Organic electroluminescent device comprising a hole injection layer and electron injection layer with zero-valent metal
11011723 · 2021-05-18
Assignee
Inventors
Cpc classification
H10K71/00
ELECTRICITY
Y02P70/50
GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
International classification
Abstract
The present invention relates to an organic electroluminescent device comprising an hole injection layer and electron injection layer with zero-valent metal, and a method of manufacturing the same. In particular the present invention relates to an organic electroluminescent device comprising an anode layer, at least one electron transport layer, at least one electron injection layer, a cathode layer, and an emission layer, wherein the emission layer is arranged between the anode layer and the cathode layer, wherein the at least a first electron transport layer and the injection layer are arranged between the emission layer and the cathode layer, wherein the electron injection layer is arranged in direct contact to the first transport electron layer, wherein the first electron transport layer is arranged nearer to the anode layer and the electron injection layer is arranged nearer to the cathode layer, wherein at least the first electron transport layer comprises an organic phosphine matrix compound, and a first zero-valent alkali metal; and the electron injection layer comprises a second zero-valent metal of an alkaline earth metal and/or rare earth metal, and an alkali metal halide.
Claims
1. An organic electroluminescent device comprising an anode layer, at least one electron transport layer, an electron injection layer, an cathode layer, and an emission layer, wherein the emission layer is arranged between the anode layer and the cathode layer, wherein the at least a first electron transport layer and the electron injection layer are arranged between the emission layer and the cathode layer, wherein the electron injection layer is arranged in direct contact to the first transport electron layer, wherein the first electron transport layer is arranged nearer to the anode layer and the electron injection layer is arranged nearer to the cathode layer, characterized in that at least the first electron transport layer comprises: an organic phosphine matrix compound, and a first zero-valent aka metal; and the electron injection layer comprises: a second zero-valent metal of an alkaline earth metal and/or rare earth metal, and an alkali metal halide; and wherein the first zero-valent alkali metal of the electron transport layer and the alkali metal of the alkali metal halide of the electron injection layer are the same.
2. The organic electroluminescent device according to claim 1, wherein the first electron transport layer comprises a gradient distribution of the first zero-valent alkali metal.
3. The organic electroluminescent device according to claim 1, wherein the electron injection layer comprises a gradient distribution of the alkali metal halide.
4. The organic electroluminescent device according to claim 1, wherein the electron injection layer comprises a mixture of the second zero-valent metal, which is an alkaline earth metal and/or rare earth metal, and the alkali metal halide.
5. The organic electroluminescent device according to claim 1, wherein the first zero-valent alkali metal is selected from Li, Na, K, or Rb.
6. The organic electroluminescent device according to claim 1, wherein the second zero-valent metal, which is an alkaline earth metal and/or rare earth metal, are selected from Mg, Ca, Sr, Ba, Yb, Sm, Eu, Nd, Tb, Gd, Ce, or La.
7. The organic electroluminescent device according to claim 1, wherein the organic phosphine matrix compound comprises at least one P═X group, wherein X is O, S, or Se.
8. The organic electroluminescent device according to claim 1, wherein the organic phosphine matrix compound has a molecular weight of ≥400 and ≤1800 g/mol.
9. The organic electroluminescent device according to claim 1, wherein the organic phosphine matrix compound comprises at least one group selected from: triazine, pyrimidine, C.sub.10 to C.sub.40 aryl, wherein at least two rings are annelated, C.sub.3 to C.sub.40 heteroaryl, wherein at least two rings are annelated.
