Organic light-emitting device

An organic light-emitting device including a first electrode; a second electrode facing the first electrode; and an organic layer between the first electrode and the second electrode, the organic layer including an emission layer, wherein the organic layer includes at least one organometallic compound represented by Formula 1, below, and at least one condensed cyclic compound represented by Formula 40, below:

CROSS-REFERENCE TO RELATED APPLICATION

Korean Patent Application No. 10-2014-0096759, filed on Jul. 29, 2014, in the Korean Intellectual Property Office, and entitled: “Organic Light-Emitting Device,” is incorporated by reference herein in its entirety.

BACKGROUND

Embodiments relate to an organic light-emitting device.

2. Description of the Related Art

Organic light emitting devices are self-emission devices that have wide viewing angles, high contrast ratios, short response times, and excellent brightness, driving voltage, and response speed characteristics, and produce full-color images.

SUMMARY

Embodiments are directed to an organic light-emitting device.

The embodiments may provide an organic light-emitting device with high efficiency.

One or more embodiments may include an organic light-emitting display device including: a first electrode; a second electrode facing the first electrode; and an organic layer including an emission layer that is disposed between the first electrode and the second electrode, wherein the organic layer includes at least one compound selected from organometallic compounds represented by Formula 1 below and at least one compound selected from condensed cyclic compounds represented by Formula 40 below:
M(L1)n1(L2)n2<Formula 1>

wherein in Formula 1,

M is iridium (Ir),

L1is selected from a monovalent organic ligand, a divalent organic ligand, a trivalent organic ligand, and a tetravalent organic ligand, and is different from L1;

L2is selected from ligands represented by Formula 2;

when n1 is two or more, two or more L1may be identical or different, and when n2 is two or more, two or more L2may be identical to different:

wherein in Formulae 2 and 40,

* and *′ each indicate a binding site to M in Formula 1;

n41 is an integer selected from 1, 2, 3, and 4, and when n41 is 2 or more, a plurality of —(Ar41)j—(R48)kare identical or different;

2 or more substituents selected from R5to R8are optionally linked to each other so as to form a substituted or unsubstituted C6-C20saturated ring or a substituted or unsubstituted C6-C20unsaturated ring;

R45and R46are optionally linked to each other so as to form a substituted or unsubstituted C6-C20saturated ring or a substituted or unsubstituted C6-C20unsaturated ring;

i, j, and k are each independently an integer selected from 0, 1, 2, and 3, and when i is 2 or more, a plurality of R47are identical or different, when j are 2 or more, a plurality of Ar47are identical or different, and when k is 2 or more, a plurality of R48are identical or different,

DETAILED DESCRIPTION

In the FIGURE, the dimensions of layers and regions may be exaggerated for clarity of illustration. Like reference numerals refer to like elements throughout.

The FIGURE illustrates a schematic view of an organic light-emitting device10according to an embodiment. The organic light-emitting device10may include a first electrode110, an organic layer150, and a second electrode190.

In the FIGURE, a substrate may be additionally disposed under the first electrode110or above the second electrode190. The substrate may be a glass substrate or transparent plastic substrate, each with excellent mechanical strength, thermal stability, transparency, surface smoothness, ease of handling, and water repellency.

The first electrode110may be formed by depositing or sputtering a material for forming the first electrode on the substrate. When the first electrode10is an anode, the material for the first electrode may be selected from materials with a high work function to make holes be easily injected. The first electrode110may be a reflective electrode or a transmissive electrode. The material for the first electrode may be a transparent and highly conductive material, and examples of such a material are indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide (SnO2), and zinc oxide (ZnO). When the first electrode110is a semi-transmissive electrode or a reflective electrode, as a material for forming the first electrode, at least one of magnesium (Mg), aluminum (Al), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), magnesium-silver (Mg—Ag) may be used.

The first electrode110may have a single-layer structure, or a multi-layer structure including two or more layers. For example, the first electrode110may have a three-layered structure of ITO/Ag/ITO, but the structure of the first electrode110is not limited thereto.

The organic layer150may be disposed on the first electrode110. The organic layer150may include an emission layer.

When the first electrode110is an anode and the second electrode190is a cathode, the organic layer150may further include a hole transport region disposed between the first electrode and the emission layer, and an electron transport region disposed between the emission layer and the second electrode.

In some embodiments, the organic layer150may include i) a hole transport region that is disposed between the first electrode110, which is an anode, and the emission layer and includes at least one selected from a hole injection layer, a hole transport layer, a buffer layer, and an electron blocking layer, and ii) an electron transport region that is disposed between the emission layer and the second electrode190, which is a cathode, and includes at least one selected from a hole blocking layer, an electron transport layer, and an electron injection layer.

The organic layer may include at least one organometallic compound represented by Formula 1 and at least one condensed cyclic compound represented by Formula 40.
M(L1)n1(L2)n2<Formula 1>

M in Formula 1 may be iridium (Ir).

In Formula 1, L1may be selected from a monovalent organic ligand, a divalent organic ligand, a trivalent organic ligand, and a tetravalent organic ligand, and L2may be selected from ligands represented by Formula 2, wherein L1is different from L2. L1and L2in Formula 2 will be described in detail below.

In Formula 1, n1 may be 0, 1, 2, or 4, and n2 may be 1, 2, or 3.

In some embodiments, R1to R8may be each independently selected from a hydrogen, a deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid or a salt thereof, a sulfonic acid or a salt thereof, a phosphoric acid or a salt thereof, a substituted or unsubstituted C1-C20alkyl group, a substituted or unsubstituted C1-C20alkoxy group, a substituted or unsubstituted C6-C20aryl group, a substituted or unsubstituted C1-C20heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, and —Si(Q3)(Q4)(Q5),

Q3to Q5may be each independently selected from a hydrogen, a C1-C20alkyl group, a C1-C20alkoxy group, a phenyl group, a naphthyl group, a pyridinyl group, a pyrimidinyl group, a triazinyl group, a quinolinyl group, and an isoquinolinyl group, but they are not limited thereto.

