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.
Highly stretchable and robust strain sensors are rapidly emerging as promising candidates for a diverse of wearable electronics. The main challenge for the practical application of wearable electronics is the energy consumption and device aging. Energy consumption mainly depends on the conductivity of the sensor, and it is a key factor in determining device aging. Here, we design a liquid metal (LM)-embedded hydrogel as a sensing material to overcome the barrier of energy consumption and device aging of wearable electronics. The sensing material simultaneously exhibits high conductivity (up to 22 S m À1 ), low elastic modulus (23 kPa), and ultrahigh stretchability (1500%) with excellent robustness (consistent performance against 12 000 mechanical cycling). A motion monitoring system is composed of intrinsically soft LM-embedded hydrogel as sensing material, a microcontroller, signal-processing circuits, Bluetooth transceiver, and self-organizing map developed software for the visualization of multi-dimensional data. This system integrating multiple functions including signal conditioning, processing, and wireless transmission achieves monitor hand gesture as well as sign-to-verbal translation. This approach
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