Co-host material, light emitting layer composition, and light emitting device

1. A co-host material comprising:

a first compound represented by formula I of

wherein X is selected from carbon and silicon; each R 1 is independently selected from any of hydrogen, carbazole, dibenzocarbazole, dibenzofuran and dibenzothiophene, and at least one of R 1 is carbazole connected to a benzene ring through a nitrogen atom in the carbazole; each R 2 is independently selected from the group consisting of hydrogen, substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C6-C30 arylene, and substituted or unsubstituted C3-C30 heteroarylene; and in the case of substitution, at least one hydrogen of the C1-C12 alkyl, the C6-C30 arylene, and the C3-C30 heteroarylene is substituted with at least one selected from the group consisting of halogen atom, hydroxyl group, amino group, aryl group, ester group, thiol group, cyano group, and nitro group, and/or at least one methylene is substituted with at least one selected from the group consisting of oxygen atom, imino group, sulfone group, carbonyl group, arylene, —C(═O)O—, sulfur atom, and nitroso group; and

a second compound represented by formula II of

wherein each Y is independently selected from carbon and nitrogen, and at least one of Y is nitrogen; each Ar is independently selected from C6-C30 arylene and a single bond, wherein the single bond means that R is directly connected to a benzene ring through the single bond; each R is independently selected from at least one in the group consisting of halogen, halogen-substituted C1-C6 alkyl, sulfonyl group, carbonyl group, thiol group, cyano group and nitro group, and at least one of R is halogen or halogen-substituted C1-C6 alkyl, wherein C6-C30 arylene is optionally substituted by at least one selected from the group consisting of halogen atom, halogen-substituted C1-C6 alkyl, hydroxyl group, amino group, aryl group, ester group, thiol group, cyano group and nitro group.

2. The co-host material of claim 1 , wherein at least one of Ar is phenyl or naphthyl, and at least one of R is trifluoromethyl or cyano group.

3. The co-host material of claim 1 , wherein each R 2 is independently selected from H or C1-C4 alkyl.

4. The co-host material of claim 1 , wherein the co-host material satisfies energy level relationship of:

|HOMO 1 −HOMO 2 |>0.3 eV;

|LUMO 1 −LUMO 2 |>0.2 eV;

|HOMO 1 −LUMO 2 |>3.5 eV, or |HOMO 2 −LUMO 1 |>3.5 eV;

ΔEst>0.3 eV;

T 11 >2.65 eV, and T 12 >2.65 eV;

wherein, | | represents an absolute value, HOMO 1 is the highest occupied molecular orbital level of the first compound, HOMO 2 is the highest occupied molecular orbital level of the second compound, LUMO 1 is the lowest unoccupied molecular orbital level of the first compound, LUMO 2 is the lowest unoccupied molecular orbital level of the second compound, Δ Est is a difference between the triplet excited state energy and the singlet excited state energy of the co-host material, T 11 is the triplet excited state energy of the first compound, and T 12 is the triplet excited state energy of the second compound.

5. The co-host material of claim 1 , wherein

in the co-host material, the first compound is present in a mass percentage of 40% to 60%, and the second compound is present in a mass percentage of 40% to 60%.

6. The co-host material of claim 1 , wherein

in the co-host material, the first compound is present in a mass percentage of 48% to 52%, and the second compound is present in a mass percentage of 48% to 52%.

7. The co-host material of claim 1 , wherein the first compound is at least one selected from in the group consisting of:

8. The co-host material of claim 1 , wherein the second compound is at least one selected from in the group consisting of:

9. The co-host material of claim 1 , wherein the co-host material is not an exciplex.

10. A composition for forming a light emitting layer, comprising:

the co-host material according to claim 1 ; and

a thermally activated delayed fluorescent material doped in the co-host material.

11. The composition of claim 10 , wherein

in the composition, the thermally activated delayed fluorescent material is present in a mass percentage of 0.5% to 40%; and the co-host material is present in a mass percentage of 60% to 99.5%.

12. The composition of claim 10 , wherein

in the composition, the thermally activated delayed fluorescent material is present in mass percentage of 1% to 10%; and the co-host material 1 is present in a mass percentage of 90% to 99%.

13. The composition of claim 10 , wherein the thermally activated delayed fluorescent material is at least one selected from the group consisting of a backbone polymeric thermally activated delayed fluorescent polymer, a side chain thermally activated delayed fluorescent polymer, and a dendritic thermally activated delayed fluorescent compound.

14. The composition of claim 10 , wherein the thermally activated delayed fluorescent material comprises compound of:

15. The composition of claim 10 , wherein the co-host material is not an exciplex.

16. A light emitting device, comprising:

a light emitting layer formed from the composition of claim 10 ; and

an anode and a cathode disposed on two sides of the light emitting layer respectively.

17. The light emitting device of claim 16 , further comprising:

a hole injection layer disposed between the anode and the light emitting layer;

a hole transport layer disposed between the hole injection layer and the light emitting layer;

an electron injection layer disposed between the cathode and the light emitting layer; and

an electron transport layer disposed between the electron injection layer and the light emitting layer.

18. The light emitting device of claim 16 , wherein the light emitting layer has a thickness of 10 nm to 100 nm.

19. The light emitting device of claim 16 , wherein the light emitting device is a red light emitting device, a green light emitting device or a blue light emitting device.

20. The light emitting device of claim 16 , wherein the thermally activated delayed fluorescent material comprises compound of: