WO2018203830A1

WO2018203830A1 - A sulfone additive for conducting polymers

Info

Publication number: WO2018203830A1
Application number: PCT/SG2018/050216
Authority: WO
Inventors: Qiang Zhu; Xizu Wang; Tao TANG; Xiang Yun Debbie SOO; Jian Wei XU
Original assignee: Agency for Science Technology and Research Singapore
Current assignee: Agency for Science Technology and Research Singapore
Priority date: 2017-05-03
Filing date: 2018-05-03
Publication date: 2018-11-08
Anticipated expiration: 2019-11-03

Abstract

A conducting polymer composition, and a method for its preparation, comprising PEDOT:PSS and an acyclic, disubstituted sulfone is provided. In a preferred embodiment, the acyclic, disubstituted sulfone has a Formula (I). In another embodiment, the present invention relates to a substrate coated with the conducting polymer composition and a process to make said conducting polymer composition, comprising: (i) oxidizing an acyclic, disubstituted thioether to the acyclic, disubstituted sulfone, and (ii) mixing the acyclic, distributed sulfone with the PETDOT:PSS.

Description

A SULFONE ADDITIVE FOR CONDUCTING POLYMERS

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority of Singapore patent application No. 10201703601T filed on 3 May 2017, the content of which is incorporated herein by reference in its entirety for all purposes.

TECHNICAL FIELD

[0002] Various embodiments relate to a conducting polymer composition and a method of preparing the conducting polymer composition.

BACKGROUND

[0003] In the current market, thermoelectric (TE) devices have been successfully employed in many industrial niche applications. The most successful one is Seiko Watch with a thermoelectric module as electricity generator. Such a TE module generates electricity through taking advantage of the temperature gradient between human body and the ambient temperature. Another example is to use a thermoelectric generator in a BMW car. The car engines generate a lot of waste heat which is usually released to ambient environment. However, through installation of thermoelectric module in the car engine, the temperature gradient between the car engine and ambient environment can be successfully converted into electricity. This electricity can be used to cool the driver's seat. In these two thermoelectric (TE) modules, the most important material is the TE material. The efficiency of the thermoelectric materials is evaluated via the dimensionless figure-of-merit: ΖΊ = S² T/K, where S, σ, T and κ are Seebeck coefficient, electrical conductivity, thermal conductivity and absolute temperature, respectively. In order to achieve good TE material, higher ZT is required, which is further governed by Seebeck coefficient, electrical conductivity and thermal conductivity.

[0004] Traditionally, inorganic metals or metal alloys have been widely studied as TE materials. These inorganic materials include Bi₂Te₃, BiSb, SiGe and other metal alloys achieving a commendable ZT of about 2. These materials were also fabricated into various devices, which were used in niche applications including refrigeration and power generation. Nevertheless, these inorganic materials are intrinsically disadvantaged by their scarcity on earth, non -flexibility and toxicity, which limited their wide application in thermoelectric applications. Meanwhile, these inorganic materials are also rigid, which makes them almost impossible to be used for electronic printing. However, this electronic printing is necessary for printing electronics and flexible wearables.

[0005] To overcome above mentioned drawbacks, conducting polymers (CPs) are currently studied as an alternative given its advantages, such as large abundance, tunable electric conductivity and low thermal conductivity. The typical CPs that are widely studied to date include polyacetylene, polypyrrole (PPy), polyaniline (PANI), polythiophene (PTH) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The TE performance of CPs is still much lower than their inorganic counterparts due to their intrinsically low electric conductivity and moderate Seebeck coefficient. In order to improve its electronic performance, several approaches have been widely investigated to improve TE performance of the CPs, including 1): developing nanostructures of CPs, 2): hybridization with nanostructures, including metallic and carbon-based materials and 3): surface modifications or post-treatment. In the first approach, various CP nanostructures, such as PEDOT nanostructures including nanorods, nanofibers, nanotubes, and PPy nanotubes have been systematically studied; and a significant improvement in TE performance has been observed in comparison with their counterpart bulky CPs. However, the synthesis and fabrication of such nanostructures can sometimes involve complicated synthesis and disproportionate scale -up, which limits its industrial applications. The 2^nd approach has been widely investigated, which takes the advantages of each respective component of the hybrid, high electric conductivity or high Seebeck coefficient, to "balance" the composite materials' properties. Thus, an optimum power factor can be obtained via higher energy-filtering efficiency through the joint adjunct between nanoparticle and CPs. The highest ZT obtained so far is about 0.1 and mechanism for this hybrid material is unfortunately not fully understood due to many challenging factors in the complicated system involved. The 3 approach is to tune the surface morphology thorough various doping approaches or post treatments. In this approach, PEDOT:PSS has been the dominant CP to be extensively studied with various post treatments. The main aim for process or treatment is to remove the insulating polymer PSS in PEDOT:PSS. Various organic solvents (dimethylsulfoxide (DMSO), ethylene glycol (EG) and alcohols) and inorganic salts have also been widely used to increase its electric conductivity in a few magnitudes so that the power factor can be significantly increased. Post treatment, such as immersion of the PEDOT:PSS films into EG or acid bath was also studied, following a similar idea. The highest ZT, up to 0.4, was reported by Pipe et al. via such an approach.

