Design and parameter study of a thermoelectric generator for waste heat recycling in flexible micro-light-emitting diodes

Abstract

• A 3D model is proposed for studying heat recycling in micro-light-emitting diode. • An annular thermocouple design is preferred under a heat source array. • Effect of external load can be mitigated through thermocouple parameter study. • A relatively high specific power output density of 40 µW/cm 2 .K 2 is predicted. Flexible thermoelectric generators have attracted a tremendous amount of attention as they enable waste heat recovery in a wide range of applications ranging from flexible displays to biomedical devices. However, design limitations still exist in flexible micro thermoelectric generators, in particular for applications with a heat source array such as in flexible micro-light-emitting diodes. Hence, this paper proposes a thin film flexible annular thermoelectric generator design that specifically aims for heat recycling in flexible micro-light-emitting diodes for the first time. In order to evaluate the generator performance, a three-dimensional steady-state model is constructed and a systematic study on design parameters is carried out based on the finite element method. The model first takes into account the heat transfer from a heat source array to the thermocouples. Seebeck, Peltier, as well as Joule heating effects, are then considered to evaluate the specific power density of the generator. Additionally, critical design parameters including thermocouple structural dimensions, thermocouple numbers, and substrate thickness have been thoroughly investigated. After model validation using experimental data from the literature, the results show that the relationship between the thermocouple design parameters and the output power is nonmonotonic and for each parameter, a certain optimum range can be found, in which the obtained output power does not vary significantly (within 95% of the maximum output power P max ). The thickness of the flexible substrate is inversely correlated to the output power. Moreover, the metallic thermocouples serve as a heat sink that helps to lower the temperature of the active region by ∼ 3 °C. Overall, the model predicts an impressive specific power density of ∼ 40 µW/cm 2 .K 2 , thus demonstrating the potential applicability of using flexible thermoelectric generators to recycle heat from micro-light-emitting diodes while providing a path to further improve the performance of flexible thermoelectric generators.