Enhanced thermoelectric performance of graphene at room temperature by cut-off phonon frequency

Based on the full electron-phonon interactions and temperature-induced phonon renormalization, both electrical transport and thermal transport of graphene are systematically studied under different cut-off phonon frequencies. When the electron concentration is less than 1013 cm-2, the electrical transport properties increase with the cut-off phonon frequency. Otherwise, the electrical transport properties are nearly the same between 1013 cm-2 and 1015 cm-2, indicating that the contribution of cut-off phonon frequency decreases with the electron concentration. Considering the three-phonon, four-phonon, and phonon-electron scattering processes, the lattice thermal conductivity is studied, showing a value of 1357 W/mK at room temperature. At Van Hove singularity (5 x 1014 cm-2), the lattice thermal conductivity changes from 1357 W/mK to 557 W/mK. The effect of cut-off phonon frequency on thermal transport is nearly negligible. The electrical/phonon transport property accumulation concerning the mean free path shows the quantitative relationship between the mean free path and transport property, indicating a key mean free path of 186 nm. With a grain boundary of 186 nm, the ZT changes from 0.22 to 0.56 under a cut-off phonon frequency of 0 cm-1, while increasing from 0.64 to 1.23 under a cut-off phonon frequency of 30 cm-1. This work provides a strategy to enhance the thermoelectric property by regulating the electron-phonon coupling strength through cut-off phonon frequency.