# Improved stability of organic electrochemical transistor performance with a low swelling mixed conducting polymer: a comparative study with PEDOT:PSS

Natalia Pereira Menezes, Tommaso Nicolini, Micah Barker, André Augusto Mariano, César Augusto Dartora, Guillaume Wantz, Natalie Stingelin,

Mamatimin Abbas, Olivier J Dautel, Damien Thuau

<figure><img src="image_1.png" /></figure>

► To cite this version:

Natalia Pereira Menezes, Tommaso Nicolini, Micah Barker, André Augusto Mariano, César Augusto Dartora, et al. Improved stability of organic electrochemical transistor performance with a low swelling mixed conducting polymer: a comparative study with PEDOT:PSS. Journal of Materials Chemistry C, 2023, 11 (19), pp.6296-6300. 10.1039/D3TC00108C. hal-04236284

HAL Id: hal-04236284

https://hal.science/hal-04236284v1

Submitted on 6 Nov 2023

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_2.png" /></figure>

Distributed under a Creative Commons CC0 1.0 - Universal - International License
Improved stability of organic electrochemical transistor performance with
a low swelling mixed conducting polymer: a comparative study with
PEDOT:PSS

Natalia Pereira Menezes<sup>a,d</sup>, Tommaso Nicolini<sup>b</sup>, Micah Barker<sup>b</sup>, André Augusto Mariano<sup>c</sup>, César Augusto Dartora<sup>a</sup>, Guillaume Wantz<sup>d</sup>, Natalie Stingelin<sup>b,e</sup>, Mamatimin Abbas<sup>d</sup>, Olivier J. Dautel<sup>f</sup>, Damien Thuau<sup>d*</sup>

<sup>a</sup>PIPE, Universidade Federal do Paraná, Cel. Francisco H. dos Santos Avenue, 100 - Jardim das Américas, Curitiba, 81530-000, Paraná, Brazil

<sup>b</sup>Université de Bordeaux, CNRS Bordeaux INP/ENSCBP, Laboratoire de Chimie des Polymères Organiques, UMR 5629, Allée Geoffroy Saint-Hilaire, Pessac 33615, France

<sup>c</sup>PPGEE, Universidade Federal do Paraná, Cel. Francisco H. dos Santos Avenue, 100 - Jardim das Américas, Curitiba, 81530-000, Paraná, Brazil

<sup>d</sup>CNRS Bordeaux INP/ENSCBP Laboratoire de l'Intégration du Matériau au Système UMR 5218, Université de Bordeaux, 16 Avenue Pey Berland, Pessac Cedex, 33607, France

<sup>e</sup>School of Materials Science & Engineering and School of Chemical& Biomolecular Engineering Georgia Institute of Technology 901 Atlantic Dr, Atlanta, GA 30318, USA

<sup>f</sup> Institut Charles Gerhardt Montpellier, UMR 5253 Univ. Montpellier-CNRS-ENSCM. Campus CNRS-Bâtiment Balard, 1919, route de Mende, 34293 Montpellier Cedex 05, France

*e-mail: [damien.thuau@ims-bordeaux.fr](mailto:damien.thuau@ims-bordeaux.fr)

**Abstract**

Organic electrochemical transistors (OECTs) are bioelectronics devices which are capable of tracking biological events with extremely high sensitivity. Despite promising advances in terms of steady state performance, stable long-term electrochemical characteristics in complex environments need to be achieved in order for OECTs to open the market of biosensing applications. This work demonstrates the electrochemical performance stability of OECTs with a low swelling mixed conductor, poly[3-(6-hydroxy)hexylthiophene] (P3HHT) soaked in an electrolyte for up to 40 days, and the influence of the nature of the electrolyte on device performances.

