Electron Injection Layer for an Organic Light-Emitting Diode (OLED)

Abstract

The invention relates to Organic light emitting diode comprising at least one emission layer, an electron injection layer and at least one cathode electrode, wherein: the electron injection layer comprises an organic phosphine compound, wherein the electron injection layer is free of a metal, metal salt, metal complex and metal organic compound; the cathode electrode comprises at least a first cathode electrode layer, wherein the first cathode electrode layer comprises a first zero-valent metal selected from the group comprising alkali metal, alkaline earth metal, rare earth metal and/or a group 3 transition metal; and the electron injection layer is arranged in direct contact to the first cathode electrode layer.

Claims

1. Organic light emitting diode comprising at least one emission layer, an electron injection layer and at least one cathode electrode, wherein: the electron injection layer comprises an organic phosphine compound, wherein the electron injection layer is free of a metal, metal salt, metal complex and metal organic compound; the cathode electrode comprises at least a first cathode electrode layer, wherein the first cathode electrode layer comprises a first zero-valent metal selected from the group comprising alkali metal, alkaline earth metal, rare earth metal and/or a group 3 transition metal; and the electron injection layer is arranged in direct contact to the first cathode electrode layer.

2. The organic light emitting diode according to claim 1, wherein the organic phosphine compound of the electron injection layer is a compound having the Formula Ia: ##STR00154## wherein: X is selected from O, S, or Se; R.sup.1 and R.sup.2 are independently selected from 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.5 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; and A.sup.1 is phenyl or selected from Formula (II): ##STR00155## 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.5 to C.sub.20 heteroarylene; or A.sup.1 is selected from Formula (III) ##STR00156## wherein n is selected from 0 or 1; m is selected from 1 or 2; o is selected from 1 or 2; and m is 1 if o is 2; Ar.sup.1 is selected from substituted or unsubstituted C.sub.6 to C.sub.20 arylene and substituted or unsubstituted C.sub.5 to C.sub.20 heteroarylene; Ar.sup.2 is selected from substituted or unsubstituted C.sub.18 to C.sub.40 arylene and substituted or unsubstituted C.sub.10 to C.sub.40 heteroarylene; 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 and substituted or unsubstituted C.sub.5 to C.sub.20 heteroaryl; wherein the cathode electrode comprises at least a first cathode electrode layer, wherein the first cathode electrode layer comprises a first zero-valent metal selected from the group comprising alkali metal, alkaline earth metal, rare earth metal and/or a group 3 transition metal; and the electron injection layer is arranged in direct contact to the first cathode electrode layer.

3. The organic light emitting diode according to claim 1, wherein the first cathode electrode layer is free of a metal halide and/or free of a metal organic complex.

4. The organic light emitting diode according to claim 1, wherein the first cathode electrode layer further comprises a second zero-valent metal, wherein the second zero-valent metal is selected from a main group metal or a transition metal, wherein the second zero-valent metal is selected different from the first zero-valent metal.

5. The organic light emitting diode according to claim 1, wherein the cathode electrode further comprises a second cathode electrode layer, wherein the second cathode electrode layer comprises at least a third metal, in form of a zero-valent metal, alloy and/or as oxide, wherein the third metal is selected from a main group metal, transition metal and/or rare earth metal.

6. The organic light emitting diode according to claim 1, further comprising at least one electron transport layer comprising at least one matrix compound, wherein the electron injection layer is contacting sandwiched between the first cathode electrode layer and the electron transport layer.

7. The organic light emitting diode according to claim 2, wherein Ar.sup.1 is selected from substituted C.sub.6 to C.sub.20 arylene, and/or substituted C.sub.5 to C.sub.20 heteroarylene, wherein the C.sub.6 to C.sub.20 arylene, and/or C.sub.5 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; Ar.sup.2 is selected from substituted C.sub.18 to C.sub.40 arylene and/or substituted C.sub.10 to C.sub.40 heteroarylene, wherein the C.sub.18 to C.sub.40 arylene and/or C.sub.10 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; and.

