Conductive polymer in organic solvent with fluorinated compound

Abstract

The present invention relates to a composition comprising: a) at least one organic solvent; b) at least one conductive polymer, preferably a cationic polymer; c) at least one fluorinated compound; d) at least one polymeric anion, wherein the at least one polymeric anion is a copolymer comprising ionic and non-ionic repeating units. The present invention also relates to a layered structure comprising the composition, to a process for the production of the composition, to a process for the production of the layered structure and to devices comprising the layered structure as well as to the use of the composition in devices to achieve a prolongation of lifetime.

Claims

1. A composition comprising: a) at least one organic solvent; b) at least one conductive polymer; c) at least one fluorinated compound, wherein the at least one fluorinated compound is a non-ionic compound; d) at least one polymeric anion, wherein the at least one polymeric anion is a copolymer comprising ionic and non-ionic repeating units.

2. The composition according to claim 1, wherein copolymer comprises polymerized styrene monomer units at least a part of which is sulfonated and polymerized non-sulfonated monomer units and wherein molar ratio of the non-sulfonated monomer units is at least 5%, based on the total amount of monomer units in the copolymer.

3. The composition according to claim 1, wherein the copolymer is a hydrogenated styrene-isoprene block copolymer with the structure A-B-C-B-A, in which the block A corresponds to a polystyrene block which is at least partially substituted with tert-butyl groups, the block B corresponds to a block of alternating copolymerised ethylen-propylene units and the block C corresponds to a sulphonated polystyrene block.

4. The composition according to claim 1, wherein the at least one organic solvent a) is selected from the group consisting of an aprotic, a polar, a non-polar and a non-polar, aprotic organic solvent or a mixture of at least two of these.

5. The composition according to claim 1, wherein the composition comprises as the at least one fluorinated compound c) a compound comprising at least one aliphatic or aromatic residue in which at least 10% of the hydrogen atoms are substituted by fluorine atoms.

6. The composition according to claim 1, wherein the composition comprises as the at least one fluorinated compound c) a fluorinated compound having a molecular weight of less than 2,100 g/mol.

7. The composition according to claim 1, wherein the at least one fluorinated compound c) is a mono-, di- or trialkoxysilane, in which at least one fluorinated aliphatic or a fluorinated aromatic group is bond to the Si atom.

8. The composition according to claim 1, wherein the at least one fluorinated compound c) is a polymeric fluorinated compound.

9. The composition according to claim 1, wherein the at least one fluorinated compound c) has a vapor pressure of less than 40 mbar at 100 C. (determined at a pressure of 1 bar).

10. The composition according to claim 1, wherein the at least one conductive polymer b) is a cationic polythiophene.

11. The composition according to claim 10, wherein the cationic polythiophene and the at least one polymeric anion d) are present in the form of a polythiophene: polymeric anion-complex.

12. The composition according to claim 1, wherein the composition comprises: a) 70 to 99.5 wt.-% of the at least one organic solvent; b) 0.05 to 4 wt.-% of the at least one conductive polymer; c) 0.05 to 10 wt.-% of the at least one fluorinated compound; d) 0.05 to 13 wt.-% of the at least one polymeric anion; e) 0 to 6 wt.-% of at least one further additive; wherein the sum of components a) to e) is 100 wt.-%.

13. The composition according to claim 1, wherein the water content of the composition is not more than 2 wt.-%, based on the total weight of the composition.

14. A process for the production of a layered structure, comprising the process steps: I) providing of a substrate with a first surface; II) superimposing the substrate at least partially on its first surface with a composition according to claim 1; III) at least partially removing the at least one organic solvent a) from the composition, thereby obtaining an electrically conductive layer superimposed on the substrate.

15. A layered structure obtainable by the process according to claim 14.

16. A layered structure comprising the following layers: i. a substrate with a first surface; ii. a first layer superimposing at least a part of the substrate surface; wherein the first layer comprises: a) at least one conductive polymer; b) at least one fluorinated compound, wherein the at least one fluorinated compound is a non-ionic compound; c) at least one polymeric anion, wherein the at least one polymeric anion is a copolymer comprising ionic and non-ionic repeating units.

