Electroluminescent device comprising a defined layer arrangement comprising a light emitting layer, a hole transport layer and an electron transport layer

Abstract

The present invention is directed to an electroluminescent device comprising: —at least one node layer, —at least one cathode layer, —at least one light emitting layer, —at least one first hole transport layer, —at least a first electron transport layer; wherein for increasing power efficiency the compositions of the light emitting layer, the hole transport layer and the electron transport layer are matched to one another, wherein—the at least one light emitting layer is arranged between the anode layer and the cathode layer, wherein the at least one light emitting layer comprises: —at least one fluorescent emitter compound embedded in at least one polar emitter host compound, wherein—the at least one polar emitter host compound has at least three aromatic rings, which are independently selected from carbocyclic rings and heterocyclic rings; —the at least one first hole transport layer is arranged between the anode layer and the light emitting layer, wherein the at least one first hole transport layer comprises: —at least one electrical p-dopant, or—at least one electrical p-dopant and at least one first hole transport matrix compound; —the at least one first electron transport layer is arranged between the cathode layer and the light emitting layer, wherein the first electron transport layer comprises: —at least one redox n-dopant, and—at least one first electron transport matrix compound.

Claims

1. An electroluminescent device comprising: at least one anode layer, at least one cathode layer, at least one light emitting layer, at least one first hole transport layer, at least a first electron transport layer; wherein for increasing power efficiency the compositions of the light emitting layer, the hole transport layer and the electron transport layer are matched to one another, wherein the at least one light emitting layer is arranged between the anode layer and the cathode layer, wherein the at least one light emitting layer comprises: at least one fluorescent emitter compound embedded in at least one polar emitter host compound, wherein the at least one polar emitter host compound has at least three aromatic rings, which are independently selected from carbocyclic rings and heterocyclic rings; the at least one first hole transport layer is arranged between the anode layer and the light emitting layer, wherein the at least one first hole transport layer comprises: at least one electrical p-dopant, or at least one electrical p-dopant and at least one first hole transport matrix compound; the at least one first electron transport layer is arranged between the cathode layer and the light emitting layer, wherein the first electron transport layer comprises: at least one redox n-dopant, and at least one first electron transport matrix compound.

2. The electroluminescent device according to claim 1 comprising: at least one anode layer, at least one cathode layer, at least one light emitting layer, at least one first hole transport layer, at least a first electron transport layer; wherein for increasing power efficiency the compositions of the light emitting layer, the hole transport layer and the electron transport layer are matched to one another, wherein the at least one light emitting layer is arranged between the anode layer and the cathode layer, wherein the at least one light emitting layer comprises: at least one fluorescent emitter compound embedded in at least one polar emitter host compound, wherein the at least one polar emitter host compound has at least three aromatic rings, which are independently selected from carbocyclic rings and heterocyclic rings, and has a gas phase dipole moment, computed using the hybrid functional B3LYP with a Gaussian 6-31G* basis set as implemented in the program package TURBOMOLE V6.5 for the lowest energy conformer found by the program package TURBOMOLE V6.5 using the hybrid functional B3LYP with a Gaussian 6-31G* basis set, in the range from about ≥0.2 Debye to about ≤2.0 Debye; the at least one first hole transport layer is arranged between the anode layer and the light emitting layer, wherein the at least one first hole transport layer comprises: at least one electrical p-dopant, or at least one electrical p-dopant and at least one first hole transport matrix compound; the at least one first electron transport layer is arranged between the cathode layer and the light emitting layer, wherein the first electron transport layer comprises: at least one redox n-dopant, and at least one first electron transport matrix compound.

3. The electroluminescent device of claim 1, wherein for the at least one light emitting layer: the emitter host compound comprises 4, 5, 6, 7, 8, 9, 10, 11 or 12 aromatic rings, which are independently selected from carbocyclic rings and heterocyclic rings; and for the at least one first hole transport layer: the electrical p-dopant is selected from the group comprising: a) organic compounds comprising at least one electron withdrawing group(s) selected from: (i) perhalogenated alkyl, (ii) carbonyl group, (iii) sulfonyl group, (iv) nitrile group and (v) nitro group; b) metal oxides, metal salts and metal complexes, wherein the metal in the metal oxide, metal salt and/or the metal complex; and the optional at least one first hole transport matrix compound is selected from covalent compounds comprising a conjugated system of at least 6 delocalized electrons; for the at least one first electron transport layer: the redox n-dopant is selected from the group comprising: a) elemental metals; b) organic radicals; c) transition metal complexes, wherein the transition metal is selected from 3.sup.rd, 4.sup.th, 5.sup.th 6.sup.th, 7.sup.rd, 8.sup.th, 9.sup.th or 10.sup.th group of the Periodic Table and is in oxidation state (—I), (0), (I) or (II); the at least one first electron transport matrix compound is selected from covalent compounds comprising a conjugated system of at least 6 delocalized electrons.