[0006] Despite the promising results with PEDOT:PSS, the flaws of the current dopants in PEDOT:PSS is the corrosiveness and toxicity of these doping components, such as DMSO and various acids. All these additives are in liquid form with high boiling point. During the process of film curing, high temperature has to be employed to remove these additives in ambient environment. When DMSO and inorganic acids are used to dope PEDOT:PSS, a closed encasement or fume-hood is required for preparation and film curing, as toxic and hazardous vapors are generated in the process. Meanwhile, a safety concern from industry has also arisen due to higher and higher requirements for wearables, touchable screens and flexible devices.

[0007] In view of the above, there exists a need for an improved conducting polymer composition, that may be used as organic semiconductors in various electronic devices, that overcomes or at least alleviates one or more of the above problems.

SUMMARY

[0008] In a first aspect, there is provided a conducting polymer composition. The conducting polymer composition comprises PEDOT:PSS and an acyclic, disubstituted sulfone.

[0009] In a second aspect, there is provided a method for making a conducting polymer composition comprising PEDOT:PSS and an acyclic, disubstituted sulfone. The method comprises (i) oxidizing an acyclic, disubstituted thioether to the acyclic, disubstituted sulfone and (ii) mixing the acyclic, disubstituted sulfone with PEDOT:PSS.

[0010] In a third aspect, there is provided a process of making a substrate coated with a conducting polymer composition comprising PEDOT:PSS and an acyclic, disubstituted sulfone. The process comprises providing a substrate, applying the conducting polymer composition on the substrate and drying the applied composition to form the substrate coated with a conducting polymer composition comprising PEDOT:PSS and an acyclic, disubstituted sulfone.

[0011] In a fourth aspect, there is provided a substrate coated with a conducting polymer composition comprising PEDOT:PSS and an acyclic, disubstituted sulfone. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The invention will be better understood with reference to the detailed description when considered in conjunction with the non-limiting examples and the accompanying drawings, in which:

[0013] FIG. 1 is a schematic drawing illustrating sulfones structures identified as additive to PEDOT: PSS.

[0014] FIG. 2 is a schematic drawing illustrating the general reaction scheme for sulfone synthesis.

[0015] FIG. 3 illustrates the fabrication process for the film with sulfone additive to PEDOT: PSS.

[0016] FIG. 4 is a graph showing the electric conductivity for PEDOT: PSS with various additive loadings. The highest electrical conductivity up to 1080 S/cm is obtained at a 3wt% loading of the dimethyl sulfone (DMS0₂).

[0017] FIG. 5 is a graph showing the Seebeck coefficient with respect to DMS0₂ concentration (wt%). The highest Seebeck coefficient of 23 μν/Κ is obtained for a composition with a lwt% loading of the DMS0_2.

[0018] FIG. 6 is a graph showing the power factor with respect to DMS0₂ concentration (wt%).

The optimum power factor of 32 μ^,\\7πιΚ is obtained at a 3wt% loading of the DMS0_2.

[0019] FIG. 7 is a graph showing the film thickness variation and electric conductivity changes for PEDOT:PSS-doped conducting polymers, which are post treated with several solvents. By performing a post treatment, an electric conductivity of up to 1800 S/cm was measured.

[0020] FIG. 8A is a graph showing the electric conductivity as an indicator of the long-term stability of premixing solution of PEDOT:PSS and dimethyl sulfone.

[0021] FIG. 8B is a photograph showing a comparison of PEDOT:PSS doped by DMSO/trifluoroacetic acid and by sulfone, respectively.

[0022] FIG. 9A is a ^-NMR spectrum of diphenyl sulfone.

[0023] FIG. 9B is a ¹³C-NMR spectrum of diphenyl sulfone.

DETAILED DESCRIPTION

[0024] In order to meet the above described demand, a series of sulfone analogs (structure shown in FIG. 1) has been designed and used as dopant to PEDOT:PSS. The sulfones are non- toxic, non-volatile, and chemically stable, giving such sulfones a competitive edge over the current dopants such as DMSO, MeOH, sulfuric acid etc., that are toxic, corrosive, and non- environmentally friendly. Furthermore, sulfones doped PEDOT: PSS films are stable and film properties including electrical conductivity remain unchanged over 3-6 months, making it highly desired for industrial applications.

[0025] Therefore, in a first aspect, there is provided a conducting polymer composition. The conducting polymer composition comprises PEDOT:PSS and an acyclic, disubstituted sulfone.

[0026] The term "composition" as used herein, refers to a mixture of components. Comprised in this composition may be PEDOT:PSS and an acyclic, disubstituted sulfone. Further components which may be comprised in this mixture are, for example, water. The PEDOT:PSS may thus be provided as an aqueous solution. The PEDOT:PSS may be comprised or contained in this solution in about 0.1 wt% to about 50 wt%, or in about 0.1 wt% to about 30 wt%, or in about 0.1 wt% to about 10 wt%, or in about 0.1 wt% to about 5 wt%, or in about 1.0 wt% to about 50 wt%, or in about 1.0 wt% to about 30 wt%, or in about 1.0 wt% to about 10 wt%, or in about 1.0 wt% to about 5.0 wt%, or in about 1.0 wt% to about 2.0 wt%, or in about 1.0 wt% to about 1.6 wt%, preferably in about 1.2 wt% to about 1.6 wt%.

