Mechanically robust stretchable semiconductor metallization for skin-inspired organic transistors

Partially Degradable N-Type Conjugated Random Copolymers for Intrinsically Stretchable Organic Field-Effect Transistors

In this study, a series of conjugated homopolymers (P1 and P5) and random copolymers (P2-P4) by copolymerizing naphthalene diimide (NDI) as the acceptor with varying ratios of two donor units, thiophene-imine-thiophene (TIT) and thiophene-vinylene-thiophene (TVT) is developed. The inclusion of TIT imparted degradability to the random copolymers under acidic conditions, offering a sustainable solution for electronic waste management. Structural analysis revealed that TIT favored edge-on molecular orientation, while TVT promoted face-on and end-to-end orientations. The synergistic combination of TIT and TVT in copolymerization resulted in balanced structural and functional properties with partial degradability conferred using the TIT units. The random copolymer P3, with an optimal equimolar TIT/TVT ratio, demonstrates superior electrical and mechanical performance. P3 exhibits an initial charge mobility of 0.10 cm2 V⁻¹ s⁻¹ and maintained mobility of 0.0017 cm2 V⁻¹ s⁻¹ under 20% strain, significantly outperforming P1 in mobility at almost strain levels. P3 also achieved a mobility retention of 31.3% under 20% strain, compared to 12.2% for P5. This study demonstrates that the copolymerization of TIT and TVT enables the fine-tuning of solid-state packing modes and molecular orientations, thereby improving both the stretchability and environmental sustainability of the materials.

Conjugated Multiblock Copolymers and Microcracked Gold Electrodes Applied for the Intrinsically Stretchable Field-Effect Transistor

The rise of flexible electronic devices has led to extensive research into conjugated polymer structural engineering. Integrating polymer channels and contact electrodes, warranting high stretchability, is still critical, and the microcracked gold technique provides a potential strategy to integrate them. Conjugated block copolymers have gained significant attention due to their high flexibility, allowing for tailored polymer structures to meet the specific requirements of different device characteristics. In this study, novel N-type multiblock copolymers (multi-BCPs) composed of rigid poly(naphthalene diimide-alt-bithiophene) and flexible polyisobutylene segments were successfully synthesized as polymer semiconductors for the first time. The materials are named based on the weight fraction of soft segments: NDI (0 wt %), mAB73 (27 wt %), and mAB60 (40 wt %). The study explores the mechanical properties, crystallinity, and electrical performance of flexible multi-BCPs. The results show that introducing soft segments significantly enhances stretchability, with crack-onset strains beyond 100% because of their low elastic moduli of 40-50 MPa. Furthermore, the OFET device of mAB73 achieves unchanged mobility under 100% strain, outperforming mAB60 due to excessive polyisobutylene blocks. At the end of this study, an integrated stretchable device with high stretchability is fulfilled by utilizing the microcracked gold technique to combine the multi-BCP channels and contact electrodes. The integrated device can be applied to biomedical electronics without toxic or corrosive electrode materials. The influencing factors, including contact resistance, channel charge mobility, and electrode resistance, are systematically studied to investigate the integrated device's mobility-stretchability relationship. The results indicate that the contact resistance between the multi-BCP channels and contact electrodes is essential to the device's performance. Among these, mAB73, containing soft segments, exhibits more stability than NDI due to the microcracked gold electrodes with infiltrated gold nanoparticles in the rubbery channel surface. Appropriately incorporating soft segments significantly enhances mobility retention under tensile strains, highlighting the potential of multi-BCP designs in stretchable electronic applications.

Recent Progress in Intrinsically Stretchable Sensors Based on Organic Field-Effect Transistors

Organic field-effect transistors (OFETs) are an ideal platform for intrinsically stretchable sensors due to their diverse mechanisms and unique electrical signal amplification characteristics. The remarkable advantages of intrinsically stretchable sensors lie in their molecular tunability, lightweight design, mechanical robustness, solution processability, and low Young's modulus, which enable them to seamlessly conform to three-dimensional curved surfaces while maintaining electrical performance under significant deformations. Intrinsically stretchable sensors have been widely applied in smart wearables, electronic skin, biological detection, and environmental protection. In this review, we summarize the recent progress in intrinsically stretchable sensors based on OFETs, including advancements in functional layer materials, sensing mechanisms, and applications such as gas sensors, strain sensors, stress sensors, proximity sensors, and temperature sensors. The conclusions and future outlook discuss the challenges and future outlook for stretchable OFET-based sensors.

Skin-Mountable Functional Electronic Materials for Bio-Integrated Devices

Skin-mountable electronic materials are being intensively evaluated for use in bio-integrated devices that can mutually interact with the human body. Over the past decade, functional electronic materials inspired by the skin are developed with new functionalities to address the limitations of traditional electronic materials for bio-integrated devices. Herein, the recent progress in skin-mountable functional electronic materials for skin-like electronics is introduced with a focus on five perspectives that entail essential functionalities: stretchability, self-healing ability, biocompatibility, breathability, and biodegradability. All functionalities are advanced with each strategy through rational material designs. The skin-mountable functional materials enable the fabrication of bio-integrated electronic devices, which can lead to new paradigms of electronics combining with the human body.

