JP-2026514469-A - Carbazole compounds and organic electroluminescent elements

JP2026514469AJP 2026514469 AJP2026514469 AJP 2026514469AJP-2026514469-A

Abstract

【assignment】 The object of the present invention is to provide a compound with a high refractive index in the 450 nm to 750 nm range and a low extinction coefficient in the capping layer, in order to improve the light extraction efficiency of organic EL elements. [Solution] This invention focuses on the fact that certain carbazole compounds exhibit excellent thin-film stability and durability, and that the refractive index can be improved by adjusting the molecular structure. By designing the molecules and using them as materials to constitute the capping layer, an organic EL element with excellent luminescence efficiency was obtained.

Inventors

加瀬幸喜
梁炳善
車 ▲ヒョン▼旭
金熙載
平山雄太
林秀一

Assignees

保土谷化学工業株式会社

Dates

Publication Date: 20260511
Application Date: 20240417
Priority Date: 20230418

Claims (12)

A carbazole compound represented by the following general formula (A) or (B). (In the formula, Ar, A, and B each represent a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, or a substituted or unsubstituted condensed polycyclic aromatic group, provided that at least one of A and B is a substituted or unsubstituted oxazolopyridyl group or a substituted or unsubstituted oxazolopyradyl group.) L1 to L3 represent a single-bonded, unsubstituted, divalent aromatic hydrocarbon group, an unsubstituted, divalent aromatic heterocyclic group, or an unsubstituted, divalent condensed polycyclic aromatic group.
The carbazole compound described in claim 1 is represented by the following general formula (C) or (D). (In formula (C) or (D), Ar, A, B, and L1 to L3 are as defined in the general formula (A) or (B) above.)
The carbazole compound according to claim 2, wherein L1 to L3 in the general formula (C) or (D) represents a single bond, an unsubstituted phenylene group, or an unsubstituted naphthylene group.
The carbazole compound according to claim 3, wherein L1 to L3 in the general formula (C) or (D) is a single bond, an unsubstituted 1,4-phenylene group, or an unsubstituted 2,6-naphthylene group.
The carbazole compound according to claim 4, wherein Ar, A, and B in the general formula (C) or (D) are a substituted or unsubstituted phenyl group, a substituted or unsubstituted naphthyl group, a substituted or unsubstituted quinolyl group, a substituted or unsubstituted isoquinolyl group, a substituted or unsubstituted quinoxalyl group, a substituted or unsubstituted phenantrenyl group, a substituted or unsubstituted phenantronyl group, a substituted or unsubstituted dibenzofuranyl group, a substituted or unsubstituted dibenzothienyl group, a substituted or unsubstituted benzoxazolyl group, a substituted or unsubstituted benzothiazolyl group, a substituted or unsubstituted benzofuranyl group, a substituted or unsubstituted benzothienyl group, a substituted or unsubstituted oxazolopyridyl group, or a substituted or unsubstituted oxazolopyradyl group.
The carbazole compound according to claim 5, wherein Ar in the general formula (C) or (D) represents an unsubstituted phenyl group, an unsubstituted naphthyl group, an unsubstituted quinolyl group, an unsubstituted isoquinolyl group, an unsubstituted quinoxalyl group, an unsubstituted phenantrenyl group, an unsubstituted phenanthronyl group, an unsubstituted dibenzofuranyl group, an unsubstituted dibenzothienyl group, an unsubstituted benzoxazolyl group, an unsubstituted benzothiazolyl group, an unsubstituted benzofuranyl group, an unsubstituted benzothienyl group, an unsubstituted oxazolopyridyl group, or an unsubstituted oxazolopyradyl group.
The carbazole compound according to claim 6, wherein at least one of A and B in the general formula (C) or (D) is a substituted or unsubstituted 2-oxazolopyridyl group, a substituted or unsubstituted 5-oxazolopyridyl group, or a substituted or unsubstituted 2-oxazolopyridyl group.
The carbazole compound according to claim 7, wherein A and B in the general formula (C) or (D) represent a substituted or unsubstituted 2-oxazolopyridyl group, a substituted or unsubstituted 5-oxazolopyridyl group, or a substituted or unsubstituted 2-oxazolopyridyl group.
An organic EL element having at least an anode electrode, a hole transport layer, a light-emitting layer, an electron transport layer, a cathode electrode, and a capping layer in this order, wherein the capping layer contains a carbazole compound represented by the general formula (A) or (B) described in claim 1.
An organic EL element characterized in that, when the capping layer described in claim 9 is fabricated to a thickness of 30 nm to 120 nm, the refractive index of the capping layer is 1.70 or higher within the range of 450 nm to 750 nm for the transmitted light wavelength.
An organic EL element according to claim 9, wherein the capping layer is a laminated or mixed layer composed of two or more compounds, and at least one of the compounds is a carbazole compound represented by the general formula (A) or (B).
An electronic device or electronic element having a pair of electrodes and at least one organic layer sandwiched between them, wherein the organic layer contains a carbazole compound represented by the general formula (A) or (B) described in claim 1.

