FORMULATION CONTAINING A CROSSLINKABLE POLYMER

Abstract

The present invention relates to a formulation comprising at least one crosslinkable polymer and at least one organic solvent, wherein the at least one crosslinkable polymer is contained in the formulation in a concentration of at least 0.5 g/L, wherein the at least one organic solvent has a boiling point of at least 200° C., characterized in that the solubility of the at least one crosslinkable polymer in the at least one organic solvent is such that the crosslinkable polymer at a concentration of 30 g/L starts to precipitate if 60 vol.-% or less of ethanol is added to the formulation, to the use of these formulations for the preparation of electronic or optoelectronic devices, to a process for the preparation of electronic or optoelectronic devices using these formulations as well as to electronic or optoelectronic devices.

Claims

1.-24. (canceled)

25. A formulation comprising at least one crosslinkable polymer and at least one organic solvent, wherein the at least one crosslinkable polymer is contained in the formulation in a concentration of at least 0.5 g/L, wherein the at least one organic solvent has a boiling point of at least 200° C., wherein the solubility of the at least one crosslinkable polymer in the at least one organic solvent is such that the crosslinkable polymer at a concentration of 30 g/L starts to precipitate if 60 vol.-% or less of ethanol is added to the formulation.

26. The formulation according to claim 25, wherein the formulation comprises one organic solvent.

27. The formulation according to claim 25, wherein the formulation comprises one crosslinkable polymer.

28. The formulation according to claim 25, wherein the crosslinkable polymer starts to precipitate if 45 vol.-% of less of ethanol is added to the formulation.

29. The formulation according to claim 25, wherein it has a viscosity of ≤25 mPas.

30. The formulation according to claim 25, wherein it has a surface tension in the range from 15 to 70 mN/m.

31. The formulation according to claim 25, wherein the at least one solvent is selected from 1-Methylnaphthalene, 1-Methoxynaphthalene, 3-Phenoxytoluene, Cyclohexylhexanoate and Menthylisovalerate.

32. The formulation according to claim 25, wherein the at least one crosslinkable polymer has a solubility of ≥0.5 g/L in the at least one organic solvent.

33. The formulation according to claim 25, wherein the concentration of the at least one crosslinkable in the formulation is in the range from 0.5 to 50 g/L.

34. The formulation according to claim 25, wherein the at least one crosslinkable polymer has a molecular weight M.sub.w in the range from 1,000 to 2,000,000 g/mol.

35. The formulation according to claim 25, wherein the crosslinkable polymer contains at least one crosslinkable repeating unit.

36. The formulation according to claim 25, wherein the proportion of the at least one crosslinkable repeating unit in the crosslinkable polymer is in the range from 0.01 to 50 mol %, based on 100 mol % of all repeating units in the polymer.

37. The formulation according to claim 25, wherein the crosslinkable polymer contains at least one repeating unit which has charge transporting properties.

38. The formulation according to claim 25, wherein the proportion of the at least one repeating unit which has charge-transporting properties in the polymer is in the range from 10 to 80 mol %, based on 100 mol % of all repeating units in the polymer.

39. The formulation according to claim 25, wherein the crosslinkable polymer contains at least one repeating unit which contains aromatic structures having 6 to 40 C atoms, which are typically used as polymer backbone.

40. The formulation according to claim 25, wherein the proportion of the at least one repeating unit which contains aromatic structures having 6 to 40 C atoms, which are typically used as polymer backbone, in the polymer is in the range from 10 to 80 mol %, based on 100 mol % of all repeating units in the polymer.

41. A method comprising providing the a formulation according to claim 25 and preparing an electronic or optoelectronic device selected from the group consisting of organic electroluminescent devices (OLED), organic field-effect transistors (OFETs), organic integrated circuits (O-ICs), organic thin-film transistors (TFTs), organic solar cells (O-SCs), organic laser diodes (O-lasers), organic photovoltaic (OPV) elements or devices or organic photoreceptors (OPCs).