In some embodiments, R1to R8may be each independently:

Q3to Q5and Q33to Q35may be each independently selected from a hydrogen, a C1-C20alkyl group, a C1-C20alkoxy group, a phenyl group, a naphthyl group, a pyridinyl group, a pyrimidinyl group, a triazinyl group, a quinolinyl group, and an isoquinolinyl group, but they are not limited thereto.

In some embodiments, R1to R8may be each independently selected from:

Q3to Q5and Q33to Q35may be each independently selected from a hydrogen, a C1-C20alkyl group, a C1-C20alkoxy group, a phenyl group, a naphthyl group, a pyridinyl group, a pyrimidinyl group, a triazinyl group, a quinolinyl group, and an isoquinolinyl group, but they are not limited thereto.

2 or more of R5to R8may be separate or may be optionally linked to each other so as to form a substituted or unsubstituted C6-C20saturated ring or a substituted or unsubstituted C6-C20unsaturated ring.

* and *′ in Formula 2 are binding sites to M in Formula 1.

L2in Formula 1 may be selected from a ligand represented by Formula 2A below and a ligand represented by Formula 2B below.

R1to R4, R6, and R7in Formulae 2A and 2B may be each independently selected from:

R6and R7may be separate or may be linked to each other so as to optionally form a substituted or unsubstituted C6-C20saturated ring or a substituted or unsubstituted C6-C20unsaturated ring.

* and *′ each indicate a binding site to M in Formula 1.

In some embodiments, L1in Formula 1 may be selected from ligands represented by Formula 3 below.

W1to W4in Formula 3 may be each independently carbon (C) or nitrogen (N).

In some embodiments, in Formula 3, W1may be N and W4may be C, but they are not limited thereto.

In some embodiments, in Formula 3, W2and W3may be C, but they are not limited thereto.

CW1and CW2may be each independently a C5-C60cyclic group or a C2-C60heterocyclic group. For example, CW1may be a cyclic or heterocyclic group including a ring that includes W1and W2in a ring. For example, CW2may be a cyclic or heterocyclic group including a ring that includes W3and W4in a ring.

For example, CW1and CW2in Formula 3 may be each independently a benzene, a naphthalene, a fluorene, a spiro-fluorene, an indene, a pyrrol, a thiophene, a furan, a imidazole, a pyrazole, a thiazole, a isothiazole, a oxazole, a isooxazole, a triazole, a pyridine, a pyrazine, a pyrimidine, a pyridazine, a quinoline, an isoquinoline, a benzoquinoline, a quinoxaline, a quinazoline, a carbazole, a benzoimidazole, a benzofuran, a benzothiphene, an isobenzothiphene, a benzooxazole, a isobenzooxazole, a triazole, a tetrazole, an oxadiazole, a triazine, a dibenzofuran, a dibenzothiophene, a benzofuropyridine, or a benzothienopyridine.

In some embodiments, in Formula 3, CW1may be a benzene or a pyridine, and CW2may be a pyridine, a triazole, an imidazole, a pyrazole, a benzofuropyridine or a benzothienopyridine, but they are not limited thereto.

a and b in Formula 3 may be each independently an integer selected from 1, 2, 3, 4, and 5. For example, a and b may be each independently 1 or 3, but they are not limited thereto.

a in Formula 3 indicates the number of R13, and when a is 2 or more, two or more R13may be identical or different.

b in Formula 3 indicates the number of R14, and when a is 2 or more, two or more R14may be identical or different.

* and *′ in Formula 3 are binding sites to M in Formula 1.

In some embodiments, L1in Formula 1 may be selected from ligands represented by Formula 3A below.

R13and R14in Formula 3A may be each independently selected from:

Q3to Q5and Q33to Q35may be each independently selected from a hydrogen, a C1-C20alkyl group, a C1-C20alkoxy group, a phenyl group, a naphthyl group, a pyridinyl group, a pyrimidinyl group, a triazinyl group, a quinolinyl group, and an isoquinolinyl group, but they are not limited thereto.

a and b in Formula 3A may be each independently an integer selected from 0, 1, 2, and 3. For example, a and b may be each independently 1 or 3, but they are not limited thereto.

* and *′ in Formula 3A are binding sites to M in Formula 1.

In some embodiments, the organometallic compound may be represented by Formulae 1A or 1B below, but is not limited thereto.

M, R1to R4, R11to R14, a4, b4, n1, and n2 in Formula 1A may be the same already explained above with respect to Formula 1.

For example, in Formulae 1A and 1B,

M may be iridium (Ir),

n1 and n2 may be each independently 1 or 2, the sum of n1 and n2 may be 3;

a C1-C20alkyl group and a C1-C20alkoxy group, each substituted with at least one selected from —F, —CN, and —NO2;

wherein R12may be selected from a C1-C20alkyl group and —N(Q41)(Q42),

wherein Q41and Q42are each independently selected from a hydrogen, a C1-C20alkyl group, a phenyl group, a naphthyl group, and an anthracenyl group, and

a and b may be each independently an integer selected from 0, 1, 2, and 3.

n1 in Formula 1 indicates the number of L1, and may be 0, 1, 2, or 4. When n1 is 2 or more, 2 or more L1may be identical or different.

n2 in Formula 1 indicates the number of L2, and may be 0, 1, 2, or 3. When n2 is 2 or more, 2 or more L2may be identical or different.

For example, in Formula 1, n1 may be 1 and n2 may be 2; or n1 may be 2 and n2 may be 1. However, n1 and n2 are not limited thereto.

The organometallic compound represented by Formula 1 may be one of Compounds 1 to 18 below, but is not limited thereto.

In Formula 40, X41may be N or C(R41), X42may be N or C(R42), X43may be N or C(R43), and X44may be N or C(R44), wherein at least one of X41to X44may be N;

According to an embodiment, Ar41in Formula 40 may be selected from:

In some embodiments, Ar41in Formula 40 may be each independently represented by one of Formulae 41-1 to 41-34 below.

In Formulae 41-1 to 41-34,

d1 may be an integer selected from 1 to 4, d2 may be an integer selected from 1 to 3, d3 may be an integer selected from 1 to 6, d4 may be an integer selected from 1 to 8, d5 may be an integer selected from 1 and 2, and d6 may be an integer selected from 1 to 5.

