An organic electroluminescent device comprising a first electrode formed on a substrate, an organic light emitting layer formed on the first electrode, and a second electrode facing the first electrode formed on the organic layer; wherein the organic layer comprises a hole injection layer, a hole transport layer formed on the hole injection layer, a light-emitting layer formed on the hole transport layer, an electron buffer layer formed on the light-emitting layer, and an electron transport zone formed on the electron buffer layer; wherein the electron transport zone comprises an electron transport layer formed on the electron buffer layer, and an electron injection layer formed on the electron transport layer; wherein the electron buffer layer comprises a compound comprising a nitrogen-containing heteroaryl selected from the compounds represented by the following formulae 1 to 3: H-(Cz-L 1) a -M ----------- H-(Cz) b -L 1 -M ----------- wherein Cz represents the following structure: A represents B represents C represents R 1 to R 5 each independently represent hydrogen, deuterium, a halogen, a substituted or unsubstituted (C1-C30)alkyl, a substituted or unsubstituted (C6-C30)aryl, a substituted or unsubstituted (5- to 30-membered)heteroaryl, or -SiR 6 R 7 R 8; or R 1 to R 5 each independently are linked to an adjacent substituent(s) to form a mono- or polycyclic, substituted or unsubstituted (C3-C30) alicyclic or aromatic ring, whose carbon atom(s) may be replaced with at least one hetero atom selected from nitrogen, oxygen, and sulfur; R 6 to R 8 each independently represent a substituted or unsubstituted (C1-C30) alkyl, or a substituted or unsubstituted (C6-C30) aryl; L 1 represents a single bond, a substituted or unsubstituted (C6-C30) arylene, or a substituted or unsubstituted (5- to 30-membered) heteroarylene; M represents a substituted or unsubstituted (C6-C30) aryl, or a substituted or unsubstituted (5- to 30-membered)heteroaryl; Cz, L 1, and M may be fused to an adjacent substituent(s) to form a ring; X 1 to X 3 each independently represent -N(Rg)- or -C(R 10)(R 11)-; Y represents -O-, -S-, -C(R 12)(R 13)-, -Si(R 14)(R 15)-, or -N(R 16)-; R 9 to R 16 each independently represent hydrogen, deuterium, a halogen, a substituted or unsubstituted (C1-C30)alkyl, a substituted or unsubstituted (C6-C30)aryl, a substituted or unsubstituted (5- to 30-membered)heteroaryl, a substituted or unsubstituted (5- to 7-membered) heterocycloalkyl, or a (5- to 7-membered) heterocycloalkyl fused with at least one substituted or unsubstituted aromatic ring, and Rg to R 16 may be the same or different; and R 10 and R 11 may be linked to each other to form a mono- or polycyclic, substituted or unsubstituted (C3-C30) alicyclic or aromatic ring, whose carbon atom(s) may be replaced with at least one hetero atom selected from nitrogen, oxygen, and sulfur; a, b, and d each independently represent an integer of 1 to 3; c, e, and g each independently represent an integer of 1 to 4; f represents 1 or 2; and where a, b, c, d, e, f, or g is an integer of 2 or more, each of (Cz-Li), each of (Cz), each of R 1, each of R 2, each of R 3, each of R 4, or each of R 5 may be the same or different. Cz represents the following structure: A represents B represents C represents R 1 to R 5 each independently represent hydrogen, deuterium, a halogen, a substituted or unsubstituted (C1-C30)alkyl, a substituted or unsubstituted (C6-C30)aryl, a substituted or unsubstituted (5- to 30-membered)heteroaryl, or -SiR 6 R 7 R 8; or R 1 to R 5 each independently are linked to an adjacent substituent(s) to form a mono- or polycyclic, substituted or unsubstituted (C3-C30) alicyclic or aromatic ring, whose carbon atom(s) may be replaced with at least one hetero atom selected from nitrogen, oxygen, and sulfur; R 6 to R 8 each independently represent a substituted or unsubstituted (C1-C30) alkyl, or a substituted or unsubstituted (C6-C30) aryl; L 1 represents a single bond, a substituted or unsubstituted (C6-C30) arylene, or a substituted or unsubstituted (5- to 30-membered) heteroarylene; M represents a substituted or unsubstituted (C6-C30) aryl, or a substituted or unsubstituted (5- to 30-membered)heteroaryl; Cz, L 1, and M may be fused to an adjacent substituent(s) to form a ring; X 1 to X 3 each independently represent -N(Rg)- or -C(R 10)(R 11)-; Y represents -O-, -S-, -C(R 12)(R 13)-, -Si(R 14)(R 15)-, or -N(R 16)-; R 9 to R 16 each independently represent hydrogen, deuterium, a halogen, a substituted or unsubstituted (C1-C30)alkyl, a substituted or unsubstituted (C6-C30)aryl, a substituted or unsubstituted (5- to 30-membered)heteroaryl, a substituted or unsubstituted (5- to 7-membered) heterocycloalkyl, or a (5- to 7-membered) heterocycloalkyl fused with at least one substituted or unsubstituted aromatic ring, and Rg to R 16 may be the same or different; and R 10 and R 11 may be linked to each other to form a mono- or polycyclic, substituted or unsubstituted (C3-C30) alicyclic or aromatic ring, whose carbon atom(s) may be replaced with at least one hetero atom selected from nitrogen, oxygen, and sulfur; a, b, and d each independently represent an integer of 1 to 3; c, e, and g each independently represent an integer of 1 to 4; f represents 1 or 2; and where a, b, c, d, e, f, or g is an integer of 2 or more, each of (Cz-Li), each of (Cz), each of R 1, each of R 2, each of R 3, each of R 4, or each of R 5 may be the same or different.