42. The method according to claim 41 for the preparation of organic electroluminescent devices (OLED).

43. An electronic or optoelectronic device selected from the group consisting of organic electroluminescent device (OLED), organic field-effect transistor (OFETs), organic integrated circuit (O-ICs), organic thin-film transistor (TFTs), organic solar cell (O-SCs), organic laser diode (O-lasers), organic photovoltaic (OPV) element or device and organic photoreceptor (OPCs), having one or more active layers, where at least one of these active layers comprises the formulation as claimed in claim 25.

44. A process for the preparation of an electronic or optoelectronic device having a layer containing a crosslinked polymer with a high degree of crosslinking, wherein a) a formulation of the present invention is applied to a substrate or another layer via a deposition method, b) the applied formulation is dried in that the at least one solvent is evaporated, and c) the crosslinkable polymer is crosslinked.

45. The process according to claim 44, wherein as deposition method a printing technique is used.

46. The process according to claim 45, wherein as printing technique ink jet printing is used.

47. The process according to claim 44, wherein the crosslinking is conducted using elevated temperature.

48. A process for the preparation of an electronic or optoelectronic device, having a layer containing at least one crosslinked polymer with a specific degree of crosslinking, wherein this degree is obtained in that a formulation according to claim 25 is used, wherein this degree can be increased in that at least one organic solvent having a boiling point of at least 200° C. is used in which the solubility of the at least one crosslinkable polymer is such that the at least one crosslinkable polymer at a concentration of 30 g/L starts to precipitate if a lower amount of ethanol is added to the formulation, and wherein this degree can be decreased in that at least one organic solvent having a boiling point of at least 200° C. is used in which the solubility of the at least one crosslinkable polymer is such that the at least one crosslinkable polymer at a concentration of 30 g/L starts to precipitate if a higher amount of ethanol is added to the formulation.

Description

WORKING EXAMPLES

[0219] Part A:

[0220] Synthesis of the Monomers

[0221] The monomers for preparing the crosslinkable polymer Po2 according to the present invention are already described in the prior art, are commercially available or are prepared according to the literature procedure and are summarized in the following Table 1:

TABLE-US-00002 TABLE 1 monomer structure synthesis according to Mo1-Bo [00034] WO 2013/156130 A1 Mo2-Bo [00035] WO 2010/097155 A1 Mo3-Br [00036] Macromolecules 2000, 33, 2016-2020

[0222] Part B:

[0223] Synthesis of the Polymers

[0224] Preparation of polymer Po2 according to the present invention.

[0225] Polymer Po2 according to the present invention is prepared by SUZUKI coupling according to the method described in WO 2010/097155 A1 from the monomers disclosed in Part A.

[0226] Polymer Po2 prepared in this manner contains the structural units after removal of the leaving groups in the percentages indicated in Table 2 (percentages=mol %). In the case of polymer Po2 which is prepared from monomers which have aldehyde groups, these are converted into crosslinkable vinyl groups after the polymerization by means of the WITTIG reaction in accordance with the process described in WO 2010/097155 A1. The polymer listed in Table 2 and used in Part C thus has crosslinkable vinyl groups instead of the aldehyde groups originally.

[0227] The palladium and bromine contents of the polymer is determined by ICPMS. The determined values are below 10 ppm.

[0228] The molecular weight M.sub.w and the polydispersity D are determined by means of gel permeation chromatography (GPC) (model: Agilent HPLC System Series 1100) (column: PL-RapidH from Polymer Laboratories, solvent: THF with 0.12% by volume o-dichlorobenzene, detection: UV and Refractive index, temperature: 40° C.). Calibration is with polystyrene standards.

TABLE-US-00003 TABLE 2 Polymer Mo A % Mo B % Mo C % Mw/D Po2 Mo3-Br 50 Mo1-Bo 40 Mo2-Bo 10 82K

[0229] Part C:

[0230] Preparation of the Polymer Inks

[0231] The polymer was mixed with each of the pure solvents mentioned in examples 1 to 5 of the following Table 3 in a glass bottle. The dissolution occurred at room temperature under magnetic stirring in argon atmosphere. After complete dissolution of the polymer, the ink was filtered through a 0.2 μm PTFE filter with argon overlay. If the ink was used for inkjet printing, the ink was additionally degassed at a reduced pressure of 20 mbar for 5 minutes.

