Temperature-Strain-Pressure Multimodal Sensor Based on Copper(I) Iodide Nanoparticles Embedded Highly Stretchable Thermoelectric Fiber for Wearable Electronics

With the advancement of smart wearable electronic devices and IoT technologies, the mobile medical field has significantly progressed. Wearable electronic devices for personalized healthcare systems, which can monitor human body conditions in real-time, have garnered considerable attention. These devices necessitate smart sensors inspired by the human skin somatosensory system to accurately detect human body data such as movement, body temperature, and human-object contact. Therefore, flexible and stretchable sensors capable of detecting both mechanical and thermal stimuli are required, and the use of thermoelectric (TE) materials becomes essential to achieve this.
Fiber-type sensors are ideal for wearable devices due to their lightweight, flexibility, and ease of integration into clothing. However, existing TE fibers are still limited in practical use in wearable electronic devices for the following reasons: (1) TE fibers composed of carbon or organic materials exhibit insufficient TE performance to effectively detect temperature changes; (2) TE fibers made from rigid inorganic materials lack stretchability, limiting their capacity to detect mechanical deformation. These material constraints must be addressed to further advance wearable sensor technology.
In this study, we developed a stretchable TE fiber-based multimodal sensor using copper(I) iodide (CuI), a p-type semiconductor material with a wide bandgap. CuI is environmentally friendly and composed of nontoxic and naturally abundant elements. Using a novel solution-based chemical synthesis method, CuI nanoparticles (CuINPs) were embedded into polyurethane (PU) polymer fibers. This design enables the CuI fiber sensor to maintain high electrical conductivity (2.965 S/cm) and TE performance (Seebeck coefficient of ~203.6 μV/K and power factor of ~12.29 μW/mK²) while achieving extensive stretchability and durability. The CuI fiber sensor demonstrated a maximum tensile strain of approximately 835 %, with stable performance across over 10,000 stretching cycles. It exhibited a high gauge factor of approximately 3.89 for strain sensing up to 200 %, and a capacitive pressure sensor configuration allowed high-pressure sensing up to approximately 84 kPa with a resolution of 250 Pa. Integration into a wearable smart glove showcased its capability to simultaneously and independently detect temperature changes, tensile strain, and pressure, highlighting its practical application in wearable electronic devices.