Organic Electroluminescent Device and a Solid Composition for Use Therein

Abstract

Organic electroluminescent device comprising an anode, a cathode, at least one emission layer and an organic semiconducting layer; wherein the organic semiconducting layer is arranged between the at least one emission layer and the cathode; wherein the organic semiconducting layer comprises; a) a first organic compound comprising a first C.sub.10 to C.sub.42 arene structural moiety and/or a first C.sub.2 to C.sub.42 heteroarene structural moiety, wherein i) the dipole moment of the first organic compound, computed by the TURBOMOLE V6.sub..5 program package using hybrid functional B3LYP and Gaussian 6-.sub.31G* basis set, is from 0 to 2.5 Debye; and ii) the LUMO energy level of the first organic compound in the absolute scale taking vacuum energy level as zero, computed by the TURBOMOLE V6.sub..5 program package using hybrid functional B.sub.3LYP and Gaussian 6-.sub.31G* basis set, is in the range from −1.7 eV to −2.1 eV; and b) a second organic compound comprising a second C.sub.10 to C.sub.42 arene structural moiety and/or a second C.sub.2 to C.sub.42 heteroarene structural moiety and in addition at least one polar group selected from phosphine oxide and phosphine sulfide, wherein in) the dipole moment of the second organic compound, computed by the TURBOMOLE V6.sub..5 program package using hybrid functional B.sub.3LYP and Gaussian 6-.sub.31G* basis set, is from 1.5 to 10 Debye; and iv) the LUMO energy level of the second organic compound in the absolute scale taking vacuum energy level as zero is less than 0.25 eV higher or lower than the LUMO energy level of the first organic compound; wherein it is provided that the first organic compound and the second organic compound are different from each other.

Claims

1. Organic electroluminescent device comprising an anode, a cathode, at least one emission layer and an organic semiconducting layer; wherein the organic semiconducting layer is arranged between the at least one emission layer and the cathode; wherein the organic semiconducting layer comprises: a) a first organic compound comprising a first C.sub.10 to C.sub.42 arene structural moiety and/or a first C.sub.2 to C.sub.42 heteroarene structural moiety, wherein i) the dipole moment of the first organic compound, computed by the TURBOMOLE V6.5 program package using hybrid functional B3LYP and Gaussian 6-31G* basis set, is from 0 to 2.5 Debye; and ii) the LUMO energy level of the first organic compound in the absolute scale taking vacuum energy level as zero, computed by the TURBOMOLE V6.5 program package using hybrid functional B3LYP and Gaussian 6-31G* basis set, is in the range from −1.7 eV to −2.1 eV; and b) a second organic compound comprising a second C.sub.10 to C.sub.42 arene structural moiety and/or a second C.sub.2 to C.sub.42 heteroarene structural moiety and in addition at least one polar group selected from phosphine oxide and phosphine sulfide, wherein iii) the dipole moment of the second organic compound, computed by the TURBOMOLE V6.5 program package using hybrid functional B3LYP and Gaussian 6-31G* basis set, is from 1.5 to 10 Debye; and iv) the LUMO energy level of the second organic compound in the absolute scale taking vacuum energy level as zero is less than 0.25 eV higher or lower than the LUMO energy level of the first organic compound; wherein it is provided that the first organic compound and the second organic compound are different from each other.

2. Organic electroluminescent device according to claim 1, wherein the first organic compound and the second organic compound only comprise atoms selected from the group consisting of C, H, B, Si, Ge, O, N, P, S, F and I.

3. Organic electroluminescent device according to claim 1, wherein the organic semiconducting layer further comprises an electrical n-dopant.

4. Organic electroluminescent device according to claim 3, wherein the n-dopant is a metal salt comprising at least one metal cation and at least one anion.

5. Organic electroluminescent device according to claim 4, wherein the metal cation of the metal salt is selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals.

6. Organic electroluminescent device according to claim 4, wherein the anion of the metal salt is selected from the group consisting of quinolinolate, phosphine oxide phenolate and borate.

7. Organic electroluminescent device according to claim 1, wherein the weight ratio of the first organic compound to the second organic compound is from 99:1 to 1:99.

8. Organic electroluminescent device according to claim 1, wherein the molar weight of the first organic compound and the second organic compound is, respectively, from 300 to 3000 g/mol.

9. Organic electroluminescent device according to claim 1, in the second organic compound a) the polar group is phosphine oxide; and/or b) the C.sub.10 to C.sub.42 arene structural moiety and/or the C.sub.2 to C.sub.42 heteroarene structural moiety comprises at least two.

