JP5742307B2 - Organic EL device - Google Patents

Description

  The present invention relates to a polymer organic EL element.

  Conventionally, a low molecular type organic EL element and a high molecular type organic EL element are known. The low molecular type organic EL element is configured using a low molecular material, in other words, a material having a LUMO value of 2.6 eV or more in an organic layer located between an anode and a cathode. Since such a low molecular organic layer can be formed by a vacuum deposition method, it is possible to form an organic EL element having a high temperature durability and a long life. On the other hand, there is a problem that the manufacturing cost becomes very high because a large-scale apparatus in which a number of vacuum deposition apparatuses (vacuum deposition chambers) are connected is necessary.

  On the other hand, the polymer type organic EL element is constituted by using a polymer material whose organic layer exhibits a LUMO value of less than 2.6 eV in other words. Such a polymer organic layer has a large molecular weight, and thus is formed using a coating method such as a spin coating method or an ink jet method instead of vacuum deposition. For this reason, compared with a low molecular-type organic EL element, the vacuum evaporation process in a manufacturing process can be reduced, and a manufacturing cost can be made low by extension.

  By the way, in the polymer type organic EL element, the LUMO value of the material constituting the organic layer is small as described above. Is easily formed. Therefore, in a polymer type organic EL device, as a constituent material of the cathode, a metal having a low work function close to the LUMO value of the polymer material constituting the organic layer, specifically, an alkali metal, an alkaline earth metal, a lanthanoid Etc. are used. For example, Patent Document 1 discloses a polymer organic EL element having a cathode made of such a metal material.

  The polymer light emitting device described in Patent Document 1 has a light emitting layer containing a polymeric fluorescent substance, and the cathode is made of at least one metal selected from the group consisting of alkali metals, alkaline earth metals, and lanthanoids. Contains. As described above, when an alkali metal, an alkaline earth metal, or a lanthanoid is employed as the constituent material of the cathode, the electron injection barrier at the interface between the light emitting layer containing the polymeric phosphor and the cathode can be reduced.

  In Patent Document 1, at least selected from the group consisting of fluorides and oxides of alkali metals, fluorides and oxides of alkaline earth metals, and fluorides and oxides of lanthanoids between the light emitting layer and the cathode. A buffer layer having an average film thickness of 2 nm or less containing one kind of compound is provided. This buffer layer is considered to have the same effect as that frequently used in the low-molecular-type organic EL device. That is, it is considered that the purpose is to improve the effect of electron injection characteristics by forming an electric double layer at the interface between the light emitting layer and the cathode.

JP 2000-299189 A

  By the way, as a constituent material of the cathode, there are very few metal materials having a work function of 2.6 eV or less. In addition, the lower the work function, the lower the stability of the metal in the atmosphere, making it difficult to handle the metal. For this reason, it is difficult to eliminate a very large electron injection barrier while stabilizing the interface state in a configuration in which an organic layer having a LUMO value of less than 2.6 eV is in contact with the cathode.

  For this reason, as described in Patent Document 1, the cathode and the light emitting layer selected from alkali metal, alkaline earth metal, and lanthanoid are made of a fluoride or oxide of a metal material constituting the cathode. In order to improve the element characteristics (electron injection characteristics), it is preferable to provide a buffer layer and reduce the electron injection barrier by the effect of the electric double layer.

  However, as a result of intensive studies by the inventor, it has been confirmed that the luminance life is reduced in the configuration described in Patent Document 1. In other words, the configuration described in Patent Document 1 has a problem in terms of luminance life, although the device characteristics can be improved by reducing the electron injection barrier.

  The present invention has been made in view of the above problems, and an object of the present invention is to improve both element characteristics and luminance life in a polymer organic EL element.

  The present inventor has intensively studied an organic EL element in which at least one organic layer having an LUMO value of less than 2.6 eV is disposed between the anode and the cathode. As a result, the cathode is composed of lithium fluoride, an electron injection layer adjacent to the organic layer, and calcium, and the electron injection layer is provided with a metal layer adjacent to the side opposite to the organic layer. The knowledge that lithium diffuses in the organic layer was obtained. Moreover, the knowledge that calcium fluoride was formed in the vicinity of an interface by the brightness | luminance fall was acquired.

  From these findings, a substitution reaction occurs between lithium fluoride and calcium, and calcium fluoride having a polarization lower than that of lithium fluoride is generated, so that the effect of forming an electric double layer is weakened and electron injection characteristics are reduced. Deteriorates. Due to the deterioration of the electron injection characteristics, the recombination center of holes and electrons is closer to the cathode side than the initial state, leading to the conclusion that the light emission efficiency is lowered (that is, the luminance is lowered). The recombination center is set so as to balance the hole injection from the anode and the electron injection from the cathode, and is usually set at the center of the organic layer (particularly the center of the light emitting layer) in the initial state.

  The following invention is based on this finding. In addition, the result of earnest examination by this inventor is demonstrated in the beginning of embodiment mentioned later.

In order to achieve the above object, the invention described in claim 1
An organic EL device comprising at least one organic layer having an LUMO value of less than 2.6 eV between an anode and a cathode,
The cathode is in contact with the organic layer and has a three-layer structure of an electron injection layer, a first metal layer, and a second metal layer from the organic layer side,
The electron injection layer is made of lithium fluoride,
The first metal layer is a mixture of calcium and aluminum,
The second metal layer is Ri Do aluminum, characterized Rukoto to have a thickness of 100 nm.

  According to this, since the first metal layer includes calcium (2.87 eV) having a low work function, the electron injection barrier at the interface between the organic layer and the cathode can be reduced.

  In addition, since the electron injection layer made of lithium fluoride is provided between the first metal layer and the organic layer, the electron injection barrier can be further reduced by the effect of the electric double layer.

