Coordination Complex and Electronic Device Comprising the Same

Abstract

The present invention relates to an electronic device comprising a hole injection layer and/or a hole transport layer and/or a hole generating layer, wherein at least one of the hole injection layer, the hole transport layer and the hole generating layer comprises a coordination complex comprising at least one electropositive atom M having an electro-negativity value according to Allen of less than 2.4 and at least one ligand L having the following structure:

##STR00001##

wherein R.sup.1 and R.sup.2 are independently selected from the group, consisting of C.sub.1 to C.sub.30 hydrocarbyl groups and C.sub.2 to C.sub.30 heterocyclic groups, wherein R.sup.1 and/or R.sup.2 may optionally be substituted with at least one of CN, F, Cl, Br and I.

Claims

1. An electronic device comprising: a hole injection layer and/or a hole transport layer and/or a hole generating layer; wherein at least one of the hole injection layer, the hole transport layer, or the hole generating layer comprises a coordination complex having the general formula (I)— ##STR00032## wherein— M is an electropositive atom having an electro-negativity value according to Allen of less than 2.4; n is 1; m is 2 or 3; and R.sup.1 and R.sup.2 are independently selected from the group consisting of C.sub.1 to C.sub.30 hydrocarbyl and C.sub.2 to C.sub.30 heterocyclic group, wherein R.sup.1 and R.sup.2 are each substituted with substituents selected from the group consisting of CN, F, Cl, Br, and I, and the ratio of substituents:hydrogen in each of the R.sup.1 and R.sup.2 is ≥1.

2-4. (canceled)

5. The electronic device of claim 1, wherein (i) M is a metal capable of forming a divalent or trivalent cation, or (ii) M is selected from the group consisting of Ti, Cr, Mn, Fe, Co, Ni, Zn, and Cu.

6. (canceled)

7. The electronic device of claim 1, wherein the ratio of substituents:hydrogen in each of the R.sup.1 and R.sup.2 is ≥2.

8. (canceled)

9. The electronic device of claim 1, wherein R.sup.1, R.sup.2, or both R.sup.1 and R.sup.2 is perhalogenated.

10. The electronic device of claim 1, wherein the coordination complex having the general formula (I) is bis((1,1,1-trifluoro-N-(perfluorophenyl)methyl)-sulfonamido)zinc: ##STR00033##

11. The electronic device of claim 1, wherein the coordination complex having the general formula (I) is bis((N-3,5-bis(trifluoromethyl)phenyl)-1,1,1-trifluoromethyl)sulfonamido)zinc: ##STR00034##

12. The electronic device of claim 1, wherein the coordination complex having the general formula (I) is bis((1,1,1-trifluoro-N-(perfluoropyridin-4-yl)-methyl)sulfonamido)zinc: ##STR00035##

13. The electronic device of claim 1, wherein the coordination complex having the general formula (I) is bis((1,1,1-trifluoro-N-(2,5,6-trifluoropyrimidin-4-yl)-methyl)sulfonamido)zinc: ##STR00036##

14. The electronic device of claim 1, wherein the coordination complex having the general formula (I) is bis((1,1,2,2,2-pentafluoro-N-(perfluoropyridin-4-yl)ethyl)sulfonamido)zinc: ##STR00037##

15. The electronic device of claim 1, wherein the coordination complex having the general formula (I) is bis((1,1,1-trifluoro-N-(perfluoropyridin-4-yl)methyl)sulfonamido)manganese: ##STR00038##

16. The electronic device of claim 1, wherein the coordination complex having the general formula (I) is magnesium (perfluoropyridin-4-yl)((trifluoromethyl)sulfonyl)amide: ##STR00039##

17. The electronic device of claim 1, wherein the coordination complex having the general formula (I) is magnesium (2,3,5-trifluoro-6-(trifluoromethyl)pyridin-4-yl)((trifluoromethyl)sulfonyl)amide: ##STR00040##

18. The electronic device of claim 1, wherein the coordination complex having the general formula (I) is bis((1,1,1-trifluoro-N-(2,3,5-trifluoro-6-(trifluorometyl)pyridin-4-yl)methyl)sulfonamido)zinc: ##STR00041##

19. The electronic device of claim 1, wherein the coordination complex having the general formula (I) is bis((1,1,2,2,3,3,4,4,4-nonafluoro-N-(perfluoropyridin-4-yl)butyl)sulfonamido)zinc: ##STR00042##

20. The electronic device of claim 1, wherein the coordination complex having the general formula (I) is bis((1,1,2,2,3,3,4,4,4-nonafluoro-N-(perfluorophenyl)butyl)sulfonamido)zinc: ##STR00043##

21. A method for preparing an electronic device according to claim 1, the method comprising heating the coordination complex.

