Enhanced thermoelectric properties of electropolymerized poly (3,4-ethylenedioxythiophene) thin films by optimizing electrolyte temperature and thermal annealing temperature

doi:10.1016/j.orgel.2018.01.028

Organic Electronics

Volume 55, April 2018, Pages 112-116

https://doi.org/10.1016/j.orgel.2018.01.028 Get rights and content

Highlights

•
Effect of electrolyte temperature on doped PEDOT thin films were investigated.
•
Effect of thermal annealing temperature on PEDOT thin films were investigated.
•
CV analysis was implemented with different electrolyte temperatures.
•
Charge-trapping related defects decreased with increased annealing temperature.
•
Moderate annealing treatment can improve the thermoelectric performance.

Abstract

Effects of electrolyte temperature and annealing temperature on ClO₄-doped poly (3,4-ethylenedioxythiophene) (PEDOT) thin films were investigated. Prior to the electropolymerization of the thin films, we performed cyclic voltammetry (CV) analysis while changing the electrolyte temperature between 0 °C and 60 °C. The current density increased with increasing electrolyte temperature, and the onset oxidation potential was mostly constant at approximately 1.3 V. From the CV analysis, we determined the electropolymerization condition of electrolyte temperature 50 °C and applied potential 1.52 V. Following the electropolymerization of the PEDOT thin films, thermal annealing was implemented in the range 80 °C to 140 °C with a mixture of argon (95%) and hydrogen (5%) gases at atmospheric pressure. ESR analysis showed that the intensity of the ESR spectra decreased with increased annealing temperature because of the decrease of charge-trapping related defects. In the annealed samples, the electrical conductivity of PEDOT thin films increased and the Seebeck coefficient decreased with increased annealing temperature; this was supported by the ESR analysis results. As a result, PEDOT thin films annealed at 80 °C and 100 °C exhibited a maximum power factor of 0.8 μW/(m·K²). Therefore, we conclude that the moderate annealing treatment enabled the thermoelectric performance to improve.

Introduction

Poly(3,4-ethylenedioxythiophene) (PEDOT) is a conjugated polymer that is widely used in organic electronics. The characteristics of PEDOT, including high electrical conductivity by doping as well as high stability, make it highly attractive for electronic devices, for example thermoelectric devices [[1], [2], [3]], solar cells [4,5], field-effect transistors [6,7], and electroluminescent devices [8,9]. In particular, the interest in organic thermoelectric devices has been growing since the internet of things (IoT) has begun to be widely spread by using wireless sensor nodes that are powered from energy harvesting techniques [10]. The organic thermoelectric devices harvest electricity from waste heat below 200 °C, which occupies a large portion of waste heat generated from households or even human bodies, by utilizing the diffusion of charge carriers induced by the temperature gradient.

PEDOT thin films are highly useful for organic thermoelectric devices, but a pure form of PEDOT is not soluble in common solvents, and is infusible at reasonable temperatures [[11], [12], [13]]. To solve these problems, there are two main approaches. The first is to synthesize the PEDOT in the presence of water-soluble poly(styrenesulfonic acid) (PSS), working as a charge-balancing dopant [14,15], followed by printing (spin coating and drop casting) on a substrate. The second is to form PEDOT by electropolymerization from 3,4-ethylenedioxythiophene (EDOT) with dopant in common solvent [16,17].

For the fabrication of PEDOT thin films as thermoelectric materials, spin-coated or drop-cast PEDOT:PSS thin films have been extensively studied, and have exhibited high thermoelectric performance [[18], [19], [20]]. On the other hand, the electropolymerization method has excellent potential for reducing the manufacturing costs because the polymerization and deposition can be carried out in a single step. However, to the best of our knowledge, there have been few reports presenting the PEDOT thermoelectric thin films by electropolymerization [[21], [22], [23]]. This is because the thermoelectric performance of PEDOT thin films fabricated by electropolymerization is lower than that of PEDOT:PSS thin films fabricated by printing methods.

