Organic Electronic Device and Display Device Comprising the Organic Electronic Device as well as Organic Compounds for Use in Organic Electronic Devices

Abstract

The present invention relates to an organic electronic device comprising a semiconductor layer which comprises a compound of formula (1).

Claims

1. An organic electronic device comprising an anode, a cathode, at least one photoactive layer and an organic semiconductor layer, wherein the organic semiconductor layer is arranged between the at least one photoactive layer and the cathode; and wherein the organic semiconductor layer comprises a compound of Formula (1): ##STR00059## wherein one of R.sup.1 to R.sup.5 is a single bond to the 3-position (marked as “*”) of the 2-azaindolizine moiety, the further R.sup.1 to R.sup.5 and R.sup.6 to R.sup.9 are independently selected from H, D, substituted or unsubstituted C.sub.6 to C.sub.18 aryl, substituted or unsubstituted C.sub.3 to C.sub.20 heteroaryl, C.sub.1 to C.sub.16 alkyl, C.sub.1 to C.sub.16 alkoxy, C.sub.3 to C.sub.16 branched alkyl, C.sub.3 to C.sub.16 cyclic alkyl, C.sub.3 to C.sub.16 branched alkoxy, C.sub.3 to C.sub.16 cyclic alkoxy, partially or perfluorinated C.sub.1 to C.sub.16 alkyl, partially or perfluorinated C.sub.1 to C.sub.16 alkoxy, partially or perdeuterated C.sub.1 to C.sub.16 alkyl, partially or perdeuterated C.sub.1 to C.sub.16 alkoxy, PX.sup.1(R.sup.10).sub.2, F or CN, and/or wherein any two of adjacent R.sup.1-R.sup.9 can be suitably substituted and linked together to form an unsubstituted or an C.sub.6 to C.sub.18 aryl-, C.sub.3 to C.sub.20 heteroaryl-, or C.sub.1 to C.sub.16 alkyl-substituted aromatic or heteroaromatic ring; L is selected from a substituted or unsubstituted C.sub.6 to C.sub.24 arylene group or a substituted or unsubstituted C.sub.2 to C.sub.24 heteroarylene group; Ar is selected from a substituted or unsubstituted C.sub.6 to C.sub.32 aryl group, substituted or unsubstituted C.sub.3 to C.sub.32 heteroaryl group or an unsubstituted or substituted C.sub.2 to C.sub.6 alkenyl group; wherein the substituents of L and Ar are independently selected from: H, D, C.sub.6 to C.sub.18 aryl, C.sub.3 to C.sub.20 heteroaryl, C.sub.1 to C.sub.16 alkyl, C.sub.1 to C.sub.16 alkoxy, C.sub.3 to C.sub.16 branched alkyl, C.sub.3 to C.sub.16 cyclic alkyl, C.sub.3 to C.sub.16 branched alkoxy, C.sub.3 to C.sub.16 cyclic alkoxy, partially or perfluorinated C.sub.1 to C.sub.16 alkyl, partially or perfluorinated C.sub.1 to C.sub.16 alkoxy, partially or perdeuterated C.sub.1 to C.sub.16 alkyl, partially or perdeuterated C.sub.1 to C.sub.16 alkoxy, F, CN or PX.sup.1(R.sup.10).sub.2, wherein the substituents may be linked via a single bond or a heteroatom to form a ring, wherein R.sup.10 is independently selected from C.sub.6 to C.sub.12 aryl, C.sub.3 to C.sub.12 heteroaryl, C.sub.1 to C.sub.16 alkyl, C.sub.1 to C.sub.16 alkoxy, partially or perfluorinated C.sub.1 to C.sub.16 alkyl, partially or perfluorinated C.sub.1 to C.sub.16 alkoxy, partially or perdeuterated C.sub.1 to C.sub.16 alkyl, partially or perdeuterated C.sub.1 to C.sub.16 alkoxy; and X.sup.1 is selected from O, S or Se.

