Hole-blocking materials for organic light emitting diodes

1. An organic light emitting device comprising:

an emissive layer comprising a blue phosphorescent emitter;

an electron transport layer; and

a hole blocking layer between the emissive layer and the electron transport layer, wherein the hole blocking layer comprises a palladium complex represented by Formula I or Formula II:

wherein:

each of R 1 , R 2 , R 3 , R 4 , and R 5 independently represents halogen, hydroxyl, nitro, cyanide, thiol, or substituted or unsubstituted C 1 -C 4 alkyl, alkoxy, amino, or aryl;

each n is independently an integer as limited by valency;

each of Y 1a , Y 1b , Y 1c , Y 1d , Y 1e , Y 1f , Y 2a , Y 2b , Y 2c , Y 2d , Y 2e , Y 2f , Y 3a , Y 3b , Y 3c , Y 3d , Y 3e , Y 3f , Y 4a , Y 4b , Y 4c , Y 4d , Y 4e , Y 4f , Y 5a , Y 5b , Y 5c , Y 5d , and Y 5e independently represents C, N, Si, O, or S;

Y 1a , Y 1b , Y 1c , Y 1d , Y 1e , and Y 1f form aryl or heteroaryl group Ar 3 ;

Y 2a , Y 2b , Y 2c , Y 2d , Y 2e , and Y 2f form aryl or heteroaryl group Ar 4 ;

Y 3 a, Y 3 b, Y 3 c, Y 3 d, Y 3 e, and Y 3 f form aryl or heteroaryl group Ar 2 ;

Y 4 a, Y 4 b, Y 4 c, Y 4 d, Y 4 e, and Y 4 f form aryl or heteroaryl group Ar 1 ;

Y 5 a, Y 5b , Y 5 c, Y 5d , and Y 5 e, form at least a part of aryl or heteroaryl group Ar 5 ;

each of X 1 and X 2 independently represents NR, PR, CRR′, SiRR′, CRR′, SiRR′, O, S, S═O, O=S═O, Se, Se═O, or O=Se═O, where each of R and R′ independently represents hydrogen, halogen, hydroxyl, nitro, cyanide, thiol, or optionally substituted C 1 -C 4 alkyl, alkoxy, amino, or aryl; and

each of L 1 , L 2 , and L 3 is present or absent, with at least one of L 1 and L 2 present, and each L 1 , L 2 , and L 3 present independently represents a linking atom or group optionally substituted, valency permitting, with one or more of alkyl, alkoxy, alkenyl, alkynyl, hydroxy, amine, amide, thiol, aryl, heteroaryl, cycloalkyl, and heterocyclyl moieties;

wherein:

each of R 1 , R 3 , R 4 , and R 5 independently represents halogen, hydroxyl, nitro, cyanide, thiol, or substituted or unsubstituted C 1 -C 4 alkyl, alkoxy, amino, or aryl;

each n is independently an integer as limited by valency;

each of Y 1a , Y 1b , Y 1c , Y 1d , Y 1e , Y 1f , Y 2 a, Y 2 b, Y 2 c, Y 2 d, Y 2 e, Y 2 f, Y 4 a, Y 4 b, Y 4 c, Y 4 d, Y 4 e, Y 5a , Y 5b , Y 5 e, Y 5a , and Y 5e independently represents one of C, N, Si, O, and S;

Y 1a , Y 1b , Y 1c , Y 1d , Y 1e , and Y 1f form aryl or heteroaryl group Ar 3 ;

Y 2a , Y 2 b, Y 2 c, Y 2 d, Y 2 e, and Y 2f form aryl or heteroaryl group Ar 4 ;

Y 4 a Y 4b , Y 4 c Y 4d , and Y 4 e form at least a part of aryl or heteroaryl group Ar 1 ;

Y 5a , Y 5b , Y 5c , Y 5 d, and Y 5e form at least a part of aryl or heteroaryl group Ar 5 ;

X 2 represents NR, PR, CRR′, SiRR′, CRR′, SiRR′, O, S, S═O, O=S═O, Se, Se═O, O=Se═O, where each of R and R′ independently represents hydrogen, halogen, hydroxyl, nitro, cyanide, thiol, or optionally substituted C 1 -C 4 alkyl, alkoxy, amino, or aryl; and

each of L 1 and L 3 is independently present or absent, and each L 1 and L 3 present independently represents a linking atom or group optionally substituted, valency permitting, with one or more of alkyl, alkoxy, alkenyl, alkynyl, hydroxy, amine, amide, thiol, aryl, heteroaryl, cycloalkyl, and heterocyclyl moieties.