17. The layered structure according to claim 16, wherein (i) the at least one conductive polymer is a cationic polythiophene; (ii) the at least one fluorinated compound is a compound comprising at least one aliphatic or aromatic residue in which at least 10% of the hydrogen atoms are substituted by fluorine atoms; and (iii) the at least one polymeric anion is a copolymer comprising polymerized styrene monomer units at least a part of which is sulfonated and polymerized non-sulfonated monomer units, and wherein the molar ratio of the non-sulfonated monomer units is at least 5%, based on the total amount of monomer units in the copolymer.

18. A device comprising a layered structure according to claim 16.

19. The device according to claim 18, wherein the device is selected from the group consisting of an OLED, a display, an organic solar cell, a hybrid solar cell, a field effect transistor, a touchscreen or a thermoelectric generator or a combination of at least two thereof.

Description

(1) The invention is now explained in more detail with the aid of test methods and non-limiting FIGURES and examples.

(2) FIG. 1 shows an OLED with a standard architecture and encapsulation. The structure is as follows: glass substrate (1) ITO bottom electrode (2) PEDOT hole-injection layer (3) NPB hole-transport layer (60 nm) (4) Alq3 emitter layer (50 nm) (5) LiF top electrode (0.3 nm) (6) Al layer (moisture trap) (200 nm) (7) cover glass (8) sealant (glue) (9)

(3) The PEDOT hole-injection layer (3) can be prepared with the composition according to the present invention.

(4) Test Methods

(5) To evaluate the functional behaviour of a layer of the composition employed in the process according to the invention concerning the layered structure or the device, the procedure is as follows:

(6) Viscosity

(7) The viscosity is measured using a Rheometer (Haake RV1). The rheometer is equipped with a thermostat, a DG 43 beaker (Haake) and a DG 43 rotary (Haake). 12 ml of the dispersion are filled into the beaker. The temperature is fixed at 20 C. using the thermostat. In order to equilibrate the temperature the liquid is kept at a sheer-rate of 50 s-1 for 240 seconds. Subsequently the sheer-rate is increase to 100 s.sup.1 or 700 s.sup.1 (see each measurement). The liquid is then kept for 30 seconds at this sheer-rate. Over the next 30 seconds 30 viscosity measurements are made at the above mentioned sheer-rate (1 measurement/second). The average of those 30 measurements is the final viscosity value.

(8) Solids Content:

(9) The solids content was determined gravimetric using a precision scale (Mettler AE 240). First the empty weighing bottle including lid is weight (weight A). Then about 3 g of dispersion to be analyzed is filled quickly into the bottle, closed by the lid and weighed again to determine the exact total weight B. The bottle is then placed in a fume hood without a lit for about 3 hours to allow the evaporation of volatile solvents at room temperature. In a second step the bottle is placed in a drying oven with ventilation (Memmert UNB200) at 100 C. for 16 hours. When the sample bottle is removed from the oven, immediate coverage by the glass lid is important due to the hygroscopic nature of the dry dispersion material. After 10-15 min of cooling down period the bottle is weighed again including lid to determine weight C. There is always a repeat determination of 2 samples.
Calculation of the solids contents: wt. % solids content=100(CA)/(BA)

(10) Water Contents Measurement by Karl-Fischer Titration:

(11) The water content is determined by Karl Fischer titration. A Metrohm 787 KF Titrino with a 703 titration stand is used to this end. The titration vessel is filled with analytical grade methanol so that about 1 cm of the platinum electrode is submerged. Then approximately 5 ml of Hydranal buffer acid is pipetted in. The titration cell is automatically dried by starting the KFT program. Preparation is complete when the message KFT conditioned appears. Approximately 5 ml of the dispersion to be analysed is then introduced into the titration vessel using a syringe and the exact mass of the dispersion used is determined by back-weighing the syringe. The titration is then started. The measured value is determined as the mean of three individual measurements.

(12) Kelvin Probe:

(13) The dispersion was spin-coated on ozonized ITO, dried for 15 min at 200 C. and the work function was determined via Kelvin probe force microscopy.