TABLE-US-00004 Example 1 [00037] 1-Methyl- naphthalene Example 2 [00038] 1-Methoxy- naphthalene Example 3 [00039] 3-Phenoxy- toluene Example 4 [00040] Cyclohexyl- hexanoate Example 5 [00041] Menthyl- isovalerate

[0232] Part D

[0233] Precipitation Test: Polymer-Solvent Affinity

[0234] Ethanol Precipitation Test

[0235] A 1.5 ml solution of polymer Po2 was prepared at 30 g/L with each solvent in glass bottles. A high concentration facilitated the visualization of the onset of the precipitation. Ethanol was added to the mixture dropwise under magnetic stirring. The amount of ethanol added at which the mixture started to precipitate (appeared milky) was recorded.

[0236] Acetone Precipitation Test

[0237] A 1.5 ml solution of polymer Po2 was prepared at 30 g/L with each solvent in glass bottles. Acetone was added to the mixture dropwise under magnetic stirring. The amount of acetone added at which the mixture started to precipitate (appeared milky) was recorded.

[0238] The volume of ethanol and acetone needed to start the precipitation of polymer Po2 (30 g/L) in different inks using different solvent is shown in the following table 4.

TABLE-US-00005 TABLE 4 Vol. % of Vol. % of Solvent ethanol acetone 1-Methylnaphthalene 30 178 1-Methoxynaphthalene 27 180 3-Phenoxytoluene 23 120 Cyclohexylhexanoate 21 97 Menthylisovalerate 13 59

[0239] Part E:

[0240] Preparation of the Thin Polymer Films

[0241] The solutions of examples 1 to 5 are filled into DMC cartridges. An Inkjet printer is used to deposit large area films of 20 mm×20 mm. After the films are deposited, they are dried under vacuum for 4 minutes under 10.sup.−3 mbar.

[0242] To proceed to the crosslinking reaction, the film is placed on a hotplate at 225° C. for 30 minutes under nitrogen atmosphere (glovebox).

[0243] Part F:

[0244] Characterization of the Stability of the Thin Polymer Films

[0245] The polymer inks were prepared at 5 g/L. A 4 cm.sup.2 square layer was printed from each ink onto a glass substrate at a resolution adjusted from 362.86 DPI (Drop Per Inch) to 1270 DPI. The wet film was dried in a vacuum chamber at 10.sup.−4 mbar for 4 minutes. The dried layer was then annealed on a hotplate in a nitrogen atmosphere for 30 minutes at 225° C. to initiate the crosslinking reaction in the film.

[0246] To test the solvent resistance of the thin polymer films having a thickness of 70 nm, 90 pl of 3-Phenoxytoluene (3-PT) was dropped by inkjet printing on the center of each layer. (A solvent in which the polymer has a high solubility is used to observe whether the crosslinking reaction successfully happened). After five minutes soaking, 3-Phenoxytoluene was dried in the vacuum chamber under 10.sup.−4 mbar for 4 minutes. The chemical damage was then characterized by surface analysis according to the method described in WO 2018/104202 A1. The damage was observed by interferometry and the cross-section of the damage was analysed. Thin films processed using a formulation of the present invention have a high solvent resistance, showed by a small damage observed on the film surface. The results are shown in the following table 5 as well as in FIG. 1.

TABLE-US-00006 TABLE 5 Thin film Damage (in nm) from 3-PT processing solvent on the thin film surface 1-Methylnaphthalene 98 1-Methoxynaphthalene 100 3-Phenoxytoluene 63 Cyclohexylhexanoate 10 Menthylisovalerate 13

[0247] As can be seen from table 5, the damage of the thin films of polymer Po2 decreases with a decreasing amount of ethanol as well as acetone needed to start the precipitation of the polymer in the respective formulation (see table 4).

