Organic electroluminescent device comprising a redox-doped electron transport layer and an auxiliary electron transport layer

Abstract

The present invention relates to an organic electroluminescent device, particularly to an organic light emitting diode (OLED) including an ETL stack of at least two electron transport layers, wherein the first electron transport layer comprises a first electron transport matrix compound and the second electron transport layer comprises second electron transport matrix compound and a redox n-dopant, and a device comprising the OLED.

Claims

1. An organic electroluminescent device comprising an anode, a cathode, an emission layer arranged between the anode and the cathode, a first electron transport layer comprising a first electron transport matrix, a second electron transport layer comprising a second electron transport matrix and a redox n-dopant, wherein the first electron transport layer and the second electron transport layer are arranged between the emission layer and the cathode, wherein the first electron transport layer is arranged closer to the emission layer than the second electron transport layer and the second electron transport layer is arranged closer to the cathode than the first electron transport layer; wherein at least the first electron transport matrix comprises a matrix compound according to Chemical Formula I: ##STR00045## wherein A.sup.1, A.sup.2, A.sup.3 and A.sup.4 is independently selected from single bond, an unsubstituted or substituted C.sub.6 to C.sub.30 arylene and an unsubstituted or substituted C.sub.1 to C.sub.30 heteroarylene; A.sup.5 is selected from an unsubstituted or substituted C.sub.6 to C.sub.40 aryl group and/or from an unsubstituted or substituted C.sub.2 to C.sub.40 heteroaryl group; R.sup.1 to R.sup.5 are independently a substituted or unsubstituted C.sub.6 to C.sub.30 aryl group, a substituted or unsubstituted C.sub.2 to C.sub.30 heteroaryl group; a to e are independently an integer of 0 or 1 and 4≤a+b+c+d+e≤5; and wherein in the substituted group, at least one hydrogen is replaced by (i) deuterium, (ii) a halogen, (iii) a C.sub.2 to C.sub.60 tertiary amino group, wherein the nitrogen atom of the tertiary amino group is substituted with two independently selected C.sub.1 to C.sub.30 hydrocarbyl groups or the nitrogen atom of the C.sub.2 to C.sub.60 tertiary amino group forms a C.sub.1 to C.sub.30 heterocyclic group, (iv) a C.sub.2 to C.sub.60 phosphine oxide group, wherein the phosphorus atom of the phosphine oxide group is substituted with two C.sub.1 to C.sub.30 groups independently selected from hydrocarbyl, halogenated hydrocarbyl and hydrocarbyloxy or the phosphorus atom of the phosphine oxide group forms a C.sub.1 to C.sub.30 heterocyclic group, (v) a C.sub.1 to C.sub.22 silyl group, (vi) a C.sub.1 to C.sub.30 alkyl group, (vii) a C.sub.1 to C.sub.10 alkylsilyl group, (viii) a C.sub.6 to C.sub.22 arylsilyl group, (ix) a C.sub.3 to C.sub.30 cycloalkyl group, (x) a C.sub.2 to C.sub.30 heterocycloalkyl group, (xi) a C.sub.6 to C.sub.30 aryl group, (xii) a C.sub.2 to C.sub.30 heteroaryl group, (xiii) a C.sub.1 to C.sub.20 alkoxy group, (xiv) a C.sub.1 to C.sub.30 perfluoro-hydrocarbyl group, (xv) a C.sub.1 to C.sub.10 trifluoroalkyl group, or (xvi) a cyano group, and the redox dopant is a) an elemental electropositive metal selected from an alkali metal, an alkaline earth metal, a rare earth metal, a transition metal, or a combination thereof, wherein the transition metal is selected from the group consisting of Ti, V, Cr, and Mn; and/or b) an electrically neutral metal complex having redox potential which has a value which is more negative than −1.7 V, if measured by cyclic voltammetry against ferrocene/ferrocenium reference redox couple; and/or c) an electrically neutral organic radical having redox potential which has a value which is more negative than −1.7 V, if measured by cyclic voltammetry against ferrocene/ferrocenium reference redox couple.

