JPH0521163A - Organic thin film light emitting element - Google Patents

Abstract

PURPOSE:To eliminate electrical defects by pin holes to prevent short circuit and to improve brightness by composing a hole injection layer with a hole injection substance bound by a polystyrene resin in an organic thin film light emitting element having electrodes, a light emitting layer, and a charge injection layer comprising at least tire hole injection layer. CONSTITUTION:A positive electrode 2 comprising a translucent film such as Au, Ni, and a transparent conductive film such as ITO, SmO2 is deposited on a transparent substrate 1 comprising glass etc. A hole injection layer 3, a light emitting layer 4, and an electron injection layer 5 are successively laminated on the positive electrode. A negative electrode 6 is provided on the electron injection layer. In this constitution, (8-hydroxyquinoline) aluminium is used for the light emitting agent of the light emitting layer 4. The injection layer 3 is composed of a hole injection substance bound by a polystyrene resin. Where, for the injection substance, it is used a diamine-type compound such as 1,1-bis(4- N1N-ditriaminophenyl) cyclohexane etc., hydroxyquinoline etc. For the negative electrode 6, Mg, Mg/Ag etc., are used. The negative electrode 6 and the positive- electrode 2 are connected with a DC power supply 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hole injection layer of an organic thin film light emitting device, and more particularly to a light emitting device having excellent film forming properties of the hole injection layer.

[0002]

2. Description of the Related Art With the rapid increase in demand for flat displays replacing conventional cathode ray tubes, various display elements have been vigorously developed and put into practical use. An electroluminescence element (hereinafter referred to as an EL element) is also adapted to such a need, and in particular, as an all solid state spontaneous light emitting element,
It attracts attention due to its high resolution and high visibility that other displays do not have. At present, what has been put into practical use is an EL element made of an inorganic material using a ZnS / Mn system in the light emitting layer. However, this type of inorganic EL element has a problem that the driving method is complicated and the manufacturing cost is high because the driving voltage required for light emission is as high as about 200V. Also,
Since the efficiency of blue light emission is low, full colorization is difficult.

On the other hand, a thin-film light emitting device using an organic material can drastically reduce the driving voltage required for light emission, and has the possibility of being fully colored by adding various light emitting materials. Research has become active in recent years. In particular, in the laminated type composed of electrode / hole injection layer / light emitting layer, tris (8-hydroxyquinoline) aluminum is used as the light emitting agent and 1,1′-bis (4-N, N-ditriaminophenyl) is used as the hole injection agent. 10V by using cyclohexane
The development was spurred since it was reported that a high brightness of 1000 cd / m ² or more was obtained with the following applied voltage (Appl. Phys. Lett. 51, 913, (1987)).

Specific structures and materials of the organic light-emitting device, which are currently widely studied, will be described below with reference to the drawings. FIG. 1 is a typical structural sectional view of a laminated structure type (light emission proceeds in a direction indicated by an arrow in the drawing). On a transparent substrate 1 made of glass or the like, a positive electrode 2 made of a semi-permeable film of gold, nickel or the like or a transparent conductive film of indium tin oxide (ITO), tin oxide (SnO ₂ ) or the like is heated by resistance heating or electron beam evaporation. Formed by sputtering. It is desirable that the electrode 2 has a thickness of 100 to 3000 Å in order to have transparency. Next, an organic thin film is sequentially formed on the hole injection layer 3 and the light emitting layer 4.

As the hole injecting substance, in addition to diamine compounds such as 1,1'-bis (4-N, N-ditriaminophenyl) cyclohexane, hydrazone compounds,
Stilbene compounds and the like are used. In addition to the metal complex compound such as tris (8-hydroxyquinoline) aluminum, a distyrylbenzene compound, a perylene-based compound, or the like is used as the light emitting substance. Both layers can be formed by spin coating, casting, LB method, resistance heating vapor deposition, electron beam vapor deposition and the like, but at present the resistance heating vapor deposition method is the mainstream because of its excellent emission characteristics. Further, the film thickness of both layers is 200 to 3000 Å, preferably 300 in the resistance heating vapor deposition method.
It is ~ 1500Å. Finally, the negative electrode 5 is formed by vapor deposition. As a material for the electrode 5, M having a small work function is used.
g, Mg / Ag, In, Ca, Al or the like is used.

FIG. 2 is a sectional view showing another element structure. (Light emission proceeds in the direction indicated by the arrow in the figure). On a transparent substrate 1 such as glass, a positive electrode 2 made of a semi-permeable film such as gold or nickel or a transparent conductive film such as indium tin oxide (ITO) or tin oxide (SnO ₂ ) is formed in the same manner as in FIG. Three layers of the hole injection layer 3, the light emitting layer 4, and the electron injection layer 5 are formed.
As the electron injecting agent, diphenoquinone compounds, perylene compounds, oxadiazol compounds and the like are used. The hole injecting layer 3, the light emitting layer 4, and the electron injecting layer 5 all have a thickness of 20 as in the case of FIG.
It is 0 to 3000Å, preferably 300 to 1500Å.
Finally, the negative electrode 6 is vapor-deposited using Mg, Mg / Ag, In, Ca, Al or the like.

