SOLVENT COATABLE OLED EMITTER COMPOSITION CONTAINING NON-PLASMONIC MOLECULAR NOBLE METAL NANOPARTICLES AND EMITTER MATERIALS IN NONCRYSTALLIZABLE MOLECULAR ORGANIC SEMICONDUCTORS
20190074467 ยท 2019-03-07
Assignee
Inventors
Cpc classification
H10K50/115
ELECTRICITY
H10K85/621
ELECTRICITY
International classification
Abstract
Embodiments of this disclosure includes a solvent coatable emitter composition that includes an emitter material; and noble metal nanoparticles having a median size of less than or equal to 5 nanometers, wherein the size distribution is less than 20%.
Claims
1. A solvent coatable emitter composition comprising: an emitter material; and noble metal nanoparticles having a median size of less than or equal to 5 nanometers, wherein the size distribution is less than 20%.
2. The emitter composition of claim 1, wherein the median size of less than or equal to 2 nanometers.
3. The emitter composition of claim 1, wherein the noble metal nanoparticles are chosen from copper nanoparticles, silver nanoparticles, or gold nanoparticles.
4. The emitter composition of claim 1, wherein the emitter material is a triplet emitter.
5. The emitter composition of claim 1, wherein the emitter material is a thermally activated delayed fluorescence emitter.
6. The emitter composition of claim 1, further comprising a non-crystallizable molecular glass organic semiconductor.
7. The emitter composition of claim 6, wherein the non-crystallizable molecular glass organic semiconductor is a hole-transporting molecular glass mixture.
8. The emitter composition of claim 6, wherein the non-crystallizable molecular glass organic semiconductor is an electron-transporting molecular glass mixture.
9. The emitter composition of claim 6, wherein the non-crystallizable molecular organic glass semiconductor is an ambipolar molecular glass mixture.
10. The emitter composition of claim 6, wherein the non-crystallizable molecular glass organic semiconductor is a high-entropy molecular glass mixture.
11. The emitter composition of claim 6, wherein the non-crystallizable molecular organic semiconductor is an isomeric molecular glass mixture.
12. The emitter composition of claim 6, wherein the non-crystallizable molecular organic semiconductor is selected from the group consisting of glass mixtures 4, 6, 7, 8, 9, 22, 32, 50, 60, 65, 70, 73, 80, 85, 90, 95, 100, 105, 110, 115, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 132, 133, 134, 135, and 136.
13. The emitter composition of claim 1, wherein the refractive index of the emitter composition is less than the refractive index of an emitter composition without the noble metal nanoparticles.
14. An OLED multilayer electroluminescent device comprising: a light-emitting layer (LEL) disposed between a cathode and an anode, the light-emitting layer comprising the emitter composition of claim 1 and a high-entropy non-crystallizable molecular semiconductor mixture host; and, at least one charge-transporting layer, wherein the charge transporting layer is disposed between: (A) the cathode and the light-emitting layer; (B) the anode and the light-emitting layer; or (C) both (A) and (B).
15. The OLED device of claim 14, wherein the device is bottom emitting.
16. The OLED device of claim 14, wherein the device is top emitting.
17. The OLED device of claim 14, wherein the noble metal nanoparticles are chosen from gold nanoparticles, copper nanoparticles, or silver nanoparticles.
18. A method of making a light-emitting layer comprising: dissolving an emitter in a solvent to form an emitter solvent; adding a noble metal nanoparticle to the emitter solvent to form a nanoparticle/emitter solution; coating the nanoparticle/emitter solution onto a host material; and removing the solvent at a temperature of 25 C. or less than 25 C.
19. The method of making a light-emitting layer of claim 18, wherein the nanoparticle/emitter solution has a concentration of non-plasmonic molecular noble metal from 0.50 volume percent to 6 volume percent in the emitter/nanoparticle solution.
20. A method of making a light-emitting layer comprising: forming a light-emitting layer; coating the light-emitting layer with a noble metal solution, wherein noble metal solution comprises noble metal nanoparticles dispersed in solvent; and removing the solvent at a temperature less than 50 C.
Description
BRIEF DESCRIPTION OF FIGURES
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DETAILED DESCRIPTION
[0041] Throughout this document, the following terms will have the following meanings.
[0042] The term prompt fluorescence means instantaneous fluorescence in few nanoseconds.
[0043] The term delayed luminescence means fluorescence and/or phosphorescence which is emitted after instantaneous fluorescence.
[0044] The term time gated data means the internal charge coupled device camera comprised of a sensor and a gated image intensifier. The image intensifier could be switched rapidly on and off through the application of positive and negative potentials and thus acting as a very fast shutter. The time between the excitation of the sample and the opening of the shutter is referred to as the time delay. The time that the gate voltage remained on is called the gate width. The spectral information/data collected by varying the delay and the gate width is called time gated data.
[0045] The term Gate width means the time that the gate voltage remained on.
[0046] The term steady state spectroscopy means that the samples are continuously irradiated with a continuous beam of light, excited states are continuously created and eliminated.
[0047] The term blue shift means displacement of the emission peak towards shorter wavelength.
[0048] The term red shift means displacement of the emission peak towards shorter wavelength.
[0049] The term full width at half maxima (FWHM) means the width of a spectrum at half of the maximum intensity.
[0050] Time resolved emission means the emission recorded at various time scales.
[0051] The term host means a non-crystallizable organic glass mixture.
