Organic electroluminescent element

1 . An organic electroluminescent element comprising at least one organic compound layer between a pair of electrodes, wherein the at least one organic compound layer includes at least one luminescent layer, the luminescent layer comprises at least one luminescent dopant and plural host compounds, and the main peak in an emission spectrum of a single-layer film comprising only the plural host compounds prepared under the same film-forming conditions under which the luminescent layer is prepared has a wavelength that is at least 15 nm longer than the main peak wavelength of an emission spectrum of each of the plural host compounds.

2 . The organic electroluminescent element according to claim 1 , wherein at least one of the plural host compounds contained in the luminescent layer is a compound having an electron affinity Ea of 2.8 eV or more.

3 . The organic electroluminescent element according to claim 1 , wherein at least one of the plural host compounds contained in the luminescent layer is a compound having an ionization potential Ip of 5.4 eV or less.

4 . The organic electroluminescent element according to claim 3 , wherein at least one of the plural host compounds contained in the luminescent layer is a compound having an electron affinity Ea of 2.8 eV or more.

5 . The organic electroluminescent element according to claim 1 , wherein the main peak in an emission spectrum of a single-layer film comprising only the plural host compounds prepared under the same film-forming conditions under which the luminescent layer is prepared has a wavelength that is 20 to 120 nm longer than the main peak wavelength of an emission spectrum of each of the plural host compounds.

6 . The organic electroluminescent element according to claim 1 , wherein the main peak in an emission spectrum of a single-layer film comprising only the plural host compounds prepared under the same film-forming conditions under which the luminescent layer is prepared has a wavelength that is 30 to 100 nm longer than the main peak wavelength of an emission spectrum of each of the plural host compounds.

7 . The organic electroluminescent element according to claim 1 , wherein at least one of the plural host compounds contained in the luminescent layer is a compound represented by formula (A-1):

wherein in formula (A-1), L represents a connecting group; Z A1 represents an atom group necessary for forming a nitrogen-containing heterocyclic ring; n A1 represents an integer of 2 or greater; and the compound represented by formula (A-1) has at least three nitrogen atoms in the molecule.

8 . The organic electroluminescent element according to claim 1 , wherein at least one of the plural host compounds contained in the luminescent layer is a compound represented by formula (B-1):

wherein in formula (B-1), L B1 represents a connecting group; Z B1 represents an atom group necessary for forming an aromatic hydrocarbon ring or an aromatic heterocyclic ring; n B1 represents an integer of 2 or greater; and the compound represented by formula (B-1) has at least three nitrogen atoms in the molecule.

9 . The organic electroluminescent element according to claim 1 , wherein at least one of the plural host compounds contained in the luminescent layer is a compound represented by formula (C-1):

wherein in formula (C-1), R C1 , R C2 , R C3 , and R C4 each independently represent a hydrogen atom or a substituent.

10 . The organic electroluminescent element according to claim 1 , wherein at least one of the plural host compounds contained in the luminescent layer is a compound represented by formula (D-1):

wherein in formula (D-1), L represents a connecting group; Z D1 and Z D2 each independently represent a monovalent atom group; Z D1 and Z D2 may be bonded to each other to form a nitrogen-containing heterocyclic ring; n D1 represents an integer of 2 or greater; and

the compound represented by formula (D-1) has at least three nitrogen atoms in the molecule.

11 . The organic electroluminescent element according to claim 1 , wherein at least one of the plural host compounds contained in the luminescent layer is a compound represented by formula (E-1):

wherein in formula (E-1), L E1 represents a connecting group; and n E1 represents an integer of 2 or greater.

12 . The organic electroluminescent element according to claim 1 , wherein the light emitted from the luminescent dopant contained in the luminescent layer is phosphorescent light.

13 . The organic electroluminescent element according to claim 1 , in which the relationships of ΔIp>0 eV and ΔEa>0 eV are satisfied, wherein Ip(D) represents an ionization potential of the luminescent dopant; Ip(H)min represents the minimum ionization potential among those of the plural host compounds; ΔIp represents Ip(D)−Ip(H)min; Ea(D) represents an electron affinity of the luminescent dopant; Ea(H)max represents the maximum electron affinity among those of the plural host compounds; and ΔEa represents Ea(H)max−Ea(D).

14 . The organic electroluminescent element according to claim 1 , wherein the luminescent layer is formed by a vapor deposition method in which a mixture of the plural host compounds is used as a deposition source.

15 . A method of producing an organic electroluminescent element, the method comprising forming at least one luminescent layer between a pair of electrodes by a vapor deposition method in which at least one luminescent dopant and a mixture of plural host compounds are used as deposition sources, wherein the main peak in an emission spectrum of a single-layer film comprising only the plural host compounds prepared under the same film-forming conditions under which the luminescent layer is prepared has a wavelength that is at least 15 nm longer than the main peak wavelength of an emission spectrum of each of the plural host compounds.