10. The organic electroluminescent device according to claim 1, wherein the organic phosphine matrix compound is a compound having the Formula I: ##STR00042## wherein: X is selected from O, S, or Se; R.sup.1 and R.sup.2 are independently selected from substituted or unsubstituted C.sub.1 to C.sub.12 alkyl, substituted or unsubstituted C.sub.6 to C.sub.20 aryl, or substituted or unsubstituted C.sub.3 to C.sub.20 heteroaryl; or R.sup.1 and R.sup.2 are bridged with an alkene-di-yl group forming with the P atom a substituted or unsubstituted five, six or seven membered ring; wherein the substituent on C.sub.1 to C.sub.12 alkyl is selected from C.sub.6 to C.sub.18 aryl, the substituent on C.sub.6 to C.sub.20 aryl and/or C.sub.3 to C.sub.20 heteroaryl is selected from C.sub.1 to C.sub.12 alkyl or C.sub.1 to C.sub.12 heteroalkyl; and A.sup.1 is substituted or unsubstituted C.sub.1 to C.sub.12 alkyl, substituted or unsubstituted C.sub.6 to C.sub.40 aryl, substituted or unsubstituted C.sub.3 to C.sub.40 heteroaryl, wherein the substituent on C.sub.1 to C.sub.12 alkyl is selected from C.sub.6 to C.sub.18 aryl, and the substituent on C.sub.6 to C.sub.40 aryl and/or C.sub.3 to C.sub.40 heteroaryl is selected from C.sub.1 to C.sub.12 alkyl or C.sub.1 to C.sub.12 heteroalkyl; or A.sup.1 is selected from Formula (II): ##STR00043## wherein R.sup.3 is selected from C.sub.1 to C.sub.8 alkane-di-yl, substituted or unsubstituted C.sub.6 to C.sub.20 arylene, or substituted or unsubstituted C.sub.3 to C.sub.20 heteroarylene, wherein the substituent on C.sub.6 to C.sub.20 arylene, and/or C.sub.3 to C.sub.20 heteroarylene is selected from C.sub.1 to C.sub.12 alkyl or C.sub.1 to C.sub.12 heteroalkyl; or A.sup.1 is selected from Formula (III) ##STR00044## wherein n is selected from 0 or 1; m is selected from 1 or 2; o is selected from 1 or 2; and wherein m is 1 if o is 2; Ar.sup.1 is selected from substituted or unsubstituted C.sub.6 to C.sub.20 arylene or substituted or unsubstituted C.sub.3 to C.sub.20 heteroarylene, wherein the substituent on C.sub.6 to C.sub.20 arylene or C.sub.3 to C.sub.20 heteroarylene is selected from C.sub.1 to C.sub.12 alkyl and/or C.sub.1 to C.sub.12 heteroalkyl; Ar.sup.2 is selected from substituted or unsubstituted C.sub.10 to C.sub.40 arylene or substituted or unsubstituted C.sub.3 to C.sub.40 heteroarylene, wherein the substituent on C.sub.10 to C.sub.40 arylene or C.sub.3 to C.sub.40 heteroarylene is selected from C.sub.1 to C.sub.12 alkyl, C.sub.1 to C.sub.12 heteroalkyl, OH, CN and/or halogen; R.sup.4 is selected from H, C.sub.1 to C.sub.12 alkyl, substituted or unsubstituted C.sub.6 to C.sub.20 aryl or substituted or unsubstituted C.sub.3 to C.sub.20 heteroaryl, wherein the substituent on C.sub.6 to C.sub.20 aryl or C.sub.3 to C.sub.20 heteroaryl is selected from C.sub.1 to C.sub.12 alkyl, C.sub.1 to C.sub.12 heteroalkyl, C.sub.6 to C.sub.20 aryl, C.sub.5 to C.sub.20 heteroaryl, OH, CN and/or halogen.
11. The organic electroluminescent device according to claim 10, wherein Ar.sup.1 is selected from substituted C.sub.6 to C.sub.20 arylene, and/or substituted C.sub.3 to C.sub.20 heteroarylene, wherein the C.sub.6 to C.sub.20 arylene, and/or C.sub.3 to C.sub.20 heteroarylene is substituted with at least one C.sub.1 to C.sub.12 alkyl and/or at least one C.sub.1 to C.sub.12 heteroalkyl group; or Ar.sup.2 is selected from substituted C.sub.10 to C.sub.40 arylene and/or substituted C.sub.3 to C.sub.40 heteroarylene, wherein the C.sub.18 to C.sub.40 arylene and/or C.sub.3 to C.sub.40 heteroarylene is substituted with at least one C.sub.1 to C.sub.12 alkyl and/or at least one C.sub.1 to C.sub.12 heteroalkyl group.