2. The organic electroluminescent device according to claim 1, wherein the matrix compound (I) is a compound according to Chemical Formula (Ia) ##STR00046## wherein, in Chemical Formula Ia, Ar.sup.1 is selected from C.sub.6 to C.sub.12 arylene and C.sub.1 to C.sub.11 heteroarylene; R.sup.1 to R.sup.5 are independently a substituted or unsubstituted C6 to C30 aryl group, a substituted or unsubstituted C.sub.2 to C.sub.30 heteroaryl group; a to e are independently an integer of 0 or 1 and 4≤a+b+c+d+e≤5; L is a single bond, a substituted or unsubstituted C.sub.6 to C.sub.30 arylene group, or a substituted or unsubstituted C.sub.2 to C.sub.30 heteroarylene group; ET is a unsubstituted C.sub.6 to C.sub.40 aryl or a unsubstituted C.sub.5 to C.sub.40 heteroaryl group, or a substituted C.sub.6 to C.sub.40 aryl or a substituted C.sub.5 to C.sub.40 heteroaryl group; and wherein in the substituted group, at least one hydrogen is replaced by (i) deuterium, (ii) a halogen, (iii) a C.sub.2 to C.sub.60 tertiary amino group, wherein the nitrogen atom of the C.sub.2 to C.sub.60 tertiary amino group is substituted with two independently selected C.sub.1 to C.sub.30 hydrocarbyl groups or forms a C.sub.1 to C.sub.30 heterocyclic group, (iv) a C.sub.2 to C.sub.60 phosphine oxide group, wherein the phosphorus atom of the phosphine oxide group is substituted with two C.sub.1 to C.sub.30 groups independently selected from hydrocarbyl, halogenated hydrocarbyl and hydrocarbyloxy or the phosphorus atom of the phosphine oxide group forms a C.sub.1 to C.sub.30 heterocyclic group, (v) a C.sub.1 to C.sub.22 silyl group, (vi) a C.sub.1 to C.sub.30 alkyl group, (vii) a C.sub.1 to C.sub.10 alkylsilyl group, (viii) a C.sub.6 to C.sub.22 arylsilyl group, (ix) a C.sub.3 to C.sub.30 cycloalkyl group, (x) a C.sub.2 to C.sub.30 heterocycloalkyl group, (xi) a C.sub.6 to C.sub.30 aryl group, (xii) a C.sub.2 to C.sub.30 heteroaryl group, (xiii) a C.sub.1 to C.sub.20 alkoxy group, (xiv) a C.sub.1 to C.sub.30 perfluoro-hydrocarbyl group, (xv) a C.sub.1 to C.sub.10 trifluoroalkyl group, or (xvi) a cyano group.

3. The organic electroluminescent device according to claim 1, wherein the matrix compound (I) is a compound according to Chemical Formula (Ib) ##STR00047## wherein in Chemical Formula Ib: X.sup.1 to X.sup.11 are independently, N, C, or CR.sup.a; R.sup.a is independently, hydrogen, deuterium, a C.sub.1 to C.sub.30 alkyl group, a C.sub.3 to C.sub.30 cycloalkyl group, a C.sub.6 to C.sub.30 aryl group, a C.sub.6 to C.sub.30 diarylamine group, a C.sub.1 to C.sub.30 alkoxy group, a C.sub.3 to C.sub.21 silyl group, a C.sub.3 to C.sub.21 silyloxy group, a C.sub.1 to C.sub.30 alkylthiol group, a C.sub.6 to C.sub.30 arylthiol group, a halogen, a C.sub.1 to C.sub.30 halogenated hydrocarbyl group, a cyano group; R.sup.1 to R.sup.5 are independently a substituted or unsubstituted C.sub.6 to C.sub.30 aryl group, a substituted or unsubstituted C.sub.2 to C.sub.30 heteroaryl group; a to e are independently an integer of 0 or 1 and 4≤a+b+c+d+e≤5; L is a single bond, a substituted or unsubstituted C.sub.6 to C.sub.30 arylene group, a substituted or unsubstituted C.sub.2 to C.sub.30 heteroarylene group; ET is a unsubstituted C.sub.6 to C.sub.40 aryl or a unsubstituted C.sub.2 to C.sub.40 heteroaryl group, or a substituted C.sub.6 to C.sub.40 aryl or a substituted C.sub.2 to C.sub.40 heteroaryl group; and wherein in the substituted group, at least one hydrogen is replaced by (i) deuterium, (ii) a halogen, (iii) a C.sub.1 to C.sub.60 tertiary amino group, wherein the nitrogen atom of the C.sub.2 to C.sub.60 tertiary amino group is substituted with two independently selected C.sub.1 to C.sub.30 hydrocarbyl groups or forms a C.sub.1 to C.sub.30 heterocyclic group, (iv) a C.sub.2 to C.sub.60 phosphine oxide group, wherein the phosphorus atom of the phosphine oxide group is substituted with two C.sub.1 to C.sub.30 groups independently selected from hydrocarbyl, halogenated hydrocarbyl and hydrocarbyloxy or the phosphorus atom of the phosphine oxide group forms a C.sub.1 to C.sub.30 heterocyclic group, (v) a C.sub.1 to C.sub.22 silyl group, (vi) a C.sub.1 to C.sub.30 alkyl group, (vii) a C.sub.1 to C.sub.10 alkylsilyl group, (viii) a C.sub.6 to C.sub.22 arylsilyl group, (ix) a C.sub.3 to C.sub.30 cycloalkyl group, (x) a C.sub.2 to C.sub.30 heterocycloalkyl group, (xi) a C.sub.6 to C.sub.30 aryl group, (xii) a C.sub.2 to C.sub.30 heteroaryl group, (xiii) a C.sub.1 to C.sub.20 alkoxy group, (xiv) a C.sub.1 to C.sub.30 perfluoro-hydrocarbyl group, (xv) a C.sub.1 to C.sub.10 trifluoroalkyl group, or (xvi) a cyano group.

