Highly Sensitive Screen-Printed Thermocouples Based on Novel Graphene Ink

Temperature monitoring systems are becoming increasingly important, e.g., in Internet of Things applications where reliable low cost and low power sensor elements are needed. These requirements are met by printed temperature sensors such as thermocouples.<br/>In this work printed thermocouples were developed based on a novel 2D-graphene based, additive-free ink in which the role of typical additives is taken over by van der Waals (vdW) interactions between the graphene flakes [1]. This leads to a very good processability of the ink while maintaining the electronic properties of the 2D material.<br/>Thin films based on this material exhibited a very high Seebeck coefficient of (45.01 ± 0.46) µV/K, exceeding other carbon-based inks. Therefore, the material seemed very promising for the application in thermocouples. Subsequently, thermocouples consisting of the 2D-graphene based material and various other conductor materials such as silver were fully screen printed onto flexible PI substrates with very high temperature durability.<br/>The all-printed thermocouples proved to be very useful for reliable temperature measurements and exhibited a linear response over a large temperature range (20°C – 200°C) and a high sensitivity of &gt;44µV/K. The devices performed as reliable as commercial K-type thermocouples. The cross sensitivity of the devices, the long-term stability and the dependence on varying process parameters and film morphology will be discussed.<br/>In addition to single sensors, a sensor array was designed and fabricated which allows for the measurement of spatial temperature distributions. This opens a new field of potential applications such as battery health monitoring in electric vehicles.