(14) Production of OLEDs:

(15) A) Substrate Cleaning

(16) ITO-precoated and pre-patterned (by etching, pattern: 24 parallel ITO stripes, 2 mm wide to allow for 8 individually connected diodes, OPTREX) glass substrates (5 cm5 cm) are cleaned by the following process before use: 1. thorough rinsing with acetone, isopropanol and water, 2. ultrasound treatment in a bath at 70 C. in a 0.3% strength Mucasol solution (Merz) for 15 min, 3. thorough rinsing with water, 4. drying by spinning off in a centrifuge, 5. UV/ozone treatment (PR-100, UVP Inc., Cambridge, GB) for 15 min directly before use.
B) Application of the Hole Injection Layer (HIL): PEDOT:Counterion-Layer For the production of the PEDOT:counter-ion layer HIL the composition is first filtered by a 0.45 m PVDF syringe filter and then applied onto the above mentioned substrate or electrode layer (layer sequence glass substrate/ITO). The coating composition was applied onto the electrode by means of a pipette to completely cover the area. Excess dispersion was spun off by spin coating. Thereafter, a drying process on a hot-plate was carried out in one step: 5 min at 200 C. in air. This leads to an approximately 50 nm thick homogenous layer. The layer thickness was measured by profilometer (Tencor, Alphastep 500).
C) Application of the Hole-Transport and Emitter Layer The ITO substrate which was coated by the dispersion of invention in the previous step is now transferred into to a vacuum vapour deposition chamber (Univex 350, Leypold). Here the hole transport layer N,N-bis(naphthalene-1-yl)-N,N-bis(phenyl)benzidine (NPB) with a thickness of 60 nm followed by tris-(8-hydroxyquinoline)aluminium (Alq3) of 50 nm thickness are deposited. The pressure during deposition is <510.sup.6 mbar. The deposition rate is 1 Angstrom/s. Rate and layer thickness are monitored by quartz crystal microbalances (QCMs).
D) Cell Application of the Metal Cathode The layer system is then transferred to a glovebox with nitrogen and integrated vacuum deposition system (Edwards) and metallised with metal electrodes. To this end the substrate is placed on a shadow mask with the layer system facing downwards. The shadow mask comprises of 2 mm wide rectangular slots, which cross the ITO strips at right angles. Under a pressure of <510.sup.6 mbar, a 0.3 nm thick LiF layer followed by a 200 nm thick aluminium layer are deposited in succession from two evaporation boats. The deposition rates are 1 Angstrom/s for LiF and 10 Angstrom/s for Al. The surface area of the individual OLEDs is 4.0 mm.sup.2. The devices are then encapsulated with a special cover glass providing a void on the inside. In this void a moisture getter (SAES, DFX/SS-30-A/F/10180.14) is placed. The cover glass is glued onto the device under nitrogen using a two-component glue. Now the devices were ready for OLED characterisation in air.

(17) Schematic of an OLED with this Standard Architecture glass//ITO//PEDOT HIL//NPB (60 nm)//Alq3 (50 nm)//LiF(0.3 nm)//Al(200 nm) can be seen in FIG. 1.
E) OLED Characterization The two electrodes of the OLED are connected to (brought into contact with) a power supply using electrical wires and contact pins. The positive pole is connected to the ITO electrode, the negative pole to the metal electrode. The OLED current and the electroluminescence intensity are plotted against the voltage. The electroluminescence is detected with a photodiode (EG&G C30809) calibrated with a luminance meter (Minolta LS-100) to absolute luminance. The live time is then determined by applying a constant current of I=1.92 mA (48 mA/cm.sup.2) to the arrangements and monitoring the voltage and light intensity as a function of time.
Electrical Conductivity:

(18) The electrical conductivity means the inverse of the specific resistance. The specific resistance is calculated from the product of surface resistance and layer thickness of the conductive polymer layer. The surface resistance is determined for conductive polymers in accordance with DIN EN ISO 3915. In concrete terms, the polymer to be investigated is applied as a homogeneous film by means of a spin coater to a glass substrate 50 mm50 mm in size thoroughly cleaned by the abovementioned substrate cleaning process. In this procedure, the coating composition was applied onto the electrode by means of a pipette to completely cover the area. Excess dispersion was spun off by spin coating using the same conditions as in the section Application of the hole injection layer (HIL):PEDOT:counterion layer. This leads to an approximately 50 nm thick homogenous layer for all materials.

(19) In all cases silver electrodes of 2.0 cm length at a distance of 2.0 cm are vapour-deposited on to the polymer layer via a shadow mask. The square region of the layer between the electrodes is then separated electrically from the remainder of the layer by scratching two lines with a scalpel. The surface resistance is measured between the Ag electrodes with the aid of an ohmmeter (Keithley 614). The thickness of the polymer layer is determined with the aid of a Stylus Profilometer (Dektac 150, Veeco) at the places scratched away.

