US-12622129-B2 - Organic electroluminescent device

US12622129B2US 12622129 B2US12622129 B2US 12622129B2US-12622129-B2

Abstract

Provided is a blue light emitting organic EL device having high emission efficiency and a long lifetime. This organic EL device includes one or more light emitting layers between an anode and a cathode opposite to each other, wherein at least one of the light emitting layers includes a first host selected from indolocarbazole compounds, a second host selected from the compounds represented by the following general formula (2), and, as a light emitting dopant, a polycyclic aromatic compound represented by the following general formula (3) or a polycyclic aromatic compound represented by the general formula (3) as a substructure, wherein Y 4 is B, P, P═O, P═S, Al, Ga, As, Si—R 4 or Ge—R 5 , and X 4 is O, N—Ar 4 , S or Se.

Inventors

Satoshi UKIGAI
Masashi Tada
Munetomo INOUE
Ayaka TERADA
Sayuri KITERA

Assignees

NIPPON STEEL CHEMICAL & MATERIAL CO., LTD.

Dates

Publication Date: 20260505
Application Date: 20210319
Priority Date: 20200331

Claims (11)

1 . An organic electroluminescent device comprising one or more light emitting layers between an anode and a cathode opposite to each other, wherein at least one of the light emitting layers comprises a first host selected from compounds represented by the following general formula (1), a second host selected from compounds represented by the following general formula (2), and, as a light emitting dopant, a polycyclic aromatic compound represented by the following general formula (3) or a polycyclic aromatic compound having a structure represented by the general formula (3) as a substructure: wherein Z is an indolocarbazole ring-containing group represented by the general formula (1a), * is a bonding site to L 1 , the ring A is a heterocyclic ring represented by formula (1b), and the nitrogen-containing five-membered ring in formula (1b) is condensed with the two adjacent benzene rings in formula (1a), L 1 and L 2 are each independently a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 17 carbons, Ar 1 and Ar 2 are each independently a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 17 carbon atoms, or a linked aromatic group formed by linking 2 to 8 of these groups, R 1 is each independently an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 17 carbon atoms, a represents an integer of 1 to 3, b represents an integer of 0 to 3, and c and d each independently represent an integer of 0 to 4, e represents an integer of 0 to 2, and f represents an integer of 0 to 3, wherein X 1 each independently represents N or CH, and at least one X 1 represents N; Ar 3 each independently represents a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 17 carbon atoms, or a linked aromatic group formed by linking 2 to 8 aromatic rings thereof, wherein the C ring, the D ring, and the E ring are each independently a substituted or unsubstituted aromatic hydrocarbon ring having 6 to 24 carbon atoms or a substituted or unsubstituted aromatic heterocyclic ring having 3 to 17 carbon atoms, Y 4 is B, P, P═O, P═S, Al, Ga, As, Si—R 4 or Ge—R 5 , R 4 and R 5 are each independently an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 17 carbon atoms, X 4 is each independently O, N—Ar 4 , S or Se, Ar 4 is each independently a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 17 carbon atoms, or a linked aromatic group formed by linking 2 to 8 of these groups, N—Ar 4 is optionally bonded to any of the C ring, the D ring, or the E ring to form a heterocyclic ring containing N, R 3 each independently represents a cyano group, deuterium, a diarylamino group having 12 to 44 carbon atoms, an arylheteroarylamino group having 12 to 44 carbon atoms, a diheteroarylamino group having 12 to 44 carbon atoms, an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 17 carbon atoms, at least one hydrogen atom in the C ring, the D ring, the E ring, R 3 , R 4 , R 5 , and Ar 4 is optionally replaced with a halogen or deuterium atom, and v each independently represents an integer of 0 to 4, and x represents an integer of 0 to 3.
2 . The organic electroluminescent device according to claim 1 , wherein the polycyclic aromatic compound having the structure represented by the general formula (3) as a substructure is a polycyclic aromatic compound represented by the general formula (4) below: wherein the F ring, the G ring, the H ring, the I ring, and the J ring are each independently a substituted or unsubstituted aromatic hydrocarbon ring having 6 to 24 carbon atoms or a substituted or unsubstituted aromatic heterocyclic ring having 3 to 17 carbon atoms, and X 4 , Y 4 , R 3 , x, and v are as defined in general formula (3), w represents an integer of 0 to 4, y represents an integer of 0 to 3, and z represents an integer of 0 to 2, and at least one hydrogen atom in the F ring, the G ring, the H ring, the I ring, and the J ring is optionally replaced with a halogen or deuterium atom.
