Two-dimensional (2D) semiconductor MoSi2N4 is a potential candidate for thermoelectric materials due to its high Seebeck coefficient. However, its high lattice thermal conductivity limits its applications in the field of thermoelectric. Here, we constructed an unsymmetrical 2D Janus semiconductor XMoSiN2(X=S, Se, Te) based on MoSi2N4 to significantly reduce the lattice thermal conductivity to only one-sixth that of MoSi2N4 at 300 K. We found that XMoSiN2 had an ultra-high carrier mobility up to 4640 cm2V-1s-1 leading to a metal-like electrical conductivity. Meanwhile, XMoSiN2 reserved the high Seebeck coefficient of MoSi2N4. The lower lattice thermal conductivity and metal-like electrical conductivity resulted in excellent thermoelectric performance. TeMoSiN2 possessed a record-high ZT value of 3.57 at 900 K. We believed that other materials with a similar structure to XMoSiN2 can also be potential candidates for high-performance thermoelectric materials. Our work provides valuable insights into designing novel high-performance thermoelectric materials.

Two-dimensional (2D) of transition metal dichalcogenides (TMDCs) are potential candidates for thermoelectric (TE) applications due to their unique structural properties. In this paper, we constructed an 2D monolayer TMDCs semiconductor γ-PbSn2(X=S, Se, Te) and first-principles calculations and Boltzmann transport theory are used to study the thermoelectric performance. We found that γ-PbSnX2 had an ultra-high carrier mobility up to 4.04×103 cm2V−1s−1 leading to a metal-like electrical conductivity. Meanwhile, γ-PbSnX2 both have high Seebeck coefficients, resulting in high power-factors, and also shows intrinsic low lattice thermal conductivity of 6-8 W/mK at room temperature. The lower lattice thermal conductivity and high power-factors resulted in excellent thermoelectric performance. The high ZT values of γ-PbSnS2 and γ-PbSnSe2 were as high as 2.65 and 2.96 at 900 K, respectively. The result suggests that the monolayer γ-PbSnX2 are better candidates for excellent thermoelectric performance.