* and *′ indicate binding sites to a neighboring atom.

In some embodiments, Ar41in Formula 40 may be selected from:

a phenalenylene group, a phenanthrenylene group, an anthracenylene group, a triphenylenylene group, a pyrenylene group, a chrysenylene group, a benzopyrenylene group, and a phenanthrolinylene group, each substituted with at least one selected from a deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid or a salt thereof, a sulfonic acid or a salt thereof, a phosphoric acid or a salt thereof, a C1-C20alkyl group, a C1-C20alkoxy group, a phenyl group, a naphthyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, and a triazinyl group, but is not limited thereto.

In some embodiments, Ar41in Formula 40 may be each independently represented by one of Formulae 42-1 to 42-3 below:

* and *′ in Formulae 42-1 to 42-3 indicate binding sites to a neighboring atom.

In some embodiments, R41to R44, R47, and R48may be each independently selected from:

wherein Q3to Q5and Q33to Q35may be each independently selected from a hydrogen, a C1-C20alkyl group, a C1-C20alkoxy group, a phenyl group, a naphthyl group, a pyridinyl group, a pyrimidinyl group, a triazinyl group, a quinolinyl group, and an isoquinolinyl group, but they are not limited thereto.

In some embodiments, R45and R46may be each independently selected from:

a C1-C20alkyl group and a C1-C20alkoxy group;

a phenyl group, a naphthyl group, a phenanthrenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthrolinyl group, a benzoimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, and a benzoxazolyl group, each substituted with at least one selected from a deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid or a salt thereof, a sulfonic acid or a salt thereof, a phosphoric acid or a salt thereof, a C1-C20alkyl group, a C1-C20alkoxy group, a phenyl group, a naphthyl group, a phenanthrenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthrolinyl group, a benzoimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, and a benzoxazolyl group but they are not limited thereto.

R45and R46may be separate or may be optionally linked to each other so as to form a substituted or unsubstituted C6-C20saturated ring or a substituted or unsubstituted C6-C20unsaturated ring.

In some embodiments, R45and R46in Formula 40 may be each independently selected from:

wherein R45and R46may be linked to each other by a single bond.

i, j, and k in Formula 40 may be integers selected from 0, 1, 2, and 3.

i indicates the number of R47, and when i is 2 or more, a plurality of R47may be identical or different.

j indicates the number of Ar41, and when j is 2 or more, a plurality of Ar41may be identical or different.

k indicates the number of R48, and when k is 2 or more, a plurality of R48may be identical or different.

The condensed cyclic compound may be represented by Formula 40A below.

In Formula 40A,

Ar41may be represented by any one of Formulae 42-1 to 42-3 below;

R45and R46may be each independently selected from:

a C1-C20alkyl group and a C1-C20alkoxy group;

wherein R45and R46may be linked to each other by a single bond;

n41 may be 1;

j may be 1; and

k may be 1 or 2.

In some embodiments, the condensed cyclic compound may be represented by one of Formulae 40B to 40I below.

In Formulae 40B to 40I,

Ar41may be represented by any one of Formulae 42-1 to 42-3;

R45and R46may be each independently selected from:

a C1-C20alkyl group and a C1-C20alkoxy group;

The condensed cyclic compound represented by Formula 40 may be one of Compounds A1 to A25 below, but is not limited thereto.

In some embodiments, the organometallic compound represented by Formula 1 and the condensed cyclic compound represented by Formula 40 may be included in the emission layer of the organic layer150.

In some embodiments, in the organic layer, e.g., in the emission layer, an amount of the condensed cyclic compound represented by Formula 40 may be greater than an amount of the organometallic compound.

In some embodiments, an amount of the organometallic compound represented by Formula 1 in the organic layer, e.g., in the emission layer, may be in a range of about 0.1 to about 30 parts by weight based on 100 parts by weight of the condensed cyclic compound represented by Formula 40, but is not limited thereto.

In the case of the organometallic compound represented by Formula 1, when R5to R8in Formula 2′ below are electron withdrawing groups (EWG), an electron density of a benzene ring may be low. As a result, light emitted by the organometallic compound may be light that is hypsochromically shifted. For example, the light may be light that is shifted to blue spectrum. Also, a ligand of the organometallic compound may easily trap electrons, and more electrons are likely to combine with holes that are provided to an emission layer to form more excited excitons. Therefore, an organic light-emitting device using the organometallic compound may have a high luminescent efficiency.

A benzimidazole group in the ligand may be an electron donating group (EDG), and may contribute to an increase in an electron density of a transition metal. Therefore, in the organometallic compound, an electronic stability of HOMO energy level may be improved, so that an energy band gap between HOMO energy level and LUMO energy level may increase. As a result, light emitted by the organometallic compound may be light that is hypsochromically shifted, e.g., deep blue. Also, an amount of electrons or holes trapped may be controlled, and thus the organic light-emitting device using the organometallic complex may have a high luminescent efficiency.

A ligand represented by Formula 2, which may be L2in the organometallic compound represented by Formula 1, may easily trap electrons, more electrons may be likely to combine with holes that are provided to an emission layer to form more excited excitons. Accordingly, an organic light-emitting device using the organometallic compound may have high luminescent efficiency.

The condensed cyclic compound represented by Formula 40 may include a core represented by Formula 1′, below. Due to the inclusion of the core, high glass transition temperature may be obtained. Accordingly, when an organic light-emitting device including the condensed cyclic compound represented by Formula 1 is preserved and/or driven, a resistance to heat generated between organic layers or between an organic layer and an electrode and a resistance to high-temperature environments may increase. Thus, the organic light-emitting device including the condensed cyclic compound represented by Formula 1 may have long lifespan characteristics.

The condensed cyclic compound represented by Formula 40 may trap more holes and electrons in an organic light-emitting device, and thus, more excitions may be formed. The condensed cyclic compound may have relatively high exposure resistance to charge, and thus, the organic light-emitting device including the condensed cyclic compound may have a high efficiency and long lifespan.