Description

This invention relates to compounds suitable for self-emissive electronic elements suitable for various display devices, particularly carbazole compounds suitable for organic electroluminescent elements (hereinafter abbreviated as organic EL elements), and organic EL elements, electronic elements, and electronic devices using said compounds. Because organic EL elements are self-emissive, they offer brighter and more visible displays compared to liquid crystal elements, enabling sharper image reproduction, which has led to active research into them. In 1987, C. W. Tang et al. at Eastman Kodak made organic EL elements using organic materials practical by developing a multilayer structure element in which various roles are assigned to each material. They stacked a phosphor capable of transporting electrons and an organic material capable of transporting holes, and by injecting both charges into the phosphor layer to cause light emission, they achieved a high brightness of 1000 cd/ m² or more at a voltage of 10 V or less (see, for example, Patent Documents 1 and 2). To date, numerous improvements have been made to the practical application of organic EL elements. By further subdividing the roles of each layer in the multilayer structure, and sequentially arranging the anode, hole injection layer, hole transport layer, light-emitting layer, electron transport layer, electron injection layer, and cathode on the substrate, high efficiency and durability have been achieved by creating a bottom-emission light-emitting element that emits light from the bottom (see, for example, Non-Patent Document 1). In recent years, light-emitting devices with a top-emission structure, which use a metal with a high work function as the anode and emit light from the top, have come into use. While bottom-emission structures, which extract light from the bottom where the pixel circuit is located, have a limited area for the light-emitting region, top-emission light-emitting devices have the advantage of a larger light-emitting region because the pixel circuit does not obstruct the light as it is extracted from the top. In top-emission light-emitting devices, translucent electrodes such as LiF/Al/Ag (see, for example, Non-Patent Document 2), Ca/Mg (see, for example, Non-Patent Document 3), and LiF/MgAg are used as cathodes. In such light-emitting devices, when light emitted from the light-emitting layer is incident on another film, if it is incident at an angle greater than a certain degree, it undergoes total internal reflection at the interface between the light-emitting layer and the other film. Therefore, only a portion of the emitted light was utilized. Recently, to improve the light extraction efficiency, light-emitting devices have been proposed that have a high-refractive-index "capping layer" on the outside of a low-refractive-index translucent electrode (see, for example, Non-Patent Documents 2 and 3). As an effect of the capping layer in a top-emission light-emitting element, in a light-emitting element using Ir(ppy) 3 as the light-emitting material, the current efficiency was 38 cd/A without a capping layer, while in a light-emitting element using ZnSe with a film thickness of 60 nm as a capping layer, an efficiency improvement of approximately 1.7 times was observed, reaching 64 cd/A. Furthermore, it has been shown that the maximum transmittance point of the translucent electrode and the capping layer do not necessarily coincide with the maximum efficiency point, and that the point of maximum light extraction efficiency is determined by interference effects (see, for example, Non-Patent Document 3). Conventionally, the use of a high-resolution metal mask has been proposed for forming the capping layer. However, under high-temperature conditions, the metal mask becomes distorted due to heat, leading to a decrease in alignment accuracy. Therefore, ZnSe, which has a high melting point of over 1100°C, cannot be deposited in the correct position using a high-resolution metal mask, potentially adversely affecting the light-emitting element (see, for example, Non-Patent Document 3). Furthermore, even with film deposition by sputtering, it adversely affects the light-emitting element, making capping layers composed of inorganic materials unsuitable for use. In addition, it has been proposed to use tris(8-hydroxyquinoline)aluminum (hereinafter abbreviated as Alq3 ) as a capping layer to adjust the refractive index (see, for example, Non-Patent Document 2). However, Alq3 is known as an organic EL material commonly used as a green light-emitting material or electron transport material, and it has weak absorption around 450 nm, which is close to the emission wavelength of blue light-emitting materials. Therefore, in the case of blue light-emitting elements, there were problems such as a decrease in color purity and a decrease in light extraction efficiency. To improve the characteristics of organic EL elements and significantly enhanc