Organic electroluminescent device emitting green light

1. An organic electroluminescent device comprising a light-emitting layer B comprising:

(i) a host material H P , which has a lowermost excited singlet state energy level S1 P and a lowermost excited triplet state energy level T1 P , a highest occupied molecular orbital HOMO(H P ) having an energy E HOMO (H P ) and a lowest unoccupied molecular orbital LUMO(H P ) having an energy E LUMO (H P );

(ii) a phosphorescence material E B , which has a lowermost excited singlet state energy level S1 E and a lowermost excited triplet state energy level T1 E , a highest occupied molecular orbital HOMO(E E ) having an energy E HOMO (E E ) and a lowest unoccupied molecular orbital LUMO(E E ) having an energy E LUMO (E E ); and

(iii) a small full width at half maximum (FWHM) emitter S B , which has a lowermost excited singlet state energy level S1 S and a lowermost excited triplet state energy level T1 S , a highest occupied molecular orbital HOMO(E S ) having an energy E HOMO (E S ) and a lowest unoccupied molecular orbital LUMO(E S ) having an energy E LUMO (E S ),

wherein E B transfers energy to S B and S B emits light with an emission maximum between 500 nm to 560 nm,

and wherein the relations expressed by the following formulas (1) to (4) apply:

T 1 E >S 1 S   (1)

T 1 P >T 1 S   (2)

T 1 P >T 1 E   (3)

T 1 P >S 1 E   (4).

2. The organic electroluminescent device according to claim 1 , wherein the small FWHM emitter S B is characterized in that it has an emission spectrum, which exhibits a full width at half maximum (FWHM) of less than or equal to 0.25 eV.

3. The organic electroluminescent device according to claim 1 , wherein the device exhibits an emission maximum λ max (D) of 500 nm to 560 nm.

4. The organic electroluminescent device according to claim 1 , wherein the small FWHM emitter S B emits light with an emission maximum between 510 nm to 550 nm.

5. The organic electroluminescent device according to claim 1 , wherein the device exhibits an emission maximum λ max (D) of 510 nm to 550 nm.

6. The organic electroluminescent device according to claim 1 , wherein the light-emitting layer B additionally comprises

(iv) a host material H N , which has a lowermost excited singlet state energy level S1 N , a lowermost excited triplet state energy level T1 N , a highest occupied molecular orbital HOMO(H N ) having an energy E HOMO (H N ) and a lowest unoccupied molecular orbital LUMO(H N ) having an energy E LUMO (H N );

wherein the relations expressed by the following formulas (2N), (3N), and (4N) apply:

T 1 N >T 1 S   (2N)

T 1 N >T 1 E   (3N)

T 1 N >S 1 E   (4N),

and wherein the relations expressed by the following formulas (5) to (11) apply:

E LUMO ( H P )> E LUMO ( S B )  (5)

E LUMO ( H P )> E LUMO ( E B )  (6)

E HOMO ( H P )< E HOMO ( E B )  (7)

E LUMO ( H N )< E LUMO ( S B )  (8)

E HOMO ( H N )< E HOMO ( S B )  (9)

E LUMO ( H N )< E LUMO ( E B )  (10)

E HOMO ( H N )< E HOMO ( E B )  (11).

7. The organic electroluminescent device according to claim 1 , wherein the small FWHM emitter S B is selected from the group consisting of a fluorescent emitter and a thermally activated delayed fluorescence (TADF) emitter.

8. The organic electroluminescent device according to claim 1 , wherein the small FWHM emitter S B is a boron-based material.

9. The organic electroluminescent device according to claim 1 , wherein the small FWHM emitter S B is characterized in that it has a ΔE ST value, which corresponds to the energy difference between S1 S and T1 S , of less than 0.4 eV.

10. The organic electroluminescent device according to claim 1 , wherein the phosphorescence material E B comprises or consists of a structure of formula I,

wherein

M is selected from the group consisting of Ir, Pt, Au, Eu, Ru, Re, Ag, and Cu;

n is an integer of 1 to 3,

X and Y are each independently a bidentate monoanionic ligand.

11. The organic electroluminescent device according to claim 1 , wherein the light-emitting layer B comprises:

(i) 22-70% by weight of the host compound H P ;

(ii) 0-70% by weight of the host compound H N ;

(iii) 5-10% by weight of the phosphorescence material E B ; and

(iv) 1-5% by weight of the emitter S B ; and optionally

(v) 0-72% by weight of one or more solvents.

12. The organic electroluminescent device according to claim 1 , wherein the light-emitting layer B comprises:

(i) 10-30% by weight of the host compound H P ;

(ii) 40-74% by weight of the host compound H N ;

(iii) 15-30% by weight of the phosphorescence material E B ; and

(iv) 1-5% by weight of the emitter S B ; and optionally

(v) 0-34% by weight of one or more solvents.

13. A method for generating green light at a wavelength of from 500 to 560 nm, comprising the steps of:

(i) providing an organic electroluminescent device according to claim 1 ; and

(ii) applying an electrical current to said organic electroluminescent device.