The condensed cyclic compound may have an excellent hole transport ability. Accordingly, an organic light-emitting device using the condensed cyclic compound may provide a higher efficiency than when a carbazole-based compound is used. When a carbazole-based compound is used, balancing charge in an emission layer may be difficult.

In the cyclic condensed compound, an indenopyridine ring may include a nitrogen atom (N), and charges may be easily trapped in the condensed cyclic compound. Therefore, when the condensed cyclic compound represented by Formula 40 is used as a host, many trapped charges may be likely to be moved to a dopant from the host, and an efficiency of the organic light-emitting device may be improved.

A synthesis method of the organometallic compound represented by Formula 1 and the condensed cyclic compound represented by Formula 40 may be understood in view of the following synthesis examples.

The organic layer150may further include a hole transport region disposed between the first electrode and the emission layer, and an electron transport region disposed between the emission layer and the second electrode.

The hole transport region may include at least one selected from a hole injection layer (HIL), a hole transport layer (HTL), a buffer layer, and an electron blocking layer (EBL), and the electron transport region may include at least one selected from a hole blocking layer (HBL), an electron transport layer (ETL), and an electron injection layer (EIL), but they are not limited thereto.

The hole transport region may have a single-layered structure formed of a single material, a single-layered structure formed of a plurality of different materials, or a multi-layered structure having a plurality of layers formed of a plurality of different materials.

For example, the hole transport region may have a single-layered structure formed of a plurality of different materials, or a structure of hole injection layer/hole transport layer, a structure of hole injection layer/hole transport layer/buffer layer, a structure of hole injection layer/buffer layer, a structure of hole transport layer/buffer layer, or a structure of hole injection layer/hole transport layer/electron blocking layer, wherein layers of each structure are sequentially stacked from the first electrode110in this stated order, but are not limited thereto.

When the hole transport region includes a hole injection layer, the hole injection layer may be formed on the first electrode110by using various methods, such as vacuum deposition, spin coating casting, a Langmuir-Blodgett (LB) method, ink-jet printing, laser-printing, or laser-induced thermal imaging.

When a hole injection layer is formed by vacuum deposition, for example, the vacuum deposition may be performed at a temperature of a deposition temperature of about 100 to about 500° C., at a vacuum degree of about 10−8to about 10−3torr, and at a deposition rate of about 0.01 to about 100 Å/sec in consideration of a compound for a hole injection layer to be deposited, and the structure of a hole injection layer to be formed.

When a hole injection layer is formed by spin coating, the spin coating may be performed at a coating rate of about 2000 rpm to about 5000 rpm, and at a temperature of about 80° C. to 200° C. in consideration of a compound for a hole injection layer to be deposited, and the structure of a hole injection layer to be formed.

When the hole transport region includes a hole transport layer, the hole transport layer may be formed on the first electrode110or the hole injection layer by using various methods, such as vacuum deposition, spin coating, casting, a LB method, ink-jet printing, laser-printing, or laser-induced thermal imaging. When the hole transport layer is formed by vacuum deposition or spin coating, deposition and coating conditions for the hole transport layer may be determined by referring to the deposition and coating conditions for the hole injection layer.

wherein in Formulae 201 and 202,

L201to L205may be the same as explained in connection with Ar41;

xa1 to xa4 may be each independently selected from 0, 1, 2, and 3;

xa5 may be selected from 1, 2, 3, 4, and 5; and

wherein in Formulae 201 and 202,

L201to L205may be each independently selected from:

xa1 to xa4 may be each independently 0, 1, or 2;

For example, the compound represented by Formula 201 may be represented by Formula 201A-1 below, but is not limited thereto.

For example, the compound represented by Formula 202 may be represented by Formula 202A below, but is not limited thereto.

For example, in Formulae 201A, 201A-1, and 202A,

L201to L203may be each independently selected from

xa1 to xa3 may be each independently 0 or 1;

R203, R211, and R212may be each independently selected from:

a C1-C20alkyl group and a C1-C20alkoxy group;

R215and R216are each independently selected from

R213and R214in Formulae 201A, and 201A-1 may bind to each other to form a saturated or unsaturated ring.

The compound represented by Formula 201, and the compound represented by Formula 202 may each include compounds HT1 to HT20 illustrated below, but are not limited thereto.

A thickness of the hole transport region may be in a range of about 100 Å to about 10000 Å, e.g., about 100 Å to about 1000 Å. When the hole transport region includes a hole injection layer and a hole transport layer, the thickness of the hole injection layer may be in a range of about 100 Å to about 10000 Å, e.g., about 100 Å to about 1000 Å, and the thickness of the hole transport layer may be in a range of about 50 Å to about 2000 Å, e.g., about 100 Å to about 1500 Å. When the thicknesses of the hole transport region, the hole injection layer, and the hole transport layer are within these ranges, satisfactory hole transporting characteristics may be obtained without a substantial increase in driving voltage.

The hole transport region may further include, in addition to the hole injection layer and the hole transport layer, at least one of a buffer layer and an electron blocking layer. Since the buffer layer may compensate for an optical resonance distance according to a wavelength of light emitted from the emission layer, light-emission efficiency of a formed organic light-emitting device may be improved. For use as a material included in the buffer layer, materials that are included in the hole transport region may be used. The electron blocking layer prevents injection of electrons from the electron transport region.

An emission layer may be formed on the first electrode110or the hole transport region by using various methods, such as vacuum deposition, spin coating, casting, a LB method, ink-jet printing, laser-printing, or laser-induced thermal imaging. When the emission layer is formed by vacuum deposition or spin coating, deposition and coating conditions for the emission layer may be determined by referring to the deposition and coating conditions for the hole injection layer.

When the organic light-emitting device10is a full color organic light-emitting device, the emission layer may be patterned into a red emission layer, a green emission layer, or a blue emission layer, according to a sub pixel. In some embodiments, the emission layer may have a stacked structure of a red emission layer, a green emission layer, and a blue emission layer, or may include a red-light emission material, a green-light emission material, and a blue-light emission material, which are mixed with each other in a single layer, to emit white light.

The emission layer may include the organometallic compound represented by Formula 1 and the condensed cyclic compound represented by Formula 40.