8. The organic light emitting diode according to claim 2, wherein: R.sup.1 and R.sup.2 are independently selected from substituted C.sub.6 to C.sub.20 aryl, or substituted C.sub.5 to C.sub.20 heteroaryl, wherein the C.sub.6 to C.sub.20 aryl, and/or C.sub.5 to C.sub.20 heteroaryl 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; and/or R.sup.3 is independently selected from substituted C.sub.6 to C.sub.20 arylene, or substituted C.sub.5 to C.sub.20 heteroarylene, wherein the C.sub.6 to C.sub.20 arylene, and/or C.sub.5 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; and/or R.sup.4 is independently selected from substituted C.sub.6 to C.sub.20 aryl, or substituted C.sub.5 to C.sub.20 heteroaryl, wherein the C.sub.6 to C.sub.20 aryl, and/or C.sub.5 to C.sub.20 heteroaryl 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.

9. The organic light emitting diode according to claim 2, wherein for o=2 the organic phosphine compound of the electron injection layer is a compound having the Formula Ib: ##STR00157## or o=1 the organic phosphine compound of the electron injection layer is a compound having the Formula Ic, Id, Ie or If: ##STR00158##

10. The organic light emitting diode according to claim 2, wherein R.sup.1 and R.sup.2 is independently selected from C.sub.1 to C.sub.4 alkyl, unsubstituted or substituted C.sub.6 to C.sub.10 aryl, or unsubstituted or substituted C.sub.5 to C.sub.10 heteroaryl, wherein the C.sub.6 to C.sub.10 aryl, and/or C.sub.5 to C.sub.10 heteroaryl 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; and/or X is O or S; and/or R.sup.3 is selected from C.sub.1 to C.sub.6 alkane-di-yl, unsubstituted or substituted C.sub.6 to C.sub.10 arylene or unsubstituted or substituted C.sub.5 to C.sub.10 heteroarylene; and/or R.sup.4 is selected from H, phenyl, biphenyl, terphenyl, fluorenyl, naphthyl, anthranyl, phenanthryl, pyrenyl, carbazoyl, dibenzofuranyl, dinapthofuranyl; and/or n is 0, 1 or 2; m is 1 or 2 and n is 0 or 1, or m is 2 and n is 2; and/or Ar.sup.1 is selected from phenylene, biphenylene, terphenylene, naphthylene, fluorenylene, pyridylene, quinolinylene, and pyrimidinylene; and/or Ar.sup.2 is selected from fluorenylene, anthranylene, pyrenylene, phenanthrylene, carbazoylene, benzo[c]acridinylene, dibenzo[c,h]acridinylene, dibenzo[a,j]acridinylene.

11. The organic light emitting diode according to claim 2, wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, Ar.sup.1 and/or Ar.sup.2 are unsubstituted.

12. The organic light emitting diode according to claim 2, wherein Ar.sup.2 is selected from a compound according to Formula IVa to IVh: ##STR00159## ##STR00160##

13. The organic light emitting diode according to claim 2, wherein the compound of Formula (I) is selected from a compound according to: ##STR00161## ##STR00162## ##STR00163## ##STR00164## ##STR00165## ##STR00166## ##STR00167## ##STR00168##

14. A method of manufacturing an organic light emitting diode, according to claim 1, wherein on the substrate an anode electrode is deposited and on the anode electrode the other layers of hole injection layer, hole transport layer, optional an electron blocking layer, emission layer, optional hole blocking layer, optional electron transport layer, electron injection layer, and first cathode electrode layer, are deposited in that order; or the layers are deposited the other way around, starting with the first cathode electrode layer;

15. Electronic device comprising at least one organic light emitting diode, according to claim 1.

16. The organic light emitting diode according to claim 4, wherein the second zero-valent metal is selected from the group consisting of Li, Na, K, Cs, Mg, Ca, Sr, Ba, Sc, Y, Ti, V, Cr, Mn, Mn, Fe, Fe, Co, Co, Ni, Cu, Cu, Zn, Ag, Au, Au, Al, Ga, In, Sn, Sn, Te, Bi, and Pb.

17. The organic light emitting diode according to claim 4, wherein the second zero-valent metal is selected from the group consisting of Ag, Au, Zn, Te, Yb, Ga, Bi, Ba, Ca, and Al.

