Thermoelectric properties of monolayer MoSi2N4 and MoGe2N4 with large Seebeck coefficient and high carrier mobility: A first principles study

Thermoelectric technology can realize the direct conversion of heat energy and electricity, so the thermoelectric materials have been extensively studied in recent years. Inspired by the recent synthesis of high-quality monolayer MoSi 2 N 4 through chemical vapor deposition method, this work has systematically investigated the stability, electronic, thermoelectric and phonon transport properties for monolayer MoSi 2 N 4 and MoGe 2 N 4 using first principles calculations combined with Boltzmann transport theory. Results demonstrate that MoSi 2 N 4 and MoGe 2 N 4 monolayers exhibit large Seebeck coefficients, the maximum value is about 1600 ​μV ​K −1 for MoSi 2 N 4 and 1500 ​μV ​K −1 for MoGe 2 N 4 . High carrier mobilities are also predicted for both monolayer MoSi 2 N 4 and MoGe 2 N 4 , especially for MoGe 2 N 4 , the hole mobility reaches up to 1980.47 (2065.98) cm 2 V −1 s −1 in x ( y ) direction. In addition, monolayer MoGe 2 N 4 has a lattice thermal conductivity of 81 ​W ​m −1 ​K − 1 at 300 ​K, while MoSi 2 N 4 has a much higher lattice thermal conductivity of 260 ​W ​m − 1 ​K − 1 . Due to the high lattice thermal conductivity, the thermoelectric figure of merit ( ZT ) value of MoGe 2 N 4 and MoSi 2 N 4 are not too high. The maximum ZT value of monolayer MoGe 2 N 4 is 0.94 ​at 900 ​K, more than twice that of MoSi 2 N 4 because of the lower lattice thermal conductivity, which makes MoGe 2 N 4 more suitable for thermoelectric applications. Improved thermoelectric performance may be realized by reducing the lattice thermal conductivity. This work would provide supports and references for further theoretical and experimental research. Monolayer MoSi 2 N 4 and MoGe 2 N 4 have great potential application in thermoelectric field. MoSi 2 N 4 and MoGe 2 N 4 exhibit large Seebeck coefficient, high carrier mobility, and the maximum ZT values can reach 0.41 for MoSi 2 N 4 and 0.94 for MoGe 2 N 4 at 900 ​K. • Thermoelectric properties of monolayer MoSi 2 N 4 and MoGe 2 N 4 are fully investigated. • MoGe 2 N 4 shows large Seebeck coefficient, up to about 1500 ​μV ​K −1 . • MoGe 2 N 4 exhibits high hole carrier mobility of 2065.98 ​cm 2 ​V −1 ​s −1 in y direction. • Lattice thermal conductivity of MoGe 2 N 4 is 81 ​W ​m − 1 ​K − 1 at 300 ​K. • Maximum ZT value of monolayer MoGe 2 N 4 is 0.94 ​at 900 ​K.