4. The electroluminescent device according to claim 1, wherein the emitter host compound has a gas phase dipole moment, computed using the hybrid functional B3LYP with a Gaussian 6-31G* basis set as implemented in the program package TURBOMOLE V6.5 for the lowest energy conformer found by the program package TURBOMOLE V6.5 using the hybrid functional B3LYP with a Gaussian 6-31G* basis set, in the range from about ≥0.3 Debye to about ≤1.8 Debye; the first electron transport matrix compound comprises at least one phosphine oxide group or at least one phenanthroline group.

5. The electroluminescent device according to claim 1, wherein the polar emitter host compound is an anthracene compound represented by the chemical Formula 1: ##STR00098## wherein A.sup.1 is selected from the group comprising a substituted or unsubstituted C.sub.6-C.sub.60 aryl or C.sub.6-C.sub.60 heteroaryl; A.sup.2 is selected from the group comprising a substituted or unsubstituted C.sub.1 to C.sub.10 alkyl group, a substituted or unsubstituted C.sub.6-C.sub.60 aryl or C.sub.6-C.sub.60 heteroaryl; A.sup.3 is selected from the group comprising a substituted or unsubstituted C.sub.1 to C.sub.10 alkyl group, a substituted or unsubstituted C.sub.6-C.sub.60 aryl or C.sub.6-C.sub.60 heteroaryl; A.sup.4 is selected from the group comprising a substituted or unsubstituted C.sub.6-C.sub.60 aryl or C.sub.6-C.sub.60 heteroaryl; and the first electron transport matrix compound has the chemical formula 2: ##STR00099## wherein X is selected from O, S, Se; R.sup.1 and R.sup.2 are independently selected from C.sub.1 to C.sub.12 alkyl, C.sub.6 to C.sub.20 aryl and C.sub.5 to C.sub.20 heteroaryl; R.sup.3 is selected from formula (2A), ##STR00100## or formula (2B) ##STR00101## wherein * marks the position in the respective R.sup.4 or Ar.sup.1 group for binding the R.sup.4 or Ar.sup.1 to the phosphorus atom in formula (2); R.sup.4 is selected from C.sub.1 to C.sub.8 alkyl, C.sub.6 to C.sub.20 aryl and C.sub.5 to C.sub.20 heteroaryl; Ar.sup.1 is selected from C.sub.6 to C.sub.20 aryl and C.sub.5 to C.sub.20 heteroaryl; Ar.sup.2 is selected from C.sub.18 to C.sub.40 aryl and C.sub.10 to C.sub.40 heteroaryl; R.sup.5 is selected from H, C.sub.1 to C.sub.12 alkyl, C.sub.6 to C.sub.20 aryl and C.sub.5 to C.sub.20 heteroaryl n is selected from 0, 1, or 2.

6. The electroluminescent device according to claim 5, wherein in chemical Formula 1 the hetero atom of the C.sub.6-C.sub.60 heteroaryl is selected from the group comprising N, O and/or S; and in chemical Formula 2 at least one or all of R.sup.1, R.sup.2, R.sup.5, Ar.sup.1 and Ar.sup.2 are substituted with C.sub.1 to C.sub.12 alkyl and C.sub.1 to C.sub.12 heteroalkyl groups.

7. The electroluminescent device according to claim 5, wherein in chemical Formula 1: the C.sub.6-C.sub.60 heteroaryl comprises at least one five-membered ring; or the C.sub.6-C.sub.60 aryl comprises an anthracene or benzoanthracene; or the C.sub.6-C.sub.60 heteroaryl comprises a benzofuran, dibenzofuran, benzo-naphtofuran or dinaphtofuran; and in chemical Formula 2: two substituents selected from R.sup.1, R.sup.2 and R.sup.3 form with the phosphorus atom a 7-membered phosphepine ring.

8. The electroluminescent device according to claim 5, wherein in chemical Formula 1: A.sup.4 has the following formulas (IIa) to (IIi): ##STR00102## wherein * marks the binding position for the respective A.sup.4 group to the anthracene compound.

