JP2015037168A - Organic light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic light-emitting element which enables the reduction in driving voltage.SOLUTION: An organic light-emitting element comprises an organic layer 20. The organic layer 20 includes a polar region, and two nonpolar regions having the polar region sandwiched therebetween. The polar layer includes 50 vol.% or more of an organic polar compound having a dipole moment of 1[D] or larger. Each nonpolar region is composed of at least one nonpolar layer; the at least one nonpolar layer is made of only an organic compound having a dipole moment of smaller than 1[D]. The polar region includes a light-emitting layer 140; the total thickness of the polar region is 1.5 or lower times the thickness of the light-emitting layer 140. The light-emitting layer 140 includes at least one polar layer. The at least one polar layer included in the light-emitting layer 140 includes a total of 30 vol.% or more of the organic polar compound having a dipole moment of 4[D] or larger. As to all the polar layer in the polar region, the sum total ΣPof a parameter Pexpressed by the formula (1) is 150[D nm] or larger. P=Σ(μ×d×φ(1) (where drepresents a layer thickness, μrepresents a dipole moment of the organic polar compound i, and φrepresents a volume fraction of the organic polar compound i).

Description

  The present invention relates to an organic light emitting device.

  Organic light-emitting devices exhibit excellent characteristics such as self-emission and low power consumption, and generally have a structure in which a light-emitting layer in which an organic compound containing a light-emitting material is formed in a thin film is sandwiched between an anode and a cathode. doing. A voltage is applied between these electrodes to recombine holes and electrons in the light emitting layer, thereby exciting the light emitting material to emit light.

  On the other hand, research for extending the lifetime of such an organic light emitting device has been conducted. For example, in Patent Document 1, an electron transporting material and an organic compound having a polarity larger than that of the electron transporting material are provided between the cathode and the light emitting layer in order to suppress a decrease in luminance and an increase in driving voltage. An organic electroluminescent device having a mixed layer is described. In Patent Document 2, by using a charge transporting thin film containing a charge transporting material combined with a fullerene compound having a polar functional group and a charge transporting material as a hole injecting layer, the light transmittance of the hole injecting layer is increased. It is described that it improves.

JP 2010-251585 A JP 2010-123930 A

  By the way, for example, in the case of the organic light-emitting device described in Patent Document 1, 2,2-bi (9,10-diphenylanthracene) to which a highly polar organic compound such as dipyrenyladamantane (PY-AD) is added is included. A mixed layer is provided between the light emitting layer and the cathode. However, when the addition amount of a polar compound such as PY-AD is about 5% by volume to 10% by volume, an increase in drive voltage can be suppressed to some extent, but when the amount is increased to about 60% by volume, an increase in drive voltage is observed. . In addition, in the case of the organic light emitting device described in Patent Document 2, in order to obtain a good hole injection effect as a charge transporting thin film, a film thickness of a certain level or more is required, and the driving voltage increases when the film thickness is increased. There is a fear.

  An object of the present invention is to reduce a charge injection voltage in an organic light emitting device.

According to the present invention, there is provided an organic light emitting device comprising an anode, an organic layer including at least one light emitting layer, and a cathode in order, wherein the organic layer is in contact with the polar region from both sides. The polar region includes at least one polar layer, the nonpolar region includes one or more nonpolar layers, and the polar layer has a dipole moment of 1. [D] is a layer containing at least one organic polar compound of 50% by volume or more in total, and the nonpolar layer is a layer composed only of an organic compound having a dipole moment of less than 1 [D], and the polarity The region includes the light emitting layer, and the total thickness of the polar region is not more than 1.5 times the thickness of the light emitting layer, and the light emitting layer includes at least one polar layer, At least one of the included polar layers is bipolar Wherein moments 4 [D] or more in total of at least one organic polar compound 30 vol% or more, the for all polar layer of polar regions, the sum .SIGMA.P _j parameters P _j represented by the following formula (1) An organic light-emitting element characterized by having a thickness of 150 [D · nm] or more is provided.

P _j = Σ (μ _ij × d _j × φ _ij ) (1)
In the formula (1), _dj is a film thickness of an arbitrary polar layer j, μ _ij is a dipole moment of an arbitrary organic polar compound i having a dipole moment of 1D or more in the polar layer j, and φ _ij Is the volume fraction of the organic polar compound i in the polar layer j. Further, Σ means taking the sum of all kinds of organic polar compounds contained in the polar layer j.

Here, it is preferable that the organic layer includes a hole transport layer and an electron transport layer, and the polar region includes the light emitting layer and either the hole transport layer or the electron transport layer.
Further, it is preferable that the organic layer includes a hole transport layer and an electron transport layer, the light emitting layer coincides with the polar region, and the hole transport layer and the electron transport layer are the nonpolar layers.
Furthermore, the sum .SIGMA.P _j of the parameter _{P j} is preferably at 250 [D · nm] or less.
Sum .SIGMA.P _j of the parameter _{P j} is preferably not less 200 [D · nm].

  According to the present invention, the charge injection voltage in the organic light emitting device is reduced. That is, a polar layer is formed in the organic layer between the anode and the cathode of the organic light emitting device, and the polar layer is sandwiched between nonpolar layers, thereby reducing the charge injection voltage without hindering charge transport, Drive voltage decreases.

It is a schematic sectional drawing which shows an example of the organic light emitting element to which this embodiment is applied. It is an energy band figure of the organic light emitting element whose all layers which comprise an organic layer are nonpolar layers. It is an energy band figure of the organic light emitting element whose light emitting layer is a polar layer and whose hole transport layer and electron transport layer are nonpolar layers. It is an energy band figure of the organic light emitting element of the other structure whose light emitting layer is a polar layer and whose hole transport layer and electron transport layer are nonpolar layers.

  Hereinafter, embodiments of the present invention will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary. That is, the dimensions, materials, shapes, relative arrangements, and the like of the components described in the embodiments are not intended to limit the scope of the present invention unless otherwise specified, and are merely illustrative examples. . The drawings used are examples for explaining the present embodiment and do not represent actual sizes. The size, positional relationship, and the like of the members shown in each drawing may be exaggerated for clarity of explanation. Further, in this specification, “on” such as “on the layer” is not necessarily limited to the case where it is formed in contact with the upper surface, and is formed on the upper side in a separated manner or between layers. It is used in a sense that includes an intervening layer.

<Organic light emitting device 10>
FIG. 1 is a schematic cross-sectional view showing an example of an organic light emitting device 10 to which the present embodiment is applied.
As shown in FIG. 1, the organic light emitting device 10 includes a substrate 110, a first electrode (anode) 120 formed on the substrate 110, a second electrode (cathode) 160, and a first electrode (anode) 120. The organic layer 20 including a plurality of layers including the light emitting layer 140 is provided between the second electrode (cathode) 160.

As shown in FIG. 1, the organic layer 20 is formed between the light emitting layer 140 and the first electrode 120, the hole transport layer 130, and the light emitting layer 140 and the second electrode (cathode) 160. And an electron transport layer 150.
As will be described later, in the present embodiment, the organic layer 20 has a polar region containing an organic compound having a large dipole moment and two nonpolar regions made of an organic compound having a small dipole moment. The sex region is configured to sandwich the polar region in contact with both sides.