2. The organic light emitting device of claim 1 , wherein one or more of Ar 1 , Ar 2 , Ar 3 , Ar 4 , and Ar 5 is independently a substituted or unsubstituted phenyl, pyridinyl, diazinyl, triazinyl, pyrazolyl, triazolyl, methyl-imidazolyl, furanyl, or thiophenyl group.

3. The organic light emitting device of claim 1 , wherein the palladium complex comprises at least one of Pd3O3 (palladium (II) 2-(3-(3-(pyridin-2-yl)phenoxy)phenyl)pyridine), Pd3O3-dtb (palladium (II) 2-(3-(3-(pyridin-2-yl)phenoxy)phenyl)-t-butylpyridine), Pd3O3-tbu (palladium (II) 2-(3-(3-(t-butylpyridin-2-yl)phenoxy)phenyl)-t-butylpyridine), and PdON3 (palladium (II) 2-(3-(3-(pyridin-2-yl)phenoxy)carbazolyl)pyridine).

4. The organic light emitting device of claim 1 , wherein the hole blocking layer comprises a neat film of the palladium complex.

5. The organic light emitting device of claim 1 , wherein the hole blocking layer comprises a doped film comprising the palladium complex and a host material.

6. The organic light emitting device of claim 5 , wherein a concentration of the palladium complex in the host material is at least 5 wt %.

7. The organic light emitting device of claim 6 , wherein the concentration of the palladium complex in the host material is less than 50 wt %.

8. The organic light emitting device of claim 7 , wherein the concentration of the palladium complex in the host material is less than 25 wt %.

9. The organic light emitting device of claim 5 , wherein the host material comprises a carbazole-based host having one to three carbazole skeletons.

10. The organic light emitting device of claim 9 , wherein the carbazole-based host is represented by one of Formulas 1-3:

wherein each of R 1 -R 9 independently represents halogen, hydroxyl, nitro, cyanide, thiol, or optionally substituted alkyl, alkenyl, alkynyl, aryl, heteroaryl, cycloalkane, cycloalkane, heterocyclyl, amino, alkoxy, haloalkyl, arylalkane, or arylalkene.

11. The organic light emitting device of claim 10 , wherein the carbazole-based host comprises tris-PCz (9,9′,9″-triphenyl-9H,9′H,9″H-3,3′:6′3″-tercarbazole), CBP (4,4-di(9H-carbazol-9-yl) biphenyl), mCBP (3,3-di(9H-carbazol-9-yl) biphenyl), mCP (meta-di(carbazolyl) phenyl), or a combination thereof.

12. The organic light emitting device of claim 1 , wherein the blue phosphorescent emitter comprises platinum (II) 9-(pyridin-2-yl)-2-(9-(pyridin-2-yl)-9H-carbazol-2-yloxy)-9H-carbazole.

13. The organic light emitting device of claim 1 , wherein the emissive layer comprises two or more doped films comprising the blue phosphorescent emitter, each doped film having a different concentration of the blue phosphorescent emitter.

14. The organic light emitting device of claim 13 , wherein the emissive layer comprises a first doped film comprising the blue phosphorescent emitter and a second doped film comprising the blue phosphorescent emitter.

15. The organic light emitting device of claim 14 , wherein a concentration of the blue phosphorescent emitter in the first doped film is in a range of 15 wt % to 25 wt % and a concentration of the blue phosphorescent emitter in the second doped film is in a range of 5 wt % to 15 wt %.

16. The organic light emitting device of claim 14 , wherein the emissive layer further comprises a third doped film comprising the blue phosphorescent emitter.

17. The organic light emitting device of claim 16 , wherein a concentration of the blue phosphorescent emitter in the third doped film is in a range of 5 wt % to 10 wt %.