Conducting polymers are promising material candidates in diverse applications including energy storage, flexible electronics, and bioelectronics. However, the fabrication of conducting polymers has mostly relied on conventional approaches such as ink-jet printing, screen printing, and electron-beam lithography, whose limitations have hampered rapid innovations and broad applications of conducting polymers. Here we introduce a high-performance 3D printable conducting polymer ink based on poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) for 3D printing of conducting polymers. The resultant superior printability enables facile fabrication of conducting polymers into high resolution and high aspect ratio microstructures, which can be integrated with other materials such as insulating elastomers via multi-material 3D printing. The 3D-printed conducting polymers can also be converted into highly conductive and soft hydrogel microstructures. We further demonstrate fast and streamlined fabrications of various conducting polymer devices, such as a soft neural probe capable of in vivo single-unit recording.

/pdf/3d-printing-of-conducting-polymers-4knarpty3r.pdf

3D printing of conducting polymers.

The increasingly intimate contact between electronics and the human body necessitates the development of stretchable energy storage devices that can conform and adapt to the skin. As such, the development of stretchable batteries and supercapacitors has received significant attention in recent years. This review provides an overview of the general operating principles of batteries and supercapacitors and the requirements to make these devices stretchable. The following sections provide an in-depth analysis of different strategies to convert the conventionally rigid electrochemical energy storage materials into stretchable form factors. Namely, the strategies of strain engineering, rigid island geometry, fiber-like geometry, and intrinsic stretchability are discussed. A wide range of materials are covered for each strategy, including polymers, metals, and ceramics. By comparing the achieved electrochemical performance and strain capability of these different materials strategies, we allow for a side-by-side comparison of the most promising strategies for enabling stretchable electrochemical energy storage. The final section consists of an outlook for future developments and challenges for stretchable supercapacitors and batteries.

Stretchable electrochemical energy storage devices

The concept of flexible electronics has been around for several decades. In principle, anything thin or very long can become flexible. While cables and wiring are the prime example for flexibility, it was not until the space race that silicon wafers used for solar cells in satellites were thinned to increase their power per weight ratio, thus allowing a certain degree of warping. This concept permitted the first flexible solar cells in the 1960s (Crabb and Treble, 1967). The development of conductive polymers (Shirakawa et al., 1977), organic semiconductors, and amorphous silicon (Chittick et al., 1969; Okaniwa et al., 1983) in the following decades meant huge strides toward flexibility and processability, and thus these materials became the base for electronic devices in applications that require bending, rolling, folding, and stretching, among other properties that cannot be fulfilled by conventional electronics (Cheng and Wagner, 2009) (Figure 1). Presently there is great interest in new materials and fabrication techniques which allow for highperformance scalable electronic devices to be manufactured directly onto flexible substrates. This interest has also extended to not only flexibility but also properties like stretchability and healability which can be achieved by utilizing elastomeric substrates with strong molecular interactions (Oh et al., 2016; Kang et al., 2018). Likewise, biocompatibility and biodegradability has been achieved through polymers that do not cause adverse effect to the body and can be broken down into smaller constituent pieces after utilization (Bettinger and Bao, 2010; Irimia-Vladu et al., 2010; Liu H. et al., 2019). This new progress is now enabling devices which can conform to complex and dynamic surfaces, such as those found in biological systems and bioinspired soft robotics. These next-generation flexible electronics open up a wide range of exciting new applications such as flexible lighting and display technologies for consumer electronics, architecture, and textiles, wearables with sensors that help monitor our health and habits, implantable electronics for improved medical imaging and diagnostics, as well as extending the functionality of robots and unmanned aircraft through lightweight and conformable energy harvesting devices and sensors. While conventional electronics are very capable of these functions, flexible electronics are intended to expand the mechanical features to adhere to novel form factors through hybrid strategies, or as standalone solutions where the application does not require high computation power, intended to be highly robust to deformation, low cost, thin, or disposable. The definition of flexibility differs from application to application. From bending and rolling for easier handling of large area photovoltaics, to conforming onto irregular shapes, folding, twisting, stretching, and deforming required for devices in electronic skin, all while maintaining device performance and reliability. While early progress and many important innovations have already been achieved, the field of flexible electronics has many challenges before it becomes part of our daily life. This represents a huge opportunity for scientific research and development to rapidly and considerably advance this area (Figure 2). In this article the status, key challenges and opportunities for the field of nextgeneration flexible devices are elaborated in terms of materials, fabrication and specific applications. Edited and Reviewed by: Jhonathan Prieto Rojas, King Fahd University of Petroleum and Minerals, Saudi Arabia

/pdf/flexible-electronics-status-challenges-and-opportunities-1lo1qzxlod.pdf

Flexible Electronics: Status, Challenges and Opportunities

Electrolyte-gated transistors (EGTs), capable of transducing biological and biochemical inputs into amplified electronic signals and stably operating in aqueous environments, have emerged as fundamental building blocks in bioelectronics. In this Primer, the different EGT architectures are described with the fundamental mechanisms underpinning their functional operation, providing insight into key experiments including necessary data analysis and validation. Several organic and inorganic materials used in the EGT structures and the different fabrication approaches for an optimal experimental design are presented and compared. The functional bio-layers and/or biosystems integrated into or interfaced to EGTs, including self-organization and self-assembly strategies, are reviewed. Relevant and promising applications are discussed, including two-dimensional and three-dimensional cell monitoring, ultra-sensitive biosensors, electrophysiology, synaptic and neuromorphic bio-interfaces, prosthetics and robotics. Advantages, limitations and possible optimizations are also surveyed. Finally, current issues and future directions for further developments and applications are discussed. Electrolyte-gated transistors (EGTs) are fundamental building blocks of bioelectronics, which transduce biological inputs to electrical signals. This Primer examines the different architectures of EGTs, their mechanism of operation and practical considerations related to their wide range of applications.