(Polar region)
In the present embodiment, the polar region includes at least one polar layer. The polar layer is a layer containing at least 50% by volume in total of at least one organic polar compound having a dipole moment of 1 [D (Debye)]] or more. Furthermore, it is preferable that the polar layer contains 70 vol% or more in total of at least one organic polar compound having a dipole moment of 1 [D] or more. The light emitting layer 140 is included in this polar region and not included in the nonpolar region. The light emitting layer 140 includes one or more layers.
The polar region may include the hole transport layer 130 and / or the electron transport layer 150, but most preferably the polar region matches the light emitting layer 140. When the polar region includes the whole or a part of the hole transport layer 130 and / or the electron transport layer 150, the portion included in the polar region in the hole transport layer 130 and the electron transport layer 150 needs to be a polar layer. is there. Moreover, when the light emitting layer 140 is formed of a plurality of layers, it may include a nonpolar layer.

The light-emitting layer 140 includes at least one polar layer. In at least one of the polar layers included in the light-emitting layer, an organic polar compound having a dipole moment of 4 [D] or more is 30% by volume or more, preferably 50 volumes. % Or more, more preferably 70% by volume or more.
When the dipole moment of the organic polar compound contained in the polar layer is excessively small, the spontaneous polarization (surface potential) generated in the polar layer, which will be described later, is small, so that the hole transport layer 130 and the electron transport layer 150 are formed. The effect of the present invention that the internal electric field (which works in the direction of preventing charge injection) is not relaxed and charge injection becomes easy cannot be obtained.

Examples of the organic polar compound having a dipole moment of 4 [D] or more include, for example, Alq ₃ (tris (8-quinolinolato) aluminum: dipole moment 4.1 [D]), OXD-7 (2, 2- (3 , 1-phenylene) bis [5- (4-tert-butylphenyl) -1,3,4-oxadiazole]: dipole moment 6.6 [D]), FIrpic (iridium (III) bis ((4 , 6-difluorophenyl) pyridinate-N, C2 ′) picolinate: dipole moment 6.3 [D]), (4′-fluoro-1,1′-biphenyl) -4-olato) bis (2-methyl- 8-quinolinolato) gallium (dipole moment 10.2 [D]), (4′-chloro-1,1′-biphenyl) -4-orato) bis (2-methyl-8-quinolinolato) gallium (dipole) Moment 9.7 [D]), (1,1′-biphenyl) -4-olato) bis (2-methyl-8-quinolinolato) gallium dipole moment 8.6 [D]), (4′-fluoro- 1,1′-biphenyl) -4-orato) bis (2-methyl-8-quinolinolato) aluminum (dipole moment 5.6 [D]), (4′-chloro-1,1′-phenyl) -4 -Olato) bis (2-methyl-8-quinolinolato) aluminum (dipole moment 5.1 [D]), (1,1'-biphenyl) -4-olato) bis (2-methyl-8-quinolinolato) aluminum (Dipole moment 4.0 [D]) and organic compounds represented by the following structural formulas (1-1) to (1-9).

  An organic polar compound having a dipole moment of 1 [D] or more and less than 4 [D] can also constitute the polar layer. Examples of such organic polar compounds include bis (2-methyl-8-quinolinolato) gallium chloride (dipole moment 1.8 [D]), 4,4,8,8, -tetrakis (1H-pyrazole- 1-yl) pyraza ball (dipole moment 1.8 [D]), organic compounds represented by the following structural formulas (2-1) to (2-6), and the like.

Here, n is the number of polar layers constituting the polar region, and a parameter P _j represented by the following formula (1) is defined for an arbitrary polar layer j (j = 1 to n). The parameter P _j is a parameter representing the magnitude of polarity as the polar layer.
P _j = Σ (μ _ij × φ _ij × d _j ) (1)
Here, the number (kind) of organic polar compounds having a dipole moment of 1 [D] or more included in an arbitrary polar layer j is m _j . In formula (1), _dj is the film thickness of an arbitrary polar layer j. Μ _ij is a dipole moment of any organic polar compound i (i = 1 to _{m j} ) whose dipole moment included in the polar layer j is 1 [D] or more, and φ _ij is a polarity It is the volume fraction of the organic polar compound i in the layer j. Further, Σ means that for an arbitrary polar layer j, the sum (i = 1 to _{m j} ) is taken for all organic polar compounds having a dipole moment included in the polar layer j of 1 [D] or more. .

In the organic light emitting device 10 to which the present exemplary embodiment is applied, for a plurality of polar layers j constituting the polar region, ΣP _j obtained by summing up the parameters P _j represented by the above formula (1) is usually It is the range of 150-250 [D * nm], Preferably, it is the range of 150-200 [D * nm].
If the sum .SIGMA.P _j parameters P _j is excessively small, the spontaneous polarization occurring in the polar layer described later (surface potential) is reduced, an internal electric field formed in the hole transport layer 130 and electron transport layer 150 ( The effect of the present invention that the charge injection becomes easy cannot be obtained. On the other hand, when the total sum ΣP _j of the parameters P _j is excessively large, the internal electric field formed in the light emitting layer 140 (which works in the direction of preventing charge injection) becomes too large, and therefore recombination of holes and electrons is caused. It becomes difficult to occur, and luminous efficiency falls.

Here, the total thickness (total film thickness) of the polar layers constituting the polar region of the organic light emitting element 10 is adjusted to be within a range of 1.5 times or less the thickness of the light emitting layer 140. . Among these, the case where the total thickness of the polar layer is one time the thickness of the light emitting layer 140, that is, the case where the polar layer is composed of only the light emitting layer 140 is most preferable.
Moreover, the sum total (total film thickness) of the film thickness of a polar layer is the range of 5 nm-200 nm normally, Preferably, it is the range of 20 nm-50 nm. If the sum of the thicknesses of the polar layers (total thickness) is excessively thin, charges tend to accumulate at the interface between the nonpolar layer and the polar layer when the element is driven, and there is a tendency for luminance deterioration to be accelerated. When the thickness of the polar layer is excessively large, the charge transport property between the layers tends to be lowered. In addition, the driving voltage of the element tends to increase.

(Nonpolar region)
In the present embodiment, the nonpolar region is composed of only a nonpolar layer containing only an organic compound having a dipole moment of less than 1 [D], and is in contact with both sides of the polar region using the light emitting layer 140 as an example. It is arranged so as to sandwich. The nonpolar layer constituting the nonpolar region may be a single layer or a multilayer of two or more layers.
Examples of the organic compound having a dipole moment of less than 1 [D] include NPB (α-NPD, N, N′-di (1-naphthyl) -N, N′-diphenyl-benzidine), TBB (trans-bisbenzyl). ), CBP (4,4′-bis (carbazol-9-yl) -biphenyl), tris (2,6-dimethyl-4-biphenyl) borane, Ir (ppy) ₃ (tris (2-phenylpyridine) iridium ( III)) and organic compounds represented by the following structural formulas (3-1) to (3-3).

  In addition, in the organic light emitting device 10 to which the present exemplary embodiment is applied, when the organic layer 20 includes the hole transport layer 130, the light emitting layer 140, and the electron transport layer 150, the light emitting layer 140, the hole transport layer, and the like. A part of the side of 130 in contact with the light emitting layer 140 and / or a part of the side of the electron transport layer 150 in contact with the light emitting layer 140 may form a polar region.

When the polar region in the organic layer 20 is composed of a part of the light emitting layer 140 and the hole transport layer 130 on the side in contact with the light emitting layer 140, the hole transport layer 130 has a multilayer structure of two or more layers, and at least the side in contact with the light emitting layer 140 Is a polar layer containing 30% by volume or more of an organic polar compound having a dipole moment of 4 [D] or more, and at least one layer in contact with the first electrode 120 has a dipole moment of less than 1 [D]. What is necessary is just to set it as the nonpolar layer which consists only of organic compounds.
Further, when the polar region in the organic layer 20 is composed of a part of the light emitting layer 140 and the electron transporting layer 150 on the side in contact with the light emitting layer 140, the electron transporting layer 150 has a multilayer structure of two or more layers. One layer in contact is a polar layer containing 30% by volume or more of an organic polar compound having a dipole moment of 4 [D] or more, and at least one layer in contact with the second electrode 160 has a dipole moment of less than 1 [D]. What is necessary is just to set it as the nonpolar layer which consists only of organic compounds.

