This theoretical project aims at opening new ways to improve the thermoelectric efficiency of materials, by exploring the phonon drag effect, which arises from the momentum transfer (or drag) between the out-of-equilibrium phonon and electron populations, and which is responsible for the strong increase in Seebeck and Peltier coefficients of thermoelectric materials at low temperature. The concept we aim to explore is the use of substrate as an external phonon bath to provide additional out-of-equilibrium phonons, in order to enhance phonon drag effect and shift it to higher temperatures in the conducting channel. We aim to describe the coupled dynamics of electrons and phonons via an approach based on Density Functional Theory and on the solution of coupled Boltzmann transport equations for electrons and phonons which was recently developed in our group, and to extend it by including the effect of interface and substrate. The study will first focus on phonon drag in graphite, in link with our new collaboration with experimentalists in the framework of ANR project DragHunt. A successful internship can be followed by a PhD on related subject, financed by ANR DragHunt.