Further, the composition may comprise an aqueous solution of PEDOT:PSS, to which the acyclic, disubstituted sulfone is added in a certain weight percentage range. For clarity, it is noted that the weight percentage range refers to an added amount and that the weight percentage calculation is based on the amount of the aqueous PEDOT:PSS solution, as opposed to the total weight of the aqueous PEDOT:PSS solution together with the acyclic, disubstituted sulfone.

[0027] The term "acyclic, disubstituted sulfone" as used herein refers to a sulfur atom, which is covalently bonded to two oxygen atoms, and both oxygen atoms are formally bonded to the sulfur by a double bond. It is understood that a sulfur atom with two oxygen atoms would be commonly referred to as a "sulfone" or "sulphone". The sulfone, as it has two vacant valences, may be further bonded to two moieties with each bond being a single bond. The two substituents may be described as Ri and R₂, which may each be any organic moiety. Hence, the sulfone may be a disubstituted sulfone. Ri and R₂ may be the same or different. Ri and R₂ may be independent of each other, which means that they are not connected to each other by a bond. Hence, Ri and R₂ may not form a cyclic structure with each other, and the disubstituted sulfone may therefore be understood to be an acyclic, disubstituted sulfone. [0028] Advantageously, the acyclic, disubstituted sulfone provides unique properties, which may be attributed to the two oxygen atoms on the sulfur, and the acyclic nature of Ri and R₂. Hence, the compounds of the present disclosure may differ in their electronical and sterical properties from, for example, the sulfolanes, which are cyclic, disubstituted sulfones. This is because the two oxygen atoms in the sulfolanes are differently arranged on the sulfur atoms, in order to accommodate for the ring closure of the cyclic substituents within the sulfolane. In contrast, the two oxygen atoms in the present disclosure, as the substituents Ri and R₂ are acyclic, would be arranged in a different manner, as the substituents Ri and R₂ do not have to accommodate for a ring closure. Naturally, the different arrangement of the oxygen atoms results in properties of the compounds of the present disclosure, which are electronically and sterically distinguished from, for example, sulfolanes. Similarly, the electronical and sterical properties of the compounds of the present disclosure may be distinguished from, for example, acyclic sulfoxides. This is because sulfoxides only contain one oxygen atom, as opposed to two contained in the sulfolane. As oxygen has a strong electronegativity, the absence of one of these atoms on the sulfur would have a strong impact on the electronical environment of the compound. Accordingly, in sulfoxides, the sulfur would retain one electron lone pair, which is absent from the sulfones of the present disclosure. As the absence of one oxygen atom also has sterical consequences (an additional oxygen atom double bonded to the sulfur would have different sterical demands from an electron lone pair), it can be concluded that the presence of one additional oxygen atom results in properties of the compounds of the present disclosure, which are electronically and sterically distinguished from, for example, acyclic sulfoxides. The combination of the acyclic nature and the two oxygen atoms results in a unique sterical and electronical constellation, which results in the unique properties observed for the compounds of the present disclosure. Due to interaction of the sulfolanes, as presented herein, with the PEDOT:PSS, the conducting polymer composition arising from the PEDOT:PSS combined with the acyclic, disubstituted sulfone results in the advantages presented herein.

[0029] In various embodiments, the acyclic, disubstituted sulfone may have a Formula (I)

wherein Ri and R₂ are independently selected from the group consisting of substituted or unsubstituted, linear or branched alkyl with 1 to 50 carbon atoms; substituted or unsubstituted, linear or branched alkenyl with 2 to 50 carbon atoms; substituted or unsubstituted, linear or branched alkoxy with 1 to 50 carbon atoms; substituted or unsubstituted cycloalkyl with 3 to 50 carbon atoms; substituted or unsubstituted cycloalkenyl with 5 to 50 carbon atoms; substituted or unsubstituted aryl with 5 to 14 carbon atoms; and substituted or unsubstituted heteroaryl with 5 to 14 carbon atoms.

[0030] The term "alkyl" as used herein, as a group or part of a group, refers to a linear or branched aliphatic hydrocarbon group, preferably a C1-C25 alkyl, more preferably a C1-C10 alkyl, most preferably C1-C5 alkyl unless otherwise noted. Examples of suitable straight and branched C1-C10 alkyl substituents include methyl, ethyl, n-propyl, 2-propyl, n-butyl, sec -butyl, t-butyl, hexyl, and the like. The group may be a terminal group or a bridging group.

