Ultrahigh power factors in P-type 1T-ZrX2（X=S, Se）single layers

The thermoelectric performances of 1 T-ZrX2（X=S and Se） single layers were investigated using a combination of density functional calculations and semi-classical Boltzmann transport theory. Because of the high hole mobilities at 300 K, ultrahigh power factors（PF = S2σ） were found in the P-type compounds;these values were 11.95 and 13.58 mWK 2 m1 for 1T-ZrS2 and 1T-ZrSe2 single layers, respectively.However, because of the Lorenz relation between the electrical conductivity（σ） and an electron’s thermal conductivity(Kel) given by the Wiedemann-Franz law, the electronic figures of merit(ZelT = PF T/Kel) at 300 K were approximately 0.67 and 0.75 for the N-and P-type 1T-ZrSe2, respectively. In addition, the lattice thermal conductivities(KPh) were calculated, giving values of 1.43 and 0.97 W K 1 m1 for 1T-ZrS2 and 1T-ZrSe2 single layers, respectively. Therefore, because of the lower KPh/Kel ratio, the P-type 1T-ZrX2 single layers possess higher fngure-of-merits(ZT = ZelT/(1+(KPh/Kel)) than their counterparts. This signifies that the P-type samples demonstrate better thermoelectric performance than the N-type ones. The thermoelectric properties of metastable 2H-ZrX2（X = S and Se） single layers were also investigated.