18. The organic light emitting diode according to claim 4, wherein the second zero-valent metal is selected from the group consisting of Ag, Zn, Te, Yb, Ga, and Bi.

19. The organic light emitting diode according to claim 5, wherein the third metal is selected from zero-valent Ag, Al, Cu and Au, MgAg alloy, indium tin oxide, indium zinc oxide, ytterbium oxide, or indium gallium zinc oxide.

20. The organic light emitting diode according to claim 5, wherein the third metal is selected from Ag, Al, or MgAg alloy.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0442] 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:

[0443] FIG. 1 is a schematic sectional view of an organic light-emitting diode (OLED), according to an exemplary embodiment of the present invention;

[0444] FIG. 2 is a schematic sectional view of an OLED, according to an exemplary embodiment of the present invention.

[0445] FIG. 3. is a schematic sectional view of an OLED, according to another exemplary embodiment of the present invention.

[0446] FIG. 4 is a schematic sectional view of a tandem OLED comprising a charge generation layer, according to an exemplary embodiment of the present invention.

[0447] FIG. 5 is a schematic sectional view of a tandem OLED comprising a charge generation layer and an ETL stack, according to an exemplary embodiment of the present invention

[0448] FIG. 6 is a graph showing the operating voltage of an OLED according to invention plotted against the layer thickness of the electron injection layer according to invention.

DETAILED DESCRIPTION

[0449] 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.

[0450] 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.

[0451] 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 electrode 120, a hole injection layer (HIL) 130, a hole transport layer (HTL) 140, an emission layer (EML) 150, an electron transport layer (ETL) 160. Onto the electron transport layer (ETL) 160 an electron injection layer (EIL) 180 is disposed. The electron injection layer (EIL) 180 comprising or consisting of an organic phosphine compound selected from the group of organic phosphine oxide compound or an organic thioxophosphine compound or an organic selenoxophosphine compound, wherein the electron injection layer (EIL) 180 is formed directly on the ETL 160. The first cathode electrode layer 191 is disposed directly onto the electron injection layer (EIL) 180.

[0452] Instead of a single electron transport layer 160, optional an electron transport layer stack (ETL) can be used.

[0453] 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 an electron transport layer stack (ETL stack) 160.

[0454] Referring to FIG. 2 the OLED 100 includes a substrate 110, an anode electrode 120, a hole injection layer (HIL) 130, a hole transport layer (HTL) 140, an electron blocking layer (EBL) 145, an emission layer (EML) 150, an electron transport layer stack (ETL) 160 and an electron injection layer (EIL 180). The ETL stack 160 comprises a first electron transport layer (ETL1) 160a and a second electron transport layer (ETL2) 160b. The second electron transport layer 160b is disposed directly on the emission layer 150. The first electron transport layer 160a is disposed directly on the second electron transport layer. The electron injection layer (EIL) 180 comprising or consisting of an organic phosphine compound selected from the group of an organic phosphine oxide compound or an organic thioxophosphine compound or an organic selenoxophosphine compound, is disposed directly on the first electron transport layer 160a. The first cathode electrode layer 191 is disposed directly onto the electron injection layer (EIL) 180.

[0455] FIG. 3 is a schematic sectional view of an OLED 100, according to another exemplary embodiment of the present invention. FIG. 3 differs from FIG. 1 in that the OLED 100 of FIG. 2 comprises an electron blocking layer (EBL) 145, a hole blocking layer (HBL) 155 and a second cathode electrode layer 192.

[0456] Referring to FIG. 3 the OLED 100 includes a substrate 110, an anode electrode 120, a hole injection layer (HIL) 130, a hole transport layer (HTL) 140, an electron blocking layer (EBL) 145, an 181 (EML) 150, a hole blocking layer (HBL) 155, an electron transport layer (ETL) 160 and an electron injection layer (EIL) 180. The electron injection layer (EIL) 180 comprising or consisting of an organic phosphine compound selected from the group of an organic phosphine oxide compound or an organic thioxophosphine compound or an organic selenoxophosphine compound, wherein the electron injection layer (EIL) 180 is disposed directly on the ETL 160. The first cathode electrode layer 191 is disposed directly onto the electron injection layer (EIL) 180. The second cathode electrode layer 192 is disposed directly onto the first cathode electrode layer 191. The first and second cathode electrode layer together form the cathode electrode 190.