  When the polar region in the organic layer 20 is composed of a part of the hole transport layer 130 on the side in contact with the light-emitting layer 140 and a part of the light-emitting layer 140 and the electron transport layer 150 on the side in contact with the light-emitting layer 140, A multi-layer structure having at least one layer, at least one layer in contact with the light-emitting layer 140 is a polar layer containing 30% by volume or more of an organic polar compound having a dipole moment of 4 [D] or more, and at least a side in contact with the first electrode 120 Is a nonpolar layer made of only an organic compound having a dipole moment of less than 1 [D], the electron transport layer 150 has a multilayer structure of two or more layers, and at least one layer in contact with the light emitting layer 140 is A polar layer containing 30% by volume or more of an organic polar compound having a dipole moment of 4 [D] or more, and at least one layer in contact with the second electrode 160 is a dipole moment. There may be a non-polar layer consisting only of an organic compound of less than 1 [D].

  In the organic light emitting device 10 to which the present exemplary embodiment is applied, when the organic layer 20 includes the hole transport layer 130, the light emitting layer 140, and the electron transport layer 150, the light emitting layer 140 has a dipole moment of 4. [D] The hole transport layer 130 and the electron transport layer 150 formed in contact with both sides of the light-emitting layer 140 coincide with a polar region containing an organic polar compound that is equal to or greater than [D], and the dipole moment is less than 1 [D]. It is preferable that it is a nonpolar layer which consists only of these organic compounds. The hole transport layer 130, the light emitting layer 140, and the electron transport layer 150 may each be a single layer or a multilayer of two or more layers.

Next, the reason why the drive voltage is reduced in the organic light emitting device to which the embodiment of the present invention is applied will be described.
In general, in an organic light emitting device, an anode material having a high work function and a cathode material having a low work function are used in order to reduce the energy barrier between the organic layer and the electrode. Therefore, a potential corresponding to the difference between the work function φ ₁ [eV] of the anode material and the work function φ ₂ [eV] of the cathode material, that is, the built-in potential V _bi [ V] (= φ ₁ / e−φ ₂ / e, where e is the elementary charge). The direction of the built-in potential, work function phi ₁ of the anode material for work function greater than phi ₂ of the cathode material, are opposite to the direction of the potential applied from the outside to drive the organic light emitting element.

FIG. 2 is an energy band diagram of an organic light-emitting device in which any layer constituting the organic layer 20 (see FIG. 1) is a nonpolar layer. About the same structure as FIG. 1, the same code | symbol is used and detailed description is abbreviate | omitted. The same applies to FIGS. 3 and 4 below.
2A includes an organic layer 20 between an anode (first electrode) 120 and a cathode (second electrode) 160, and the organic layer 20 has a hole transport layer 130, a light emitting layer 140, FIG. 2B is an energy band diagram at the time of a circuit short-circuit (external applied voltage: V _ex = 0) in an organic light-emitting device composed of an electron transport layer 150, and each layer is a nonpolar layer. FIG. It is an energy band figure of time (external application voltage: _Vex = _Vbi ).

Here, when the externally applied voltage shown in FIG. 2A is zero, charge injection is performed in the hole transport layer 130 and the electron transport layer 150 by the built-in potential V _bi due to the work function difference between the anode 120 and the cathode 160, respectively. An internal electric field is formed in the direction of obstruction. On the other hand, as shown in FIG. 2B, when an external voltage corresponding to the built-in potential V _bi is applied (when V _ex = V _bi ), the hole transport layer 130 and the electron transport layer 150 are formed. The electric field that has been cancelled is cancelled, and charge injection becomes possible. In other words, charge injection from the anode 120 and cathode 160 to no organic layer 20 the polarity layer (see FIG. 1) is exceeded built-in potential V _bi of externally applied voltage V _ex is equivalent to the work function difference between the two electrodes Happens for the first time in case.

Next, consider an organic light emitting device in which the light emitting layer 140 is a polar layer containing an organic polar compound having a large dipole moment, and the hole transport layer 130 and the electron transport layer 150 are nonpolar layers. FIG. 3 shows an energy band diagram of an organic light-emitting device having such an organic layer structure.
That is, FIG. 3 is an energy band diagram of an organic light emitting device in which the light emitting layer 140 is a polar layer and the hole transport layer 130 and the electron transport layer 150 are nonpolar layers.
3A is an energy band diagram when a circuit is short-circuited, and FIG. 3B is an energy band diagram when a voltage is applied. Here, it is assumed that the organic light-emitting element is formed from the anode 120 side as usual. On the other hand, it has been found that most organic polar compounds having a large dipole moment have a positive potential on the upper surface of the deposited film (the magnitude of the potential is V _p ). Here, to simplify the explanation, it is assumed that the spontaneous potential V _p generated in the polar layer (light emitting layer 140) by the dipole moment is equal to the built-in potential V _bi and the dielectric constant of each layer of the organic layer 20 is also equal. .

As described above, when the surface potential of the polar layer is positive and V _p = V _bi in the organic light-emitting element formed from the anode side, when the circuit is short-circuited (externally applied voltage: V _ex = The energy band diagram of 0) is as shown in FIG. That is, the electric field formed in the light emitting layer 140 is increased by the spontaneous potential V _p (the cathode side becomes positive) by the polar layer, compared with the case without the polar layer shown in FIG. On the other hand, the electric fields formed in the hole transport layer 130 and the electron transport layer 150 are relaxed. In particular, when the spontaneous potential _{V p} with a polar layer is equal to the built-in potential _{V bi} is formed on the hole transport layer 130 and electron transport layer 150 in the case (FIG. 2 (a)) only the built-in potential _{V bi} is present The applied electric field is completely canceled as shown in FIG. In this case, the internal electric field in a direction that prevents charge injection into the hole transport layer 130 and the electron transport layer 150 due to the spontaneous potential V _p of the polar layer (the light emitting layer 140), even though no external voltage is applied. Does not occur, and charge injection into these layers becomes possible.

Further, an energy band diagram when an external voltage corresponding to the built-in potential is applied (when V _ex = V _bi ) is as shown in FIG. In this case, an electric field in the direction of accelerating charge injection is formed in the hole transport layer 130 and the electron transport layer 150 by the spontaneous potential V _p of the polar layer (the light emitting layer 140), and charge injection into these layers is performed. More encouraged.
As described above, when there is a polar layer, the electric field formed in the light emitting layer 140 is increased, which hinders charge transport. However, in the light emitting layer 140, although the charge transport is slow, the probability of recombination increases conversely, so the light emission efficiency does not decrease so much. When viewed as the entire device, the effect of promoting the injection into the hole transport layer 130 and the electron transport layer 150 due to the presence of the polar layer is still effective even if the decrease in the light emission efficiency in the light emitting layer 140 is compensated, and the drive voltage is reduced. An effect is obtained.