4. The organic electroluminescent device according to claim 1, wherein the compound (I) is a compound according to formula (Ic) ##STR00048## wherein in formula Ic: R.sup.1 to R.sup.5 are independently a substituted or unsubstituted C.sub.6 to C.sub.30 aryl group, a substituted or unsubstituted C.sub.2 to C.sub.30 heteroaryl group; a to e are independently an integer of 0 or 1 and 4≤a+b+c+d+e≤5, L is a single bond, a substituted or unsubstituted C.sub.6 to C.sub.30 arylene group, a substituted or unsubstituted C.sub.2 to C.sub.30 heteroarylene group, and ET is a unsubstituted C.sub.6 to C.sub.40 aryl or a unsubstituted C.sub.2 to C.sub.40 heteroaryl group, or a substituted C.sub.6 to C.sub.40 aryl or a substituted C.sub.2 to C.sub.40 heteroaryl group; and wherein in the substituted group, at least one hydrogen is replaced by (i) deuterium, (ii) a halogen, (iii) a C.sub.1 to C.sub.60 tertiary amino group, wherein the nitrogen atom of the C.sub.2 to C.sub.60 tertiary amino group is substituted with two independently selected C.sub.1 to C.sub.30 hydrocarbyl groups or forms a C.sub.1 to C.sub.30 heterocyclic group, (iv) a C.sub.2 to C.sub.60 phosphine oxide group, wherein the phosphorus atom of the phosphine oxide group is substituted with two C.sub.1 to C.sub.30 groups independently selected from hydrocarbyl, halogenated hydrocarbyl and hydrocarbyloxy or the phosphorus atom of the phosphine oxide group forms a C.sub.1 to C.sub.30 heterocyclic group (v) a C.sub.1 to C.sub.22 silyl group, (vi) a C.sub.1 to C.sub.30 alkyl group, (vii) a C.sub.1 to C.sub.10 alkylsilyl group, (viii) a C.sub.6 to C.sub.22 arylsilyl group, (ix) a C.sub.3 to C.sub.30 cycloalkyl group, (x) a C.sub.2 to C.sub.30 heterocycloalkyl group, (xi) a C.sub.6 to C.sub.30 aryl group, (xii) a C.sub.2 to C.sub.30 heteroaryl group, (xiii) a C.sub.1 to C.sub.20 alkoxy group, (xiv) a C.sub.1 to C.sub.30 perfluoro-hydrocarbyl group, (xv) a C.sub.1 to C.sub.10 trifluoroalkyl group, or (xvi) a cyano group.

5. The organic electroluminescent device according to claim 2, wherein the ET group is a C.sub.2 to C.sub.30 heteroaryl group.

6. The organic electroluminescent device according to claim 2, wherein the ET group includes at least one N, with the proviso that ET is not a carbazolyl group.

7. The organic electroluminescent device according to claim 1, wherein the second electron transport matrix comprises a heterocyclic group containing at least one nitrogen atom and/or the second electron transport matrix comprises at least one phosphine oxide group.

8. The organic electroluminescent device according to claim 1, which is an organic light emitting diode.

9. An electronic device comprising the organic electroluminescent device according to claim 1.

10. The electronic device according to claim 9, wherein the electronic device is a display device.

11. The electronic device according to claim 9, wherein the display device comprises the organic light emitting diode according to claim 8.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a cross-sectional view showing an organic light emitting diode according to an embodiment of the invention.

(2) FIGS. 2 and 3 are cross-sectional views specifically showing a part of an organic layer of an organic light emitting diode according to an embodiment of the invention.

(3) Hereinafter, the figures are illustrated in more detail with reference to examples. However, the present disclosure is not limited to the following figures.

(4) FIGS. 1 to 3 are schematic cross-sectional views of organic light emitting diodes 100, 300, and 400 according to an embodiment of the present invention. Hereinafter, referring to FIG. 1, a structure of an organic light emitting diode according to an embodiment of the present invention and a method of manufacturing the same are as follows. The organic light emitting diode 100 has a structure where an anode 110, a stack of organic layers 105 including an optional hole transport region; an emission layer 130; and a cathode 150 that are sequentially stacked.

(5) A substrate may be disposed on the anode 110 or under the cathode 150. The substrate may be selected from usual substrate used in a general organic light emitting diode and may be a glass substrate or a transparent plastic substrate.

(6) The anode 110 may be formed by depositing or sputtering an anode material on a substrate. The anode material may be selected from materials having a high work function that makes hole injection easy. The anode 110 may be a reflective electrode, a transflective electrode, or a transmissive electrode. The anode material may use indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide (SnO.sub.2), zinc oxide (ZnO), and the like. Or, it may be a metal such as silver (Ag), or gold (Au), or an alloy thereof.

(7) The anode 110 may have a monolayer or a multi-layer structure of two or more layers.

(8) The organic light emitting diodes 100, 300, and 400 according to an embodiment of the present invention may include a hole transport region; an emission layer 130; and an first electron transport layer 33 comprising a compound according to formula I.