(20) The invention is now explained in more detail with the aid of test methods and non-limiting examples.

EXAMPLES

Example 1: PEDOT:Counterion-Complex in MTBE without Fluorinated Compound (Comparative Example)

(21) In a 1 L three-necked round-bottom flask equipped with mechanical stirrer 7.9 g of 3,4-ethylenedioxythiophene (Heraeus Deutschland GmbH & Co KG, Germany) were added to a mixture of 130 g of methyl tert-butyl ether (MTBE), 215 g of a solution of sulfonated block-copolymer in cyclohexane/heptane-mixture (Kraton Nexar MD 9150, 11.0% solids) and 9 g of para-toluene sulfonic acid (Aldrich) and stirred for 30 min. 15 g of dibenzoylperoxide (Aldrich) were added and the mixture was heated to reflux. After 6 h the mixture was allowed to cool to room temperature and diluted with 1175 g of methyl tert-butyl ether. After two days residual solids were filtered off and the filtrate was purified by diafiltration (ceramic membrane filter (Pall Schumasiv), pore size 50 nm, part number 88519721) in order to remove low molecular weight impurities <50 nm.

(22) Analysis:

(23) Solids content: 2.1% (gravimetric)

(24) Water content: 0.2% (Karl-Fischer-Titration)

(25) Solvent composition: 88% methyl tert-butyl ether, 6% cyclohexane, 6% n-heptane;

(26) Ratio PEDOT:counter-ion: 1:3 (w/w)

(27) Work function: 4.87 eV (Kelvin Probe)

Example 2: PEDOT:Counterion-Complex in MTBE without Fluorinated Compound (Comparative Example)

(28) 100 g of Example 1 are mixed with 200 g of methyl tert-butyl ether. The material is filtered through 0.45 m.

(29) Analysis:

(30) Solvent composition: 96% methyl tert-butyl ether, 2% cyclohexane, 2% n-heptane;

(31) Conductivity: 2.110.sup.4 S/cm

Example 3: PEDOT:Counterion-Complex in MTBE with Fluorinated Compound (Inventive Example)

(32) 0.5 g of 1H,1H,2H,2H-perfluorodecyl triethoxysilane were added to 55 g of the dispersion obtained in example 1 and sonicated for 10 h and filtered through a filter with a pore size of 0.45 m. 50 g of this mixture are mixed with 100 g of tert-butyl methyl ether. The material is filtered through 0.45 m.

(33) Analysis

(34) Water content: <0.1% (Karl-Fischer-Titration)

(35) Solvent composition: 96% methyl tert-butyl ether, 2% cyclohexane, 2% n-heptane;

(36) Work function: 5.70 eV (Kelvin Probe)

(37) Conductivity: 910.sup.5 S/cm

Example 4: PEDOT:Counterion-Complex in Butyl Benzoate without Fluorinated Additive (Comparative Example)

(38) In a 1 L three-necked round-bottom flask equipped with mechanical stirrer a mixture of 401 g of butyl benzoate (ABCR GmbH), 233 g of a solution of sulfonated block-copolymer in butyl benzoate (Kraton Nexar MD 9150, 11.8% solids) and 24 g of dibenzoyl peroxide was stirred and purged with nitrogen for 30 min. The mixture was heated to 60 C. and 12.5 g of 3,4-ethylenedioxythiophene (Heraeus Deutschland GmbH & Co KG, Germany) and 45 g butyl benzoate were added via syringe. After stirring 6 h at 60 C. and 1 h at 130 C. the mixture was allowed to cool to room temperature. 732 g of the dispersion were diluted with 1320 g of butyl benzoate. The resulting dispersion was sonicated for 8 h and filtered (pore size 0.2 m).

(39) Analysis

(40) Solvent composition: 100% butyl benzoate

(41) Conductivity: 2.010.sup.3 S/cm

Example 5: PEDOT:Counterion-Complex in Butyl Benzoate with Fluorinated Compound (Inventive Example)

(42) 0.05 g of pentafluorostyrene/tert-butylstyrene copolymer (momomer ratio 90/10; ABCR GmbH, Karlsruhe, Germany) were added to 9.95 g of the dispersion of example 3 and the mixture was stirred for 1 h at 60 C. until the polymer was completely dissolved.

