Anisotropic Electron and Phonon Transport Properties in Pnictogen Chalcohalides: PnSI (Pn = Sb, Bi)

Semiconducting heavy pnictogen-containing chalcohalides are gaining wide attention in thermoelectrics, ascribed to their inherently low thermal conductivity. The present work uses first-principles computations to report the excellent thermoelectric performance of weak van der Waals 1D PnSI (Pn = Sb, Bi) crystals. Considering the substantial anisotropy in the crystal structure, the direction-dependent electron and phonon transport properties are studied. At 500 K, SbSI and BiSI exhibit ultralow lattice thermal conductivities (k(L)) of 0.260 W m(-1 )K(-1 ) (0.428 W m(-1 ) K-1 ) and 0.182 W m(-1 ) K-1 (0.311 W m(-1 ) K-1 ) along the x-direction (y-direction). Simultaneously, the moderate power factors of 4.03 (12.19) and 4.43 (7.91) mW m(-1) K-2 are realized at specific hole concentrations under similar conditions. Eventually, the combination of ultralow k L and moderate power factor in the y-direction turned into excellent figure of merit, zT of 1.97 (1.78) and 2.71 (1.71) at 500 K with 7.0 x 10(19) (2.7 x 10(19)) and 4.4 x 10(19) (2.0 x 10(19)) cm(-3) carriers for p-type (n-type) SbSI and BiSI, respectively. Therefore, both chalcohalides can rival the existing mid-temperature thermoelectric materials.