Exceptional thermoelectric performance of two-dimensional carbon phosphide originated from high anisotropy

Two-dimensional (2D) materials have been extensively explored in the applications of thermoelectrics, owing to their unique quantum confinement effect. Herein, using ab initio density functional theory and Boltzmann transport theory, we investigate the thermoelectric properties for the semiconducting α and β phases of 2D carbon phosphide (CP), which have been experimentally synthesized. Our results show that their puckered geometry with ridges lead to dramatic anisotropy in both phonon and electron transport behaviors. As a result of the orthogonality between the prominent electrical and thermal conducting directions, outstanding thermoelectric performance is obtained along the armchair direction in both CP allotropes. In particular, owing to the stronger anharmonic phonon scattering rates, degenerated valleys at the electronic band edges, and more pronounced anisotropy, α-CP exhibits higher power factor and lower thermal conductivity in comparison to β-CP along the thermoelectric-preferred direction. Finally, the maximum figure of merit (ZT) values for p-type doping reach 8.91 in α-CP and 3.09 in β-CP, indicating that both the 2D CP allotropes are highly promising candidates for thermoelectric materials. Our results provide new insights into the exploration of thermoelectric materials and optimization of their performance.