(9) Referring to FIG. 2, the hole transport region of the stack of organic layers 105 may include at least two layered hole transport layers, and in this case, the hole transport layer contacting the emission layer (130) is defined as a first hole transport layer 135 and a the hole transport layer contacting the anode (110) is defined as a second hole transport layer 34. The stack of organic layers 105 further includes two electron transport layers, namely first electron transport layer 33 and the second electron transport layer 31. The hole transport region of the stack 105 may further include at least one of a hole injection layer, a hole transport layer, an electron blocking layer, and a buffer layer.

(10) The hole transport region of the stack 105 may include only hole injection layer or only hole transport layer. Or, the hole transport region may have a structure where a hole injection layer 36/hole transport layer 34 or hole injection layer 36/hole transport layer 34/electron blocking layer (135) is sequentially stacked from the anode 110.

(11) For example, the hole injection layer 36 and the electron injection layer 37 can be additionally included, so that an OLED may comprises an anode 110/hole injection layer 36/hole transport layer 34/electron blocking layer 135/emission layer 130/first electron transport layer 33/second electron transport layer 31/electron injection layer 37/cathode 150, which are sequentially stacked.

(12) According to another aspect of the invention, the organic electroluminescent device (400) comprises a anode (110), a hole injection layer (36), a hole transport layer (34), optional an electron blocking layer (135), an emission layer (130), first electron transport layer (33), second electron transport layer (31), an optional electron injection layer (37), a cathode (150) wherein the layers are arranged in that order.

(13) The hole injection layer 36 may improve interface properties between ITO as an anode and an organic material used for the hole transport layer 34, and is applied on a non-planarized ITO and thus planarizes the surface of the ITO. For example, the hole injection layer 36 may include a material having a median value of the energy level of its highest occupied molecular orbital (HOMO) between the work function of ITO and the energy level of the HOMO of the hole transport layer 34, in order to adjust a difference between the work function of ITO as an anode and the energy level of the HOMO of the hole transport layer 34.

(14) When the hole transport region includes a hole injection layer 36, the hole injection layer may be formed on the anode 110 by any of a variety of methods, for example, vacuum deposition, spin coating, casting, Langmuir-Blodgett (LB) method, or the like.

(15) When hole injection layer is formed using vacuum deposition, vacuum deposition conditions may vary depending on the material that is used to form the hole injection layer, and the desired structure and thermal properties of the hole injection layer to be formed and for example, vacuum deposition may be performed at a temperature of about 100° C. to about 500° C., a pressure of about 10.sup.−6 Pa to about 10.sup.−1 Pa, and a deposition rate of about 0.1 to about 10 nm/sec, but the deposition conditions are not limited thereto.

(16) When the hole injection layer is formed using spin coating, the coating conditions may vary depending on the material that is used to form the hole injection layer, and the desired structure and thermal properties of the hole injection layer to be formed. For example, the coating rate may be in the range of about 2000 rpm to about 5000 rpm, and a temperature at which heat treatment is performed to remove a solvent after coating may be in a range of about 80° C. to about 200° C., but the coating conditions are not limited thereto.

(17) Conditions for forming the hole transport layer and the electron blocking layer may be defined based on the above-described formation conditions for the hole injection layer.

(18) A thickness of the hole transport part of the charge transport region may be from about 10 nm to about 1000 nm, for example, about 10 nm to about 100 nm. When the hole transport transport part of the charge transport region includes the hole injection layer and the hole transport layer, a thickness of the hole injection layer may be from about 10 nm to about 1000 nm, for example about 10 nm to about 100 nm and a thickness of the hole transport layer may be from about 5 nm to about 200 nm, for example about 10 nm to about 150 nm. When the thicknesses of the hole transport part of the charge transport region, the HIL, and the HTL are within these ranges, satisfactory hole transport characteristics may be obtained without a substantial increase in driving voltage.

(19) Hole transport matrix materials used in the hole transport region are not particularly limited. Preferred are covalent compounds comprising a conjugated system of at least 6 delocalized electrons. Typical examples of hole transport matrix materials which are widely used in hole transport layers are polycyclic aromatic hydrocarbons, triaryl amine compounds and heterocyclic aromatic compounds. Suitable ranges of frontier orbital energy levels of hole transport matrices useful in various layer of the hole transport region are well-known. In terms of the redox potential of the redox couple HTL matrix/cation radical of the HTL matrix, the preferred values (if measured for example by cyclic voltammetry against ferrocene/ferrocenium redox couple as reference) may be in the range 0.0-1.0 V, more preferably in the range 0.2-0.7 V, even more preferably in the range 0.3-0.5 V.

(20) The hole transport region of the stack of organic layers may further include a charge-generating material to improve conductivity, in addition to the materials as described above. The charge-generating material may be homogeneously or non-homogeneously dispersed in the hole transport region.

