ELECTRICALLY CONDUCTING PEDOT SOL-GEL DERIVED COATING

Abstract

An electrically conducting organic-inorganic sol-gel derived coating. Films are generated exhibiting good electrical conductivity with high resistance to substrate delamination. PEDOT:PSS is used as the conducting polymer dispersed within an organic-inorganic hybrid sol-gel.

Claims

1. A substrate having a transparent or semi-transparent coating configured to be electrically conducting, the coating comprising: a sol-gel derived organic-inorganic oxide network resultant from condensation reactions of at least one organic and at least one inorganic sol-gel precursor compounds; an electrically conducting polymer comprising poly(3,4-ethylenedioxythiophene) (PEDOT) and a sulfonated polymer incorporated within the network.

2. The substrate as claimed in claim 1 wherein the sulfonated polymer is poly(styrene sulfonate) (PSS).

3. The substrate as claimed in claim 1 wherein the sulfonated polymer comprises a sulfonated poly(amic acid) (SPAA) or a sulfonated poly(imide) (SPI).

4. The substrate as claimed in claim 1 wherein the sol-gel precursor compounds comprise a silane and a silicate.

5. The substrate as claimed in claim 4 wherein silane comprises any on or a combination of the set of: tetramethoxysilane (TMOS); tetraethoxysilane (TEOS); 3-glycidoxypropylmethoxysilane (GLYMO).

6. The substrate as claimed in claim 4 wherein the silicate comprises any one or a combination of the set of: tetraethoxy orthosilicate (TEOS); methyltriethoxy orthosilicate (MTEOS); phenyltriethoxy orthosilicate (PTEOS); octyltriethoxy orthosilicate (OTEOS); dimethyldiethoxy orthosilicate (DMDEOS); methyltrimethoxy orthosilicate (MTMOS); phenyltrimethoxy orthosilicate (PTMOS); tetramethoxy orthosilicate (TMOS).

7. The substrate as claimed in claim 1 wherein the network comprises a polysiloxane.

8. The substrate as claimed in claim 7 wherein the polysiloxane comprised a linear polysiloxane having a silicone-oxygen backbone.

9. The substrate as claimed in claim 1 wherein the coating further comprises a corrosion inhibitor.

10. The substrate as claimed in claim 9 wherein the corrosion inhibitor comprises any one or a combination of the following set of: a modified orthophosphate; a polyphosphate; a calcium modified silicone gel; a lithium grease; a synthetic hydrocarbon oil; a mineral oil; an organic molybdenum compound.

11. The substrate as claimed in claim 1 wherein the coating further comprises any one or a combination of the following set of: silica based particles; nanofibers or nanoparticles; carbon nanotubes; carbon graphene.

12. An optoelectronic device comprising a coated substrate as claimed in claim 1.

13. An optoelectronic device wherein the substrate as claimed in claim 1 is configured as an electrode.

14. A method of coating a substrate with a transparent or semi-transparent electrically conducting coating comprising: preparing an organic-inorganic hybrid sol-gel from at least one organic and at least one inorganic sol-gel precursor compounds; adding a poly(3,4-ethylenedioxythiophene) PEDOT:sulfonated polymer to the sol-gel to form a pre-coating mixture; applying the mixture to a substrate; curing the mixture at the substrate.

15. The method as claimed in claim 14 wherein the step of curing comprises curing at a temperature below 100 C.

16. The method as claimed in claim 14 further comprising adding a linear polysiloxane to the sol-gel.

17. The method as claimed in claim 14 wherein a ratio of the PEDOT:sulfonated polymer to sol-gel is: (1.5 to 2.5) PEDOT:sulfonated polymer to (0.5 to 1.5) sol-gel.

18. The method as claimed in claim 14 further comprising adding to the sol-gel or mixture any one or a combination of the following set of: silica based particles; HBr; nanofibres or nanoparticles; carbon nanotubes; carbon graphene; silver based compounds; formic acid; DMSO; Methanol.

19. The method as claimed in claim 14 wherein the sol-gel precursor compounds comprise a silane and a silicate.

20. The method as claimed in claim 14 wherein silane comprises any on or a combination of the set of: tetramethoxysilane (TMOS); tetraethoxysilane (TEOS); 3-glycidoxypropylmethoxysilane (GLYMO).