22. The method of claim 21, further comprising: vaporizing the coordination complex of the general formula (I) to form a vapor of the coordination complex; and depositing the vapor of the coordination complex on a solid support.

23. The method of claim 22, wherein the vaporizing and the depositing, respectively, comprise co-vaporizing and co-depositing the coordination complex with a matrix material.

24. The method of claim 23, wherein the matrix material is an organic matrix material.

25. The method of claim 23, wherein the matrix material is selected from the group consisting of a triazine compound, a hydroxyquinoline derivative, a benzazole derivative, and a silole derivative.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0154] 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:

[0155] FIG. 1 is a schematic sectional view of an organic light-emitting diode (OLED), according to an exemplary embodiment of the present invention;

[0156] FIG. 2 is a schematic sectional view of an OLED, according to an exemplary embodiment of the present invention.

[0157] 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.

[0158] FIG. 4 shows the crystal structure of the inventive inverse coordination complex E3, having the summary formula C.sub.42F.sub.48N.sub.6O.sub.13S.sub.6Zn.sub.4.

EMBODIMENTS OF THE INVENTIVE DEVICE

[0159] 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.

[0160] 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.

[0161] 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 directly 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.

[0162] Instead of a single electron transport layer 160, optionally an electron transport layer stack (ETL) can be used.

[0163] 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.

[0164] 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.

[0165] 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 and a second emission layer.

[0166] 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.

[0167] 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.

[0168] 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.

Experimental Part

Preparation of Inventive Metal Complexes

Exemplary Compound E2

[0169] The Compound has been Prepared According to Scheme 1

##STR00014##

1. Step 1: Synthesis of 1,1,1-trifluoro-N-(perfluorophenyl)methanesulfonamide

[0170] A 250 mL Schlenk flask was heated in vacuum and after cooling was purged with nitrogen. Perfluoroaniline was dissolved in 100 mL toluene and the solution was cooled to −80° C. A 1.7 M t-Butyllithium solution was added dropwise via syringe over 10 min. The reaction solution changed from clear to cloudy and was stirred for 1 h at −80° C. After that, the solution was allowed to warm to −60° C. and 1.1 eq of trifluoromethanesulfonic anhydride was added dropwise to the solution. Then the cooling bath was removed and the reaction mixture was allowed to warm slowly to ambient temperature and stirred overnight, whereby the color changed to light orange. Additionally, a white solid formed. The precipitated by-product lithium trifluoromethanesulfonate was filtered off by suction filtration over a sintered glass filter and washed with 2×30 mL toluene and 30 mL n-hexane. The orange filtrate was evaporated and dried in high vacuum forming crystals. The crude product was then purified by bulb-to-bulb distillation (135° C. @ 1.2×10.sup.−1 mbar) resulting in a crystalline colorless solid (main fraction).

.sup.1H NMR [d.sup.6-DMSO, ppm] δ: 13.09 (s, 1H, N−H).
.sup.13C{.sup.1H} NMR [d.sup.6-DMSO, ppm] δ: 116.75 (m, Ci-C6F5), 120.74 (q, .sup.1J.sub.CF=325 Hz, CF.sub.3), 136.39, 138.35 (2m, .sup.2J.sub.CF=247 Hz, m-C6F5), 137.08, 139.06 (2m, .sup.2J.sub.CF=247 Hz, p-C6F5), 142.98, 144.93 (2m, .sup.2J.sub.CF=247, Hz o-C6F5).
.sup.19F NMR [d.sup.6-DMSO, ppm] δ: −77.45 (m, CF.sub.3), −148.12 (m, C.sub.6F.sub.5), −160.79 (m, p-C.sub.6F.sub.5), −164.51 (m, C.sub.6F.sub.5).
ESI-MS: m/z-neg=314 (M-H).
EI-MS: m/z=315 (M), 182 (M-SO.sub.2CF.sub.3), 69 (CF.sub.3).