2. The organic electronic device of claim 1, whereby the substituents of the further R.sup.1 to R.sup.5 and R.sup.6 to R.sup.9 which do not form a single bond to the 3-position of the 2-azaindolizine moiety are independently selected from D, —CH═, C.sub.6 to C.sub.18 aryl, C.sub.3 to C.sub.20 heteroaryl, C.sub.1 to C.sub.16 alkyl, C.sub.1 to C.sub.16 alkoxy, C.sub.3 to C.sub.16 branched alkyl, C.sub.3 to C.sub.16 cyclic alkyl, C.sub.3 to C.sub.16 branched alkoxy, C.sub.3 to C.sub.16 cyclic alkoxy, partially or perfluorinated C.sub.1 to C.sub.16 alkyl, partially or perfluorinated C.sub.1 to C.sub.16 alkoxy, partially or perdeuterated C.sub.1 to C.sub.16 alkyl, partially or perdeuterated C.sub.1 to C.sub.16 alkoxy, PX.sup.1(R.sup.10).sub.2, F or CN.

3. The organic electronic device of claim 1 whereby the compound has the following formula (1a): ##STR00060##

4. The organic electronic device of claim 1, whereby the organic layer and/or the compound of formula (1) are non-emissive.

5. The organic electronic device of claim 1, whereby the R.sup.1 to R.sup.9 which do not form a single bond to the 3-position of the 2-azaindolizine moiety are independently selected from H, —CH═, C.sub.1 to C.sub.4 alkyl, F or CN.

6. The organic electronic device of claim 1, whereby the compound of formula (1) is selected from one of the following formulas (2a) to (2f): ##STR00061## ##STR00062## wherein R.sup.11 is independently selected from D, C.sub.6 to C.sub.18 aryl, C.sub.3 to C.sub.20 heteroaryl, C.sub.1 to C.sub.16 alkyl, C.sub.1 to C.sub.16 alkoxy, C.sub.3 to C.sub.16 branched alkyl, C.sub.3 to C.sub.16 cyclic alkyl, C.sub.3 to C.sub.16 branched alkoxy, C.sub.3 to C.sub.16 cyclic alkoxy, partially or perfluorinated C.sub.1 to C.sub.16 alkyl, partially or perfluorinated C.sub.1 to C.sub.16 alkoxy, partially or perdeuterated C.sub.1 to C.sub.16 alkyl, partially or perdeuterated C.sub.1 to C.sub.16 alkoxy, PX.sup.1(R.sup.10).sub.2, F or CN; and n is an integer from 0 to 4.

7. The organic electronic device of claim 1, whereby the moiety L is selected from any of the following moieties E1 to E26: ##STR00063## ##STR00064## ##STR00065## ##STR00066## wherein X.sup.2 is selected from O or S; R.sup.12 and R.sup.13 are independently selected from H, C.sub.1 to C.sub.16 alkyl, C.sub.1 to C.sub.16 alkoxy, C.sub.6 to C.sub.18 aryl, C.sub.3 to C.sub.20 heteroaryl, perfluorinated C.sub.1 to C.sub.16 alkyl, perfluorinated C.sub.1 to C.sub.16 alkoxy.

8. The organic electronic device of claim 1, whereby the moiety Ar is selected from any of the following moieties D1 to D76: ##STR00067## ##STR00068## ##STR00069## ##STR00070## ##STR00071## ##STR00072## ##STR00073## ##STR00074## ##STR00075## ##STR00076## ##STR00077## wherein R.sup.14, R.sup.15 and R.sup.16 are independently selected from H, C.sub.1 to C.sub.16 alkyl, C.sub.1 to C.sub.16 alkoxy, C.sub.6 to C.sub.18 s aryl, C.sub.3 to C.sub.20 heteroaryl, perfluorinated C.sub.1 to C.sub.16 alkyl, perfluorinated C.sub.1 to C.sub.16 alkoxy, wherein R.sup.14 and R.sup.15 may be linked via a single bond or a heteroatom to form a ring.

9. The organic electronic device of claim 1, whereby the organic semiconductor layer comprises a redox n-dopant.

10. The organic electronic device of claim 1, whereby the organic semiconductor layer comprises a metal.

11. The organic electronic device of claim 1, whereby the organic semiconductor layer comprises a metal selected from alkali metals, alkaline earth metals, rare earth metals and metals of the first transition period Ti, V, Cr and Mn.