[0052] In one or more embodiments, the solvent coatable light emitting composition includes a non-crystallizable molecular glass organic semiconductor, emitter material dissolved in a solvent, and non-plasmonic molecular noble metal nanoparticles having a median size of less than or equal to 5 nanometers, in which the size distribution is less than 20%.
[0053] In some embodiments, the non-plasmonic molecular noble metal nanoparticles of the emitter composition have median size of less than or equal to 2 nanometers in which the size distribution is less than 20%.
[0054] In one or more embodiments, the non-plasmonic molecular noble metal nanoparticles are chosen from gold nanoparticles, silver nanoparticles, platinum nanoparticles, palladium nanoparticles, rhodium nanoparticles, iridium nanoparticles, or copper nanoparticles. The nanoparticles are typically stabilized in aqueous or organic solvents. Typical stabilizers include dodecanethiol, citrate surfactant, gelatin (GEL), polyvinylpyrrolidone (PVP), or polyvinyl alcohol (PVA), four-chained disulfide, tetraalkylammonium cations, ionic liquids.
[0055] In one or more embodiments, the emitter composition has a refractive index of less than the refractive index of a comparative emitter composition. The comparative emitter composition includes the same components and the same amount of each component as compared to the emitter compositions of this disclosure, except that the comparative emitter composition does not include the non-plasmonic molecular noble metal nanoparticles having a median size of less than or equal to 5 nanometers, wherein the size distribution is less than 20%.
[0056] In embodiments, the organic light emitting diode (OLED) device includes a cathode, an anode, a light-emitting layer (LEL) disposed therebetween, and charge-transporting layers disposed between (A) the cathode and the light-emitting layer, (B) the anode and the light-emitting layer, or (C) both (A) and (B). The light-emitting layer (LEL) includes a high-entropy non-crystallizable molecular semiconductor mixture host, an emitter, and non-plasmonic molecular noble metal particles size of equal to or less than 5 nm.
[0057] In some embodiments, the OLED device is bottom emitting. In other embodiments, the OLED device is top emitting, and in further embodiments, the OLED device may be both top emitting and bottom emitting.
[0058] In some embodiments, the OLED device includes a multilayer electroluminescent device comprising a cathode, an anode, optional charge-injecting layers, charge-transporting layers, and a light-emitting layer (LEL). The light-emitting layer includes a neat host or a mixed-host, wherein the neat host or both members of the mixed host are high-entropy non-crystallizable molecular semiconductor mixtures comprising three or more than three components. The host material can be hole-transporting, electron-transporting, or ambipolar, that is capable on transporting both positive and negative charges (electrons). In some embodiments, the host material includes a mixed-host, which is a mixture of a hole-transporting high-entropy non-crystallizable material and an electron-transporting high-entropy non-crystallizable material. However, in some embodiments of the OLED, as demonstrated in U.S. Patent Publication No. 2015/0053894, the high-entropy non-crystallizable materials can be mixed with highly crystalline materials at high concentration to yield a new mixture that is non-crystallizable and soluble. Thus, the mixed-host may be either a mixture of a high-entropy hole-transporting material, as described herein, and an electron-transporting crystallizable material, or a high-entropy electron-transporting material and a hole-transporting crystallizable material. Whereas, neat host materials may contain either hole transporting properties or electron transporting properties.
[0059] To achieve a highly efficient phosphorescent OLED, triplet emitter-dopants are usually embedded in a suitable host to reduce concentration quenching. A good host material should fulfill the following requirements: (1) the triplet energy must be higher compared to the emitter, which prevents energy back transfer to the host material, (2) suitable energy levels aligned with the neighboring layers for efficient charge carrier injection to obtain a low driving voltage; (3) decent charge carrier transporting abilities to increase the chance for hole and electron recombination within the emitting layer; and (4) the HOMO (highest occupied molecular orbital) of the host materials should be deeper than that of the emitters, while the LUMO (lowest unoccupied molecular orbital) of the host materials should be shallower than that of the emitters.
[0060] Blue phosphorescent and thermally assisting delayed fluorescent emitters have higher triplet energy than green, yellow and red emitters, in that order. Thus, blue emitters require higher triplet host (2.8 eV to 3.0 eV) than green, yellow and red emitters.
[0061] In mixed-host systems, the triplet energy of the individual host should meet the requirements described above such that the triplet energy of the mixed host is greater than the emitter. The triplet energy of the host materials is estimated from the phosphorescence emission of the host at or below 77 K.
[0062] In one or more embodiments, the light-emitting layer of the device of this disclosure includes host material, emitter material, and non-plasmonic noble metal nanoparticles having a median size of less than or equal to 5 nanometers, wherein the size distribution is less than 20%. In one or more embodiments, the emitter material includes an emitter-dopant. The emitter-dopant may be present in an amount of up to 20 wt. % of the host, from 0.1 to 18.0 wt. % of the host, from 0.5 to 10 wt.% of the host, or from 0.1 to 5 wt. %. The emitter-dopant may include a fluorescent emitter, a phosphorescent emitter, a thermally delayed fluorescent emitter, or a combination thereof.
[0063] In embodiments, the solvent of the solvent coatable emitter composition may include polar organic solvents. A non-limiting list of polar organic solvents includes: chloroform, tetrahydrofuran (THF), dichloromethane, acetonitrile, acetone, methylacetate, ethyl acetate, and toluene.
[0064] The emitter dopant can be a fluorescent emitter, a phosphorescent emitter, or a thermally delayed fluorescent emitter. The composition of the host is adjusted for the type of emitter. For example, high-triplet energy host is required for phosphorescent and thermally activated delayed fluorescence (TADF) emitters.
