Compound and organic semiconducting layer, organic electronic device, display device and lighting device comprising the same

Abstract

The present invention relates to a compound of the Formula (I) ##STR00001##
wherein at least one of R.sup.1 to R.sup.10 and/or Ar.sup.4 is a group having the Formula (II) ##STR00002##
wherein the asterisk symbol “*” in Formula (II) represents the position of binding of the group having the Formula (II); L is selected from substituted or unsubstituted C.sub.6 to C.sub.18 arylene; Ar.sup.1 is selected from substituted or unsubstituted C.sub.3 to C.sub.24 heteroaryl, wherein the heteroaryl comprises at least two N-atoms; Ar.sup.2 and Ar.sup.3 are independently selected from substituted or unsubstituted C.sub.6 to C.sub.24 aryl and/or substituted or unsubstituted C.sub.4 to C.sub.24 heteroaryl, wherein Ar.sup.2 and Ar.sup.3 are selected differently from each other; Ar.sup.4 is selected from the group consisting of substituted or unsubstituted C.sub.1 to C.sub.16 alkyl, substituted or unsubstituted C.sub.6 to C.sub.24 aryl, substituted or unsubstituted C.sub.2 to C.sub.24 heteroaryl and a group having the general Formula (II); R.sup.1 to R.sup.10 are independently selected from the group consisting of H, D, F, C.sub.1 to C.sub.20 alkyl, C.sub.6 to C.sub.20 aryl, C.sub.2 to C.sub.20 heteroaryl and a group having the Formula (II); and R.sup.1 and R.sup.2; or R.sup.2 and R.sup.3 or R.sup.3; and R.sup.4; or R.sup.5 and R.sup.6 may independently from each other form a fused ring or system of fused rings; a semiconducting layer comprising the same, an organic electronic device comprising the same as well as a display or a lighting device comprising the organic electronic device.

Claims

1. Compound of the Formula (I) ##STR00038## wherein at least one of R.sup.1 to R.sup.10 and/or Ar.sup.4 is a group having the Formula (II) ##STR00039## wherein the asterisk symbol “*” in Formula (II) represents the position of binding of the group having the Formula (II); L is selected from substituted or unsubstituted C.sub.6 to C.sub.18 arylene; Ar.sup.1 is selected from substituted or unsubstituted C.sub.3 to C.sub.24 heteroaryl, wherein the heteroaryl comprises at least two N-atoms; Ar.sup.2 and Ar.sup.3 are independently selected from substituted or unsubstituted C.sub.6 to C.sub.24 aryl and/or substituted or unsubstituted C.sub.4 to C.sub.24 heteroaryl, wherein Ar.sup.2 and Ar.sup.3 are selected differently from each other; Ar.sup.4 is selected from the group consisting of substituted or unsubstituted C.sub.1 to C.sub.16 alkyl, substituted or unsubstituted C.sub.6 to C.sub.24 aryl, substituted or unsubstituted C.sub.2 to C.sub.24 heteroaryl and a group having the general Formula (II); R.sup.1 to R.sup.10 are independently selected from the group consisting of H, D, F, C.sub.1 to C.sub.20 alkyl, C.sub.6 to C.sub.20 aryl, C.sub.2 to C.sub.20 heteroaryl and a group having the Formula (II); and R.sup.1 and R.sup.2; or R.sup.2 and R.sup.3; or R.sup.3 and R.sup.4; or R.sup.5 and R.sup.6 may independently from each other form a fused ring or a system of fused rings; wherein, in the respective substituted groups, the substituents each are independently selected from the group consisting of D, F, C.sub.1 to C.sub.20 linear alkyl, C.sub.3 to C.sub.20 branched alkyl, C.sub.3 to C.sub.20 cyclic alkyl, C.sub.1 to C.sub.20 linear alkoxy, C.sub.3 to C.sub.20 branched alkoxy, C.sub.1 to C.sub.12 linear fluorinated alkyl, C.sub.1 to C.sub.12 linear fluorinated alkoxy, C.sub.3 to C.sub.12 branched fluorinated cyclic alkyl, C.sub.3 to C.sub.20 fluorinated cyclic alkyl, C.sub.3 to C.sub.12 fluorinated cyclic alkoxy, CN, RCN, C.sub.6 to C.sub.20 aryl, C.sub.2 to C.sub.20 heteroaryl, OR, SR, (C═O)R, (C═O)NR.sub.2, SiR.sub.3, (S═O)R, (S═O).sub.2R, (P═O)R.sub.2; wherein each R is independently selected from the group consisting of C.sub.1 to C.sub.20 linear alkyl, C.sub.1 to C.sub.20 alkoxy, C.sub.1 to C.sub.20 thioalkyl, C.sub.3 to C.sub.20 branched alkyl, C.sub.3 to C.sub.20 cyclic alkyl, C.sub.3 to C.sub.20 branched alkoxy, C.sub.3 to C.sub.20 cyclic alkoxy, C.sub.3 to C.sub.20 branched thioalkyl, C.sub.3 to C.sub.20 cyclic thioalkyl, C.sub.6 to C.sub.20 aryl and C.sub.2 to C.sub.20 heteroaryl.