  Further, the first metal layer does not contain only calcium but also contains the same aluminum as the constituent material of the second metal layer. Thereby, the volume density of calcium in a 1st metal layer can be reduced compared with a calcium simple substance. In addition, calcium and aluminum have a large difference in atomic radii, and as can be seen from Hume Rosary's law, they are very difficult to dissolve (in other words, it is difficult to form an alloy). For this reason, calcium is present not only in a single metal but is dispersed in the first metal layer. Therefore, by these effects, the reaction probability of calcium and lithium fluoride can be reduced, that is, the substitution reaction can be suppressed. In the first metal layer, calcium is present not only in a simple substance, but exhibits the original characteristics (low work function) of calcium.

  As described above, according to the present invention, both the device characteristics and the luminance life can be improved. This point has been actually confirmed by the present inventors.

As claimed in claim 2,
The first metal layer preferably contains calcium in the range of 25 vol% or more and 40 vol% or less.

  According to this, the luminance life can be further improved as compared with the configuration in which calcium is less than 25 vol% and the configuration in which calcium exceeds 40 vol%. This point has been actually confirmed by the present inventors.

  In addition, when calcium is less than 25 vol%, since there is little calcium in a 1st metal layer, the effect of the high electron injection characteristic of calcium falls. This is considered to be due to the high driving voltage and the influence of element heat generation. On the other hand, when calcium exceeds 40 vol%, it is considered that the effect of reducing the reaction probability with lithium fluoride by dispersing calcium is weakened.

As claimed in claim 3,
The film thickness of the first metal layer is preferably set in the range of 1 nm to 4 nm. Especially, as described in claim 4, it is preferable that the thickness of the first metal layer is set to 2 nm.

  According to this, compared with the structure whose film thickness of a 1st metal layer is less than 1 nm, and the structure exceeding 4 nm, a brightness | luminance lifetime can be improved further. In particular, when it is 2 nm, the luminance life can be most improved. This point has been actually confirmed by the present inventors.

  When the film thickness exceeds 4 nm, segregation of calcium or the like is likely to occur in the non-solid solution first alloy layer, and it is considered that the effect of reducing the reaction probability with lithium fluoride by dispersing calcium is weakened. .

As claimed in claim 5,
Between the anode and the organic layer, a hole transport layer that does not contain a dopant having a donor property or an acceptor property is preferably in contact with the anode.

  In the case of a hole transport material (specifically, a conductive polymer) containing a dopant having a donor property or an acceptor property, a dopant having a donor property or an acceptor property can be added to the polymer which is a host material, thereby providing conductivity. Is expressed. For this reason, a charge transfer complex etc. may be formed between adjacent organic layers, and there exists a possibility that a brightness | luminance may fall. On the other hand, in the present invention, since the hole transport layer does not contain a dopant having a donor property or an acceptor property, the luminance life can be further improved.

Especially as claimed in claim 6
As a constituent material of the hole transport layer, a material having a structure represented by Chemical Formula 2 is preferably employed.

  According to this, when forming a polymer type organic layer on the hole transport layer by a coating method, the hole transport layer does not dissolve in the solvent. For this reason, the freedom degree of selection of the constituent material of an organic layer can be improved.

It is sectional drawing which shows schematic structure of the organic EL element which this inventor used for examination. It is a figure which shows the analysis result of lithium distribution by TOF-SIMS. It is a figure which shows the analysis result of the calcium distribution by TOF-SIMS. It is a figure which shows the analysis result of the calcium compound distribution by TOF-SIMS. It is the figure which put together the structure of the organic EL element formed in each Example and each comparative example, and the test result of the relative luminance in the durability test 100h with respect to initial luminance. It is a figure which shows the relationship between vol% of calcium in a 1st metal layer, and a relative luminance. It is a figure which shows the relationship between the film thickness of a 1st metal layer, and relative luminance. In Example 1, it is a figure which shows the analysis result of lithium distribution by TOF-SIMS.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following, common or related elements are given the same reference numerals.

(Background to the creation of the present invention)
First, the background of the inventor's creation of the present invention will be described.

  The present inventor has intensively studied a polymer type organic EL element in which at least one organic layer having an LUMO value of less than 2.6 eV is disposed between an anode and a cathode.

  FIG. 1 shows a schematic configuration of an organic EL element 100 used for examination by the present inventors. The organic EL element 100 includes an anode 20 disposed on one surface of a transparent substrate 10, a hole transport layer 30 disposed on a surface of the anode 20 opposite to the substrate 10, and a surface opposite to the anode 20 of the hole transport layer 30. The organic layer 40 including the light emitting layer is disposed on the surface, and the cathode 50 is disposed on the surface of the organic layer 40 opposite to the hole transport layer 30. The cathode 50 has a three-layer structure of an electron injection layer 51, a first metal layer 52, and a second metal layer 53 from the organic layer 40 side.

Specifically, ITO is used as the anode 20 and the material of the hole transport layer 30 is represented by the compound 1, N, N, N ′, N ′, N ″, N ″ -Hexakis- (4 '-methyl-biphenyl-4-yl) -benzene-1,3,5-triamine was used.

  In addition, as a material of the organic layer 40, compound 2, specifically, Poly [(9,9-dioctylfluorenyl-2,7-diyl) -co- (1,4-benzo- {2,1 ', 3 } -thiadiazole)] (ADS233YE). Furthermore, lithium fluoride (hereinafter referred to as LiF) is used as the electron injection layer 51 constituting the cathode 50, calcium (hereinafter referred to as Ca) as the first metal layer 52, and aluminum (hereinafter referred to as Al) as the second metal layer 53. Used).

  And the organic EL element 100 of such a structure was formed by the method shown below.

