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

The thermoelectric performances of 1T-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 = S^2δ） were found in the P-type compounds; these values were -11.95 and -13.58 rnW K^- 2 m^- 1 for 1 T-ZrS2 and 1 T-ZrSe2 single layers, respectively. However, because of the Lorenz relation between the electrical conductivity （σ） and an electron＇s thermal conductivity （Ket） given by the Wiedemann-Franz law, the electronic figures of merit （Zest - PF. T/Kel） at 300 K were approximately 0.67 and 0.75 for the N- and P-type IT-ZrSe2, respectively. In addition, the lattice thermal conductivities （t%h） were calculated, giving values of -1.43 and -0.97 W K^-1 m^-1 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 figure-of-merits （ZT = ZesT/ （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.