[0007]

As described above, although the thin film light emitting device using an organic material strongly suggests the possibility of low voltage driving and full colorization, the problem to be solved in terms of performance. There are many left. In particular, the problem of characteristic deterioration due to long-time driving of about 10,000 hours is a hardware that must be overcome. The thickness of the organic thin film is 1
Since the thickness is less than or equal to μm, the film forming property is good, and electrical defects such as pinholes do not occur during the film formation. Furthermore, since it is a thin film, the electric field and / or current applied to the element during light emission. Therefore, it is necessary to develop materials and study film formation methods so that short circuits do not occur. In particular, the resistance heating vapor deposition film has problems that electrical defects are likely to occur and that a short circuit is likely to occur during light emission. Further, from the viewpoint of mass productivity, development of an inexpensive organic material that can be easily mass-produced and improvement of an element forming method are important technical subjects.

The present invention has been made in view of the above points, and an object thereof is to provide an organic thin film light emitting device having excellent film forming properties by developing a binder in a resin dispersion film.

[0009]

According to the present invention, there is provided a charge injection layer having a pair of electrodes consisting of a positive electrode and a negative electrode, a light emitting layer and a charge injection layer sandwiched therebetween. Is formed of at least a hole injection layer of an electron injection layer and a hole injection layer, and the hole injection layer is formed of a hole injection material and polystyrene resin.

Specific examples of the diamine compounds are represented by the chemical formula I-1.
Or a hydrazone compound represented by the chemical formula II-14.
-1 to Chemical Formula II-21 and stilbene compounds are shown in Chemical Formulas III-1 to III-4.

[0011]

[Chemical 5]

[0012]

[Chemical 6]

[0013]

[Chemical 7]

[0014]

[Chemical 8]

[0015]

[Chemical 9]

[0016]

In an organic thin film light emitting device in which a light emitting layer and a hole injection layer are laminated, a favorable film can be formed by using a dispersion film of a hole injection substance and a polystyrene resin binder in the hole injection layer. In addition, there are few electrical defects such as pinholes generated in the film, the function of preventing a short circuit phenomenon caused by an electric field or a current applied to the element at the time of light emission, and good results are also obtained in light emission characteristics. In addition, diamine compounds, hydrazone compounds and stilbene compounds give good results as the hole injecting substance.

[0017]

Embodiments of the present invention will now be described with reference to the drawings. In the present invention, the dispersion film composed of the hole injecting substance introduced as the hole injecting layer and the polystyrene binder is formed by spin coating, casting or the like using a coating solution prepared by dissolving both in an appropriate organic solvent. It is formed. The weight ratio of the hole injecting substance to the total amount of the hole injecting substance and the polystyrene binder at the time of blending the coating liquid is 30 to 80%, preferably 40 to 70%. The thickness of the hole injection layer dispersion film is 500 to 3000Å, preferably 800 to 2000Å.

Example 1 A glass substrate of 50 mm square provided with ITO having a film thickness of about 1000 Å was used as a substrate, and the substrate was set on a spin coater. 1 part by weight of polystyrene resin is added to dichloromethane 500
Rotation speed: 5000r using coating solution dissolved in parts by weight
The hole injection layer was spin-coated on the substrate by pm at ˜1000Å. Next, the substrate coated with the hole injection layer was set in a resistance heating vapor deposition device to form a light emitting layer. During film formation, the pressure inside the vacuum chamber was reduced to 6 × 10 ⁻⁶ Torr. The luminescent agent, (8-hydroxyquinoline) with aluminum, ball - heated in the range of bets temperature 100 to 300 ⁰ C, was 600Å formed the deposition rate under the conditions of 2 Å / sec. Finally, the sample was taken out of the vacuum chamber, a stainless mask consisting of 16 dot patterns with a diameter of 5 mm was attached, and it was newly set in the resistance heating vapor deposition device to form Mg / Ag (10: 1 ratio) as the negative electrode. did.

Example 2 As in the case of Example 1, ITO having a film thickness of up to 1000 Å was provided.
A hole injecting layer and a light emitting layer are formed using the same material, the same manufacturing method, and the same conditions as in Example 1, using 0 mm square glass as the substrate.
Next, after forming the light emitting layer, a perylene tetracarboxylic acid derivative having a structural formula (IV) shown below was used as an electron injection layer without breaking the vacuum of the vacuum chamber, and a heating temperature of 150 to 30
700 Å was formed under conditions of 0 ° C. and a film forming rate of 3 Å / sec.
Finally, as in Example 1, the sample was taken out of the vacuum chamber, a stainless mask consisting of 16 dot patterns with a diameter of 5 mm was attached, and the sample was newly set in the resistance heating vapor deposition device and Mg / Ag ( 10: 1 ratio) was formed.