(21) The charge-generating material may be, for example, a p-dopant. The p-dopant may be one of a quinone derivative, a metal oxide, and a cyano group-containing compound, but is not limited thereto. Non-limiting examples of the p-dopant are quinone derivatives such as tetracyanoquinonedimethane (TCNQ), 2,3,5,6-tetrafluoro-tetracyano-1,4-benzoquinonedimethane (F4-TCNQ), and the like; metal oxides such as tungsten oxide, molybdenum oxide, and the like; and cyano-containing compounds such as compound HT-D1 below.

(22) ##STR00011##

(23) The hole transport part of the charge transport region may further include a buffer layer.

(24) The buffer layer may compensate for an optical resonance distance of light according to a wavelength of the light emitted from the EML, and thus may increase efficiency.

(25) The emission layer (EML) may be formed on the hole transport region by using vacuum deposition, spin coating, casting, LB method, or the like. When the emission layer is formed using vacuum deposition or spin coating, the conditions for deposition and coating may be similar to those for the formation of the hole injection layer, though the conditions for the deposition and coating may vary depending on the material that is used to form the emission layer. The emission layer may include an emitter host (EML host) and an emitter dopant (further only emitter).

(26) The emitter may be a red, green, or blue emitter.

(27) In one embodiment, the emitter host is an anthracene matrix compound represented by formula 400 below:

(28) ##STR00012##

(29) In formula 400, Ar.sub.111 and Ar.sub.112 may be each independently a substituted or unsubstituted C.sub.6-C.sub.60 arylene group; Ar.sub.113 to Ar.sub.116 may be each independently a substituted or unsubstituted C.sub.1-C.sub.10 alkyl group or a substituted or unsubstituted C.sub.6-C.sub.60 aryl group; and g, h, i, and j may be each independently an integer from 0 to 4. In some embodiments, Ar.sub.111 and Ar.sub.112 in formula 400 may be each independently one of a phenylene group, a naphthylene group, a phenanthrenylene group, or a pyrenylene group; or a phenylene group, a naphthylene group, a phenanthrenylene group, a fluorenyl group, or a pyrenylene group, each substituted with at least one of a phenyl group, a naphthyl group, or an anthryl group.

(30) In formula 400, g, h, i, and j may be each independently an integer of 0, 1, or 2. In formula 400, Ar.sub.113 to Ar.sub.116 may be each independently one of a C.sub.1-C.sub.10 alkyl group substituted with at least one of a phenyl group, a naphthyl group, or an anthryl group; a phenyl group, a naphthyl group, an anthryl group, a pyrenyl group, a phenanthrenyl group, or a fluorenyl group; a phenyl group, a naphthyl group, an anthryl group, a pyrenyl group, a phenanthrenyl group, or a fluorenyl group, each substituted with at least one of a deuterium atom, a halogen atom, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxyl group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C.sub.1-C.sub.60 alkyl group, a C.sub.2-C.sub.60 alkenyl group, a C.sub.2-C.sub.60 alkynyl group, a C.sub.1-C.sub.60 alkoxy group, a phenyl group, a naphthyl group, an anthryl group, a pyrenyl group, a phenanthrenyl group, or a fluorenyl group; or

(31) ##STR00013## or formulas (Y2) or (Y3)

(32) ##STR00014##

(33) Wherein in the formulas (Y2) and (Y3), X is selected from an oxygen atom and a sulfur atom, but embodiments of the invention are not limited thereto.

(34) In the formula (2Y), any one of R.sub.11 to R.sub.14 is used for bonding to Ar.sub.111. R.sub.11 to R.sub.14 that are not used for bonding to Ar.sub.111 and R.sub.15 to R.sub.20 are the same as R.sub.1 to R.sub.8.

(35) In the formula (3Y), any one of R.sub.21 to R.sub.24 is used for bonding to Ar.sub.111. R.sub.21 to R.sub.24 that are not used for bonding to Ar.sub.111 and R.sub.25 to R.sub.30 are the same as R.sub.1 to R.sub.8.

(36) Preferably, the EML host comprises between one and three heteroatoms selected from the group consisting of N, O or S. More preferred the EML host comprises one heteroatom selected from S or O.

(37) According to a further aspect of the invention, the emitter host respectively has a reduction potential which, if measured under the same conditions by cyclic voltammetry against Fc/Fc.sup.+ in tetrahydrofuran, has a value more negative than the respective value obtained for 7-([1,1′-biphenyl]-4-yl)dibenzo[c,h]acridine, preferably more negative than the respective value for 9,9′,10,10′-tetraphenyl-2,2′-bianthracene, more preferably more negative than the respective value for 2,9-di([1,1′-biphenyl]-4-yl)-4,7-diphenyl-1,10-phenanthroline, even more preferably more negative than the respective value for 2,4,7,9-tetraphenyl-1,10-phenanthroline, even more preferably more negative than the respective value for 9,10-di(naphthalen-2-yl)-2-phenylanthracene, even more preferably more negative than the respective value for 2,9-bis(2-methoxyphenyl)-4,7-diphenyl-1,10-phenanthroline, most preferably more negative than the respective value for 9,9′-spirobi[fluorene]-2,7-diylbis(diphenylphosphine oxide).

