FR3059671A1 - ELECTRICALLY CONDUCTIVE AND TRANSPARENT POLYMERIC COMPOSITION BASED ON POLY (3,4-ETHYLENEDIOXYTHIOPHENE) AND POLYELECTROLYTE - Google Patents

Abstract

The invention relates to an electrically conductive polymer composition based on a PEDOT: polyelectrolyte complex, said composition being characterized in that it further comprises, as an additive, a polyelectrolyte salt.

Description

Holder (s): ARKEMA FRANCE Public limited company, UNIVERSITE DE BORDEAUX Public establishment, THE POLYTECHNIC INSTITUTE OF BORDEAUX, NATIONAL CENTER FOR SCIENTIFIC RESEARCH.

Agent (s): API CONSEIL.

loAJ ELECTRICALLY CONDUCTIVE AND TRANSPARENT POLYMER COMPOSITION BASED ON POLY (3,4ETHYLENEDIOXYTHIOPHENE) AND POLYELECTROLYTE.

The invention relates to an electrically conductive polymer composition based on a PEDOT: polyelectrolyte complex, said composition being characterized in that it additionally comprises, as an additive, a polyelectrolyte salt.

PEDOTPSTFSI absorption coefficient conductivity

250

FR 3 059 671 - A1 "

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PSTFSIK added (mass%)

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ELECTRICALLY CONDUCTIVE AND TRANSPARENT POLYMER COMPOSITION BASED ON POLY (3,4-ETHYLENEDIOXYTHIOPHENE) AND POLYELECTROLYTE [Field of the Invention [0001] The invention relates to the field of electrically conductive and transparent polymer compositions, based on poly (3, 4-ethylenedioxythiophene) and polyelectrolyte, intended to be used in the form of films in optoelectronic devices.

[Prior art] Poly (3,4-ethylenedioxythiophene), known by the abbreviation PEDOT, is a polymer which was discovered in the laboratories of Bayer AG in Germany, in collaboration with the AGFA group, at the end from the 1980s. It is used in particular in organic electronics applications, in particular in photovoltaic cells, but more generally in optoelectronic applications, because of its good conductivity, its oxidation stability. and its transparency.

PEDOT is a polymer insoluble in common solvents. It is generally associated with a poly (styrene-co-styrene sulfonate) (PSS) polymer, which allows it to be dispersed in water. PSS is a polyelectrolyte that acts as a charge controller, forming colloidal particles consisting of a tangle of PSS chains linked to PEDOT, with a PEDOT-rich core covered with a PSS-rich crown. These particles are commercially available with different degrees of conductivity.

PEDOT: PSS can be easily deposited in the form of a thin film by common methods such as "spin coating" or "Doctor Blading" or by "inkjet" type printing. For many optoelectronic devices, the layers of PEDOT: PSS are arranged between an electrode layer composed of indium tin oxide (ITO) and a layer of active organic material. The PEDOT: PSS provides a better function of the electrode, smoothes the rough surface of ΙΊΤΟ and consequently limits short circuits, and it protects the active organic layer from free indium and oxygen, giving the system a duration of extended life.

It is now well known that the conductivity of PEDOT: PSS can be increased by more than three orders of magnitude thanks to the addition, in its formulation, of cosolvents with high boiling point, such as ethylene glycol (EG), diethylene glycol (DEG), dimethyl sulfoxide (DMSO), Ν, Ν-dimethylformamide (DMF) or sorbitol.

Ref: 0514-ARK79

Thus, in the article entitled “On the mechanism of conductivity enhancement in poly (3,4ethylenedioxythiophene): poly (styrene sulfonate) film through solvent treatement” Polymer, 2004,45, 8443-8450, Ouyang et al highlighted the increase in the conductivity of PEDOT: PSS in the presence of ethylene glycol. In the article "Morphological change and Moblity Enhancement in PEDOT: PSS by adding Cosolvent", Adv. Matters, 2013, 1-6, Q. Wei et al described the influence of ethylene glycol and DMSO on the conductivity of PEDOT: PSS. In the article "A morphological model for the solvent-enhanced conductivity of PEDOT: PSS thin films" Adv. Funct. Matter, 2008, 18, 865-871, A. Mantovani Nardes et al, described the efficacy of sorbitol on the conductivity of PEDOT: PSS films.

Other studies have also shown that treating PEDOT: PSS with certain salts or ionic liquids can cause a similar increase in the conductivity of a PEDOT: PSS film. Such results have for example been described in the following articles: “Salt-induced charge screening and significant conductivuty enhancement of conducting PEDOT: PSS”, Y. Xia and J. Ouyang, Macromolecules, 2009, 42, 4141-4147 and “A new approach to hydrophobia and water-resistant PEDOT: PSS films using ionic liquids ”M. Dobbelin et al, J. Mater. Chem., 2008, 18, 5354-5358. In the article entitled “Solution-processed poly (3,4-ethylenedioxythiophene) thin films as transparent conductors: effect of p-toluenesulfonic acid in dimethyl sulfoxide”, ACS, 2014, 6, 1779217803, S. Mukherjee et al also showed the effectiveness of the combination of paratoluenesulfonic acid with DMSO on increasing the conductivity.

However, for certain applications such as invisible anti-electrostatic coatings, nanotube-polymer composite electrodes for example or even organic light-emitting diodes (OLED), it is sought to produce relatively thick films to preserve certain mechanical properties, while preserving a very high transparency as well as conductivity. It therefore appears necessary to further improve the transmittance of the electrically conductive polymer films in order to be able to manufacture them over greater thicknesses.

