JP5627809B2 - Organic EL display device - Google Patents

Description

  The present invention relates to an organic EL display device.

  In recent years, research and development of organic EL display devices using organic EL elements have been active.

  The organic EL display device includes a plurality of red organic EL elements, green organic EL elements, and blue organic EL elements, and can display full-color images by independently emitting light and not emitting light as pixels.

  The organic EL element has a pair of electrodes and a light emitting layer formed of an organic compound between the pair of electrodes. The light-emitting layer has a fluorescent light-emitting material or a phosphorescent light-emitting material as it is or as a guest material having a small weight ratio, for example.

  Each color organic EL element has been developed so that it can be driven at a low voltage. At this time, the layer structure in the element is designed so that the difference in driving voltage between the organic EL elements of the respective colors does not become large and low voltage driving can be performed in any emission color.

  While development of fluorescent light-emitting materials and phosphorescent light-emitting materials is being performed, Patent Document 1 discloses that delayed fluorescent materials are used for organic EL elements.

JP 2004-241374 A

  It is theoretically difficult to set the internal quantum yield to 100% with a fluorescent material. On the other hand, in the phosphorescent material, the internal quantum yield can theoretically be 100%.

  However, in the case of an organic EL element having a light emitting layer including a phosphorescent light emitting material as a guest material in the host material, the band gap of the host material must be widened compared to the case of having a fluorescent light emitting material that emits the same color. .

In the case of emitting a certain color, it is necessary that the lowest excited triplet state T ₁ of the phosphorescent material has an energy level corresponding to the color. Lowest excited singlet state S ₁ of the phosphorescent material is higher than its T _1, also T ₁ of the host material having the phosphorescent material is greater than T ₁ of the phosphorescent material, and S ₁ is the host material of the host material greater than of T _1.

In the case of fluorescent materials that emit the same color, the excited state corresponding to that color is S ₁ instead of T ₁ . That is, when the emission of the same color, low if S ₁ of the fluorescent material of S ₁ and phosphorescent S ₁ to compare the fluorescent material of the material. Therefore, when the phosphorescent light emitting material is used as the guest material, the S ₁ of the host material has to be higher than that when the fluorescent material is used, and as a result, the band gap of the host material must be widened.

  In order to move carriers (electrons or holes) from the adjacent layer to the light emitting layer, it is important that the light emitting layer does not widen the energy barrier with the layer adjacent to the light emitting layer. When the band gap of the host material becomes wide, the HOMO or LUMO of the host material is separated from the HOMO or LUMO of the adjacent layer, and the barrier becomes high.

  In that case, it is necessary to select an optimum material for the adjacent layer or to create a new compound. In that case, it is necessary to consider whether the carrier injection from the electrode is good or bad, and as a result, the layer structure of the organic EL element must be redesigned from the beginning.

  Incidentally, Patent Document 1 discloses a delayed fluorescent material. In this delayed fluorescent material, a strong delayed fluorescent spectrum and a phosphorescent spectrum were observed in the range of 520 nm to 750 nm, and the actual emission wavelengths shown in the figure are peaks with a maximum emission wavelength exceeding 550 nm and peaks exceeding 600 nm. It is composed of That is, this delayed fluorescent material is not a light emitting material that emits primary colors such as green and blue in terms of color purity.

Therefore, the present invention
Each of the organic EL elements has a red organic EL element, a green organic EL element, and a blue organic EL element as a pixel, and each of the organic EL elements includes a pair of electrodes, a hole transport layer, and a light emitting layer,
The light emitting layer of the green organic EL element has a thermally excited delayed fluorescent material, the green organic EL element and the blue organic EL element have a resonator structure between the pair of electrodes, and the green organic The order of interference of the resonator structure of the EL element and the blue organic EL element is secondary, and the hole transport layers of the green organic EL element and the blue organic EL element are provided with the same film thickness in common. An organic EL display device is provided.

