Organic element for low voltage electroluminescent devices

1. An OLED device comprising a cathode, a light emitting layer and an anode, in that order, and, having located between the cathode and the light emitting layer, a further layer containing an alkali metal or alkaline earth metal salt of a 2-(2-hydroxyphenyl)phenanthroline derivative,

wherein the alkali metal or alkaline earth metal salt of a 2-(2-hydroxyphenyl)phenanthroline derivative is according to Formula (MC):

wherein:

M is an alkali metal or alkaline earth metal;

R 1 and R 2 are independently an alkyl group or an aryl group; and

n is an integer from 0-7 and p is an integer from 0-4.

2. The device of claim 1 wherein M is lithium.

3. The device of claim 1 wherein the metal salt of a 2-(2-hydroxyphenyl)phenanthroline derivative is:

4. The device of claim 1 wherein the further layer additionally contains more than 10% by volume of a fused ring aromatic compound chosen from anthracenes and tetracenes.

5. The device of claim 4 wherein the fused ring aromatic compound is a tetracene represented by Formula (2):

wherein:

Ar 1 -Ar 4 represent independently selected aromatic groups;

R 1 -R 4 represent hydrogen or independently selected substituents.

6. The device of claim 5 wherein in Formula (2), Ar 1 and Ar 4 are the same group; independently of Ar 1 and Ar 4 , Ar 2 and Ar 3 are the same group; and R 1 and R 4 are not hydrogen and represent the same group.

7. The device of claim 4 wherein the fused ring aromatic compound is an anthracene represented by Formula (3):

wherein:

W 9 and W 10 are independently selected from phenyl, biphenyl, naphthyl and anthracenyl groups, and W 1 -W 8 are independently selected from hydrogen, alkyl and phenyl groups.

8. The device of claim 1 wherein the further layer is directly adjacent to the light-emitting layer and further contains an additional layer, located between the further layer and the cathode, containing a cyclometallated organic alkali or alkaline earth metal complex represented by Formula (4′)

wherein:

Z and the dashed arc represent two or three atoms and the bonds necessary to complete a 5- or 6-membered ring with M;

each A represents H or a substituent and each B represents an independently selected substituent on the Z atoms, provided that two or more substituents may combine to form a fused ring or a fused ring system;

j is an integer from 0-3 and k is 1 or 2;

M represents an alkali or alkaline earth metal; and

m and n are independently selected integers selected to provide a neutral charge on the complex.

9. The device of claim 8 wherein the cyclometallated organic complex of an alkali or alkaline earth metal in the additional layer is represented by Formula (5):

wherein:

each r a and r b represents an independently selected substituent, provided two substituents may combine to form a ring;

s is an integer from 0-3;

t is an integer from 0-3; and

n is an integer.

10. The device of claim 8 wherein the cyclometallated organic complex of an alkali or alkaline earth metal in the additional layer is according to Formula (MC):

wherein:

M is an alkali metal or alkaline earth metal;

R 1 and R 2 are independently an alkyl or an aryl group; and

n is an integer from 0-7 and p is an integer from 0-4.

11. An OLED device comprising a cathode, a light emitting layer and an anode, in that order, and, having located between the cathode and the light emitting layer, a further layer containing an alkali metal or alkaline earth metal salt of a 2-(2-hydroxyphenyl)phenanthroline derivative,

wherein the alkali metal or alkaline earth metal salt of a 2-(2-hydroxyphenyl)phenanthroline derivative is according to Formula (MC):

wherein:

M is an alkali metal or alkaline earth metal;

R 1 and R 2 are independently an alkyl group or an aryl group; and

n is an integer from 0-7 and p is an integer from 0-4;

wherein the further layer is directly adjacent to the cathode and further contains an additional layer, located between the further layer and the light-emitting layer, wherein the additional layer contains an anthracene.