The Applicant has therefore sought to synthesize another conductive polymer composition, which is at least as conductive as PEDOT: PSS, but which has better transparency for equal film thickness.

[Technical problem] The invention therefore aims to remedy the drawbacks of the prior art. The invention aims in particular to provide an electrically polymer composition

Ref: 0514-ARK79 conductive based on a PEDOT complex: polyelectrolyte which is such that, when applied in the form of a film on a substrate, the film has a higher transmittance than conventional conductive polymer films of equal thickness, and retains a high transmittance, preferably greater than 85%, and more preferably greater than 90% at high film thickness, preferably greater than 500nm, while retaining satisfactory conductivity.

[Short description of the invention] Surprisingly, it has been discovered that an electrically conductive polymer composition based on a PEDOT: polyelectrolyte complex, said composition being characterized in that it further comprises, as 'additive, a polyelectrolyte salt;

makes it possible to obtain, when applied in the form of a film to a substrate, a very high transmittance, greater than 90%, even at high thickness, for example greater than 500 nm, while retaining a satisfactory conductivity.

According to other optional characteristics of the composition:

- The polyelectrolyte salt is of the same type as the polyelectrolyte of the complex;

- the PEDOT: polyelectrolyte complex is chosen from one of the following complexes: PEDOT: PSTFSI, PEDOT: PSS, PEDOT: acrylic polyelectrolyte, or PEDOT: methacrylic polyelectrolyte;

- the PEDOT: polyelectrolyte complex is in the form of an aqueous dispersion;

- when the complex is PEDOT: PSTFSI, the PSTFSI salt is chosen from PSTFSIH, PSTFSINa or PSTFSIK;

- The mass percentage of polyelectrolyte salt relative to the total dry mass of the PEDOT complex: polyelectrolyte, is between 30 and 150% by mass, preferably between 30 and 100% by mass;

when the complex is PEDOT PSTFSI, the molecular weight by weight of the added PSTFSI salt is between 20,000 g / mol and 350,000 g / mol, preferably between 50,000 g / mol and 350,000 g / mol and more preferably between 100,000 g / mol and 350,000 g / mol;

Ref: 0514-ARK79

the molecular weight by weight of the PSTFSI of the PEDOT complex: PSTFSI is between 100,000 and 350,000 g / mol, preferably between 250,000 and 350,000 g / mol;

the composition also comprises one or more high-boiling co-solvents, chosen from glycols, preferably ethylene glycol (EG), dimethylformamide (DMF) or dimethylsulfoxide (DMSO);

the composition comprises one or more additives chosen from fluorosurfactants, and / or salts, said salts being chosen from paratoluenesulfonic acid (p-TSA) and / or lithium bis (trifluoromethanesulfonyl) imide (LiTFSI);

the composition comprises: a PEDOT complex: PSTFSI in aqueous dispersion and between 30 and 100% by mass of PSTFSI salt relative to the total dry mass of the PEDOT complex: PSTFSI, and between 3 and 15% by weight of DMSO relative by weight of the aqueous dispersion of PEDOT: PSTFSI and of PSTFSI salt, and / or between 0.05% and 3% by weight of salts of LiTFSI and / or p-TSA relative to the weight of the aqueous dispersion of PEDOT: PSTFSI and PSTFSI salt and / or less than 0.05% by weight of fluorosurfactant chosen from non-ionic linear perfluorinated polyethoxylated alcohols, relative to the weight of the aqueous dispersion of PEDOT: PSTFSI and PSTFSI salt.

The invention further relates to a process for the preparation of an electrically conductive polymer composition based on a PEDOT: polyelectrolyte complex, said process comprising the following steps: mixing 3,4-ethylenedioxythiophene (EDOT) with a polyelectrolyte in aqueous solution, add to the EDOTpolyelectrolyte mixture an oxidizing system so as to polymerize the EDOT into poly 3,4ethylenedioxythiophene (PEDOT) and to form a PEDOT complex: polyelectrolyte in aqueous dispersion, purify the PEDOT complex: polyelectrolyte, add to the aqueous dispersion of PEDOT: polyelectrolyte a salt of polyelectrolyte.

According to other optional characteristics of the process:

- The polyelectrolyte salt added to the aqueous dispersion is of the same type as the polyelectrolyte of the complex;

- The polyelectrolyte is an acrylic polyelectrolyte, a methacrylic polyelectrolyte or the poly 4-styrenesulfonyl (trifluoromethane-sulfonyl) imide (PSTFSI) or the poly (styrene-co-styrene sulfonate) (PSS);

Ref: 0514-ARK79

- the oxidizing system is a mixture of ammonium persulfate and ferric chloride;

- when the polyelectrolyte chosen is PSTFSI, the EDOT / PSTFSI molar ratio in the EDOT-PSTFSI mixture is between 0.5 and 0.8;

the process further comprises the steps of adding, in the aqueous dispersion of PEDOT: polyelectrolyte and of polyelectrolyte salt, of dimethylsulfoxide (DMSO) in proportions of between 3 and 15% by mass relative to the weight of said aqueous dispersion, and / or the addition of one or more salts chosen from paratoluenesulfonic acid (p-TSA) and lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) in proportions of between 0.05 and 3% by mass relative to the weight of said aqueous dispersion, and / or the addition of one or more fluorosurfactants chosen from nonionic linear perfluorinated polyethoxylated alcohols, in proportions of less than 0.05% relative to the weight of said aqueous dispersion.