12. The organic electronic device of claim 1, whereby the at least one photoactive layer is a light-emitting layer.

13. The organic electronic device of claim 1, whereby the organic electronic device is an electroluminescent device.

14. A display device comprising an organic electronic device according to claim 1.

15. A compound of formula (1), whereby Ar is selected from a substituted or unsubstituted C.sub.12 to C.sub.32 aryl group, substituted or unsubstituted C.sub.3 to C.sub.32 heteroaryl group or an unsubstituted or substituted C.sub.2-C.sub.6 alkenyl group, and the following compounds are excluded: ##STR00078## ##STR00079##

16. The organic electronic device of claim 1, wherein X.sup.1 is O.

17. The organic electronic device of claim 7, wherein X.sup.2 is O.

18. The organic electronic device of claim 13, wherein the electroluminescent device is an organic light emitting diode.

Description

DESCRIPTION OF THE DRAWINGS

[0225] The aforementioned components, as well as the claimed components and the components to be used in accordance with the invention in the described embodiments, are not subject to any special exceptions with respect to their size, shape, material selection and technical concept such that the selection criteria known in the pertinent field can be applied without limitations.

[0226] Additional details, characteristics and advantages of the object of the invention are disclosed in the dependent claims and the following description of the respective figures which in an exemplary fashion show preferred embodiments according to the invention. Any embodiment does not necessarily represent the full scope of the invention, however, and reference is made therefore to the claims and herein for interpreting the scope of the invention. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the present invention as claimed.

[0227] FIG. 2 is a schematic sectional view of an organic electronic device, according to an exemplary embodiment of the present invention;

[0228] FIG. 2 is a schematic sectional view of an organic light-emitting diode (OLED), according to an exemplary embodiment of the present invention;

[0229] FIG. 3 is a schematic sectional view of an OLED, according to an exemplary embodiment of the present invention.

[0230] FIG. 4 is a schematic sectional view of an OLED comprising a charge generation layer and two emission layers, according to an exemplary embodiment of the present invention.

[0231] Hereinafter, the figures are illustrated in more detail with reference to examples. However, the present disclosure is not limited to the following figures.

[0232] 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.

[0233] FIG. 1 is a schematic sectional view of an organic electronic device 100, according to an exemplary embodiment of the present invention. The organic electronic device 100 includes a substrate 110, an anode 120, a photoactive layer (PAL) 125, an organic semiconductor layer comprising a compound of formula (1) 160. The organic semiconductor layer comprising compound of formula (1) 160 is formed on the PAL 125. Onto the organic semiconductor layer 160, a cathode 190 is disposed.

[0234] FIG. 2 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 110, 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.

[0235] Instead of a single electron transport layer 160, optionally an electron transport layer stack (ETL) can be used.

[0236] FIG. 3 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.

[0237] Referring to FIG. 3, 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.

[0238] Preferably, the organic semiconductor layer comprising a compound of Formula (1) may be an ETL.

[0239] FIG. 4 is a schematic sectional view of an OLED 100, according to another exemplary embodiment of the present invention. FIG. 4 differs from FIG. 3 in that the OLED 100 of FIG. 4 further comprises a charge generation layer (CGL) and a second emission layer (151).

[0240] Referring to FIG. 4, the OLED 100 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.

[0241] Preferably, the organic semiconductor layer comprising a compound of Formula (1) may be an n-type CGL.

[0242] Preferably, the organic semiconductor layer comprising a compound of Formula (1) may be the first ETL, n-type CGL and/or second ETL.

[0243] While not shown in FIG. 1, FIG. 2, FIG. 3 and FIG. 4, a sealing layer may further be formed on the cathode electrodes 190, in order to seal the OLEDs 100. In addition, various other modifications may be applied thereto.

[0244] Hereinafter, the embodiments are illustrated in more detail with reference to examples. However, the present disclosure is not limited to the following examples.

DETAILED DESCRIPTION

[0245] The invention is furthermore illustrated by the following examples which are illustrative only and non-binding.

