CN103730588B - A kind of laminated organic electroluminescent device based on monolayer luminescence unit - Google Patents

Abstract

The invention relates to a laminated organic electroluminescent device based on a single-layer light-emitting unit, which belongs to the technical field of organic electroluminescent devices. The device is sequentially composed of a substrate, an anode, an alternately arranged single-layer organic light-emitting unit, a charge generation layer, and a cathode. The single-layer organic light-emitting unit is composed of an organic light-emitting dye doped in the matrix material in the form of a dopant. The matrix material of the odd-numbered layer light-emitting unit adopts an organic material with high hole mobility, and the matrix material of the even-numbered layer light-emitting unit adopts Organic materials with high electron mobility. Since the light-emitting unit adopts a single-layer structure, the number of functional layers of the laminated device is reduced, which is beneficial to the preparation of the laminated device. In addition, because the carrier transport polarity of the organic material used in the charge generation layer is inconsistent with the parent material of the adjacent single-layer light-emitting unit, it ensures that the exciton recombination region of each light-emitting unit is far away from the cathode and anode, which weakens the traditional The exciton quenching effect in the single-layer device ensures that the stacked device with this structure has better performance.

Description

A stacked organic electroluminescent device based on a single-layer light-emitting unit

technical field

The invention belongs to the technical field of organic electroluminescent devices, in particular to a laminated organic electroluminescent device based on a single-layer light-emitting unit.

Background technique

Due to its potential advantages in full-color display, liquid crystal backlight and solid-state lighting applications, organic electroluminescent devices have set off a research boom in the world in recent years. Organic electroluminescent technology has the advantages of low energy consumption, active light emission, wide viewing angle, fast response speed, flexible display, and low cost, making it promising to become a new generation of flat panel display technology. Research institutions and large companies are optimistic about using it as a new generation of solid-state lighting sources.

The concept of stacked organic electroluminescent devices was first proposed by the Forrest research group of Princeton University. In order to achieve full-color display, they stacked red, green, and blue primary color unit devices vertically through the middle electrode [Appl.Phys.Lett .(1996) 69,2959; Adv.Mater(1999) 11,907], but the unit devices of the laminated device of this structure are controlled by their own independent current sources, and the preparation process and testing process are complicated. Since 2003, many well-known scientific research institutions in the world have carried out research on a new type of stacked organic light-emitting device [Appl. Mater. (2008) 20,324], this stacked device vertically connects the light-emitting units in series through the charge generation layer. The current efficiency and external quantum efficiency of stacked organic electroluminescent devices are proportional to the number of the same stacked light-emitting units at the same current density, so high luminous brightness and efficiency can be obtained at a small current density . In a stacked organic electroluminescent device, each light-emitting unit is generally composed of organic functional layers such as a hole transport layer, a light-emitting layer, and an electron transport layer, which leads to too many layers in the stacked device, and the preparation process It is complicated and not conducive to large-scale commercial production, thus restricting the application of stacked organic electroluminescent devices. In 2003, Gao Y.D. et al. reported a single-layer organic electroluminescent device with a simple structure [Appl.Phys.Lett.(2003) 82,155]. Although the brightness of the device can reach ^16000cd /m The exciton recombination region of the device is close to the electrode, causing the excitons to be easily quenched at the electrode, so the efficiency of the single-layer device with this structure is still not as good as that of the multi-layer device. Considering that the light-emitting unit of the stacked device is far away from the electrode, if a single-layer light-emitting unit device is introduced into the stacked device, it can not only simplify the preparation process of the stacked device, but also solve the problem of excitons in the single-layer device through structural design. Due to the quenching problem at the electrode, good luminescent performance is achieved. Unfortunately, no researchers have proposed such a stacked organic electroluminescent device based on a single-layer light-emitting unit so far.

Contents of the invention

The invention aims at the shortcoming of the complex structure of the laminated organic electroluminescent device, and provides a laminated organic electroluminescent device based on a single-layer organic light-emitting unit. The stacked organic electroluminescent device is composed of a substrate, an anode, alternately arranged single-layer organic light-emitting units, charge generation layers, and cathodes. The number of single-layer organic light-emitting units is N, and the number of charge generation layers is N-1. , N is an integer greater than or equal to 2;

Different from the traditional light-emitting unit composed of a hole transport layer, a light-emitting layer and an electron transport layer, each light-emitting unit of the laminated device with the structure of the present invention is a single-layer structure.