  First, after forming ITO as the anode 20 with a thickness of 150 nm on one surface of a transparent substrate 10 made of glass or the like, the compound 1 shown in the chemical formula 3 is formed with a thickness of 60 nm by vacuum deposition, A hole transport layer 30 was obtained. Next, a polymer light emitting material having a weight average molecular weight of 40000 is purified by dissolving the above-described compound 2 in a xylene solvent to form a coating solution, and this coating solution is formed on the hole transport layer 30 by a spin coating method. Apply with. And it was set as the organic layer 40 (light emitting layer) of thickness 100nm by making it dry at 120 degreeC. Next, LiF was formed as the electron injection layer 51 in a thickness of 1 nm, Ca was formed as the first metal layer 52 in a thickness of 2 nm, and Al was formed as the second metal layer 53 in a thickness of 100 nm by a vacuum deposition method. . Finally, a metal can (not shown) and the substrate 10 on which the element was formed were attached to each other with a photo-curing resin in a glove box, thereby sealing the manufactured element.

The organic EL device 100 thus formed was subjected to a durability test at an initial luminance of 800 cd / m ² by DC driving in an environment of 85 ° C. A sample (−40%) in which the luminance decreased by 40% with respect to the initial luminance was created, and the state analysis of the organic EL element 100 was performed.

The analysis method and conditions are as follows.
Analysis method: Time-of-flight secondary ion mass spectrometry (TOF-SIMS)
Analysis method: Depth direction mass spectrometry from cathode surface Conditions: Sputter source (Cs), Analytical primary ion (Bi)
FIG. 2 shows the analysis result of the Li distribution in the depth direction, and FIG. 3 shows the analysis result of the Ca distribution in the depth direction. FIG. 4 shows the analysis results of the Ca compound distribution in the depth direction in a sample (−40%) that is reduced by 40% with respect to the initial luminance. In FIG. 2, the sample Li in the initial state is indicated by a solid line, and the sample Li that has been reduced by 40% is indicated by a broken line. In FIG. 3, the sample Ca in the initial state is indicated by a solid line, and the sample Ca reduced by 40% is indicated by a broken line. 2 and 3, the one-dot chain line indicates In, and the two-dot chain line indicates Al. In FIG. 4, calcium fluoride (hereinafter referred to as CaF) is indicated by a solid line, calcium carbide (CaC) is indicated by a broken line, calcium oxide (CaO) is indicated by a one-dot chain line, and calcium hydroxide (CaOH) is indicated by a two-dot chain line. . Both In and Al are indicated by dotted lines. 2 to 4, the count number on the vertical axis indicates the number of detected ion species.

  In FIGS. 2 and 3, the distribution (Li or Ca) also has a width in the sample in the initial state, but because of the influence by the sputter source ion (knock-on) during the depth direction analysis, the actual diffusion It does not indicate.

  As shown in FIG. 3, Ca hardly shows a change in the distribution in the depth direction between the initial state and the luminance reduction. That is, it can be seen that Ca is not diffused. On the other hand, as shown in FIG. 2, the distribution of Li spreads toward the organic layer 40 due to a decrease in luminance as compared with the initial state. That is, it has been found that Li diffuses into the organic layer 40 as the luminance decreases.

  Further, as shown in FIG. 4, it was confirmed that CaF was remarkably present in the vicinity of the interface between the cathode 50 and the organic layer 40 in a state where the luminance was lowered.

From the above analysis results, it is considered that the substitution reaction shown below proceeds at the interface between the cathode 50 and the organic layer 40 during durability.
(Duration reaction formula) 2LiF + Ca ²⁺ ⇒CaF ₂ + 2Li ⁺
By this reaction, at least a part of LiF at the interface reacts with Ca and is replaced with CaF ₂ . The electronegativity of Li and Ca is 0.98 and 1.00, respectively. From this relationship Li <Ca, CaF ₂ is less polarized than LiF.

For this reason, when the fluoride at the interface changes to CaF ₂ having a weak polarization, the effect of forming the electric double layer becomes weak, and the electron injection characteristics deteriorate. It is considered that the electron injection amount is reduced due to the deterioration of the electron injection characteristics, and the recombination center of holes and electrons is shifted to the cathode 50 side, so that the light emission efficiency is reduced (that is, the luminance is reduced).

  The recombination center is set so as to balance the hole injection from the anode 20 and the electron injection from the cathode 50, and is usually set at the center of the organic layer 40 (particularly the center of the light emitting layer) in the initial state. The

  As described above, the present inventor concluded that the substitution reaction of fluoride (LiF) proceeds at the interface between the cathode 50 and the organic layer 40, thereby deteriorating the electron injection characteristics and thus the luminance life. It came. Then, in order to suppress the deterioration of the electron injection characteristics, the idea was to reduce the reaction probability of LiF and Ca.

  In order to suppress the deterioration of the electron injection characteristics, it is conceivable to use a metal for the first metal layer 52 in which the fluoride after the reaction has a larger polarization. In this case, however, two problems arise, which is not realistic.

  The first problem is that an element having a lower electronegativity than the metal element of the fluoride used for the electron injection layer 51 must be selected for the first metal layer 52. For this reason, there is a high possibility that an element having a very small work function is adopted as the material of the first metal layer 52. If the work function is low, its stability is also low, so it is very difficult to handle.

  As a second problem, when a material that is relatively stable, that is, a work function is large, is selected for the first metal layer 52, the fluoride metal used for the electron injection layer 51 is the same as the material of the first metal layer 52. A value larger than the work function is adopted. In this case, there is a high possibility that the electronegativity of the metal element of the fluoride is increased. When the electronegativity is large, the polarization of fluoride is reduced, and the effect of forming an electric double layer is reduced. That is, element characteristics (electron injection characteristics) are deteriorated.

  The embodiment described below is based on these findings. Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
The schematic configuration (component) of the organic EL element 100 according to the present embodiment is the same as the prototype shown in FIG. Therefore, illustration is omitted. The difference from the prototype is mainly the constituent material of the cathode 50 having a three-layer structure of the electron injection layer 51, the first metal layer 52, and the second metal layer 53 from the organic layer 40 side.