[0457] In the description above the method of manufacture an OLED 100 of the present invention is started with a substrate 110 onto which an anode electrode 120 is formed, on the anode electrode 120, an hole injection layer 130, hole transport layer 140, optional an electron blocking layer 145, an emission layer 150, optional a hole blocking layer 155, optional at least one electron transport layer 160, an electron injection layer 180, a first cathode electrode layer 191 and an optional second cathode electrode layer 192 are formed, in that order or the other way around.

[0458] FIG. 4 is a schematic sectional view of a tandem OLED 100, according to another exemplary embodiment of the present invention. FIG. 4 differs from FIG. 2 in that the OLED 100 of FIG. 4 further comprises a charge generation layer and a second emission layer.

[0459] Referring to FIG. 4 the OLED 200 includes a substrate 110, an anode electrode 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 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, an electron injection layer (EIL) 180, a first cathode electrode layer 191 and a second cathode electrode layer 192. The electron injection layer 180 comprising or consisting of an organic phosphine compound selected from the group of organic phosphine oxide compound or an organic thioxophosphine compound or an organic selenoxophosphine compound is disposed directly onto the second electron transport layer 161 and the first cathode electrode layer 191 is disposed directly onto the electron injection layer 180.

[0460] In the description above the method of manufacture an OLED 100 of the present invention is started with a substrate 110 onto which an anode electrode 120 is formed, on the anode electrode 120, a first hole injection layer 130, first hole transport layer 140, optional a first electron blocking layer 145, a first emission layer 150, optional a first hole blocking layer 155, optional an ETL stack 160, comprising a first electron transport layer 160a and a second electron transport layer 160b, an n-type CGL 185, a p-type CGL 135, a second hole transport layer 141, optional a second electron blocking layer 146, a second emission layer 151, an optional second hole blocking layer 156, an optional at least one second electron transport layer 161, an electron injection layer 180, a first cathode electrode layer 191 and an optional second cathode electrode layer 192 are formed, in that order or the other way around.

[0461] FIG. 5 is a schematic sectional view of a tandem OLED 100, according to another exemplary embodiment of the present invention. FIG. 5 differs from FIG. 4 in that the OLED 100 of FIG. 5 further comprises an ETL stack 160.

[0462] Referring to FIG. 5 the OLED 200 includes a substrate 110, an anode electrode 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, an ETL stack (ETL) 160, an n-type charge generation layer (n-type CGL) 185, a 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 third electron transport layer (ETL) 161, an electron injection layer (EIL) 180, a first cathode electrode layer 191 and a second cathode electrode layer 192. The ETL stack 160 comprises a first electron transport layer (ETL1) 160a and a second electron transport layer (ETL2) 160b. The second electron transport layer 160b is disposed directly on the first emission layer 150. The first electron transport layer 160a is disposed directly on the second electron transport layer 160b. The electron injection layer 180 comprising or consisting of an organic phosphine compound selected from the group of organic phosphine oxide compound or an organic thioxophosphine compound or an organic selenoxophosphine compound is disposed directly onto the second electron transport layer 161 and the first cathode electrode layer 191 is disposed directly onto the electron injection layer 180.

[0463] While not shown in FIG. 1, FIG. 2, FIG. 3, FIG. 4 and FIG. 5, 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.

[0464] FIG. 6 shows the effect of the thickness of the electron injection layer (EIL) according to invention on the operating voltage of a fluorescent blue OLED. Organic phosphine compound (Va) is used as electron injection layer with a thickness ranging from 1 to 10 nm. 2 nm Yb is used as first cathode electrode layer. 100 nm Al is used as second cathode electrode layer. The electron injection layer is contacting sandwiched between an electron transport layer and the first cathode electrode layer. The electron transport layer comprises non-polar anthracene compound ETM-1 and the thickness is 34 nm. The emission layer comprises 97 wt.- % of ABH113 (Sun Fine Chemicals) as a host and 3 wt.- % of NUBD370 (Sun Fine Chemicals) as a fluorescent blue dopant. The lowest operating voltage is achieved for an EIL thickness of more than 1 nm and less than 6 nm. A thickness range of ?1 nm and ?5 nm is particularly preferred. The lowest operating voltage is observed for an EIL thickness of 3 to 4 nm.