Step 2: Synthesis of bis((1,1,1-trifluoro-N-(perfluorophenyl)methyl)-sulfonamido)zinc

[0171] A 100 mL Schlenk flask was heated in vacuum and after cooling was purged with nitrogen. 1,1,1-Trifluoro-N-(perfluorophenyl)methanesulfonamide was dissolved in 10 mL toluene and 0.5 eq of diethylzinc in hexane was added dropwise to the solution via syringe at ambient temperature. During the addition a fog was forming and the reaction solution became jelly and cloudy. The solution was stirred for further 30 min at this temperature. After that, 30 mL n-hexane were added and a white precipitate formed, which was filtered over a sintered glass filter (pore 4) under inert atmosphere. The filter cake was twice washed with 15 mL n-hexane and dried in high vacuum at 100° C. for 2 h

Yield: 660 mg (0.95 mmol, 60% based on 1,1,1-trifluoro-N-perfluorophenyl)methanesulfonamide) as a white solid.
.sup.13C{.sup.1H} NMR [d.sup.6-DMSO, ppm] δ: 121.68 (q, .sup.1J.sub.CF=328 Hz, CF.sub.3), 123.56 (m, Ci-C6F5), 133.98, 135.91 (2m, .sup.2J.sub.CF=243 Hz, p-C6F5), 136.15, 138.13 (2m, .sup.2J.sub.CF=249 Hz, m-C6F5), 142.33, 144.24 (2m, .sup.2J.sub.CF=240, Hz o-C.sub.6F.sub.5).
.sup.19F NMR [d.sup.6-DMSO, ppm] δ: −77.52 (m, CF.sub.3), −150.43 (m, C.sub.6F.sub.5), −166.77 (m, C.sub.6F.sub.5), −168.23 (m, p-C.sub.6F.sub.5).
ESI-MS: m/z-neg=314 (M−Zn−L).
EI-MS: m/z=692 (M), 559 (M-SO.sub.2CF.sub.3) 315 (C.sub.6F.sub.5NHSO.sub.2CF.sub.3), 182 (C.sub.6F.sub.5NH), 69 (CF.sub.3).

Exemplary Compound E3

[0172] 9.1 g E2 has been sublimed at the temperature 240° C. and pressure 10.sup.−3 Pa. yield 5.9 g (65%).

[0173] The sublimed material formed colorless crystals. One crystal of an appropriate shape and size (0.094×0.052×0.043 mm.sup.3) has been closed under Ar atmosphere in a glass capillary and analyzed on Kappa Apex II diffractometer (Bruker-AXS, Karlsruhe, Germany) with monochromatic X-ray radiation from a source provided with molybdenum cathode (k=71.073 pm). Overall 37362 reflexions were collected within the theta range 1.881 to 28.306°.

[0174] The structure was resolved by direct method (SHELXS-97, Sheldrick, 2008) and refined with a full-matrix least-squares method (SHELXL-2014/7, Olex2 (Dolomanov, 2017).

Exemplary Compound E4

Step 1: Synthesis of N-(3,5-bis(trifluoromethyl)phenyl)-1,1,1-trifluoromethanesulfonamide

[0175] ##STR00015##

[0176] A 100 mL Schlenk flask was heated in vacuum and after cooling was purged with nitrogen. The 3,5-bis(trifluoromethyl)aniline was dissolved in 40 mL toluene and the solution was cooled to −80° C. The t-Butyllithium solution was added dropwise via syringe over 15 min. The resulting yellow solution was stirred for 1.5 h at −80° C. The trifluoromethanesulfonic anhydride was added at −80° C. The cooling bath was removed and the reaction mixture was allowed to warm slowly to ambient temperature and stirred overnight. The reaction was then cooled in an ice-bath to <10° C. and 70 ml 10% aqueous H2SO4-Solution was added slowly. The aqueous phase was extracted three times with 75 mL diethyl ether and the combined organic phases were washed with 100 mL water, dried over sodium sulphate and the solvent removed under reduced pressure. The resulting brownish oil was distilled from bulb to bulb at 120° C. and 2e-02 mbar.

Yield: 5.23 g (83% based on anhydride); slightly yellow oil, crystallizes slowly

Step 2: Synthesis of bis((N-(3,5-bis(trifluoromethyl)phenyl)-1,1,1-trifluoromethyl)sulfonamido)zinc

[0177] ##STR00016##

[0178] N-(3,5-bis(trifluoromethyl)phenyl)-1,1,1-trifluoromethanesulfonamide was dissolved in toluene in a dried Schlenk flask. A 1 M solution of diethylzine in toluene was added dropwise and the resulting thick suspension was stirred overnight. The solid was filtered off under inert conditions and washed with 20 ml dry hexane an dried under high vacuum overnight.

