Optimization of material properties and performance of flexible thermoelectric generators with/without graphene

• This study successfully manufactures a high-performance flexible thermoelectric module. • Two different elastomer designs and thin copper sheets with the sandwich method are developed. • Blending graphene into polydimethylsiloxane improves the thermal conductivity by 9.6 times. • Blending graphene into polydimethylsiloxane enhances the output power by 4,681 times under active heating and cooling. • The errors between numerical simulations and experiment are between 4.6–5.2%. With the advancement of energy harvesting methods, the power level consumed by electronic circuits and sensors has been reduced so that self-sufficiency in power can be achieved, and the use of flexible thermoelectric generators to supply electrical energy is one of these methods. In this study, the manufacture of flexible thermoelectric generators is successfully developed and verified using a numerical method. The process follows the sandwich method of the conventional thermoelectric module and utilizes two different elastomers (polydimethylsiloxane and Eco-Flex) and thin copper sheets. Among the nine cases designed by the Taguchi method, the maximum tensile strength of the elastomer is 0.967 MPa, stemming from the operation conditions of 6 min stirring time, 85 °C heating temperature, and 3 h heating time. This strength is substantially higher than those of the other eight cases. The open-circuit voltage of the manufactured flexible thermoelectric generator with an internal resistance of 1.5 Ω is 0.011 V. The output power under a temperature difference of 75 °C is 11 μW. After blending graphene into polydimethylsiloxane, the elastomer’s thermal conductivity at 370 K rises by 9.6 folds. This results in the output power being lifted to 0.0515 W (75 °C temperature difference), accounting for an amplification of 4,681 times. Numerical simulations are also performed to aid in figuring out the detailed performance of the flexible thermoelectric generator. The errors between numerical simulations and experiments are between 4.6 % and 5.2 %, showing the reliability of the numerical predictions. The fabricated flexible thermoelectric generators can be practically used for green power generation by harvesting industrial low-temperature waste heat and biothermal energy, potentially driving sensors on industrial devices, the human body, and animals.