[0065] Examples of fluorescent emitters include coumarin dyes such as 2,3,5,6-1H,4H-tetrahydro-8-trichloromethylquinolizino(9,9a,1gh) coumarin, cyanine-based dyes such as 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyrylene)-4H-pyran, pyridine-based dyes such as 1-ethyl-2-(4-(p-dimethylaminophenyl)-1,3 -butadienyl)-pyridium perchlorate, xanthene-based dyes such as rhodamine B, and oxazine-based dyes. The fluorescent material can also include inorganic phosphors.
[0066] Examples of phosphorescent emitters include Ir(ppy)3 (fac tris(2-phenylpyridine) iridium) (green) or FIrpic (iridium(III)bis[4,6-di-(fluorophenyl)-pyridinato-N, C2] picolinate) (blue), a red phosphorescent dopant RD61 available from UDC. Other blue phosphorescence emitter include iridium (III) bis(4,6-difluorophenylpyridinato) tetrakis(1-pyrazolyl)borate (FIr6) (HOMO level=6.1 eV, LUMO level=3.1 eV, T1=2.71 eV), iridium (III) bis[4,6-(di-fluorophenyl)-pyridinato-N, C2]picolinate (FIrpic), iridium (III) tris[N-(4-cyanophenyl)-N-methylimidazole-2-ylidene-C2, C2] (Ir(cn-pmic)3), tris((3,5-difluoro-4-cyanophenyl)pyridine)iridium (FCNIr), and Ir(cnbic)3, and complexes of heavy atom metals such as platinum (Pt), rhenium (Re), ruthenium (Ru), copper (Cu), and osmium (Os). (2,4-Pentanedionato) bis[2-(2-quinolinyl) phenyl] iridium(III), Bis[5-methyl-2-(2-pyridinyl-N) Phenyl-C] (2,4-pentanedionato-O2, O4) iridium(III), Bis [2-(2-benzothiazolyl-N3)phenolato-O]zinc,Bis [2-(4,6-difluorophenyl)pyridinato-C2,N] (picolinato)iridium(III), Bis [2-(1-isoquinolinyl-N)phenyl-C](2,4-pentanedionato-O2,O4)iridium(III), Tris[2-(benzo [b]thiophen-2-yl)pyridinato-C3,N]iridium(III), Bis [2-(1isoquinolinyl-N)phenyl-C] (2,4-pentanedionato-O2,O4)iridium(III), Bis[2-(2-pyridinyl-N)phenyl-C](2,4-pentanedionato-O2,O4)iridium(III), Dichlorotris(1,10-phenanthroline)ruthenium(II) hydrate, Bis(2-benzo [b]thiophen-2-ylpyridine)(acetylacetonate)iridium(III), Lithium tetra(2-methyl-8-hydroxyquinolinato)boron, bis(2,2-bipyridyl)dichlororuthenium(II) hexahydrate, and other emitting materials capable of phosphorescence.
[0067] Examples of thermally activated delayed fluorescence (TADF) emitter-dopants include, but are not limited to: 2,5-bis(carbazol-9-yl)-1,4-dicyanobenzene (4CzTPN described in Mater. Horiz., 2014, 1, 264-269; the Organic Luminescent Compound with Delayed Fluorescence of US application 20140145149 to Lin; Chun et al; the delayed fluorescence material of US application 20140138669 to Nakagawa, and Tetsuya (Fukuoka, J P) Adachi, Chihaya (Fukuoka, J P) the benzothiophene or benzofuran fused to a carbazoles delayed fluorescent material of US application 20140145151 to Xia;
[0068] The light-emitting layer (LEL) of this disclosure also includes noble metal nanoparticles having a size median of equal to or less than 5 nm, or equal to or less than 2 nm. Examples of noble metal nanoparticles include gold nanoparticles, silver nanoparticles, platinum nanoparticles, palladium nanoparticles, rhodium nanoparticles, iridium nanoparticles, or copper nanoparticles. The nanoparticles are typically stabilized in aqueous or organic solvents. Typical stabilizers include dodecanethiol, citrate surfactant, gelatin (GEL), polyvinylpyrrolidone (PVP), or polyvinyl alcohol (PVA), four-chained disulfide, tetraalkylammonium cations, ionic liquids.
[0069] In some embodiments, the non-plasmonic molecular noble metal nanoparticles are incorporated into the light emitting layer via a solvent coatable noble metal solution, in which noble metal nanoparticles are dissolved in a solvent, organic or aqueous, and added to an emitter solution to form a noble metal/emitter solution. The noble metal/emitter solution is applied to the host material. The solvent is evaporated at room temperature or temperatures less than 25 C.
[0070] In some embodiments, the nanoparticle/emitter solution has a concentration of non-plasmonic molecular noble metal from 0.50 volume percent to 6.0 volume percent based on the amount of a 1 mg/mL stock solution in the emitter/nanoparticle solution. In one or more embodiments, the nanoparticle/emitter solution has a concentration of non-plasmonic molecular noble metal from 0.75 volume percent to 3.0 volume percent, and in other embodiments, the nanoparticle/emitter solution has a concentration of non-plasmonic molecular noble metal from 0.75 volume percent to 2.0 volume percent.
[0071] In other embodiments the light-emitter layer is formed by added the emitter to the host or creating a light-emitting layer. The light-emitting layer is coated with noble metal solution, in which the noble metal solution includes noble metal nanoparticles dissolved in a solvent, organic or aqueous. The solvent is removed at low temperatures and under atmospheric conditions. Low temperatures include temperatures less than 50 C. or less than 25 C.