2. Compound according to claim 1, wherein L is selected from the group consisting of phenylene, biphenylene, terphenylene, phenanthrylene, triphenylylene, and naphthylene.

3. Compound according to claim 1, wherein Ar.sup.1 is triazine or pyrimidine.

4. Compound according to claim 1, wherein Ar.sup.3 is biphenyl, naphthyl, dibenzofuranyl, or dibenzothiophenyl.

5. Compound according to claim 1, wherein Ar.sup.2 is phenyl.

6. Compound according to claim 1, wherein Ar.sup.4 is selected from the group consisting of phenyl, biphenyl, terphenyl, naphthyl, and a group having the Formula (II).

7. Compound according to claim 1, wherein R.sup.1 and R.sup.2 form together a fused ring.

8. Compound according to claim 1, wherein the compound of Formula (I) has one of the following Formulas (Ia), (Ib), (Ic) and (Id): ##STR00040##

9. Compound according to claim 1, wherein the compound has one of the following structures A-1 to A-15: ##STR00041## ##STR00042## ##STR00043## ##STR00044## ##STR00045##

10. Organic semiconducting layer comprising a compound of Formula (I) according to claim 1.

11. Organic semiconducting layer according to claim 10, wherein the organic semiconducting layer further comprises a metal, a metal salt, or an alkali or alkaline earth metal complex.

12. Organic semiconducting layer according to claim 11, wherein the alkali or alkaline earth metal complex is an organic alkali or alkaline earth metal complex.

13. Organic semiconducting layer according to claim 10, wherein the organic semiconducting layer further comprises 8-hydroxyquinolinolato lithium or alkali borate.

14. Organic electronic device comprising an organic semiconducting layer according to claim 10.

15. Organic electronic device according to claim 14 further comprising an anode, an emission layer, and a cathode, wherein the organic semiconducting layer is arranged between the emission layer and the cathode.

16. Display device comprising the organic electronic device according to claim 14.

17. Lighting device comprising the organic electronic device according to claim 14.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

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

(3) FIG. 2 is a schematic sectional view of an OLED, according to an exemplary embodiment of the present invention.

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

DETAILED DESCRIPTION

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

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

(7) FIG. 1 is a schematic sectional view of an organic light-emitting diode (OLED) 100, according to an exemplary embodiment of the present invention. The OLED 100 includes a substrate 110, an anode 120, a hole injection layer (HIL) 130, a hole transport layer (HTL) 140, an emission layer (EML) 150, an electron transport layer (ETL) 160. The electron transport layer (ETL) 160 is formed on the EML 150. Onto the electron transport layer (ETL) 160, an electron injection layer (EIL) 180 is disposed. The cathode 190 is disposed directly onto the electron injection layer (EIL) 180.

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

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

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

(11) Preferably, the organic semiconducting layer comprising a compound of Formula (I) may be an ETL.

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

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

(14) Preferably, the organic semiconducting layer comprising a compound of Formula (I) may be the first ETL, n-type CGL and/or second ETL.