[0020]

[Chemical 10]

When a DC voltage was applied to the organic thin film light emitting devices in the above two examples, uniform light emission of green (emission center wavelength: 550 nm) was obtained. In addition, all of the 16 dot patterns of 5 mm in diameter on the 50 mm square glass substrate did not cause a short circuit phenomenon and stayed within the range of 5% variation in light emission characteristics. Furthermore, in the device of Example 1, under an applied voltage of 15 V, 2400 cd / m ² (current density 100 m
A / cm ² ), in the device of Example 2, an applied voltage of 1
2520 cd / m ² under 5 V (current density 95 mA / c
A high-luminance luminescence of m ² ) was obtained.

Example 3 A device was formed by using II-6 of the hydrazone compounds as the hole injecting material and using the same method and conditions as in Example 1 except for the other materials. When a DC voltage was applied to the organic light emitting device in the above example, green (light emission center wavelength:
A uniform emission of 550 nm) was obtained. Also, the 50m
Dot pattern 16 with a diameter of 5 mm on an m-square glass substrate
All the individual patterns did not cause a short circuit phenomenon, and the variation in emission characteristics was within the range of 7%. Furthermore, under an applied voltage of 15 V, 2050 cd / m ² (current density 120 mA
A high-luminance luminescence of / cm ² ) was obtained.

Example 4 A device was formed by using III-2 of the stilbene compounds as the hole injecting material, and using the same method and conditions as in Example 1 for the other materials. When a DC voltage was applied to the organic light-emitting device in the above-mentioned example, uniform light emission of green color (emission center wavelength: 550 nm) was obtained. Also, the 5
All 16 dot patterns with a diameter of 5 mm on a 0 mm square glass substrate did not cause a short circuit phenomenon, and the variation in light emission characteristics was within the range of 7%. Furthermore, under an applied voltage of 15 V, 2240 cd / m ² (current density 110
A high-luminance light emission of mA / cm ² ) was obtained.

[0024]

According to the present invention, a pair of electrodes composed of a positive electrode and a negative electrode, a light emitting layer and a charge injection layer sandwiched between the electrodes are provided, and the charge injection layer is an electron injection layer and a hole injection layer. Of the layers, at least the hole injection layer is formed. In this case, since the hole injection layer is formed of the hole injection material and the polystyrene resin, a good film can be formed and electrical properties such as pinholes generated in the film can be formed. It is possible to obtain an organic thin film light emitting device which has few defects and can prevent a short circuit phenomenon which is caused by an electric field or a current applied to the device during light emission and which is excellent in high-luminance light emission.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of a laminated structure type element.

FIG. 2 is a cross-sectional view showing another structure of a laminated structure type element.

[Explanation of symbols]

1 Insulating transparent substrate 2 positive electrode 3 Hole injection layer 4 Light emitting layer 5 Electron injection layer 6 Negative electrode 7 DC power supply

Claims (4)

[Claims] 1. A pair of electrodes consisting of a positive electrode and a negative electrode, and a light emitting layer and a charge injection layer sandwiched therebetween, wherein the charge injection layer is at least a positive electrode of an electron injection layer and a hole injection layer. An organic thin film light emitting device comprising a hole injection layer, wherein the hole injection layer comprises a hole injection material and polystyrene resin. 2. The organic thin film light emitting device according to claim 1, wherein the hole injecting substance is a diamine compound represented by the general formula (I). [Chemical 1] (In the general formula (I), A is the following general formula (IA), (IB)
Or (IC). [Chemical 2] R ₁ , R ₂ , R ₃ and R ₄ are an optionally substituted alkyl group, an allyl group, an aryl group and an aralkyl group. In the general formula (IA), (IB) or (IC), R ₅ , R ₆ and
R ₇ and R ₈ are hydrogen atoms, halogens, optionally substituted alkyl groups and alkoxy groups, and X is —C (R ₁₉ ) (R ₂₀ ) —.
(R ₁₉ and R ₂₀ are hydrogen atoms and alkyl groups), --O--, --S
─,> C ₆ H ₁₀ . ) 3. The organic thin film light emitting device according to claim 1, wherein the hole injecting substance is a hydrazone compound represented by the general formula (II). [Chemical 3] (R ₉ represents a hydrogen atom, an alkyl group, a halogen atom or an alkoxy group, and R ₁₀ and R ₁₁ represent an optionally substituted alkyl group, an aryl group, an aralkyl group, R ₁₂ and R ₁₃
Is an optionally substituted alkyl group, aryl group, aralkyl group or tenyl group. ) 4. The organic thin film light emitting device according to claim 1, wherein the hole injecting substance is a stilbene compound represented by the general formula (III). [Chemical 4] (R ₁₄ represents a hydrogen atom, an alkyl group, a halogen group or an alkoxy group, R ₁₅ and R ₁₆ represent an aryl group or an aralkyl group which may be substituted, and R ₁₇ and R ₁₈ may be substituted. It is a good aryl group.)