[0031] The term "alkenyl", as used herein, as a group or part of a group, denotes an aliphatic hydrocarbon group containing at least one carbon-carbon double bond and which may be straight or branched preferably having 2-20 carbon atoms, more preferably 2-10 carbon atoms, most preferably 2-6 carbon atoms, in the normal chain. The group may contain a plurality of double bonds in the normal chain and the orientation about each is independently E or Z. Exemplary alkenyl groups include, but are not limited to, ethenyl, propenyl, butenyl, pentenyl, hexenyl, heptenyl, octenyl and nonenyl. The group may be a terminal group or a bridging group.

[0032] The term "substituted or unsubstituted" as used herein means the group to which this term refers may be unsubstituted, or may be substituted with one or more groups independently selected from alkyl, alkenyl, alkynyl, thioalkyl, cycloalkyl, cycloalkylalkyl, cycloalkenyl, cycloalkylalkenyl, heterocycloalkyl, cycloalkylheteroalkyl, cycloalkyloxy, cycloalkenyloxy, cycloamino, halo, carboxyl, haloalkyl, haloalkynyl, alkynyloxy, heteroalkyl, heteroalkyloxy, hydroxyl, hydroxyalkyl, alkoxy, thioalkoxy, alkenyloxy, haloalkoxy, haloalkenyl, haloalkynyl, haloalkenyloxy, nitro, amino, nitroalkyl, nitroalkenyl, nitroalkynyl, nitroheterocyclyl, alkylamino, dialkylamino, alkenylamine, aminoalkyl, alkynylamino, acyl, alkyloxy, alkyloxyalkyl, alkyloxyaryl, alkyloxycarbonyl, alkyloxycycloalkyl, alkyloxyheteroaryl, alkyloxyheterocycloalkyl, alkenoyl, alkynoyl, acylamino, diacylamino, acyloxy, alkylsulfonyloxy, heterocyclic, heterocycloalkenyl, heterocycloalkyl, heterocycloalkylalkyl, heterocycloalkylalkenyl, heterocycloalkylheteroalkyl, heterocycloalkyloxy, heterocycloalkenyloxy, heterocycloxy, heterocycloamino, haloheterocycloalkyl, alkylsulfinyl, alkylsulfonyl, alkylsulfenyl, alkylcarbonyloxy, alkylthio, acylthio, aminosulfonyl, phosphorus - containing groups such as phosphono and phosphinyl, sulfinyl, sulfinylamino, sulfonyl, sulfonylamino, aryl, heteroaryl, heteroarylalkyl, heteroarylalkenyl, heteroarylheteroalkyl, heteroarylamino, heteroaryloxy, arylalkenyl, arylalkyl, alkylaryl, alkylheteroaryl, aryloxy, arylsulfonyl, cyano, cyanate, isocyanate, -C(0)NH(alkyl), and -C(0)N(alkyl)2.

[0033] The term "cycloalkyl" as used herein refers to a saturated monocyclic or fused or spiro polycyclic, carbocycle preferably containing from 3 to 20 carbons per ring, such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl and the like, unless otherwise specified. It includes monocyclic systems such as cyclopropyl and cyclohexyl, bicyclic systems such as decalin, and polycyclic systems such as adamantane. A cycloalkyl group typically is a C3-C12 alkyl group. The group may be a terminal group or a bridging group.

[0034] The term "cycloalkenyl" means a non-aromatic monocyclic or multicyclic ring system containing at least one carbon-carbon double bond and preferably having from 5-10 carbon atoms per ring. Exemplary monocyclic cycloalkenyl rings include cyclopentenyl, cyclohexenyl or cycloheptenyl. The cycloalkenyl group may be substituted by one or more substituent groups. A cycloalkenyl group typically is a C₅-C12 alkenyl group. The group may be a terminal group or a bridging group.

[0035] The term "aryl" as used herein as a group or part of a group denotes (i) a substituted or unsubstituted monocyclic, or fused polycyclic, aromatic carbocycle (ring structure having ring atoms that are all carbon) preferably having from 5 to 18 atoms per ring. Examples of aryl groups include phenyl, naphthyl, and the like; (ii) an optionally substituted partially saturated bicyclic aromatic carbocyclic moiety in which a phenyl and a C₅-7 cycloalkyl or C₅- 7 cycloalkenyl group are fused together to form a cyclic structure, such as tetrahydronaphthyl, indenyl or indanyl. The group may be a terminal group or a bridging group. Typically an aryl group is a C₅-C14 aryl group. [0036] The term "heteroaryl" either alone or part of a group refers to groups containing an aromatic ring (preferably a 5 or 6 membered aromatic ring) having one or more heteroatoms as ring atoms in the aromatic ring with the remainder of the ring atoms being carbon atoms. Suitable heteroatoms include nitrogen, oxygen and sulfur. Examples of heteroaryl include thiophene, benzothiophene, benzofuran, benzimidazole, benzoxazole, benzothiazole, benzisothiazole, furan, isoindolizine, xantholene, phenoxatine, pyrrole, imidazole, pyrazole, pyridine, pyrazine, pyrimidine, pyridazine, tetrazole, indole, isoindole, lH-indazole, purine, quinoline, isoquinoline, phthalazine, naphthyridine, quinoxaline, cinnoline, carbazole, phenanthridine, acridine, phenazine, thiazole, isothiazole, phenothiazine, oxazole, isooxazole, furazane, phenoxazine, 2-, 3- or 4- pyridyl, 2-, 3-, 4-, 5-, or 8- quinolyl, 1-, 3-, 4-, or 5- isoquinolinyl 1-, 2-, or 3- indolyl, and 2-, or 3-thienyl. Typically a heteroaryl group is a 5 to 14 membered group.