The invention also relates to a transparent conductive polymer film, the composition of which conforms to that described above, said film being formed by application, on a substrate, of one or more layer (s) of said composition.

According to another characteristic, such a film has, for a thickness greater than 500 nm, a transmittance greater than 90% and a film resistance less than 500Q.sq ' ¹ .

The invention finally relates to an optoelectronic device comprising such a film, the composition of which conforms to that described above, said optoelectronic device being a photovoltaic cell, a liquid crystal screen, a touch screen, a flexible screen, an electrophoretic screen, an organic light emitting diode, an invisible anti-electrostatic coating, a composite electrode, a transistor.

Other features and advantages of the invention will appear on reading the following description given by way of illustrative and nonlimiting example, with reference to the appended figures which represent:

• Figure 1, curves illustrating the evolution of the absorption coefficient and the conductivity of a film whose composition comprises a PEDOT complex: PSTFSI, as a function of the mass percentage of PSTFSI salt added as an additive in the composition;

Ref: 0514-ARK79 • Figure 2, a curve illustrating the evolution of the merit factor (FoM) of a PEDOT-based composition: PSTFSI as a function of the mass percentage of additive added to the composition, the additive being PSTFSIK salt;

FIG. 3, curves illustrating the evolution of the transmittance (T) of a conductive polymer film as a function of its thickness, for films formed from a first unformulated composition (filled squares) based on PEDOT: PSTFSI, and for films formed from a second formulation (empty squares) based on PEDOT: PSTFSI in which PSTFSIK has been added as an additive;

FIG. 4, curves illustrating the evolution of the film resistance (R) as a function of the thickness, for films formed from a first unformulated composition (filled squares) based on PEDOT: PSTFSI, and for films formed from a second composition formulated (empty circles) based on PEDOT: PSTFSI in which PSTFSIK has been added as an additive;

• Figure 5, curves illustrating the evolution of transmittance (T) as a function of the thickness of a film formed from a composition formulated based on PEDOT: PSTFSI in which PSTFSIK was added as that additive in different proportions;

FIG. 6, curves illustrating the evolution of the film resistance (R) as a function of the thickness of a film formed from a composition formulated based on PEDOT: PSTFSI in which PSTFSIK has been added as an additive in different proportions.

[Detailed description of the invention!

The term "polyelectrolyte" denotes an ionic conductive polymer.

The term "PEDOT complex: polyelectrolyte" as used refers to a mixture of PEDOT with a polyelectrolyte in which the polyelectrolyte forms colloidal particles consisting of an entanglement of chains connected to PEDOT to form a three-dimensional network comprising a core rich in PEDOT covered with a crown rich in polyelectrolyte. The use of the polyelectrolyte as complexing agent for PEDOT gives a stable aqueous dispersion.

The term "transmittance", denoted by "T", denotes the ratio between the light flux passing through a conductive polymer film and the incident light flux.

Ref: 0514-ARK79 The “absorption coefficient”, denoted “a” thereafter, designates the ratio between the absorbance A and the optical path traveled, that is to say the thickness d of the polymer film whose absorption coefficient is measured. Absorbance A is linked to transmittance T by the formula A = -log ₁₀ (T). The absorption coefficient a can therefore be calculated according to the following formula:

a = A / d = -log ₁₀ (T) / d (1) The "film resistance", denoted R below and measured in ohms per square (Ω sq ' ¹ ), denotes the electrical resistance measured for thin films per film square. This means that a square film with a resistance of 100 Ω sq ' ¹ always has an actual resistance of 100 Ω regardless of the size of the square.

The "electrical conductivity" of a film, expressed in Siemens / cm (S.cm ' ¹ ) and denoted σ in the following, is the ability of the constituent composition of the film to allow the electrical charges to move freely and thus allow the passage of an electric current. The electrical conductivity of a film is related to the film resistance by the following equation:

o = (1 / (R * d)) (2) where d represents the thickness of the film.

The "merit factor" as used in the present description and noted "FoM", is a quantity used to characterize the performance of films made from electrically conductive polymer compositions. To facilitate the comparison of the optoelectronic properties of the different compositions, with different film thicknesses, the merit factor FoM is calculated according to equation (4) below, from equation (3) below by K. Ellmer ( from the publication of K.EIImer, Nat.Photon 2012,6,809-817):

Γ (λ = 550nm) (1 +

188.5

R (3)

FoM = ^σ PC & opt

188.5 (Fr (4) in which o _DC represents the electrical conductivity for a direct current, o _0pt represents the optical conductivity at 550nm, T the transmittance and R the film resistance.

Ref: 0514-ARK79

The merit factor is therefore maximized with a high transmittance T and a low film resistance R.

In order to be able to produce extremely transparent electrically conductive polymer films, the applicant is particularly interested in an electrically conductive polymer composition advantageously comprising a PEDOT complex: anionic polyelectrolyte and more particularly a poly (3,4ethylenedioxythiophene) complex: Poly (4 -styrene trifluoromethane (bissulfonylimide)), subsequently noted PEDOT: PSTFSI. Such a complex has optoelectronic properties as a function of the PEDOT concentration which are very similar to that of the PEDOT: PSS complex. On the other hand, the PEDOT: PSTFSI complex has an absorption coefficient, measured at 550nm (a at 550nm = 2), slightly lower than that of PEDOT: PSS (a at 550nm = 3.5). Therefore, the PEDOT: PSTFSI complex is inherently slightly more transparent than the PEDOT: PSS.