[0072] High-entropy non-crystallizable molecular glass mixtures are defined as a mixture of compatible organic monomeric molecules with an infinitely low crystallization rate under the most favorable conditions. These mixtures can be formed in a one-part reaction of a multifunctional nucleus with a mixture of substituents. The non-crystallizability and the high-entropy of the mixture is controlled by the structural dissymmetry of the nucleus, the substituents, or a combination thereof, and the number of components making up the mixture. In cases, where the nucleus is highly symmetric and rigid, the components with similar (non-distinct) substituents might crystallize out under the right conditions. Thus it is advantageous when possible to avoid those components, by designing an asymmetric glass mixture, wherein all the components of the mixture have distinct substituents. Without being bound to theory, we predict that the asymmetric mixtures are more likely to be fully non-crystallizable.
[0073] Increasing the number of components of the glass mixture, by adding more substituents is another way to enhance the non-crystallizability and the entropy of the glass mixtures having highly symmetric and rigid nuclei.
[0074] The high-entropy non-crystallizable glass mixtures of this disclosure are described by Molaire in United States Patent Application 2015/0275076 filed Mar. 22, 2015, United States Patent Application 2015/0053894, filed Aug. 25, 2014; United States Patent Application 2015/0179714, filed Dec. 21, 2014; WIPO Patent Publication No. WO/2015/148327, filed Mar. 22, 2015; WIPO Patent Publication No. WO/2015/117100, filed Feb. 2, 2015; WIPO Patent Publication No. WO/2015/031242, filed Aug. 25, 2014; WIPO Patent Publication No. WO/2015/095859, filed Dec. 22, 2014; WIPO Patent Publication No. WO/2017/053426, filed Sep. 21, 2016, and incorporated by reference into this disclosure in its entirety.
[0075] In some embodiments, the light-emitting layer includes the high-entropy non-crystallizable glass mixture hosts and dopant-emitter. The high-entropy non-crystallizable glass mixture hosts may include hole-transporting, electron-transporting, or ambipolar. The high-entropy non-crystallizable glass mixture host and the emitter dopant should be chosen so that a hole-transporting host is combined with an electron-trapping emitter-dopant or an electron-transporting host with a hole-trapping emitter-dopant. Ambipolar host can be used with either type of emitter-dopant.
[0076] Specific examples of high-entropy non-crystallizable hosts include those disclosed in International PCT Application No. PCT/US2016/052884, which is incorporated by reference herein in its entirety. Specific examples of high-entropy non-crystallizable hosts include the isomeric hole-transporting materials.
[0077] Specific examples of non-crystallizable hosts include those disclosed in U.S. provisional patent application Ser. No. 6,221,605, such as the isomeric hole-transporting materials:
##STR00001## ##STR00002##
[0078] The isomeric ambipolar materials
##STR00003## ##STR00004##
[0079] The isomeric electron-transporting non-crystallizable mixtures
##STR00005## ##STR00006##
[0080] The non-crystallizable hole-transporting materials of United States Patent Application 20150275076, Non-crystallizable Pi-conjugated Molecular Glass Mixtures, Charge Transporting Molecular Glass Mixtures, Luminescent Molecular Glass Mixtures, or Combinations Thereof for Organic Light Emitting Diodes and other Organic Electronics and Photonics Applications
##STR00007## ##STR00008## ##STR00009##
[0081] Other examples of non-crystallizable glass mixtures include
##STR00010## ##STR00011## ##STR00012## ##STR00013## ##STR00014## ##STR00015## ##STR00016## ##STR00017## ##STR00018## ##STR00019## ##STR00020## ##STR00021## ##STR00022## ##STR00023## ##STR00024## ##STR00025## ##STR00026## ##STR00027## ##STR00028## ##STR00029## ##STR00030## ##STR00031## ##STR00032## ##STR00033## ##STR00034##
[0082] Hole-Transporting Glass Mixture 121 contains the following compounds:
##STR00035## ##STR00036##
[0083] Hole-Transporting Glass Mixture 122 contains the following compounds:
##STR00037## ##STR00038##
[0084] Ambipolar Glass Mixture 123 contains the following compounds:
##STR00039## ##STR00040## ##STR00041##
[0085] Ambipolar Glass Mixture 124 contains the following compounds:
##STR00042## ##STR00043##
[0086] Electron-Transporting Glass Mixture 125 contains the following compounds:
##STR00044##
[0087] Hole-Transporting Glass Mixture 126 contains the following compounds:
##STR00045## ##STR00046##
[0088] Hole-Transporting Glass Mixture 127 contains the following compounds:
##STR00047## ##STR00048## ##STR00049## ##STR00050## ##STR00051##
[0089] Hole-Transporting Glass Mixture 128 contains the following compounds:
##STR00052## ##STR00053##
[0090] Electron-Transporting Glass Mixture 129 contains the following compounds:
##STR00054## ##STR00055##
[0091] Hole-Transporting Glass Mixture 130 contains the following compounds:
##STR00056## ##STR00057##
[0092] Electron-Transporting Glass Mixture 132 contains the following compounds:
##STR00058##
[0093] Hole-Transporting Glass Mixture 133 contains the following compounds:
##STR00059##
[0094] Hole-Transporting Glass Mixture 134 contains the following compounds:
##STR00060## ##STR00061##
[0095] Electron-Transporting Glass Mixture 135 contains the following compounds:
##STR00062##
[0096] Ambipolar Glass Mixture 136 contains the following compounds:
##STR00063## ##STR00064##
GENERAL DEVICE ARCHITECTURE
[0097] Embodiments of this disclosure include simple structures comprising a single anode and cathode to more complex devices, such as passive matrix displays comprised of orthogonal arrays of anodes and cathodes to form pixels, and active-matrix displays where each pixel is controlled independently, for example, with a thin film transistor (TFT).
