Heesuk Kim

The integration of functional electronic structures into curved geometries remains challenging, as conventional approaches rely on post-shaping or adhesive-assisted assembly that separate structure formation from shape definition. Here, we present a sequential-photocuring-assisted fabrication strategy that transforms planar multilayer structures into curved forms within a single material system. A wavelength-selective acrylate–epoxy resin is designed to create a deformable intermediate state under visible light, followed by a fixation-enabled final state through UV-triggered curing. A gradient-like curing strategy, involving time-dependent evolution of conversion during sequential irradiation, allows controlled partial epoxy conversion and provides both processability and subsequent reactivity. The second curing step induces simultaneous interfacial bonding and structural stiffening, enabling adhesive-free integration and fixation of the mold-imposed geometry. A multilayer patch antenna operating at 28 GHz is fabricated and transformed from planar to curved geometry while maintaining its performance. This approach provides a material-based framework for integrating planar-fabricated structures into three-dimensional form factors without thermoforming or adhesives.

Fiber‐shaped electronics are essential for unobtrusive wearable monitoring due to their seamless integration into textiles. However, achieving both high sensitivity and stable interconnectivity within a single, monolithic platform remains a significant challenge. Here, we present a facile and novel strategy to fabricate monolithic function‐tunable fibers (FTFs) with spatially controlled electromechanical properties via a vertical encapsulation‐induced densification mechanism. By engineering asymmetric AgNW percolation networks, we precisely tune the gauge factor (GF) within a single 1D architecture, creating highly sensitive strain sensors (SS, GF = 93.2 beyond 50% strain) and strain‐insensitive conductive threads (CT, GF = 6.46). The SS detects deformations as small as 1%, while the CT maintains robust pathways even under 90% strain with an 8.9‐fold reduction in sensitivity compared to the SS. The FTFs (SS‐CT) exhibit exceptional durability, maintaining structural integrity and electrical continuity over 10 000 stretching cycles and 45 washing cycles. The practical utility has been demonstrated through an underwater strain‐responsive light‐emitting diode switch and a waterproof near‐field communication antenna integrated into a junctionless, single‐fiber platform. This monolithic approach eliminates the need for heterogeneous bonding agents, providing a promising pathway for durable, high‐performance, and fiber‐based wearable electronics.

Ultrathin two-dimensional (2D) transition metal dichalcogenides (TMDs) exhibit unique band structures, allowing promising thermoelectric properties. Achieving a high power factor (PF) for thermoelectric generators (TEGs) requires optimizing both the Seebeck coefficient (S) and electrical conductivity (σ). Conventional surface charge-transfer doping can be a solution to enhance σ by introducing additional electrons. However, residual organic dopants act as charged impurities, degrading charge transport and lowering PF due to the intensified trade-off between carrier concentration and S. We propose a charged-impurity-free diffusion doping method for CVD-grown molybdenum disulfide (MoS₂) to enhance PF. By depositing organic dopants on the contact region and enabling electron diffusion into the channel via carrier concentration gradients, σ is improved while maintaining high S. This approach achieves a record-high PF of 1698 μW/mK² for CVD-grown TMDs. Our strategy offers a promising pathway to enhance thermoelectric performance, not limited by the exacerbated trade-off relationship observed in conventional doping methods.

Hydrogel-based ionic thermoelectric (i-TE) materials that rely on ion migration driven by thermal gradients have emerged as promising candidates for efficient low-grade heat harvesting. They offer high Seebeck coefficients, mechanical flexibility, and biocompatibility, making them especially attractive for wearable electronics and biomedical applications. Among various i-TE materials, hydrogels are particularly notable due to their unique structure and ability to modulate ion diffusion via interactions between the polymer network and ionic species. Despite increasing interest in hydrogel-based i-TE materials, the fundamental mechanisms governing thermodiffusive ion transport remain poorly understood, especially when compared to the more established thermo-galvanic processes. Moreover, the unique composite architecture of these materials combining polymer matrices with diverse ionic components presents significant challenges for rational design and performance optimization. This review addresses these challenges by systematically analyzing the fundamental mechanisms of hydrogel-based i-TE materials, with a particular focus on the Soret effect and the roles of polymer networks and ionic conductors. It also provides critical insights into practical applications such as wearable thermoelectric generators and capacitive energy storage devices. Furthermore, we propose innovative strategies to overcome key limitations, those related to long-term stability and mechanical durability. By consolidating current knowledge and identifying future research opportunities, this review establishes a foundation for the development of next-generation flexible and efficient hydrogel-based i-TE materials.

We propose a novel design of thermoelectric (TE) effect-based soft temperature sensors for directly monitoring localized subtle temperature stimuli. This design integrates rheology-engineered three-dimensional (3D) printing of high-performance carbon-based TE materials and polymer-based viscoelastic materials with low thermal conductivity. Rheological engineering of carbon nanotube (CNT) TE inks ensures the 3D printing of highly sensitive TE sensing units on directly written 3D soft platforms. Additionally, we pre-dope CNT inks with p- and n-type organic dopants to achieve high sensitivity and a fast response to temperature changes. The introduced 3D soft platforms with low thermal conductivity lead to an efficient thermal gradient on TE sensing units in the out-of-plane direction. Furthermore, encapsulating the temperature sensor array with the same polymer-based materials as the 3D soft platforms facilitates independent detection of localized temperature stimuli by minimizing thermal interaction between sensing units, resulting in precise temperature mapping by localized detection. Our 3D-printed soft temperature sensors exhibit high sensitivity to relatively small temperature changes, with a minimum sensing resolution of 0.1 K within tens of milliseconds. Moreover, the temperature sensor array not only detects localized temperature stimuli by imaging the temperature distribution but also demonstrates remarkable mechanical reliability against repetitive deformation with high accuracy.