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

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

(17) Experimental Data

(18) Preparation of Compounds of Formula (I)

(19) Compounds of formula (I) may be prepared as described below.

(20) Potassium carbonate (20 mmol, 2 eq.) is dissolved in ˜10 ml of deionized water, the solution is degassed with N.sub.2 for 30 min. Dioxane (40 ml) is degassed in a 100 mL 3-necked round bottom flask with N.sub.2 for 30 min. The flask is then charged with corresponding aryl boronic ester (10 mmol, 1 eq.), chlorotriazine (22 mmol, 1.1 eq.) and tetrakis(triphenylphosphin)palladium(0) (0.2 mmol, 0.02 eq.) under a positive nitrogen pressure. The degassed potassium carbonate solution is added using a syringe, nitrogen purged reflux condenser is attached to the flask and a reaction mixture heated to 90° C. with stirring for 12 h. The mixture is allowed to cool down to the room temperature, a precipitate is collected by filtration, washed with water, methanol, dried in vacuum at 40° C. to give a crude product, which could be further purified by re-crystallization or trituration with appropriate solvents. Final purification is achieved by sublimation in a high vacuum.

(21) TABLE-US-00001 Starting materials and products Yield and Aryl boronic ester and chlorotriazine Product MS data 0 52% 663 [M + H].sup.+ 89% 663 [M + H].sup.+ 78% 663 [M + H].sup.+ 69% 663 [M + H].sup.+ 66% 613 [M + H].sup.+ 0 38% 611 [M + H].sup.+

(22) Melting Point

(23) The melting point (mp) is determined as peak temperatures from the DSC curves of the above TGA-DSC measurement or from separate DSC measurements (Mettler Toledo DSC822e, heating of samples from room temperature to completeness of melting with heating rate 10 K/min under a stream of pure nitrogen. Sample amounts of 4 to 6 mg are placed in a 40 μL Mettler Toledo aluminum pan with lid, a <1 mm hole is pierced into the lid).

(24) The melting point of a compound of Formula (I) may be selected in the range of about 260 to about 350° C., preferably about 270 to about 330° C., also preferred about 280 to about 320° C.

(25) Glass Transition Temperature

(26) The glass transition temperature (Tg) is measured under nitrogen and using a heating rate of 10 K per min in a Mettler Toledo DSC 822e differential scanning calorimeter as described in DIN EN ISO 11357, published in March 2010.

(27) The glass transition temperature of a compound of Formula (I) may be selected in the range of about 115 to about 200° C., preferably about 120 to about 190° C., also preferred about 125 to about 180° C.

(28) Reduction Potential

(29) The reduction potential is determined by cyclic voltammetry with potenioststic device Metrohm PGSTAT30 and software Metrohm Autolab GPES at room temperature. The redox potentials given at particular compounds were measured in an argon de-aerated, dry 0.1M THF 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 (Metrohm Silver rod electrode), consisting of a silver wire covered by silver chloride and immersed directly in the measured solution, with the scan rate 100 mV/s. The first run was done in the broadest range of the potential set on the working electrodes, and the range was then adjusted within subsequent runs appropriately. The final three runs were done with the addition of ferrocene (in 0.1M concentration) as the standard. The average of potentials corresponding to cathodic and anodic peak of the studied compound, after subtraction of the average of cathodic and anodic potentials observed for the standard Fc+/Fc redox couple, afforded finally the values reported above. All studied compounds as well as the reported comparative compounds showed well-defined reversible electrochemical behaviour.

(30) Rate Onset Temperature

(31) The rate onset temperature (T.sub.RO) is determined by loading 100 mg compound into a VTE source. As VTE source a point source for organic materials is used as supplied by Kurt J. Lesker Company (www.lesker.com) or CreaPhys GmbH (http://www.creaphys.com). The VTE source is heated at a constant rate of 15 K/min at a pressure of less than 10.sup.−5 mbar and the temperature inside the source measured with a thermocouple. Evaporation of the compound is detected with a QCM detector which detects deposition of the compound on the quartz crystal of the detector. The deposition rate on the quartz crystal is measured in Ångstrom per second. To determine the rate onset temperature, the deposition rate is plotted against the VTE source temperature. The rate onset is the temperature at which noticeable deposition on the QCM detector occurs. For accurate results, the VTE source is heated and cooled three time and only results from the second and third run are used to determine the rate onset temperature.