[0098] There are numerous configurations of the organic layers wherein the present invention can be successfully practiced. Essential requirements are a cathode, an anode, an HTL and an LEL. A typical structure contains a substrate, an anode, an optional hole-injecting layer, a hole-transporting layer, a light-emitting layer, an electron-transporting layer, and a cathode. These layers are described in detail below. Note that the substrate may alternatively be located adjacent to the cathode, or the substrate may actually constitute the anode or cathode. Also, the total combined thickness of the organic layers is less than 600 nm, less than 500 nm, or from 5 nm to 450 nm.
SUBSTRATE
[0099] The substrate can either be light transmissive or opaque, depending on the intended direction of light emission. The light transmissive property is desirable for viewing the electroluminescence (EL) emission through the substrate. Transparent glass or organic material is commonly employed in such cases. For applications where the EL emission is viewed through the top electrode, the transmissive characteristic of the bottom support is immaterial, and therefore can be light transmissive, light absorbing or light reflective. Substrates for use in this case include, but are not limited to, glass, plastic, semiconductor materials, ceramics, and circuit board materials. Of course it is necessary to provide in these device configurations a light-transparent top electrode.
ANODE
[0100] The conductive anode layer is commonly formed over the substrate and, when EL emission is viewed through the anode, should be transparent or substantially transparent to the emission of interest. Common transparent anode materials used in this invention are indium-tin oxide (ITO) and tin oxide, but other metal oxides can work including, but not limited to, aluminum- or indium-doped zinc oxide (IZO), magnesium-indium oxide, and nickel-tungsten oxide. In addition to these oxides, metal nitrides, such as gallium nitride, and metal selenides, such as zinc selenide, and metal sulfides, such as zinc sulfide, can be used in layer. For applications where EL emission is viewed through the top electrode, the transmissive characteristics of layer are immaterial and any conductive material can be used, transparent, opaque or reflective. Example conductors for this application include, but are not limited to, gold, iridium, molybdenum, palladium, and platinum. Typical anode materials, transmissive or otherwise, have a work function of 4.1 eV or greater. Desired anode materials are commonly deposited by any suitable means such as evaporation, sputtering, chemical vapor deposition, or electrochemical means. Anodes can be patterned using well-known photolithographic processes.
HOLE-INJECTING LAYER (HIL)
[0101] Optionally, a hole-injecting layer may be disposed between anode and hole-transporting layer. The hole-injecting material can serve to improve the film formation property of subsequent organic layers and to facilitate injection of holes into the hole-transporting layer. Suitable materials for use in the hole-injecting layer include, but are not limited to, porphyrinic compounds such as those described in U.S. Pat. No. 4,720,432, and plasma-deposited fluorocarbon polymers such as those described in U.S. Pat. No. 6,208,075. Alternative hole-injecting materials reportedly useful in organic EL devices are described in EP 0 891 121 A1 and EP 1 029 909 A1.
HOLE-TRANSPORT LAYER (HTL)
[0102] The hole-transporting layer of the organic EL device contains at least one hole-transporting compound such as an aromatic tertiary amine, where the latter is understood to be a compound containing at least one trivalent nitrogen atom that is bonded only to carbon atoms, at least one of which is a member of an aromatic ring. In one form the aromatic tertiary amine can be an arylamine, such as a monoarylamine, diarylamine, triarylamine, or a polymeric arylamine group. Exemplary monomeric triarylamines are illustrated by Klupfel et al. U.S. Pat. No. 3,180,730. Other suitable triarylamines substituted with one or more vinyl radicals and/or comprising at least one active hydrogen containing group are disclosed by Brantley et al U.S. Pat. Nos. 3,567,450 and 3,658,520.
[0103] One particular class of aromatic tertiary amines includes those which include at least two aromatic tertiary amine moieties as described in U.S. Pat. Nos. 4,720,432 and 5,061,569. Such compounds include those represented by structural formula (II).
##STR00065##
[0104] In formula (II), Q.sub.1 and Q.sub.2 are independently selected aromatic tertiary amine moieties and G is a linking group such as an arylene, cycloalkylene, or alkylene group of a carbon to carbon bond. In one embodiment, at least one of Q.sub.1 or Q.sub.2 contains a polycyclic fused ring group, e.g., a naphthalene. When G is an aryl group, it is conveniently a phenylene, biphenylene, or naphthalene group.
[0105] A useful class of triarylamine groups satisfying structural formula (II) and containing two triarylamine groups is represented by structural formula (III):
##STR00066##
[0106] In formula (III), R.sup.11 and R.sup.12 each independently represents a hydrogen atom, an aryl group, or an alkyl group or R.sup.11 and R.sup.12 together represent the atoms completing a cycloalkyl group; and R.sup.13 and R.sup.14 each independently represents an aryl group, which is in turn substituted with a diaryl substituted amino group, as indicated by structural formula (IV):
##STR00067##
[0107] In formula (IV), R.sup.15 and R.sup.16 are independently selected aryl groups. In one embodiment, at least one of R.sup.15 and R.sup.16 contains a polycyclic fused ring group, e.g., naphthalene.
