Processing-Controlled Seebeck Modulation in Laser-Induced Graphene for Flexible Temperature Sensors

Classical thermocouples are too rigid for accurate temperature measurement on curved or irregular surfaces, necessitating the development of flexible sensors. These sensors are typically composed of materials such as printed inks and flexible substrates and utilize the Seebeck effect for high sensitivity, with optimized designs enhancing performance in wearable, environmental, and structural monitoring applications. This study proposes a flexible temperature sensor based on the Seebeck effect, fabricated using laser-induced graphene (LIG) technology. Unlike conventional thermocouples composed of two dissimilar materials, each leg of the proposed LIG thermocouple is fabricated by using different laser configurations. Each configuration results in a unique microstructure and defect population, enabling tuning of the Seebeck coefficient by controlling phonon scattering at grain boundaries. Increasing the laser fluence increases the IG/ID ratio, indicating a higher number of defects in LIG, and reduces the crystalline size, thereby increasing grain boundaries and further improving the Seebeck coefficient. Furthermore, a thermopile approach is employed to enhance the Seebeck response by connecting two LIG thermocouples in series, increasing the Seebeck coefficient from 2.68 μV/°C to 5.67 μV/°C. This study demonstrates the advantages and versatility of LIG technology for fabricating flexible thermocouples. The proposed process is rapid, cost-effective, and suitable for large-scale production, making it a promising solution for advanced temperature-sensing applications.