12. The organic electroluminescent device according to claim 10, wherein Ar.sup.1 is selected from substituted C.sub.6 to C.sub.20 arylene and/or substituted C.sub.3 to C.sub.20 heteroarylene, wherein the C.sub.6 to C.sub.20 arylene and/or C.sub.3 to C.sub.20 heteroarylene is substituted with at least one C.sub.1 to C.sub.6 alkyl and/or C.sub.1 to C.sub.6 heteroalkyl group; or Ar.sup.2 is selected from substituted C.sub.10 to C.sub.40 arylene and/or substituted C.sub.3 to C.sub.40 heteroarylene, wherein the C.sub.18 to C.sub.40 arylene and/or C.sub.3 to C.sub.40 heteroarylene is substituted with at least one C.sub.1 to C.sub.6 alkyl and/or C.sub.1 to C.sub.6 heteroalkyl group.
13. The organic electroluminescent device according to claim 10, wherein Ar.sup.1 is selected from substituted C.sub.6 to C.sub.20 arylene and/or substituted C.sub.3 to C.sub.20 heteroarylene, wherein the C.sub.6 to C.sub.20 arylene and/or C.sub.3 to C.sub.20 heteroarylene is substituted with at least one C.sub.1 to C.sub.4 alkyl and/or C.sub.1 to C.sub.4 heteroalkyl group; or Ar.sup.2 is selected from substituted C.sub.10 to C.sub.40 arylene and/or substituted C.sub.3 to C.sub.40 heteroarylene, wherein the C.sub.18 to C.sub.40 arylene and/or C.sub.3 to C.sub.40 heteroarylene is substituted with at least one C.sub.1 to C.sub.4 alkyl and/or C.sub.1 to C.sub.4 heteroalkyl group.
14. The organic electroluminescent device according to claim 10, wherein the compound of Formula (I) is selected from a compound according to: Formula Va to Vz: ##STR00045## ##STR00046## or Formula Vg to Vx: ##STR00047## ##STR00048## ##STR00049## ##STR00050## Formula Vy, Vy1, Vz: ##STR00051##
15. The organic electroluminescent device according to claim 1, wherein the electronic device is a display device, a light emitting device, a thin film transistor, a battery or a photovoltaic cell.
16. A method of manufacture of at least a first electron transport layer and an electron injection layer of an organic electroluminescent device according to claim 1, comprising the steps of: forming a first electron transport layer, comprising an organic phosphine matrix compound; and forming an electron injection layer, comprising an alkali metal halide and a second zero-valent metal, which is a rare earth metal and/or alkaline earth metal, directly onto the first electron transport layer; wherein the second zero-valent metal, which is a rare earth metal and/or alkaline earth metal reduces the alkali halide to a first zero-valent alkali metal and the obtained first zero-valent alkali metal diffuses into the organic phosphine matrix compound of the first electron transport layer.
Description
DESCRIPTION OF THE DRAWINGS
(1) These and/or other aspects and advantages will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings, of which:
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(9) Reference will now be made in detail to the exemplary aspects, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The exemplary embodiments are described below, in order to explain the aspects, by referring to the figures.
(10) Herein, when a first element is referred to as being formed or disposed “on” 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” a second element, no other elements are disposed there between.
(11) The term “contacting sandwiched” refers to an arrangement of three layers whereby the layer in the middle is in direct contact with the two adjacent layers.
(12) The organic light emitting diodes according to an embodiment may include an anode layer, at least one first electron transport layer, an electron injection layer, a cathode layer, and an emission layer.
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(20) A substrate may be further disposed under the anode 120 or on the cathode 190. The substrate may be a substrate that is used in a general organic light emitting diode and may be a glass substrate or a transparent plastic substrate with strong mechanical strength, thermal stability, transparency, surface smoothness, ease of handling, and water resistance.
(21) The hole injection layer 130 may improve interface properties between ITO as an anode and an organic material used for the hole transport layer 140, and may be applied on a non-planarized ITO and thus may planarize the surface of the ITO. For example, the hole injection layer 130 may include a material having particularly desirable conductivity between a work function of ITO and HOMO of the hole transport layer 140, which are a second zero-valent metal of an alkaline earth metal and/or rare earth metal, and an alkali metal halide, in order to adjust a difference in work function of ITO as an anode and HOMO of the hole transport layer 140.
(22) When the hole transport region comprises a hole injection layer 130, the hole injection layer may be formed on the anode 120 by any of a variety of methods, for example, vacuum deposition, spin coating, casting, Langmuir-Blodgett (LB) method, or the like.