Next, FIG. 4 is an energy band diagram of an organic light emitting device having another configuration in which the light emitting layer 140 is a polar layer and the hole transport layer 130 and the electron transport layer 150 are nonpolar layers. That is, FIG. 4 is different from the organic light emitting device of FIG. 3 only in that V _p is smaller than V _bi , and shows an energy band diagram of the organic light emitting device having the same configuration except for the above.
As described above, FIG. 2 considers the case where the spontaneous potential V _{p of the} polar layer (light emitting layer 140) is 0, and FIG. 3 considers the case where V _p is equal to V _bi . However, after all, the external applied voltage _{V ex} charge starts to be injected into the hole transport layer 130 and electron transport layer 150 is represented by _V ex _{= V} bi -V _p, the energy band diagram at this time is as shown in FIG. 4 become. That is, when the organic layer is composed of a polar layer and a nonpolar layer sandwiching it from both sides, the externally applied voltage at which charge injection is started can be reduced by the spontaneous potential of the polar layer. .
3 and 4 described above is for the case where the organic light emitting element is formed from the anode side and an organic polar compound having a large dipole moment with a positive surface potential after film formation is used as the polar layer. Is. On the other hand, when the organic light emitting device is formed from the cathode side, if an organic polar compound having a large dipole moment with a negative surface potential after film formation is used as the polar layer, the same effect as in FIG. And the charge injection voltage decreases.

In order to select an organic compound to be used for the polar layer and the nonpolar layer of the organic light emitting device of this embodiment, it is necessary to know the dipole moment values of the light emitting material, the hole transport material, and the electron transport material. Some dipole moment values of organic compounds can be found in known literature. In addition, an organic compound that is not known in the known literature can be obtained by calculation using a molecular orbital method if the chemical structure of the compound is known.
The magnitude of the spontaneous potential V _p generated in the polar layer can be known by measuring the surface potential of the polar layer. That is, it is considered that the spontaneous potential of the polar layer corresponds to the surface potential. Here, the surface potential of the polar layer is determined by using the dipole moment of the polar compound, the orientation order parameter, and the film thickness as factors. In the present embodiment, the contribution of the alignment order parameter to the surface potential is considered to be so small that it can be ignored.
Therefore, the parameter P _j represented by the formula (1) is considered to have technical significance as an index for determining the spontaneous potential of the polar layer generated by including the polar compound. At this time, the volume fraction of the polar compound contained in the polar layer gives the contribution rate of the dipole moment that determines the spontaneous potential.

  Hereinafter, each configuration of the organic layer 20 (the hole transport layer 130, the light emitting layer 140, and the electron transport layer 150) of the organic light emitting device 10 to which the exemplary embodiment is applied will be described.

(Hole transport layer 130)
The hole transport layer 130 is a layer having a function of receiving holes from the first electrode (anode) 120 side and transporting them to the second electrode (cathode) 160 side. Examples of the material used for the hole transport layer 130 include a low molecular compound and a high molecular compound. For example, pyrrole derivative, carbazole derivative, polyarylalkane derivative, pyrazoline derivative, pyrazolone derivative, phenylenediamine derivative, arylamine derivative, amino-substituted chalcone derivative, styrylanthracene derivative, fluorenone derivative, hydrazone derivative, stilbene derivative, silazane derivative, aromatic Tertiary amine compounds, styrylamine compounds, aromatic dimethylidin compounds, phthalocyanine compounds, porphyrin compounds, thiophene derivatives, organic silane derivatives, carbon and the like can be mentioned.

  As a specific material for forming the hole transport layer 130, for example, TPD (N, N′-diphenyl-N, N′-bis (3-methylphenyl) -1,1′-biphenyl-4,4′diamine is used. ); Α-NPD (4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl); m-MTDATA (4,4 ′, 4 ″ -tris (3-methylphenylphenylamino) And low molecular triphenylamine derivatives such as () triphenylamine); polyvinylcarbazole; and polymer compounds obtained by polymerizing the triphenylamine derivative by introducing a polymerizable substituent. The hole transport layer 130 may have a single-layer structure composed of one or more of the materials described above, or may have a multilayer structure composed of a plurality of layers having the same composition or different compositions.

  The hole transport layer 130 may contain an electron accepting dopant. Examples of the electron-accepting dopant include an inorganic compound or an organic compound that is electron-accepting and has a property of oxidizing an organic compound. Specifically, examples of the inorganic compound include metal halides such as ferric chloride, aluminum chloride, gallium chloride, indium chloride, and antimony pentachloride; metal oxides such as vanadium pentoxide and molybdenum trioxide. Examples of the organic compound include compounds having a nitro group, halogen, cyano group, trifluoromethyl group and the like as a substituent, quinone compounds, acid anhydride compounds, fullerenes, and the like.

  The thickness of the hole transport layer 130 depends on the conductivity of each layer and is not particularly limited. In the present embodiment, the thickness of the hole transport layer 130 is preferably 1 nm to 1 μm, and preferably 5 nm to More preferably, it is 500 nm.

Although not shown, a hole injection layer may be provided between the hole transport layer 130 and the first electrode (anode) 120 in this embodiment. Further, a hole transporting intermediate layer may be provided between the light emitting layer 140 and the hole transport layer 130. Each layer may be composed of a plurality of layers.
As the hole injection layer, a known hole injection material can be used. Specifically, for example, conductive polymers such as polyacetylene, polyparaphenylene, polyaniline, polythiophene, polyparaphenylene vinylene; organic compounds such as arylamine and phthalocyanine; vanadium oxide, zinc oxide, molybdenum oxide, ruthenium oxide, oxidation An oxide such as titanium may be used. These can contain the above-mentioned electron-accepting dopant. Examples of using dopants include a mixture of poly (3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) (PEDOT / PSS), polyaniline (PANI) and polystyrene sulfonic acid (PSS). A mixture (PANI / PSS) etc. are mentioned.

  In the present embodiment, the thickness of the hole injection layer is 1 μm or less. Moreover, it is preferable that they are 0.1 nm-1 micrometer, It is more preferable that they are 0.5 nm-500 nm, It is further more preferable that they are 1 nm-300 nm. The hole injection layer may have a single layer structure composed of one or more of the above-described materials, or may have a multilayer structure composed of a plurality of layers having the same composition or different compositions.

(Light emitting layer 140)
In the present embodiment, when a voltage electric field is applied to the organic light emitting device 10, the light emitting layer 140 receives holes from the first electrode (anode) 120 and the hole transport layer 130, and receives the second electrode (cathode) 160, electrons. This is a layer having a function of receiving electrons from the transport layer 150 and emitting light by providing a recombination field of holes and electrons. The light emitting layer 140 may be composed of only a light emitting material, or may include a host material and a light emitting material.

  As the light emitting material, a light emitting organic material can be used. Moreover, a phosphorescent luminescent material, a fluorescent luminescent material, etc. are mentioned. Moreover, in the case of a luminescent organic material, any of a luminescent low molecular compound and a luminescent high molecular compound can be used. As the luminescent organic material, a phosphorescent organic compound and a metal complex are preferable. Some metal complexes exhibit phosphorescence, and such metal complexes are also preferably used.

As the phosphorescent light emitting material, a complex containing a transition metal atom or a lanthanoid atom is generally used. In this embodiment, it is particularly preferable to use a cyclometalated complex as the metal complex of the light-emitting organic material from the viewpoint of improving the light emission efficiency. Examples of cyclometalated complexes include 2-phenylpyridine derivatives, 7,8-benzoquinoline derivatives, 2- (2-thienyl) pyridine derivatives, 2- (1-naphthyl) pyridine derivatives, 2-phenylquinoline derivatives, and the like. Examples thereof include iridium (Ir), palladium (Pd), and platinum (Pt) complexes having a ligand. Among these, iridium (Ir) complexes are particularly preferable. For example, iridium (Ir) complexes having three ligands such as Ir (ppy) ₃ , Ir (Fppy) ₃ , Ir (piq) ₃ , and Ir (bzq) ₃ are used. Iridium (Ir) complexes of two ligands such as FIrpic, (ppy) ₂ Ir (acac), (btp) ₂ Ir (acac) and (bzq) ₂ Ir (acac);

  The cyclometalated complex may have other ligands in addition to the ligands necessary for forming the cyclometalated complex. The cyclometalated complex includes a compound that emits light from triplet excitons, which is preferable from the viewpoint of improving luminous efficiency.