The applicant is also interested in PEDOT complexes: acrylic polyelectrolyte, or PEDOT: methacrylic polyelectrolyte, due to the transparency property of some of these polyelectrolytes.

The PEDOT: polyelectrolyte complexes studied are in the form of a stable aqueous dispersion, the viscosity of which is such that the dispersion shows the characteristics of a gel, which facilitates the production of thin films by known techniques. "Spin coating" or "Doctor Blading" for example.

Surprisingly, the Applicant has noticed that the addition of a polyelectrolyte salt, as an additive, in the aqueous dispersion of PEDOT: polyelectrolyte, makes it possible to significantly lower the absorption coefficient , without lowering the electrical conductivity too much. Such a composition then makes it possible to produce thicker conductive films, with a transmittance T at least as high, or even higher.

Preferably, the polyelectrolyte salt is of the same type as the polyelectrolyte of the PEDOT complex: polyelectrolyte in aqueous dispersion.

Depending on the intended application, that is to say depending on the optoelectronic device in which a film of such a composition of transparent conductive polymer is intended to be integrated, a good compromise between transmittance and electrical conductivity can therefore be found. The compromise is obtained by varying in particular the quantity of polyelectrolyte salt added to the dispersion, but also by

Ref: 0514-ARK79 varying the molecular weight by weight of the polyelectrolyte constituting the complex on the one hand and of the polyelectrolyte salt added on the other hand.

The results obtained with compositions based on PEDOT: acrylic polyelectrolyte, or PEDOT: methacrylic polyelectrolyte, in which a salt of the polyelectrolyte used for the complex has been added, are very advantageous in terms of transmittance because the addition of the salt polyelectrolyte can significantly lower the absorption coefficient. The electrical conductivity of these compositions is however lower than that obtained for a composition based on PEDOT: PSTFSI, salt of PSTFSI.

When the composition comprises the PEDOT: PSTFSI complex, the PSTFSI salt can be chosen from PSTFSI H, that is to say the polyelectrolyte in acid form with an H ⁺ counterion, PSTFSIK or PSTFSINa or other salts of the same family. Preferably, it is the PSTFSIK.

For optimal conductivity of the composition, the molecular weight by weight of the PSTFSI of the complex is advantageously between 100,000 and 350,000 g / mol. More preferably, it is between 250,000 and 350,000 g / mol. The dispersity is advantageously between 1.5 and 2.4.

The mass percentage of PSTFSI salt is preferably between 30% and 150% by mass relative to the total dry mass of the PEDOT complex: PSTFSI, and more preferably it is between 30 and 100% by mass.

Advantageously, the molecular weight by weight of the free PSTFSI salt added to the dispersion is between 20,000 g / mol and 350,000 g / mol, preferably between 50,000 g / mol and 350,000 g / mol and more preferably between 100,000 g / mol and 350,000 g / mol. The dispersity is advantageously between 1.5 and 2.4.

Polymerization of polyelectrolytes can be carried out by radical polymerization or by controlled radical polymerization, whether by nitroxides, RAFT (acronym for "Reversible Addition-Fragmentation Chain Transfer") or by ATRP (acronym for " radical polymerization by atom transfer ”).

In the example of PSTFSI, it is for example synthesized by RAFT by mixing, according to the molecular weight targeted for the polymer, a determined amount of STFSI monomer, a chain transfer agent, and azo-bis isobutyronitrile (AIBN) in dimethylformamide (DMF).

Ref: 0514-ARK79 The PEDOT complex: polyelectrolyte is synthesized by oxidative polymerization of the 3,4-ethylenedioxythiophene monomer (EDOT) in an aqueous solution of the polyelectrolyte previously synthesized. The EDOT monomer mixture with the polyelectrolyte is vigorously stirred under a nitrogen atmosphere, then an oxidizing system is added in order to polymerize the EDOT into PEDOT and to form the PEDOT: polyelectrolyte complex. The oxidizing system is preferably a mixture of ammonium persulfate (NH4) ₂ S ₂ O8 and ferric chloride FeCl ₃ . The complex obtained is then purified with one or more ion exchange resins. These ion exchange resins may for example be resins sold by the company LANXESS under the brand Lewatit.

The PEDOT: Polyelectrolyte complex is then in the form of an aqueous dispersion, to which a salt of said polyelectrolyte is added.

To further improve the electrical conductivity of the composition, an additional step consists in adding to the aqueous dispersion of PEDOT: polyelectrolyte and polyelectrolyte salt, a co-solvent with high boiling point. The solvent with a high boiling point can be chosen from glycols and preferably ethylene glycol (EG), dimethylformamide (DMF) or dimethylsulfoxide (DMSO). DMSO is preferred, however. It is preferably added in proportions of between 3 and 15% by mass relative to the mass of the aqueous dispersion of PEDOT: polyelectrolyte and of polyelectrolyte salt. Preferably, this proportion is around 5% by mass. With such a proportion of DMSO in the composition, an increase in conductivity of a factor of 200 is observed, without the absorption coefficient being affected. Above 15%, the conductivity no longer increases and the viscosity of the dispersion changes, causing difficulties thereafter in making a film deposit.

To this aqueous dispersion, can also be added salts to further increase the conductivity. These salts are advantageously chosen from paratoluenesulfonic acid (pTSA) and / or lithium bis (trifluoromethanesulfonyl) imide (LiTFSI). These salts are advantageously added in mass proportions of between 0.05% and 3% relative to the mass of the aqueous dispersion of PEDOT: polyelectrolyte and of polyelectrolyte salt.

