Strong interlayer coupling in two-dimensional PbSe with high thermoelectric performance

It was generally assumed that weak van der Waals interactions exist between neighboring layers in the two-dimensional group-IV chalcogenides. Using PbSe as a prototypal example, however, we find additional strong coupling Pb-Pb layers, evidenced by detailed analysis of differential charge density. The resembles covalent-like bond and exhibits harmonicity around equilibrium distance, which can be fine tuned to obviously reduce phonon thermal conductivity but slightly change electronic transport PbSe. As consequence, maximum ZT value 2.5 realized at 900 K for p-type system. Our work offers an effective feasible design strategy enhance thermoelectric performance similar layered structures.