Impurity Substitution Enhances Thermoelectric Figure of Merit in Zigzag Graphene Nanoribbons

Saeideh Ramezani Akbarabadi,Mojtaba Madadi Asl,Charles Rosenblatt

doi:10.1155/2021/8110754

Abstract

The thermoelectric properties of zigzag graphene nanoribbons (ZGNRs) are sensitive to chemical modification. In this study, we employed density functional theory (DFT) combined with the nonequilibrium green’s function (NEGF) formalism to investigate the thermoelectric properties of a ZGNR system by impurity substitution of single and double nitrogen (N) atoms into the edge of the nanoribbon. N-doping changes the electronic transmission probability near the Fermi energy and suppresses the phononic transmission. This results in a modified electrical conductance, thermal conductance, and thermopower. Ultimately, simultaneous increase of the thermopower and suppression of the electron and phonon contributions to the thermal conductance leads to the significant enhancement of the figure of merit in the perturbed (i.e., doped) system compared to the unperturbed (i.e., nondoped) system. Increasing the number of dopants not only changes the nature of transport and the sign of thermopower but also further suppresses the electron and phonon contributions to the thermal conductance, resulting in an enhanced thermoelectric figure of merit. Our results may be relevant for the development of ZGNR devices with enhanced thermoelectric efficiency.

Highlights

Low-dimensional thermoelectric devices can be potentially utilized for a wide range of applications, e.g., in cooling, heating, and energy harvesting systems [1, 2]
Limited efficiency of thermoelectric systems critically restricts the practical use of the thermoelectric effect at the nanoscale. e efficiency of a thermoelectric system can be expressed by the figure of merit, i.e., ZT S2TG/K. e figure of merit is shaped by the interplay between the thermopower or Seebeck coefficient (S), electrical conductance (G), thermal conductance (K), and temperature (T)
A comparison between the results obtained for the unperturbed system with those obtained from the perturbed system showed that the electrical conductance, electron and phonon contributions to the thermal conductance and thermopower are notably modified in the doped system resulting in an enhanced thermoelectric figure of merit

Summary

Introduction

Low-dimensional thermoelectric devices can be potentially utilized for a wide range of applications, e.g., in cooling, heating, and energy harvesting systems [1, 2]. A comparison between the results obtained for the unperturbed system with those obtained from the perturbed system showed that the electrical conductance, electron and phonon contributions to the thermal conductance and thermopower are notably modified in the doped system resulting in an enhanced thermoelectric figure of merit.

Results

Conclusion