9. The electroluminescent device according to claim 5, wherein the anthracene compound according to chemical Formula 1 is selected from the group of Formula B1 to B7: ##STR00103## ##STR00104## and the first electron transport aromatic matrix compound comprising a phosphine oxide group according to chemical Formula 2 is selected from the group of Formula Va to Vai: Formula Va to Ve: ##STR00105## ##STR00106## or Formula Vf to Vq: ##STR00107## ##STR00108## ##STR00109## or Formula Vr to Vt: ##STR00110## Formula Vu to Vai: ##STR00111## ##STR00112## ##STR00113##

10. The electroluminescent device according to claim 1, wherein the device comprises in addition a second electron transport layer comprising at least one second electron transport matrix compound which is selected from covalent compounds comprising a conjugated system of at least 6 delocalized electrons; wherein the second electron transport layer is arranged between the first electron transport layer and the light emitting layer.

11. The electroluminescent device according to claim 1, wherein the second electron transport compound has a redox potential, measured by cyclic voltammetry with potentiostatic device Metrohm PGSTAT30 and software Metrohm Autolab GPES at room temperature, in an argon de-aerated, dry 0.1M tetrahydrofuran solution of the tested substance, under argon atmosphere, with 0.1M tetrabutylammonium hexafluorophosphate supporting electrolyte, between platinum working electrodes and with an Ag/AgCl pseudo-standard electrode consisting of a silver wire covered by silver chloride and immersed directly in the measured solution, with the scan rate 100 mV/s, in the range from −2.2 to −2.4 V, against ferrocene/ferrocenium redox couple as a reference.

12. The electroluminescent device according to claim 1, wherein the second electron transport aromatic matrix compound has a gas phase dipole moment, computed using the hybrid functional B3LYP with a Gaussian 6-31G* basis set as implemented in the program package TURBOMOLE V6.5 for the lowest energy conformer found by the program package TURBOMOLE V6.5 using the hybrid functional B3LYP with a Gaussian 6-31G* basis set, in the range from 0.1 Debye to 5.0 Debye.

13. The electroluminescent device according to claim 1, wherein the first hole transport layer is arranged adjacent to the anode layer.

14. The electroluminescent device according to claim 13, comprises in addition a second hole transport layer comprising a second hole transport matrix compound which is selected from covalent compounds comprising a conjugated system of at least 6 delocalized electrons.

15. A display device comprising at least one electroluminescent device according to claim 1.

16. A lighting device comprising at least one electroluminescent device according to claim 1.

17. The electroluminescent device of claim 3, wherein at least three aromatic rings in the emitter host compound are condensed aromatic rings.

18. The electroluminescent device of claim 3, wherein at least one aromatic ring of the emitter host compound is a five- or six-membered heterocyclic ring.

19. The electroluminescent device of claim 3, wherein at least one aromatic ring is a five-membered heterocyclic ring containing one atom selected from the group consisting of N, O, and S.

20. The electroluminescent device of claim 19, wherein the five-membered heterocyclic ring is a furan ring.

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, the structure of an organic light emitting diode according to an embodiment of the present invention and the 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 a hole transport region (not shown); an electron transport region (not shown); 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 the first electron transport layer 31.

(9) Referring to FIG. 2, 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 second hole transport layer 135 and the hole transport layer contacting the anode (110) is defined as a first hole transport layer 34. The stack of organic layers 105 further includes two electron transport layers, namely first electron transport layer 31 and the second electron transport layer 33. The first hole transport layer of the stack 105 may have the function of a hole injection layer, and a third hole transport layer, having the function of an electron blocking layer and/or the function of a buffer layer, may be further sandwiched between the second hole transport layer 135 and the emission layer 130.

(10) The hole transport region of the stack 105 may include only a hole injection layer or only a hole transport layer. Or, the hole transport region may have a structure as depicted on FIG. 3, 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, an electron injection layer 37 can be additionally included, so that an OLED may comprises an anode 110/first hole transport layer having hole injection function 36/second hole transport layer 34/third hole transport layer having electron blocking function 135/emission layer 130/second electron transport layer 33/first electron transport layer 31/electron injection layer 37/cathode 150, which are sequentially stacked.

(12) According to FIG. 3, the organic electroluminescent device (400) comprises an anode (110), a first hole transport layer (36), a second hole transport layer (34), optional an electron blocking layer (135), an emission layer (130), an optional second electron transport layer (33), first electron transport layer (31), an optional electron injection layer (37), a cathode (150) wherein the layers are arranged in that order.