[0108] Another class of aromatic tertiary amine groups are the tetraaryldiamines. Tetraaryldiamines groups include two diarylamino groups, such as indicated by formula (IV), linked through an arylene group. Useful tetraaryldiamines include those represented by formula (V):
##STR00068##
[0109] In formula (V), Are is selected from arylene group, such as a phenylene or anthracene group, n is an integer of from 1 to 4, and Ar, R.sup.7, R.sup.8, and R.sup.9 are independently selected aryl groups.
[0110] In a typical embodiment, at least one of Ar, R.sup.7, R.sup.8, and R.sup.9 is a polycyclic fused ring group, e.g., a naphthalene.
[0111] The various alkyl, alkylene, aryl, and arylene groups of the foregoing structural formulae (II), (III), (IV), (V), can each in turn be substituted. Typical substituents include alkyl groups, alkoxy groups, aryl groups, aryloxy groups, and halogen such as fluoride, chloride, and bromide. The various alkyl and alkylene groups typically contain from about 1 to 6 carbon atoms. The cycloalkyl moieties can contain from 3 to about 10 carbon atoms, but typically contain five, six, or seven ring carbon atoms (e.g., cyclopentyl, cyclohexyl, and cycloheptyl ring structures). The aryl and arylene groups are usually phenyl and phenylene moieties.
[0112] The hole-transporting layer can be formed of a single or a mixture of aromatic tertiary amine compounds. Specifically, one may employ a triarylamine, such as a triarylamine satisfying the formula (III), in combination with a tetraaryldiamine, such as indicated by formula (V). When a triarylamine is employed in combination with a tetraaryldiamine, the latter is positioned as a layer interposed between the triarylamine and the electron injecting and transporting layer. Illustrative of useful aromatic tertiary amines are the following:
[0113] 1,1 Bis(4-di-p-tolylaminophenyl)cyclohexane
[0114] 1,1-Bis(4-di-p-tolylaminophenyl)-4-phenylcyclohexane
[0115] 4,4-Bis(diphenylamino)quadriphenyl
[0116] Bis(4-dimethylamino-2-methylphenyl)-phenylmethane
[0117] N,N,N-Tri(p-tolyl)amine
[0118] 4-(di-p-tolylamino)-4-[4(di-p-tolylamino)-styryl]stilbene
[0119] N,N,N,N-Tetra-p-tolyl-4-4-diaminobiphenyl
[0120] N,N,N,N-Tetraphenyl-4,4-diaminobiphenyl
[0121] N,N,N,N-tetra-1-naphthyl-4,4-diaminobiphenyl
[0122] N,N,N,N-tetra-2-naphthyl-4,4-diaminobiphenyl
[0123] N-Phenylcarbazole
[0124] 4,4-Bis[N-(1-naphthyl)-N-phenylamino]biphenyl
[0125] 4,4-Bis[N-(1-naphthyl)-N-(2-naphthyl)amino]biphenyl
[0126] 4,4-Bis [N-(1-naphthyl)-N-phenylamino]p-terphenyl
[0127] 4,4-Bis[N-(2-naphthyl)-N-phenylamino]biphenyl
[0128] 4,4-Bis[N-(3-acenaphthenyl)-N-phenylamino]biphenyl
[0129] 1,5-Bis [N-(1-naphthyl)-N-phenylamino]naphthalene
[0130] 4,4-Bis[N-(9-anthryl)-N-phenylamino]biphenyl
[0131] 4,4-Bis [N-(1-anthryl)-N-phenylamino]-p-terphenyl
[0132] 4,4-Bis[N-(2-phenanthryl)-N-phenylamino]biphenyl
[0133] 4,4-Bis[N-(8-fluoranthenyl)-N-phenylamino]biphenyl
[0134] 4,4-Bis[N-(2-pyrenyl)-N-phenylamino]biphenyl
[0135] 4,4-Bis[N-(2-naphthacenyl)-N-phenylamino]biphenyl
[0136] 4,4-Bis [N-(2-perylenyl)-N-phenylamino]biphenyl
[0137] 4,4-Bis[N-(1-coronenyl)-N-phenylamino]biphenyl
[0138] 2,6-Bis(di-p-tolylamino)naphthalene
[0139] 2,6-Bis[di-(1-naphthyl)amino]naphthalene
[0140] 2,6-Bis[N-(1-naphthyl)-N-(-2-naphthyl)amino]naphthalene
[0141] N,N,N,N-Tetra(2-naphthyl)-4,4-diamino-p-terphenyl
[0142] 4,4-Bis{N-phenyl-N-[4-(1-naphthyl)-phenyl]amino}biphenyl
[0143] 4,4-Bis[N-phenyl-N-(2-pyrenyl)amino]biphenyl
[0144] 2,6-Bis[N,N-di(2-naphthyl)amine]fluorine
[0145] 1,5-Bis[N-(1-naphthyl)-N-phenylamino]naphthalene
[0146] Another class of useful hole-transporting materials includes polycyclic aromatic compounds as described in EP 1 009 041. In addition, polymeric hole-transporting materials can be used such as poly(N-vinylcarbazole) (PVK), polythiophenes, polypyrrole, polyaniline, and copolymers such as poly(3,4-ethylenedioxythiophene)/poly (4-styrenesulfonate) also called PEDOT/PSS. In addition, polymeric hole-transporting materials can be used such as poly(N-vinylcarbazole) (PVK), polythiophenes, polypyrrole, polyaniline, and copolymers such as poly(3,4-ethylenedioxythiophene)/poly (4-styrenesulfonate) also called PEDOT/PSS.
