JP2007027386A - Organic EL element and organic EL display device - Google Patents

Abstract

A structure advantageous in increasing the luminance and extending the life of an organic EL element is provided.
An organic EL element OLED according to the present invention is a non-injection type organic EL element, and includes a pair of electrodes E1 and E2 facing each other, a light emitting material EM and an electron donor ED interposed therebetween. And a light emitting layer EMT made of a mixture containing the electron acceptor EA.
[Selection] Figure 1

Description

  The present invention relates to an organic EL element and an organic EL display device.

  Organic electroluminescence elements are required to have high brightness and long life. For this reason, many technologies that meet such demands have been proposed.

  For example, Patent Document 1 describes that an organic EL element employs a structure in which a laminated body in which a plurality of light emitting units are stacked via layers forming equipotential surfaces is sandwiched between an anode and a cathode. . In this structure, since a plurality of light emitting units are connected in series, high current efficiency (or quantum efficiency) can be realized, and therefore, it is advantageous for high luminance and long life of the device.

Patent Document 2 describes a structure similar to that described in Patent Document 1. In the structure described in Patent Document 2, an electrically insulating charge generation layer is used instead of a layer forming an equipotential surface.
JP 2003-45676 A JP 2003-272860 A

  An object of the present invention is to provide a structure that is advantageous for increasing the luminance and extending the life of an organic EL element.

  According to the first aspect of the present invention, there is provided a pair of electrodes facing each other, and a light emitting layer that is interposed between them and is made of a mixture including a light emitting material, an electron donor, and an electron acceptor. A non-injection type organic EL device is provided.

  According to a second aspect of the present invention, there is provided an organic EL display device comprising a plurality of pixels, each pixel including an organic EL element according to the first aspect.

  ADVANTAGE OF THE INVENTION According to this invention, the structure advantageous for high-intensity and long lifetime of an organic EL element is provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same referential mark is attached | subjected to the same or similar component, and the overlapping description is abbreviate | omitted.

  FIG. 1 is a cross-sectional view schematically showing an organic EL element according to one embodiment of the present invention. This organic EL element OLED includes electrodes E1 and E2 and a light emitting layer EMT. The electrodes E1 and E2 face each other. The light emitting layer EMT is interposed between the electrodes E1 and E2.

  The light emitting layer EMT is made of a mixture containing a light emitting material EM, an electron donor ED, and an electron acceptor EA. The light emitting material EM includes a host material HST and a dopant DPT.

  This organic EL element OLED is a non-injection type organic EL element. That is, the organic EL element OLED can emit light without injecting charges from the outside into the light emitting layer EMT. This will be described below.

  In this organic EL element OLED, at least a part of the electron donor ED and the electron acceptor EA forms a charge transfer complex. Therefore, when a voltage is applied between the electrodes E1 and E2, electrons and holes move in opposite directions along the voltage application direction. Some of them recombine during these charge transfer processes. As a result, the light emitter LM is excited in the vicinity of the position where recombination occurs, and as a result, the light emitting layer EMT emits light.

  In this organic EL element OLED, the number of holes generated in the light emitting layer EMT is equal to the number of electrons. Therefore, high quantum efficiency can be realized. In addition, in this organic EL element OLED, light is emitted without injecting charges into the light emitting layer EMT from the outside, so that there are very few restrictions on the materials of the electrodes E1 and E2. Therefore, a material that does not easily cause deterioration of the organic EL element OLED with time can be used for the electrodes E1 and E2. Therefore, this structure is advantageous for increasing the luminance and extending the life of the organic EL element OLED.

As the host material HST, organic substances or organometallic compounds such as anthracenes, amines, styryls, siloles, azoles, polyphenyls, and metal complexes can be used. For example, as the host material HST, diphenylanthracene derivative, biscarbazole, styrylamine, distyrylarylene, oxazole, oxadiazole, benzimidazole, tris (8-hydroxyquinolate) aluminum (Alq ₃ ) and the like may be used. .

As the dopant DPT, organic substances or organic metal compounds such as dicyanomethylenepyrans, dicyanos, phenoxazones, thioxanthenes, rubrenes, styryls, coumarins, quinacridones, condensed polycyclic aromatic rings, and heavy metal complexes are used. Can be used. For example, as a dopant DPT, a complex (Ir (ppy) ₃ ) in which coumarin, rubrene, perylene, azathioxanthene, N-methylquinacridone, diphenylnaphthacene, perifuranthene, and phenylpyridine are coordinated to iridium three times is used. Also good.