(23) 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.−8 torr to about 10.sup.−3 torr, and a deposition rate of about 0.01 to about 100 Å/sec, but the deposition conditions are not limited thereto.
(24) 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.
(25) 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.
(26) A thickness of the hole transport region may be from about 100 Å to about 10000 Å, for example, about 100 Å to about 1000 Å. When the hole transport region comprises the hole injection layer and the hole transport layer, a thickness of the hole injection layer may be from about 100 Å to about 10,000 Å, for example about 100 Å to about 1000 Å and a thickness of the hole transport layer may be from about 50 Å to about 2,000 Å, for example about 100 Å to about 1500 Å. When the thicknesses of the hole transport region, the HIL, and the HTL are within these ranges, satisfactory hole transport characteristics may be obtained without a substantial increase in operating voltage.
(27) A thickness of the emission layer may be about 100 Å to about 1000 Å, for example about 200 Å to about 600 Å. When the thickness of the emission layer is within these ranges, the emission layer may have improved emission characteristics without a substantial increase in an operating voltage.
(28) Next, an electron transport region is disposed on the emission layer.
(29) The electron transport region may include at least one of a second electron transport layer, a first electron transport layer, and an electron injection layer.
(30) The thickness of the electron transport layer may be from about 20 Å to about 1000 Å, for example about 30 Å to about 300 Å. When the thickness of the electron transport layer is within these ranges, the electron transport layer may have improved electron transport auxiliary ability without a substantial increase in operating voltage.
(31) A thickness of the electron transport layer may be about 100 Å to about 1000 Å, for example about 150 Å to about 500 Å. 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 operating voltage.
(32) In addition, the electron transport region may include an electron injection layer (EIL) that may facilitate injection of electrons from the anode.
(33) A thickness of the EIL may be from about 1 Å to about 100 Å, or about 3 Å to about 90 Å. 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 operating voltage.
(34) The anode can be disposed on the organic layer. A material for the anode 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 anode 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, the anode 150 may be formed as a light-transmissive electrode from, for example, indium tin oxide ITO) or indium zinc oxide IZO).
(35) According to another aspect of the invention, a method of manufacturing an organic electroluminescent device is provided, wherein on an anode electrode (120) the other layers of hole injection layer (130), hole transport layer (140), optional an electron blocking layer, an emission layer (150), optional second electron transport layer (162), first electron transport layer (161), electron injection layer (180), and a cathode (190), are deposited in that order; or the layers are deposited the other way around, starting with the cathode (190).
(36) According to another aspect of the invention, a method of manufacturing an organic electroluminescent device is provided, wherein on an anode electrode (120) the other layers of hole injection layer (130), hole transport layer (140), optional an electron blocking layer, an emission layer (150), optional second electron transport layer (162), first electron transport layer (161), a second electron injection layer (182), a first electron injection layer (185), and a cathode (190), are deposited in that order; or the layers are deposited the other way around, starting with the cathode (190).
(37) Hereinafter, the embodiments are illustrated in more detail with reference to examples. However, the present disclosure is not limited to the following examples.
(38) General Procedure for Fabrication of Organic Electroluminescent Devices
(39) OLEDs were prepared to demonstrate the technical benefit utilizing the organic phosphine compounds, preferably compounds of formula I, in an electron transport layer of an organic electroluminescent device.
(40) The organic phosphine compounds may be synthesized as described in WO2013079217A1, WO2015052284A1, WO2016162440A1, EP15195877.4 and EP16164871.2.
(41) Top Emission Devices
(42) For top emission devices—Examples 1 to 18 and comparative examples 1 to 3, glass was cut to a size of 50 mm×50 mm×0.7 mm, ultrasonically cleaned with isopropyl alcohol for 5 minutes and then with pure water for 5 minutes, and cleaned again with UV ozone for 30 minutes. The anode electrode is formed on the glass by depositing 100 nm silver in ultra-high vacuum of 10.sup.−7 mbar at a rate of 0.01 to 1 Å/s.