The emission layer may include a host and a dopant. For example, the host may include the condensed cyclic compound represented by Formula 40 and the dopant may include the organometallic compound represented by Formula 1.

In an implementation, the dopant may include at least one selected from a fluorescent dopant and a phosphorescent dopant.

When the dopant includes a phosphorescent dopant, the phosphorescent dopant may include the organometallic compound represented by Formula 1.

The fluorescent dopant may include at least one selected from DPAVBi, BDAVBi, TBPe, DCM, DCJTB, Coumarin 6, and C545T.

An amount of the dopant included in the emission layer may be, e.g., about 0.01 to about 15 parts by weight, based on 100 parts by weight of the host, but is not limited thereto.

Then, an electron transport region may be disposed on the emission layer.

The electron transport region may include at least one selected from a hole blocking layer, an electron transport layer (ETL), and an electron injection layer, but is not limited thereto.

For example, the electron transport region may have a structure of electron transport layer/electron injection layer or a structure of hole blocking layer/electron transport layer/electron injection layer, wherein layers of each structure are sequentially stacked from the emission layer in the stated order, but is not limited thereto.

According to an embodiment, the organic layer150of the organic light-emitting device may include an electron transport region disposed between the emission layer and the second electrode190.

The electron transport region may include a hole blocking layer. The hole blocking layer may be formed, when the emission layer includes a phosphorescent dopant, to prevent diffusion of excitons or holes into an electron transport layer.

When the electron transport region includes a hole blocking layer, the hole blocking layer may be formed on the emission layer by using various methods, such as vacuum deposition, spin coating casting, a LB method, ink-jet printing, laser-printing, or laser-induced thermal imaging. When the hole blocking layer is formed by vacuum deposition or spin coating, deposition and coating conditions for the hole blocking layer may be determined by referring to the deposition and coating conditions for the hole injection layer.

The hole blocking layer may include, e.g., at least one of BCP and Bphen, but is not limited thereto.

A thickness of the hole blocking layer may be in a range of about 20 Å to about 1000 Å, e.g., about 30 Å to about 300 Å. When the thickness of the hole blocking layer is within these ranges, the hole blocking layer may have improved hole blocking ability without a substantial increase in driving voltage.

The electron transport region may include an electron transport layer. The electron transport layer may be formed on the emission layer or the hole blocking layer by using various methods, such as vacuum deposition, spin coating casting, a LB method, ink-jet printing, laser-printing, or laser-induced thermal imaging. When an electron transport layer is formed by vacuum deposition or spin coating, deposition and coating conditions for the electron transport layer may be determined by referring to the deposition and coating conditions for the hole injection layer.

According to an embodiment, the organic layer150of the organic light-emitting device may include an electron transport region disposed between the emission layer and the second electrode190. The electron transport region may include at least one selected from an electron transport layer and an electron injection layer.

The electron transport layer may further include at least one selected from BCP, Bphen, Alg3, Balq, TAZ, and NTAZ.

According to another embodiment, the electron transport layer may include at least one compound selected from a compound represented by Formula 601 and a compound represented by Formula 602 illustrated below.
Ar601-[(L601)xe1-E601]xe2<Formula 601>

In Formula 601,

a naphthalene group, a heptalene group, a fluorenene group, a spiro-fluorenene group, a benzofluorenene group, a dibenzofluorenene group, a phenalene group, a phenanthrene group, a anthracene group, a fluoranthene group, a triphenylene group, a pyrene group, a chrysene group, a naphthacene group, a picene group, a perylene group, a pentaphene group, and an indenoanthracene group, each substituted with at least one selected from a deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid or a salt thereof, a phosphoric acid or a salt thereof, a C1-C60alkyl group, a C2-C60alkenyl group, a C2-C60alkynyl group, a C1-C60alkoxy, a C3-C10cycloalkyl group, a C1-C10heterocycloalkyl group, a C3-C10cycloalkenyl group, a C1-C10heterocycloalkenyl group, a C6-C60aryl group, a C6-C60aryloxy, a C6-C60arylthio group, a C1-C60heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, and —Si(Q301)(Q302)(Q303) (wherein Q301to Q303are each independently selected from a hydrogen, a C1-C60alkyl group, a C2-C60alkenyl group, a C2-C60aryl group, and a C1-C60heteroaryl group);

L601may be the same as explained in connection with L201;

xe1 may be selected from 0, 1, 2, and 3; and

xe2 may be selected from 1, 2, 3, and 4.

In Formula 602,

L611to L616may be the same as explained in connection with L201;

xe611 to xe616 may be each independently selected from 0, 1, 2, and 3.

The compound represented by Formula 601 and the compound represented by Formula 602 may each be selected from Compounds ET1 to ET15 illustrated below.

A thickness of the electron transport layer may be in a range of about 100 Å to about 1000 Å, e.g., about 150 Å to about 500 Å. When the thickness of the electron transport layer is within the range described above, the electron transport layer may have satisfactory electron transport characteristics without a substantial increase in driving voltage.

The metal-containing material may include a Li complex. The Li complex may include, e.g., Compound ET-D1 (lithium quinolate, LiQ) or ET-D2.

The electron transport region may include an electron injection layer that allows electrons to be easily provided from the second electrode190.

The electron injection layer may be formed on the electron transport layer by using various methods, such as vacuum deposition, spin coating casting, a LB method, ink-jet printing, laser-printing, or laser-induced thermal imaging. When an electron injection layer is formed by vacuum deposition or spin coating, deposition and coating conditions for the electron injection layer may be determined by referring to the deposition and coating conditions for the hole injection layer.

The electron injection layer may include at least one selected from, LiF, NaCl, CsF, Li2O, BaO, and LiQ.

The second electrode190may be disposed on the organic layer150having such a structure. The second electrode190may be a cathode that is an electron injection electrode, and in this regard, a material for forming the second electrode190may be a material having a low work function, and such a material may be metal, alloy, an electrically conductive compound, or a mixture thereof. Detailed examples of the second electrode190are lithium (Li), magnesium (Mg), aluminum (Al), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), or magnesium-silver (Mg—Ag). According to another embodiment, the material for forming the second electrode190may be ITO or IZO. The second electrode190may be a reflective electrode, a semi-transmissive electrode, or a transmissive electrode.

