Ultralow lattice thermal conductivity in monolayer C3N as compared to graphene

Using density functional theory and the Boltzmann transport equation for phonons, we demonstrate that the thermal conductivity is massively reduced in monolayer CN as compared to isostructural graphene. We show that larger phase space for three-phonon scattering processes is available in monolayer CN, which results in much shorter phonon life-times. Although both materials are characterized by sp hybridisation, anharmonicity effects are found to be enhanced for the C-N and C-C bonds in monolayer CN, reflected by a Grüneisen parameter of -8.5 as compared to -2.2 in graphene. The combination of these properties with the fact that monolayer CN is organic, non-toxic, and built of earth abundant elements gives rise to great potential in thermoelectric applications.