  In the organic EL element 10, a transparent or translucent anode 20 is formed on one surface of a transparent substrate 10 made of glass or the like. As a constituent material of the anode 20, a known conductive substance that is transparent or translucent and can form electrodes can be used. In this embodiment, an anode 20 made of indium tin oxide (ITO) is employed.

  A hole transport layer 30 is disposed on the surface of the anode 20 opposite to the substrate 10. The material of the hole transport layer 30 is not particularly limited, but a material that does not contain a dopant having a donor property or an acceptor property is preferably adopted. In the case of a hole transport material (specifically, a conductive polymer) containing a dopant having a donor property or an acceptor property, a dopant having a donor property or an acceptor property can be added to the polymer which is a host material, thereby providing conductivity. Is expressed. This is because in such a conductive polymer, the dopant diffuses into the organic layer 40 to form a charge transfer complex or the like with the polymer constituting the organic layer 40, which may reduce the luminance. .

  In addition, as a material that does not contain a dopant having a donor property or an acceptor property, a triphenylamine derivative material having a relatively small molecular weight and a high hole transport property can be employed. In the present embodiment, the hole transport layer 30 made of the compound 1 shown in the above chemical formula 3 is employed. Since this compound 1 is a low molecule, it can be formed by, for example, a vacuum deposition method. Further, when the polymer type organic layer 40 is formed on the hole transport layer 30 by a coating method, the hole transport layer 30 does not dissolve in the solvent. For this reason, the freedom degree of selection of the constituent material of the organic layer 40 can be improved. The compound 1 is shown in a prior application by the present applicant (Japanese Patent Application Laid-Open No. 2010-192587, Japanese Patent Application Laid-Open No. 2005-276802, and many others), and detailed description thereof is omitted.

  The organic layer 40 includes a light emitting layer. Further, it is made of a polymer material having a LUMO value of less than 2.6 eV, such as polyfluorene. As the organic layer 40, either a single layer (only a light emitting layer) or a structure in which a plurality of layers are laminated can be adopted. In general, a material exhibiting an LUMO value of less than 2.6 eV has a higher molecular weight than a material having an LUMO value of 2.6 eV or more, and is a polymer, so that it cannot be formed by a vacuum deposition method. For this reason, it is formed using a spin coat method, an ink jet method, a printing method, a dip coat method, a spray method or the like. As a result, as compared with the configuration employing the organic layer 40 made of a low molecular material, the vacuum deposition step in the manufacturing process of the organic EL element 100 can be reduced, and the manufacturing cost can be reduced.

  The cathode 50 is in contact with the organic layer 40 and has a three-layer structure of an electron injection layer 51, a first metal layer 52, and a second metal layer 53 from the organic layer 40 side.

  As the electron injection layer 51, a material capable of forming an electric double layer at the interface with the organic layer 40 and thereby reducing the electron injection barrier can be employed. Such materials include alkali metal or alkaline earth metal fluorides. In the present embodiment, the electron injection layer 51 is made of LiF, which is an alkali metal fluoride.

  For the first metal layer 52, a material that can reduce the electron injection barrier at the interface with the organic layer 40 made of a polymer material (a material having a LUMO value of less than 2.6 eV) can be used. As such a material, there is a metal having a small work function (in other words, a metal having a work function close to the LUMO value of the polymer of the organic layer 40), specifically, an alkali metal or an alkaline earth metal. In the present embodiment, the first metal layer 52 includes Ca (work function 2.87 eV) which is an alkaline earth metal.

  In the present embodiment, the alkali metal or alkaline earth metal is dispersed in the matrix to reduce the reaction probability with the alkali metal or alkaline earth metal fluoride forming the electron injection layer 51. The metal layer 52 includes a matrix.

  The material used for the matrix is not particularly limited as long as it can stably maintain the dispersion of alkali metal or alkaline earth metal and has conductivity as an electrode material. Considering this point, metal materials, conductive polymers, and the like are conceivable.

  In the case of a conductive polymer, generally a guest substance corresponding to a donor or an acceptor is added to a host material (polymer). When the guest substance is added in this manner, carriers are generated in the host material and conductivity is exhibited. However, the diffusion of donors and acceptors into the organic layer 40 may form charge transfer complex molecules with the polymer of the organic layer 40, which may reduce the luminance lifetime. Therefore, the matrix is preferably a metal material, and in particular, a matrix having a relatively high work function and having stability in the atmosphere and good conductivity is preferable.

  Also, the metal mixture forms a solid solution in many metal combinations. This solid solution has a structure in which an added metal atom is substituted at a metal atom position of a matrix. When the solid solution is formed in this way, the problem is that it changes to properties as an alloy. When a solid solution is formed in the first metal layer 52 described above, the characteristics of the alkali metal or alkaline earth metal alone, that is, the low work function cannot be utilized. Considering this point, it is preferable that the combination of the metal material used as the matrix and the alkali metal or alkaline earth metal is a combination that does not form a solid solution.

Here, the conditions for forming a solid solution are indicated by Hume Rosary's law. This rule is expressed by the following equation (Equation 1), where R0 is the atomic radius of the metal element constituting the matrix and R1 is the atomic radius of the added alkali metal or alkaline earth metal element.
(Expression 1) {| R0−R1 | / R0} × 100 ≦ 15
And when two metal elements satisfy | fill the relationship of Numerical formula 1, it has shown that it is easy to form a solid solution. For example, in the case of Ag and Mg, the value on the left side of Formula 1 is about 6%, which indicates that the combination is easy to form a solid solution. In the case of Cr and Mg, the left side of Equation 1 is about 7%, and it can be seen that this combination also easily forms a solid solution. In the case of Al and Li, the value on the left side of Equation 1 is 21%, which indicates that it is difficult to form a solid solution. From Formula 1, if the difference in atomic radius between two metal elements is large, it is difficult to form a solid solution.