Hereinbefore, the organic light-emitting device has been described with reference to the FIGURE, but is not limited thereto.

A C1-C60alkyl group used herein refers to a linear or branched aliphatic hydrocarbon monovalent group having 1 to 60 carbon atoms, and detailed examples thereof are a methyl group, an ethyl group, a propyl group, an isobutyl group, a sec-butyl group, a ter-butyl group, a pentyl group, an iso-amyl group, and a hexyl group. A C1-C60alkylene group used herein refers to a divalent group having the same structure as the C1-C60alkyl group.

A C2-C60alkenyl group used herein refers to a hydrocarbon group formed by substituting at least one carbon double bond in the middle or terminal of the C2-C60alkyl group, and detailed examples thereof are an ethenyl group, a prophenyl group, and a butenyl group. A C2-C60alkylene group used herein refers to a divalent group having the same structure as the C2-C60alkyl group.

A C2-C60alkynyl group used herein refers to a hydrocarbon group formed by substituting at least one carbon trip bond in the middle or terminal of the C2-C60alkyl group, and detailed examples thereof are an ethynyl group, and a propynyl group. A C2-C60alkylene group used herein refers to a divalent group having the same structure as the C2-C60alkyl group.

A C1-C10heterocycloalkyl group used herein refers to a monovalent monocyclic group having at least one hetero atom selected from N, O, P, and S as a ring-forming atom and 1 to 10 carbon atoms, and detailed examples thereof are a tetrahydrofuranyl group, and a tetrahydrothiophenyl group. A C1-C10heterocycloalkylene group used herein refers to a divalent group having the same structure as the C1-C10heterocycloalkyl group.

A C3-C10cycloalkenyl group used herein refers to a monovalent monocyclic group that has 3 to 10 carbon atoms and at least one double bond in the ring thereof and does not have aromacity, and detailed examples thereof are a cyclopentenyl group, a cyclohexenyl group, and a cycloheptenyl group. A C3-C10cycloalkenylene group used herein refers to a divalent group having the same structure as the C3-C10cycloalkenyl group.

A C1-C10heterocycloalkenyl group used herein refers to a monovalent monocyclic group that has at least one hetero atom selected from N, O, P, and S as a ring-forming atom, 1 to 10 carbon atoms, and at least one double bond in its ring. Detailed examples of the C1-C10heterocycloalkenyl group are a 2,3-hydrofuranyl group and a 2,3-hydrothiophenyl group. A C1-C10heterocycloalkenylene group used herein refers to a divalent group having the same structure as the C1-C10heterocycloalkenyl group.

A monovalent non-aromatic condensed polycyclic group used herein refers to a monovalent group (for example, having 8 to 60 carbon atoms) that has two or more rings condensed to each other, only carbon atoms as a ring forming atom, and non-aromacity in the entire molecular structure. A detailed example of the monovalent non-aromatic condensed polycyclic group is a fluorenyl group. A divalent non-aromatic condensed polycyclic group used herein refers to a divalent group having the same structure as the monovalent non-aromatic condensed polycyclic group.

A monovalent non-aromatic condensed heteropolycyclic group used herein refers to a momovalent group (for example, having 2 to 60 carbon atoms) that has two or more rings condensed to each other, has a heteroatom selected from N, O P, and S, other than carbon atoms, as a ring forming atom, and has non-aromacity in the entire molecular structure. An example of the monovalent non-aromatic condensed heteropolycyclic group is a carbazolyl group. A divalent non-aromatic condensed heteropolycyclic group used herein refers to a divalent group having the same structure as the monovalent non-aromatic condensed heteropolycyclic group.

Hereinafter, an organic light-emitting device according to an embodiment is described in detail with reference to Synthesis Example and Examples. However, the organic light-emitting device is not limited thereto. The wording “B was used instead of A” used in describing Synthesis Examples means that a molar equivalent of A was identical to a molar equivalent of B.

EXAMPLES

Synthesis Example 1-1

Synthesis of Compound 1

Synthesis of Intermediate 1-1

Intermediate 1-1 was synthesized according to Reaction Scheme 1-(1):

3.6 g (17.3 mmol) of 2-(2,4-difluorophenyl)-4-methylpyridine was dissolved in 45 mL of 2-ethoxyethanol, and then 2.4 g (7.6 mmol) of iridiumchloride hydrate and 15 mL of distilled water was added thereto, and the result was stirred at 130° C. for 20 hours. After the reaction stopped, a reaction solution was cooled to ambient temperature, and a precipitate was filtered, and then the precipitate was washed with methanol and dried under a vacuum condition to obtain 4.3 g of Intermediate 1-1 (yield: 60%) that is a dimer.

Synthesis of Compound 1

Compound 1 was synthesized according to Reaction Scheme 1-(2) below:

1.0 g (1.03 mmol) of Intermediate 1-1 obtained by Reaction Scheme 1-(1), 0.48 g (2.44 mmol) of 2-(2,4-difluoro-3-trifluoromethylphenyl)-4-methylpyridine, and 0.34 g (2.46 mmol) of K2CO3were dissolved in 30 mL of 2-ethoxyethanol and stirred at 130° C. for 12 hours. After the reaction stopped, a reaction solution was cooled to ambient temperature (25° C.), and the precipitate was filtered and washed with methanol. The obtained precipitate was dissolved in dichloromethane and was filtered through a silica short pad, and then a filtrated dichloromethane solution was heated, and methanol was added dropwise thereto, and the solution was precipitated to obtain 0.60 g of Compound 1 (yield: 53%).