/pdf/electrolyte-gated-transistors-for-enhanced-performance-28xl9bz8pl.pdf

Electrolyte-gated transistors for enhanced performance bioelectronics

Conducting polymers, such as the p-doped poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), have enabled the development of an array of opto- and bio-electronics devices. However, to make these technologies truly pervasive, stable and easily processable, n-doped conducting polymers are also needed. Despite major efforts, no n-type equivalents to the benchmark PEDOT:PSS exist to date. Here, we report on the development of poly(benzimidazobenzophenanthroline):poly(ethyleneimine) (BBL:PEI) as an ethanol-based n-type conductive ink. BBL:PEI thin films yield an n-type electrical conductivity reaching 8 S cm−1, along with excellent thermal, ambient, and solvent stability. This printable n-type mixed ion-electron conductor has several technological implications for realizing high-performance organic electronic devices, as demonstrated for organic thermoelectric generators with record high power output and n-type organic electrochemical transistors with a unique depletion mode of operation. BBL:PEI inks hold promise for the development of next-generation bioelectronics and wearable devices, in particular targeting novel functionality, efficiency, and power performance. The development of n-type conductive polymer inks is critical for the development of next-generation opto-electronic devices that rely on efficient hole and electron transport. Here, the authors report an alcohol-based, high performance and stable n-type conductive ink for printed electronics.

/pdf/a-high-conductivity-n-type-polymeric-ink-for-printed-2ubiqyzcrq.pdf

A high-conductivity n-type polymeric ink for printed electronics.

The communication outposts of the emerging Internet of Things are embodied by ordinary items, which desirably include all-printed flexible sensors, actuators, displays and akin organic electronic interface devices in combination with silicon-based digital signal processing and communication technologies. However, hybrid integration of smart electronic labels is partly hampered due to a lack of technology that (de)multiplex signals between silicon chips and printed electronic devices. Here, we report all-printed 4-to-7 decoders and seven-bit shift registers, including over 100 organic electrochemical transistors each, thus minimizing the number of terminals required to drive monolithically integrated all-printed electrochromic displays. These relatively advanced circuits are enabled by a reduction of the transistor footprint, an effort which includes several further developments of materials and screen printing processes. Our findings demonstrate that digital circuits based on organic electrochemical transistors (OECTs) provide a unique bridge between all-printed organic electronics (OEs) and low-cost silicon chip technology for Internet of Things applications. Though designing digital circuits using organic electrochemical transistors (OECTs) is promising due to their high performance, inherent large footprint limits adoption. Here, the authors report staggered top-gate OECTs for all-printed integrated circuits with fast switching and small footprint.

/pdf/all-printed-large-scale-integrated-circuits-based-on-organic-3yzyfokp8l.pdf

All-printed large-scale integrated circuits based on organic electrochemical transistors.

The potential of the screen printing method for large-scale production of organic electrochemical transistors (OECTs), combining high production yield with low cost, is here demonstrated. Fully screen-printed OECTs of 1 mm2 area, based on poly(3,4-ethylenedioxythiophene) doped with poly(styrensulfonate) (PEDOT:PSS), have been manufactured on flexible polyethylene terephthalate (PET) substrates. The goal of this project effort has been to explore and develop the printing processing to enable high yield and stable transistor parameters, targeting miniaturized digital OECT circuits for large-scale integration (LSI). Of the 760 OECTs manufactured in one batch on a PET sheet, only two devices were found malfunctioning, thus achieving an overall manufacturing yield of 99.7%. A drain current ON/OFF ratio at least equal to 400 was applied as the strict exclusion principle for the yield, motivated by proper operation in LSI circuits. This consistent performance of low-footprint OECTs allows for the integration of PEDOT:PSS-based OECTs into complex logic circuits operating at high stability and accuracy.

/pdf/high-yield-manufacturing-of-fully-screen-printed-organic-2r7mdsxllt.pdf

High yield manufacturing of fully screen-printed organic electrochemical transistors

Flexible Active Matrix Addressed Displays Manufactured by Screen Printing

Here, we report all-screen printed display driver circuits, based on organic electrochemical transistors (OECTs), and their monolithic integration with organic electrochromic displays (OECDs). Both ...

https://iopscience.iop.org/article/10.1088/2058-8585/ab7ab4/pdf

Monolithic integration of display driver circuits and displays manufactured by screen printing

https://www.onlinelibrary.wiley.com/doi/epdf/10.1002/admt.202100555

Jan Strandberg

Papers

All-printed large-scale integrated circuits based on organic electrochemical transistors.

High yield manufacturing of fully screen-printed organic electrochemical transistors

Flexible Active Matrix Addressed Displays Manufactured by Screen Printing

Monolithic integration of display driver circuits and displays manufactured by screen printing

Designing Inverters Based on Screen Printed Organic Electrochemical Transistors Targeting Low-Voltage and High-Frequency Operation