Flexible temperature sensor using laser induced graphene (LIG) based on processing-controlled seebeck contrast

Flexible temperature sensors and thermocouples offer precise temperature measurement on curved and irregular surfaces, making them ideal for wearable, environmental, and structural monitoring applications. This work presents a flexible Seebeck effect-based temperature sensor fabricated using Laser-Induced Graphene (LIG). Unlike conventional thermocouples, each leg was created with different laser configurations, where the defective structure of LIG plays a crucial role in enhancing the Seebeck coefficient by increasing phonon scattering at grain boundaries. Higher laser fluence leads to an increased <i>I_G/I_D</i> ratio, indicating a higher defect density, and a reduction in crystalline size (<i>L_a</i>), which results in more grain boundaries that further improve thermoelectric performance. To enhance sensitivity, a thermopile approach was implemented, connecting two LIG thermocouples in series, effectively increasing the Seebeck coefficient from 2.68 <i>μV/&deg;C</i> to 5.67 <i>μV/&deg;C</i>. The proposed sensor demonstrates great potential for next-generation temperature-sensing applications in various fields, including flexible electronics, healthcare, and industrial monitoring.