(13) The first hole transport layer 36 includes at least one electrical p-dopant which may be a material having a median value of the energy level of its highest occupied molecular orbital (HOMO) between the work function of the anode and the energy level of the HOMO of the second hole transport matrix of the second hole transport layer 34, in order to adjust a difference between the work function of the anode and the energy level of the HOMO of the second hole transport matrix of the hole transport layer 34.

(14) Synthesis of Auxiliary Compounds

(15) Compounds ETM-7, ETM-10 and ETM-11 were prepared by methods disclosed in WO2011/154131 and in WO2016/171356.

(16) General Procedure for Fabrication of OLEDs

(17) Model devices were prepared using auxiliary materials according to formulas F1, F2 and PD-2:

(18) ##STR00093##

(19) biphenyl-4-yl(9,9-diphenyl-9H-fluoren-2-yl)-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-amine, CAS 1242056-42-3, F1;

(20) ##STR00094##

(21) N,N-bis(4-(dibenzo[b,d]furan-4-yl)phenyl)-[1,1′: 4′,1″-terphenyl]-4-amine, CAS 1198399-61-9, F2;

(22) ##STR00095##

(23) 2,2′,2″-(cyclopropane-1,2,3-triylidene)tris(2-(p-cyanotetrafluorophenyl)acetonitrile), CAS 1224447-88-4, PD-2.

(24) Compound ETM-12 has the following formula:

(25) ##STR00096##
and its redox potential is −2.27 V.

Device Example 1 (Top Emitting Blue OLED)

(26) On a glass substrate, a 100 nm thick silver layer is deposited by vacuum thermal evaporation (VTE) as an anode, followed by a 10 nm thick first hole transport layer of a compound according to F1 doped with a compound according to formula PD2, wherein the matrix to dopant weight ratio is of 92:8 wt.-%, by a 117 nm thick undoped second hole transport layer made of neat compound according to formula F1 and by 5 nm thick undoped third hole transport layer made of neat compound according to formula F2. Subsequently, a blue fluorescent emitting layer of compound B1 (Sun Fine Chemicals) doped with fluorescent emitter NUBD370 (Sun Fine Chemicals) (97:3 wt %) is deposited with a thickness of 20 nm. A 5 nm thick second electron transport layer of the tested second electron transport matrix compound of table 3 and 33 nm thick first electron transport layer of the first electron transport matrix compound (Vr) doped with elemental ytterbium (90:10 wt %) or, alternatively, with metal alloy ND1 comprising 2.6 wt % Na and 97.4% Zn, are deposited subsequently on the emitting layer. Finally, a silver layer with a thickness of 11 nm is deposited as a cathode on top of the metal-doped layer, followed by 75 nm thick optical outcoupling layer made of neat compound according to formula F1.

(27) 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.

(28) Evaluation of Device Experiments

(29) 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.

(30) The brightness of the device is measured using a calibrated photo diode. The lifetime LT is defined as the time spent till the brightness of the device is reduced to 97% of its initial value.

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

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

(33) To determine the power efficiency in lm/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.

(34) In bottom emission devices, the emission is predominately Lambertian and quantified in percent external quantum efficiency (EQE) and power efficiency in lm/W. The results in terms of operational voltage and current efficiency C.sub.eff are shown in Table 3.

(35) Table 3a: Top emission device (inventive, see above) comprising a 20 nm thick emission layer consisting of compound B-1 (having dipole moment, computed using the hybrid functional B3LYP with a Gaussian 6-31G* basis set as implemented in the program package TURBOMOLE V6.5 for the lowest energy conformer found by the program package TURBOMOLE V6.5 using the hybrid functional B3LYP with a Gaussian 6-31G* basis set, 0.94 Debye) with 3 wt % NUBD-370, undoped 5 nm thick second electron transport layer (ETL), 33 nm thick first electron transport layer (EIL1) comprising the first electron transport matrix compound of formula 2, for example compound Vr, doped with 10 wt % of given n-dopant and a 11 nm thin silver cathode. ND-1 is an alloy comprising 2.6 wt % Na and 97.4% Zn.