Therefore, to increase the thermoelectric performance of the electropolymerized PEDOT thin films, it is necessary to study and optimize the deposition conditions. Zhang et al. prepared PEDOT thin films via galvanostatic polymerization of 3,4-ethylenedioxythiophene in propylene carbonate containing sulfated poly(bhydroxyethers) [21]. In our previous study, PEDOT films were synthesized via potentiostatic polymerization with several counter ions (ClO₄, PF₆, and BF₄) [23]. In the electrodeposition of inorganic materials, it is known that inorganic film properties can be controlled by the electrolyte temperature [24,25], but there have been few reports presenting the PEODT thin films by electropolymerization with different electrolyte temperatures [21].

In this work, we prepared electrolytes including EDOT and ClO₄ as a dopant with different electrolyte temperatures, and investigated the redox behavior of PEDOT by cyclic voltammetry (CV). The PEDOT thin films were electropolymerized on the basis of the CV analysis results. Following the film preparation, thermal annealing was carried out to further increase the thermoelectric performance [[26], [27], [28], [29]]. Finally, we explored the relationship between the film properties and the annealing temperature.

Section snippets

Experimental procedure

In order to efficiently deposit PEDOT thin films, we first investigated the optimum oxidation potential and response current by CV analysis with different electrolyte temperatures using an automatic polarization system (HSV-110, Hokuto Denko). In this analysis, 0.1 M EDOT and 0.01 M dopant (LiClO₄) were dissolved in an organic solvent (acetonitrile, 100 ml), and the electrolyte temperature was varied from 0 °C to 60 °C using an L-shaped heater (B-74-KH14075LA, YAMAMOTO-MS). A standard

Cyclic voltammetry at different electrolyte temperatures

To investigate the redox behavior of PEDOT at various electrolyte temperatures, we performed CV analysis, as shown in Fig. 1. In this study, only the first cycles for each electrolyte temperature were presented because it is necessary to examine the differences of redox behavior at each electrolyte temperature. The CVs of all the electrolyte temperatures show irreversible oxidation peaks, and a reductive process occurred as the potential was decreased. It can be observed that the onset

Conclusions

To investigate the effects of electrolyte temperature and annealing temperature on the characteristics of PEDOT thin films with ClO₄ dopant, we first performed CV analysis. The current density increased with increasing the electrolyte temperature, and the E_onset was mostly constant at approximately 1.3 V. Thus, we determined the electropolymerization condition at an electrolyte temperature of 50 °C and potential of 1.52 V. The completed PEDOT thin films were thermally annealed with the range

Acknowledgements

This study was partly supported by JSPS KAKENHI Grant Number 16H04282 and a grant of research and education at the Engineering School of Tokai University. The authors acknowledge K. Kato at Lintec Ltd. for valuable discussion.

References (40)

S.H. Eom et al.
Org. Electron.
(2009)
W. Hong et al.
Electrochem. Commun.
(2008)
H. Rost et al.
Synth. Met.
(2004)
S. Sakamoto et al.
Chem. Phys. Lett.
(2005)
D. Champier
Energy Convers. Manage
(2017)
A.M. Nardes et al.
Org. Electron.
(2008)
F. Jonas et al.
Electrochim. Acta
(1994)
S.K.M. Jonsson et al.
Synth. Met.
(2003)
J. Hwang et al.
Org. Electron.
(2006)
X. Du et al.
Electrochim. Acta
(2003)

L. Zhang et al.

J. Polym. Sci. Part B Polym. Phys.

(2017)

L. Jinlong et al.

J. Solid State Chem.

(2016)

Z. Zainal et al.

Mater. Lett.

(2004)

Y. Kim et al.

Org. Electron.

(2009)

Z. Xiong et al.

Org. Electron.