10. Organic electroluminescent device according to claim 1, wherein the C.sub.10 to C.sub.42 arene structural moiety and/or the C.sub.2 to C.sub.42 heteroarene structural moiety comprised in the first organic compound comprises at least two fused aromatic rings.

11. Compound having formula E3 ##STR00014##

12. Organic electroluminescent device according to claim 4, wherein the metal cation of the metal salt is selected from the group consisting of Li, Na, K, Rb, Cs, Mg, Ca, Sr, and Ba.

13. Organic electroluminescent device according to claim 1, wherein the weight ratio of the first organic compound to the second organic compound is from 19:1 to 1:19.

14. Organic electroluminescent device according to claim 1, wherein the weight ratio of the first organic compound to the second organic compound is from 2:3 to 3:2.

15. Organic electroluminescent device according to claim 1, wherein the molar weight of the first organic compound and the second organic compound is, respectively, from 450 to 1500 g/mol.

16. Organic electroluminescent device according to claim 1, wherein the molar weight of the first organic compound and the second organic compound is, respectively, from 500 to 1000 g/mol.

17. Organic electroluminescent device according to claim 9, wherein the C.sub.10 to C.sub.42 arene structural moiety and/or the C.sub.2 to C.sub.42 heteroarene structural moiety comprises at least three fused aromatic rings.

18. Organic electroluminescent device according to claim 9, wherein the C.sub.10 to C.sub.42 arene structural moiety and/or the C.sub.2 to C.sub.42 heteroarene structural moiety comprises at least four fused aromatic rings.

19. Organic electroluminescent device according to claim 10, wherein the C.sub.10 to C.sub.42 arene structural moiety and/or the C.sub.2 to C.sub.42 heteroarene structural moiety comprised in the first organic compound comprises at least three fused aromatic rings.

20. Organic electroluminescent device according to claim 10, wherein the C.sub.10 to C.sub.42 arene structural moiety and/or the C.sub.2 to C.sub.42 heteroarene structural moiety comprised in the first organic compound comprises at least four fused aromatic rings.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0186] These and/or other aspects and advantages of the present invention will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings, of which:

[0187] FIG. 1 is a schematic sectional view of an organic light-emitting diode (OLED), according to an exemplary embodiment of the present invention;

[0188] FIG. 2 is a schematic sectional view of an OLED, according to an exemplary embodiment of the present invention.

[0189] FIG. 3 is a schematic sectional view of a tandem OLED comprising a charge generation layer, according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION

[0190] Reference will now be made in detail to the exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The exemplary embodiments are described below, in order to explain the aspects of the present invention, by referring to the figures.

[0191] Herein, when a first element is referred to as being formed or disposed “on” or “onto” a second element, the first element can be disposed directly on the second element, or one or more other elements may be disposed there between. When a first element is referred to as being formed or disposed “directly on” or “directly onto” a second element, no other elements are disposed there between.

[0192] FIG. 1 is a schematic sectional view of an organic light-emitting diode (OLED) 100, according to an exemplary embodiment of the present invention. The OLED 100 includes a substrate no, an anode 120, a hole injection layer (HIL) 130, a hole transport layer (HTL) 140, an emission layer (EML) 150, an electron transport layer (ETL) 160. The electron transport layer (ETL) 160 is formed on the EML 150. Onto the electron transport layer (ETL) 160, an electron injection layer (EIL) 180 is disposed. The cathode 190 is disposed directly onto the electron injection layer (EIL) 180.

[0193] Instead of a single electron transport layer 160, optionally an electron transport layer stack (ETL) can be used.

[0194] FIG. 2 is a schematic sectional view of an OLED 100, according to another exemplary embodiment of the present invention. FIG. 2 differs from FIG. 1 in that the OLED 100 of FIG. 2 comprises an electron blocking layer (EBL) 145 and a hole blocking layer (HBL) 155.

[0195] Referring to FIG. 2, the OLED 100 includes a substrate 110, an anode 120, a hole injection layer (HIL) 130, a hole transport layer (HTL) 140, an electron blocking layer (EBL) 145, an emission layer (EML) 150, a hole blocking layer (HBL) 155, an electron transport layer (ETL) 160, an electron injection layer (EIL) 180 and a cathode electrode 190.

[0196] Preferably, the organic semiconducting layer comprising a composition according to invention or consisting of the composition according to invention may be an EML, an HBL or an ETL.