EXAMPLES

[0465] Organic phosphine compounds may be synthesized as described in JP2004095221, US 20030144487, WO2015/097225A1 and EP15195877.

General Procedure

[0466] Bottom Emission Devices with an Evaporated Emission Layer For bottom emission devicesExamples 1 to 10 and comparative examples 1 to 2, a 15 ?/cm.sup.2 glass substrate (available from Corning Co.) with 100 nm ITO 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 a first electrode.

[0467] Then, 92 wt.- % of Biphenyl-4-yl(9,9-diphenyl-9H-fluoren-2-yl)-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-amine and 8 wt.- % of 2,2,2-(cyclopropane-1,2,3-triylidene)tris(2-(p-cyanotetrafluorophenyl)acetonitrile) was vacuum deposited on the ITO electrode, 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 was vacuum deposited on the HIL, to form a HTL having a thickness of 120 nm. 97 wt.- % of ABH113 (Sun Fine Chemicals) as a host and 3 wt.- % of NUBD370 (Sun Fine Chemicals) as a dopant were deposited on the HTL, to form a blue-emitting EML with a thickness of 20 nm.

[0468] Then, the electron transport layer is formed by deposing a first organic matrix compound according to examples 1 to 10 and comparative example 1 and 2 by deposing the compound from a first deposition source directly on the EML. Further, the thickness d (in nm) of the ETL can be taken from Table 8.

[0469] Then, the electron injection layer is formed by deposing an organic phosphine compound according to example 1 to 10 and comparative examples 1 and 2 directly on the electron transport layer. The composition and thickness of the electron injection layer can be taken from Table 8.

[0470] For comparative example 2, a 0.4 nm thick layer of LiF is deposited on the electron injection layer, thereby forming a second electron injection layer.

[0471] The first cathode electrode 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 ?/s) in order to generate a homogeneous cathode electrode with a thickness of 5 to 1000 nm. Then, the optional second cathode electrode layer is deposed directly on to the first cathode electrode layer under the same conditions. The composition and thickness of the first and second cathode electrode layer can be taken from Table 8.

[0472] 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.

[0473] Bottom Emission Devices with a Solution-Processed Emission Layer

[0474] For bottom emission devices, a glass substrate with 100 nm Ag 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 a first electrode.

[0475] Then, PEDOT:PSS (Clevios P VP AI 4083) is spin-coated directly on top of the first electrode to form a 55 nm thick HIL. The HIL is baked on hotplate at 150? C. for 5 min Then, a light-emitting polymer, for example MEH-PPV, is spin-coated directly on top of the HIL to form a 40 nm thick EML. The EML is baked on a hotplate at 80? C. for 10 min The device is transferred to an evaporation chamber and the following layers are deposited in high vacuum.

[0476] Organic phosphine compound (Vr) is deposed directly on top of the EML to form an EIL with a thickness of 4 nm. A first cathode electrode layer is formed by depositing a 2 nm thick layer of ytterbium directly on top of the EIL. A second cathode electrode layer is formed by deposing a 100 nm thick layer of aluminium directly on top of the first cathode electrode layer.

[0477] Top Emission Devices

[0478] For top emission devicesExamples 11 to 15, the anode electrode was formed from 100 nm silver on glass which is prepared by the same methods as described above.

[0479] Then, 92 wt.- % 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 wt.- % of 2,2,2-(cyclopropane-1,2,3-triylidene)tris(2-(p-cyanotetrafluorophenyl)acetonitrile) is vacuum deposited on the ITO elec-trode, 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 (CAS 1242056-42-3) is vacuum deposited on the HIL, to form a HTL having a thickness of 125 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.

[0480] 97 wt.- % of 2-(10-phenyl-9-anthracenyl)-benzo[b]naphtho[2,3-d]furan as a host and 3 wt.- % of NUBD370 (Sun Fine Chemicals) as a dopant are deposited on the EBL, to form a blue-emitting EML with a thickness of 20 nm.