*Keywords:* organic mixed conductors, organic electrochemical transistors, performance stability, P3HHT, PEDOT:PSS

Organic electrochemical transistors (OECTs) are gaining interest in the field of bioelectronics due to their potential biocompatibility, high transconductance and low operating voltage, which makes them ideal biosensors. [1-4] To date, OECTs have been employed for monitoring brain activity [5, 6], cell integrity [7, 8], neuromorphic systems [9], barrier tissue arrangement [10], chemical and biological sensor [11-13] and more recently to detect COVID-19. [14] Their high transconductance ($g_m$) comes from the mixed ionic and electronic conduction properties of the active conjugated polymer where
electrochemical doping/de-doping occurs throughout the volume of the channel through the interaction with ions from the electrolyte. The performance of an OECT is defined commonly by its maximum transconductance which is related to the electron and ion mobility and volumetric capacitance of the channel material, defined by the latter's chemical structure and morphology. Although a high $g_m$ is the key parameter of highly sensitive transducers, device stability represents another important feature of OECTs for efficient implantable biosensors.

To date, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is the most reported active conjugated polymer for depletion mode OECTs due to its solution processability, biocompatibility and commercial availability. However, when immersed in water, PEDOT:PSS-based OECTs have been reported to exhibit deterioration in their electrical characteristics. For instance, parasitic reactions with dissolved oxygen at relatively high $V_{GS}$ (0.5V) have been considered as a possible cause for the instability for OECT devices operated in aqueous solutions. [15-16] Despite this effect can be suppressed by deaerating the solution with high-purity nitrogen gas as well as maintaining a nitrogen atmosphere on top of the solution, a significant drain current decay have been reported when $V_{GS}$ pulses were applied to PEDOT:PSS. Furthermore, the degradation of PEDOT:PSS based OECT performance have recently been shown to originate from the swelling of the PEDOT:PSS. Losses in channel conductivity was attributed to the fact that styrene sulfonate captures large amounts of water throughout the repetitive intercalation-extraction of ions during doping/dedoping operation. This causes expansion-shrinking of the PEDOT:PSS film leading to poor device stability. [17-20] The introduction of 3-glycidyloxypropyl)trimethoxysilane (GOPS) as chemical cross-linker into the PEDOT:PSS to enhance the performance stability of OECT has led to highly different responses. On the one hand, PEDOT:PSS crosslinked with fresh GOPS, soaked in DI water and preconditioned, was reported to be stable over 50 continuous cycles in an aqueous environment. [21] On the other hand, a considerable negative current shift found to be caused by the water absorption of PSS, and by the presence of the non-conductive species in the cross-linked network, implied that GOPS was insufficient to prevent the deterioration of electrical conductivity in water immersion. [22] Note that crystallized PEDOT:PSS films that were left in a bath of concentrated sulfuric acid exhibited a relatively good material stability over 20 days. [23]

Alternatively, conducting or semiconducting polymer backbones have been functionalised with polar side chains leading to bulk electrochemical doping, and high volumetric capacitances. [24, 25] Yet, these functionalizations to the polymer backbone that can affect the electronic charge transport, leads to higher susceptibility to environmental conditions, and influence the structural, mechanical and electronic properties of the material. [26, 27] In this work, we present performance stability and influence of the electrolyte on the transistor parameters in accumulation mode OECTs with a low swelling mixed conductor, poly[3-(6-hydroxy)hexylthiophene] (P3HHT) [28] with the view to explore the materials space towards future materials discovery.
The OECT, shown in **Figure 1.a**, were fabricated by a two-step UV-photolithography process, in which a 4-inch borosilicate glass wafer was cleaned in ultrasound bath, first immersed in Hellmanex III soap and DI water for 10 minutes and then rinsed 3 times in DI water for 10 minutes. Titanium (2 nm) and gold (100 nm) were evaporated on the surface of the substrate by e-beam and thermal evaporation, respectively. The first step of UV-photolithography defined metal pads, interconnects, and source and drain electrodes. Then, SU-8 dielectric layer was patterned. The final architecture is displayed in Figure 1(b), where the channel length and width are respectively 10 µm and 100 µm. The P3HHT film was deposited onto this structure via doctor blade at ambient conditions from solution (15 mg/mL NMP heated to 60 °C under stirring) and dried overnight at room temperature, leading to a film of approximately 110 nm as previously described. [28] Control samples with PEDOT:PSS films were obtained by mixing 5% (v/v) ethylene glycol and 0.25% (v/v) 4-dodecylbenzenesulfonic acid (DBSA) and 1% (v/v) (3-glycidyloxypropyl)trimethoxysilane (GOPS) all purchased from Sigma-Aldrich with PEDOT:PSS (Clevios PH1000) purchased from Heraeus. The films were then annealed at 120 °C for 1h, resulting in films with a thickness of about 150 nm.

