Multifunctional hydrogels with properties including transparency, flexibility, self-healing, and high electrical conductivity have attracted great attention for their potential application to soft electronic devices. The presence of an ionic species can make hydrogels conductive in nature. However, the conductivity of hydrogels is often influenced by temperature, due to the change of the internal nano/microscopic structure when temperature reaches the sol−gel phase transition temperature. In this regard, by introducing a novel surface-capacitive sensor device based on polymers with lower critical solution temperature (LCST) behavior, near-perfect stimulus discriminability of touch and temperature may be realized. Here, we demonstrate a multimodal sensor that can monitor the location of touch points and temperature simultaneously, using poly(N-isopropylacrylamide) (PNIPAAm) in hybrid poly(vinyl alcohol) (PVA) and sodium tetraborate decahydrate cross-linked hydrogels doped with poly(sodium acrylate) (SA) [w/w/w = 5:2.7:1−3]. This multimodal sensor exhibits a response time of 0.3 s and a temperature coefficient of resistance of −0.58% K −1 from 20 to 40 °C. In addition, the LCST behavior of PNIPAAmincorporated PVA/SA gels is investigated. Incorporation of LCST polymers into high-end hydrogel systems may contribute to the development of temperature-dependent soft electronics that can be applied in smart windows.

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Hybrid materials in optoelectronic devices can provide synergistic effects that complementarily enhance the properties of each component. Here, flexible high-performance graphene hybrid photodetectors (PDs) are developed by introducing gold nanostars (GNSs) and perovskites for strong light trapping with hot electron transfer and efficient light harvesting characteristics, respectively. While pristine graphene PDs do not exhibit discernible photodetection properties due to the very low photon absorption and ultrafast charge carrier recombination, graphene PDs functionalized with GNSs and a densely covered perovskite layer exhibit outstanding photoresponsive properties with a photoresponsivity (R) of 5.90 × 104 A W−1 and a specific detectivity of 1.31 × 1013 Jones, the highest values among those reported for perovskite-functionalized graphene PDs thus far. Moreover, we fabricated a flexible 10 × 10 PD array that shows well-resolved spatiotemporal mapping of light signals with excellent operational and mechanical stabilities at a bending radius down to 3 mm and in repeated bending tests for over 1000 cycles. Comprehensive analyses using finite-difference time-domain (FDTD) theoretical calculations, scanning near-field optical microscopy, and photoluminescence mapping reveal the effective light trapping effect of GNSs and the charge carrier transfer between the perovskite and graphene. This work provides a new design platform for flexible and high-performance photodetection systems.

The recent development of neuromorphic devices with low power consumption and rapid response has been driven primarily by the growing demand for braininspired computing in human-like machines and human-machine interfaces. Remarkable progress has been made in developing neuromorphic bioelectronics that combine neuromorphic devices with electronic sensors. In this review, we provide an overview of semiconducting polymer-based neuromorphic devices and their applications in neuromorphic bioelectronics. We focus on recent advances in semiconducting polymer-based three-terminal artificial synapses that mimic neural communication behaviors. Various types of semiconducting polymers and synaptic platforms have been investigated, allowing significant improvement in their performance and expansion of their functionality. Proper selection of materials and device structures can help artificial sensory synapses to react to various external stimuli and to further modulate electrical signals. Advances in semiconducting polymer-based neuromorphic bioelectronics will accelerate the commercialization of human-machine interfacial systems, including intelligent prosthetics and implantable diagnostic devices.