[0481] Then the electron transport layer is formed by deposing a first organic matrix compound according to examples 10 to 15 by deposing the compound from a first deposition source directly on the EML. Further, the thickness d (in nm) of the ETL can be taken from Table 9.

[0482] Then, the electron injection layer according to the invention is formed by deposing an organic phosphine compound according to examples 11 to 15 directly on the electron transport layer. The composition and thickness of the electron injection layer can be taken from Table 9.

[0483] The first cathode electrode layer is evaporated at ultra-high vacuum of10.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 ?/s) in order to generate a homogeneous cathode electrode with a thickness of 5 to 1000 nm. Then, the optional second cathode electrode layer is deposed directly on to top of the first cathode electrode layer under the same conditions. The composition and thickness of the first and second cathode electrode layer can be taken from Table 9.

[0484] 60 nm biphenyl-4-yl(9,9-diphenyl-9H-fluoren-2-yl)-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-amine (CAS 1242056-42-3) is deposed directly on top of the second cathode electrode layer.

[0485] 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.

[0486] 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. Lifetime LT of top emission device is measured at ambient conditions (20? C.) and 8 mA/cm.sup.2. 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.

[0487] 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.

[0488] In top emission devices, the emission is forward directed, non-Lambertian and also highly dependent on the mirco-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.

[0489] Technical Effect of the Invention [0490] a) Bottom emission device with fluorescent blue emission layer, electron transport layer and electron injection layer

[0491] The beneficial effect of the electron injection layer according to the invention on the performance of bottom emission devices can be seen in Table 8.

[0492] An electron transport layer comprising an anthracene compound as first organic matrix compound is used in Example 1 to 10 and in comparative examples 1 and 2. The anthracene compounds may have a dipole moment of ?0 Debye and ?2.5 Debye, see Table 5.

[0493] In comparative example 1, the electron injection layer comprising organic phosphine oxide compound (Vr) is in direct contact with the aluminium cathode electrode. The operating voltage is very high at 4.7 V.

[0494] In comparative example 2, the electron injection layer comprising organic phosphine oxide compound (Vr) is in direct contact with a thin layer of LiF. The LiF layer is contacting sandwiched between the electron injection layer and the aluminium cathode electrode. The operating voltage is 3.2 V and thereby significantly lower than in comparative example 1. However, this improvement in operating voltage is achieved by using toxic and thermally unstable LiF.

[0495] In example 1, the electron injection layer comprising organic phosphine oxide compound (Vr) is in direct contact with a first cathode electrode layer of 0.4 nm layer of lithium and a second cathode electrode layer of 100 nm aluminium. The operating voltage is 3.3 V and therefore comparable to comparative example 2. However, this very low operating voltage is achieved by using lithium instead of LiF. Lithiuim is thermally stable and, additionally, it is not a toxic compound and therefore can be easily handled in manufacturing processes. Additionally, the operating voltage is significantly lower than in comparative example 1, where high workfuntion metal aluminium is used. Lithium has a workfunction of 2.95 eV while aluminium has a workfunction of 4.3 eV. Therefore, the workfunction of lithium is significantly lower than the workfunction of aluminium and it is therefore easier to inject electrons from a lithium layer into the electron injection layer comprising a phosphine compound.

[0496] In example 2, a first cathode electrode layer of 2 nm ytterbium is used in place of lithium. The operating voltage is unchanged. The same operating voltage is obtained in example 3, where barium is used to form the first cathode electrode layer. Ytterbium and barium have a workfunction which is lower than the workfunction of aluminium.

[0497] In example 4 to 10, various electron injection layers comprising an organic phosphine compound of formula (Ia) are tested. In all examples the first cathode electrode layer is formed from 2 nm ytterbium and the second cathode electrode layer is formed from 100 nm aluminium.

[0498] In example 4 to 6, the electron injection layer comprises an organic phosphine compound of formula (II). The operating voltage is 3.3 and 3.4 V.

[0499] In example 7 to 10, the electron injection layer comprises an organic phosphine compound of formula (III). The operating voltage is between 3.2 and 3.4 V.