(32) To achieve good control over the evaporation rate of an organic compound, the rate onset temperature may be in the range of 200 to 255° C. If the rate onset temperature is below 200° C. the evaporation may be too rapid and therefore difficult to control. If the rate onset temperature is above 255° C. the evaporation rate may be too low which may result in low tact time and decomposition of the organic compound in VTE source may occur due to prolonged exposure to elevated temperatures.

(33) The rate onset temperature is an indirect measure of the volatility of a compound. The higher the rate onset temperature the lower is the volatility of a compound.

(34) The rate onset temperature of a compound of Formula (I) may be selected in the range of about 230 to about 300° C., preferably about 240 to about 290° C.

(35) Dipole Moment

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

(37) $\stackrel{.fwdarw.}{\mu }=\underset{i}{\overset{N}{.Math.}}{q}_i\stackrel{.fwdarw.}{r_1}$$.Math.\stackrel{.fwdarw.}{\mu }.Math.=\sqrt{{\mu }_x^2+{\mu }_y^2+{\mu }_z^2}$

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

(39) The dipole moment is determined by a semi-empirical molecular orbital method.

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

(41) The dipole moment of a compound of Formula (I) may be selected in the range of about 3 to about 6 Debye, preferably about 3.2 to about 6 Debye, also preferred about 3.4 to about 6 Debye.

(42) HOMO and LUMO

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

(44) The HOMO of a compound of Formula (I) may be selected in the range of about −5.4 to about −5.9 eV, preferably about −5.5 to about −5.8 eV, also preferred about −5.6 to about −5.7 eV.

(45) The LUMO of a compound of Formula (I) may be selected in the range of about −1.8 to about −2.1 eV, preferably about −1.85 to about −2.08 eV, also preferred about −1.9 to about −2.05 eV.

(46) General Procedure for Fabrication of OLEDs

(47) For top emission OLED devices, examples 1 to 5 and comparative example 1, a glass substrate 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, to prepare the substrate. 100 nm Ag were deposited on the substrate at a pressure of 10.sup.−5 to 10.sup.−7 mbar to form an anode.

(48) Then, 92 vol.-% Biphenyl-4-yl(9,9-diphenyl-9H-fluoren-2-yl)-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-amine (CAS 1242056-42-3) with 8 vol.-% 2,2′,2″-(cyclopropane-1,2,3-triylidene)tris(2-(p-cyanotetrafluorophenyl)acetonitrile) was vacuum deposited on the anode, to form a hole injection layer (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 was vacuum deposited on the HIL, to form a hole transport layer (HTL) having a thickness of 118 nm.

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

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

(51) Then, 2,4-diphenyl-6-(4′,5′,6′-triphenyl-[1,1′:2′,1″:3″,1″′:3″′, 1″″-quinquephenyl]-3″″-yl)-1,3,5-triazine was deposited on the EML, to form a hole blocking layer (HBL) with a thickness of 5 nm.

(52) Then, the electron transport layer (ETL) is formed on the hole blocking layer with a thickness of 31 nm by co-deposition of a matrix compound and an alkali organic complex. The composition of the ETL is shown in Table 2.

(53) Then, the electron injection layer (EIL) is formed on the electron transporting layer by deposing Yb with a thickness of 2 nm.

(54) Ag is evaporated at a rate of 0.01 to 1 Å/s at 10.sup.−7 mbar to form a cathode with a thickness of 11 nm.

(55) A cap layer of Biphenyl-4-yl(9,9-diphenyl-9H-fluoren-2-yl)-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-amine is formed on the cathode with a thickness of 75 nm.

(56) 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.

