Facile Synthesis of a Carbon Nano Dot‐Based Wearable Flexible Thermoelectric Device

Abstract A facile method of synthesizing flexible thin films of carbon nano dots (CNDs) and Polyvinyl Pyrrolidone (PVP) on cellulose based substrates is developed and their thermoelectric properties are demonstrated through the fabrication of a wearable device. Alongside enhanced thermoelectric performance, the CND thin films are biocompatible, low cost and scalable, all essential criteria for wearable thermoelectric devices. A critical window of the CND loading concentration on the cellulose‐based substrate is observed, with significantly enhanced Seebeck coefficient and Power Factor of thin films, demonstrating that the trade‐off principles for thermoelectric materials must be carefully tuned. The highest Seebeck coefficient of –358.45 µV·K −1 , power factor of 0.03 µW·m −1 ·K −2 and the lowest thermal conductivity of 0.086 W·m −1 ·K −1 at room temperature is achieved with a CND loading concentration of 9.32 g cm −2 . A wearable thermoelectric device is fabricated using n‐type CND films with copper electrodes. When worn, the device can generate voltage and current of ≈70 mV and ≈15 nA, respectively, at ΔT of 10 K.