Self-Healing Materials for Bioelectronic Devices

Though the history of self-healing materials stretches far back to the mid-20th century, it is only in recent years where such unique classes of materials have begun to find use in bioelectronics-itself a burgeoning area of research. Inspired by the natural ability of biological tissue to self-repair, self-healing materials play a multifaceted role in the context of soft, wireless bioelectronic systems, in that they can not only serve as a protective outer shell or substrate for the internal electronic circuitry-analogous to the mechanical barrier that skin provides for the human body-but also, and most importantly, act as an active sensing safeguard against mechanical damage to preserve device functionality and enhance overall durability. This perspective presents the historical overview, general design principles, recent developments, and future outlook of self-healing materials for bioelectronic devices, which integrates topics in many research disciplines-from materials science and chemistry to electronics and bioengineering-together.

A water-resistant, ultrathin, conformable organic photodetector for vital sign monitoring

Ultrathin flexible photodetectors can be conformably integrated with the human body, offering promising advancements for emerging skin-interfaced sensors. However, the susceptibility to degradation in ambient and particularly in aqueous environments hinders their practical application. Here, we report a 3.2-micrometer-thick water-resistant organic photodetector capable of reliably monitoring vital sign while submerged underwater. Embedding the organic photoactive layer in an adhesive elastomer matrix induces multidimensional hybrid phase separation, enabling high adhesiveness of the photoactive layer on both the top and bottom surfaces with maintained charge transport. This improves the water-immersion stability of the photoactive layer and ensures the robust sealing of interfaces within the device, notably suppressing fluid ingression in aqueous environments. Consequently, our fabricated ultrathin organic photodetector demonstrates stability in deionized water or cell nutrient media over extended periods, high detectivity, and resilience to cyclic mechanical deformation. We also showcase its potential for vital sign monitoring while submerged underwater.

Intrinsically Stretchable Floating Gate Memory Transistors for Data Storage of Electronic Skin Devices

To propel electronic skin (e-skin) to the next level by integrating artificial intelligence features with advanced sensory capabilities, it is imperative to develop stretchable memory device technology. A stretchable memory device for e-skin must offer, in particular, long-term data storage while ensuring the security of personal information under any type of deformation. However, despite the significance of these needs, technology related to stretchable memory devices remains in its infancy. Here, we report an intrinsically stretchable floating gate (FG) polymer memory transistor. The device features a dual-stimuli (optical and electrical) writing system to prevent easy erasure of recorded data. An FG comprising an intermixture of Ag nanoparticles and elastomer and with proper energy-band alignment between the semiconductor and dielectric facilitated sustainable memory performance, while achieving a high memory on/off ratio (>105) and a long retention time (106 s) with the ability to withstand 50% uniaxial or 30% biaxial strain. In addition, our memory transistor exhibited high mechanical durability over multiple stretching cycles (1000 times), along with excellent environmental stability with respect to factors such as temperature, moisture, air, and delamination. Finally, we fabricated a 7 × 7 active-matrix memory transistor array for personalized storage of e-skin data and successfully demonstrated its functionality.

Autonomous self-healing supramolecular polymer transistors for skin electronics

Skin-like field-effect transistors are key elements of bio-integrated devices for future user-interactive electronic-skin applications. Despite recent rapid developments in skin-like stretchable transistors, imparting self-healing ability while maintaining necessary electrical performance to these transistors remains a challenge. Herein, we describe a stretchable polymer transistor capable of autonomous self-healing. The active material consists of a blend of an electrically insulating supramolecular polymer with either semiconducting polymers or vapor-deposited metal nanoclusters. A key feature is to employ the same supramolecular self-healing polymer matrix for all active layers, i.e., conductor/semiconductor/dielectric layers, in the skin-like transistor. This provides adhesion and intimate contact between layers, which facilitates effective charge injection and transport under strain after self-healing. Finally, we fabricate skin-like self-healing circuits, including NAND and NOR gates and inverters, both of which are critical components of arithmetic logic units. This work greatly advances practical self-healing skin electronics.

Kinetically controlled metal-elastomer nanophases for environmentally resilient stretchable electronics

Nanophase mixtures, leveraging the complementary strengths of each component, are vital for composites to overcome limitations posed by single elemental materials. Among these, metal-elastomer nanophases are particularly important, holding various practical applications for stretchable electronics. However, the methodology and understanding of nanophase mixing metals and elastomers are limited due to difficulties in blending caused by thermodynamic incompatibility. Here, we present a controlled method using kinetics to mix metal atoms with elastomeric chains on the nanoscale. We find that the chain migration flux and metal deposition rate are key factors, allowing the formation of reticular nanophases when kinetically in-phase. Moreover, we observe spontaneous structural evolution, resulting in gyrified structures akin to the human brain. The hybridized gyrified reticular nanophases exhibit strain-invariant metallic electrical conductivity up to 156% areal strain, unparalleled durability in organic solvents and aqueous environments with pH 2-13, and high mechanical robustness, a prerequisite for environmentally resilient devices.