As the electron donor ED, organic substances such as arylamines and organometallic compounds can be used. For example, as the electron donor ED, N, N, N ′, N′-tetraphenyl-4,4′-diaminophenyl, N, N′-diphenyl-N, N′-di (3-methylphenyl) -4 , 4′-diaminobiphenyl, 2,2-bis (4-di-p-tolylaminophenyl) propane, N, N, N ′, N′-tetra-p-tolyl-4,4′-diaminobiphenyl, bis (4-Di-p-tolylaminophenyl) phenylmethane, N, N′-diphenyl-N, N′-di (4-methoxyphenyl) -4,4′-diaminobiphenyl, N, N, N ′, N '-Tetraphenyl-4,4'-diaminodiphenyl ether, 4,4'-bis (diphenylamino) quadriphenyl, 4-N, N-diphenylamino- (2-diphenylvinyl) benzene, 3-methoxy-4' -N, N-diphenyla Nosylbenzene, N-phenylcarbazole, 1,1-bis (4-di-p-triaminophenyl) -cyclohexane, 1,1-bis (4-di-p-triaminophenyl) -4-phenylcyclohexane, Bis (4-dimethylamino-2-methylphenyl) -phenylmethane, N, N, N-tri (p-tolyl) amine, 4- (di-p-tolylamino) -4 ′-[4 (di-p- Tolylamino) styryl] stilbene, N, N, N ′, N′-tetraphenyl-4,4′-diamino-biphenyl N-phenylcarbazole, 4,4′-bis [N- (1-naphthyl) -N-phenyl -Amino] biphenyl, 4,4 ″ -bis [N- (1-naphthyl) -N-phenyl-amino] p-terphenyl, 4,4′-bis [N- (3-acenaphthenyl) -N-phenyl -A No] biphenyl, 1,5-bis [N- (1-naphthyl) -N-phenyl-amino] naphthalene, 4,4′-bis [N- (9-anthryl) -N-phenyl-amino] biphenyl, 4, , 4 ″ -bis [N- (1-anthryl) -N-phenyl-amino] p-terphenyl, 4,4′-bis [N- (2-phenanthryl) -N-phenyl-amino] biphenyl, 4, , 4′-bis [N- (8-fluoranthenyl) -N-phenyl-amino] biphenyl, 4,4′-bis [N- (2-pyrenyl) -N-phenyl-amino] biphenyl, 4,4 '-Bis [N- (2-perylenyl) -N-phenyl-amino] biphenyl, 4,4'-bis [N- (1-coronenyl) -N-phenyl-amino] biphenyl, 2,6-bis (di -P-tolylamino) naphthalene, 2,6- Bis [di- (1-naphthyl) amino] naphthalene, 2,6-bis [N- (1-naphthyl) -N- (2-naphthyl) amino] naphthalene, 4.4 ″ -bis [N, N— Di (2-naphthyl) amino] terphenyl, 4.4'-bis {N-phenyl-N- [4- (1-naphthyl) phenyl] amino} biphenyl, 4,4'-bis [N-phenyl-N -(2-pyrenyl) -amino] biphenyl, 2,6-bis [N, N-di (2-naphthyl) amino] fluorene, 4,4 "-bis (N, N-di-p-tolylamino) ter Phenyl, bis (N-1-naphthyl) (N-2-naphthyl) amine, 4,4′-bis [N- (2-naphthyl) -N-phenyl-amino] biphenyl (α-NPD), spiro-NPB , spiro -TAD, 2-TNATA, oxine coordination of Alq ₃ Of one hydrogen atom may be used, such as aluminum complexes and substituted with a methyl group (BAlq) In each of the other two oxine ligand with one substituting phenylphenol ligand.

As the electron acceptor EA, inorganic substances and organic substances such as metal oxides and metal halides can be used. For example, as the electron acceptor EA, vanadium pentoxide (V ₂ O ₅ ), rhenium heptoxide (Re ₂ O ₇ ), ferric chloride, ferric bromide, ferric iodide, aluminum chloride, bromide Aluminum, aluminum iodide, gallium chloride, gallium bromide, gallium iodide, indium chloride, indium bromide, indium iodide, antimony pentachloride, arsenic pentafluoride, boron trifluoride, dicyano-dichloroquinone (DDQ), Trinitrofluorenone (TNF), tetracyanoquinodimethane (TCNQ), tetrafluoro-tetracyanoquinodimethane (4F-TCNQ) and the like may be used.

  As described above, the organic EL element OLED is a non-injection type organic EL element. Therefore, it is not necessary to consider a work function or the like when selecting materials for the electrodes E1 and E2. Therefore, various conductive materials can be used as the materials for the electrodes E1 and E2. For example, as materials for the electrodes E1 and E2, a conductive oxide such as indium tin oxide (ITO), a metal such as aluminum, and an alloy may be used.

  The organic EL element OLED can further include a layer other than the light emitting layer EMT between the electrodes E1 and E2. For example, the organic EL element OLED may further include an insulating layer between the electrode E1 and the light emitting layer EMT or between the electrode E2 and the light emitting layer EMT.

  As described above, the organic EL element OLED is a non-injection type organic EL element. Therefore, a DC voltage may be applied between the electrodes E1 and E2, or an AC voltage may be applied.

  This organic EL element OLED can be used, for example, in a display device. Hereinafter, an example of a display device using the organic EL element OLED of FIG. 1 will be described.

