First-principles investigation of the significant anisotropy and ultrahigh thermoelectric efficiency of a novel two-dimensional Ga_(2)I_(2)S_(2) at room temperature

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 Ga2I2S2.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 Ga2I2S2 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 Sn2BiX(ZT∼1.70 and∼2.45 at 300 K)(2020 Nano Energy 67104283).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.