Organic electroluminescent device comprising an electron buffer layer and an electron transport layer

1. An organic electroluminescent device comprising a first electrode, a second electrode facing the first electrode, a light-emitting layer between the first electrode and the second electrode, and an electron transport layer and an electron buffer layer between the light-emitting layer and the second electrode, wherein the electron buffer layer comprises a compound represented by any one of the following formulae 5 to 8, and the electron transport layer comprises a compound represented by the following formula 2:

wherein

Y 1 represents N or CR 13 ;

Ar 1 and Ar 2 , Ar 5 to Ar 9 , and Ar 13 to A 19 , each independently represent hydrogen, deuterium, a halogen, a cyano, a substituted or unsubstituted (C1-C30)alkyl, a substituted or unsubstituted (C6-C50)aryl, a substituted or unsubstituted (3- to 50-membered)heteroaryl, a substituted or unsubstituted (C3-C30)cycloalkyl, a substituted or unsubstituted (C1-C30)alkoxy, a substituted or unsubstituted tri(C1-C30)alkylsilyl, a substituted or unsubstituted di(C1-C30)alkyl(C6-C30)arylsilyl, a substituted or unsubstituted (C1-C30)alkyldi(C6-C30)arylsilyl, a substituted or unsubstituted tri(C6-C30)arylsilyl, a substituted or unsubstituted mono- or di-(C1-C30)alkylamino, a substituted or unsubstituted mono- or di-(C6-C30)arylamino, or a substituted or unsubstituted (C1-C30)alkyl(C6-C30)arylamino, or may be linked to an adjacent substituent to form a substituted or unsubstituted, mono- or polycyclic, (C3-C30) alicyclic, aromatic, or a combination of alicyclic and aromatic ring, whose carbon atom(s) may be replaced with at least one heteroatom selected from nitrogen, oxygen, and sulfur;

L represents a single bond, a substituted or unsubstituted (C6-C50)arylene, or a substituted or unsubstituted (5- to 50-membered)heteroarylene; and

X represents CRaRb, NRc, O, or S, wherein Ra, Rb, and Rc are each independently identical to the definition of Ar 1 ;

K represents CRd or N, wherein Rd is identical to the definition of Ar 1 ;

M represents O or S;

A 1 represents —N═, —NR 7 —, —O—, or —S—;

B 1 represents —N═, —NR 8 —, —O—, or —S—, with a proviso that B 1 is —NR 8 —, —O—, or —S— when A 1 is —N═, and B 1 is —N═, —O—, or —S— when A 1 is —NR 7 —;

R 1 represents a substituted or unsubstituted (C6-C30)aryl wherein the substituents of the (C6-30)aryl are at least one selected from the group consisting of deuterium, a (C1-30)alkyl, a (C6-30)aryl(C1-C30)alkyl and a (C1-C30)alkyl(C6-30)aryl;

R 2 to R 4 , R 7 , and R 8 each independently represent hydrogen, deuterium, a halogen, a cyano, a substituted or unsubstituted (C1-C30)alkyl, a substituted or unsubstituted (C6-C30)aryl, a substituted or unsubstituted (3- to 30-membered)heteroaryl, a substituted or unsubstituted (C3-C30)cycloalkyl, a substituted or unsubstituted (C1-C30)alkoxy, a substituted or unsubstituted tri(C1-C30)alkylsilyl, a substituted or unsubstituted di(C1-C30)alkyl(C6-C30)arylsilyl, a substituted or unsubstituted (C1-C30)alkyldi(C6-C30)arylsilyl, a substituted or unsubstituted tri(C6-C30)arylsilyl, a substituted or unsubstituted mono- or di-(C1-C30)alkylamino, a substituted or unsubstituted mono- or di-(C6-C30)arylamino, or a substituted or unsubstituted (C1-C30)alkyl(C6-C30)arylamino, or may be linked to an adjacent substituent to form a substituted or unsubstituted, mono- or polycyclic, (C3-C30) alicyclic, aromatic, or a combination of alicyclic and aromatic ring, whose carbon atom(s) may be replaced with at least one heteroatom selected from nitrogen, oxygen, and sulfur;

h, i, and p each independently represent an integer of 1 to 4, q and q each independently represent an integer of 1 to 3, and n, o, r, and s each independently represent 1 or 2;

a represents 1, b and c each independently represent 1 or 2, and d represents an integer of 1 to 4; and

the heteroaryl(ene) contains at least one heteroatom selected from B, N, O, S, Si, and P.

2. The organic electroluminescent device according to claim 1 , wherein the compound represented by any one of formulae 5 to 8 is selected from the group consisting of:

3. The organic electroluminescent device according to claim 1 , wherein the compound represented by formula 2 is selected from the group consisting of:

4. The organic electroluminescent device according to claim 1 , wherein the light-emitting layer comprises a host compound and a dopant compound, the LUMO (lowest unoccupied molecular orbital) energy level of the electron buffer layer is higher than the LUMO energy level of the host compound, and the LUMO energy level of the electron transport layer is higher or lower than the LUMO energy level of the electron buffer layer.

5. The organic electroluminescent device according to claim 1 , wherein the LUMO energy level of the light-emitting layer (Ah), the LUMO energy level of the electron buffer layer (Ab), and the LUMO energy level of the electron transport layer (Ae) satisfy the following equations (1) and (2):

| Ae−Ab|≤ 0.3 eV  (1)

| Ab−Ah|≤ 0.4 eV  (2).

6. The organic electroluminescent device according to claim 1 , wherein the LUMO energy level of the electron buffer layer (Ab) and the LUMO energy level of the electron transport layer (Ae) satisfy the following equation (3), equation (4), or both of them:

Ae≤Ab+ 0.2 eV  (3)

Ab≤Ae+ 0.2 eV  (4).

7. The organic electroluminescent device according to claim 1 , wherein the electron transport layer further comprises a reductive dopant.