<figure><img src="image_3.png" /><figcaption>**Figure 1.** Organic electrochemical transistors. (a) Device schematic, and (b) top view of the microfabricated OECT. Width and length are 100 µm and 10 µm respectively.</figcaption></figure>

The electrical measurements were conducted using three different electrolytes (NaCl, KCl, and $KPF_6$) at the same concentration of 0.1 mol/L with an Ag/AgCl pellet (Phymep) as the gate electrode. The steady-state characteristics were acquired using a semiconductor device analyzer (Keithley 4200S). As for the electrical stability tests, 400 mVpp pulses were applied to the gate using a waveform generator (Agilent 33500B) while a -0.6 V source-drain bias was applied with the semiconductor device analyzer, which was also used to acquire the OECTs response to the stimuli.
First, we discuss the performance of OECTs of P3HHT and PEDOT:PSS (Figure 2.a) based on their drain current ($I_{DS}$) response to application of successive gate potential pulses ($|\Delta V_{GS}| = 0.4$ V, 20 s pulse period) at constant drain potential ($V_{DS} = -0.6$ V) continuously over a period of up to 15 minutes. The devices thereby were operated in an aqueous solution of KCl, a common electrolyte used in electrochemical devices that is also found in various important target applications such as biological media. [29,30] For the accumulation-type P3HHT based OECT, we observe that, remarkably after 15 minutes of successive $V_{GS}$ pulses or after 50 pulses (P50), the maximum $I_{DS}$ measured is identical to the initial pulse ($I_{Dmax,P1} = 2.667 \times 10^{-5}$ A, $I_{Dmax,P50} = 2.660 \times 10^{-5}$ A) (Figure 2b, top panel). Furthermore, magnifying the pulses we find that successive application of $V_{GS}$ steps from 0 to -0.4 to 0 V leads to an initially sharp increase of $I_{DS}$ followed by a slower ramp-like increase and finally a sharp $I_{DS}$ drop (Figure 2b, bottom panel). The dynamics of the electrochemical doping/dedoping of OECTs depend on the mobility of ions inside the organic mixed conductor film (i.e. injection/extraction, diffusion and transport within the channel). Similar dynamics were recently reported for both accumulation and depletion mode OECTs. [31] Note that the ionic mobility can be significantly enhanced through the optimization of amount of hydration of the channel. [20,32,33] In addition, the type of electrolyte and its concentration have been reported to have influence on the transient responses. [34] Herein, the $I_{DS}$ traces are significantly non-symmetric, which indicates slow on-off switching kinetics of the P3HHT-based OECT. In stark contrast, for the depletion-type PEDOT:PSS based OECT, the maximum $I_{DS}$ measured after 50 $V_{GS}$ pulses (Figure 2.c) is significantly deteriorating, i.e. we find it to be notably lower than that measured during the first pulse (numbers). Specifically, the “on” current ($I_{DS-ON}$) measured at $V_{GS} = 0$ V for the depletion-type PEDOT:PSS OECT drastically decreases over time during continuous application of $V_{GS}$ pulses. Meanwhile, we observe in the magnified pulses that the current traces appear significantly more symmetric than those of the P3HHT devices. Overall, these initial results indicate that the transduction performance of the PEDOT:PSS based OECT is significantly less stable than that of the P3HHT based device during continuous on-off cycling despite the former showing higher current magnitudes and faster on-off switching.
<figure><img src="image_4.png" /><figcaption>**Figure 2.** a) Chemical structures of P3HHT, left, and PEDOT:PSS, right. Drain current ($I_{DS}$) response of organic electrochemical transistors (OECTs) produced with b) P3HHT or c) PEDOT:PSS as the active channel material to consecutive gate potential ($V_{GS}$) pulses (indicated P1 to Pn) applied continuously over 15 minutes. Pulses P1, P2, P49, and P50 are magnified for clarity. Devices operated in 0.1 M KCl at a drain voltage ($|V_{DS}|$) of 0.6 V.</figcaption></figure>

