Thermoelectric Properties Of The New Two-dimensional Carbon Structure Nanoribbons

The thermoelectric materials have been gaining more and more attention,as one of the effective ways to alleviate the worsening environmental and energy problems.Lowdimensional carbon structure thermoelectric materials,as a new thermoelectric material,have gradually become one of the important frontier researches in the field of thermoelectricity,with broad applications for flexible,low-cost power devices and self-powered sensors.In recent years,much more efforts have been paid to these related researches,and their key performance indicators have been continuously improved.In this thesis,we studied the thermoelectric transport properties of the twin graphene nanoribbons based on the first principles combined with the non-equilibrium Green's function method.The main content includes two parts:1)The effects of different edges on the thermoelectric performance of twin graphene nanoribbons have been studied.The results show that the thermoelectric performance with armchair edge is better than a zigzag one because of its larger power factor.At room temperature,the ZT value of 0.6 can be observed in armchair twin graphene nanoribbons.Moreover,the ZT value can be further enhanced to 1.1 by introducing defects,which is mainly due to strong phonon scattering and phonon localization.2)The effect of strain on the thermoelectric properties of twin graphene nanoribbons at room temperature have been investigated.The results show that the strains will reduce the thermoelectric properties of armchair twin graphene nanoribbon;for the armchair twin graphene nanoribbon with three defects,the thermoelectric properties are not significantly decreased by the strain,which even improved the thermoelectric performance sometimes.Specifically,when the compressive strain is-6% and-9%,the thermoelectric performance can be enhanced,and the maximum ZT value can reach 0.9.This is mainly because the total thermal conductance gets reduced,but the power factor hasn't.In addition,when the tensile strain is 9%,the armchair twin graphene nanoribbons become conductor.