[0037] In various embodiments, Ri and R₂ may be independently selected from the group consisting of substituted or unsubstituted, linear or branched alkyl with 1 to 10 carbon atoms and substituted or unsubstituted aryl with 5 to 14 carbon atoms. In embodiments, wherein Ri and R₂ may be independently selected from the group consisting of substituted or unsubstituted, linear or branched alkyl with 1 to 10 carbon atoms, each substituted or unsubstituted, linear or branched alkyl with 1 to 10 carbon atoms may be independently selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl and 2-hydroxy-ethyl.

[0038] In various embodiments, the acyclic, disubstituted sulfone may have an alkyl substituent as Ri and an optionally substituted aryl substituent as R₂. Accordingly, the acyclic, disubstituted sulfone may have a Formula (II)

Formula (II), wherein W is, at each occurrence, independently selected from the group consisting of OH, N0₂, F, CI, Br and I, m is selected from an integer ranging from 0 to 5, and

n is selected from an integer ranging from 1 to 5.

[0039] In various embodiments, the acyclic, disubstituted sulfone may have an optionally hydroxylated phenyl substituent as Ri and an optionally substituted phenyl substituted as R₂. Accordingly, the acyclic, disubstituted sulfone may have a Formula (III)

Formula (III), wherein X is, at each occurrence, selected from the group consisting of F, CI, Br and I, and m and p are independently selected from an integer ranging from 0 to 5.

[0040] In various embodiments, the acyclic, disubstituted sulfone may have a phenyl substituent optionally substituted with nitro as Ri and an optionally halogenated phenyl substituted as R₂. Accordingly, the acyclic, disubstituted sulfone may have a Formula (IV)

Formula (IV) wherein X is, at each occurrence, selected from the group consisting of F, CI, Br and I, m is selected from an integer ranging from 0 to 5, and

q is selected from an integer ranging from 0 to 3.

[0041] According to various embodiments, each substituted or unsubstituted aryl with 5 to 14 carbon atoms may be independently selected from the group consisting of phenyl, 2,4- dihydroxyphenyl, 2,4,6-trinitrophenyl, 2,4-difluorophenyl, 4-hydroxyphenyl, 2,3- dihydroxyphenyl, 2,4,5-trihydroxyphenyl, 3,4-dihydroxyphenyl, 3,4,5-trihydroxyphenyl, 2- fluorophenyl, 4-nitrophenyl, 2,4-dinitrophenyl, and 4-bromophenyl. [0042] According to various embodiments Ri and R₂ may be identical. Alternatively, they may be different.

[0043] In a preferred embodiment, Ri and R₂ may be methyl. In case both Ri and R₂ are methyl, the sulfone may be a dimethyl sulfone, or abbreviated as DMS0₂. In another preferred embodiment, Ri and R₂ may be phenyl.

[0044] The conducting polymer composition may comprise at most 10 wt% of the acyclic, disubstituted sulfone, based on an aqueous solution of PEDOT:PSS. The aqueous solution may be in a concentration as defined before. In a preferred embodiment, the percentage of PEDOT:PSS in water may be about 1.0 wt% to about 2.0 wt%. As previously mentioned, the weight percentage is based on PEDOT:PSS as an aqueous solution, and the acyclic, disubstituted sulfone may be added, percentage-wise, in addition to the PEDOT:PSS aqueous solution. In other words, the PEDOT:PSS aqueous solution is considered to be 100wt%, to which at most 10 wt% of the acyclic, disubstituted sulfone may be added. In preferred embodiments, the conducting polymer composition may comprise at most 8 wt%, or at most 5 wt%, or at most 3 wt%, or at most 2 wt%, or at most 1 wt% of the acyclic, disubstituted sulfone.

[0045] According to various embodiments, the acyclic, disubstituted sulfone may have a molecular weight of between about 94 g/mol to about 400 g/mol. In preferred embodiments, the acyclic, disubstituted sulfone may have a molecular weight of between about 94 g/mol to about 300 g/mol, or of between about 94 g/mol to about 250 g/mol, or of between about 94 g/mol to about 200 g/mol. Advantageously, by having a lower molecular weight, the effects of the sulfone as a functional group are more pronounced, which results in the unique properties of the compounds.

[0046] According to various embodiments, the PEDOT:PSS may be provided in a mixing ratio of about 1: 1 to about 1:5, or in a mixing ratio of about 1: 1 to about 1:4, or in a mixing ratio of about 1 : 1 to about 1 :3, or preferably in a mixing ratio of about 1:2.5.