[0197] FIG. 3 is a schematic sectional view of a tandem OLED 200, according to another exemplary embodiment of the present invention. FIG. 3 differs from FIG. 2 in that the OLED 100 of FIG. 3 further comprises a charge generation layer (CGL) and a second emission layer (151).

[0198] Referring to FIG. 3, the OLED 200 includes a substrate 110, an anode 120, a first hole injection layer (HIL) 130, a first hole transport layer (HTL) 140, a first electron blocking layer (EBL) 145, a first emission layer (EML) 150, a first hole blocking layer (HBL) 155, a first electron transport layer (ETL) 160, an n-type charge generation layer (n-type CGL) 185, a hole generating layer (p-type charge generation layer; p-type GCL) 135, a second hole transport layer (HTL) 141, a second electron blocking layer (EBL) 146, a second emission layer (EML) 151, a second hole blocking layer (EBL) 156, a second electron transport layer (ETL) 161, a second electron injection layer (EIL) 181 and a cathode 190.

[0199] Preferably, the organic semiconducting layer according to invention may be the first EML, first HBL, first ETL, n-type CGL and/or second EML, second HBL, second ETL.

[0200] While not shown in FIG. 1, FIG. 2 and FIG. 3, a sealing layer may further be formed on the cathode electrodes 190, in order to seal the OLEDs 100 and 200. In addition, various other modifications may be applied thereto.

[0201] Hereinafter, one or more exemplary embodiments of the present invention will be described in detail with reference to the following examples. However, these examples are not intended to limit the purpose and scope of the one or more exemplary embodiments of the present invention.

[0202] Table 1 shows the effect of the invention on results obtained from Device example 1 described in detail in the experimental part below.

TABLE-US-00001 TABLE1 CEff/CIEy LT97 Lum j Voltage at 0.045 LT97 30 mA/cm.sup.2 ETL (cd/m.sup.2) CIEy (mA/cm.sup.2) (V) (cd/A) (h) (h) E1:LiQ 942 0.047 12.5 3.94 160 330 85 (50:50) (102%) (102%) (89%) (92%) B1:LiQ 879 0.045 12.5 3.85 157 353 92 (50:50) (100%) (100%) (100%) (100%) E1:E2:LiQ 858 0.044 11.7 3.77 166 300 77 (25:25:50) (98%) (106%) (85%) (84%)

[0203] The invention enabled tuning voltage/efficiency ratio while keeping lifetime in an acceptable range.

EXPERIMENTAL PART

[0204] General Methods

[0205] Dipole Moment

[0206] The dipole moment [{right arrow over (μ)}] of a molecule containing N atoms is given by:

[00001]$\stackrel{.fwdarw.}{\mu }=\underset{i}{\overset{N}{.Math.}}{q}_i\stackrel{.fwdarw.}{r_1}$$.Math.\stackrel{.fwdarw.}{\mu }.Math.=\sqrt{{\mu }_x^2+{\mu }_y^2+{\mu }_2^2}$

[0207] where q.sub.1 and {right arrow over (r.sub.1)} are the partial charge and position of atom i in the molecule.

[0208] The dipole moment is determined by a semi-empirical molecular orbital method.

[0209] The geometries of the molecular structures are optimized using the hybrid functional B3LYP with the 6-31G* basis set in the gas phase as implemented in the program package TURBOMOLE V6.5 (TURBOMOLE GmbH, Litzenhardtstrasse 19, 76135 Karlsruhe, Germany), If more than one conformation is viable, the conformation with the lowest total energy is selected to determine the bond lengths of the molecules.

[0210] Calculated HOMO and LUMP

[0211] The HOMO and LUMO are calculated with the program package TURBOMOLE V6.5 (TURBOMOLE GmbH, Litzenhardtstrasse 19, 76135 Karlsruhe, Germany). The optimized geometries and the HOMO and LUMO energy levels of the molecular structures are determined by applying the hybrid functional B3LYP with a 6-31G* basis set in the gas phase. If more than one conformation is viable, the conformation with the lowest total energy is selected.

[0212] The invention is furthermore illustrated by the following examples which are illustrative only and non-binding.