[0248] This means that a thin polymer film processed from an ink formulation precipitating at 30 g/L if a lower amount of ethanol is added to the formulation is more stable against solvent exposure than a thin polymer film processed from an ink formulation precipitating at 30 g/L if a higher amount of ethanol is added to the formulation.

[0249] Consequently, thin polymer films processed from cyclohexylhexanoate and from Menthylisovalerate are more stable against solvent exposure than thin polymer films processed from 1-Methylnaphthalene, from 1-Methoxynaphthalene and from 3-Phenoxytoluene.

[0250] A high degree of crosslinking means that the damage is preferably less than 50 nm, more preferably less than 20 nm, based on an original thickness of 70 nm. This means that the damage is preferably less than 70%, more preferably less than 30%. Consequently, thin polymer films processed from cyclohexylhexanoate and from menthylisovalerate have a high degree of crosslinking.

[0251] Part G:

[0252] Quantification of the Degree of Crosslinking in the Thin Polymer Films

[0253] DSC (Differential Scanning Calorimetry) of the polymers was performed under ambient atmosphere using TA analysis Discovery DSC. Samples (ca. 2 mg) were measured in standard aluminum crucibles with a closed lid. Sample thermograms were recorded from a single heating ramp starting at room temperature to 300° C. at a heating rate of 20 K min.sup.−1. The temperature range was determined by preliminary test runs so that the crosslinking reaction could occur. DSC measurements were done with the polymer powder and the polymer films. The powder was grinded with a pestle in a mortar for optimum thermal contact between the powder and the crucible. The polymer films were obtained by pouring 30 μl of a polymer solution of 50 g/L into the crucible. Most of the solvent was removed by placing the crucible into the vacuum chamber for two hours.

[0254] Degree of crosslinking X.sub.(Sx):

[00001]$X_{\left(\mathrm{Sx}\right)}=\frac{\Delta H_{\left(\mathrm{Sx}\right)}}{\Delta H_{\left(S0\right)}}*100$

[0255] ΔH.sub.(Sx) enthalpy of polymer in film

[0256] ΔH.sub.(S0) enthalpy of polymer in powder

[0257] The degree of crosslinking in a film processed from a formulation of the present invention is preferably >15%, more preferably >50%.

[0258] The DSC results from the films of polymer Po2 films obtained from the five IJP solvents of examples 1 to 5 are shown in the following Table 6.

TABLE-US-00007 TABLE 6 Crosslinking Cross-linking Solvent enthalpy [J g.sup.−1] degree [%] 1-Methylnaphthalene 5.7 12.2 1-Methoxynaphthalene 4.3 9.2 3-Phenoxytoluene 6.4 15 Cyclohexylhexanoate 9.4 20.1 Menthylisovalerate 24.7 52.9 Powder of Po2 46.7 100

[0259] Part H:

[0260] Kinetic Reaction of Crosslinking in Solution

[0261] The crosslinkable polymer Po2 was dissolved in the different solvents at a concentration of 50 g/L. Each of the polymer solution was divided into multiple glass bottles of 1 ml, so that each bottle could be heated at one specific temperature. After degassing and argon overlay, the bottles were sealed. The bottles were placed into an aluminum block covering the whole bottle (except the cap) standing on a hotplate. Each of these bottles was heated up at a fixed temperature for three hours while stirring to avoid a non-homogenous solution. After heating, the bottles were placed into a cold-water bath to cool down to room temperature. The viscosity of the solutions before and after the heating procedure was measured at room temperature, with a shear rate of 500 s.sup.−1 by using Thermo Scientific™ HAAKE™ MARS™ III Rheometer. A very quick increase of viscosity regarding the heating temperature is characteristic of a fast kinetic reaction. The Formulations of the present invention lead to a fast crosslinking reaction.

[0262] Consequently, ink formulations precipitating at 30 g/L if a lower amount of ethanol is added to the formulation have a faster crosslinking reaction than ink formulations precipitating at 30 g/L if a higher amount of ethanol is added to the formulation. The achieved results are shown in FIG. 2.