Synthesis Example 2-1

Synthesis of Compound A1

Compound A1 was synthesized according to Reaction Scheme 2-(1) below:

Synthesis of Intermediate A1-1

5 g (1 eq, 29.06 mmol) of 2-bromo-3-methylpyridine, 6.12 g (1.05 eq, 30.52 mmol) of 4-bromophenylboronic acid, and 1.34 g (0.04 eq, 1.16 mmol) of Pd(PPh3)4(tetrakis(triphenylphosphine)palladium(0)) were placed in a reaction flask and vacuum dried, and the reaction flask was filled with nitrogen gas thereafter. 72 mL of toluene was added to the reaction flask so as to dissolve the compounds, and 36 mL of ethanol and 36 mL 2.0 M of sodium carbonate solution (2.5 eq, 72.65 mmol) were added thereto, and the result was refluxed and stirred for 3 hours at 120° C. When the reaction stopped, the reaction product was washed with distilled water, and then was extracted by using ethyl acetate to collect an organic layer. The organic layer was dried by using anhydrous magnesium sulfate, and then a solvent was removed therefrom by distilling under reduced pressure. The obtained residue was separated and purified by silica gel column chromatography to produce 4.5 g (yield: 60%) of Intermediate A1-1. Intermediate 1 was identified by1H-NMR and APCI-MS.

Synthesis of Intermediate A1-2

5.88 g (1 eq, 21.14 mmol) of 2-(4-bromophenyl) nicotinic acid that was quantitatively obtained by allowing Intermediate A1-1 to react with KMnO4solution was placed in a reaction flask and was reacted with 30 g of polyphosphoric acid. After the reaction stopped, the result was placed in a beaker containing sodium hydroxide solution (5N), and then the result was stirred at ambient temperature and filtered. 3.3 g of Intermediate A1-2 (yield: 60%) as a yellow solid was obtained. Intermediate 2 was identified by1H-NMR and APCI-MS.

Synthesis of Intermediate A1-3

3.29 g (1 eq, 14, 09 mmol) of 2-bromobiphenyl was placed in a reaction flask and was dissolved in 150 mL of tetrahydrofuran (THF). 4.67 mL (14.09 eq, 8.78 mmol) of 1.6 M n-BuLi was added dropwise to the reaction flask at −78° C. After stirring the solution for 30 minutes at −78° C., 3.3 g (0.9 eq, 12.69 mmol) of Intermediate A1-2 was added thereto, and then the resultant solution was stirred for 5 hours. When the reaction stopped, the reaction product was washed with distilled water, and then extracted by using ethyl acetate to collect an organic layer. A solvent was evaporated from the collected organic layer, and then, the residue was placed in a flask, and 5 mL of MeSO3H was added dropwise thereto to cause a reaction. The reaction solution was extracted by using ethyl acetate and then an organic layer was collected therefrom. The collected organic layer was dried by using anhydrous magnesium sulfate, and then the solvent was removed therefrom by distilling under reduced pressure. The obtained residue was separated and purified by silica gel column chromatography to produce 3.4 g of Intermediate A1-3 (yield: 70%). Intermediate A1-3 was identified by1H-NMR and APCI-MS.

Synthesis of Compound A1

3.4 g (1 eq, 8.57 mmol) of Intermediate A1-3, 2.81 g (1.03 eq, 9.43 mmol) of 9-phenylanthracen-10-ylboronic acid, and 396 mg (0.04 eq, 0.343 mmol) of Pd(PPh3)4(tetrakis(triphenylphosphine)palladium(0)) were placed in a reaction flask and vacuum dried, and the reaction flask was filled with nitrogen gas thereafter. 40 mL of toluene was added to the flask so as to dissolve the reactants. Next, 15 mL (2.5 eq, 21.4 mmol) of ethanol and 15 mL (2.5 eq, 21.4 mmol) of 2.0 M sodium carbonate solution were added thereto, and the result was refluxed and stirred for 3 hours at 120° C. When the reaction stopped, the reaction product was washed with distilled water, and then extracted by using ethyl acetate to collect an organic layer. The collected organic layer was dried by using anhydrous magnesium sulfate, and then the solvent was removed therefrom by distilling under reduced pressure. The obtained residue was separated and purified by silica gel column chromatography to produce 3.8 g of Compound 1 (yield: 78%). Compound A1 was identified by 1H-NMR and APCI-MS.

Synthesis Example 2-2

Synthesis of Compound A2

Compound A2 was synthesized according to Reaction Scheme 2-(2) below:

Synthesis of Intermediate A2-1

2.83 g (1 eq, 29.06 mmol) of methyl 2-chloronicotinate, 6.12 g (1.05 eq, 30.52 mmol) of 4-bromophenylboronic acid, and 1.34 g (0.04 eq, 1.16 mmol) of Pd(PPh3)4(tetrakis(triphenylphosphine)palladium(0)) were placed in a reaction flask and vacuum dried, and the reaction flask was filled with nitrogen gas thereafter. 72 mL of toluene was added to the flask so as to dissolve the compounds, and 36 mL of ethanol and 36 mL (2.5 eq, 72.65 mmol) of 2.0 M sodium carbonate solution were added thereto, and the result was refluxed and stirred for 3 hours at 120° C. When the reaction stopped, the reaction product was washed with distilled water, and then extracted by using ethyl acetate to collect an organic layer. The collected organic layer was dried by using anhydrous magnesium sulfate, and then the solvent was removed therefrom by distilling under reduced pressure. The obtained residue was separated and purified by silica gel column chromatography to produce 3.37 g (yield: 60%) of Intermediate A2-1. Compound A2-1 was identified by1H-NMR and APCI-MS.

Synthesis of Intermediate A2-2

3.37 g (1 eq, 11.54 mmol) of Intermediate A2-1 was placed in a reaction flask and vacuum dried, and the reaction flask was filled with nitrogen gas thereafter. 100 mL of tetrahydrofuran (THF) was added thereto, and then 9.6 mL of 3.0 M methylmagnesium chloride (CH3MgCl) was slowly added dropwise thereto. When the reaction stopped, the reaction product was washed with distilled water, and then extracted by using ethyl acetate to collect an organic layer. The collected organic layer was dried by using anhydrous magnesium sulfate, and then the solvent was removed therefrom by distilling under reduced pressure. The obtained residue was placed in a flask, and then 30 g of polyphosphoric acid was added thereto, and then the result was refluxed and stirred at 190° C. When the reaction stopped, the reaction product was washed with distilled water, and then extracted by using ethyl acetate to collect an organic layer. The collected organic layer was dried by using anhydrous magnesium sulfate, and then the solvent was removed therefrom by distilling under reduced pressure. The obtained residue was separated and purified by silica gel column chromatography to produce 1.6 g (yield: 70%) of Intermediate A2-2. Intermediate A2-2 was identified by1H-NMR and APCI-MS.

