Film forming composition and organic electroluminescent device

1. A film-forming composition, which is a composition used to form a film of a hole-injecting/transporting layer of an organic electroluminescent device, wherein the film-forming composition contains a hole-injecting/transporting material and/or an electron-accepting compound and a liquid in which the material and/or the compound have been dissolved;

the liquid contains two or more different first solvents having either a boiling point of at least 200° C. or a vapor pressure of 1 torr at 25° C. or lower, a molecule of said first solvents having one selected from the group consisting of an aromatic ring and an oxygen atom; an aliphatic ring and an oxygen atom; and an aromatic ring, and aliphatic ring and an oxygen atom;

wherein one first solvent has a higher evaporability than another first solvent which has a lower evaporability and either a higher boiling point or a lower vapor pressure at 25° C.; and

a ratio W a /W b of 1 to 2.5 where W a is the weight proportion of the first solvent having a higher evaporability and W b is the weight proportion of the first solvent having a lower evaporability; and

the amount of the first solvent contained in the composition is 3 wt % or more.

2. The film-forming composition according to claim 1 , wherein the liquid consists essentially of the first solvents only.

3. The film-forming composition according to claim 1 , wherein the liquid contains the first solvents and a second solvent which is not classified into the same type as the first solvents, a molecule of said second solvent having one selected from the group consisting of an aromatic ring and an oxygen atom; an aliphatic ring and an oxygen atom; and an aromatic ring, an aliphatic ring and an oxygen atom; and a ratio W 2 /W 1 , where W 2 is the weight proportion of the second solvent and W 1 is the weight proportion of the first solvent, is 1 to 20.

4. The film-forming composition according to claim 3 , wherein the ratio W 2 /W 1 is 1 to 2.5.

5. The film-forming composition according to claim 1 , wherein the first solvents are aromatic esters.

6. The film-forming composition according to claim 1 , wherein the first solvents comprise a benzoate.

7. The film-forming composition according to claim 1 , wherein the first solvents comprise ethyl benzoate.

8. The film-forming composition according to claim 1 , wherein the one first solvent having a higher evaporability is a benzoate, and the other first solvent having a lower evaporability is an acetate having an aromatic ring.

9. The film-forming composition according to claim 8 , wherein the benzoate is ethyl benzoate, and the acetate having an aromatic ring is 2-phenoxyethyl acetate.

10. The film-forming composition according to claim 1 , wherein the hole-injecting/transporting material is an aromatic amine compound, and the electron-accepting compound is an aromatic boron compound and/or its salt.

11. The film-forming composition according to claim 1 , wherein moisture contained in the composition is 1 wt % or less.

12. The film-forming composition according to claim 1 , comprising a hole-injecting/transporting material which is a polymeric compound having intramolecular hole-transporting sites.

13. The film-forming composition according to claim 12 , wherein the polymeric compound is polymeric aromatic amine containing tertiary aromatic amino groups as a constitutional unit of its backbone.

14. The film-forming composition according to claim 13 , wherein the polymeric compound has the structure shown in Formula (I) as a constitutional unit:

wherein the groups Ar 11 to Ar 14 represent divalent aromatic ring groups, each of which may have a substituent independently chosen, the groups R 11 and R 12 represent monovalent aromatic ring groups, each of which may have a substituent independently chosen, and X represents a direct bond or a binding group selected from the following groups:

wherein the aromatic ring groups include both groups derived from aromatic hydrocarbon ring and groups derived from aromatic heterocyclic groups.

15. The film-forming composition according to claim 14 , wherein the structure shown in Formula (I) is one of (I-1), (I-2), (I-3) and (I-4) below

16. The film-forming composition according to claim 15 , wherein the structure shown in Formula (I) is (I-3).

17. The film-forming composition according to claim 1 , wherein the amount of the hole-injecting/transporting material contained in the film-forming composition is 0.05 to 50 wt %.

18. The film-forming composition according to claim 10 , wherein the aromatic boron compound and/or its salt is of formula (D-30) below

19. The film-forming composition according to claim 1 , wherein a ratio W e /W p , where W e is the weight proportion of the electron-accepting compound relative to the film-forming composition and W p is the weight proportion of the hole-injecting/transporting material relative to the film-forming composition, is 0.001 to 1.

20. The film-forming composition according to claim 3 , wherein the second solvent is at least one of

aromatic ester having a boiling point less than 200° C. and a vapor pressure higher than 1 torr at 25° C.;

aromatic ether;

alicyclic ketone; and

alicyclic alcohol.

21. The film-forming composition according to claim 3 , wherein the second solvent is at least one of anisole and cyclohexanone.

22. An organic electroluminescent device, which is an organic electroluminescent device having a hole-injecting/transporting layer, wherein the hole-injecting/transporting layer is formed of the film-forming composition according to claim 1 .

23. The film-forming composition according to claim 1 , wherein the liquid consists of a first aromatic ester and a second aromatic ester.

24. The film-forming composition according to claim 1 , wherein the liquid consists of ethylbenzoate and 2-phenoxyethyl acetate.

25. The film-forming composition according to claim 1 , wherein the ratio W a /W b is 1 to 2.

26. The film-forming composition according to claim 1 , which does not contain either anisole or cyclohexanone.