In addition, in order to improve the wettability of the composition on certain substrates, in particular glass or plastic substrates, a flurorosurfactant from the Zonyl family is added to the composition (registered trademark marketed by the company Dupont to designate non-ionic linear perfluorinated polyethoxylated alcohols). The

Ref: 0514-ARK79

Zonyl added to the composition is more particularly the fluorosurfactant sold under the trade name Zonyl FS300, the formula of which is as follows:

This fluorosurfactant is preferably added in proportions of less than 0.05% by mass relative to the mass of the aqueous dispersion of PEDOT: polyelectrolyte and of polyelectrolyte salt.

The composition thus obtained can be applied in the form of films on any type of substrate, such as glass, plastic, metal, textile, skin, etc. The deposition of the composition in the form of a film can be carried out by well-known "Spin-Coating", "Doctor Blading" or even "Spray-coating" methods. The film obtained is dried at a temperature between 25 and 200 ° C for less than an hour.

Such a film thus deposited can be mono- or multilayer. The maximum thickness of each layer varies depending on the application technique used. Layer thicknesses of 600nm could be obtained by the “doctor blading” technique. It is thus possible to deposit several successive layers to create a film with a thickness of up to 1pm.

Such a film is intended to be integrated into optoelectronic devices, among which we can for example quote: a photovoltaic cell, a liquid crystal screen, a touch screen, a flexible screen, an electrophoretic screen, an organic light emitting diode , a composite electrode, an invisible anti-electrostatic coating, a transistor. This list is not exhaustive and is only an example of targeted applications.

The following examples illustrate, without limitation, the scope of the invention:

All the examples presented below relate to PEDOTPSTFSI compositions; PSTFSIK free in which the PSTFSIK salt content was varied. Monolayer films of thickness varying between 100 and 600 nm were prepared from these compositions.

Ref: 0514-ARK79 Regarding the PEDOT complex: PSTFSI, it can be synthesized from different salts of PSTFSI and in particular from PSTFSIK or PSTFSIH. Whatever salt is used, the procedure for the synthesis of the PEDOT complex: PSTFSI remains the same. Using one salt over another affects the optoelectronic properties of the final complex. Thus, a PEDOT: PSTFSI complex synthesized from PSTFSIH has an electrical conductivity and a higher factor of merit than a complex synthesized from PSTFSIK.

In the experimental examples below, demonstrating the increase in the transmittance of a PEDOT composition: PSTFSI by adding a PSTFSI salt to said composition, it is PSTFSIK which was used for the synthesis of the PEDOT complex: PSTFSI.

The molecular weight by weight Mw and the dispersity (D) of the PSTFSI polyelectrolytes are measured by steric exclusion chromatography (SEC), with a SEC / GPC device from the company Agilent, in dimethylformamide (DMF) at 75 °. C with polystyrene calibration.

1. Preparation of conductive films

1.1 Synthesis of PSTFSIK Under an Argon atmosphere, ethanedioyl dichloride (8 ml) and N, N-dimethylformamide (DMF - 0.348 g) were added to 160 ml of anhydrous acetonitrile. During the formation of a Vilsmeier-Haack complex, the solution turns yellow and sodium 4vinylbenzenesulfonate (16 g) is added with vigorous stirring of the solution.

After 24 hours, the solution comprising newly formed 4-styrenesulfonyl chloride is filtered to remove the precipitated NaCl.

In another reactor, 32.4 ml of triethylamine and 11.56 g of trifluoromethanesulfonamide are mixed with 120 ml of anhydrous acetonitrile and allowed to stir. After 1 hour, the triethylamine / trifluoromethanesulfonamide / acetonitrile solution was introduced under vacuum and with vigorous stirring into the cooled solution (T = 0 ° C) of 4-styrenesulfonyl chloride / acetonitrile. Then, the mixture is warmed to room temperature and with stirring for 16 h.

Ref: 0514-ARK79 The monomer obtained was transferred to dichloromethane and then washed twice with an aqueous solution of NaHCO ₃ (4%) and once with 1M HCl, in order to remove the salts. Then, the dichloromethane was removed and an ion exchange reaction in aqueous solution was carried out using an excess of K ₂ CO ₃ , in order to obtain a potassium salt of STFSI. It is possible here to use another salt in order to produce a salt different from the potassium salt.

The polyelectrolyte PSTFSIK was synthesized by radical polymerization controlled by reversible chain transfer by addition-fragmentation (RAFT) by mixing, as a function of the molecular weight by targeted weight of the polymer, the appropriate quantity of the STFSI monomer, of a chain transfer agent and azo-bis isobutyronitrile (AIBN) in dimethylformamide (DMF). The chain transfer agent used is, for example, an H ₂ 5Ci2-SC (S) 2-C (CH ₃ ) ₂ COOH type trithiocarbonate. After several freeze-thaw cycles, the mixture is left at 65 ° C for several hours to a few weeks (depending on the molecular weight by weight which must be obtained) for polymerization.

Following the polymerization, the preparation of the polymer is finalized after precipitation in tetrahydrofuran (THF), filtration, washing with THF and drying in a vacuum oven at 65 ° C for at least one day.