[0246] In the following the preparation of several inventive compounds is shown, using the following General Method:

[0247] General Method:

[0248] A flask was flushed with nitrogen and charged with both starting materials (cf. Table 1) in a 1:1 ratio. The organic solvent was added and the mixture was de-aerated. A second flask was charged with the base and water and was de-aerated as well. The aqueous base was added to the starting materials under nitrogen and the reaction was started by the addition of the catalyst. The reaction mixture was heated to the given temperature until TLC showed full conversion. The mixture was then cooled to room temperature and the product was purified according to the methods given in Table 2:

TABLE-US-00001 TABLE 1 Starting materials for the reactions according to General Method: No Starting material 1 Starting material 2 A2 [00038] [00039] A3 [00040] [00041] A7 [00042] [00043] A8 [00044] [00045] A10 [00046] [00047] A11 [00048] [00049] A13 [00050] [00051] A14 [00052] [00053] A16 [00054] [00055]

TABLE-US-00002 TABLE 2 Reaction conditions for the reactions of General Method A Solvent Amount (Yield) No Catalyst/Base Temp. Work-up and purification ESI m/z A2 Tetrakis 1,4-dioxane/ product precipitates, washed  8.1 g (52%) (triphenylphosphine) H2O 8/1 with water and n-hexane , m/z = 549 palladium(0) 80° C. dissolved in CHCl3, filtered [M + H].sup.+ 2 mol %, Potassium through SiO2 and carbonate precipitated with hexane, 2 eq, 2M recrystallized from chlorobenzene A3 Tetrakis (triphenyl 1,4-dioxane/ product precipitates, washed 19.7 g (97%) phosphine) H2O 4/1 with 1,4-dioxane, water and m/z = 578 palladium(0) 80° C. MeOH, dissolved in DCM [M + H].sup.+ 2 mol %, Potassium and filtered through carbonate Florisil ®, recrystallized 2 eq, 2M from chlorobenzene A7 Dichloro [1,1′- 1,4-dioxane/ product precipitates, washed  4.5 g (26%) bis(diphenylphosphino) H2O 6/1 with water and n-hexane, m/z = 472 ferrocene]palladium(II) 80° C. dissolved in hot [M + Na].sup.+ 4.5 mol %, Potassium chlorobenzene, filtered carbonate through Alox N and 2 eq, 2M allowed to crystallize A8 Dichloro 1,1′- toluene/THF/ product precipitates, washed 4.85 g (38%) bis(diphenylphosphino) H2O 5/2/1 with water and n-hexane, m/z = 538 ferrocene]palladium(II) 80° C. soxhlet with THF, [M + H].sup.+ 3 mol %, Potassium precipitated by addition of carbonate n-hexane 2 eq, 2M A10 Dichloro 1,1′- 1,4-dioxane/ Product precipitates, filter  8.6 g (66%) bis(diphenylphosphino) H20 4/1 off and wash with water and m/z = 600 ferrocene]palladium(II) 80° C. dioxane, dissolved in DCM [M + H].sup.+ 3 mol %, Potassium and filtered through through carbonate Florisil®, recrystallization 2 eq, 2M from toluene A11 Sphos Pd(crotyl)Cl THF product precipitates, washed 4.67 g (67%) 2 mol %, 45° C. with water and hexane, m/z = 524 Tripotassium recrystallized from DMF [M + H].sup.+ phosphate 2.5 eq A13 Sphos Pd(crotyl)Cl toluene/THF/ product precipitates, washed  2.6 g (55%) 6 mol %, H2O 5/2/1 with water, toluene and m/z = 588 Tripotassium 55° C.->80° C. THF, soxhlet with DCM, [M + H].sup.+ phosphate product precipitates 2.5 eq A14 Dichloro 1,1′- toluene/THF/ product precipitates, washed 5.66 g (48%) bis(diphenylphosphino) H.sub.2O 5/2/1 with water, dissolved in hot m/z = 598 ferrocene]palladium(II) 80° C. chlorobenzene, filtered [M + H].sup.+ 3 mol %, Potassium through SiO2 and allowed carbonate to crystallize, filtered and 2 eq, 2M washed with n-hexane A16 Dichloro 1,1′- toluene/THF/ solvent removed, solid 6.55 g (46%) bis(diphenylphosphino) H2O 5/2/1 washed with water and m/z = 498 ferrocene]palladium(II) 80° C. extracted by soxhlet with [M + H].sup.+ 3 mol %, Potassium chlorobenzene, product carbonate crystallized 2 eq, 2M

[0249] Compound A1 was synthesized as follows:

[0250] A flask was flushed with nitrogen and charged with the aldehyde A1-A (structure below) and di(2-pyridyl) ketone in a 1:1 ratio.