3 . The organic electroluminescent device according to claim 1 , wherein the polycyclic aromatic compound having the structure represented by the general formula (3) as a substructure is a boron-containing polycyclic aromatic compound represented by the general formula (5) below: wherein X 9 each independently represents N—Ar 6 , O, or S, and at least one X 9 represents N—Ar 6 , Ar 6 each independently represents a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, a substituted or unsubstituted aromatic heterocyclic ring group having 3 to 17 carbon atoms, or a linked aromatic group formed by linking 2 to 8 aromatic rings thereof, N—Ar 6 is optionally bonded with the aforementioned aromatic ring to form a heterocyclic ring containing N, R 9 each independently represents a cyano group, deuterium, a diarylamino group having 12 to 44 carbon atoms, an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 17 carbon atoms, and m and n each independently represent an integer of 0 to 4, o and p each independently represent an integer of 0 to 3, and q represents an integer of 0 to 2.
4 . The organic electroluminescent device according to claim 1 , wherein the general formula (2) is formula (6) below: wherein Ar 3 and X 1 are as defined in the general formula (2), R 2 each independently represents deuterium, an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a triarylsilyl group, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 17 carbon atoms, and g and h each independently represent an integer of 0 to 4.
5 . The organic electroluminescent device according to claim 1 , wherein the general formula (2) is formula (7) below: wherein Ar 3 and X 1 are as defined in the general formula (2) and R 2 is as defined in formula (6), g, h, i, and j each independently represent an integer of 0 to 4.
6 . The organic electroluminescent device according to claim 1 , wherein all three X 1 in the general formula (2) are N.
7 . The organic electroluminescent device according to claim 1 , wherein the general formula (1) is formula (8a) or formula (8b) below: wherein L 3 and L 4 each independently represent a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms or a substituted or unsubstituted aromatic heterocyclic group having 6 to 17 carbon atoms, Ar 4 and Ar 5 each independently represent a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, a substituted or unsubstituted aromatic heterocyclic ring group having 6 to 17 carbon atoms, or a linked aromatic group formed by linking 2 to 8 of these groups, and k and l each independently represent an integer of 0 to 3.
8 . The organic electroluminescent device according to claim 1 , wherein the light emitting dopant has a difference between excited singlet energy (S1) and excited triplet energy (T1) (Δ EST) of more than zero and 0.20 eV or less.
9 . The organic electroluminescent device according to claim 8 , wherein the Δ EST is more than zero and 0.10 eV or less.
10 . The organic electroluminescent device according to claim 1 , comprising 0.10 to 10% by mass of a light emitting dopant and 99.9 to 90% by mass of a host comprising 10 to 90% by mass of the first host and 90 to 10% by mass of the second host.
11 . An organic electroluminescent device comprising one or more light emitting layers between an anode and a cathode opposite to each other, wherein at least one of the light emitting layers comprises a first host selected from compounds represented by the following general formula (1), a second host selected from compounds represented by the following general formula (2), and a light emitting dopant having a difference between excited singlet energy (S1) and excited triplet energy (T1) (ΔEST) of more than zero and 0.20 eV or less: wherein Z is an indolocarbazole ring-containing group represented by the general formula (1a), * is a bonding site to with L 1 , the ring A is a heterocyclic ring represented by formula (1b), and the nitrogen-containing five-membered ring in formula (1b) is condensed with the two adjacent benzene rings in formula (1a), L 1 and L 2 are each independently a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 17 carbons, Ar 1 and Ar 2 are each independently a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, a substituted or unsubstituted aromatic heterocyclic groups having 3 to 17 carbon atoms, or a linked aromatic group formed by linking 2 to 8 of these groups, R 1 is each independently an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 17 carbon atoms, a represents an integer of 1 to 3, b represents an integer of 0 to 3, and c and d each independently represent an integer of 0 to 4, e represents an integer of 0 to 2, and f represents an integer of 0 to 3, wherein X 1 each independently represents N or CH, and at least one X 1 represents N; Ar 3 each independently represents a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 17 carbon atoms, or a linked aromatic group formed by linking 2 to 8 aromatic rings thereof.