(43) Then, 92 vol.-% of biphenyl-4-yl(9,9-diphenyl-9H-fluoren-2-yl)-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-amine (CAS 1242056-42-3) and 8 vol.-% of 2,2′,2″-(cyclopropane-1,2,3-triylidene)tris(2-(p-cyanotetrafluorophenyl)acetonitrile) is vacuum deposited on the anode, to form a HIL having a thickness of 10 nm. Then biphenyl-4-yl(9,9-diphenyl-9H-fluoren-2-yl)-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-amine is vacuum deposited on the HIL, to form a HTL having a thickness of 121 nm. Then N,N-bis(4-(dibenzo[b,d]furan-4-yl)phenyl)-[1,1′:4′,1″-terphenyl]-4-amine is deposed directly on top of the HTL to form an EBL with a thickness of 5 nm.
(44) 97 vol.-% of 2-(10-phenyl-9-anthracenyl)-benzo[b]naphtho[2,3-d]furan as a host and 3 vol.-% of blue emitter dopant described in WO2015-174682 are deposited on the EBL, to form a blue-emitting EML with a thickness of 20 nm.
(45) Then, a hole blocking layer is formed by deposing 6 nm 2,4-diphenyl-6-(4′,5′,6′-triphenyl-[1,1′:2′,1″:3″,1′″:3″″,1″″-quinquephenyl]-3″″-yl)-1,3,5-triazine (CAS 2032364-64-8, WO 2016171358) directly onto the emission layer.
(46) Then, the first electron transport layer is formed by deposing the first electron transport matrix compound according to examples 1 to 11 and comparative examples 1 to 2 directly onto the hole blocking layer.
(47) The first electron transport layer may further comprise an alkali organic complex, see examples 12 to 18. In this case, the first matrix compound is deposed from a first deposition source and the alkali organic complex from a second deposition source directly on the hole blocking layer. The composition and thickness of the first electron transport layer can be taken from Table 1 to 3.
(48) Then, the electron injection layer is deposed on the first electron transport layer by deposing the halide of the first metal from a first deposition source and the second metal from a second deposition source directly on the first electron transport layer. The composition and thickness can be taken from Tables 1 to 3.
(49) Then, the cathode layer is evaporated at ultra-high vacuum of 10.sup.−7 mbar. Therefore, a thermal single co-evaporation of one or several metals is performed with a rate of 0, 1 to 10 nm/s (0.01 to 1 Å/s) in order to generate a homogeneous cathode electrode with a thickness of 5 to 1000 nm. The cathode layer is formed by deposing 12 nm Mg:Ag (15:85 vol.-%) directly onto the electron injection layer.
(50) Then 60 nm biphenyl-4-yl(9,9-diphenyl-9H-fluoren-2-yl)-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-amine is deposed directly onto the cathode layer.
(51) 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.
(52) To assess the performance of the inventive examples compared to the prior art, the current efficiency is measured under ambient conditions (20° C.). Current voltage measurements are performed using a Keithley 2400 sourcemeter, and recorded in V. At 10 mA/cm.sup.2 for bottom emission and 10 mA/cm.sup.2 for top emission devices, a calibrated spectrometer CAS140 from Instrument Systems is used for measurement of CIE coordinates and brightness in Candela. Lifetime LT of bottom emission device is measured at ambient conditions (20° C.) and 10 mA/cm.sup.2, using a Keithley 2400 sourcemeter, and recorded in hours. In bottom emission devices, the emission is predominately Lambertian and quantified in percent external quantum efficiency (EQE). To determine the efficiency EQE in % the light output of the device is measured using a calibrated photodiode at 10 mA/cm2.
(53) In top emission devices, the emission is forward directed, non-Lambertian and also highly dependent on the micro-cavity. Therefore, the efficiency EQE will be higher compared to bottom emission devices. To determine the efficiency EQE in % the light output of the device is measured using a calibrated photodiode at 10 mA/cm2.
Technical Effect of the Invention
(54) In Table 1 are shown results for top emission OLEDs wherein the electron injection layer has different compositions. The first electron transport layer is formed from 31 nm organic phosphine compound Vu.
(55) In comparative example 1, the electron injection layer comprises 1.3 nm KI. The operating voltage is 6 V and the cd/A efficiency is 5 cd/A and the EQE efficiency is 8.8%.
(56) In comparative example 2, the electron injection layer comprises 1.3 nm Yb. The operating voltage is very high at ≥5 V, therefore the efficiency has not been measured.
