A comprehensive comparison of micro heterojunction thermoelectric generators based on a carrier transport model

To be a crucial aspect in the performance of thermoelectric generators, carrier transport in thermoelectric materials cannot be captured by existing multiphysics models. In this work, a carrier transport model for heterojunction thermoelectric generators (TEG) is developed with the drift-diffusion equation comprehensively considering the effect of carrier mobility on the current density. Subsequently, based on the concept of inverse- and homo-heterojunction, three micro TEG are designed considering Si and Si_0.7Ge_0.3 bases with the doped boron and arsenic and compared with the original design for revealing the effects of load resistance and temperature difference on the thermoelectric performance. It has been demonstrated that for homo-heterojunction, the thermoelectric power and conversion efficiency are significantly improved at hot temperatures from 600 to 1000 K, with a maximum improvement of 18.09% compared to the conventional TEG. For inverse-heterojunction, the optimal temperature of the thermoelectric performance is 1100–1300 K, and its efficiency is 23.50% higher than that of the conventional TEG. Both the doping impurity ionization and intrinsic carrier excitation contribute to a high density of majority carriers and are responsible for the better performance of homo-heterojunction at low working temperatures. For inverse-heterojunction, a high working temperature can significantly promote the excitation of minority carriers because of the built-in electric field and leads to better performance. Finally, we propose a novel heterojunction by combining both homo- and inverse-heterojunction which can improve thermoelectric efficiency by up to 27.72%.