Substrate; the substrate material can be a rigid substrate such as glass or silicon, or a flexible substrate such as polyethylene terephthalate or polymethyl methacrylate;

Anode; the anode can be transparent metal oxide ITO, FTO, or high work function metal Ag, Au, Cu, etc., and any anode material can also be used, and an anode buffer layer can also be inserted between the anode and the light-emitting unit layer to improve the space. Hole injection, the anode buffer layer can use MoO ₃ , WO ₃ , V ₂ O ₅ and so on.

Cathode; the cathode can be metals such as Al, Ca, Ba, etc. with low work function, or any other cathode material, and a modification layer such as LiF, Cs ₂ CO ₃ can also be inserted between the organic light-emitting unit and the cathode to improve electron injection, The thickness of the modification layer is generally less than 2 nm.

There are multiple single-layer organic light-emitting units between the anode and the cathode. The thickness of the single-layer organic light-emitting unit is 50-150nm. It is composed of organic light-emitting dyes doped in a single matrix material in the form of dopants. The parent material of the unit is an organic material with high hole mobility, such as 4,4′,4″-tris(N-3-methylphenyl-N-phenylamino)triphenylamine (4,4′,4 ″-Tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine, m-MTDATA), 4,4′-bis(9-carbazole)biphenyl (4,4′-Bis(N-carbazolyl)- 1,1′-biphenyl, CBP), 1,3-di-9-carbazolylbenzene (1,3-Di-9-carbazolylbenzene, MCP), N,N′-diphenyl-N,N′- Bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (N,N′-Bis(3-methylphenyl)-N,N′-bis(phenyl)benzidine, TPD ), etc., without limitation. The parent material of the light-emitting unit of the even layer adopts an organic material with high electron mobility, such as 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (1,3,5- Tris(1-phenyl-1H-benzimidazol-2-yl)-benzene, TPBi), 2,9-dimethyl-4,7-biphenyl-1,10-phenanthroline (2,9-Dimethyl-4 ,7-diphenyl-1,10-phenanhroline, BCP), 4,7-diphenyl-1,10-phenanthroline (4,7-diphenyl-1,10-Phenanthroline, Bphen), three (8-hydroxy Quinoline) aluminum (Aluminum Tris (8-Hydroxyquinolinate), Alq ₃ ) and the like, but not limited thereto. Organic luminescent dyes can use fluorescent luminescent materials or phosphorescent luminescent materials, such as bis(4,6-difluorophenylpyridine-C2,N)pyridinium iridium (Bis[2-(4,6-difluorophenyl)pyridinato-C2 ,N](picolinato)iridium(III),FIrPic), three(2-phenylpyridinium-C2,N)iridium(III)(Tris(2-phenylpyridinato-C2,N)iridium(III),Ir(ppy ) ₃ ), acetylacetonate bis (1-phenylisoquinoline-C2, N) iridium (III) (Bis (1-phenyl-isoquinoline-C2, N) (acetylacetonato) iridium (III), Ir (piq ) ₂ (acac)), acetylacetonate bis(2-phenylbenzothiazole-C2,N) iridium(III)(Bis(2-phenyl-benzothiazole-C2,N)(acetylacetonate)iridium(III), Ir(bt) ₂ (acac)), etc., can use any high-efficiency luminescent dye and is not limited thereto. The doping concentration of the luminescent dye is 0.1wt% to 30wt%, so as to facilitate the energy transfer between the matrix and the luminescent dye.

Between every two organic light-emitting units is a charge generation layer; each charge generation layer is composed of an N-type semiconductor layer/metal layer/P-type semiconductor layer, and the parent material of the N-type semiconductor layer can be TPBi, BCP, Bphen, Alq ₃ For the electron transport material, one or more of Li, Na, K, Rb, Cs, Mg, Cs ₂ CO ₃ is used as the N-type dopant, and any N-type dopant material can be used and is not limited thereto. The parent material of the P-type semiconductor can be N,N'-diphenyl-N,N'-(1-naphthyl)-1,1'-biphenyl-4,4'-diamine, (N,N '-Bis-(1-naphthalenyl)-N,N'-bis-phenyl-(1,1'-biphenyl)-4,4'-diamine, NPB), 4,4'-cyclohexyl bis[N,N - Di-(4-methylphenyl)aniline] (Di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane, TAPC), CBP, MCP and other materials with good hole transport properties, P-type doped Miscellaneous agent can use 2,3,5,6-tetrafluoro-7,7',8,8'-tetracyanoquinodimethylmethane (tetrafluorotetracyanoquinodimethylethane, F4-TCNQ), FeCl ₃ , or MoO ₃ , WO ₃ , V ₂ O ₅ and other oxides, any P-type dopant material can be used and is not limited thereto. The triplet energy level of the parent material of the selected N and P type semiconductor layers must be greater than that of the dye in the adjacent light-emitting unit, and the doping concentration of N and P type dopants is 1wt% to 50wt%. The metal layer can use Ag, Au, etc. or metals co-doped in different proportions, and is not limited thereto.