[0047] In a second aspect, there is provided a method for making a conducting polymer composition comprising PEDOT:PSS and an acyclic, disubstituted sulfone. The method comprises (i) oxidizing an acyclic, disubstituted thioether to the acyclic, disubstituted sulfone and (ii) mixing the acyclic, disubstituted sulfone with PEDOT:PSS. The acyclic, disubstituted thioether may be oxidized two-fold. An initial oxidation may form an acyclic, disubstituted sulfoxide, while a subsequent oxidation may form the acyclic, disubstituted sulfone. Preferably, both oxidations may occur in a one -pot reaction. In various embodiments, the oxidation in step (i) comprises exposing the acyclic, disubstituted thioether to an oxidizing reagent at a temperature below ambient temperature. A suitable oxidation reagent may be selected from the group consisting of hydrogen peroxide, a hypervalent iodine species, such as PIFA (PhCOCF₃), l,3,5-triazo-2,4,6-triphosphorine-2,2,4,4,6,6-tetrachloride (TAPC), potassium permanganate and meta-chloroperoxybenzoic acid (mCPBA). A suitable temperature for the exposure of the acyclic, disubstituted thioether to the oxidation reagent may be below ambient temperature, whereby ambient temperature refers to a temperature, which may be between 15°C and 25 °C, or between 18°C and 22°C. As mentioned before, the solution may be mixed in the second step. While any mixing method may be used, in preferred embodiments, the mixing may be undertaken by vortexing the solution.

[0048] In various embodiments, the mixing in step (ii) may comprise providing a PEDOT:PSS solution, adding the acyclic, disubstituted sulfone and shaking the resulting mixture. In various embodiments, the mixing in step (ii) further comprises sonicating the resulting mixture. In various embodiments, after step (ii), the resulting mixture may be filtered and kept at a temperature below ambient temperature.

[0049] In a third aspect, there may be provided a process of making a substrate coated with a conducting polymer composition comprising PEDOT:PSS and an acyclic, disubstituted sulfone, the process comprising providing a substrate, applying the conducting polymer composition on the substrate and drying the applied composition to form the substrate coated with a conducting polymer composition comprising PEDOT:PSS and an acyclic, disubstituted sulfone. The conducting polymer composition may be applied on the substrate, without any particular limitation, by drop casting, spin coating, dip coating, spray coating, flow coating, screen printing, or the like, or a combination comprising at least one of the foregoing.

[0050] Accordingly, in a fourth aspect, there may be provided a substrate coated with a conducting polymer composition comprising PEDOT:PSS and an acyclic, disubstituted sulfone. The substrate coated with a conducting polymer composition comprising PEDOT:PSS and an acyclic, disubstituted sulfone may be further post-treated with an additional solvent. The additional solvent may be selected from the group consisting of acetone, dichlorome thane, DMF, DMSO, EG, hexane, methanol, ethyl acetate, THF, water and chloroform. The substrate coated with a conducting polymer composition comprising PEDOT:PSS and an acyclic, disubstituted sulfone may be applied in solar cells, OLED's, thermoelectric devices, touch panel displays and flexible wearables.

[0051] Summarizing the above, a series of sulfones was synthesized as a dopant for conventional PEDOT: PSS to raise the electrical conductivity significantly. It could be used to be an alternative to the common used PEDOT:PSS additives such as dimethyl sulfoxide (DMSO), N- methyl pyrrolidone (NMP), ethylene glycol, mineral and organic acids, to improve the electrical conductivity. Important features of the disclosed sulfone additives are: The conducting polymer composition can be made using a simple and clean process with the disclosed sulfone additives; no additional pre-treatment or post-treatment is required. The conducting polymer composition of sulfone additive and PEDOT:PSS can be stored at below 4 degree for a long time period and it does not affect its performance, particularly its electrical conductivity.

[0052] Unlike conventional additives to PEDOT:PSS, such as DMSO, ethylene glycol or acids, chemically modified sulfones with hydroxyl, nitro substituents (shown in FIG.l) are identified. The molecular weight of these sulfones is between 80 g/mol to 400 g/mol. These additives are solid, non-toxic and non-volatile, have never been used as a dopant to improve the electrical conductivity of PEDOT:PSS via the alignment of PEDOT:PSS induced by the uniform crystallization of sulfone additives.

[0053] Hereinafter, the present disclosure will be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, lengths and sizes of layers and regions may be exaggerated for clarity.

EXAMPLES

[0054] In this disclosure, a series of sulfone compounds containing two same or different substituents derived from alkyl, aryl, haloalkyl, functional group substituted aryl groups have been identified and synthesized. The structure of these compounds is shown in FIG. 1. The general synthesis for sulfones was very simple usually involving sulfides undergoing organic oxidation with meta-chloroperoxybenzoic acid and transforming the intermediate sulfoxide finally into the desired sulfone itself, as seen in FIG. 2. The synthetic step is illustrated in example 5. In the synthesis, various oxidation reagents can be used, which may include, but are not limited to, hydrogen peroxide (H₂O₂), sodium/potassium sulfate and meta- chloroperoxybenzoic acid (mCPBA). Average 80% yield and simple filtration can afford the desired sulfones, which are ready for doping PEDOT:PSS.

