GaInX₃ (X = S, Se, Te): Ultra-low thermal conductivity and excellent thermoelectric performance

Seeking intrinsically low thermal conductivity materials is a viable strategy in the pursuit of high-performance thermoelectric materials. Here, by using first-principles calculations and semiclassical Boltzmann transport theory, we systemically investigate the carrier transport and thermoelectric properties of monolayer Janus GaInX₃ (X = S, Se, Te). It is found that the lattice thermal conductivities can reach values as low as 3.07 W⋅m⁻¹⋅K⁻¹, 1.16 W⋅m⁻¹⋅K⁻¹ and 0.57 W⋅m⁻¹⋅K⁻¹ for GaInS₃, GaInSe₃, and GaInTe₃, respectively, at room temperature. This notably low thermal conductivity is attributed to strong acoustic-optical phonon coupling caused by the presence of low-frequency optical phonons in GaInX₃ materials. Furthermore, by integrating the characteristics of electronic and thermal transport, the dimensionless figure of merit ZT can reach maximum values of 0.95, 2.37, and 3.00 for GaInS₃, GaInSe₃, and GaInTe₃, respectively. Our results suggest that monolayer Janus GaInX₃ (X = S, Se, Te) is a promising candidate for thermoelectric and heat management applications.