  In the present embodiment, based on the above points, the metal element constituting the matrix is Al. In the case of Al, since the work function is large (4.28 eV) and stable in the air, handling is easy. It also has good conductivity. Furthermore, it is less expensive than Au, Ag, Pt and the like. Moreover, in the combination of Al and Ca, the value of the left side of Formula 1 shows a very large value of about 44%. For this reason, since it is very difficult to dissolve, Ca can be held in the first metal layer 52 as a single metal and Ca can be dispersed. Thus, in this embodiment, the 1st metal layer 52 mixes Ca and Al.

  In the present embodiment, Ca is contained in the first metal layer 52 in the range of 25 vol% or more and 40 vol% or less. The film thickness of the first metal layer 52 is set in the range of 1 nm to 4 nm, more preferably 2 nm.

  As a constituent material of the second metal layer 53, a material having a large work function and excellent conductivity so as to protect the lower layer (the first metal layer 52 and the electron injection layer 51) constituting the cathode 50 is used. Can be used. Examples of such a material include Al, Au, Ag, and Pt. Among these, Al is preferable in terms of cost. In the present embodiment, the second metal layer 53 is made of Al.

  Next, functions and effects of the organic EL element 100 according to this embodiment will be described.

  In the present embodiment, the first metal layer 52 constituting the cathode 50 has Ca (work function 2.87 eV). For this reason, it is possible to reduce the electron injection barrier at the interface of the organic layer 40 made of a polymer material (LUMO value less than 2.6 eV).

  In addition, an electron injection layer 51 made of LiF is provided between the first metal layer 52 and the organic layer 40. Therefore, the electron injection barrier at the interface with the organic layer 40 can be further reduced by the effect of forming the electric double layer.

  Further, the first metal layer 52 does not contain only Ca, but also contains the same Al as the constituent material of the second metal layer 53. For this reason, the volume density of Ca in the first metal layer 52 (the proportion of Ca in the first metal layer 52) is smaller than that of Ca alone. Therefore, compared with the first metal layer 52 made of only Ca, the reaction probability of Ca and LiF can be reduced, that is, the substitution reaction can be suppressed.

  Further, Ca and Al have a large difference in atomic radius, and as can be seen from Equation 1 (Fume Rosary's law), it is very difficult to dissolve. For this reason, in the first metal layer 52, Ca is present in a small amount as a single metal and is dispersed in Al. Therefore, the electron injection barrier at the interface of the organic layer 40 can be reduced by Ca existing in the first metal layer 52 as a single metal.

  As described above, according to the present embodiment, both element characteristics (electron injection characteristics) and luminance life can be improved.

  In addition, since the combination which is hard to form a solid solution is employ | adopted as a combination of the metal which comprises the 1st metal layer 52, precipitation of the alkali metal or alkaline-earth metal element added to a matrix, layer separation, etc. may arise. Conceivable.

  For this reason, as a more preferable form, the first metal layer 52 may contain Ca in the range of 25 vol% or more and 40 vol% or less. According to this, the luminance life can be further improved as compared with the configuration in which Ca is less than 25 vol% and the configuration in which Ca exceeds 40 vol%.

  In addition, when Ca is less than 25 vol%, since there is little Ca in the first metal layer 52, the effect of high electron injection characteristics of Ca having a low work function is reduced, and accordingly, a high driving voltage is generated, and element heat generation or the like occurs. It is thought to influence. On the other hand, when Ca exceeds 40 vol%, it is thought that there is much Ca and the effect of dispersing Ca and reducing the reaction probability with LiF is weakened.

  The thickness of the first metal layer 52 is preferably in the range of 1 nm to 4 nm. According to this, compared with the structure whose thickness is less than 1 nm and exceeds 4 nm, the luminance life can be further improved. In particular, when the thickness of the first metal layer 52 is 2 nm, the luminance life can be most improved.

  If the film thickness exceeds 4 nm, the thick film tends to cause segregation of Ca in the non-solid solution first metal layer 52, and the effect of dispersing Ca and reducing the reaction probability with LiF. It seems to be weakened.

  Next, the grounds for adopting the above configuration will be described with reference to Examples 1 to 4 and Comparative Examples 1 to 7.

(Comparative Example 1)
This Comparative Example 1 has the same configuration as the prototype shown in the description of the process leading to the creation of the present invention. Specifically, after forming ITO as the anode 20 with a thickness of 150 nm on one surface of a transparent substrate 10 made of glass or the like, the compound 1 shown in the chemical formula 3 is formed with a thickness of 60 nm by a vacuum deposition method. Thus, a hole transport layer 30 was obtained. Next, the compound 2 described above, that is, Poly [(9,9-dioctylfluorenyl-2,7-diyl) -co- (1,4-benzo- {2,1 ', 3} -thiadiazole) manufactured by American Dye Source Co., Ltd. ] (ADS233YE), a polymer light emitting material having a weight average molecular weight of 40,000 is purified and dissolved in a xylene solvent to form a coating solution, and this coating solution is applied onto the hole transport layer 30 by spin coating. To do. And it was set as the organic layer 40 (light emitting layer) of thickness 100nm by making it dry at 120 degreeC. Next, LiF was formed as the electron injection layer 51 in a thickness of 1 nm, Ca was formed as the first metal layer 52 in a thickness of 2 nm, and Al was formed as the second metal layer 53 in a thickness of 100 nm by a vacuum deposition method. . Finally, the fabricated element was sealed by bonding a metal can (not shown) and the substrate 10 on which the element was formed with a photocurable resin in a glove box.

The organic EL element 100 thus formed was subjected to a durability test at an initial luminance of 800 cd / m ² by DC driving in an 85 ° C. environment.