[0500] In summary, a wide range of organic phosphine compounds can be used in the electron injection layer according to the invention.

TABLE-US-00008 TABLE 8 Bottom emission device comprising an emission layer, electron transport layer (ETL), electron injection layer comprising an organic phosphine compound and a cathode electrode comprising a first cathode electrode layer and optionally a second cathode electrode layer d (cathode d (cathode U d d d Cathode electrode Cathode electrode at 10 (ETL)/ (EIL1)/ (EIL1)/ electrode layer electrode layer 2)/ mA/ ETL nm EIL1 nm EIL2 nm layer 1 1)/nm layer 2 nm cm.sup.2/V Comparative ADN 36 Compound (Vr) 4 Al 100 4.7 example 1 Comparative ADN 36 Compound (Vr) 4 LiF 0.4 Al 100 3.2 example 2 Example 1 ETM-1 34 Compound (Vr) 4 Li 0.4 Al 100 3.3 Example 2 ETM-1 34 Compound (Vr) 4 Yb 2 Al 100 3.3 Example 3 ETM-1 34 Compound (Vr) 4 Ba 2 Al 100 3.2 Example 4 ETM-1 34 Compound (Va) 4 Yb 2 Al 100 3.35 Example 5 ETM-1 34 Compound (Vb) 4 Yb 2 Al 100 3.3 Example 6 ETM-1 34 Compound (Vd) 4 Yb 2 Al 100 3.4 Example 7 ETM-1 34 Compound (Vf) 4 Yb 2 Al 100 3.3 Example 8 ETM-1 34 Compound (Vj) 4 Yb 2 Al 100 3.2 Example 9 ETM-1 34 Compound (Vq) 4 Yb 2 Al 100 3.4 Example 10 ETM-1 34 Compound (Vl) 4 Yb 2 Al 100 3.3 [0501] b) Top emission device with fluorescent blue emission layer, electron transport layer and electron injection layer

[0502] The beneficial effect of the electron injection layer according to the invention on the performance of top emission devices can be seen in Table 9.

[0503] The electron injection layer comprising organic phosphine compound (Vr) is in direct contact with a first cathode electrode layer which consists of 2 nm ytterbium. In example 11 and 12, the second cathode electrode layer consists of 11 nm Ag. In example 13 to 15, the second cathode electrode layer consists of 13 nm MgAg alloy (15:85 vol.- %).

[0504] An electron transport layer is used in examples 11 to 15. The electron transport layer comprises a first organic matrix compound with a dipole moment of ?0 Debye and ?2.5 Debye, see Table 9. In examples 11 and 13 to 15, triazine compound ETM-28 is used. In example 12, dibenzo[c,h]acridine compound ETM-15 is used.

[0505] In all examples, the operating voltage is very low at 3.2 to 3.3 V, the external quantum efficiency is very high at 15.5 to 16.5% EQE and the lifetime is high at 44 to 60 hours see Table 9.

TABLE-US-00009 TABLE 9 Top emission device comprising an emission layer, electron transport layer (ETL), electron injection layer comprising an organic phosphine compound and a cathode electrode comprising a first cathode electrode layer and a second cathode electrode layer d d EQE (cathode (cathode U at LT d d Cathode electrode Cathode electrode at 10 10 at 8 (ETL)/ (EIL)/ electrode layer 1)/ electrode layer 2)/ mA/ mA/ mA/ ETL nm EIL nm layer 1 nm layer 2 nm cm.sup.2/V cm.sup.2/% cm.sup.2/h Example ETM-28 29 Compound 4 Yb 2 Ag 11 3.3 16.5 44 11 (Vr) Example ETM-15 29 Compound 4 Yb 2 Ag 11 3.2 15.6 46 12 (Vr) Mg:Ag Example ETM-28 29 Compound 4 Yb 2 (15:85 13 3.2 15.5 60 13 (Vd) vol.-%) Example ETM-28 29 Compound 4 Yb 2 Mg:Ag 13 3.2 15.5 60 14 (Vq) (15:85 vol.-%) Example ETM-28 29 Compound 4 Yb 2 Mg:Ag 13 3.3 16 50 15 (Vr) (15:85 vol.-%)

[0506] 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.