(43) Solvent composition: 100% butyl benzoate

(44) Conductivity: 2.310.sup.3 S/cm

Example 6: OLED-Device Testing of Example 2 and 3 as Hole Injection Layer

(45) The dispersion from Examples 2 and 3 were used to prepare OLEDs. The film thickness of the layers according to the invention was 50 nm. The graphs plotting current and electroluminescence against voltage and the lifetime measurements for the OLEDs are compared. For the OLED diode characteristics at the lifetime measurement the values for voltage and luminance are extracted at constant current 48 mA/cm.sup.2 (forward bias). The voltage and luminance at t=0 h are U.sub.0 and L.sub.0 respectively. The efficacy at U.sub.0 is calculated as the quotient of L.sub.0/current I. As a measure of stability the voltage and luminance at t=150 h including U.sub.150h, L.sub.150h, the percentage of initial luminance (L.sub.0/L.sub.150h00) and the voltage increase U.sub.150hU.sub.0 are stated showing the change.

(46) TABLE-US-00001 TABLE 1 OLED characteristics for example 3 containing a small molecule fluorinated compound according to the invention and example 2 as a reference comparing voltage and luminance at constant current of 48 mA/cm.sup.2 at time 0 h and after 150 h as a life time measurement. (Initial Voltage U.sub.0; Initial Luminance L.sub.0; Efficiency at initial voltage; Voltage after 150 h U.sub.150 h; Luminance after 150 h L.sub.150 h; Luminance decrease L.sub.150 h/L.sub.0 h; Voltage increase U.sub.150 h - U.sub.0) Device data of ITO//HIL//NPB//ALQ.sub.3//LiF//Al OLEDs at I = const. = 48 mA/cm.sup.2 U.sub.0 L.sub.0 Efficacy at U.sub.0 U.sub.150 h L.sub.150 h L.sub.150 h/L.sub.0 U.sub.150 h U.sub.0 [V] [cd/m.sup.2] [cd/A] [V] [cd/m.sup.2] [%] [V] Example 3 5.12 1018 2.12 5.82 860 84 0.70 (inventive) Example 2 6.33 1169 2.44 7.31 893 76 0.98 (comparative)

(47) The example demonstrates that the dispersions according to example 3 shows a great improvement as hole injection with lower initial voltage, less voltage increase over time and improved life-time stability compared to example 2.

Example 7: OLED Device Testing of Example 4 and 5

(48) The dispersions from Example 4 and 5 were used to prepare OLEDs. The film thickness of the layers according to the invention was 50 nm.

(49) The graphs plotting current and electroluminescence against voltage and the lifetime measurements for the OLEDs are compared. For the OLED diode characteristics at the lifetime measurement the values for voltage and luminance are extracted at constant current 48 mA/cm.sup.2 (forward bias). The voltage and luminance at t=0 h are U.sub.0 and L.sub.0 respectively. The efficacy at U.sub.0 is calculated as the quotient of L.sub.0/current I. As a measure of stability the voltage and luminance at t=150 h including U.sub.150h, L.sub.150h, the percentage of initial luminance (L.sub.0/L.sub.150h*100) and the voltage increase U.sub.150hU.sub.0 are stated showing the change.

(50) TABLE-US-00002 TABLE 2 OLED characteristics for example 4 and 5 comparing voltage and luminance at constant current of 48 mA/cm.sup.2 at time 0 h and after 150 h as a life time measurement. (Initial Voltage U.sub.0; Initial Luminance L.sub.0; Efficacy at initial voltage; Voltage after 150 h U.sub.150 h; Luminance after 150 h L.sub.150 h; Luminance decrease L.sub.150 h/L.sub.0 h; Voltage increase U.sub.150 h U.sub.0) Device data of ITO//HIL//NPB//ALQ.sub.3//LiF//Al OLEDs at I = const. = 48 mA/cm.sup.2 U.sub.0 L.sub.0 Efficacy at U.sub.0 U.sub.150 h L.sub.150 h L.sub.150 h/L.sub.0 U.sub.150 h U.sub.0 [V] [cd/m.sup.2] [cd/A] [V] [cd/m.sup.2] [%] [V] Example 5 5.95 1069 2.23 6.34 843 79 0.39 (inventive) Example 4 7.36 1277 2.66 8.37 760 60 1.01 (comparative)

(51) The example demonstrates that the dispersions according to example 5 shows a great improvement as hole injection with lower initial voltage, less voltage increase over time and improved life-time stability compared to example 4.