  FIG. 2 is a plan view schematically showing an example of a display device using the organic EL element of FIG. This display device is an organic EL display device adopting an active matrix driving method.

  The organic EL display device of FIG. 2 includes an array substrate AS, a video signal line driver XDR, and a scanning signal line driver YDR.

  The array substrate AS includes, for example, an insulating substrate SUB such as a glass substrate.

  Pixels PX are arranged on the substrate SUB. On the substrate SUB, the scanning signal lines SL each extending in the row direction (X direction) of the pixels PX are arranged in the column direction (Y direction) of the pixels PX, and the video signal lines each extending in the Y direction. DL is arranged in the X direction. The scanning signal line SL and the video signal line DL are connected to the video signal line driver XDR and the scanning signal line driver YDR, respectively.

  Each pixel PX includes an organic EL element OLED, a pixel switch SW, and a capacitor C. In this example, the pixel switch SW is a p-channel thin film transistor, its gate is connected to the scanning signal line SL, and its source is connected to the video signal line DL. The organic EL element OLED and the capacitor C are connected in parallel between the drain of the pixel switch SW and the ground terminal.

  In this example, the video signal line driver XDR and the scanning signal line driver YDR are mounted on COG (chip on glass). The video signal line driver XDR and the scanning signal line driver YDR may be mounted by TCP (tape carrier package) instead of COG mounting.

  When displaying an image on this organic EL display device, for example, the scanning signal lines SL are driven in a line sequential manner. In the writing period in which a video signal is written to a certain pixel PX, first, the scanning signal line driver YDR closes the switch SW to the scanning signal line SL to which the previous pixel PX is connected (ON) and the scanning signal is a voltage signal. In this state, the video signal line driver XDR outputs the video signal as a voltage signal to the video signal line DL to which the previous pixel PX is connected. Thereafter, the scanning signal line driver YDR outputs a scanning signal as a voltage signal that opens (OFF) the switch SW to the scanning signal line SL to which the previous pixel PX is connected.

  In the effective display period in which the switch SW is open (OFF), the capacitor C maintains the voltage between the electrodes E1 and E2 of the organic EL element OLED at a level substantially equal to the value set in the writing period. The organic EL element OLED emits light with a luminance corresponding to the voltage between the electrodes E1 and E2.

Examples of the present invention will be described below.
In this example, the organic EL element OLED of FIG. 1 was produced by the following method.
First, an electrode E1 made of ITO was formed on a glass substrate by a sputtering method.

Next, a host HST, a dopant DPT, an electron donor ED, and an electron acceptor EA were co-evaporated on the electrode E1, thereby forming a light emitting layer EMT having a thickness of 50 nm. Here, Alq ₃ was used as the host HST, Green dopant GD1 (manufactured by Kodak) was used as the dopant DPT, BAlq was used as the electron donor ED, and vanadium pentoxide was used as the electron acceptor EA. Further, this deposition is performed in the light emitting layer EMT, in which the content of the host HST is 60% by weight, the content of the dopant DPT is 10% by weight, the content of the electron donor ED is 20% by weight, and the content of the electron acceptor EA is 10% by weight. %.

  Thereafter, an electrode E2 made of ITO and having a thickness of 50 nm was formed on the light emitting layer EMT by an evaporation method using ECR (electron cyclotron resonance) plasma. As described above, the organic EL element OLED in FIG. 1 was obtained.

  Next, a direct current voltage was applied between the electrodes E1 and E2 of the organic EL element OLED, and the magnitude thereof was gradually increased. As a result, this organic EL element OLED emitted green light when the voltage applied between the electrodes E1 and E2 was 20 V or higher. That is, this organic EL element OLED emitted light at a relatively low voltage.

  Further, a DC voltage of 20 V was continuously applied between the electrodes E1 and E2 of the organic EL element OLED, and the time until the luminance became 50% at the start of voltage application was examined. As a result, this time was 200 hours. That is, this organic EL element OLED had a sufficiently long life.

1 is a cross-sectional view schematically showing an organic EL element according to one embodiment of the present invention. The top view which shows roughly an example of the display apparatus using the organic EL element of FIG.

Explanation of symbols

  AS ... array substrate, C ... capacitor, DL ... video signal line, DPT ... dopant, E1 ... electrode, E2 ... electrode, EA ... electron acceptor, ED ... electron donor, EM ... light emitting material, EMT ... light emitting layer, HST ... Host material, OLED ... Organic EL element, PX ... Pixel, SL ... Scanning signal line, SUB ... Insulating substrate, SW ... Pixel switch, XDR ... Video signal line driver, YDR ... Scanning signal line driver

Claims (2)

  A non-injection type organic EL device comprising: a pair of electrodes facing each other; and a light emitting layer formed between the light emitting material, the electron donor, and the electron acceptor.   An organic EL display device comprising a plurality of pixels, each pixel including the organic EL element according to claim 1.

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