(2012)

N. Hatsuta et al.

J. Alloys Compd.

(2016)

M. Ouyang et al.

J. Electroanal. Chem.

(2011)

V. Lyutov et al.

Electrochim. Acta

(2014)

C. Kvarnström et al.

Electrochim. Acta

(1999)

P. Damlin et al.

J. Electroanal. Chem.

(2004)

Cited by (17)

Electro-templating of prussian blue nanoparticles in PEDOT:PSS and soluble silkworm protein for hydrogen peroxide sensing
2023, Talanta
Citation Excerpt :
However, as known, EDOT is not soluble in water. Therefore, solvents such as acetonitrile [53–56], methanol and water, ethanol [32] based mixtures, dimethylsulfoxide (DMSO), or dichloromethane [57,58] have been widely used to process PEDOT-based electroactive interfaces. Undoubtedly, resulting composites successfully serve their target purpose; these solvents are toxic to environmental and medical health.
Herein, we demonstrate a high-accuracy H₂O₂ selective organic-inorganic 3D-heterointerface based on catalytically in-situ reduced Prussian-blue nanoparticles (PBNPs), Poly (3,4-ethylene dioxythiophene):poly (styrene sulfonic acid) (PEDOT:PSS) and water-soluble Silkworm protein (SWp). PBNPs were immobilized on an indium tin oxide-coated glass (ITO) electrode through the electrochemical polymerization process of PEDOT:PSS and the yielding intertwining composite was templated by the use of SWp, simultaneously. Since PSS and SWp act as poly-anionic and poly-cationic charge compensating elements, the sensing system's potential cycling and amperometric response stability have been significantly enhanced thanks to the arising physical blockage effect. Constructed sensing system showed a substantially high sensitivity (1031.7 μA mM⁻¹ cm⁻²) and a low limit of detection value (LOD, 0.29 μM) between 1 and 130 μM H₂O₂. Eliminating the possible signal disruptions by common anion and cations in tap water, the (PEDOT:PSS:PB):SWp interface successfully selected H₂O₂ between the concentration of 10–40 μM with high recovery and relatively low RSDs oscillating between 94.2-110.9% and 2.9–5.1%, respectively. It is thought that the proposed heterointerface can be used in the field of sensor, biosensor and fuel cell systems run by H₂O₂ assay based on 3D scaffold-templated conductive polymer-PBNPs network.
The stability of poly (3, 4-ethylenedioxythiophene) based on electrochemical polymerization and photoelectro-corrosion conditions
2022, Polymer Degradation and Stability
Citation Excerpt :
The surface of PEDOT prepared in PD was uniform and smooth, while the distribution was uneven in GS and PS [7]. The polymerization current was increased with the increasing of polymerization temperature [23]. In addition, the growth of PEDOT was affected by the concentration of polymerization electrolyte, which was linear growth at NaCl concentration of 10 mM and exponential growth at 100 mM [24].
The stability of poly (3, 4-ethylenedioxythiophene) (PEDOT) was studied based on the photoelectro-corrosion. The type of electrolyte can affect morphology, crystallinity, crystal grain size, and hydrophilicity of PEDOT. The polymerization time was shortened and the crystal grain size of PEDOT was increased, and the corresponding PEDOT dissolution was increased under photoelectro-corrosion, along with the order of in the electrolyte containing Cl⁻, SO₄²⁻, PO₄³⁻, and ClO₄⁻. The improved stability was attributed to increased crystallinity, small crystal grain size, and decreased hydrophilicity of PEDOT. The peroxidation of PEDOT caused partial deformation and more dissolution. The increase of applied potential and photoelectro-corrosion temperature led to the increase of PEDOT dissolution. Twenty kinds of dissolution products were detected under photoelectro-corrosion of PEDOT. Some dissolution products with corresponding m/z of 262, 284, 325, 561, 645, 704, and 713 were found to have some toxicology concerns. This means it is important to consider such degradation products in terms of their generation, potential release, and possible biological contact.
Enzyme-free detection of hydrogen peroxide with a hybrid transducing system based on sodium carboxymethyl cellulose, poly(3,4-ethylenedioxythiophene) and prussian blue nanoparticles
2021, Analytica Chimica Acta
Citation Excerpt :