Example 1
After forming ITO as the anode 20 with a thickness of 150 nm on one surface of a transparent substrate 10 made of glass or the like, the compound 1 represented by the above chemical formula 3 is formed with a thickness of 60 nm by a vacuum deposition method. A transport layer 30 was obtained. Next, a polymer light emitting material having a weight average molecular weight of 40000 is purified by dissolving the above-described compound 2 in a xylene solvent to form a coating solution, and this coating solution is formed on the hole transport layer 30 by a spin coating method. Apply with. And it was set as the organic layer 40 (light emitting layer) of thickness 100nm by making it dry at 120 degreeC. Next, LiF having a thickness of 1 nm is formed as the electron injection layer 51 by vacuum deposition, and then Ca and Al are vapor-deposited together at a deposition rate ratio of 1: 3. A first metal layer 52 was formed. Next, Al having a thickness of 100 nm was formed as the second metal layer 53 by a vacuum deposition method. Finally, the fabricated element was sealed by bonding a metal can (not shown) and the substrate 10 on which the element was formed with a photocurable resin in a glove box.

The organic EL element 100 thus formed was subjected to a durability test at an initial luminance of 800 cd / m ² by DC driving in an 85 ° C. environment.

(Comparative Example 2)
After forming ITO as the anode 20 with a thickness of 150 nm on one surface of a transparent substrate 10 made of glass or the like, the compound 1 represented by the above chemical formula 3 is formed with a thickness of 60 nm by a vacuum deposition method. A transport layer 30 was obtained. Next, a polymer light emitting material having a weight average molecular weight of 40000 is purified by dissolving the above-described compound 2 in a xylene solvent to form a coating solution, and this coating solution is formed on the hole transport layer 30 by a spin coating method. Apply with. And it was set as the organic layer 40 (light emitting layer) of thickness 100nm by making it dry at 120 degreeC. Next, LiF having a thickness of 1 nm was formed as the electron injection layer 51 by a vacuum evaporation method, and then Al having a thickness of 100 nm was formed as the second metal layer 53 by a vacuum evaporation method. Finally, the fabricated element was sealed by bonding a metal can (not shown) and the substrate 10 on which the element was formed with a photocurable resin in a glove box.

The organic EL element 100 thus formed was subjected to a durability test at an initial luminance of 800 cd / m ² by DC driving in an 85 ° C. environment.

(Comparative Example 3)
After forming ITO as the anode 20 with a thickness of 150 nm on one surface of a transparent substrate 10 made of glass or the like, the compound 1 represented by the above chemical formula 3 is formed with a thickness of 60 nm by a vacuum deposition method. A transport layer 30 was obtained. Next, a polymer light emitting material having a weight average molecular weight of 40000 is purified by dissolving the above-described compound 2 in a xylene solvent to form a coating solution, and this coating solution is formed on the hole transport layer 30 by a spin coating method. Apply with. And it was set as the organic layer 40 (light emitting layer) of thickness 100nm by making it dry at 120 degreeC. Next, after forming LiF with a thickness of 1 nm as the electron injection layer 51 by a vacuum deposition method, both Ca and Al are vapor-deposited at a deposition rate ratio of 1: 6, whereby a thickness of 2 nm containing Ca and Al is obtained. A first metal layer 52 was formed. Next, Al having a thickness of 100 nm was formed as the second metal layer 53 by a vacuum deposition method. Finally, the fabricated element was sealed by bonding a metal can (not shown) and the substrate 10 on which the element was formed with a photocurable resin in a glove box.

The organic EL element 100 thus formed was subjected to a durability test at an initial luminance of 800 cd / m ² by DC driving in an 85 ° C. environment.

(Example 2)
After forming ITO as the anode 20 with a thickness of 150 nm on one surface of a transparent substrate 10 made of glass or the like, the compound 1 represented by the above chemical formula 3 is formed with a thickness of 60 nm by a vacuum deposition method. A transport layer 30 was obtained. Next, a polymer light emitting material having a weight average molecular weight of 40000 is purified by dissolving the above-described compound 2 in a xylene solvent to form a coating solution, and this coating solution is formed on the hole transport layer 30 by a spin coating method. Apply with. And it was set as the organic layer 40 (light emitting layer) of thickness 100nm by making it dry at 120 degreeC. Next, after forming LiF with a thickness of 1 nm as the electron injection layer 51 by vacuum deposition, Ca and Al are vapor-deposited together at a deposition rate ratio of 2: 3, so that the thickness of Ca and Al is 2 nm. A first metal layer 52 was formed. Next, Al having a thickness of 100 nm was formed as the second metal layer 53 by a vacuum deposition method. Finally, the fabricated element was sealed by bonding a metal can (not shown) and the substrate 10 on which the element was formed with a photocurable resin in a glove box.

The organic EL element 100 thus formed was subjected to a durability test at an initial luminance of 800 cd / m ² by DC driving in an 85 ° C. environment.

(Example 3)
After forming ITO as the anode 20 with a thickness of 150 nm on one surface of a transparent substrate 10 made of glass or the like, the compound 1 represented by the above chemical formula 3 is formed with a thickness of 60 nm by a vacuum deposition method. A transport layer 30 was obtained. Next, a polymer light emitting material having a weight average molecular weight of 40000 is purified by dissolving the above-described compound 2 in a xylene solvent to form a coating solution, and this coating solution is formed on the hole transport layer 30 by a spin coating method. Apply with. And it was set as the organic layer 40 (light emitting layer) of thickness 100nm by making it dry at 120 degreeC. Next, LiF having a thickness of 1 nm is formed as the electron injection layer 51 by vacuum deposition, and then Ca and Al are vapor-deposited together at a deposition rate ratio of 1: 3. A first metal layer 52 was formed. Next, Al having a thickness of 100 nm was formed as the second metal layer 53 by a vacuum deposition method. Finally, the fabricated element was sealed by bonding a metal can (not shown) and the substrate 10 on which the element was formed with a photocurable resin in a glove box.

The organic EL element 100 thus formed was subjected to a durability test at an initial luminance of 800 cd / m ² by DC driving in an 85 ° C. environment.