To explore further whether OECTs of P3HHT can consistently show greater stability than OECTs of PEDOT:PSS also over the long term and in different operating conditions, we tracked the evolution of the OECT performance while the devices were subjected to continuous immersion in various aqueous electrolytes over several days. Such conditions are interesting to investigate in the context of bioelectronics applications like chronic implants in ionically diverse, complex biological media. Specifically, we measured the transfer characteristics ($I_D$ vs $V_{GS}$ at constant $V_{DS}$) of devices immersed in aqueous KCl, NaCl (0.1 M) at time intervals of 10 days over a total of 40 days and their corresponding transconductance, $g_m$, i.e. the figure-of-merit of OECTs. Additionally, we performed
similar experiments with KPF<sub>6</sub> (0.1 M) to investigate the effect of a larger anion presenting virtually no
solvation sphere on the stability of these devices.

The data shown in the Supporting Information (Figure S1) displays the I<sub>DS ON</sub> current and g<sub>m max</sub> normalized to the very first measurement (t<sub>0</sub>) before device immersion to highlight the differences in performance stability. Non-normalized curves are given in Figure S2. Note that the V<sub>GS</sub> sweep range used to operate P3HHT (V<sub>GS</sub> = 0 to -0.6 V) and PEDOT:PSS devices (V<sub>GS</sub> = -0.2 to 0.6 V) vary due to the different natures of the accumulation-type P3HHT and depletion-type PEDOT:PSS devices.

Immediate observations can be made (Figure S1 and S2). PEDOT:PSS OECTs generally show
significantly less reproducible I<sub>DS</sub> and g<sub>m</sub> traces over time despite exhibiting up to two orders of
magnitude higher performance than those of P3HHT devices due to the larger amount of charge
carrier and charge carrier mobility in PEDOT:PSS. Importantly, a PEDOT:PSS device immersed in
KCl (Figure S1.a) shows a decrease of the “on” current by 30% (from |I<sub>DS-ON,t0</sub>| = 4.0x10<sup>-3</sup> A to |I<sub>DS-ON,t40</sub>| = 2.8x10<sup>-3</sup> A at V<sub>GS</sub> = -0.2 V) after 40 days (t<sub>40</sub>) of immersion, which leads to the lowering of the
maximum transconductance (g<sub>m-max</sub>) by 60% (g<sub>m-max,t0</sub> = 5.8x10<sup>-3</sup> S, g<sub>m-max,t40</sub> = 2.3x10<sup>-3</sup> S). Meanwhile,
an OECT of P3HHT only shows a decrease of I<sub>DS-ON</sub> by up to 24% (from |I<sub>DS-ON,t0</sub>| = 4.1x10<sup>-5</sup> A to |I<sub>DS-ON,t40</sub>| = 3.1x10<sup>-5</sup> A at V<sub>GS</sub> = -0.6 V) and of g<sub>m-max</sub> by 17% (g<sub>m-max,t0</sub> = 3.0x10<sup>-4</sup> S, g<sub>m-max,t40</sub> = 2.5x10<sup>-4</sup> S)
after 40 days in KCl. Similarly, another PEDOT:PSS device immersed in NaCl electrolyte (Figure
S1.b) exhibits up to 46% decrease of I<sub>DS-ON</sub> and subsequent 44% loss of g<sub>m-max</sub> after 40 days, while an
OECT of P3HHT in the same conditions only exhibits an I<sub>DS-ON</sub> loss of 40% and a g<sub>m-max</sub> loss of up to
27%. Even more drastic is the performance loss during immersion of a PEDOT:PSS device in KPF<sub>6</sub>
(Figure S1.c), in which it exhibits up to 87% decrease of g<sub>m-max</sub> after 40 days with a corresponding I<sub>DS-ON</sub> drop of 96%. A device of P3HHT, in contrasts, shows only up to 23% I<sub>DS-ON</sub> loss and 36% decrease
of g<sub>m-max</sub> after 40 days in KPF<sub>6</sub>.