LIGHT-EMITTING LAYER (LEL)
[0147] As more fully described in U.S. Pat. Nos. 4,769,292 and 5,935,721, the light-emitting layer (LEL) of the OLED multilayer electroluminescent device includes a host and an emitter-dopant. The emitter dopant is chosen from luminescent material or fluorescent material where electroluminescence is produced as a result of electron-hole pair recombination in this region. The luminescent material can also phosphorescent or thermally delayed fluorescent. The host materials in the light-emitting layer can be an electron-transporting material, as defined below, a hole-transporting material, as defined above, or another material or combination of materials that support hole-electron recombination. The emitter-dopant is usually chosen from highly fluorescent dyes, but phosphorescent compounds, e.g., transition metal complexes as described in WO 98/55561, WO 00/18851, WO 00/57676, and WO 00/70655 are also useful. Emitter-dopants are typically coated as 0.01 to 10% by weight into the host material.
[0148] An important relationship for choosing a dye as a dopant is a comparison of the bandgap potential which is defined as the energy difference between the highest occupied molecular orbital and the lowest unoccupied molecular orbital of the molecule. For efficient energy transfer from the host to the dopant molecule, a necessary condition is that the band gap of the dopant is smaller than that of the host material.
[0149] Emitting molecules known to be of use include, but are not limited to, those disclosed in U.S. Pat. Nos. 4,768,292, 5,141,671, 5,150,006, 5,151,629, 5,405,709, 5,484,922, 5,593,788, 5,645,948, 5,683,823, 5,755,999, 5,928,802, 5,935,720, 5,935,721, and 6,020,078.
PHOTOPHYSICAL CHARACTERIZATION
Delayed Luminescence Spectra Collection
[0150]
Time Gated Data Collection
[0151] Triplet emission coming from simple intersystem crossing (ISC) from singlet exciton to triplet exciton follows an exponential decay. If we keep the gate width shorter than the excited state lifetime, we will see triplets. To collect the emission, the gate width was kept constant at 1 microsecond and the delay was varied. A simple collection scheme is shown in
[0152] Two types of fluorescence processes are frequently encountered in studying the photophysics of OLED emittersinstantaneous or prompt fluorescence (PF) and delayed fluorescence (DF). The PF was recorded with the delay set to zero and with a short gate width 100 ns. Since the delayed fluorescence emission is so large and obeys algebraic decay laws, the choice of an adequate detection width is tricky. As the delay time increases the decay becomes much slower. A constant detection width in linear time is a problem since the signal decreases at longer delay time. Hence, the delayed fluorescence signal collection was maintained at exponentially increasing intervals, making the data collection delays evenly spaced on log scale.
[0153] For time delays up to 1 microsecond (s), gate width was maintained at 100 nanoseconds (ns). Beyond 1 s time delay, the gate width was maintained at 10% of the delay, because it is believed to be a good compromise between time resolution and signal strength [C. Rothe and A. Monkman, Physical Review B, 68(7), (2003)]. To obtain true decay kinetics, the measured data points need to be scaled by the corresponding detection window. This was achieved by dividing each integrated value by the corresponding gate width. The pulse-to-pulse variation in the energy of the laser pulses was recorded using a standard joule/meter and was noted to be +2%.
Steady State Spectroscopy of Gold Nanoparticles
[0154] Room temperature absorption and emission spectra of gold nanoparticles (Au Nps) at a very low concentration dispersed in polystyrene matrix is shown in
EXAMPLES
Comparative Example 1: Red Phosphorescent Emitter Ir(Piq)3 Neat Film
[0155] A 10 mg sample of tris [1-phenylisoquinoline-C2, N] iridium(III) (Ir(Piq)3), a red phosphorescent emitter obtained from Sigma Aldrich, was weighed and mixed with 10 ml of chloroform to make stock solutions with 1 milligram per milliliter (mg/mL) concentration. The solutions were stirred for about an hour to dissolve the emitter material completely.
[0156] A few drops of the stock solution were dropped onto clean 2 mm thick quartz discs obtained from Ted Pella Inc., placed in a Petri dish with a cover and dried while refrigerated to enforce slow solvent evaporation for about 2 hours in the dark to form drop cast neat films. The drop cast neat films were stored in glass containers, wrapped in aluminum foil to avoid light exposure and retained in a desiccator.
Example 1: Red Phosphorescent Emitter Ir(Piq)3 Neat Film Incorporating Gold Nanoparticles
[0157] Dodecanethiol capped Au nanoparticles (Au Nps) of average diameter of 2 nm obtained from Nanocomposix and were incorporated into the Ir(Piq)3 stock solution. L
[0158] Chloroform (10 mL) was added to a bottle containing 5 mg of Au nanoparticles to form a chloroform-Au solution. The chloroform-Au solution was stirred for about an hour. A 2 L sample of chloroform-Au solution (0.5 mg/ml) was added to 20 L of Ir(Piq)3 stock solution to form an Au-emitter solution. A few drops of the Au-emitter solution stock solution were dropped onto clean 2 mm thick quartz discs obtained from Ted Pella Inc., placed in a Petri dish with a cover, and were dried while refrigerated to enforce slow solvent evaporation for about 2 hours in the dark to form Au doped drop cast neat films. The Au doped drop cast neat films were stored in glass containers, wrapped in aluminum foil to avoid light exposure and retained in a desiccator.