(38) The emitter is mixed in a small amount to cause light emission, and may be generally a material such as a metal complex that emits light by multiple excitation into a triplet or more. The emitter may be, for example an inorganic, organic, or organometallic compound, and one or more kinds thereof may be used.

(39) The emitter may be a fluorescent emitter, for example ter-fluorene, the structures are shown below. 4.4′-bis(4-diphenyl amiostyryl)biphenyl (DPAVBi), 2,5,8,11-tetra-tert-butyl perylene (TBPe), and Compound 4 below are examples of fluorescent blue emitters.

(40) ##STR00015##

(41) According to another aspect, the organic semiconductor layer comprising a compound of formula I is arranged between a fluorescent blue emission layer and the cathode electrode.

(42) The emitter may be a phosphorescent emitter, and examples of the phosphorescent emitters may be organometallic compounds including Ir, Pt, Os, Ti, Zr, Hf, Eu, Tb, Tm, Fe, Co, Ni, Ru, Rh, Pd, or a combination thereof. The phosphorescent emitter may be, for example a compound represented by formula Z, but is not limited thereto:
L.sub.2MX  (Z).

(43) In formula Z, M is a metal, and L and X are the same or different, and are a ligand to form a complex compound with M.

(44) The M may be, for example Ir, Pt, Os, Ti, Zr, Hf, Eu, Tb, Tm, Fe, Co, Ni, Ru, Rh, Pd or, in a polynuclear complex, a combination thereof, and the L and X may be, for example, a bidendate ligand.

(45) A thickness of the emission layer may be about 10 nm to about 100 nm, for example about 20 nm to about 60 nm. When the thickness of the emission layer is within these ranges, the emission layer may have improved emission characteristics without a substantial increase in a driving voltage.

(46) Next, the electron transport region of the stack of organic layers 105 may be disposed on the emission layer.

(47) The electron transport region of the stack of organic layers includes at least the first electron transport layer and the second electron transport layer. The electron transport region of the stack of organic layers may further include an electron injection layer.

(48) For example, the electron transport region of the stack of organic layers may have a structure of the first electron transport layer/second electron transport layer/electron injection layer but is not limited thereto. For example, an organic light emitting diode according to an embodiment of the present invention includes at least two electron transport layers in the electron transport region of the stack of organic layers 105, and in this case, the electron transport layer contacting the emission layer is defined as the first electron transport layer 33.

(49) The electron transport layer may include two or more different electron transport matrix compounds.

(50) The formation conditions of the first electron transport layer 33, second electron transport layer 31, and electron injection layer 37 of the electron transport region of the stack of organic layers refer to the formation conditions of the hole injection layer.

(51) The thickness of the first electron transport layer may be from about 2 nm to about 100 nm, for example about 3 nm to about 30 nm. When the thickness of the first electron transport layer is within these ranges, the first electron transport layer may have improved electron transport auxiliary ability without a substantial increase in driving voltage.

(52) A thickness of the second electron transport layer may be about 10 nm to about 100 nm, for example about 15 nm to about 50 nm. When the thickness of the electron transport layer is within these ranges, the electron transport layer may have satisfactory electron transporting ability without a substantial increase in driving voltage.

(53) According to another aspect of the invention, the organic electroluminescent device further comprises an electron injection layer between the second electron transport layer and the cathode.

(54) The electron injection layer (EIL) 37 may facilitate injection of electrons from the cathode 150.

(55) According to another aspect of the invention, the electron injection layer 37 comprises: (i) an electropositive metal selected from alkali metals, alkaline earth metals and rare earth metals in substantially elemental form, preferably selected from Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Eu and Yb, more preferably from Li, Na, Mg, Ca, Sr and Yb, even more preferably from Li and Yb, most preferably Yb; and/or (ii) an alkali metal complex and/or alkali metal salt, preferably the Li complex and/or salt, more preferably a Li quinolinolate, even more preferably a lithium 8-hydroxyquinolinolate, most preferably the alkali metal salt and/or complex of the second electron transport layer is identical with the alkali metal salt and/or complex of the injection layer.

(56) The electron injection layer may include at least one selected from LiF, NaCl, CsF, Li.sub.2O, and BaO.

(57) A thickness of the EIL may be from about 0.1 nm to about 10 nm, or about 0.3 nm to about 9 nm. When the thickness of the electron injection layer is within these ranges, the electron injection layer may have satisfactory electron injection ability without a substantial increase in driving voltage.

(58) A material for the cathode 150 may be a metal, an alloy, or an electrically conductive compound that have a low work function, or a combination thereof. Specific examples of the material for the cathode 150 may be lithium (Li), magnesium (Mg), aluminum (Al), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), magnesium-silver (Mg—Ag), etc. In order to manufacture a top-emission light-emitting device having a reflective anode 110 deposited on a substrate, the cathode 150 may be formed as a transmissive electrode from, for example, indium tin oxide (ITO) or indium zinc oxide (IZO).

(59) 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

(60) Synthesis and physical properties of compound of formula I

(61) Triazine compounds of formula I may be synthesized in accordance with the methods described in PCT-KR2015-012551.