[0213] Supporting Materials for Device Experiments

[0214] F1 is

##STR00005## [0215] N-([1,1′-biphenyl]-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluoren-2-amine, CAS 1242056-42-3;

[0216] F2 is

##STR00006## [0217] N-(4-(dibenzo[b,d]furan-4-yl)phenyl)-N-(4-(9-phenyl-9H-fluoren-9-yl)phenyl)-[1,1′-biphenyl]-4-amine, CAS 1824678-59-2;

[0218] F3 is

##STR00007## [0219] 2-(3′-(9,9-dimethyl-9H-fluoren-2-yl)-[1,1′-biphenyl]-3-yl)-4,6-diphenyl-1,3,5-triazine, CAS 1955543-57-3;

[0220] F4 is

##STR00008## [0221] 2,4-diphenyl-6-(4′,5′,6′-triphenyl-[1,1′:2′,1″:3″,1′″:3′″,1″″-quinquephenyl]-3′″-yl)-1,3,5-triazine, CAS 2032364-64-8;

[0222] F5 is

##STR00009## [0223] 2-([1,1′-biphenyl]-4-yl)-4-(9,9-diphenyl-9H-fluoren-4-yl)-6-phenyl-1,3,5-triazine, CAS 1801992-44-8;

[0224] F6 is

##STR00010## [0225] 1,3-bis(9-phenyl-1,10-phenanthrolin-2-yl)benzene, CAS 721969-94-4;

[0226] B1 is

##STR00011## [0227] 4′-(4-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)naphthalen-1-yl)-[1,1′-biphenyl]-4-carbonitrile, CAS 2032421-37-5;

[0228] LiQ is lithium 8-hydroxyquinolinolate, H09 is a commercial blue emitter host and BD200 is a commercial blue emitter, both supplied by SFC, Korea;

[0229] PD2 is

##STR00012## [0230] 4,4′,4′-((1E,1′E,1″E)-cyclopropane-1,2,3-triyldenetris(cyanomethanylylidene))tris(2,3,5,6-tetrafluorobenzonitrile), CAS 1224447-88-4.

[0231] Synthesis of the Compound E2

2-([1,1′-biphenyl]-3-yl)-4-phenyl-6-(3-(10-phenylanthracen-9-yl)phenyl)-1,3,5-triazine (E2)

[0232] In a 500 mL 3-necked flask, compound A (CAS number 1689576-03-1, 15 g, 43.6 mmol, 1 eq.), boronic acid B (CAS number 1023674-81-8, 17.9 g, 49.0 mmol, 1.1 eq.) and potassium carbonate (12.0 g, 55.9 mmol, 2 eq.) together with THF (350 mL) and distilled water (87 mL), The yellow suspension was degassed by bubbling N2 through for 60 minutes. Then Pd(dppf)Cl2 (0.15 g, 0.21 mmol) was added under nitrogen counter flow. The reaction was then heated 19 h at 75° C. (bath temperature) under nitrogen. After cooling to rt and evaporation of the solvent, residue was extracted with 4 L DCM/CWoroform and the organic layer washed in portions with in total 7.5 L of water until pH neutral. After filtering over Florisil layer, the organic layer was evaporated and the residue treated by 200 mL hexane. Precipitate was filtered and dried under high vacuum two times at 120° C.

[0233] Obtained 20-3 g (73% theory) MS [M+H]+ 638.

[0234] Synthesis of the Compound E3

(3-(10-(3-(2,6-diphenylpyrimidin-4-yl)phenyl)anthracen-9-yl)phenyl)dimethylphosphine oxide (E3)

[0235] A 3-neck round bottom flask was flushed with nitrogen and charged with 2,4-diphenyl-6-(3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)pyrimidine (26.26 g, 60.46 mmol, 1 eq), (3-(10-bromoanthracen-9-yl)phenyl)dimethylphosphine oxide (25.98 g, 63.48 mmol, 1.05 eq), potassium carbonate (16.71 g, 120.9 mmol, 2 eq), tetrahydrofuran (240 mL) and water (60 mL). The reaction mixture was degassed with N2 for 30 min and the catalyst [1,1′-bis(diphenylphosphino)ferrocene]dichloropalladium(II) (0.22 g, 0.30 mmol, 0.005 eq) was added. The mixture was stirred for 3 d at 75° C.

[0236] The reaction mixture was allowed to cool to room temperature and the product was collected by filtration. The solid material was washed with water until it was neutral, washed with 3×150 mL methanol, then dried at 50° C. under vacuum for two hours. The raw product was dissolved in DCM, filtered over silica gel and the solvent was removed. The product was recrystallized from chlorobenzene and washed with hexane, then dried at 100° C. under vacuum overnight. 61% yield, ESI-MS 637 (M+H).