21. The method as claimed in claim 14 wherein the silicate comprises any one or a combination of the set of: tetraethoxy orthosilicate (TEOS); methyltriethoxy orthosilicate (MTEOS); phenyltriethoxy orthosilicate (PTEOS); octyltriethoxy orthosilicate (OTEOS); dimethyldiethoxy orthosilicate (DMDEOS); methyltrimethoxy orthosilicate (MTMOS); phenyltrimethoxy orthosilicate (PTMOS); tetramethoxy orthosilicate (TMOS).

22. The method as claimed in claim 14 comprising adding a polysiloxane to the organic-inorganic hybrid sol-gel prior to applying the mixture to the substrate.

23. A sol-gel based formulation to form a transparent or semi-transparent electrically conducting coating comprising: at least one organic and at least one inorganic sol-gel precursor compounds to form a sol-gel derived organic-inorganic oxide network; and a conducting polymer comprising poly(3,4-ethylenedioxythiophene) PEDOT:sulfonated polymer.

24. A substrate having a transparent or semi-transparent electrically conducting coating formed by a process of coating the substrate with a formulation comprising: at least one organic and at least one inorganic sol-gel precursor compounds to form a sol-gel derived organic-inorganic oxide network; and a conducting polymer comprising poly(3,4-ethylenedioxythiophene) PEDOT:sulfonated polymer.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0038] A specific implementation of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which:

[0039] FIG. 1 is a photograph of a sol-gel/PEDOT:PSS film on a glass substrate in front of a digital electrometer indicating an electrical resistance of 429;

[0040] FIG. 2 are photographs of three sol-gel/PEDOT:PSS films on a glass substrates having the thicknesses 50 nm, 100 nm and 200 nm;

[0041] FIG. 3 are transmittance spectra of the three sol-gel/PEDOT:PSS films of FIG. 2 having 50 nm, 100 nm and 200 nm thicknesses;

[0042] FIG. 4 is a AFM image of a sol-gel/PEDOT:PSS.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION

[0043] A sol-gel based system has been developed that in combination with a specific conducting polymer (PEDOT:sulfonated polymer) has been found to provide a transparent or semi-transparent coating having optimised physical, mechanical and electrical characteristics for application as an electrode in optoelectronic devices such as organic solar cells (OSCs), organic light emitting diode (OLEDs), organic photovoltaic devices (OPVs), capacitors, sensors, liquid crystal displays (LCDs), light emitting diodes (LEDs), touch panel displays, lasers, detectors and the like. The present coating may be formed from a variety of different sol precursors including organic, inorganic and organic-inorganic hybrid species. The inventors have identified silica based species as offering the desired physical and mechanical properties to yield a coating that is capable of chemically bonding to the substrate once applied and is resistant to delamination to provide a coating having the desired strength including mechanical toughness, hardness and flexibility.

[0044] Various dopant species may be added to the present sols or the pre-coating mixtures in order to optimise the mechanical, physical or electrical properties of the coating as detailed in the following examples.

Preparation of Pre-Coating Solution

EXAMPLE 1

[0045] A solution was prepared by mixing 1) 20 ml TEOS; 2) 3 ml 3-glycidyloxypropyltrimethoxysilane; 3) 500 l HNO.sub.3; 4) 40 ml 2-propanol; and 5) 40 ml water; forming approximately 100 ml of a sol.

[0046] The as-formed sol was then mixed directly with an aqueous colloidal dispersion of poly(3,4-ethylenedioxythiophene) (PEDOT):poly(styrene sulfonate) (PSS) in the amount 700 ml PEDOT:PSS water solution with 300 ml sol-gel. The PEDOT:PSS aqueous solution was prepared by dissolving 0.08 PEDOT:PSS pellets in a 100 ml.

EXAMPLE 2

[0047] The organic-inorganic hybrid pre-coating mixture was prepared in accordance with example 1. In addition, 10 g poly(dimethylsiloxane) (PDMS) was added to the hybrid sol-gel prior to combining with the PEDOT:PSS solution.

EXAMPLE 3

[0048] The organic-inorganic hybrid pre-coating mixture was prepared in accordance with example 1. In addition, 1.0 weight % silica nano-particles (10 to 20 nm) were added to the final sol prior to mixing with the PEDOT:PSS solution.

EXAMPLE 4

[0049] The organic-inorganic hybrid pre-coating mixture was prepared in accordance with example 1. In addition, a corrosion inhibitor Heucophos Zapp (ZAPP) (1 to 5 weight %) was added to the sol.