1.2 Synthesis of PEDOT: PSTFSIK The 3,4-ethylenedioxythiophene monomer (EDOT) is dispersed in an aqueous solution of PSTFSIK under a nitrogen atmosphere (concentration 8.18 mg.ml · ¹ PSTFSIK, 14 mol.ml · ¹ EDOT). An optimum complexation and a stable dispersion are obtained with a molar ratio of EDOT / PSTFSI in the mixture of between 0.5 and 0.8, and preferably of the order of 0.6. For optimal conductivity of the composition, the molecular weight by weight of the PSTFSI of the complex is advantageously between 100,000 and 350,000 g / mol and the dispersity is advantageously between 1.5 and 2.4. As part of this synthesis, PSTFSIK chooses for the synthesis of the PEDOT complex: PSTFSI has a molecular weight by weight Mw of 350,000 g / mol.

A mixture of ammonium persulfate and ferric chloride is then introduced into the mixture of EDOT-PSTFSIK, according to the molar ratio NH ₄ S ₂ O ₈ : FeCl ₃ : EDOT = 1: 0.3: 1. The The reaction mixture is vigorously stirred for 48 h (at 400 revolutions per minute) under a nitrogen atmosphere at 14 ° C. After 48 hours of polymerization at 14 ° C., the resulting dispersion of PEDOT: PSTFSI is purified by two ion exchange resins sold by the company LANXESS under the brand Lewatit, and more particularly

Ref: 0514-ARK79 resins sold under the references Lewatit S108 / H or Lewatit MP62 (150mg per 1ml of dispersion).

1.3 Formulation of the PEDOT composition: PSTFSIK supplemented with free PSTFSIK The salt of PSTFSI chosen to be added to the dispersion of PEDOT: PSTFSI previously synthesized is PSTFSIK. The apparent weight molecular mass of the PSTFSIK used was 250,000 g / mol. Its dispersity is between 1.5 and 2.4. It is previously dissolved in de-ionized water (150mg / ml). Then the PSTFSIK solution is added to the aqueous dispersion of PEDOT: PSTFSI.

Different formulated compositions were produced with different amounts of PSTFSIK added. These quantities were added relative to the total dry mass of the dispersion of PEDOT: PSTFSI previously synthesized. The amount of solid PEDOT: PSTFSI polymer in the aqueous dispersion is determined by ATG measurement (thermogravimetric analysis) by heating a sample of the dispersion to 130 ° C (the PEDOT: PSTFSI being stable up to approximately 200 ° C). Once the sample water has evaporated, the mass percentage of the solid polymer residue in the dispersion can be calculated. This mass percentage was determined in the experimental examples between 0.6 and 0.8%. This means that for 100g of dispersion, it comprises between 0.6 and 0.8 g of total dry mass of the PEDOT complex: PSTFSI. If we add 100% by mass of PSTFSI salt, this therefore means that we add as much by weight of PSTFSI salt as there is total dry mass of PEDOT: PSTFSI in the dispersion. The PSTFSI salt powder was therefore previously weighed before being dissolved in water and then added to the dispersion, so as to precisely know its content in percentage by mass relative to the total dry mass of the PEDOT polymer: PSTFSI in dispersion .

To the dispersion of PEDOT: PSTFSI, free PSTFSIK thus obtained were added 5% by mass of DMSO, and 0.04% by mass of fluorosurfactant whose commercial name is Zonyl FS-300.

The mixture was then homogenized by ultrasound for 12 s (amplitude 20% (maximum power 750W), 20 kHz, pulse 2 s).

1.4 Formation of conductive films Films were deposited by the “doctor blading” method at 70 ° C. on glass substrates previously cleaned by ultrasound in acetone and isopropanol. The

Ref: 0514-ARK79 deposition speed and height of the squeegee have been varied depending on the thickness of the film to be deposited.

The films thus deposited are then dried on a hot plate at 120 ° C for 15 minutes.

2. Methods for Characterizing the Films Made The thickness of each of the films to be compared was measured using a profilometer, such as the Brucker Dektak XT profilometer, by scanning the surface using the tip. of the profilometer.

The film resistance R of each film was determined by the four-point probe technique, using the Keithley 4200 measurement system and by applying a voltage sweep over several orders of magnitude in order to ensure that the measurement was carried out in ohmic mode.

The transmittance T of each film was measured at 550 nm using a UV / visible / near infrared spectrometer such as the Shimadzu UV3600 spectrometer. For this, the UV / visible spectra were recorded for films deposited on a glass substrate and taking this glass substrate as a reference sample.

The absorption coefficient, the conductivity and the FoM merit factor were calculated from the measured values and according to equations (1) (2) and (4) described above in the description.

3. Evaluation of the performances of the films produced

3.1 Influence of the Addition of PSTFSIK to a PEDOT Composition: PSTFSI on the Absorption Coefficient and the Conductivity [0069] In FIG. 1, curves are illustrated illustrating the evolution of the absorption coefficient a and of the conductivity electric σ of a film the composition of which comprises a PEDOT complex: PSTFSI, as a function of the mass quantity of PSTFSI salt, relative to the total dry mass of the dispersion of PEDOT: PSTFSI, added as an additive in the composition. The results presented in FIG. 1 show that the addition of free PSTFSIK, after the formation of the PEDOT complex: PSTFSI, makes it possible to reduce the absorption coefficient of the composition (and therefore increase the transparency of the conductive film). The addition of free PSTFSIK, after the formation of the PEDOT complex: PSTFSI K, also causes a decrease in the conductivity and the effect of this addition on the conductivity is weaker than the effect on the absorption coefficient for quantities of

Ref: 0514-ARK79

PSTFSI K added between 30% and about 150%. Above 150% by mass, the absorption coefficient tends to stagnate while the electrical conductivity drops further.

