First-principles investigation of the significant anisotropy and ultrahigh thermoelectric efficiency of a novel two-dimensional Ga2I2S2 at room temperature

Abstract Two-dimensional (2D) thermoelectric (TE) materials have been widely developed; however, some 2D materials exhibit isotropic phonon, electron transport properties, and poor TE performance, which limit their application scope. Thus, exploring excellent anisotropic and ultrahigh-performance TE materials are very warranted. Herein, we first investigate the phonon thermal and TE properties of a novel 2D-connectivity ternary compound named Ga 2 I 2 S 2 . This paper comprehensively studies the phonon dispersion, phonon anharmonicity, lattice thermal conductivity, electronic structure, carrier mobility, Seebeck coefficient, electrical conductivity, and the dimensionless figure of merit ( ZT ) versus carrier concentration for 2D Ga 2 I 2 S 2 . We conclude that the in-plane lattice thermal conductivities of Ga 2 I 2 S 2 at room temperature (300 K) are found to be 1.55 W mK −1 in the X -axis direction ( xx -direction) and 3.82 W mK −1 in the Y -axis direction ( yy -direction), which means its anisotropy ratio reaches 1.46. Simultaneously, the TE performance of p-type and n-type doping 2D Ga 2 I 2 S 2 also shows significant anisotropy, giving rise to the ZT peak values of p-type doping in xx - and yy -directions being 0.81 and 1.99, respectively, and those of n-type doping reach ultrahigh values of 7.12 and 2.89 at 300 K, which are obviously higher than the reported values for p-type and n-type doping ternary compound Sn 2 BiX ( ZT ∼ 1.70 and ∼2.45 at 300 K) (2020 Nano Energy 67 104283). This work demonstrates that 2D Ga 2 I 2 S 2 has high anisotropic TE conversion efficiency and can also be used as a new potential room-temperature TE material.