Materials selection rules for optimum power factor in 2-dimensional thermoelectrics

Thermoelectrics (TE) can improve the efficiency of power sources to meet ever-growing energy demand by converting waste heat into electricity. With the advent of new 2D materials and the knowledge of their material properties, the ability of these materials for future TE use need to be studied. Studies have predicted the stability of around 2000 van der Waals materials that can be exfoliated into 2D atomic films. Here, the distinct features of 2D materials like effective mass, density of states, and electron-phonon scattering deformation potentials are used to formulate simple material selection rules that can optimize TE power factor. These parameters are widely available in material databases or computationally inexpensive to calculate. Our simulations show that when inelastic scattering with optical phonons is dominant in a material, the TE power factor is highest with phonon energy of 5 kT. Further enhancement is possible with larger height in the step-like 2D density of states, lower effective mass, and higher degeneracy for the conduction band valley that participate in the transport. Employing these material selection rules help in identifying future thermoelectric materials that can have applications in thermal harvesting, thermal sensors, and electronic cooling.