The materials mentioned above can be purchased from Taiwan Hanwa Technology Co., Ltd. (company website: http://www.lumtec.com.tw).

The beneficial effects of the invention are: since the light-emitting unit adopts a single-layer structure, the number of functional layers of the laminated device is reduced, which is beneficial to the preparation of the laminated device. In addition, since the carrier transport polarity of the organic material used in the charge generation layer is inconsistent with the parent material adjacent to the single-layer light-emitting unit, it ensures that the exciton recombination region of each light-emitting unit is far away from the cathode and anode electrodes, weakening the excitons. Influenced by the quenching effect, and due to the pairing of holes and electrons in the stacked device, the carrier injection balance of the stacked device is ensured, which is conducive to the realization of high-efficiency light emission.

Description of drawings

Figure 1: Schematic diagram of the structure of a stacked organic electroluminescent device based on a single-layer light-emitting unit according to the present invention;

Among them, 1 is the substrate, 2 is the anode, 3-1, 3-2, ..., 3-N are the first light-emitting unit, the second light-emitting unit, ..., the Nth light-emitting unit, 4-1, 4- 2, ..., 4-(N-1) are respectively the first charge generation layer, the second charge generation layer, ..., the N-1th charge generation layer, and 5 is the cathode. N is an integer greater than or equal to 2.

Figure 2: The current efficiency-voltage curve of the stacked organic electroluminescent device based on the single-layer light-emitting unit of the present invention;

Fig. 3: The luminance-current density curve of the stacked organic electroluminescent device based on a single-layer light-emitting unit according to the present invention.

detailed description

The meanings of the abbreviated names in the examples are as follows:

ITO: indium tin oxide; used as a transparent anode

MoO ₃ : molybdenum oxide; it can be used as a buffer layer of ITO anode, which is beneficial to hole injection, and can also be used as a P-type dopant in the charge generation layer;

MCP: 1,3-di-9-carbazolylbenzene; the precursor for blue phosphorescent materials, with strong hole transport ability.

FIrPic: Bis(4,6-difluorophenylpyridine-C2,N)pyridyl iridium, a high-efficiency blue phosphorescent luminescent material.

Bphen: 4,7-diphenyl-1,10-phenanthroline; used as the parent material of the N-type semiconductor in the charge generation layer;

Ag: silver. 1nm silver is used for the intermediate electrode between P and N-type semiconductors in the charge generation layer.

Cs ₂ CO ₃ : cesium carbonate; it can be used not only as a cathode buffer layer, but also as a dopant for the N-type semiconductor in the charge generation layer;

TAPC: 4,4′-cyclohexylbis[N,N-bis(4-methylphenyl)aniline]; used as the parent material of P-type semiconductor in the charge generation layer;

TPBi: 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene; the parent material of the second light-emitting unit, with strong electron transport ability;

Mg:Ag:magnesium:silver with a volume ratio of 10:1 is used as the cathode.

Example 1:

The preparation of organic light-emitting devices can be carried out in a multi-source organic molecular vapor deposition system. The detailed process is as follows:

[1] The substrate material in the experiment is ITO conductive glass. First, scrub the ITO glass substrate repeatedly with acetone and ethanol cotton balls;

[2] Put the scrubbed ITO substrate into a clean beaker and use acetone, ethanol, and deionized water to ultrasonicate for 10 minutes, then dry it in an oven, and finally UV-treat the dry and clean ITO glass substrate for 10 minutes. minute;

[3] Place the processed substrate in a multi-source organic molecule vapor deposition system (see Chinese patent: ZL03110977.2, "Pot-increasing evaporation source for organic electroluminescence coating machine"), the vacuum of the evaporation system The cavity includes an organic evaporation area (8 evaporation sources) and a metal evaporation area (3 evaporation sources), and the two areas and each evaporation source are isolated from each other to avoid mutual pollution. The vacuum degree of the system can reach 10 ^-5 Pa, and the vacuum degree of the system is maintained at about 3×10 ^-4 Pa during the film growth process. The thickness and growth rate of material growth are controlled by the American IL-400 film thickness controller, and the growth rate of organic materials is controlled at The electroluminescent spectrum, luminance and current-voltage characteristics of the device are measured simultaneously by a testing system consisting of a spectrometer PR650, an ammeter Keithley-2400 and a computer. All tests are done in room temperature atmosphere.

