X2Pd3Se4 (X = K, Rb, Cs): Unexplored 2D semiconductors with high n-type transport performance

Two-dimensional (2D) materials have attracted much interest because of their special morphology and novel physical properties. In this work, we proposed three unexplored 2D materials, X2Pd3Se4 (X = K, Rb, Cs), and further investigated their stability, electronic and thermoelectric transport properties. We revealed that these materials are indirect semiconductors with band-gaps of 1.74 similar to 1.95 eV, and show "multi-valleys" convergence near conduction band minimums. Besides, the monolayers also possess high electron mobility of 10(3) similar to 10(4) cm2 center dot V-1 center dot s(-1), leading to high conductivity (10(6) similar to 10(7) Omega(-1)m(-1)), as well as high thermoelectric power factor (similar to 10(2) mW center dot K-2 center dot m(-1)). Also, because of the high group velocity and low phonon scattering rate, they also show moderate lattice thermal conductivity of 19.21 similar to 75.78 W/mK at 300 K. Nevertheless, they still deliver high thermoelectric figure of merit of 0.20 similar to 1.04 at 300 K, and increase further to 0.67 similar to 1.94 at 700 K, suggesting that they have potential applications in the field of low-medium temperature thermoelectric devices.