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

•A new family of 2D semiconductors A2B3C4 (A = K, Rb, Cs; B = Ni, Pd, Pt; C = S, Se) has been predicted based on first-principles calculations.•A perfect Kagome lattice formed by transition metal atoms have been revealed in these fifteen monolayers.•The A2B3C4 monolayers have fairly large power factor due to the loop formed by the conduction band minima.•Ultralow thermal conductivities at room temperature have been confirmed in these monolayers.