As is known, the 3,4-Ethylenedioxythiophene (EDOT) monomer is insoluble in water. Therefore, solvents such as acetonitrile [44–47], protic solvent mixture composed of methanol and water, ethanol [21], dimethylsulfoxide (DMSO) [48], dichloromethane [49] are frequently used in the synthesis of PEDOT-based electrochemical interfaces. Although electropolymerized PEDOT interfaces prepared in such aprotic solvents show high electrochemical performance, these solvents are harmful to human health and the environment.
Herein, we report a two-layered hybrid catalytic interface composed of carboxymethyl cellulose (CMC), poly (3,4-ethylene dioxythiophene) (PEDOT), Prussian blue (PB) nanoparticles and Nickel-Hexacyanoferrate (Ni-HCF) layer for the enzyme-free detection of hydrogen peroxide (H₂O₂). Whereas the first layer, CMC:PEDOT:PB, is responsible for generating amperometric signals toward H₂O₂, Ni-HCF on CMC:PEDOT:PB layer is playing an active role as an operational stability-enhancer. In the study, where the systematic optimization of the sensor electrode is presented using cyclic voltammetry (CV), amperometry and electrochemical impedance spectroscopy (EIS) technique, the physical and chemical properties of the hybrid composite systems constructed is also supported by scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) techniques. The amperometric signal generation of the H₂O₂ sensor was linear between 1 and 100 μM (R² = 0.999) with a sensitivity of 416.11 μA mM⁻¹cm⁻², providing a limit of detection (LOD) of 0.33 μM. The sensing system, which was not affected by the various interfering molecules, creates a successful sensor platform for H₂O₂ measurements in tap water with a high recovery value between 94.0% and 110.5% and relatively small RSD in the range of 0.4–5.2%.
Optimizing the thermoelectric performance of PEDOTs
2021, Advanced PEDOT Thermoelectric Materials
PEDOTs have recently emerged as a promising class of materials for thermoelectric (TE) energy harvesting, attributing to the prominent merits of high electrical conductivity, low thermal conductivity, good stability as well as commercial availability. Simultaneous optimization of the electrical conductivity, Seebeck coefficient and thermal conductivity is inherently challenging as these three performance parameters depend upon one another. Thus, it is of fundamental and practical significance to develop novel strategies for the regulation of TE performance for waste heat utilization and conversion. Posttreatment of PEDOTs by secondary dopants including polar organic solvents, inorganic salts, nonionic surfactant polymers, acids, or alkalis, reducing reagents was considered one of the most commonly adoptive approaches. The enhancement of the crystallinity of the ordered domains in PEDOTs contributed to the compromise between electrical conductivity and Seebeck coefficient. Numerous efforts have been taken in the controlled doping of PEDOTs to enhance the electrical conductivity and Seebeck coefficient simultaneously, achieving the state-of-the-art TE performance of PEDOTs (ZT∼0.25) upon doping in the presence of tosylate counterions following an in situ chemical or vapor-phase polymerization. Additionally, low dimensionality, phonon scattering, and molecular conformation are essential for excellent TE materials. To the best of our knowledge, PEDOT:PSS exhibited a record ZT value of 0.75 at room temperature via ion accumulation of an ionic liquid on the polymer surface, which is comparable to that of conventional inorganic TE materials such as bismuth telluride. This chapter systematically introduces effective approaches including doping/undoping, low dimensionality, crystal structure, phonon scattering, molecular conformation, and posttreatment to optimize TE performance of PEDOTs.
Freestanding bilayers of drop-cast single-walled carbon nanotubes and electropolymerized poly(3,4-ethylenedioxythiophene) for thermoelectric energy harvesting
2020, Organic Electronics
Citation Excerpt :
There are no results available for the PEDOT layer obtained using water/methanol because its very fragile structure prevents the measurement of these properties. As shown in Fig. 8(a), the Seebeck coefficients of the PEDOT layer obtained using acetonitrile and the SWCNT layer were 8.4 and 61.4 μV/K, respectively, which were similar to the standard value of each material [35,39,40]. The Seebeck coefficient of Sample A (28.8 μV/K) was 53% lower than that of the SWCNT layer and 3.4 times higher than that of the PEDOT layer obtained using acetonitrile.
