Dual-doped all-graphene fiber for flexible, high-performance thermoelectric temperature sensing.

High-performance temperature sensors are critical components for emerging Internet-of-Things and biomedical-electronics platforms. However, simultaneously achieving high sensitivity, mechanical compliance, and user-defined integrability remains a formidable materials-and-device challenge. Here, we report a continuous graphene fiber (GF) thermocouple technology where multiple p-n thermocouples are created in situ along a single, unbroken fiber while preserving its structural integrity. By periodically modulating surface charge-transfer doping with polyethyleneimine (PEI) and FeCl3, we formed an array of ten p-n pairs that delivered an exceptional thermocouple sensitivity of 452.32 µV K-1. The device retained ~97.8% of its initial sensitivity after 10,000 bending cycles at a 5-mm radius, confirming robustness under repeated mechanical deformation. When deployed on skin, the sensor tracked dynamic body temperature variations with a measurement error of 0.64%, validating its practical value for real-time, non-invasive health monitoring. These results establish all-carbon GF thermocouples as a high-precision and mechanically adaptable temperature-sensing platform for next-generation wearable electronics and personalized healthcare systems.