[0055] The as-prepared sulfones are used as additives to PEDOT: PSS at different ratios for electric conductivity evaluation. The fabrication of the polymer film involves several simple steps as illustrated by the summary in FIG. 3. The fabrication of the disclosed polymer film does not involve complicated mixing or coating processes. There are also no prominent dangers in the processes, which makes it easy to handle. This is an advantage for large scale based industry fabrication, as the procedures are safe and simple.

[0056] Example 1: Electrical conductivity

[0057] The performance of as-prepared film is measured for electrical conductivity and Seebeck coefficient. Electrical conductivity was measured using a 4-probe method. The Seebeck coefficient was measured by the custom-made measurement system shown in S A Peltier cooler (298 K - ΔΤ) and Peltier heater (298 K + ΔΤ), which were used to apply the temperature gradients used to induce the thermal voltage. The e-conductivity vs additive loading was plotted as shown in FIG. 4. When the sulfone is loaded at 2-3%, the electric conductivity can reach 1080 S/cm without involving any pre- or post-treatment.

[0058] Example 2: Seebeck coefficient

[0059] The Seebeck co-efficient was also studied and result is shown in FIG. 5. Similarly, highest Seebeck coefficient value at 22 μν/Κ was obtained when additive loading is lwt%.

[0060] Example 3: Power factor

[0061] The power factor vs additive loading was also plotted in FIG. 6. The highest power factor 24xlO^"6W/(mK²) (Thermoelectric performance) was obtained when the additive loading is lwt%.

[0062] Example 4: Electrical conductivity enhancement

[0063] FIG. 7 shows electrical conductivity enhancement for DMS0₂-doped PEDOT:PSS via post treatment with various solvents. In these experiments, 5wt% DMSO₂ in PEDOT:PSS was evaluated. The corresponding film thickness change vs solvent is plotted in FIG. 7. It was clearly observed that water can reduce film thickness to 3.3 μπι and increase the electrical conductivity to 1100 S/cm. Similarly, ethylene glycol can also improve electrical conductivity to 1700 S/cm and film thickness is also reduced. The electrical conductivity of formulation of sulfones doped PEDOT: PSS is also studied over 3-6 months (FIG. 8A). It was almost constant over 3 months. When PEDOT: PSS was doped with DMSO or acids, it was found that the solution cannot be stored longer than 3 days if the conductivity was to remain unchanged. However, the presently disclosed formulation shows up to 3 months stability (FIG. 8B). Some precipitates were clearly observed for PEDOT:PSS doped with acid/DMSO, while not in sulfone doped PEDOT:PSS.

[0064] Example 5: Synthesis of 4,4'-sulfonyldiphenol

[0065] Exemplary, 4,4'-thiodiphenol (1.5 g, 6.9 mmol) was added to dichloromethane (35 mL) in the reaction flask at 0 °C. Meta-chloroperoxybenzoic acid (3.09 g, 13.8 mmol) was dissolved in dichloromethane (55 mL), and added dropwise to the cool reaction mixture with stirring over 30 minutes. The reaction was allowed to warm to room temperature, and stirred overnight. The solid was then filtered and washed with dichloromethane to give a white solid. H NMR δ 6.83 - 6.86 (m, 2H, J = 9 Hz), 7.64 - 7.67 (m, 2H, J = 9 Hz); ¹³C NMR δ 116.4, 128.8, 132.6, 162.1. The ^XH

NMR spectrum and 13 C NMR spectrum is shown as FIG. 9 A and FIG. 9B, respectively.

[0066] Example 6: Formulation of sulfones to PEDOT: PSS (2 wt%)

[0067] The as-prepared sulfone (20 mg, 2 wt%) was added to PEDOT:PSS (PH1000, 1.0 g) in a centrifuge tube. The resulting mixture was shaken under vortex for 3 - 5 min. followed by sonication for 30 min. The well-mixed solution was filtered through a thick pad of cotton to afford a clear solution. The resulting solution was kept under 2-6 °C. Other formulation with different additive loading was also prepared in a similar way. The formulation can be stored few months while maintaining almost constant electrical conductivity.

[0068] Example 7: Drop-casting of formulation on glass substrate

[0069] A glass slide (2.5 cm by 2.5 cm) was placed under aqua regia for 24 hours. Then the glass slide is taken out and washed using water, methanol and acetone consecutively. The glass slide was further dried under nitrogen blow for 2 minutes. 0.4 mL of newly formulated PEDOT: PSS solution was drop-casted on pre-treated glass slide at ambient temperature. After standing for 15 minutes, the glass slide with PEDOT: PSS on the surface is transferred to the hotplate which was pre -heated at 80 °C. It was heated at 80 °C for 2 hours before it was fully cured. The glass slide was removed and cooled to room temperature for electrical conductivity tests and Seebeck measurement.

[0070] While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.