This differential effect makes it possible to synthesize a PEDOT composition: PSTFSI added with free PSTFSIK, intended for the production of conductive films having improved optoelectronic properties.

Thus, FIG. 2 represents the change in the merit factor (FoM) of films produced from the PEDOT-based composition: PSTFSI, as a function of the mass percentage of the polyelectrolyte salt added as an additive, relative to the total dry mass of the polymer in the dispersion, the polyelectrolyte salt being PSTFSIK. These merit factor values were calculated from the values shown in the figure

1. This Figure 2 shows that the addition of PSTFSIK to the PEDOT: PSTFSI complex leads to an increase in the merit factor, which therefore means that the increase in transparency compensates for the slight decrease in conductivity. The PSTFSI salt then acts as a sort of transparent filling material.

3.2 Influence of the addition or not of PSTFSI salt to a composition of

PEDOT: PSTFSI on the transmittance and the film resistance of a conductive film as a function of its thickness [0072] Figure 3 illustrates the fact that a film based on PEDOT: PSTFSI not formulated, that is to say whose composition does not include a PSTFSI salt, and having a thickness of 120 nm, has a T transmittance, of the order of 93%, equivalent to a PEDOT film: PSTFSI formulated with 87% by mass of PSTFSIK relative to the mass total dry of PEDOT complex: PSTFSI, whose thickness is 550nm. The arrow in dotted lines in FIG. 3 illustrates this gain in transmittance which makes it possible to produce thicker films. Similarly, an unformulated film about 300nm thick has a T transmittance (of the order of 87%), much lower than the T transmittance (of the order of 95%) of a film of the same thickness. but the composition of which is formulated with 87% by mass of PSTFSIK relative to the total dry mass of PEDOT complex: PSTFSI.

Similarly, it follows from Figure 4 that a film based on PEDOT: PSTFSI, formulated with 87% by mass of PSTFSIK relative to the total dry mass of PEDOT: PSTFSI complex, 550 nm thick , has a film resistance (of the order of 400 Q.sq ' ¹ ) lower than that of the unformulated film of 120nm thickness (for which R is of the order of 500 Q.sq' ¹ ). However, as illustrated on the

Ref: 0514-ARK79

Figure 3, these two films of different thickness have an equivalent transmittance T (of the order of 93%). Thus, at equivalent transmittance T, a film based on PEDOT: PSTFSI added with free PSTFSI K has a lower film resistance and a greater thickness.

3.3 Influence of the concentration of free PSTFSIK in a composition based on

PEDOT: PSTFSI on the transmittance and the film resistance of a conductive film as a function of its thickness [0074] Figures 5 and 6 respectively illustrate the transmittance T and the film resistance R of several films as a function of the thickness of each film and the PSTFSIK salt content added to the PEDOT composition: PSTFSI at the base of the film. These Figures show that the greater the thickness of the film, the more the transmittance T decreases, but that this transmittance increases with the increase in the content of PSTFSIK in the composition of the film. Likewise, the film strength R increases with the increase in the content of PSTFSIK in the composition of the film. FIGS. 5 and 6 also show that for high contents of PSTFSIK, typically greater than 150% by weight compared to the total dry mass of PEDOT: PSTFSI, the transmittance T of the films, at equal thickness, does not vary much (Figure 5) while the conductivity decreases since the film resistance R of the film increases (Figure 6). These results confirm that, in order to obtain optimum transmittance, while preserving the conductivity, the salt content of PSTFSIK relative to the total dry mass of the PEDOT complex: PSTFSI must advantageously be between 30 and 150% by mass, preferably between 30 and 100% by mass.

These results demonstrate that the composition according to the invention, based on PEDOT: polyelectrolyte and salt of said polyelectrolyte, makes it possible to produce films having improved transmittance at equal thickness, compared to films based only on PEDOT: polyelectrolyte , such as PEDOT: PSS widely known on the market. These results make it possible to produce thicker films, greater than 550 nm, having a very high transmittance (greater than 90%) while preserving good conductivity.

Ref: 0514-ARK79

Claims (18)