SYNTHESIS EXAMPLE 1

Compound A6 (in the Scheme Referred as Compound [3])

(62) ##STR00016##

(63) First Step: Synthesis of Intermediate I-5

(64) 13 g of an intermediate I-5 (61%) was obtained in the same synthesis method as the synthesis method of the compound 1 by using the intermediate I-4 (20.4 g, 34.92 mmol) and 1-bromo-3-iodobenzene (16.5 g, 52.39 mmol) under a nitrogen environment.

(65) Second Step: Synthesis of Intermediate I-6

(66) 10 g of an intermediate I-6 (74%) was obtained in the same synthesis method as the synthesis method of the intermediate I-4 by using the intermediate I-5 (12.6 g, 20.54 mmol) under a nitrogen environment.

(67) Third Step: Synthesis of Compound A6

(68) 8.7 g of compound A6 (in the scheme referred as [3]) was obtained in 68% yield by using the intermediate I-6 (10 g, 15.2 mmol) and 2-(3-bromophenyl)-4,6-diphenyl-1,3,5-triazine (7.9 g, 18.32 mmol). These reagents were dissolved in 250 mL tetrahydrofuran under a nitrogen environment, tetrakis(triphenylphosphine)palladium (0.9 g, 0.75 mmol) was added thereto, and the mixture was stirred. Then, potassium carbonate saturated in water (5.2 g, 37 mmol) was added thereto, and the mixture was heated and refluxed at 80° C. for 24 hours. When the reaction was complete, water was added to the reaction solution, dichloromethane was used to perform an extraction, an anhydrous MgSO.sub.4 was used to remove moisture therefrom, and a resultant therefrom was filtered and concentrated under a reduced pressure. This obtained residue was separated and purified through column chromatography.

(69) LC Mass (theoretical value: 842.04 g/mol, measured value: M+H.sup.+=843.03 g/mol)

(70) The benzoquinazoline compound A9 was prepared analogously. Physical properties of tested compounds of formula (I) are summarized in Table 1.

(71) Dibenzoacridine compounds of formula I may be synthesized in accordance with the methods described in WO2011/154131A1.

(72) Another alternative is demonstrated in Synthesis example 2. The procedure is generally applicable for the synthesis of compounds comprising the hexaphenylbenzene structural moiety.

SYNTHESIS EXAMPLE 2

Compound A16

Step 1: Synthesis of 7-(4-(phenylethynyl)phenyl)dibenzo[c,h]acridine

(73) ##STR00017##

(74) A three necked 250-mL round bottom flask is purged with N.sub.2. Under a constant flow of N.sub.2 7-(4-bromophenyl)dibenzo[c,h]acridine (10.0 g, 23.0 mmol), phenylacetylene (4.70 g, 46.0 mmol, 2.0 eq.), and bis (triphenylphosphine)-palladium chloride (3.23 g, 4.6 mmol, 0.2 eq.) were introduced, followed by a 1M-solution of tetrabutylammonium fluoride in THF (70 mL). The resulting mixture was warmed up to reflux and reacted for 2 h. After completion of the reaction, MeOH (70 mL) was added, and the solution was left to cool down to room temperature. The precipitate formed upon cooling was collected by filtration, washed with MeOH (2×50 mL), then hexane (3×50 mL), and finally dried under vacuum at 40° C.

(75) Yield: about 7.0 g (about 67%, yellowish solid).

Step 2: Synthesis of 7-(3′,4′,5′,6′-tetraphenyl-[1,1′:2′,1″-terphenyl]-4-yl)dibenzo[c,h]acridine

(76) ##STR00018##

(77) A three necked 100-mL round bottom flask was charged with 7-(4-(phenylethynyl)phenyl)dibenzo[c,h]acridine (6.8 g, 14.9 mmol), 2,3,4,5-tetraphenylcyclopenta-2,4-dienone (6.31 g, 16.4 mmol, 1.1 eq.), and benzophenone (35 g as molten solvent). After degassing the solids with N.sub.2, the resulting mixture was warmed up to 300° C. After 1 h of reflux at 300° C., gas evolution had stopped and the mixture was hence cooled down to ca. 80° C. Toluene (100 mL), was added, and the resulting precipitate was filtered off and washed with toluene (2×40 mL), followed by hexane (2×40 mL). The solid was then purified by trituration in hot chlorobenzene (60 mL), followed by trituration in hot MeOH (60 mL). After filtration and drying under vacuum at 120° C., the desired was isolated as a yellowish powder.

(78) Yield: about 6.8 g (about 56%, yellowish solid).

(79) The benzoacridine compound A18 was prepared analogously. In Table 1 are summarized dibenzoacridine compounds of formula I and their starting material, yield, m/z, glass transition temperature, reduction potential against Fc/Fc.sup.+ in tetrahydrofuran.