(57) In example 1, the electron injection layer comprises a physical mixture of Yb and KI with a thickness of 2 nm. The operating voltage is reduced significantly to 3.8 V. The cd/A efficiency is 4.7 cd/A and the EQE efficiency is improved to 9.2%.
(58) In example 2, the electron injection layer comprises Yb and RbI with a thickness of 2 nm. The operating voltage is low at 3.7 V and the efficiency is improved further to 6.4 cd/A and 12.6% EQE.
(59) In example 3, the electron injection layer comprises Eu and KI with a thickness of 2 nm. The operating voltage is low at 4.3 V and the efficiency is 4.7 cd/A and 9.2% EQE.
(60) In example 4, the electron injection layer comprises Ba and KI with a thickness of 2 nm. The operating voltage is low at 4.5 V and the efficiency is 4.5 cd/A and 8.8% EQE.
(61) In Table 2 results are shown for various matrix compounds in the first electron transport layer.
(62) In comparative example 3, the first electron transport layer comprises Alq3. The operating voltage is 7.3 V and the efficiency is 3.7 cd/A and 6.1% EQE.
(63) In Example 5, an organic phosphine compound Vy is used. The operating voltage is reduced significantly to 4.1 V and the efficiency is significantly improved to 5.9 cd/A and 11.6% EQE.
(64) In examples 6 and 8, two more organic phosphine compounds are used, and the operating voltage is reduced even further to 3.6 and 3.35 V, resp. The efficiency is improved even further to 6.3 cd/A and 12.9% EQE for organic phosphine compound Vu and to 7.3 cd/A and 14.7% EQE for organic phosphine compound Vv.
(65) In example 7 and 10, the electron injection layer comprises a first electron injection layer, formed from KI, in direct contact with the first electron transport layer and a second electron injection layer, formed from Yb, is in direct contact with the first electron injection layer. The operating voltage is very low and the efficiency is high.
(66) In Example 9, this thickness of the first electron transport layer is increased from 1.8 to 3 nm. The operating voltage is still low at 3.4 V and the efficiency remains high at 6.5 cd/A and 13.3% EQE.
(67) In example 11, the electron injection layer comprises a first electron injection layer, formed from Yb, in direct contact with the first electron transport layer; and a second electron injection layer, formed from KI, in direct contact with the first electron injection layer. The operating voltage is low and the efficiency is high.
(68) In summary, low operating voltage and high efficiency can be achieved independent of the composition of the electron injection layer in direct contact with the first electron transport layer, as long as one electron injection layer comprises a second zero-valent metal of an alkaline earth metal and/or rare earth metal and the other electron injection layer comprises of alkali metal halide.
(69) In Table 3 results are shown for a first electron transport layer further comprising an alkali organic complex.
(70) In example 12, the triazine compound is replaced by organic phosphine compound Vv. The operating voltage is improved substantially to 3.5 V. The efficiency is improved further at 7.9 cd/A and 16.3% EQE.
(71) In example 13, organic phosphine compound Vu is used. The operating voltage is 3.5V and the efficiency is 7.8 cd/A and 16.8% EQE.
(72) In example 14, alkali organic complex Li-1 (lithium tetra(1H-pyrazol-1-yl)borate) is used instead of LiQ. The operating voltage is reduced further to 3.2 V and the efficiency stays high at 7.5 cd/A and 16.2% EQE.
(73) In example 15, KI is replaced by RbI. The operating voltage is still low at 3.5 V and the efficiency is high at 6.3 cd/A and 13.2% EQE.
(74) In example 16, 17 and 18 the effect of the electron injection layer on the operating voltage and efficiency is tested. The composition of the first electron transport layer remains the same.
(75) In example 16, the electron injection layer comprises a physical mixture of Yb and KI. The operating voltage is 3.15 V and the efficiency is 8.8 cd/A and 16.1% EQE.
(76) In example 17, the first electron injection layer comprises KI and the second electron injection layer comprises Yb. The first electron injection layer is in direct contact with the first electron transport layer. The second electron injection layer is in direct contact with the first electron injection layer. The operating voltage is 3.2 V and efficiency high at 8.6 cd/A and 15.6% EQE.
(77) In example 18, the first electron injection layer comprises Yb and the second electron injection layer comprises KI. The layers are arranged as described for example 10. The operating voltage is 3.2 V and the efficiency is 8.8 cd/A and 15.8% EQE.