Yield: 1.12 g (69%); white solid

[0179] By vacuum sublimation, E4 converted in compound E5 having composition C.sub.54H.sub.18F.sub.54N.sub.6O.sub.13S.sub.6Zn.sub.4 and forming crystalline phase described above.

[0180] Further examples of inventive compounds were prepared analogously: E6, yield 99% based on 1,1,1-trifluoro-N-(perfluoropyridin-4-yl)methanesulfon-amide, according to Scheme 4

##STR00017##

[0181] E8, yield 81% based on 1,1,1-trifluoro-N-(2,5,6-trifluoro-pyrimidin-4-yl)methanesulfonamide)according to Scheme 5

##STR00018##

[0182] E10, yield 92% based on 1,1,2,2,2-pentafluoro-N-(perfluoro-pyridin-4-yl)ethane-1-sulfonamide, according to Scheme 6

##STR00019##

[0183] E12, yield 80%, according to Scheme 7

##STR00020##

[0184] E14, yield 90%, according to Scheme 8

##STR00021##

[0185] E16, yield 85%, according to Scheme 9

##STR00022##

[0186] E18, yield 76%, according to Scheme 10

##STR00023##

[0187] E20, yield 82%, according to Scheme 11

##STR00024##

[0188] E22, yield 68%, according to Scheme 12

##STR00025##

[0189] E24, yield 67%, according to Scheme 13

##STR00026##

Device Experiments

Generic Procedures

[0190] A 15Ω/cm.sup.2 glass substrate with 90 nm ITO (available from Corning Co.) was cut to a size of 150 mm×150 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 a first electrode.

[0191] The organic layers are deposited sequentially on the ITO layer at 10.sup.−5 Pa, see Table 1 and 2 for compositions and layer thicknesses. In the Tables 1 to 3, c refers to the concentration, and d refers to the layer thickness.

[0192] Then, the cathode electrode layer is formed by evaporating aluminum at ultra-high vacuum of 10.sup.−7 mbar and deposing the aluminum layer directly on the organic semiconductor layer. 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 thickness of the cathode electrode layer is 100 nm.

[0193] The device is protected from ambient conditions by encapsulation of the device with a glass slide. Thereby, a cavity is formed, which comprises a getter material for further protection.

[0194] Current voltage measurements are performed at the temperature 20° C. using a Keithley 2400 source meter, and recorded in V.

Experimental Results

Materials Used in Device Experiments

[0195] The formulae of the supporting materials mentioned in both tables below are as follows:

F1 is

[0196] ##STR00027##

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

F2 is

[0197] ##STR00028##

(3-(dibenzo[c,h]acridin-7-yl)phenyl)diphenylphosphine oxide, CAS 1440545-22-1;

F3 is

[0198] ##STR00029##

2,4-diphenyl-6-(3′-(triphenylen-2-yl)-[1,1′-biphenyl]-3-yl)-1,3,5-triazine, CAS 1638271-85-8;

F4 is

[0199] ##STR00030##

1,3-bis(9-phenyl-1,10-phenanthrolin-2-yl)benzene, CAS 721969-94-4;

PD-2 is

[0200] ##STR00031##

4,4′,4″-((1E,1′E,1″E)-cyclopropane-1,2,3-triylidenetris (cyanomethanylylidene))tris(2,3,5,6-tetrafluorobenzonitrile), CAS 1224447-88-4.

[0201] LiQ is lithium 8-hydroxyquinolinolate; ZnPc is zinc phtalocyanine;

ABH-113 is an emitter host and NUBD-370 and DB-200 are blue fluorescent emitter dopants, all commercially available from SFC, Korea.
ITO is indium tin oxide.

Standard Procedures

Voltage Stability:

[0202] OLEDs are driven by constant current circuits. Those circuits can supply a constant current over a given voltage range. The wider the voltage range, the wider the power losses of such devices. Hence, the change of driving voltage upon driving needs to be minimized.

[0203] The driving voltage of an OLED is temperature dependent. Therefore, voltage stability needs to be judged in thermal equilibrium. Thermal equilibrium is reached after one hour of driving.

[0204] Voltage stability is measured by taking the difference of the driving voltage after 50 hours and after 1 hour driving at a constant current density. Here, a current density of 30 mA/cm.sup.2 is used. Measurements are done at room temperature.

dU[V]=U(50 h,30 mA/cm.sup.2)−U(1 h,30 mA/cm.sup.2)

Example 1

[0205] Use of a sulfonyl amide coordination complex as a neat hole injection layer in a blue OLED

Table 1a schematically describes the model device.