  Examples of the light-emitting polymer compound include poly-p-phenylene vinylene (PPV) such as 2-methoxy-5- (2′-ethylhexyloxy) -1,4-phenylene vinylene copolymer (MEH-PPV). ) Derivatives; π-conjugated polymer compounds such as polyfluorene derivatives; polymers obtained by introducing a low molecular weight dye and tetraphenyldiamine or triphenylamine into the main chain or side chain. Moreover, a luminescent high molecular compound and a luminescent low molecular weight compound can also be used together.

  Fluorescent light emitting materials generally include benzoxazole, benzimidazole, benzothiazole, styrylbenzene, polyphenyl, diphenylbutadiene, tetraphenylbutadiene, naphthalimide, coumarin, pyran, perinone, oxadiazole, aldazine, pyralidine, cyclohexane Pentadiene, bisstyrylanthracene, quinacridone, pyrrolopyridine, thiadiazolopyridine, cyclopentadiene, styrylamine, aromatic dimethylidin compounds, condensed polycyclic aromatic compounds (anthracene, phenanthroline, pyrene, perylene, rubrene, pentacene, etc.), 8 -Various metal complexes represented by metal complexes of quinolinol, pyromethene complexes and rare earth complexes, organosilanes, and derivatives thereof.

  The thickness of the light emitting layer 140 is not specifically limited, Usually, it is preferably 2 nm to 1 μm, more preferably 3 nm to 500 nm, and further preferably 5 nm to 200 nm.

(Electron transport layer 150)
The electron transport layer 150 is a layer having a function of receiving electrons from the second electrode (cathode) 160 side and transporting them to the first electrode (anode) 120 side. Examples of the electron transport material used for the electron transport layer 150 include a low molecular compound and a high molecular compound. Specifically, pyridine derivatives, quinoline derivatives, pyrimidine derivatives, pyrazine derivatives, phthalazine derivatives, phenanthroline derivatives, triazine derivatives, triazole derivatives, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, fluorenone derivatives, anthraquinodimethane derivatives, anthrone Derivatives, diphenylquinone derivatives, thiopyran dioxide derivatives, carbodiimide derivatives, fluorenylidenemethane derivatives, distyrylpyrazine derivatives, naphthalene, perylene and other aromatic ring tetracarboxylic acid anhydrides, phthalocyanine derivatives, 8-quinolinol derivative metal complexes, Metal phthalocyanines, various metal complexes represented by metal complexes with benzoxazole and benzothiazole as ligands, organosilane derivatives represented by siloles Body, and the like.

Specific examples of materials used for the electron transport layer 150 include aluminum compounds such as tris (8-quinolinolato) aluminum (Alq ₃ ) and bis (2-methyl-8-quinolinolato) (4-phenylphenolato) aluminum. Zinc compounds such as bis [2- (2-hydroxyphenyl) benzothiazolate] titanium, 2- (4-biphenylyl) -5- (4-tert-butylphenyl) -1,3,4-oxadiazole, tris ( And boron compounds such as 2,6-dimethyl-4-biphenyl) borane.

  The electron transport layer 150 may contain an electron donating dopant. As an electron donating dopant, it is sufficient if it has an electron donating property and has a property of reducing an organic compound, an alkali metal such as Li, an alkaline earth metal such as Mg, Ca, a transition metal containing a rare earth metal, or a reduction. Organic compounds and the like are preferably used. Specific examples include Li, Na, K, Be, Mg, Ca, Sr, Ba, Y, Cs, La, Sm, Gd, and Yb. Moreover, as a reducing organic compound, a nitrogen-containing compound, a sulfur-containing compound, a phosphorus-containing compound etc. are mentioned, for example.

  The thickness of the electron transport layer 150 depends on conductivity and is not particularly limited, but is 1 μm or less in the present embodiment. Moreover, it is preferable that it is 1 nm-1 micrometer, and it is more preferable that it is 5 nm-500 nm. The electron transport layer 150 may have a single-layer structure composed of one or more of the above-described materials, or may have a multilayer structure composed of a plurality of layers having the same composition or different compositions.

Although not shown, an electron transporting intermediate layer may be provided between the light emitting layer 140 and the electron transport layer 150 in this embodiment mode. Further, a cathode buffer layer may be provided between the second electrode (cathode) 160 and the electron transport layer 150. Examples of the material for forming the electron transporting intermediate layer and the cathode buffer layer include the same materials as those for forming the electron transport layer 150 described above.
The thickness of the cathode buffer layer depends on conductivity and is not particularly limited, but in the present embodiment, it is usually preferably 1 μm or less. Moreover, it is preferable that it is 0.1 nm-1 micrometer, it is more preferable that it is 0.2 nm-500 nm, and it is especially preferable that it is 0.5 nm-100 nm. The cathode buffer layer may have a single layer structure composed of one or more of the above-described materials, or may have a multilayer structure composed of a plurality of layers having the same composition or different compositions.

  Furthermore, although not shown, in the present embodiment, holes transported from the first electrode (anode) 120 side to the light emitting layer 140 are transferred to the second electrode (cathode) 160 side of the light emitting layer 140. It is possible to provide a hole blocking layer having a function of preventing passage to the cathode) 160 side. Examples of the compound constituting the hole blocking layer include aluminum complexes such as BAlq, triazole derivatives, phenanthroline derivatives such as BCP, and the like.

  The thickness of the hole blocking layer is preferably 1 nm to 500 nm, more preferably 5 nm to 200 nm, and particularly preferably 10 nm to 100 nm. The hole blocking layer may have a single layer structure composed of one or more of the above-described materials, or may have a multilayer structure composed of a plurality of layers having the same composition or different compositions.

  Furthermore, in the present embodiment, electrons transported from the second electrode (cathode) 160 side to the light emitting layer 140 to the first electrode (anode) 120 side of the light emitting layer 140 are transferred to the first electrode (anode) 120. It is possible to provide an electron blocking layer having a function of preventing passage to the side. As examples of the compound constituting the electron blocking layer, those mentioned as the hole transport material described above can be applied.

  The thickness of the electron blocking layer is preferably 1 nm to 500 nm, more preferably 5 nm to 200 nm, and particularly preferably 10 nm to 100 nm. The hole blocking layer may have a single layer structure composed of one or more of the above-described materials, or may have a multilayer structure composed of a plurality of layers having the same composition or different compositions.

  Next, another layer configuration (the substrate 110, the first electrode 120, and the second electrode 160) of the organic light emitting device 10 will be described.

(Substrate 110)
The substrate 110 is a support for forming the organic light emitting element 10, and a material that satisfies the mechanical strength required for the organic light emitting element 10 is used.
The material of the substrate 110 is not particularly limited and can be appropriately selected depending on the purpose. When light is extracted from the substrate 110 side of the organic light emitting device 10, it is necessary to transmit light emitted from the light emitting layer 140, and a material that does not scatter or attenuate light is preferable.