Synthesis of Compound A2

1.6 g (1 eq, 5.83 mmol) of Intermediate A2-2, 1.91 g (1.1 eq, 6.42 mmol) of 9-phenylanthracen-10-ylboronic acid, and 270 mg (0.04 eq, 0.23 mmol) of Pd(PPh3)4(tetrakis(triphenylphosphine)palladium(0)) were placed in a flask and vacuum dried, and the flask was filled with nitrogen gas thereafter. 20 mL of toluene was added to the flask so as to dissolve the reactants. Next, 9 mL of ethanol and 9 mL of 2.0 M sodium carbonate solution (3 eq, 17.5 mmol) were added thereto, and the result was refluxed and stirred for 3 hours at 120° C. When the reaction stopped, the reactant was washed with distilled water, and then an extraction process of an organic layer was performed by using ethyl acetate. The collected organic layer was dried by using anhydrous magnesium sulfate, and then the solvent was removed therefrom by distilling under reduced pressure. The obtained residue was separated and purified by silica gel column chromatography to produce 1.7 g of Compound A2 (yield: 65%). Compound A2 was identified by 1H-NMR and APCI-MS.

Synthesis Example 2-3

Synthesis of Compound A3

Compound A3 was synthesized according to Reaction Scheme 2-(3) below:

Synthesis of Intermediate A3-1

Intermediate A3-1 was obtained in the same manner as in Synthesis of Intermediate A1-1, except that 2-bromophenylboronic acid was used instead of 4-bromophenylboronic acid. 5 g of Intermediate A3-1 (yield: 75%) was identified by1H-NMR and APCI-MS.

Synthesis of Intermediate A3-2

3 g of Intermediate A3-2 (yield: 89%) was obtained in the same manner as in Synthesis of Intermediate A1-2, except that Intermediate A3-1 was used instead of Intermediate A1-1. Intermediate A3-2 was identified by1H-NMR and APCI-MS.

Synthesis of Intermediate A3-3

2.6 g of Intermediate A3-2 (yield: 90%) was obtained in the same manner as in Synthesis of Intermediate 3, except that Intermediate A3-2 was used instead of Intermediate A1-2. Intermediate A3-3 was identified by 1H-NMR and APCI-MS.

Synthesis of Compound A3

1.72 g of Intermediate A3 (yield: 61%) was obtained in the same manner as in Synthesis of Compound 1, except that Intermediate A3-3 was used instead of Intermediate A1-3. Compound A3 was identified by1H-NMR and APCI-MS.

Synthesis Example 2-4

Synthesis of Compound A4

Compound A4 was synthesized according to Reaction Scheme 2-(4):

Synthesis of Intermediate A4-1

3.25 g of Intermediate A4-1 (yield: 47%) was obtained in the same manner as in Synthesis of Intermediate A2-1, except that 2-bromophenylboronic acid was used instead of 4-bromophenylboronic acid. Intermediate A4-1 was identified by1H-NMR and APCI-MS.

Synthesis of Intermediate A4-2

1.13 g of Intermediate A4-2 (yield: 60%) was obtained in the same manner as in Synthesis of Intermediate A2-2, except that Intermediate A4-1 was used instead of Intermediate A3-1, and CH3MgBr was used instead of CH3MgCl. Intermediate A4-2 was identified by1H-NMR and APCI-MS.

Synthesis of Compound A4

1.82 g of Intermediate A4 (yield: 76%) was obtained in the same manner as in Synthesis of Compound A2, except that Intermediate A4-2 was used instead of Intermediate A2-2. Compound A4 was identified by1H-NMR and APCI-MS.

An ITO glass substrate (a product of Corning Co., Ltd) with an ITO layer having a resistance and thickness of 15 Ω/cm2(500 Å) thereon was cut to a size of 50 mm×50 mm×0.7 mm, and then, sonicated by using isopropyl alcohol and pure water each for 5 minutes, and cleaned by the exposure to ultraviolet rays for 30 minutes, and then ozone, and the ITO glass substrate was mounted on a vacuum deposition apparatus.

2-TNATA was vacuum deposited on the ITO glass substrate to form a hole injection layer having a thickness of 600 Å, and then, NPB was vacuum deposited on the hole injection layer to form a hole transport layer having a thickness of 300 Å, and then, Compound A1 (host) and Compound 1 (dopant) were co-deposited at a weight ratio of 95:5 on the hole transport layer to form an emission layer having a thickness of 300 Å.

Thereafter, Compound 101, below, was deposited on the emission layer to form an electron transport layer having a thickness of 300 Å, and LiF was deposited on the electron transport layer to form an electron injection layer having a thickness of 10 Å, and A1 was deposited on the electron injection layer to form a cathode having a thickness of 1,000 Å, thereby completing the manufacture of an organic light-emitting device.

An organic light-emitting device was manufactured in the same manner as in Example 1, except that in forming an emission layer, as a host, Compound A2 was used instead of Compound A1.

An organic light-emitting device was manufactured in the same manner as in Example 1, except that in forming an emission layer, as a host, Compound A3 was used instead of Compound A1.

An organic light-emitting device was manufactured in the same manner as in Example 1, except that in forming an emission layer, as a host, Compound A4 was used instead of Compound A1.

An organic light-emitting device was manufactured in the same manner as in Example 1, except that in forming an emission layer, as a dopant, Compound 2 was used instead of Compound 1.

Evaluation Example 1

Driving voltage and efficiency of the organic light-emitting devices of Examples 1 to 5 were measured by using a current-voltage meter (Kethley SMU 236) and a luminance meter PR650 Spectroscan Source Measurement Unit. (product of PhotoResearch). Results thereof are shown in Table 1.

From Table 1, it may be that the organic light-emitting devices of Examples 1 to 5 had low driving voltage and high luminescent efficiency.

An organic light-emitting device including an organometallic compound and a condensed cyclic compound according to an embodiment may have a low driving voltage, high efficiency, high brightness, and long lifespan.