[4] This example is a stacked device with two light-emitting units stacked. The device structure is: ITO/MoO ₃ (2nm)/MCP: FIrPic (8wt%, 100nm)/charge generation layer/TPBi: FIrPic (8wt%, 100 nm)/Cs ₂ CO ₃ (0.8 nm)/Mg:Ag (10:1). The charge generation layer is: Bphen:Cs ₂ CO ₃ (5wt%, 20nm)/Ag (1nm)/TAPC:MoO ₃ (20wt%, 20nm).

The current efficiency-voltage curve and brightness-current density curve of the laminated device of the present invention are shown in Figures 2 and 3, respectively. It can be seen from the figure that the stacked organic electroluminescent device based on the single-layer light-emitting unit of the present invention has good photoelectric performance, the maximum current efficiency can reach 34.3cd/A, and the maximum brightness is 21000cd/m ² .

Although the present invention has been described in conjunction with the examples, the present invention is not limited to the above examples and accompanying drawings. For researchers in the technical field, the present invention can also be modified, and these improvements also belong to the protection scope of the claims of the present invention Inside.

Claims (4)

1. A stacked organic electroluminescent device based on a single-layer organic light-emitting unit, characterized in that: the stacked organic electroluminescent device consists of substrates, anodes, alternately arranged single-layer organic light-emitting units and charge generation layers , cathode composition, the number of single-layer organic light-emitting units is N, the number of charge generation layers is N-1, and N is an integer greater than or equal to 2; the thickness of the single-layer organic light-emitting unit is 50-150nm, which is composed of organic light-emitting dyes The form of the dopant is doped in a single matrix material, and the doping concentration of the organic luminescent dye is 0.1wt% to 30wt%; 3-methylphenyl-N-phenylamino)triphenylamine, 4,4'-bis(9-carbazole)biphenyl, 1,3-bis-9-carbazolylbenzene or N,N'-bis Phenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine is a material with high hole mobility; the parent material of the light-emitting unit of the even layer is 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, 2,9-dimethyl-4,7-biphenyl-1,10-phenanthroline, 4, 7-diphenyl-1,10-phenanthroline or tris(8-hydroxyquinoline)aluminum is a material with high electron mobility; the charge generation layer is composed of N-type semiconductor layer/metal layer/P-type semiconductor layer; organic light emitting The dyes are bis(4,6-difluorophenylpyridine-C2,N)pyridinecarboyl iridium, tris(2-phenylpyridine-C2,N)iridium(III), bis(1-phenyl acetylacetonate) Base isoquinoline-C2, N) iridium (III) or acetylacetonate bis (2-phenylbenzothiazole-C2, N) iridium (III); the parent material of the N-type semiconductor layer is 1,3, 5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene 2,9-dimethyl-4,7-biphenyl-1,10-phenanthroline, 4,7-diphenyl -1,10-phenanthroline or tris(8-hydroxyquinoline)aluminum, the N-type dopant is one or more of Li, Na, K, Rb, Cs, Mg, Cs ₂ CO ₃ , N The doping concentration of the type dopant is 1wt% to 50wt%; the parent material of the P-type semiconductor is N,N'-diphenyl-N,N'-(1-naphthyl)-1,1'-biphenyl -4,4'-diamine, 4,4'-cyclohexylbis[N,N-bis(4-methylphenyl)aniline], 4,4'-bis(9-carbazole)biphenyl or 1 ,3-di-9-carbazolylbenzene, the P-type dopant is 2,3,5,6-tetrafluoro-7,7',8,8'-tetracyanoquinodimethane, FeCl ₃ , MoO ₃ , WO ₃ or V ₂ O ₅ , the doping concentration of the P-type dopant is 1wt%˜50wt%. 2. A stacked organic electroluminescent device based on a single-layer organic light-emitting unit as claimed in claim 1, wherein the substrate is glass, silicon, polyethylene terephthalate or polymethyl Methyl acrylate. 3. A stacked organic electroluminescent device based on a single-layer organic light-emitting unit according to claim 1, wherein the anode is ITO, FTO, Ag, Au or Cu. 4. A stacked organic electroluminescent device based on a single-layer organic light-emitting unit as claimed in claim 1, wherein the cathode is made of Al, Ca or Ba.