Flexible electrochromic devices (FECDs) are extensively used in smart windows, deformable electronic displays, and wearable electronics. However, it remains very challenging to fabricate low-cost yet high-performance visible–near-infrared (vis–NIR) FECDs. In this work, we overcome this hurdle by developing a fluorinated polythiophene derivative with superior overall electrochromic performance and simple electropolymerization patterning. Fluorophenyl-modified polythiophene (band gap: 1.74 eV) can be readily synthesized via a one-step Grignard coupling with a high yield of >90% together with successive low-potential electropolymerization at 1.0 V vs Ag/AgCl. The intermolecular hydrogen bonding from the fluorine substitution of polythiophene backbones allows the facile electrodeposition of free-standing polymer films with a compact morphology and also leads to mechanical strength and electrical conductivity enhancement. Interestingly, such polymer films exhibit intriguing overall electrochromic performances with reversible color changes between deep red and light green upon doping/dedoping, including high optical contrast throughout the NIR region (max. 80% at 1600 nm), fast response time (0.93 s), high coloration efficiency (up to 752 cm2 C–1), outstanding stability against cycling (<3% reduction after 5,000 cycles), and excellent optical memory effect. The fabricated FECDs by electropolymerization patterning of such polymers display robust mechanical stability (<5% decay in optical contrast after 5,000 bending cycles with a bending radius of 1 cm) under a low driving voltage (0.85 V). We further demonstrate the applications of such patterned electrochromic devices toward deformable displays, color-changing electronic on-skin tattoos, and infrared camouflage with stable color-switching and robust mechanical properties.

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Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)-based hydrogels have emerged as ideal interfacing materials for bioelectronics because of their intriguing electrical, mechanical, and biological properties. However, the development of high-performance PEDOT:PSS-based hydrogels simultaneously achieving high conductivity, robust mechanical properties, and accessibility for advanced manufacturing technologies remains a critical challenge for further advancing such materials toward practical applications. Herein, we develop a highly conductive, intrinsically soft, tough yet stretchable PEDOT:PSS-based hydrogel via a simple PSS-chain engineering strategy of introducing thermally cross-linkable N-(hydroxymethyl)acrylamide segments. The resultant PEDOT:PSS hydrogel exhibits high electrical conductivity (1850 S m–1), high stretchability (>50%), low Young’s modulus (4 MPa), and superior toughness (400 kJ m–3), satisfying multiple property requirements for practical bioelectronic applications. Based on this material, we further develop a novel PEDOT:PSS ink with superior 3D printability for direct ink writing 3D printing, enabling us to facilely fabricate bioelectronic devices like soft skin electrodes comparable to commercial products via multi-material 3D printing.

Stretchable, adhesive, and conductive hydrogels have been regarded as ideal interfacial materials for seamless and biocompatible integration with the human body. However, existing hydrogels can rarely achieve good mechanical, electrical, and adhesive properties simultaneously, as well as limited patterning/manufacturing techniques posing severe challenges to bioelectronic research and their practical applications. Herein, we develop a stretchable, adhesive, and conductive Ti3C2Tx-polyacrylic acid hydrogel by a simple pre-crosslinking method followed by successive direct ink writing 3D printing. Pre-polymerization of acrylic acid can be initiated by mechanical mixing with Ti3C2Tx nanosheet suspension, leading to the formation of viscous 3D printable ink. Secondary free radical polymerization of the ink patterns via 3D printing can achieve a stretchable, adhesive, and conductive Ti3C2Tx-polyacrylic acid hydrogel. The as-formed hydrogel exhibits remarkable stretchability (~622%), high electrical conductivity (5.13 S m−1), and good adhesion strength on varying substrates. We further demonstrate the capability of facilely printing such hydrogels into complex geometries like mesh and rhombus patterns with high resolution and robust integration.

Supercapacitors are widely used in various fields due to their high power density, fast charging and discharging speeds, and long service life. However, with the increasing demand for flexible electronics, integrated supercapacitors in devices are also facing more challenges, such as extensibility, bending stability, and operability. Despite many reports on stretchable supercapacitors, challenges still exist in their preparation process, which involves multiple steps. Therefore, we prepared stretchable conducting polymer electrodes by depositing thiophene and 3-methylthiophene on patterned 304 stainless steel (SS 304) through electropolymerization. The cycling stability of the prepared stretchable electrodes could be further improved by protecting them with poly(vinyl alcohol)/sulfuric acid (PVA/H2SO4) gel electrolyte. Specifically, the mechanical stability of the polythiophene (PTh) electrode was improved by 2.5%, and the stability of the poly(3-methylthiophene (P3MeT) electrode was improved by 7.0%. As a result, the assembled flexible supercapacitors maintained 93% of their stability even after 10,000 cycles of strain at 100%, which indicates potential applications in flexible electronics.