Poly(3,4-ethylenedioxythiophene) (PEDOT) and single-walled carbon nanotubes (SWCNTs) are promising thermoelectric materials that exhibit flexibility and high performance. To realize improved structural and thermoelectric properties, we fabricated PEDOT/SWCNT bilayers consisting of drop-cast SWCNTs and electropolymerized PEDOT. We prepared two types of PEDOT layers using electrolyte solvents of water/methanol (Sample A) and acetonitrile (Sample B). Sample B achieved a flexible freestanding state, whereas Sample A was broken with part of the sample remaining on the substrate. Scanning electron microscopy revealed that the PEDOT layer in Sample A filled the gaps between the SWCNT bundles. The PEDOT layer in Sample B consisted of chain-like structures that mostly covered the surface of the SWCNT layer, which were speculated to increase the strength of the freestanding state. The structural properties of the bilayers were examined using Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Although slight structural differences were observed between Samples A and B, both samples exhibited the characteristics of PEDOT and SWCNTs. Measurement of the thermoelectric properties near 300 K afforded power factors of 12.5 and 13.9 μW/(m·K²) for Samples A and B, respectively. Therefore, we demonstrated the successful fabrication of freestanding PEDOT/SWCNT bilayers (Sample B) with relatively high thermoelectric performance.
Effect of backbone structure on the thermoelectric performance of indacenodithiophene-based conjugated polymers
2019, Reactive and Functional Polymers
Citation Excerpt :
Therefore, exploring the relationship between the TE properties and the polymer structure is of great significance for the design of new, high-performance organic TE materials in the future. Indacenodithiophene (IDT) unit has rigid and planar backbone, which can strengthen intermolecular interactions and facilitate high charge carrier mobilities [33–35]. Therefore, IDT unit are usually used as donor unit in building donor-acceptor (D-A) polymers, and the resulting materials exhibit high charge mobilities, good power conversion efficiencies and strong light absorption in organic field-effect transistor (OFETs) and organic photovoltaic (OPVs) applications [36–39].
Two indacenodithiophene (IDT)-based conjugated polymers, PIDT-EDOT and PIDTT-EDOT, were designed and synthesized as organic thermoelectric materials. Compared to PIDT-EDOT, the IDT unit of PIDTT-EDOT was extended by incorporating two thieno[3,2-b]thiophene (TT) units into the polymer main chain. The polymer PIDTT-EDOT showed better thermal stability and more planar conjugated structure than PIDT-EDOT. Meanwhile, different thermoelectric properties were observed when the two polymer films were doped with FeCl₃. PIDTT-EDOT showed better thermoelectric properties than PIDT-EDOT, and the highest power factor observed for PIDTT-EDOT was 0.867 μW m⁻¹ K⁻² at 453 K, which is approximately 25 times higher than that of PIDT-EDOT. These results indicate that a slight change in the polymer main chain will have a great impact on the thermoelectric properties of IDT-based conjugated polymers. The data presented herein can be used as a reference for the design of new high-performance thermoelectric materials.

View all citing articles on Scopus

View full text

Enhanced thermoelectric properties of electropolymerized poly (3,4-ethylenedioxythiophene) thin films by optimizing electrolyte temperature and thermal annealing temperature

Highlights

Abstract

Introduction

Section snippets

Experimental procedure

Cyclic voltammetry at different electrolyte temperatures

Conclusions

Acknowledgements

Org. Electron.

Electrochem. Commun.

Synth. Met.

Chem. Phys. Lett.

Energy Convers. Manage

Org. Electron.

Electrochim. Acta

Synth. Met.

Org. Electron.

Electrochim. Acta

J. Polym. Sci. Part B Polym. Phys.

J. Solid State Chem.

Mater. Lett.

Org. Electron.

Org. Electron.

J. Alloys Compd.

J. Electroanal. Chem.

Electrochim. Acta

Electrochim. Acta

J. Electroanal. Chem.