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The enhancement of thermoelectric figure of merit ZT requires to eitherincrease the power factor or reduce the phonon conductance, or even both. Ingraphene, the high phonon thermal conductivity is the main factor limiting thethermoelectric conversion. The common strategy to enhance ZT is therefore tointroduce phonon scatterers to suppress the phonon conductance while retaininghigh electrical conductance and Seebeck coefficient. Although thermoelectricperformance is eventually enhanced, all studies based on this strategy show asignificant reduction of the electrical conductance, most often leading to alower electronic performance. In this study we show that appropriate sources ofdisorder, including isotopes and vacancies at lowest electron densitypositions, can be used as phonon scatterers to reduce the phonon conductance ingraphene ribbons without degrading the electrical conductance, particularly inthe low-energy region which is the most important range for device operation.By means of atomistic calculations using semi-empirical Tight-Binding and ForceConstant models in combination with Non-Equilibrium Green function formalism,we show that the natural electronic properties of graphene ribbons can be fullypreserved while their thermoelectric efficiency is strongly enhanced. Forribbons of width M = 5 dimer lines, room-temperature ZT is enhanced from lessthan 0.26 for defect-free ribbons to more than 2.5. This study is likely to setthe milestones of a new generation of nano-devices with dual electronic,thermoelectric functionalities.

Optimizing isotope and vacancy engineering in graphene ribbons to enhance the thermoelectric performance without degrading the electronic properties