(57) To assess the performance of the inventive examples compared to the prior art, the current efficiency is measured at 20° C. The current-voltage characteristics are determined using a Keithley 2635 source measure unit by sourcing a voltage in V and measuring the current in mA flowing through the device under test. The voltage applied to the device is varied in steps of 0.1V in the range between 0V and 10V. Likewise, the luminance-voltage characteristics and CIE coordinates are determined by measuring the luminance in cd/m.sup.2 using an Instrument Systems CAS-140CT array spectrometer, which has been calibrated by Deutsche Akkreditierungsstelle (DAkkS) for each of the voltage values. The cd/A efficiency at 10 mA/cm.sup.2 is determined by interpolating the luminance-voltage and current-voltage characteristics, respectively.

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

(59) 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.

(60) Technical Effect of the Invention

(61) Properties of Compounds of Formula (I)

(62) In Table 1 are shown mp, T.sub.g, T.sub.RO, HOMO and LUMO energy levels and the dipole moments of comparative compound 1 and compounds of the Formula (I). Surprisingly, compounds of Formula (I) have lower melting points compared to comparative compound 1. Additionally, compounds of Formula (I) have glass transition temperatures in a range suitable for applications in organic electronics. The glass transition temperature should not be too low, as this may affect stability of the organic electronic device, in particular at elevated temperatures, for example for applications in the automobile sector. Additionally, the rate onset temperature of compounds of Formula (I) is in a range suitable for mass production.

(63) Surprisingly, the LUMO of compounds of formula (I) is less negative than the LUMO of comparative compounds 1. Thereby, fine-tuning of charge balance in an organic electronic device may be achieved.

(64) In Table 2 are shown the composition of the organic semiconducting layer, operating voltage, cd/A efficiency and lifetime of comparative example 1 and Examples 1 to 5.

(65) In comparative example 1, the organic semiconducting layer comprises a compound known in the art as matrix compound and LiQ as dopant.

(66) In Examples 1 to 5, the organic semiconducting layer comprises a compound of formula (I) as matrix compound and LiQ as dopant.

(67) As can be seen in Table 2, the operating voltage in Examples 1 to 5 is lower compared to comparative example 1. The cd/A efficiency is improved over comparative example 1. Lower operating voltage and higher cd/A efficiency may result in reduced power consumption. In mobile displays the battery life may be improved. Additionally, the lifetime is improved for Example 1 and 2 compared to comparative example 1. Improved lifetime is important for the long-term stability of a device.

(68) In summary, compounds of Formula (I) and organic electronic devices comprising an organic semiconducting layer comprising of compound of Formula (I) show superior performance over the state of the art.

(69) TABLE-US-00002 TABLE 1 Properties of comparative compound 1 and compounds of Formula (I) Dipole mp Tg T.sub.RO HOMO LUMO moment Referred to as: Structure (° C.) (° C.) (° C.) (eV) (eV) (Debye) Comparative compound 1 374 n.d. 268 −5.66 −2.02 1.89 A-1 333 162 305 −5.66 −2.00 2.19 A-2 317 148 286 −5.66 −2.00 1.77 A-3 290 135 256 −5.65 −1.95 2.10 A-12 284 133 246 −5.65 −1.86 1.61 A-14 206 116 232 −5.60 −2.01 2.40 A-15 340 150 290 — — — n.d. = not measurable

(70) TABLE-US-00003 TABLE 2 Performance of an organic electroluminescent device comprising an electron transport layer comprising a matrix compound and an alkali metal complex. Concentration of Concentration of Operating cd/A matrix compound Alkali alkali metal Thickness voltage at efficiency LT97 at Matrix (vol.-%) in the metal complex (vol.- of the ETL 10 mA/cm.sup.2 at 10 mA/cm.sup.2 30 mA/cm.sup.2 compound ETL complex %) in the ETL (nm) (V) (cd/A) (h) Comparative Comparative 50 LiQ 50 31 3.65 7.3 238 example 1 compound 1 Example 1 A-2 50 LiQ 50 31 3.6 7.4 280 Example 2 A-3 50 LiQ 50 31 3.6 7.5 256 Example 3 A-12 50 LiQ 50 31 3.4 7.3 — Example 4 A-14 50 LiQ 50 31 3.6 7.3 — Example 5 A-15 50 LiQ 50 31 3.55 7.3 —

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