Another intriguing observation is that operation of P3HHT devices in KPF<sub>6</sub>, which is the only electrolyte used in this work consisting of a polyatomic ion (PF<sub>6</sub><sup>-</sup>), yields I<sub>DS-ON</sub> and g<sub>m</sub> an order of magnitude higher than when operated in either KCl or NaCl. This may be explained by the fact that larger, more polarizable anions with a lower surface charge density require a smaller driving force for injection into the semiconducting polymer. [35]

**Figure 3** highlights the greater stability of the measured average maximum transconductance of accumulation type P3HHT over depletion type PEDOT:PSS devices when operated in aqueous electrolytes out of at least three devices for each condition. PEDOT:PSS devices exhibit a total of 84±28% and 75±13% *g*<sub>m-max</sub> loss for devices immersed in KPF<sub>6</sub> and KCl, respectively, while a less pronounced but still significant 51±11% loss is observed in devices immersed in NaCl after 40 days. In the case of P3HHT devices, maximum transconductance losses range from 17 to 36% after 40
days of immersion depending of the type of electrolytes used [Note: for P3HHT the largest standard
deviation amounts only to 10%].

<figure><img src="image_5.png" /></figure>

<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /><figcaption>**Figure 3.** Normalized maximum transconductance ($g_m, max$) losses measured for OECTs with P3HHT and PEDOT:PSS as the active channel material during 40 days of continuous immersion in 0.1 M aqueous solutions of a) KCl, b) NaCl, and c) $KPF_6$ electrolytes. Data are normalized to the maximum value of initial measurements. Devices are operated at a drain voltage ($|V_{DS}|$) of 0.6 V.</figcaption></figure>

P3HHT consistently shows much less pronounced degradation than PEDOT:PSS to electrolyte
exposure over long periods of time. Most notably, PEDOT:PSS appears to be particularly susceptible
to exposure to an electrolyte containing the chaotropic anion $PF_6^-$. This observation is somewhat
puzzling because it is usually the cation that takes part in the doping and dedoping of a p-type material
operating in depletion mode. However, the processes leading to the degradation of the electroactive
material constituting the OECT channel and concurrent loss of performance are due to the complex
interplay among the redox properties of the conducting polymer, solvent and electrolyte used. These
processes are not only affected by the nature of the polymer (e.g. hydrophilic vs. hydrophobic) [27,36]
but also by the electrolyte ions. In fact, according to their charge density, ions display different
interactions with water molecules and therefore very different solvation shells. [37] With its low surface charge density, PF₆⁻ can be considered a relatively hydrophobic ion, therefore its injection into the polymer layer is not accompanied by the concurrent injection of a large number of water molecules, as it is the case for alkali metals cations such as Na⁺ and K⁺ or halides like Cl⁻. This has a positive effect on the doping of low-swelling, relatively hydrophobic mixed conductors such as P3HHT but may have a negative effect on very hydrophilic materials such as PEDOT:PSS. This detrimental effect might be explained by a more pronounced deswelling when PF₆⁻ is driven into the PEDOT:PSS layer either by diffusion during a long period of exposure to KPF₆ electrolyte or during OECT operation.

Overall, our results indicate that OECTs of the accumulation type P3HHT exhibit a notably greater stability of its electrochemical performance than devices of PEDOT:PSS when operated in aqueous electrolytes of different nature with either chaotropic or kosmotropic ions which is a key requirement for resilient biosensors operating in complex environments. We suggest that this is due to the greater swelling of PEDOT:PSS in aqueous media as has been previously demonstrated in comparison to pg(2T-TT). [28] Indeed, the symmetric transient currents measured for devices of PEDOT:PSS (Figure 2) reflect the possibly too efficient uptake of hydrated ions in the channel, likely facilitated by the hygroscopic nature of the material. Although this feature aids OECT performance of this material, especially the good initial transduction performance, excessive water uptake becomes detrimental to the stability of the device. Repetitive swelling and contraction of the polymeric channel can lead to delamination, while absorbed water molecules can also act as plasticizers that further degrade the mechanical and therefore electrochemical properties of the material. As a result, OECTs of PEDOT:PSS display a significant loss of performance after on-off cycling and prolonged immersion in aqueous electrolytes. On the other hand, the less hygroscopic P3HHT is more tolerant to the influence of water on its properties and therefore devices produced from this polymer show greater stability with the compromise of displaying an overall more moderate performance. However, these performances can be largely improved upon blending, especially in terms of doping kinetics. [38] More importantly, their enhanced current retention after 40 days of immersion in diverse aqueous electrolytes prompt for the development of accumulation mode OECTs as reliable biosensors in physiological environments.

