A family of two-dimensional semiconductors with transition metal Kagome lattice, large power factor and ultralow lattice thermal conductivity

Two-dimensional (2D) materials hold promising application potential in the future, so it is worthy to explore new 2D materials with fascinating structures and functionals. Here we predict a series of 15 stable 2D semiconductors, A(2)B(3)C(4) (A = K, Rb, Cs; B = Ni, Pd, Pt; C = S, Se), using first-principles calculations. The feasibility of mechanical exfoliation from their bulk phases has been confirmed by low cleavage energies. Interestingly, a perfect Kagome lattice formed by transition metal Ni/Pd/Pt atoms have been revealed in these fifteen monolayers. All A(2)B(3)C(4) monolayers exhibit indirect band features (1.82 eV to 2.76 eV). More encouragingly, and it is theoretically proven, based on constant relaxation time (CRT) approximation, that the A(2)B(3)C(4) monolayers possess large n-type power factors (1.77 similar to 2.10 x 10(3) mu Wm(-1)K(-2)), which is mainly contributed from the loop formed by the conduction band minima in different directions in energy band structure. Furthermore, ultralow lattice thermal conductivity (0.20 Wm(-1)K(-1) to 3.04 Wm(-1)K(-1)) has been confirmed in 2D A(2)B(3)C(4) at room temperature. Finally, the thermoelectric figure of merit (ZT) of A(2)B(3)C(4) monolayers has been evaluated based on CRT approximation. These interesting findings make A(2)B(3)C(4) monolayers promising candidates for low-dimensional electronic devices.