Conformation and Quantum-Interference-Enhanced Thermoelectric Properties of Diphenyl Diketopyrrolopyrrole Derivatives.

Renad Almughathawi,Zitong Liu,Qingqing Wu,Songjun Hou,Colin Lambert,Wenjing Hong

doi:10.1021/acssensors.0c02043

Abstract

Manipulating the connectivity of external electrodes to central rings of carbon-based molecules in single molecule junctions is an effective route to tune their thermoelectrical properties. Here we investigate the connectivity dependence of the thermoelectric properties of a series of thiophene-diketopyrrolopyrrole (DPP) derivative molecules using density functional theory and tight-binding modeling, combined with quantum transport theory. We find a significant dependence of electrical conductance on the connectivity of the two thiophene rings attached to the DPP core. Interestingly, for connectivities corresponding to constructive quantum interference (CQI), different isomers obtained by rotating the thiophene rings possess the same electrical conductance while those corresponding to destructive quantum interference (DQI) show huge conductance variations upon ring rotation. Furthermore, we find that DQI connectivity leads to enhanced Seebeck coefficients, which can reach 500–700 μV/K. After including the contribution to the thermal conductance from phonons, the full figure of merit (ZT) for the CQI molecules could reach 1.5 at room temperature and it would further increase to 2 when temperature elevates to 400 K. Finally, we demonstrate that doping with tetracyanoquinodimethane can change the sign of the Seebeck coefficients by forming a charge-transfer system with the DPP.

Highlights

Manipulating the connectivity of external electrodes to central rings of carbon-based molecules in single molecule junctions is an effective route to tune their thermoelectrical properties
To reveal the effect of these features on transport properties, the a and b contact geometries between electrodes and molecules were fixed, and the b geometry is obtained by rotating the linkers and the electrodes of a relative to the DPP core by 180° around the molecule axis
On the basis of density functional theory and the quantum transport theory, the electron transport properties have been investigated for thiophene-DPP derivatives

Summary

Introduction

Manipulating the connectivity of external electrodes to central rings of carbon-based molecules in single molecule junctions is an effective route to tune their thermoelectrical properties. The foundational experiments of Nongjian Tao[1] and subsequent work exploring charge transport through single molecules connected to two metallic electrodes[2−4] have led to the design of molecular-scale components such as switches,[4−6] rectifiers,[7] and highly conjugated molecular wires.[8] A more recent goal of this research is the design of thermoelectric materials[9] or devices[10] based on single molecules or self-assembled monolayers,[11] which can convert heat into electricity and contribute to the global challenge of green energy harvesting Such organic materials and devices are potentially lightweight, flexible, environmentally friendly and cost-effective.[12,13] Diphenyl diketopyrrolopyrrole discovered by Farnum et al in 197414 has unique properties, such as good conjugation, strong electron-withdrawing ability, thermal stability and photostability, and high-fluorescence quantum efficiency.[15,16] It is widely used as a building block for organic molecules, both for fundamental studies of electronic properties and for industrial applications as dyes and pigments.[15,17]. ACS Sensors pubs.acs.org/acssensors (TCNQ), which is a well-known electron acceptor,[20,21] we found that TCNQ can be used to change the signs of the Seebeck coefficients

Objectives

Methods

Results

Conclusion