(80) TABLE-US-00001 TABLE 1 Redox potential against Comp. Starting Yield Tg Fc/Fc.sup.+ I: materials Structure of compound I [%] [° C.] [V] A1   0 62% 175 −2.25 A2 138 −2.20 A3 135 −2.20 A4 140 −2.22 A5   86% 165 −2.29 A6 139 −2.18 A7 147 −2.15 A8 0 147 −2.18 A9 144 −2.25 A10 149 −2.14 A12 — −2.18 A13 — −2.23 A15   58% 159 −2.29 A16 −2.31 A17   0 50% 175 — A18 Not ob- served −2.25
General Procedure for Fabrication of OLEDs

(81) The model bottom emitting blue fluorescent OLED is described below.

(82) It was prepared using auxiliary materials F1, F2, F3, F4 and PD-2:

(83) ##STR00043## ##STR00044##

DEVICE EXAMPLE 1

Bottom Emitting Blue OLED

(84) The blue emitting device was made by depositing a 5 nm layer of F1 doped with PD2 (matrix to dopant weight ratio of 92:8 wt %) onto an ITO-glass substrate, followed by a 125 nm undoped layer of F1 and 10 nm undoped layer of F2. Subsequently, a blue fluorescent emitting layer of ABH113 (Sun Fine Chemicals) doped with BD200 (Sun Fine Chemicals) (97:3 wt %) was deposited with a thickness of 25 nm. A 15 or 20 nm thick interlayer of the tested compound and 15 or 10 nm layer of F3 doped with elemental lithium (99.5:0.5 wt %) were deposited subsequently on the emitting layer. Finally, an aluminium layer with a thickness of 100 nm was deposited as a cathode on top of the metal-doped layer.

(85) The OLED stack may be 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.

(86) Evaluation of Device Experiments

(87) To assess the performance of the inventive examples compared to the prior art, the current efficiency is measured under ambient conditions (20° C.). Operational voltage measurements are performed using a Keithley 2400 sourcemeter, and reported in V at standard current density 10 mA/cm.sup.2 for top emission devices. For bottom emission devices, the standard current density is usually 15 mA/cm.sup.2. A calibrated spectrometer CAS140 from Instrument Systems is used for measurement of CIE coordinates and brightness in Candela. Lifetime LT of the device is measured at ambient conditions (20° C.) and standard current density 10 mA/cm.sup.2 or 15 mA/cm.sup.2, using a Keithley 2400 sourcemeter, and recorded in hours. 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.

(88) The light output in external efficiency EQE and power efficiency P.sub.eff (1 m/W) are determined at 10 mA/cm.sup.2 for top emission devices.

(89) To determine the efficiency EQE in % the light output of the device is measured using a calibrated photodiode.

(90) To determine the power efficiency in 1 m/W, in a first step the luminance in candela per square meter (cd/m.sup.2) is measured with an array spectrometer CAS140 CT from Instrument Systems which has been calibrated by Deutsche Akkreditierungsstelle (DAkkS). In a second step, the luminance is then multiplied by π and divided by the voltage and current density.

(91) In bottom emission devices, the emission is predominately Lambertian and quantified in percent external quantum efficiency (EQE) and power efficiency in 1 m/W.

(92) The auxiliary compound F4 served as a state-of-art reference; the results in terms of colour coordinates x and y, operational voltage, luminance current efficiency C.sub.eff, power efficiency P.sub.eff and quantum efficiency Q.sub.eff are shown in Table 2.

(93) TABLE-US-00002 TABLE 2 1.sup.st ETL thickness Compound Voltage/V Luminance/(cd/m.sup.2) C.sub.Eff/(cd/A) P.sub.Eff/(lm/W) Q.sub.Eff/(lm/W) (nm) (I) CIE 1931 x CIE 1931 y [15 mA/cm.sup.2] [10 mA/cm.sup.2] [15 mA/cm.sup.2] [15 mA/cm.sup.2] [15 mA/cm.sup.2] 15 A1 0.139 0.105 4.183 946 9.30 6.99 9.89 20 A2 0.137 0.110 4.005 843 8.61 6.75 8.95 20 A3 0.137 0.111 4.074 949 9.49 7.32 9.75 20 A4 0.137 0.113 4.117 932 9.53 7.27 9.72 15 A5 0.139 0.106 4.027 857 8.63 6.73 9.07 15 A6 0.138 0.108 4.310 955 9.40 6.85 9.77 15 A7 0.138 0.108 4.299 897 8.87 6.48 9.20 20 A8 0.136 0.116 4.329 970 9.57 6.94 9.51 15 A9 0.139 0.104 4.239 826 8.83 6.54 9.48 20 A10 0.136 0.117 4.456 967 9.55 6.73 9.46 15 F4 0.138 0.108 4.208 874 8.62 6.44 9.01

Technical Effect of the Invention

(94) As it may be taken from the Table 2, a majority of the tested compounds of formula (I) implemented in a state-of-art blue OLED comprising redox doped second ETL and redox doped HTL showed better results (results in boldface letters) than the state-of-art matrix compound F4 used as reference. Most impressive is the improvement in power efficiency which was achieved in all tested compounds.

(95) While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Therefore, the aforementioned embodiments should be understood to be exemplary but not limiting the present invention in any way.