Example 4
After forming ITO as the anode 20 with a thickness of 150 nm on one surface of a transparent substrate 10 made of glass or the like, the compound 1 represented by the above chemical formula 3 is formed with a thickness of 60 nm by a vacuum deposition method. A transport layer 30 was obtained. Next, a polymer light emitting material having a weight average molecular weight of 40000 is purified by dissolving the above-described compound 2 in a xylene solvent to form a coating solution, and this coating solution is formed on the hole transport layer 30 by a spin coating method. Apply with. And it was set as the organic layer 40 (light emitting layer) of thickness 100nm by making it dry at 120 degreeC. Next, after forming LiF having a thickness of 1 nm as the electron injection layer 51 by vacuum deposition, Ca and Al are vapor-deposited together at a deposition rate ratio of 1: 3, so that the thickness of 4 nm including Ca and Al is increased. A first metal layer 52 was formed. Next, Al having a thickness of 100 nm was formed as the second metal layer 53 by a vacuum deposition method. Finally, the fabricated element was sealed by bonding a metal can (not shown) and the substrate 10 on which the element was formed with a photocurable resin in a glove box.

The organic EL element 100 thus formed was subjected to a durability test at an initial luminance of 800 cd / m ² by DC driving in an 85 ° C. environment.

(Comparative Example 4)
After forming ITO as the anode 20 with a thickness of 150 nm on one surface of a transparent substrate 10 made of glass or the like, the compound 1 represented by the above chemical formula 3 is formed with a thickness of 60 nm by a vacuum deposition method. A transport layer 30 was obtained. Next, a polymer light emitting material having a weight average molecular weight of 40000 is purified by dissolving the above-described compound 2 in a xylene solvent to form a coating solution, and this coating solution is formed on the hole transport layer 30 by a spin coating method. Apply with. And it was set as the organic layer 40 (light emitting layer) of thickness 100nm by making it dry at 120 degreeC. Next, after forming LiF with a thickness of 1 nm as the electron injection layer 51 by vacuum deposition, Ca and Al are vapor-deposited together at a deposition rate ratio of 1: 3, so that the thickness of Ca and Al is 10 nm. A first metal layer 52 was formed. Next, Al having a thickness of 100 nm was formed as the second metal layer 53 by a vacuum deposition method. Finally, the fabricated element was sealed by bonding a metal can (not shown) and the substrate 10 on which the element was formed with a photocurable resin in a glove box.

The organic EL element 100 thus formed was subjected to a durability test at an initial luminance of 800 cd / m ² by DC driving in an 85 ° C. environment.

(Comparative Example 5)
After forming ITO as the anode 20 with a thickness of 150 nm on one surface of a transparent substrate 10 made of glass or the like, the compound 1 represented by the above chemical formula 3 is formed with a thickness of 60 nm by a vacuum deposition method. A transport layer 30 was obtained. Next, a polymer light emitting material having a weight average molecular weight of 40000 is purified by dissolving the above-described compound 2 in a xylene solvent to form a coating solution, and this coating solution is formed on the hole transport layer 30 by a spin coating method. Apply with. And it was set as the organic layer 40 (light emitting layer) of thickness 100nm by making it dry at 120 degreeC. Next, LiF having a thickness of 1 nm is formed as the electron injection layer 51 by vacuum deposition, and then Ca and Al are vapor-deposited together at a deposition rate ratio of 1: 3. A first metal layer 52 was formed. Next, Al having a thickness of 100 nm was formed as the second metal layer 53 by a vacuum deposition method. Finally, the fabricated element was sealed by bonding a metal can (not shown) and the substrate 10 on which the element was formed with a photocurable resin in a glove box.

The organic EL element 100 thus formed was subjected to a durability test at an initial luminance of 800 cd / m ² by DC driving in an 85 ° C. environment.

(Comparative Example 6)
After forming ITO as the anode 20 with a thickness of 150 nm on one surface of a transparent substrate 10 made of glass or the like, the compound 1 represented by the above chemical formula 3 is formed with a thickness of 60 nm by a vacuum deposition method. A transport layer 30 was obtained. Next, a polymer light emitting material having a weight average molecular weight of 40000 is purified by dissolving the above-described compound 2 in a xylene solvent to form a coating solution, and this coating solution is formed on the hole transport layer 30 by a spin coating method. Apply with. And it was set as the organic layer 40 (light emitting layer) of thickness 100nm by making it dry at 120 degreeC. Next, after forming LiF having a thickness of 1 nm as the electron injection layer 51 by vacuum deposition, both Ca and Al are vapor-deposited together at a deposition rate ratio of 7: 3, so that a thickness of 2 nm including Ca and Al is obtained. A first metal layer 52 was formed. Next, Al having a thickness of 100 nm was formed as the second metal layer 53 by a vacuum deposition method. Finally, the fabricated element was sealed by bonding a metal can (not shown) and the substrate 10 on which the element was formed with a photocurable resin in a glove box.

The organic EL element 100 thus formed was subjected to a durability test at an initial luminance of 800 cd / m ² by DC driving in an 85 ° C. environment.

(Comparative Example 7)
After forming ITO as an anode 20 with a thickness of 150 nm on one surface of a transparent substrate 10 made of glass or the like, a spin coat method is used to apply a coating solution in which PEDOT / PSS is dispersed in water. The positive hole transport layer 30 having a thickness of 60 nm was obtained by coating and drying at 120 ° C. Next, a polymer light emitting material having a weight average molecular weight of 40000 is purified by dissolving the above-described compound 2 in a xylene solvent to form a coating solution, and this coating solution is formed on the hole transport layer 30 by a spin coating method. Apply with. And it was set as the organic layer 40 (light emitting layer) of thickness 100nm by making it dry at 120 degreeC. Next, LiF having a thickness of 1 nm is formed as the electron injection layer 51 by vacuum deposition, and then Ca and Al are vapor-deposited together at a deposition rate ratio of 1: 3. A first metal layer 52 was formed. Next, Al having a thickness of 100 nm was formed as the second metal layer 53 by a vacuum deposition method. Finally, the fabricated element was sealed by bonding a metal can (not shown) and the substrate 10 on which the element was formed with a photocurable resin in a glove box.