Claims 1. An electrically conductive polymer composition based on a poly (3,4ethylenedioxythiophene: polyelectrolyte (PEDOTpolyelectrolyte) complex, said composition being characterized in that it additionally comprises, as an additive, a polyelectrolyte salt. 2. Composition according to claim 1, characterized in that the polyelectrolyte salt is of the same type as the polyelectrolyte of the complex. 3. Composition according to claim 1 or 2, characterized in that the PEDOT complex: polyelectrolyte is chosen from one of the following complexes: poly (3,4ethylenedioxythiophene: poly 4-styrenesulfonyl (trifluoromethane-sulfonyl) imide (PEDOT: PSTFSI) , poly (3,4-ethylenedioxythiophene: poly (styrene-co-styrene sulfonate) (PEDOT: PSS), PEDOT: acrylic polyelectrolyte, or PEDOTpolyelectrolyte methacrylic. 4. Composition according to one of claims 1 to 3, characterized in that when the complex is PEDOT: PSTFSI, the PSTFSI salt is chosen from poly 4styrenesulfonyl (trifluoromethane-sulfonyl) imide in acid form with a counterion H ⁺ (PSTFSIH), poly 4-styrenesulfonyl (trifluoromethane-sulfonyl) sodium imide (PSTFSINa) or poly 4-styrenesulfonyl (trifluoromethane-sulfonyl) potassium imide (PSTFSIK). 5. Composition according to one of claims 1 to 4, characterized in that the mass percentage of polyelectrolyte salt relative to the total dry mass of the PEDOT complex .polyelectrolyte, is between 30 and 150% by mass, preferably between 30 and 100% by mass. 6. Composition according to one of claims 1 to 5 characterized in that when the complex is PEDOT: PSTFSI, the molecular weight by weight of the added PSTFSI salt is between 20,000 g / mol and 350,000 g / mol, preferably between 50,000 g / mol and 350,000 g / mol and more preferably between 100,000 g / mol and 350,000 g / mol. 7. Composition according to claim 6, characterized in that when the complex is PEDOT.PSTFSI, the molecular weight by weight of the PSTFSI of the complex is Ref: 0514-ARK79 between 100,000 and 350,000 g / mol, preferably between 250,000 and 350,000 g / mol. 8. Composition according to one of claims 1 to 7, characterized in that it further comprises one or more co-solvents with high boiling point, chosen from glycols, preferably ethylene glycol (EG), dimethylformamide (DMF) or dimethylsulfoxide (DMSO). 9. Composition according to one of claims 1 to 8, characterized in that it comprises one or more additives chosen from fluorosurfactants and / or salts, said salts being chosen from paratoluenesulfonic acid (p-TSA) and / or lithium bis (trifluoromethanesulfonyl) imide (LiTFSI). 10. Composition according to one of claims 1 to 9, characterized in that it comprises: a PEDOT complex: PSTFSI in aqueous dispersion and between 30 and 100% by mass of PSTFSI salt relative to the total dry mass of the PEDOT complex: PSTFSI, and between 3 and 15% by weight of DMSO relative to the weight of the aqueous dispersion of PEDOT: PSTFSI and of salt of PSTFSI, and / or between 0.05% and 3% by weight of LiTFSI and / or p-TSA salts relative to the weight of the aqueous dispersion of PEDOT: PSTFSI and of PSTFSI salt and / or - Less than 0.05% by weight of fluorosurfactant, chosen from non-ionic linear perfluorinated polyethoxylated alcohols, relative to the weight of the aqueous dispersion of PEDOT: PSTFSI and salt of PSTFSI. 11. Process for the preparation of an electrically conductive polymer composition based on a PEDOT: polyelectrolyte complex, said process comprising the following steps: - mix 3,4-ethylenedioxythiophene (EDOT) with a polyelectrolyte in aqueous solution, - add an oxidizing system to the EDOT-polyelectrolyte mixture so as to polymerize the EDOT into poly 3,4-ethylenedioxythiophene (PEDOT) and to form a PEDOT complex: polyelectrolyte in aqueous dispersion, - purify the PEDOT complex: polyelectrolyte, Ref: 0514-ARK79 - add a polyelectrolyte salt to the aqueous dispersion of PEDOTpolyelectrolyte. 12. Method according to claim 11, characterized in that the polyelectrolyte salt 5 added to the aqueous dispersion is of the same type as the polyelectrolyte of the complex. 13. Method according to one of claims 11 to 12, characterized in that the polyelectrolyte is an acrylic polyelectrolyte, a methacrylic polyelectrolyte or the poly 4-styrenesulfonyl (trifluoromethane-sulfonyl) imide (PSTFSI) or the poly (styreneco-styrene sulfonate ) (PSS). 10 14. Method according to one of claims 11 to 13, characterized in that the oxidizing system is a mixture of ammonium persulfate and ferric chloride. 15. The method of claim 11 to 14, characterized in that when the polyelectrolyte chosen is PSTFSI, the EDOT / PSTFSI molar ratio in the EDOT-PSTFSI mixture is between 0.5 and 0.8. 15 16. Method according to one of claims 11 to 15, characterized in that it further comprises the addition, in the aqueous dispersion of PEDOTpolyelectrolyte and of polyelectrolyte salt, of dimethylsulfoxide (DMSO) in proportions of between 3 and 15% by mass relative to the weight of said aqueous dispersion, and / or the addition of one or more salts chosen from paratoluenesulfonic acid (p-TSA) and the 20 bis (trifluoromethanesulfonyl) lithium imide (LiTFSI) in proportions of between 0.05 and 3% by mass relative to the weight of said aqueous dispersion, and / or the addition of one or more fluorosurfactants chosen from polyethoxylated perfluorinated alcohols nonionic linear, in proportions of less than 0.05% relative to the weight of said aqueous dispersion. 25 17. Transparent conductive polymer film, the composition of which conforms to at least one of claims 1 to 10, said film being formed by application, on a substrate, of one or more layer (s) of said composition. 18. Optoelectronic device comprising a film according to claim 17, the composition of which conforms to at least one of claims 1 to 10, said device 30 optoelectronics being a photovoltaic cell, a liquid crystal screen, a touch screen, a flexible screen, an electrophoretic screen, a diode Ref: 0514-ARK79 organic electroluminescent, an invisible anti-electrostatic coating, a composite electrode, a transistor. Ref: 0514-ARK79 E S "b * vs o O ffl X! <ü T3 b ï £ Φ O O PEDOT: PSTFSI 1/3 5  absorption coefficient o conductivity ': i I , î t * f ..................... * 1 1 I I - 250 - 200 _T 100 100 200 300 conductivity (S.cm ’) PSTFSIK added (mass%)