[0237] Synthesis of the Compound E4

2-([1,1′-biphenyl]-3-yl)-4-phenyl-6-(3-(3,5,6-triphenylpyrazin-2-yl)phenyl)-1,3,5-triazine (E4)

[0238] A 3-neck round bottom flask was flushed with nitrogen and charged with 2,3,5-triphenyl-6-(3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)pyrazine (38.2 g, 75 mmol, 1 eq), 2-([1,1′-biphenyl]-3-yl)-4-chloro-6-phenyl-1,3,5-triazine (25.79 g, 75 mmol, 1 eq), potassium carbonate (20.73 g, 150 mmol, 2 eq), tetrahydrofuran (300 mL) and water (75 mL). The reaction mixture was degassed under vacuum and reflux and the catalyst tetrakis(triphenylphosphin)palladium(0) (1.73 g, 1.5 mmol, 0.02 eq) was added. The mixture was stirred for 19 h at 65° C.

[0239] The reaction mixture was cooled to 10° C. and the product was collected by filtration. The solid material was washed with tetrahydrofuran and water, then dried at 50° C. under vacuum for three days. The raw product was dissolved in chloroform, filtered over silica gel and the solvent was reduced to 100 mL. The product was precipitated overnight by stirring with 200 mL cyclohexane, then collected by filtration and dried.

[0240] The solid was dissolved in 250 mL chloroform and re-precipitated with 200 mL methyl tert-butyl ether overnight.

[0241] The product was obtained through filtration, then dried at 60° C. under vacuum overnight. 74% yield, ESI-MS 692 (M+H).

[0242] Synthesis of Compound E6

2-(3-(2,6-dimethylpyridin-3-yl)phenyl)-4-(2′,6′-diphenyl-[1,1′:4′,1″-terphenyl]-4-yl)-6-phenyl-1,3,5-triazine (E6)

[0243] ##STR00013##

A) 2-(2′,6′-diphenyl-[1,1′:4′,1″-terphenyl]-4-yl)-4-phenyl-6-(3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-1,3,5-triazine

[0244] A flask was flushed with nitrogen and charged with 2-(3-chlorophenyl)-4-(2′,6′-diphenyl-[1,1′:4′,1″-terphenyl]-4-yl)-6-phenyl-1,3,5-triazine (24.4 g, 39.2 mmol), 4,4,4′,4′,5,5,5′,5′-octamethyl-2,2′-bi(1,3,2-dioxaborolane) (12.9 g, 51.0 mmol), KOAc (11.5 g, 117.6 mmol), 2-Dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl (934 mg, 2.0 mmol) and tris(dibenzylidenacetone)dipalladium(0) (897 mg, 1 mmol). Anhydrous dioxane (200 mL) was added and the reaction mixture was heated to 100° C. under a nitrogen atmosphere overnight. After cooling down to room temperature, the resulting precipitate was isolated by suction filtration and washed with water (600 mL) and methanol (200 mL). The crude product was then dissolved in dichloromethane and filtered through a pad of Florisil. After rinsing with additional dichloromethane (2.5 L mL), the filtrate was concentrated, under reduced pressure. The resulting precipitate was isolated by suction filtration and washed with n-hexane (100 mL) to yield 24.6 g (36%) of the intermediate.

B) 2-(3-(2,6-dimethylpyridin-3-yl)phenyl)-4-(2′,6′-diphenyl-[1,1′:4′,1″-terphenyl]-4-yl)-6-phenyl-1,3,5-triazine (E6)

[0245] Next a flask was flushed with nitrogen and charged with 2-(2′,6′-diphenyl-[1,1′:4′,1″-terphenyl]-4-yl)-4-phenyl-6-(3′-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-1,3,5-triazine (12.2 g, 16.3 mmol), 3-bromo-2,6-dimethylpyridine (2.6 mL, 19.6 mmol), K.sub.3PO.sub.4 (8.7 g, 40.8 mmol) and chloro(crotyl)(2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl)palladium(II) (198 mg, 0.33 mmol). A mixture of deaerated dioxane and water (4:1, 100 mL) was added and the reaction mixture was heated to 50° C. under a nitrogen atmosphere overnight. After cooling down to room temperature, the resulting precipitate was isolated by suction filtration and washed with water (1.0 L) and Methanol (100 mL). The crude product was dissolved in dichloromethane and washed with an aqueous solution of NADTC (3%, 150 mL), and then with water (2×200 mL). The organic phase was dried over Na.sub.aSO.sub.4 and filtered through a pad of silicagel. After rinsing with additional dichloromethane (2.0 L), and dichloromethane/methanol (98/2, 1.5 L), the filtrate was concentrated under reduced pressure. The resulting precipitate was isolated by suction filtration to yield 6.4 g compound 1 after drying. Final purification was achieved by sublimation. ESI-MS: m/z=719.2 ([M+H].sup.+).