##STR00056##

[0251] 0.1 eq of iodine, 2 eq Ammonium Acetate and THF/EtOH 1/1 were added and the mixture was heated to reflux until TLC showed complete consumption of the starting materials. The mixture was then cooled to room temperature and the product was purified in that the solvent was removed, followed by aqueous work-up (CHCl3/Na2S2O3/H2O), precipitation from CHCl3/n-hexane, solid collected, dissolved in hot chlorobenzene, filtered through SiO2 and precipitated by addition of n-hexane. The yield was 3.7 g (19%), m/z=549 [M+H]+.

[0252] Compound A29 was synthesized as follows:

[0253] A flask was flushed with nitrogen and charged with the aldehyde A29-A (structure below) and di(pyridin-2-yl)methanone in a 1:1 ratio.

##STR00057##

[0254] 0.1 eq of iodine, 8.8 eq Ammonium Acetate and THF/EtOH 1/1 were added and the mixture was heated to reflux until TLC showed complete consumption of the starting materials. The mixture was then cooled to room temperature and diluted with MeOH and 2M NaOH. The product was filtered off and recrystallized from toluene. The yield was 3.3 g (52%), m/z=541 [M+H]+.

General Procedure for Fabrication of OLEDs

[0255] For bottom emission devices, see Example 1 to 9 and comparative example 1 in Table 3, a 15 Ω/cm.sup.2 glass substrate with 90 nm ITO (available from Corning Co.) was cut to a size of 50 mm×50 mm×0.7 mm, ultrasonically washed with isopropyl alcohol for 5 minutes and then with pure water for 5 minutes, and washed again with UV ozone for 30 minutes, to prepare the anode.

[0256] Then, 97 vol.-% Biphenyl-4-yl(9,9-diphenyl-9H-fluoren-2-yl)-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-amine (CAS 1242056-42-3) with 3 vol.-% 2,2′,2″-(cyclopropane-1,2,3-triylidene)tris(2-(p-cyanotetrafluorophenyl)acetonitrile) was vacuum deposited on the anode, to form a HIL having a thickness of 10 nm.

[0257] Then, Biphenyl-4-yl(9,9-diphenyl-9H-fluoren-2-yl)-[4-(9-phenyl-9H-carbazol-3-yl) phenyl]-amine was vacuum deposited on the HIL, to form a first HTL having a thickness of 118 nm.

[0258] Then N,N-bis(4-(dibenzo[b,d]furan-4-yl)phenyl)-[1,1′:4′,1″-terphenyl]-4-amine (CAS 1198399-61-9) was vacuum deposited on the HTL, to form an electron blocking layer (EBL) having a thickness of 5 nm.

[0259] Then 97 vol.-% H09 (Sun Fine Chemicals, Korea) as EML host and 3 vol.-% BD200 (Sun Fine Chemicals, Korea) as fluorescent blue dopant were deposited on the EBL, to form a first blue-emitting EML with a thickness of 20 nm.

[0260] Then the first hole blocking layer is formed with a thickness of 5 nm by depositing 2-(3′-(9,9-dimethyl-9H-fluoren-2-yl)-[1,1′-biphenyl]-3-yl)-4,6-diphenyl-1,3,5-triazine on the emission layer.

[0261] Then, the electron transporting layer having a thickness of 25 nm is formed on the hole blocking layer by depositing 4′-(4-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)naphthalen-1-yl)-[1,1′-biphenyl]-4-carbonitrile. The electron transport layer (ETL) comprises 50 wt.-% matrix compound and 50 wt.-% of LiQ.

[0262] Then the n-CGL was formed on ETL with a thickness of 15 nm. The composition of the n-CGL can be taken from Table 2.

[0263] Then the p-CGL was formed on n-CGL with a thickness of 10 nm by depositing Biphenyl-4-yl(9,9-diphenyl-9H-fluoren-2-yl)-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-amine (CAS 1242056-42-3) with 2,2′,2″-(cyclopropane-1,2,3-triylidene)tris(2-(p-cyanotetrafluorophenyl)acetonitrile).