(78) In summary, the benefit of low operating voltage and high efficiency is observed even when the first electron transport layer comprises an alkali organic complex.
(79) TABLE-US-00001 TABLE 1 Electron injection layer comprising various alkali metal halides and zero-valent alkaline earth and rare earth metals Composition Thickness First Composition of electron electron Operating cd/A EQE electron of electron injection injection voltage at efficiency at efficiency at matrix Thickness injection layer layer 10 mA/cm.sup.2 10 mA/cm.sup.2 10 mA/cm.sup.2 compound ETL1/nm layer (vol.-%) (nm) (V) (cd/A) (%) Comparative Vu 31 KI 100 1.3 6 5 8.8 example 1 Comperative Vu 31 Yb 100 1.3 >5 — — example 2 Example 1 Vu 31 Yb:KI 51.5:48.5 2.0 3.8 4.7 9.2 Example 2 Vu 31 Yb:RbI 51.5:48.5 2.0 3.7 6.4 12.6 Example 3 Vu 31 Eu:KI 50:49 2.0 4.3 4.7 9.2 Example 4 Vu 31 Ba:KI 50:50 2.0 4.3 4.5 8.8
(80) TABLE-US-00002 TABLE 2 Electron injection layer comprising a first and second electron injection layer Composition Composition of first of second Operating cd/A EQE First electron Thick- electron Thick- voltage efficiency efficiency electron injection Composition ness injection Composition ness at 10 at 10 at 10 matrix Thickness layer of EIL1 EIL1 layer of EIL2 EIL2 mA/cm.sup.2 mA/cm.sup.2 mA/cm.sup.2 compound ETL1/nm (EIL1) (vol.-%) (nm) (EIL2) (vol.-%) (nm) (V) (cd/A) (%) Comparative Alq3 31 Yb:KI 51:49 2 — — — 7.3 3.7 6.1 example 3 Example 5 Vy 31 Yb:KI 57:43 1.8 — — — 4.1 5.9 11.6 Example 6 Vu 31 Yb:KI 56:44 1.8 — — — 3.6 6.3 12.9 Example 7 Vu 31 KI 100 2 Yb 100 2 3.7 6.3 12 Example 8 Vv 31 Yb:KI 57:43 1.8 — — — 3.35 7.3 14.7 Example 9 Vw 31 Yb:KI 50:50 3.0 — — — 3.4 6.5 13.3 Example 10 Vw 31 KI 100 2 Yb 100 2 3.3 7.5 14.3 Example 11 Vw 31 Yb 100 2 KI 100 1.5 4 6.9 12.7
(81) TABLE-US-00003 TABLE 3 First electron transport layer doped with alkali organic complex vol.-% First first Alka- vol.-% First Second Operating cd/A EQE electron electron li or- alkali Thick- electron Thick- electron Thick- voltage efficien- efficien- matrix matrix ganic organic ness injection ness injection ness at 10 cy at 10 cy at 10 com- com- com- com- ETL/ layer EIL1/ layer EIL2/ mA/cm.sup.2 mA/cm.sup.2 mA/cm.sup.2 pound pound plex plex nm (EIL1) vol.-% nm (EIL2) vol.-% nm (V) (cd/A) (%) Example Vv 50 LiQ 50 31 Yb:KI 91:9 1.4 — — — 3.5 7.9 16.3 12 Example Vu 50 LiQ 50 31 Yb:KI 92:9 1.3 — — — 3.5 7.8 16.8 13 Example Vu 75 Li-1 25 31 Yb:KI 91:9 1.3 — — — 3.2 7.5 16.2 14 Example Vu 75 Li-1 25 31 Yb:RbI 50:50 1.6 — — — 3.5 6.3 13.2 15 Example Vx 74 Li-1 26 31 Yb:KI 52:48 1.5 — — — 3.15 8.8 16.1 16 Example Vx 75 Li-1 25 32 KI 100 1.5 Yb 100 2 3.2 8.6 15.6 17 Example Vx 74 Li-1 26 32 Yb 100 1.5 KI 100 2 3.2 8.8 15.8 18
(82) 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 claim. Therefore, the aforementioned embodiments should be understood to be exemplary but not limiting the present invention in any way.