  Specific examples of the substrate 110 include, for example, inorganic materials such as yttria-stabilized zirconia (YSZ), sapphire glass, soda glass, and quartz glass; metal nitrides such as aluminum nitride; transparent metal oxides such as alumina. Etc. Examples of organic materials include polyesters such as polyethylene terephthalate, polybutylene phthalate, and polyethylene naphthalate; polystyrene, polycarbonate, polyethersulfone, polyarylate, polyimide, polycycloolefin, norbornene resin, poly (chlorotrifluoroethylene), and the like. It is done.

  When glass is used as the substrate 110, it is preferable to use non-alkali glass as the material in order to reduce ions eluted from the glass. Moreover, when using soda-lime glass, it is preferable to use what applied barrier coats, such as a silica. In the case of an organic material, it is preferable that it is excellent in heat resistance, dimensional stability, solvent resistance, electrical insulation, and workability.

  The substrate 110 may be colorless and transparent or colored and transparent as long as it is light transmissive. In the present embodiment, it is preferably colorless and transparent in that light emitted from the light emitting layer 140 described later is not scattered or attenuated.

When it is not necessary to extract light from the substrate 110 side of the organic light emitting device 10, the material of the substrate 110 is not limited to a material that transmits light emitted from the light emitting layer 140, and an opaque material can also be used. Specifically, in addition to the above materials, silicon (Si), copper (Cu), silver (Ag), gold (Au), platinum (Pt), tungsten (W), titanium (Ti), tantalum (Ta) Niobium (Nb) or an alloy thereof; stainless steel; oxides such as SiO ₂ and Al ₂ O ₃ ; n-Si and the like.

When the substrate 110 is a metal, it is preferable that the substrate 110 and the first electrode 120 and the second electrode 160 are insulated. The thickness of the substrate 110 is appropriately selected according to the required mechanical strength. In the present embodiment, it is preferably 0.01 mm to 10 mm, more preferably 0.1 mm to 2 mm.
The shape, structure, size, and the like of the substrate 110 are not particularly limited, and can be appropriately selected depending on the use, purpose, and the like of the light-emitting element. In the present embodiment, the substrate 110 is preferably plate-shaped. As for the structure of the board | substrate 110, a single layer structure and a laminated structure are mentioned, for example. Moreover, it may be formed of a single member or may be formed of two or more members.

(First electrode 120)
The first electrode (anode) 120 normally has a function as an electrode for supplying holes to the light emitting layer 140, and the shape, structure, size, and the like are not particularly limited. Examples of the material of the first electrode 120 include metals, alloys, metal oxides, conductive compounds, and mixtures and laminates thereof. Specific examples include conductive metal oxides such as tin oxide doped with antimony or fluorine (ATO, FTO), tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), indium zinc oxide (IZO), etc. Metals such as gold, silver, chromium, nickel, copper, platinum, tungsten, titanium, tantalum, and niobium; mixtures of the aforementioned metals and conductive metal oxides, alloys such as stainless steel, copper iodide, copper sulfide, etc. Inorganic conductive materials of the above; organic conductive materials such as polyaniline, polythiophene, and polypyrrole; and laminates of these with ITO. Among these, conductive metal oxides are preferable, and ITO is particularly preferable from the viewpoints of productivity, high conductivity, transparency, and the like.

  As a film formation method of the first electrode 120, for example, a wet method such as a printing method or a coating method, a physical method such as a vacuum deposition method, a sputtering method, or an ion plating method, or a chemical method such as CVD or plasma CVD method. Etc. In this embodiment, for example, when the first electrode 120 is formed using ITO, a direct current or high frequency sputtering method, a vacuum deposition method, an ion plating method, or the like can be employed.

  The formation position of the 1st electrode 120 of the organic light emitting element 10 does not have a restriction | limiting in particular, According to the use and objective of a light emitting element, it can select suitably. In this embodiment mode, it is preferably formed over the substrate 110. The first electrode 120 may be formed on the entire area of one surface of the substrate 110 or may be formed on a part thereof. Examples of the patterning method for forming the first electrode 120 include chemical etching by photolithography or the like; physical etching by laser light irradiation or the like; vacuum deposition or sputtering using a mask; lift-off method, printing method, or the like. .

The first electrode 120 has electrical conductivity, and the surface resistance (sheet resistance) in the temperature range of −5 ° C. to 80 ° C. is preferably 10 ³ Ω / □ or less, and more preferably 10 ² Ω / □ or less. The work function is preferably 4.5 eV or more. When the first electrode 120 is light transmissive, it may be colorless and transparent or colored and transparent. In order to extract emitted light from the first electrode 120 side, the transmittance is preferably 60% or more, and more preferably 70% or more.
Although the thickness of the 1st electrode 120 is suitably selected by the material which comprises the 1st electrode 120, and is not specifically limited, Usually, about 2 nm-50 micrometers, 10 nm-1 micrometer are preferable, and also 30-250 nm is more preferable. When the film thickness is excessively thin, the surface resistance tends to increase, and when the film thickness is excessively thick, the light transmittance tends to decrease.

  By performing the surface treatment of the substrate 110 and the first electrode 120, the performance of the layer to be overcoated (eg, adhesion to the first electrode 120, surface smoothness, hole injection barrier, etc.) can be improved. . Specific surface treatment methods include high-frequency plasma treatment, sputtering treatment, corona treatment, UV (ultraviolet) ozone irradiation treatment, ultraviolet irradiation treatment, oxygen plasma treatment, and the like. The work function can be measured by, for example, ultraviolet photoelectron spectroscopy.

(Second electrode 160)
The second electrode (cathode) 160 normally has a function as an electrode for injecting electrons into the light emitting layer 140, and the shape, structure, size, and the like are not particularly limited. When light is extracted from the second electrode 160 side of the organic light emitting device 10 (when the surface on the second electrode 160 side is a surface from which light is extracted, that is, a light emitting surface), the second electrode 160 is light emitted from the light emitting layer 140. It is preferable to use a material that transmits light. On the other hand, when it is not necessary to extract light from the second electrode 160 side of the organic light emitting device 10, the second electrode 160 is not limited to a material that transmits light, and an opaque material can also be used.

  In the present embodiment, since the second electrode 160 is used as a cathode, it is preferable that the work function is low and it is chemically stable. Examples of the material constituting the second electrode 160 include metals, alloys, metal oxides, electrically conductive compounds, and mixtures thereof. Specific examples include alkali metals (Li, Na, K, Cs, etc.); magnesium (Mg) and alkaline earth metals (Ca, etc.); gold, silver, lead, aluminum, sodium-potassium alloy, lithium-aluminum alloy, Examples thereof include rare earth metals such as magnesium-silver alloy, indium, and ytterbium. Two or more of these can be used in combination.

  As a film formation method of the second electrode 160, for example, a wet method such as a printing method or a coating method; a physical method such as a vacuum deposition method, a sputtering method, or an ion plating method; a chemical method such as a CVD method or a plasma CVD method. Etc. The patterning method for forming the second electrode 160 includes chemical etching by photolithography or the like; physical etching by laser light irradiation or the like; vacuum deposition or sputtering using a mask; lift-off method or printing method. Can be mentioned.

  Although the thickness of the 2nd electrode 160 is suitably selected by the material which comprises the 2nd electrode 160, and is not specifically limited, Usually, it is about 10 nm-5 micrometers, and 50 nm-1 micrometer are preferable. The second electrode 160 may be light transmissive (can transmit light emitted from the light emitting layer 140), or may be opaque. The light transmissive second electrode 160 is also formed by depositing a thin film of the material of the second electrode 160 to a thickness of 1 nm to 10 nm, and further laminating a transparent conductive material such as ITO or IZO. be able to.

