Organic electroluminescent device

1. An organic electroluminescent device, comprising a light-emitting layer including a host material and guest material,

the host material is an exciplex formed by electron donor material and electron receptor material,

the guest material is thermal activated delayed fluorescent material,

the singlet energy level (S 1 ) of the host material is lower than the singlet energy level (S 1 ) of the guest material.

2. The organic electroluminescent device of claim 1 , wherein, an energy level difference between the singlet energy level (S 1 ) of the guest material and the singlet energy level (S 1 ) of the host material is less than 0.3 eV.

3. The organic electroluminescent device of claim 1 , wherein, an energy level difference between the singlet energy level (S 1 ) of the host material and a triplet energy level of the host material is less than 0.15 eV.

4. The organic electroluminescent device of claim 1 , wherein, an energy level difference between the singlet energy level (S 1 ) of the guest material and a triplet energy level of the guest material is less than 0.3 eV.

5. The organic electroluminescent device of claim 1 , wherein, the electron donor material has the singlet energy level (S 1 ) higher than the singlet energy level (S 1 ) of the guest material, and/or the electron receptor material has the singlet energy level (S 1 ) higher than the singlet energy level (S 1 ) of the guest material.

6. The organic electroluminescent device of claim 1 , wherein, the electron donor material and the electron receptor material have a mass ratio of 1:9 to 9:1.

7. The organic electroluminescent device of claim 6 , wherein, the electron donor material and the electron receptor material have a mass ratio of 1:5 to 5:1.

8. The organic electroluminescent device of claim 7 , wherein, the electron donor material and the electron receptor material have a mass ratio of 1:1.

9. The organic electroluminescent device of claim 1 , wherein, the electron donor material is a compound having a hole transport function, the electron donor material contains at least one of the following groups:

a carbazolyl group, an aromatic amine group, a phenyl group, a fluorene group, a silane group; and a polycyclic group, a bicyclic group or a spirocyclic group formed by any of the groups above.

10. The organic electroluminescent device of claim 9 , wherein, the electron donor material has a compound structure selected from any one of the following structural formulas:

11. The organic electroluminescent device of claim 1 , wherein, the electron receptor material is a compound having an electron transport function, the electron receptor material contains at least one of the following groups:

a pyridyl group, a pyrimidine group, a pyrazole group, an imidazolyl group, a pyrrole group, an oxazolyl group, a triazine group, a pyrazinyl group, a pyridazine group, a carbazole group, a cyan group, a phenyl group, a dibenzothiophene group, a phenyl phosphonyl group, a phenyl sulphone group; and a polycyclic group, a bicyclic group or a spirocyclic group formed by any of the groups above.

12. The organic electroluminescent device of claim 11 , wherein, the electron receptor material has a compound structure selected from any one of the following structural formulas:

13. The organic electroluminescent device of claim 1 , wherein, the thermal activated delayed fluorescent material has a compound structure selected from any one of the following structural formulas:

14. The organic electroluminescent device of claim 1 , wherein, the guest material has a doping ratio of 0.1 wt %-50 wt %.

15. The organic electroluminescent device of claim 14 , wherein, the guest material has a doping ratio of 1 wt %-20 wt %.

16. The organic electroluminescent device of claim 15 , wherein, the guest material has a doping ratio of 10 wt %.

17. The organic electroluminescent device of claim 15 , further comprising:

a first electrode, made of indium tin oxide;

a hole injection layer, made of 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazobenzophenanthrene;

a hole transport layer, made of N,N′-(di-1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine;

an electron transport layer, made of 9,10-di-(3-(3-pyridine)-phenyl)-anthracene and quinoline lithium in equal mass ratio;

an electron injection layer, made of lithium fluoride;

a second electrode, made of metal aluminum.

18. The organic electroluminescent device of claim 1 , wherein the electron donor material has a compound structure of:

the electron receptor material has a compound structure of:

the thermal activated delayed fluorescent material has a compound structure of:

wherein the exciplex is formed by mixing the electron donor material and the electron receptor material in a mass ratio of 1:1, and the thermal activated delayed fluorescent material has a doping ratio of 10 wt %.

19. The organic electroluminescent device of claim 1 , wherein the electron donor material has a compound structure of:

the electron receptor material has a compound structure of:

the thermal activated delayed fluorescent material has a compound structure of:

wherein the exciplex is formed by mixing the electron donor material and the electron receptor material in a mass ratio of 7:3, and the thermal activated delayed fluorescent material has a doping ratio of 10 wt %.

20. The organic electroluminescent device of claim 1 , wherein the electron donor material has a compound structure of:

the electron receptor material has a compound structure of:

the thermal activated delayed fluorescent material has a compound structure of:

wherein the exciplex is formed by mixing the electron donor material and the electron receptor material in a mass ratio of 1:1, and the thermal activated delayed fluorescent material has a doping ratio of 20 wt %.