Dual-mode temperature monitoring using high-performance flexible thermocouple sensors based on PEDOT:PSS/CNTs and MXene/Bi2Se3.

Due to the limited thermoelectric (TE) performance of polymer materials and the inherent rigidity of inorganic materials, developing low-cost, highly flexible, and high-performance materials for flexible thermocouple sensors (FTCSs) remains challenging. Additionally, dual-mode (contact/non-contact) temperature monitoring in FTCSs is underexplored. This study addresses these issues by using p-type (PEDOT:PSS/CNTs, 2:1) and n-type (MXene/Bi₂Se₃, 2:1) TE materials applied via screen printing and compression onto a PPSN substrate (paper/PDMS/Si₃N₄). The resulting FTCSs exhibit excellent TE properties: electrical conductivities of 61,197.88 S/m (n-type) and 55,697.77 S/m (p-type), Seebeck coefficients of 39.88 μV/K and -29.45 μV/K, and power factors (PFs) of 97.66 μW/mK² and 55.64 μW/mK², respectively. In contact mode, the sensor shows high-temperature sensitivity (S_T = 379.5 μV/°C), a broad detection range (20-200 °C), high resolution (~0.3 °C), and fast response (~12.6 ms). In non-contact mode, it maintains good sensitivity (S_Tmax = 52.67 μV/°C), a broad detection range, high resolution (~0.8 °C), and even faster response (~9.8 ms). The sensor also demonstrates strong mechanical durability, maintaining stable performance after 1000 bending cycles. When applied to dual-mode temperature monitoring in wearable devices and lithium batteries, the FTCS shows high accuracy and reliability compared to commercial K-type thermocouples, indicating significant potential for advanced medical monitoring systems and smart home technologies.