<Method for producing organic light-emitting device>
(First electrode forming step)
When manufacturing the organic light emitting device 10 (see FIG. 1) to which the present embodiment is applied, first, for example, a resistance heating vapor deposition method, an electron beam vapor deposition method, a sputtering method, an ion plating method, a CVD method is formed on the substrate 110. The first electrode 120 is formed using a method or the like. In addition, when using metal fine particles such as silver, fine particles such as copper iodide, carbon black, conductive metal oxide fine particles, and conductive polymer fine powder as the material of the first electrode 120, these are appropriately used. The 1st electrode 120 can also be formed by disperse | distributing to a binder resin solution and apply | coating on the board | substrate 110. FIG. In this case, it is also possible to form the film by using a method such as a spin coating method, a dip coating method, an ink jet method, a printing method, a spray method, or a dispenser method, followed by heat treatment.

  Subsequently, on the first electrode 120, the hole transport layer 130, the light emitting layer 140, and the electron transport layer 150, and further, if necessary, a hole injection layer, a hole transport intermediate layer, an electron transport intermediate layer, Each layer such as a cathode buffer layer is formed. In this embodiment mode, the resistance heating vapor deposition method or the coating method is more preferable for forming each layer including the light-emitting layer 140, and the coating method is particularly preferable for forming the layer containing the polymer organic compound. When film formation is performed by a coating method, a coating solution in which a material constituting a layer to be formed is dissolved or dispersed in a predetermined solvent such as an organic solvent or water is applied. When coating, various methods such as spin coating, spray coating, dip coating, ink jet, slit coating, dispenser, and printing can be used. After coating, a desired layer is formed by drying the coating solution by heating or vacuuming.

(Second electrode forming step)
Further, the second electrode 160 is formed on the electron transport layer 150. As a method of forming the second electrode 160, a method similar to the formation of the first electrode 120 described above is used.

  Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples unless it exceeds the gist.

Example 1
An organic light emitting device was produced by the following operation.
First, a glass substrate (72 mm × 55 mm, thickness: 0.7 mm, corresponding to the substrate 110) with 150 nm thick ITO (anode) (Indium Tin Oxide) on the surface was prepared. Next, a hole transport layer made of NPB (N, N-di (1-naphthyl) -N, N′-diphenylbenzidine) having a thickness of 50 nm was formed on the anode by resistance heating vapor deposition. NPB is a compound having a dipole moment of less than 1 [D], and the hole transport layer is a nonpolar layer.

Subsequently, OXD-7 (2,2- (3,1-phenylene) bis [5- (4-tert-butylphenyl), which is a polar compound having a dipole moment of 6.6 [D], is formed on the hole transport layer. ) -1,3,4-oxadiazole]) (90% by volume) with a dipole moment of less than 1 [D] Ir (ppy) ₃ (tris (2-phenylpyridine) iridium (III)) (10 volume) %), A light emitting layer having a film thickness of 30 nm was formed. The light emitting layer is a polar layer, and the parameter P defined by the formula (1) is 178 [D · nm].

  Next, an electron transport layer having a thickness of 20 nm made of tris (2,6-dimethyl-4-biphenylyl) borane (hereinafter sometimes abbreviated as PPB) was formed on the light-emitting layer. PPB is a compound having a dipole moment of less than 1 [D], and the electron transport layer is a nonpolar layer. Subsequently, a 1-nm-thick cathode buffer layer made of NaF was formed on the electron transport layer, and finally, a 100-nm-thick cathode made of Al was formed on the cathode buffer layer by sputtering to produce organic light emission. An element was produced.

Since the polar layer of the organic light emitting device of this example is only one light emitting layer, the sum ΣP _j of the parameters P _j represented by the above formula (1) for all polar layers in the polar region is 178 [D · nm].
With respect to the organic light-emitting device produced by the above operation, the voltage when the current flowing between the anode and the cathode was 1 mA / cm ² was 2.9 (V @ 1 mA / cm ² ). The results are shown in Table 1. In Table 1, the value of the parameter P _j is not calculated for a nonpolar layer made of only a compound having a dipole moment of less than 1 [D].

(Example 2)
The electron transport layer is a polar layer made of Alq ₃ having a dipole moment of 4.1 [D] and a first electron transport layer (light emitting layer side) having a thickness of 10 nm and a dipole moment of less than 1 [D]. An organic light emitting device was produced in the same manner as in Example 1 except that a non-polar layer made of PPB was used to form a two-layer structure of a second electron transport layer (cathode side) having a thickness of 10 nm.
The polar region of the organic light emitting device of this example is composed of a light emitting layer and a first electron transport layer made of Alq ₃ . The total ΣP _j of the parameters P _j for all polar layers in the polar region is 219 [D · nm]. The voltage when the current flowing between the anode and the cathode was 1 mA / cm ² was 3.2 (V @ 1 mA / cm ² ). The results are shown in Table 2.

Example 3
The hole transport layer is composed of a nonpolar layer made of NPB having a dipole moment of less than 1 [D] and a first hole transport layer (anode side) having a thickness of 40 nm, and OXD having a dipole moment of 6.6 [D]. A second hole transport layer (light emitting layer side) having a thickness of 10 nm and a polar layer composed of a material in which -7 (25% by volume) and NPB (75% by volume) with a dipole moment of 1 [D] or less are mixed An organic light-emitting device was fabricated in the same manner as in Example 1 except that the two-layer structure was made.
The polar region of the organic light emitting device of this example is composed of a second hole transport layer containing OXD-7 (25% by volume) and a light emitting layer. The total ΣP _j of the parameters P _j for all polar layers in the polar region is 195 [D · nm]. The voltage when the current flowing between the anode and the cathode was 1 mA / cm ² was 3.1 (V @ 1 mA / cm ² ). The results are shown in Table 3.

Example 4
The hole transport layer is a nonpolar layer made of NPB having a dipole moment of less than 1 [D], and a first hole transport layer (anode side) having a film thickness of 45 nm and OXD− having a dipole moment of 6.6 [D]. 7 (25% by volume) and a second hole transport layer (light emission) having a thickness of 5 nm with a polar layer composed of a material in which Ir (ppy) ₃ (75% by volume) having a dipole moment of 1 [D] or less is mixed. The first electron transport layer (light emitting layer side) having a thickness of 5 nm and a polar layer made of Alq ₃ having a dipole moment of 4.1 [D]. And a non-polar layer made of PPB having a dipole moment of less than 1 [D] and having a two-layer structure with a second electron transport layer (cathode side) having a thickness of 15 nm. An organic light emitting device was produced.
The polar region of the organic light emitting device of this example is composed of a second hole transport layer containing OXD-7 (25% by volume), a light emitting layer, and a first electron transport layer made of Alq ₃ . The total ΣP _j of the parameters P _j for all polar layers in the polar region is 207 [D · nm]. The voltage when the current flowing between the anode and the cathode was 1 mA / cm ² was 3.3 (V @ 1 mA / cm ² ). The results are shown in Table 4.

(Example 5)
The light emitting layer is composed of OXD-7 (90% by volume) which is a polar compound having a dipole moment of 6.6 [D] and Ir (ppy) ₃ (10% by volume) having a dipole moment of less than 1 [D]. The first light-emitting layer (hole transport layer side) having a thickness of 30 nm and Alq ₃ (90% by volume) and Ir (ppy) ₃ (10), which are polar compounds having a dipole moment of 4.1 [D]. An organic light-emitting device was fabricated in the same manner as in Example 1 except that a two-layer structure with a 10 nm-thick second light-emitting layer (on the electron transport layer side) composed of
The polar region of the organic light emitting device of this example is composed of two light emitting layers. The sum ΣP _j of the parameters P _j for all polar layers in the polar region is 215 [D · nm]. The voltage when the current flowing between the anode and the cathode was 1 mA / cm ² was 3.0 (V @ 1 mA / cm ² ). The results are shown in Table 5.