## Acknowledgements

This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001. O.J.D is grateful for the financial support provided by Chimie Balard Cirimat Carnot Institute through the ANR program N° 16 CARN 0008-01. G.W., N.S., O.J.D., D.T. acknowledge funding by ANR project "MAPLLE" (ANR-20-CE06-0002).
References

[1] A. Pappa, O. Parlak, G. Scheiblin, P. Mailley, A. Salleo, R. M. Owens, Trends in Biotechnology, 2018, **36**, 45

[2] J. Rivnay, R. M. Owens, G. G. Malliaras, Chem. Mater, 2014, **26**, 679

[3] J. Rivnay, P. Leleux, M. Sessolo, D. Khodagholy, T. Herve, M. Fiocchi, G. G. Malliaras, Adv. Mater., 2013, **25**, 7010

[4] D. Khodagholy, J. Rivnay, M. Sessolo, M. Gurfinkel, P. Leleux, L. H. Jimison, E. Stavrinidou, T. Herve, S. Sanaur, R. M. Owens, G. G. Malliaras, Nat. Commun., 2013, **4**, 2133

[5] J. Rivnay, P. Leleux, M. Ferro, M. Sessolo, A. Williamson, D. A. Koutsouras, D. Khodagholy, M. Ramuz, X. Strakosas, R. M. Owens, C. Benar, J. Badier, C. Bernard, G. G. Malliaras, Science Advances, 2015, **1**, 1400251

[6] A. Koutsouras, P. Leleux, M. Ramuz, J. Rivany, G. G. Malliaras, IEEE International Electron Devices Meeting, 2014, 31.4.1-31.4.4

[7] F. Curto, B. Marchiori, A. Hama, A. Pappa, M. P. Ferro, M. Braendlein, J. Rivany, M. Fiocchi, G. G. Malliaras, M. Ramuz, R. M. Owens, Microsystems and Nanoengineering, 2017, **3**, 17028

[8] S. Y. Yeung, X. Gu, C. M. Tsang, S. W. Tsao, I. Hsing, Sensors and Actuators, A: Physical, 2019, **287**, 185

[9] P. Gkoupidenis, N. Schaefer, B. Garlan, G. G. Malliaras, Advanced Materials, 2015, **27**, 7176

[10] H. Jimison, S. A. Tria, D. Khodagholy, M. Gurfinkel, E. Lanzarini, A. Hama, G. G. Malliaras, R. M. Owens, Advanced Materials, 2012, **24**, 5919

[11] S. Wustoni, S. Wang, J. R. Alvarez, T. C. Hidalgo, S. P. Nunes, S. Biosensors and Bioelectronics, 2019, **143**, 111561

[12] N. Wang, Y. Liu, Y. Fu, F. Yan, ACS Applied Materials and Interfaces, 2018, **10**, 25834

[13] G. Zhang, D. Wang, C. Wu, L. Xiong, Y. Zheng, H. Ding, G. Lu, L. Zhang, Qiu, Biosensors and Bioelectronics, 2018, **100**, 235

[14] K. Guo, S. Wustoni, A. Koklu, E. Diaz-Galicia, M. Moser, A. Hama, A. A. Alqahtani, A. N. Ahmad, F.S. Alhamlan, M. Shuaib, A. Pain, I. McCulloch, S. T. Arold, R. Grunberg, S. Inal, 2021, **5**, 666

[15] S. T. Keene, T. P. A. van der Pol, D. Zakhidov, C. H. L. Weijtens, R. A. J. Janssen, A. Salleo, Y. van de Burgt, Adv. Mater. 2020, **32**, 2000270
[16] S. T. Keene, A. Melianas, Y. van de Burgt, A. Salleo, Adv. Electron. Mater. 2019, **5**, 1800686