(36) TABLE-US-00003 TABLE 3a first V at 15 C.sub.eff/CIEy Exam- Second ETL n- mA .Math. cm.sup.−2 cd/A at 15 LT ple ETL matrix dopant V mA .Math. cm.sup.−2 h 1a ETM-7 Vr Yb 3.228 152.7 60 1b ETM-8 Vr Yb 3.275 151.6 31 1c ETM-9 Vr ND-1 3.208 142.8 43 1d ETM-12 Vr ND-1 3.249 157.9 25

(37) Comparative devices are completely analogous to the device of table 3a, except that the inventive emitter host B1 is replaced with less polar compound ABH-113 having structure according to formula C1

(38) ##STR00097##

(39) Compound C1 (CAS 1214263-47-4) has dipole moment, computed using the hybrid functional B3LYP with a Gaussian 6-31G* basis set as implemented in the program package TURBOMOLE V6.5 for the lowest energy conformer found by the program package TURBOMOLE V6.5 using the hybrid functional B3LYP with a Gaussian 6-31G* basis set, 0.14 Debye. Performance of comparative devices is given in Table 3b.

(40) TABLE-US-00004 TABLE 3b Top emission device (comparative) first V at 15 C.sub.eff/CIEy Exam- Second ETL n- mA .Math. cm.sup.−2 cd/A at 15 LT ple ETL matrix dopant V mA .Math. cm.sup.−2 h 1a ETM-7 Vr Yb 3.541 130.4 30 1b ETM-8 Vr Yb 3.594 138.5 31 1c ETM-9 Vr ND-1 3.351 112.9 5 1d ETM-12 Vr ND-1 3.538 138.1 36

(41) Comparison of results for inventive devices according to Table 3a and comparative devices according to Table 3b shows that matching the dipole moment of the emitter host with adjacent layers as required by the present invention significantly improves device performance.

(42) Analogously as in Example 1, a further device lacking the second electron transport layer was prepared. Comparative devices 2A, 2B and 2C were prepared with compound C1 as emitter host instead of compound B1. The results in terms of colour coordinate y, operational voltage, current efficiency C.sub.eff and power efficiency P.sub.eff are reported in Table 4.

(43) TABLE-US-00005 TABLE 4 C.sub.eff C.sub.eff/CIEy P.sub.eff n-dopant/ V at 10 cd/A cd/A lm/W Exam- first ETL mA .Math. cm.sup.−2 at 10 at 10 at 10 ple matrix V mA .Math. cm.sup.−2 mA .Math. cm.sup.−2 mA .Math. cm.sup.−2 CIEy1931 2a Yb/Vr 3.20 6.07 110 5.96 0.055 2b Yb/MX12 3.49 5.43 98.1 4.88 0.055 2c Yb/MX11 3.72 4.68 84.9 3.96 0.055 2A Yb/Vr 3.33 5.05 91.2 4.76 0.055 2B Yb/MX12 3.78 5.27 95.1 4.38 0.055 2C Yb/MX11 4.06 4.18 77.4 3.24 0.054

(44) Comparison of results for inventive devices 2a, 2b and 2c with results for corresponding comparative devices 2A, 2B and 2C, respectively, shows that even if the second electron transport layer is omitted, matching the dipole moment of the emitter host with adjacent layers as required by the present invention significantly improves device performance.

(45) Table 5 gives energy levels and dipole moments, computed using the hybrid functional B3LYP with a Gaussian 6-31G* basis set as implemented in the program package TURBOMOLE V6.5 for the respective lowest energy conformers found by the program package TURBOMOLE V6.5 using the hybrid functional B3LYP with a Gaussian 6-31G* basis set, for exemplary emitter hosts B1-B7.

(46) TABLE-US-00006 TABLE 5 Structure HOMO [eV] LUMO [eV] E_Gap [eV] Dipole [Debye] B1 −5.13 −1.65 3.48 0.93 B2 −5.11 −1.63 3.48 0.64 B3 −5.11 −1.65 3.46 0.92 B4 −5.21 −1.58 3.63 0.77 B5 −5.16 −1.55 3.61 1.00 B6 −5.18 −1.58 3.60 1.51 B7 −5.10 −1.64 3.46 1.37

(47) It is evident that introduction of a furane and/or thiophene ring increases the dipole moment of the lowest energy conformer in comparison with the compound C1 significantly.

(48) It is to be understood that wherever values and ranges are provided herein, all values and ranges encompassed by these values and ranges, are meant to be encompassed within the scope of the present invention. Moreover, all values that fall within these ranges, as well as the upper or lower limits of a range of values, are also contemplated by the present application.