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, there has been limited exploration of dual-mode (contact/non-contact) temperature monitoring in FTCSs, with most studies focusing solely on contact-based monitoring. This study addresses these challenges by using p-type (PEDOT:PSS/CNTs, 2:1) and n-type (MXene/Bi₂Se₃, 2:1) TE materials, applied through screen printing and compression onto a PPSN substrate (paper/polydimethylsiloxane (PDMS)/Si₃N₄). The resulting FTCS demonstrates excellent TE properties, with electrical conductivities of 61,197.88 S/m and 55,697.77 S/m, Seebeck coefficients of 39.88 μV/K and -29.45 μV/K, and power factors (PF) of 97.66 μW/mK² and 55.64 μW/mK² for the n/p-type materials, respectively. The sensor achieves outstanding performance in both modes: in contact mode, it exhibits high temperature sensitivity (S_T=376.1 μV/°C), a broad detection range (20-200°C), high resolution (~0.4°C), and fast response (~12.6 ms); in non-contact mode, it maintains relatively high sensitivity (S_Tmax=50.67 μV/°C), broad detection range (20-200°C), high resolution (~0.9°C), and even faster response (~9.8 ms). The sensor also shows strong resistance to mechanical deformation, maintaining stable performance after 1,000 bending cycles. When applied to dual-mode temperature monitoring in wearable devices and lithium batteries (LiBs), the FTCS not only shows high accuracy and reliability compared to commercial K-type thermocouples but also demonstrates the versatility needed for various applications. This suggests significant potential for integration into advanced medical monitoring systems and next-generation smart home technologies.