Claims

1. A conducting polymer composition comprising PEDOT:PSS and an acyclic, disubstituted sulfone.

2. The conducting polymer composition of claim 1, wherein the acyclic, disubstituted sulfone has a Formula (I)

O

Ri S R2

O

Formula (I), wherein Ri and R₂ are independently selected from the group consisting of substituted or unsubstituted, linear or branched alkyl with 1 to 50 carbon atoms; substituted or unsubstituted, linear or branched alkenyl with 2 to 50 carbon atoms; substituted or unsubstituted, linear or branched alkoxy with 1 to 50 carbon atoms; substituted or unsubstituted cycloalkyl with 5 to 50 carbon atoms; substituted or unsubstituted cycloalkenyl with 5 to 50 carbon atoms; substituted or unsubstituted aryl with 5 to 14 carbon atoms; and substituted or unsubstituted heteroaryl with 5 to 14 carbon atoms.

3. The conducting polymer composition of claim 2, wherein Ri and R₂ are independently selected from the group consisting of substituted or unsubstituted, linear or branched alkyl with 1 to 10 carbon atoms and substituted or unsubstituted aryl with 5 to 14 carbon atoms.

4. The conducting polymer composition of claim 3, wherein each substituted or unsubstituted, linear or branched alkyl with 1 to 10 carbon atoms is independently selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl and 2-hydroxy- ethyl.

5. The conducting polymer composition of claim 3, wherein the acyclic, disubstituted sulfone has a Formula (II)

Formula (II), wherein W is, at each occurrence, independently selected from the group consisting of OH, N0₂, F, CI, Br and I,

m is selected from an integer ranging from 0 to 5, and

n is selected from an integer ranging from 1 to 5.

6. The conducting polymer composition of claim 3, wherein the acyclic, disubstituted sulfone has a Formula (III)

Formula (III), wherein X, at each occurrence, is selected from the group consisting of F, CI, Br and I, and

m and p are independently selected from an integer ranging from 0 to 5.

7. The conducting polymer composition of claim 3, wherein the acyclic, disubstituted sulfone has a Formula (IV)

Formula (IV) wherein X, at each occurrence, is selected from the group consisting of F, CI, Br and I, m is selected from an integer ranging from 0 to 5, and

q is selected from an integer ranging from 0 to 3.

8. The conducting polymer composition of claim 3, wherein each substituted or unsubstituted aryl with 5 to 14 carbon atoms is independently selected from the group consisting of phenyl, 2,4-dihydroxyphenyl, 2,4,6-trinitrophenyl, 2,4-difluorophenyl, 4- hydroxyphenyl, 2,3-dihydroxyphenyl, 2,4,5-trihydroxyphenyl, 3,4-dihydroxyphenyl, 3,4,5-trihydroxyphenyl, 2-fluorophenyl, 4-nitrophenyl, 2,4-dinitrophenyl, and 4- bromophenyl.

9. The conducting polymer composition of any one of claims 2 to 4 and 8, wherein Ri and R₂ are identical.

10. The conducting polymer composition of any one of claims 2 to 4 and 9, wherein Ri and R₂ is methyl.

11. The conducting polymer composition of any one of claims 2, 3 and 6 to 9, wherein Ri and R₂ is phenyl.

12. The conducting polymer composition of any one of the preceding claims, comprising at most 10 wt% of the acyclic, disubstituted sulfone, based on an aqueous solution of PEDOT:PSS, wherein at most 10 wt% PEDOT:PSS is contained in the aqueous solution.

13. The conducting polymer composition of any one of the preceding claims, comprising at most 5 wt% of the acyclic, disubstituted sulfone, based on the aqueous solution of PEDOT:PSS, wherein at most 10 wt% PEDOT:PSS is contained in the aqueous solution.

14. The conducting polymer composition of any one of the preceding claims, wherein the acyclic, disubstituted sulfone has a molecular weight of between about 94 g/mol to about 400 g/mol.

15. The conducting polymer composition of any one of the preceding claims, wherein the PEDOT:PSS is provided in a mixing ratio of about 1: 1 to about 1:5.

16. A method for making a conducting polymer composition comprising PEDOT:PSS and an acyclic, disubstituted sulfone, the method comprising

(i) oxidizing an acyclic, disubstituted thioether to the acyclic, disubstituted sulfone and

(ii) mixing the acyclic, disubstituted sulfone with PEDOT:PSS.

17. The method of claim 16, wherein oxidizing in step (i) comprises exposing the acyclic, disubstituted thioether to an oxidizing reagent at a temperature below ambient temperature.

18. The method of claim 16 or 17, wherein mixing in step (ii) comprises providing a PEDOT:PSS solution, adding the acyclic, disubstituted sulfone and shaking the resulting mixture.

19. The method of any one of claims 16 to 18, wherein mixing in step (ii) further comprises sonicating the resulting mixture.

20. The method of any one of claims 16 to 19, wherein after step (ii), the resulting mixture is filtered and kept at a temperature below ambient temperature.

21. A process of making a substrate coated with a composition comprising PEDOT:PSS and an acyclic, disubstituted sulfone, the process comprising providing a substrate, applying the conducting polymer composition on the substrate and drying the applied composition to form the substrate coated with a composition comprising PEDOT:PSS and an acyclic, disubstituted sulfone.

22. A substrate coated with a composition comprising PEDOT:PSS and an acyclic, disubstituted sulfone.