μm), highly conductive (up to 1.26 × 105 S/cm), and mechanically robust and have a large alignment order of NWs, regardless of the substrate's hardness, smoothness, and hydrophilicity. Soft electroadhesion grippers utilizing as-manufactured interdigitated AgNWs-electrodes exhibit an increased shear adhesion force of up to 15.5 kPa at a driving voltage of 3 kV, indicating the strategy is very promising for the decentralized and customized manufacturing of soft electrodes for future soft electronics and robotics.

Highly Efficient Contact Doping for High-Performance Organic UV-Sensitive Phototransistors

Organic ultraviolet (UV) phototransistors are promising for diverse applications. However, wide-bandgap organic semiconductors (OSCs) with intense UV absorption tend to exhibit large contact resistance (Rc) because of an energy-level mismatch with metal electrodes. Herein, we discovered that the molecular dopant of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) was more efficient than the transition metal oxide dopant of MoO3 in doping a wide-bandgap OSC, although the former showed smaller electron affinity (EA). By efficient contact doping, a low Rc of 889 Ω·cm and a high mobility of 13.89 cm2V−1s−1 were achieved. As a result, UV-sensitive phototransistors showed high photosensitivity and responsivity.

High Precision 3D Printing for Micro to Nano Scale Biomedical and Electronic Devices

Three dimensional printing (3DP), or additive manufacturing, is an exponentially growing process in the fabrication of various technologies with applications in sectors such as electronics, biomedical, pharmaceutical and tissue engineering. Micro and nano scale printing is encouraging the innovation of the aforementioned sectors, due to the ability to control design, material and chemical properties at a highly precise level, which is advantageous in creating a high surface area to volume ratio and altering the overall products' mechanical and physical properties. In this review, micro/-nano printing technology, mainly related to lithography, inkjet and electrohydrodynamic (EHD) printing and their biomedical and electronic applications will be discussed. The current limitations to micro/-nano printing methods will be examined, covering the difficulty in achieving controlled structures at the miniscule micro and nano scale required for specific applications.

Additive Manufacturing of Conducting Polymers: Recent Advances, Challenges, and Opportunities

Conducting polymers (CPs) have been attracting great attention in the development of (bio)electronic devices. Most of the current devices are rigid two-dimensional systems and possess uncontrollable geometries and architectures that lead to poor mechanical properties presenting ion/electronic diffusion limitations. The goal of the article is to provide an overview about the additive manufacturing (AM) of conducting polymers, which is of paramount importance for the design of future wearable three-dimensional (3D) (bio)electronic devices. Among different 3D printing AM techniques, inkjet, extrusion, electrohydrodynamic, and light-based printing have been mainly used. This review article collects examples of 3D printing of conducting polymers such as poly(3,4-ethylene-dioxythiophene), polypyrrole, and polyaniline. It also shows examples of AM of these polymers combined with other polymers and/or conducting fillers such as carbon nanotubes, graphene, and silver nanowires. Afterward, the foremost applications of CPs processed by 3D printing techniques in the biomedical and energy fields, that is, wearable electronics, sensors, soft robotics for human motion, or health monitoring devices, among others, will be discussed.

Directly Patterning Conductive Polymer Electrodes on Organic Semiconductor via In Situ Polymerization in Microchannels for High-Performance Organic Transistors

Conductive polymers are considered promising electrode materials for organic transistors, but the reported devices with conductive polymer electrodes generally suffer from considerable contact resistance. Currently, it is still highly challenging to pattern conductive polymer electrodes on organic semiconductor surfaces with good structure and interface quality. Herein, we develop an in situ polymerization strategy to directly pattern the top-contacted polypyrrole (PPy) electrodes on hydrophobic surfaces of organic semiconductors by microchannel templates, which is also applicable on diverse hydrophobic and hydrophilic surfaces. Remarkably, a width-normalized contact resistance as low as 1.01 kΩ·cm is achieved in the PPy-contacted transistors. Both p-type and n-type organic field-effect transistors (OFETs) exhibit ideal electrical characteristics, including almost hysteresis-free, low threshold voltage, and good stability under long-term test. The facile patterning method and high device performance indicate that the in situ polymerization strategy in confined microchannels has application prospects in all-organic, transparent, and flexible electronics.

Strategy for Selective Printing of Gate Insulators Customized for Practical Application in Organic Integrated Devices

Direct drawing techniques have contributed to the ease of patterning soft electronic materials, which are the building blocks of analog and digital integrated circuits. In parallel with the printing of semiconductors and electrodes, selective deposition of gate insulators (GI) is an equally important factor in simplifying the fabrication of integrated devices, such as NAND and NOR gates, and memory devices. This study demonstrates the fabrication of six types of printed GI layers (high/low-k polymer and organic-inorganic hybrid material), which are utilized as GIs in organic field-effect transistors (OFETs), using the electrostatic-force-assisted dispensing printing technique. The selective printing of GIs on the gate electrodes enables us to develop practical integrated devices that go beyond unit OFET devices, exhibiting robust switching performances, non-destructive operations, and high gain values. Moreover, the flexible integrated devices fabricated using this technique exhibit excellent operational behavior. Therefore, this facile fabrication technique can pave a new path for the production of practical integrated device arrays for next-generation devices.

Organic-based inverters: basic concepts, materials, novel architectures and applications

The review article covers the materials and techniques employed to fabricate organic-based inverter circuits and highlights their novel architectures, ground-breaking performances and potential applications.