[17] G. Baschek, G. Hartwig, F. Zahradnik, Polym. 1999, **40**, 3433–3441

[18] L. Bießmann, L. P. Kreuzer, T. Widmann, N. Hohn, J.-F. Moulin, P. Müller-Buschbaum, ACS Appl. Mater. Interfaces 2018, **10**, 9865–9872

[19] K. Tang, W. Miao, S. Guo, ACS Appl. Polym. Mater. 2021, **3**, 1436–1444

[20] A. Savva, S. Wustoni, S. Inal, J. Mater. Chem. C 2018, **6**, 12023–12030

[21] S. L Bidinger, S. Han, G. G. Malliaras, T. Hasan, Appl. Phys. Lett., 2022, **120**, 073302

[22] S. Zhang, P. Kumar, A. Sarah Nouas, L. Fontaine, H. Tang, F. Cicoira, APL Mater. 2015, **3**, 014911

[23] S.-M. Kim, C.-H. Kim, Y. Kim, N. Kim, W.-J. Lee, E.-Hak Lee, D. Kim, S. Park, K. Lee, J. Rivnay, M.-H. Yoon, Nature Communications, 2018, **9**, 385

[24] C. B. Nielsen, A. Giovannitti, D. Sbircea, E. Bandiello, M. R. Niazi, D. A. Hanifi, M. Sessolo, A. Amassian, G. G. Malliaras, J. Rivnay, I. Mcculloch, J. Am. Chem. Soc., 2016, **138**, 10252

[25] A. Cendra, A. Giovannitti, V. Savva, I. Venkatraman, A. Mcculloch, S. Salleo, J. Inal, Rivnay, Advanced Functional Materials, 2019, **29**, 1

[26] A. Giovannitti, C. B. Nielsen, D. Sbircea, S. Inal, M. Donahue, M. R. Niazi, D. A. Hanifi, A. Amassian, G. G. Malliaras, J. Rivnay, I. Mcculloch, Nature Communications, 2016, **7**, 13066

[27] L. Q. Flagg, C. G. Bischak, J. W. Onorato, R. B. Rashid, C. K. Luscombe, D. S. Ginger, Journal of the American Chemical Society, 2019, **141**, 4345

[28] T. Nicolini, J. Surgaillis, A. Savva, A. D. Scaccabarozzi, R. Nakar, D. Thuau, G. Wantz, L. J. Richter, O. Dautel, G. Hadziioannou, N. Stingelin, Adv. Mater., 2021, **33**, 2005723

[29] X. Strakosas, M. Bongo, R. M. Owens, J. Appl. Polym. Sci., 2015, 41735

[30] M. Sessolo, J. Rivnay, E. Bandiello, G. Malliaras, H. Bolink, Adv. Mater., 2014, **26**, 4803

[31] Y. Zhang, B. D. Paulsen, E. A. Schafer, Q. Zeng, F. Yu, L. Yang, Y. Xue, J. Rivnay, and N. Zhao, Adv. Funct. Mater. 2023, 2214380

[32] A. Savva, R. Hallani, C. Cendra, J. Surgailis, T. C. Hidalgo, S. Wustoni, R. Wheelamanthula, X. Chen, M. Kirkus, A. Giovannitti, A. Salleo, I. McCulloch, S. Inal, Adv. Funct. Mater. 2020, **30**, 1907657.

[33] H. Jia, Z. Huang, P. Li, S. Zhang, Y. Wang, J.-Y. Wang, X. Gu, T. Lei, J. Mater. Chem. C 2021, **9**, 4927
[34] J. T. Mabeck, J. A. DeFranco, D. A. Bernards, G. G. Malliaras, S. Hocdé, C. J. Chase, Appl. Phys. Lett. 2005, **87**, 013503

[35] L. Q. Flagg, R. Giridharagopal, J. Guo, D. S. Ginger, Chem. Mater., 2018, **30**, 5380

[36] A. Savva, C. Cendra, A. Giugni, B. Torre, J. Surgailis, D. Ohayon, A. Giovannitti, I. McCulloch, E. Di Fabrizio, A. Salleo, J. Rivnay, S. Inal, Chem. Mater., 2019, **31**, 3, 927

[37] L. Q. Flagg, C. G. Bischak, R. J. Quezada, J. W. Onorato, C. K. Luscombe, D. S. Ginger, ACS Materials Lett., 2020, **2**, 254

