Tuning Phononic and Electronic Contributions of Thermoelectric in defected S-Shape Graphene Nanoribbons

TL;DR

This study explores how defect engineering in S-shape graphene nanoribbons can significantly enhance thermoelectric efficiency by tuning electronic and phononic transport properties, with potential for practical waste heat recovery.

Contribution

It demonstrates that vacancy engineering and device size control can markedly improve the thermoelectric figure of merit in graphene nanoribbons.

Findings

Maximum ZT achieved with double vacancies.

Lengthening reduces phononic thermal conductance.

Single vacancies better distinguish electronic conductance behaviors.

Abstract

Thermoelectrics as a way to use waste heat, is essential in electronic industries, but its low performance at operational temperatures makes it inappropriate in practical applications. Tailoring graphene can change its properties. In this work, we are interested in studying the transport properties of S-shape graphene structures with the single vacancy (SV) and double vacancy (DV) models. The structures are composed of a chiral part, which is an armchair graphene nanoribbon, and two zigzag graphene ribbons. We investigate the changes in the figure of merit by means of the Seebeck coefficient, electronic conductance, and electronic and phononic conductances with the vacancies in different device sizes. The transport properties of the system are studied by using the non-equilibrium Greens function method, so that the related Hamiltonians (dynamical matrices) are obtained from the tight-binding (force constant) model. The maximum figure of merit (ZT) obtains for the DVs in all lengths. Physical properties of such a system can be tuned by controlling various parameters such as the location and the type of the defects, and the device size. Our findings show that lengthening the structure can reduce phononic contribution, and single vacancies than double vacancies can better distinguish between electronic thermal conductance behavior and electronic conductance one. Namely, vacancy engineering can significantly increase thermoelectric performance. In the large devices, the SVs can increase the ZT up to 2.5 times.