[0263] Part I:

[0264] Efficiency of OLED Device: Impact of the Hole Transport Layer Processing Solvent

[0265] Description of Fabrication Process

[0266] Glass substrates covered with pre-structured ITO and bank material were cleaned using ultrasonication in isopropanol followed by de-ionized water, then dried using an air-gun and a subsequent annealing on a hot-plate at 230° C. for 2 hours.

[0267] A hole-injection layer (HIL) using a composition of a polymer (e.g. polymer P2) and a salt (e.g. salt D1) as described in WO 2016/107668 A1 was inkjet-printed onto the substrate and dried in vacuum. The HIL was then annealed at 225° C. for 30 minutes in air.

[0268] On top of the HIL, a hole-transport layer (HTL) was inkjet-printed, dried in vacuum and annealed at 180° C. for 30 minutes in nitrogen atmosphere. As material for the hole-transport layer, polymer Po2, as described in the working examples of the present application in Part B, dissolved in different solvents at a concentration of 7 g/L was used.

[0269] The green emissive layer (G-EML) was also inkjet-printed, vacuum dried and annealed at 160° C. for 10 minutes in nitrogen atmosphere. The ink for the green emissive layer contained in all working examples two host materials (i.e. HM-1 and HM-2) as well as one triplett emitter (EM-1) prepared in 3-phenoxy toluene at a concentration of 12 g/L. The materials were used in the following ratio: HM-1:HM-2:EM-1=40:40:20. The structures of the materials are the following:

##STR00042##

[0270] All inkjet printing processes were performed under yellow light and under ambient conditions.

[0271] The soluble layers were printed from a Dimatix cartridge by Pixdro LP50 printer. The printing process is composed of three steps for each layer: ink printing from the cartridge, solvent removal in a vacuum chamber, and heat treatment. The layers were dried for 3.5 minutes in a vacuum chamber under 10.sup.−4 mbar.

[0272] The devices were then transferred into a vacuum deposition chamber where the deposition of a common hole blocking layer (HBL), an electron-transport layer (ETL), and a cathode (Al) was done using thermal evaporation at a pressure of 10.sup.−7 mbar. The devices were then characterized in the glovebox.

[0273] In the hole blocking layer (HBL) ETM-1 was used as a hole-blocking material. The material has the following structure:

##STR00043##

[0274] In the electron transport layer (ETL) a 50:50 mixture of ETM-1 and LiQ was used. LiQ is lithium 8-hydroxyquinolinate.

[0275] Finally, the Al electrode is vapor-deposited. The devices were then encapsulated in a glove box in nitrogen using a cover glass and physical characterization was performed in ambient air.

[0276] An OLED is characterized by connecting the anode and cathode to a DC source and applying a voltage ramp. The incident photon currents are then measured with a calibrated photodiode at different voltages.

[0277] Simultaneously, the generated photocurrent was measured by a photodiode with the 6485 picoamperemeter from Keithley. The luminous efficiency of OLEDs can be defined as the ratio of luminance and current density:

[00002]${\eta }_L=\frac{L}{j}$

[0278] with the luminous efficiency η.sub.L in cd/A, the luminance L in cd/m.sup.2 and the current density j in mA/cm.sup.2. The current density is calculated by

[00003]$j=\frac{i}{A},$

the current I and the active area A=4.606 mm.sup.2.

RESULTS AND DISCUSSION

[0279] Three OLED devices were printed where the influence of the hole transport processing solvent was studied. The HTL was processed either from 1-methylnaphthalene, from 3-phenoxytoluene or from menthyl isolalerate. As can be seen in FIG. 3, the OLED device obtained by processing the HTL with 1-methylnaphthalene shows a very small luminous efficiency, whereas the OLED device obtained by processing the HTL using menthyl isovalerate exhibits a high efficiency.

[0280] Consequently, ink formulations containing a solvent, precipitating at 30 g/L if a lower amount of ethanol is added to the formulation, show higher OLED device efficiencies when used to process the HTL than ink formulations containing a solvent, precipitating at 30 g/L if a higher amount of ethanol is added to the formulation.