TABLE-US-00002 TABLE 1a c d Material [wt %] [nm] ITO 100 90 B2 or E3 100  3* F1 100 120  ABH113:NUBD370 97:3  20 F2:LiQ 50:50 36 Al 100 100  *E3 has been tested also as a layer only 1 nm thin.
The results are given in Table 1b

TABLE-US-00003 TABLE 1b U* EQE* U(50 h) − U(1 h) ** [V] [%] CIE-y* [V] 3 nm B2 5.28 6.6 0.090 0.275 (reference) 3 nm E3 5.38 5.7 0.094 0.246 1 nm E3 5.11 5.4 0.096 0.040 *j = 15 mA/cm.sup.2 ** j = 30 mA/cm.sup.2

[0206] Neat layers of E3 provide an advantage of better voltage stability.

Example 2

[0207] Use of a sulfonyl amide coordination complex as a p-dopant in a hole injection layer comprised in a blue OLED

Table 2a schematically describes the model device.

TABLE-US-00004 TABLE 2a c d Material [wt %] [nm] ITO 100 90 F1:p-dopant 92:8 10 (mol %#) F1 100 120 ABH113:NUBD370 3 20 F2:LiQ 50 36 Al 100 100 #based on molar amount of metal atoms
The results are given in Table 2b

TABLE-US-00005 TABLE 2b U* EQE* U(50 h) − U(1 h) ** [V] [%] CIE-y* [V] B2 8.06 7.1 0.095 0.639 (reference) E3 5.15 5.7 0.094 −0.015 *j = 15 mA/cm.sup.2 ** j = 30 mA/cm.sup.2

[0208] It is shown that a p-dopant for a HIL comprising a hole transport matrix, complex E3 is advantageous over prior art compound B2.

[0209] Specifically, HILs p-doped with E3 provide an advantage of better voltage stability. The higher efficiency observed with B2-doped HIL is practically useless, due to impractically high operational voltage of such device. In this regard, the results show that E3 is well applicable also as a p-dopant, whereas B2 can be used only in neat thin hole injection layers.

Example 3

[0210] Blue tandem OLED comprising a sulfonyl amide coordination complex as a neat hole generation layer

Table 3a schematically describes the model device.

TABLE-US-00006 TABLE 3a c d Material [wt %] [nm] ITO 100 90 F1:PD-2 92:8 10 F1 100 145 ABH113:BD200 97:3 20 F3 100 25 F4:Li 99:1 10 ZnPc 100 2 p-dopant 100 1 F1 100 30 ABH113:BD200 97:3 20 F3 100 26 F4:Li 99:1 10 Al 100 100

[0211] The results are given in Table 3b

TABLE-US-00007 TABLE 3b U* EQE* [V] [%] CIE-y* 1 nm B2 10.65 6.3 0.066 (reference) 1 nm E3 7.52 13.5 0.083 *j = 10 mA/cm.sup.2 ** j = 30 mA/cm.sup.2

[0212] The results show that E3 is suitable as a neat CGL, whereas the device with a neat B2 CGL is poor.

Example 4

[0213] Blue tandem OLED comprising a sulfonyl amide coordination complex as a p-dopant in a hole generation layer

Table 4a schematically describes the model device.

TABLE-US-00008 TABLE 4a c d Material [wt %] [nm] ITO 100 90 F1:PD-2 92:8 10 F1 100 145 ABH113:BD200 97:3 20 F3 100 25 F4:Li 99:1 10 ZnPc 100 2 F1:p-dopant  84:16 10 (mol %)# F1 100 30 ABH113:BD200 97:3 20 F3 100 26 F4:Li 99:1 10 Al 100 100 #based on molar amount of metal atoms
The results are given in Table 4b

TABLE-US-00009 TABLE 4b U* EQE* U(50 h) − U(1 h) ** [V] [%] CIE-y* [V] B2 8.98 13.4 0.082 (reference) E3 7.75 14.2 0.087 0.094 *j = 10 mA/cm.sup.2 ** j = 30 mA/cm.sup.2

[0214] The results are in accordance with Example 2 showing significantly better performance of E3 as a p-dopant in comparison with B2.

[0215] From the foregoing detailed description and examples, it will be evident that modifications and variations can be made to the compositions and methods of the invention without departing from the spirit and scope of the invention. Therefore, it is intended that all modifications made to the invention without departing from the spirit and scope of the invention come within the scope of the appended claims.