[0264] Then, Biphenyl-4-yl(9,9-diphenyl-9H-fluoren-2-yl)-[4-(9-phenyl-9H-carbazol-3-yl) phenyl]-amine was vacuum deposited on the p-CGL, to form a second HTL having a thickness of 10 nm.

[0265] A1 is evaporated at a rate of 0.01 to 1 Å/s at 10.sup.−7 mbar to form a cathode with a thickness of 100 nm.

[0266] The OLED stack is protected from ambient conditions by encapsulation of the device with a glass slide. Thereby, a cavity is formed, which includes a getter material for further protection. To assess the performance of the inventive examples compared to the prior art, the current efficiency is measured at 20° C. The current-voltage characteristic is determined using a Keithley 2635 source measure unit, by sourcing a voltage in V and measuring the current in mA flowing through the device under test. The voltage applied to the device is varied in steps of 0.1V in the range between 0V and 10V. Likewise, the luminance-voltage characteristics and CIE coordinates are determined by measuring the luminance in cd/m.sup.2 using an Instrument Systems CAS-140CT array spectrometer (calibrated by Deutsche Akkreditierungsstelle (DAkkS)) for each of the voltage values. The cd/A efficiency at 10 mA/cm2 is determined by interpolating the luminance-voltage and current-voltage characteristics, respectively.

[0267] Lifetime LT of the device is measured at ambient conditions (20° C.) and 30 mA/cm.sup.2, using a Keithley 2400 sourcemeter, and recorded in hours.

[0268] The brightness of the device is measured using a calibrated photo diode. The lifetime LT is defined as the time till the brightness of the device is reduced to 97% of its initial value.

Technical Effect of the Invention

[0269] In order to investigate the usefulness of the inventive compound preferred materials were tested in model top-emission blue OLEDs prepared as described above.

[0270] As a comparative example the following compound was used:

##STR00058##

[0271] In the following organic electronic devices were prepared according to several examples of the present invention and their properties were juxtaposed with a device according to a comparative example. The results are shown in the following Table 3:

TABLE-US-00003 TABLE 3 Properties of several organic electronic devices Concentration Concentration Thickness cd/A 1 m/W of matrix of metal organic Operating efficiency at efficiency at EQE at Matrix compound Metal dopant semiconductor voltage at 10 10 mA/cm.sup.2 10 mA/cm.sup.2 10 mA/cm.sup.2 compound (vol.-%) dopant (vol.-%) layer (nm) mA/cm.sup.2 (V) (cd/A) (1 m/W) (%) Comparative 99 Li 1 15 12 <0.1 <0.1 <0.1 A2 99 Li 1 15 4.8 6.4 4.4 5.2 A3 99 Li 1 15 4.9 6.4 4.1 5.2 A8 99 Li 1 15 5.2 5.8 3.7 5.7 A11 99 Li 1 15 5 6.6 4.1 5.2 A16 99 Li 1 15 5.4 6 3.7 5.7 A14 99 Li 1 15 5.2 6.4 4.1 5.3 A14 98 Li 2 15 5.1 6.3 4.1 5.2 A2 99 Yb 1 15 5.2 6.5 4.1 5.5 A3 99 Yb 1 15 5.4 6.7 4.3 5.2 A11 99 Yb 1 15 5.5 6.5 4.1 5.7 A11 99 Yb 1 15 5.3 6.2 3.9 5.3

[0272] The results show that in comparison with state-of-art reference, the compounds according to invention show a clearly enhanced performance, especially concerning efficiency and EQE.

[0273] The particular combinations of elements and features in the above detailed embodiments are exemplary only; the interchanging and substitution of these teachings with other teachings in this and the patents/applications incorporated by reference are also expressly contemplated. As those skilled in the art will recognize, variations, modifications, and other implementations of what is described herein can occur to those of ordinary skill in the art without departing from the spirit and the scope of the invention as claimed. Accordingly, the foregoing description is by way of example only and is not intended as limiting. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. The invention's scope is defined in the following claims and the equivalents thereto. Furthermore, reference signs used in the description and claims do not limit the scope of the invention as claimed.