Backbone Effects on the Thermoelectric Properties of Ultra-Small Bandgap Conjugated Polymers.

Dexun Xie,Jing Xiao,Tongchao Liu,Guang Shao,Quanwei Li,Jinjia Xu

doi:10.3390/polym13152486

Dexun Xie, Jing Xiao + Show 4 more

Open Access

https://doi.org/10.3390/polym13152486

Copy DOI

Abstract

Conjugated polymers with narrower bandgaps usually induce higher carrier mobility, which is vital for the improved thermoelectric performance of polymeric materials. Herein, two indacenodithiophene (IDT) based donor–acceptor (D-A) conjugated polymers (PIDT-BBT and PIDTT-BBT) were designed and synthesized, both of which exhibited low-bandgaps. PIDTT-BBT showed a more planar backbone and carrier mobility that was two orders of magnitude higher (2.74 × 10−2 cm2V−1s−1) than that of PIDT-BBT (4.52 × 10−4 cm2V−1s−1). Both exhibited excellent thermoelectric performance after doping with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, where PIDTT-BBT exhibited a larger conductivity (0.181 S cm−1) and a higher power factor (1.861 μW m−1 K−2) due to its higher carrier mobility. The maximum power factor of PIDTT-BBT reached 4.04 μW m−1 K−2 at 382 K. It is believed that conjugated polymers with a low bandgap are promising in the field of organic thermoelectric materials.

Highlights

The emergence of thermoelectric materials has enabled the possibility of transforming waste heat into a usable form of energy, whereby thermal energy is directly converted into electrical energy [1,2,3]
The κ of organic thermoelectric materials (OTEs) is generally very low [12,13], and the power factor (PF = S2σ) is often used instead of the ZT value to evaluate the performance of OTEs [14]
The cyclic voltammetry (CV) was performed on a CHI 660E electrochemical workstation, and a platinum plate was used as a working electrode, Ag/Ag+ was used as a reference electrode, and a platinum wire was used as counter electrode in 0.1 M tetrabutylammonium hexafluorophosphate (Bu4NPF6) acetonitrile solution under a nitrogen atmosphere and scan rate of 50 mV s−1

Summary

Introduction

The emergence of thermoelectric materials has enabled the possibility of transforming waste heat into a usable form of energy, whereby thermal energy is directly converted into electrical energy [1,2,3]. OTEs have developed rapidly as new types of thermoelectric materials [6,7,8]. The performances of thermoelectric materials are typically evaluated by a dimensionless figure of merit (ZT = S2σ/κ), where S, σ, and κ are the Seebeck coefficient (μV K−1), electrical conductivity (S cm−1), and thermal conductivity (μW m−1K−1), respectively [9,10]. Thermal gravimetric analysis (TGA) was performed on TGA-55 (TA Instruments, New Castle, DE, USA) from room temperature to 600 °C under a nitrogen flow with a heating rate of 10 °C min−1. M3 was received from Derthon Optoelectronic Materials Science Technology Co., Ltd., (Shenzhen, China). All reagents were in analytic grade and were used without further treatment unless otherwise noted

Synthesis of Monomers and Polymers

Preparation of Polymer Films

Results and Discussion

Conclusions