EXAMPLE 5

[0050] The pre-coating mixture was prepared via the sol-gel and the conducting polymer solutions according to example 1. To further enhance the conductivity of the cured coating, a dopant species (0.05 g silver wire) was added to the pre-coating mixture prior to layering onto the substrate and curing. According to further examples, optional and additional conductivity enhancing additives include similar or corresponding amounts of a nano fibres or carbon nano tubes.

EXAMPLE 6

[0051] The pre-coating mixture was prepared via the sol-gel and the conducting polymer solutions according to example 1. To enhance the electrical conductivity, dimethyl sulfoxide (DMSO) (1 to 5 weight % of the pre-coating mixture) was added to the pre-coating mixture.

EXAMPLE 7

[0052] The pre-coating mixture was prepared via the sol-gel and the conducting polymer solutions according to example 1. To enhance the electrical conductivity, HBr (1 to 5 weight % of the pre-coating mixture) was added to the pre-coating mixture.

Substrate Coating

Preparation of Thin Films

EXAMPLE 1

[0053] The sol-gel and PEDOT:PSS pre-coating mixture of example 1 was applied onto a glass substrate by spray coating. A strongly bonded electrically conducting film was obtained following curing at 80 C. In a further embodiment and to enhance the electrical conductivity, HBr (100 to 200 ppm concentration and 1 to 5 weight % of the pre-coating mixture) was added to the forming film. A coating was obtained having a coating thickness of 60 to 70 nm.

EXAMPLE 2

[0054] PEDOT:PSS thin films were cast on either polyacrylic plastics (PP) or glass slides (GS) by the spin-coating method at the rpm of 1000 or the spray-coating method. PP or GS were respectively cleaned by soap water, DI water, and isopropanol before applying the thin films. The casted thin films were subsequently cured by placing in an oven at 85 C. for 30 min.

[0055] Optionally, a multi-layer coating may be provided by sequential coating of further sol-gel based PEDOT:PSS mixtures with multiple curing stages.

Conductivity Enhancement

[0056] Additives such as concentrated sulphuric acid, HBr, HFA, DMSO or methanol may be added to the pre-coating mixture or the sol-gel based film once applied to the substrate prior to curing. Such additives have been found to enhance the conductivity of the final cured coating. The concentration of such additives is dependent on the species of the sol-gel but typically may be 1 to 5 weight % of the pre-coating mixture.

Characterisation of PEDOT:PSS Sol-Gel Films

[0057] The conductivities of the polymer film of example 6 were measured using a two point probe technique with a digital gauge electrometer. Two electrical contacts were made by applying a conducting silver paste on two sides of the PEDOT:PSS sol-gel film on a glass substrate. The morphology of the films was recorded using atomic force microscopy (AFM) in taping mode with a conventional AFM machine-FEI Nova NanoSEM and Vecco Nanoscope III AFM. Optical transmittance and absorption spectra of the PEDOT:PSS sol-gel films are measured using a diode array Nicolet Nexue FTIR spectrophotometer.

Results

Electrical Conductivity and Resistance

[0058] The sol-gel PEDOT:PSS film of 50 to 100 nm thickness on glass exhibited good electrical conductivity (1 k /sq) and high transparency (90%). The transparent sol-gel/PEDOT:PSS film is illustrated in FIG. 1 with an observed electrical resistance of 429. After immersion in water for one month, a negligible change in electrical conductivity was observed. Accordingly, the as-formed film illustrated good adhesion to the glass substrate was not delaminated or showed any appreciable degradation with water contact.

[0059] In a further experiment, PEDOT grade PH1000 was used in place of the standard grade PEDOT of example 6. A significantly reduced sheet resistance was observed being less than 100 /sq for a coating thickness of 50 to 100 nm.

Transmittance

[0060] The polymer film produced in accordance with example 6 provided transmittance results as detailed in FIG. 2. Three coating thicknesses were investigated including in particular film thicknesses of 50 nm (A), 100 nm (B) and 200 nm (C). Electrical conductivities of 3 k /sq for coating A, 1.5k /sq for coating B and 0.8 k /sq for coating C) were obtained.

Morphology

[0061] An AFM image of the sol-gel/PEDOT:PSS film of example 6 is shown in FIG. 4. The AFT image suggests an approximate similar size of sol-gel nanoparticles (the bright spot regions) and PEDOT:PSS particles (the darker regions). However, the darker regions may also comprise the sol-gel particles as this cannot be fully distinguished using AFM.