The organic EL element 100 thus formed was subjected to a durability test at an initial luminance of 800 cd / m ² by DC driving in an 85 ° C. environment.

  FIG. 5 summarizes the configurations of Examples 1 to 4 and Comparative Examples 1 to 7 and the evaluation results of the durability test. The evaluation result represents the relative luminance after the durability test 100 h with respect to the luminance in the initial state.

  FIG. 6 shows the composition of the first metal layer 52 when the compound 1 shown in the chemical formula 3 is used as the hole transport layer 30 and the thickness of the first metal layer 52 is 2 nm. The relationship between vol% (volume%) and relative luminance is shown. Specifically, the results of Examples 1 and 2 and Comparative Examples 1, 3, and 6 are shown. Moreover, the result of the comparative example 2 which does not have the 1st metal layer 52, ie, shows the state of Ca being 0 vol%, is also shown.

  As apparent from FIG. 6, when the Ca content in the first metal layer 52 is in the range of 25 vol% or more and 40 vol% or less (Al is in the range of 60 vol% or more and 75 vol% or less), the relative luminance, that is, the luminance life is further improved. it can. Specifically, the relative luminance can be 0.8 or more.

  In addition, when Ca is less than 25 vol%, since there is little Ca in the first metal layer 52, the effect of high electron injection characteristics of Ca having a low work function is reduced, and accordingly, a high driving voltage is generated, and element heat generation or the like occurs. It is thought to influence. On the other hand, when Ca exceeds 40 vol%, it is considered that the effect of dispersing Ca and reducing the reaction probability with LiF is weakened.

  FIG. 7 shows the first metal when the compound 1 shown in the chemical formula 3 is used as the hole transport layer 30 and the composition of the first metal layer 5 is Ca: 25 vol% and Al: 75 vol%. The relationship between the thickness of the layer 52 and relative luminance (luminance lifetime) is shown. Specifically, the results of Examples 1, 3, 4 and Comparative Examples 4, 5 are shown. Further, the result of Comparative Example 2 that does not have the first metal layer 52, that is, shows a state of a film thickness of 0 nm is also shown.

  As is clear from FIG. 7, when the thickness of the first metal layer 52 is in the range of 1 nm or more and 4 nm or less, the relative luminance (luminance life) can be further improved. Specifically, the relative luminance can be 0.8 or more. In particular, the thickness of the first metal layer 52 is preferably 2 nm because the luminance life can be most improved.

  The relative luminance decreases when the film thickness exceeds 4 nm. The thick film facilitates segregation of Ca in the non-solid solution first metal layer 52, and Ca is dispersed to form LiF. This is probably because the effect of reducing the reaction probability is weakened.

  Further, as shown in FIG. 5, from the evaluation results of Example 1 and Comparative Example 7, it is possible to improve the luminance life by using a material that does not contain a dopant having a donor property or an acceptor property as the hole transport layer 30. The point is also clear.

  As in Comparative Example 7, when a hole transport material (specifically, a conductive polymer) containing a dopant having a donor property or an acceptor property (PSS in Comparative Example 7) is used, the dopant is added to the organic layer 40. It is considered that a diffusion is caused to form a charge transfer complex or the like with the polymer constituting the organic layer 40, thereby reducing the luminance. On the other hand, when the hole transport layer 30 is formed using a material that does not contain a dopant having donor properties or acceptor properties as in Example 1, the luminance lifetime can be improved.

FIG. 8 shows that the organic EL device 100 shown in Example 1 was subjected to an endurance test for 100 hours at an initial luminance of 800 cd / m ² by DC driving in an environment of 85 ° C. The result of state analysis for luminance 0.85) is shown. Specifically, the analysis result of the distribution of Li in the depth direction is shown. The analysis method and conditions are the same as those in FIG.

  In FIG. 8, Li in the sample in the initial state is indicated by a solid line, and Li of the sample that has been reduced by 40% is indicated by a broken line. The alternate long and short dash line indicates In, and the alternate long and two short dashes line indicates Al. As is apparent from FIG. 8, it can be seen that the diffusion of Li toward the organic layer 40 side is significantly suppressed as compared with FIG.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

20 ... anode 30 ... hole transport layer 40 ... organic layer 50 ... cathode 51 ... electron injection layer 52 ... first metal layer 53 ... second metal layer 100 ...・ Organic EL device

Claims (6)

An organic EL device comprising at least one organic layer having an LUMO value of less than 2.6 eV between an anode and a cathode,
The cathode is in contact with the organic layer and has a three-layer structure of an electron injection layer, a first metal layer, and a second metal layer from the organic layer side,
The electron injection layer is made of lithium fluoride,
The first metal layer is a mixture of calcium and aluminum,
It said second metal layer, Ri Do aluminum, organic EL element characterized Rukoto to have a thickness of 100 nm.   2. The organic EL device according to claim 1, wherein the first metal layer contains calcium in a range of 25 vol% or more and 40 vol% or less.   3. The organic EL element according to claim 1, wherein the film thickness of the first metal layer is set in a range of 1 nm to 4 nm.   The organic EL element according to claim 3, wherein the thickness of the first metal layer is set to 2 nm.   The hole transport layer which does not contain the dopant which has donor property or acceptor property between the said anode and the said organic layer is provided in contact with the said anode, The any one of Claims 1-4 characterized by the above-mentioned. Organic EL element. 6. The organic EL device according to claim 5, wherein the constituent material of the hole transport layer has a structure represented by Chemical Formula 1.

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