Absorption and Emission
[0159] The absorption and emission of drop cast neat film of the phosphorescent emitter Ir(Piq)3 with and without Au nanoparticles are shown in
[0160] The spectra in
Time Resolved Emission
[0161] The time resolved emission spectra were integrated from 550 nm to 750 nm and plotted as a function of time delay as shown in
Delayed Luminescence
[0162] The delayed luminescence dynamics of the neat film and the Au Np doped Ir(PiQ)3 film is shown in
[0163] The delayed luminescence spectra resemble the respective prompt fluorescence spectra. The Au doped films showed much higher emission counts at all time scales with respect to their neat film counterparts. This is a hint that Au Nps enhance the efficiency of the films. All time resolved experiments were performed under vacuum.
[0164] Several reports have been presented on the use of noble metals to enhance the efficiency of devices by utilizing their surface plasmon resonance (SPR) properties [J. H. Park, et.al., Chem. Mater. 2004, 16,688-692]. SPR usually kicks in at around 30 nm and such sizes become comparable to layer thickness resulting in alteration of electrical properties. One remarkable feature of our claim is that our particles are on an average 2 nmorders of magnitude smaller than the ones mentioned in other reports. Not to be bound by theory, it is believed that materials with noble metal nanoparticles do not exhibit signs of SPR, but rather enhance the efficiency by decreasing or tuning the lifetime. This phenomenon has been named the Metal Assisted Lifetime Tuning (MALT).
Refractive Index Effect
[0165] In general, refractive index is a function of wavelength. The gold nanoparticles have a very low refractive index which can be tuned with size and concentration [S. Kubo et. Al; Nano Lett. 2007, 11 (3418-3423). This means adding gold nanoparticles would lower the refractive index of the EML, which would correspond to larger critical angle (from Snell's Law). This means greater amount of internal outcoupling is possible.
[0166] Transmittance is related to absorbance by Beer's Law equation as
T=10.sup.A
where T is the optical transmittance and A is the absorbance.
[0167] Based on the above equation and substituting the absorbance values, we calculated T.sub.no gold=99% and T.sub.gold=99.8%. Clearly the transmission is enhanced (
Comparative Example 2: Proprietary Phosphorescent Yellow Emitter in Non-Crystallizable Glass Mixture 22
[0168] A solution was made up consisting of 15 wt % of the of a proprietary phosphorescent yellow emitter and 85 w % of the non-crystallizable glass mixture 22 in dichloromethane. The solution was drop casted using the procedure of example 1.
Example 2: Proprietary Phosphorescent Yellow Emitter in Non-Crystallizable Glass Mixture 22 Incorporating Gold Nanoparticles
[0169] The procedure of example 1 was followed to prepare the proceeding samples.
Absorption and Emission
[0170]
Time Resolved Emission
[0171] The spectra in
Delayed Luminescence
[0172] The delayed luminescence dynamics of the neat film and the Au Np doped Ir(PiQ)3 film is shown in
Example 3: Effect of Gold Nanoparticle Concentration in Neat DMAC-DPS Films
[0173] A sample of 0.4 mg of DMAC-DPS, 10,10-(4,4-Sulfonylbis(4,1-phenylene)) bis(9,9-dimethyl-9,10-dihydroacridine) a blue TADF emitter obtained from Lumtec were weighed and added to 6.4 mL of solvent to make 1 mg/mL of solution. A 1 mL aliquote of the above solution was transferred to 6 different vials marked A-E.
[0174] The Au nanoparticles were already dispersed in THF from earlier experiments. The concentration was 1 mg/mL. An aliquot of 5 L, 10 L, 20 L, 40 L and 100 L of Au nps solution were added to the vials B, C, D, E and F to make concentrations of about 0.5%, 1%, 2%, 4% and 10% of Au nanoparticles by volume.
[0175] Absorption measurements were performed by taking a 0.1 mL aliquot of each of the solutions from the vials was added to 3 ml of THF in transparent quartz cuvettes of 1 cm path length for absorption measurements.
Example 4 Effect of Gold Nanoparticle Concentration in Ambipolar Mixture 136: DMAC-DPS (90:10 Wt./Wt.) Film
[0176] The procedure of Example 3 was used, except that the ambipolar mixture 136 host material was introduced in a 90:10 wt./wt. ratio with DMAC-DPS.
Example 5 Fabrication of and OLED Device Incorporating an Emitter Layer Containing Gold Nanoparticle: Effect of Gold Nanoparticle Concentration
[0177] A set of four devices were fabricated with structure below;
TABLE-US-00001 Anode HIL/HTL EML ETL EIL Cathode ITO PEDOT: Host (90%) TBPi LiF Al 80 nm PSS 40 nm Phosphorescent 30 nm 5 nm 100 nm Yellow Emitter (10%) 20 nm Gold Nanoparticle: 0% 1%, 2%, 6%
[0178] PEDOT: PSS, poly (3,4-ethylenedioxythiophene)-poly (styrene sulfonate), Heraeus Clevios A14083, obtained from Ossila Ltd Sheffield UK with isopropanol and spun at 3000 rpm for a minute and baked in an oven at 120 C. for 6 minutes. After cooling, a similar procedure was followed for coating the emitter layer at 3000 rpm for one minute under a nitrogen flushed glove box. The four emitter layer solutions included asymmetric glass mixture 6 and the proprietary phosphorescent yellow emitter at a ratio of 90:10 wt./wt. respectively containing 0%, 1%, 2%, and 6% gold nanoparticle. Finally, the samples were transferred to a vacuum chamber where TPBi, LiF and Al layers were evaporated. The final devices were encapsulated before exposure to room atmosphere.
[0179] The graph in
[0180] The graph in
[0181] The graph in
[0182]
Electroluminescence Study:
[0183]
Comparative Luminance Study:
[0184]