Description

TECHNICAL FIELD The present invention relates to an organic electroluminescent device or element (also referred to as an organic EL device or element). When a voltage is applied to an organic EL device, holes and electrons are injected from the anode and the cathode, respectively, into the light emitting layer. Then, the injected holes and electrons are recombined in the light emitting layer to thereby generate excitons. At this time, according to the electron spin statistics theory, singlet excitons and triplet excitons are generated at a ratio of 1:3. In the fluorescent organic EL device that uses emission caused by singlet excitons, the limit of the internal quantum efficiency is said to be 25%. On the other hand, it has been known that, in the phosphorescent organic EL device that uses emission caused by triplet excitons, the internal quantum efficiency can be enhanced up to 100% when intersystem crossing efficiently occurs from singlet excitons. However, the blue phosphorescent organic EL device has a technical problem of extending the lifetime. Further, a highly efficient organic EL device utilizing delayed fluorescence has been developed, in recent years. For example, Patent Literature 1 discloses an organic EL device utilizing the Triplet-Triplet Fusion (TTF) mechanism, which is one of the mechanisms of delayed fluorescence. The TTF mechanism utilizes a phenomenon in which a singlet exciton is generated by the collision of two triplet excitons, and it is believed that the internal quantum efficiency can be enhanced up to 40%, in theory. However, its efficiency is low as compared with the efficiency of the phosphorescent organic EL device, and thus further improvement in efficiency is desired. On the other hand, Patent Literature 2 discloses an organic EL device utilizing the Thermally Activated Delayed Fluorescence (TADF) mechanism. The TADF mechanism utilizes a phenomenon in which reverse intersystem crossing occurs from the triplet exciton to the singlet exciton in a material having a small energy difference between the singlet level and the triplet level, and it is believed that the internal quantum efficiency can be enhanced up to 100%, in theory. However, further improvement in lifetime characteristics is desired as in the phosphorescent device. Patent Literatures 3 and 4 discloses an organic EL device in which a TADF material including a polycyclic aromatic compound exemplified by the following compound is used as a light emitting dopant; however, they do not specifically disclose lifetime characteristics. CITATION LIST Patent Literature Patent Literature 1: WO2010/134350Patent Literature 2: WO2011/070963Patent Literature 3: WO2015/102118Patent Literature 4: WO2018/212169 SUMMARY OF INVENTION In order to apply an organic EL device to a display device such as a flat panel display and a light source, it is necessary to improve the emission efficiency of the device and sufficiently ensure the stability of the device at the time of driving, at the same time. An object of the present invention is to provide a practically useful organic EL device having high efficiency and a long lifetime while having a low driving voltage. The present invention is an organic electroluminescent device comprising one or more light emitting layers between an anode and a cathode opposite to each other, wherein at least one of the emitting layers comprises a first host selected from compounds represented by the following general formula (1), a second host selected from compounds represented by the following general formula (2), and, as a light emitting dopant, a polycyclic aromatic compound represented by the following general formula (3) or a polycyclic aromatic compound having a structure represented by the general formula (3) as a substructure: wherein Z is an indolocarbazole ring-containing group represented by the general formula (1a), * is a bonding site to L1, the ring A is a heterocyclic ring represented by formula (1b), and the ring A is condensed with an adjacent ring at an arbitrary position,L1 and L2 are each independently a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 17 carbon atoms. Ar1 and Ar2 are each independently a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 17 carbon atoms, or a linked aromatic group formed by linking 2 to 8 of these groups. R1 is each independently an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 17 carbon atoms. a represents an integer of 1 to 3, b represents an integer of 0 to 3, and c and d each independently represent an integer of 0 to 4, e represents an integer of 0 to 2, and f represen