[0246] Device Preparation

[0247] All inventive layers used in device examples were prepared by conventional vacuum thermal evaporation (VTE) procedure, wherein the first organic compound has been vaporized from a first vaporization source, the second organic compound from a second vaporization source and the dopant, if present, from a third vaporization source, and the compounds were co-deposited on a solid support.

Device Example 1

[0248] Top Emitting Blue OLED Comprising the First and Second Organic Compound in a n-Doped Electron Transport Layer

[0249] Device structure is shown in Table 2

TABLE-US-00002 TABLE 2 layer Material d [nm] Anode Ag 100 HIL F.sub.1:PD.sub.2 (92:8 v/v) 10 HTL F.sub.1 118 EBL F.sub.2 5 EML H.sub.09:BD.sub.200 (97:3 v/v) 20 HBL F.sub.3 5 ETL E.sub.1LiQ (50:50 v/v) 31 E.sub.1:E.sub.2:LiQ (25:25:50 v/v) B.sub.1:LiQ (50:50 v/v) EIL Yb 2 Cathode Ag:Mg (90:10) 13 Cap F.sub.1 70

Device Example 2

[0250] Top Emitting Blue OLED Comprising the First and Second Organic Compound in an Undoped Electron Transport Layer

[0251] Device structure is shown in Table 3

TABLE-US-00003 TABLE 3 layer Material d [nm] Anode Ag 100 HIL F.sub.1:PD.sub.2 (92:8 v/v) 10 HTL F.sub.1 118 EBL F.sub.2 5 EML H.sub.09:BD.sub.200 (97:3 v/v) 20 HBL F.sub.4 5 ETL E.sub.1LiQ (50:50 v/v) 31 E.sub.1:E.sub.2 (30:70 v/v) EIL Yb 2 Cathode Ag:Mg (90:10) 13 Cap F.sub.1 70

[0252] Table 4 shows the results of this experiment

TABLE-US-00004 TABLE 4 j Voltage EQE ETL (mA/cm.sup.2) (V) (%) E1:LiQ 10 3.5 15.5 (50:50) E1:E2 10 3.5 15.4 (30:70) EQE stands for external quantum efficiency.

[0253] The experiment shows that the layer according to invention, consisting only of the first organic compound and of the second organic compound, enables equally good electron injection (from state-of-art cathodes) like n-doped electron transport layers known in the art.

Device Example 3

[0254] Tandem OLED Comprising the First and Second Organic Compound in an Undoped Electron Transport Layer

[0255] Further comparison of inventive layers comprising the first and second organic compound with state-of-art layer made of compound F5 and LiQ in weight ratio 50:50 was made in a model tandem. OLED, wherein the tested electron transport layer was arranged adjacent to and in direct contact with a n-doped charge generation layer made of compound F6 and metallic lithium in weight ratio 98:2. Table 5 shows the results of this experiment.

TABLE-US-00005 TABLE 5 Voltage Ceff ETL (V) (cd/A) LT (h) dV (V) F5:LiQ 9.43 26.4 52 0.440 (50:50) E1:E2 9.58 24.8 69 0.135 (30:70) E3:E2 9.53 25.4 62 0.164 (30:70) E1:E6 9.51 25.4 66 0.127 (30:70) E3:E6 9.44 25.5 60 0.133 (30:70) El:E4 9.75 24.4 73 0.148 (30:70) E3:E4 9.56 25.1 64 0.138 (30:70) Voltage V and currenty efficiency Ceff are given for current density 10 mA/cm.sup.2, lifetime LT (defined as time necessary for luminance decrease to 97% of its initial value) and voltage rise dV (defined as change in operational voltage after 400 h device operation) are given for current density 30 mA/cm.sup.2.

[0256] The results show that at a comparable performance, the inventive layer significantly improves device stability.

[0257] The features disclosed in the foregoing description and in the dependent claims may, both separately and in any combination thereof, be material for realizing the aspects of the disclosure made in the independent claims, in diverse forms thereof.