(Comparative Example 1)
The light emitting layer is composed of CBP (4,4′-bis (carbazol-9-yl) -biphenyl) (90% by volume) which is a compound having a dipole moment of less than 1 [D] and a dipole moment of less than 1 [D]. An organic light-emitting device was produced in the same manner as in Example 1 except that the mixed material of Ir (ppy) ₃ (10% by volume) was used. That is, the organic light emitting device in this comparative example does not have a polar region.
The voltage when the current flowing between the anode and the cathode was 1 mA / cm ² was 5.5 (V @ 1 mA / cm ² ). The results are shown in Table 6.

(Comparative Example 2)
The light emitting layer is a first light emitting layer having a film thickness of 15 nm, made of a mixed material of CBP (90% by volume) and Ir (ppy) ₃ (10% by volume), which is a compound having a dipole moment of less than 1 [D]. (Hole transport layer side), OXD-7 (90% by volume) which is a polar compound having a dipole moment of 6.6 [D], and Ir (ppy) ₃ (10 volumes) having a dipole moment of less than 1 [D]. %), And an organic light emitting device was fabricated in the same manner as in Example 1, except that the second light emitting layer (on the electron transport layer side) had a thickness of 15 nm.
The sum ΣP _j of the parameters P _j for the all polar layers in the polar region is 89 [D · nm]. The voltage when the current flowing between the anode and the cathode was 1 mA / cm ² was 5.0 (V @ 1 mA / cm ² ). The results are shown in Table 7.

(Comparative Example 3)
The same operation as in Example 1 was performed to form a hole transport layer on a glass substrate with ITO. Subsequently, the hole transport layer is composed of a mixed material of CBP (90% by volume) which is a compound of less than 1 [D] and Ir (ppy) ₃ (10% by volume) of which the dipole moment is less than 1 [D]. The first light-emitting layer having a thickness of 10 nm was composed of OXD-7 (90% by volume) and Ir (ppy) ₃ (10% by volume), which are polar compounds having a dipole moment of 6.6 [D]. A film composed of a second light-emitting layer having a thickness of 8 nm, and Alq ₃ (90% by volume) and Ir (ppy) ₃ (10% by volume), which are polar compounds having a dipole moment of 4.1 [D] A third light-emitting layer having a thickness of 10 nm was sequentially formed.

Next, a 12-nm-thick first electron transporting layer, which is a polar layer made of Alq ₃ having a dipole moment of 4.1 [D], and a PPB having a dipole moment of less than 1 [D] are formed on the light-emitting layer. A second electron transport layer having a thickness of 8 nm, which is a nonpolar layer made of, was sequentially formed. Subsequently, a cathode buffer layer and a cathode were formed on the electron transport layer in the same manner as in Example 1 to produce an organic light emitting device.
Parameters P _j of the polar layer in this comparative example is 50 or less. The sum ΣP _j of the parameters P _j for the all polar layers in the polar region is 134 [D · nm]. The voltage when the current flowing between the anode and the cathode was 1 mA / cm ² was 5.1 (V @ 1 mA / cm ² ). The results are shown in Table 8.

(Comparative Example 4)
An organic light emitting device was produced in the same manner as in Example 1 except that the electron transport layer was a 20 nm thick electron transport layer made of Alq ₃ which is a polar compound having a dipole moment of 4.1 [D].
In this comparative example, the total film thickness (50 nm) of the polar region (light emitting layer and electron transport layer) exceeds 1.5 times the film thickness (30 nm) of the light emitting layer (1.67 times).
The total ΣP _j of the parameters P _j for the all polar layers in the polar region is 260 [D · nm]. The voltage when the current flowing between the anode and the cathode was 1 mA / cm ² was 3.8 (V @ 1 mA / cm ² ). The results are shown in Table 9.

(Comparative Example 5)
An organic light emitting device was produced in the same manner as in Comparative Example 1 except that the electron transport layer was an electron transport layer having a thickness of 20 nm made of Alq ₃ which is a polar compound having a dipole moment of 4.1 [D].
In this comparative example, the polar region is only the electron transport layer, and the parameter P for this layer is 82 [D · nm]. The voltage when the current flowing between the anode and the cathode was 1 mA / cm ² was 5.3 (V @ 1 mA / cm ² ). The results are shown in Table 9.

As described above, in the organic light emitting device 10 to which the present exemplary embodiment is applied, the organic layer 20 has a three-layer structure of (nonpolar region / polar region / nonpolar region), and the polar region has a dipole moment. Has a polar layer containing an organic compound having a [D] (Debye) or more, and at least one of the light emitting layers in the polar region contains an organic compound having a dipole moment of 4 [D] or more. sum .SIGMA.P _j parameters _{P j} of the formula (1) is not less 150 [D · nm] or more, the total thickness of the polar region is not more than 1.5 times the thickness of the light-emitting layer 140 Thus, the charge injection voltage in the organic light emitting device is reduced.

DESCRIPTION OF SYMBOLS 10 ... Organic light emitting element, 110 ... Board | substrate, 120 ... 1st electrode (anode), 130 ... Hole transport layer, 140 ... Light emitting layer, 150 ... Electron transport layer, 160 ... 2nd electrode (cathode)

Claims (5)

An organic light emitting device comprising an anode, an organic layer including at least one light emitting layer, and a cathode in order,
The organic layer is composed of a polar region and two nonpolar regions sandwiching the polar region from both sides,
The polar region includes at least one polar layer;
The nonpolar region consists of one or more nonpolar layers,
The polar layer is a layer containing a total of 50 vol% or more of at least one organic polar compound having a dipole moment of 1 [D] or more,
The nonpolar layer is a layer composed only of an organic compound having a dipole moment of less than 1 [D],
The polar region includes the light emitting layer, and the total thickness of the polar region is 1.5 times or less the thickness of the light emitting layer,
The light emitting layer includes at least one polar layer;
At least one of the polar layers included in the light emitting layer includes a total of 30% by volume or more of at least one organic polar compound having a dipole moment of 4 [D] or more,
The organic light-emitting element, wherein a total sum ΣP _j of parameters P _j represented by the following formula (1) is 150 [D · nm] or more for all polar layers in the polar region.
P _j = Σ (μ _ij × d _j × φ _ij ) (1)
(In the formula (1), _dj is a film thickness of an arbitrary polar layer j, μ _ij is a dipole moment of an arbitrary organic polar compound i having a dipole moment in the polar layer j of 1D or more, and φ _ij is the volume fraction of the organic polar compound i in the polar layer j, and Σ means the sum of all types of organic polar compounds contained in the polar layer j.)   The organic layer includes a hole transport layer and an electron transport layer, and the polar region includes the light emitting layer and either the hole transport layer or the electron transport layer. Organic light emitting device.   The organic layer includes a hole transport layer and an electron transport layer, the light-emitting layer coincides with the polar region, and the hole transport layer and the electron transport layer are the nonpolar layers. The organic light-emitting device described in 1. It said parameter P sum .SIGMA.P _j of _j is, 250 [D · nm] The organic light-emitting device according to any one of claims 1 to 3, wherein the less. It said parameter P sum .SIGMA.P _j of _j is, 200 [D · nm] The organic light-emitting device according to any one of claims 1 to 3, wherein the less.

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