[38] M. Barker, T. Nicolini, Y. Al Yaman, D. Thuau, O. Siscan, S. Ramachandran, E. Cloutet, C. Brochon, L. J. Richter, O. J. Dautel, G. Hadziioannou, N. Stingelin, Mater. Horiz., 2023, 10.1039/D2MH00861K

**Graphical abstract**

<figure><img src="image_8.png" /></figure>

The stability of the electrochemical performance of OECTs soaked in an electrolyte for up to 40 days produced with a low swelling mixed conductor, poly[3-(6-hydroxy)hexylthiophene] (P3HHT) showed enhanced stability in their electrochemical performance in comparison to poly(3,4ethylenedioxythiophene) : poly (styrene sulfonate) (PEDOT:PSS) based OECT.
Supporting Information for

Stable electrochemical transistor performance with a low-swelling mixed
conducting polymer

Natalia Pereira Menezesª, Tommaso Nicoliniᵇ, Micah Barkerᵇ, André Augusto Marianoᶜ, César Augusto Dartoraª, Guillaume Wantzᵈ, Natalie Stingelinᵉ, Mamatimin Abbasᵈ, Olivier J. Dautelf`, Damien Thuaud*

ªPIPE, Universidade Federal do Paraná, Cel. Francisco H. dos Santos Avenue, 100 - Jardim das Américas, Curitiba, 81530-000, Paraná, Brazil

ᵇUniversité de Bordeaux, CNRS Bordeaux INP/ENSCBP, Laboratoire de Chimie des Polymères Organiques, UMR 5629, Allée Geoffroy Saint-Hilaire, Pessac 33615, France

ᶜPPGEE, Universidade Federal do Paraná, Cel. Francisco H. dos Santos Avenue, 100 - Jardim das Américas, Curitiba, 81530-000, Paraná, Brazil

ᵈCNRS Bordeaux INP/ENSCBP Laboratoire de l'Intégration du Matériau au Système UMR 5218, Université de Bordeaux, 16 Avenue Pey Berland, Pessac Cedex, 33607, France

ᵉSchool of Materials Science & Engineering and School of Chemical& Biomolecular Engineering Georgia Institute of Technology 901 Atlantic Dr, Atlanta, GA 30318, USA

f Institut Charles Gerhardt Montpellier, UMR 5253 Univ. Montpellier-CNRS-ENSCM. Campus CNRS-Bâtiment Balard, 1919, route de Mende, 34293 Montpellier Cedex 05, France

*e-mail: [damien.thuau@ims-bordeaux.fr](mailto:damien.thuau@ims-bordeaux.fr)
<figure><img src="image_9.png" /></figure>

<figure><img src="image_10.png" /></figure>

<figure><img src="image_11.png" /></figure>

**Figure S1.** Normalized drain current ($I_{DS}$) and transconductance ($g_m$) traces measured for OECTs with P3HHT or PEDOT:PSS as the active channel material during 40 days of continuous immersion in 0.1 M aqueous solutions of a) KCl, b) NaCl, and c) $KPF_6$ electrolytes. Traces correspond to initial measurements ($t_0$, bold solid lines) and measurements done after 10, 20, 30 (solid grey lines), and 40 days ($t_{40}$, dashed lines) of continuous device immersion. Data are normalized to the maximum value of initial measurements. Devices are operated at a drain voltage ($|V_{DS}|$) of 0.6 V.
<figure><img src="image_12.png" /><figcaption>**Figure S2.** Drain current ($I_D$) and transconductance ($g_m$) measured for OECTs with P3HHT or PEDOT:PSS as the active channel material during 40 days of continuous immersion in 0.1 M aqueous solutions of a) KCl, b) NaCl, and c) $KPF_6$ electrolytes. Traces correspond to initial measurements ($t_0$, bold solid lines) and measurements done after 10, 20, 30 (solid grey lines), and 40 days ($t_{40}$, dashed lines) of continuous device immersion. Bold arrows show direction of gate potential ($V_{GS}$) sweep. Devices are operated at a drain voltage ($|V_{DS}|$) of 0.6 V.</figcaption></figure>