  According to the present invention, since the green organic EL element becomes an organic EL element with a low driving voltage using a delayed fluorescent material, an organic EL display device with low power consumption can be provided. In the green organic EL element, the emission spectrum width of light emission from the delayed fluorescent material is narrowed by the effect of the resonator structure, and light emission with high color purity can be performed. Furthermore, in this invention, a hole transport layer can be provided in the same thickness especially in a green organic EL element and a blue organic EL element among a red organic EL element, a green organic EL element, and a blue organic EL element.

Conceptual diagram showing each light emission process Schematic diagram of cross section of organic EL device of the present invention Schematic diagram of a cross section of the organic EL display device of the present invention

  The organic EL display device according to the present invention includes a red organic EL element, a green organic EL element, and a blue organic EL element as pixels, and each of the organic EL elements includes a pair of electrodes, a hole transport layer, and a light emitting layer. The light emitting layer of the green organic EL element has a delayed fluorescent material, the green organic EL element has a resonator structure between the pair of electrodes, and the green organic The organic EL display device is characterized in that the EL element and the hole transport layer of the blue organic EL element are provided in common with the same film thickness.

  In the present invention, a delayed fluorescent material is used in a green organic EL element having high light emission energy. As a result, the barrier between HOMO and the compound of the hole transport layer could be made narrower than when a phosphorescent material was used. As a result, the driving voltage can be lowered, so that even if the thickness of the light emitting layer is increased, the driving voltage does not need to be significantly increased, and the thickness of the light emitting layer is reduced within the organic compound layer disposed between the pair of electrodes. By increasing the thickness, the resonator structure of the green organic EL element can be achieved, and the light extraction of the green organic EL element is improved. Further, the hole transport layer of the green organic EL element can be formed at the same timing and with the same film thickness as the blue organic EL element. As a result, the manufacturing process is simplified. As a result, the hole transport layer can be provided so as to have an optimum thin thickness for a blue organic EL element that emits blue having a shorter wavelength than green.

The delayed fluorescent material in the present invention is a thermally excited delayed fluorescent material. Thermally excited delayed fluorescence will be described with reference to FIG. First, reference numerals in the drawing will be described. 101 is the lowest excited singlet state (S ₁ ), 102 is the ground state (S ₀ ), 103 is the lowest excited triplet state, 104 is the energy in the S ₁ state (Eg ^S1 ), and 105 is the energy in the T ₁ state (Eg ^T1 ), 106 is an intersystem crossing, 107 is delayed fluorescence, and 108 is phosphorescence.

FIG. 1 is a diagram schematically showing delayed fluorescence emission. Excitons generated by carrier recombination include excited singlet state S ₁ (101) and excited triplet state T ₁ (103). S ₁ (101) can emit light as it is. On the other hand, in a general organic compound, so resulting in heat inactivated from T _1, T ₁ does not contribute to light emission. However, in the delayed fluorescent materials such as the exemplary compounds 1 and 2, the intersystem crossing (106) from T ₁ (103) becomes S ₁ (101), and the ground state S ₀ (102) changes from S ₁ (101). It has an emission path of delayed fluorescence (107) that makes a transition. Therefore, the delayed fluorescent material can emit T ₁ (103) that has not contributed to the light emission so far, and by using the delayed fluorescent material, an organic EL element having an extremely high internal quantum efficiency similar to that of the phosphorescent material. Can be expected.

  Examples of the delayed fluorescent material include a copper complex, a platinum complex, and a palladium complex. Exemplary compounds 1 and 2 are shown as examples of the delayed fluorescent material.

Here energy difference Eg ^S1 (104) of the S ₁ (101) and the S ₀ (102), and T ₁ (103) and energy difference Eg between ^{_{S 0 (102) T1 (105}} ). Eg ^T1 (105) is lower in energy than Eg ^S1 (104) by the exchange integral.

Here, S ₁ (101) is considered for the delayed fluorescent material and the phosphorescent material for the emission of the same energy. The delayed fluorescence (107) has an emission level of S ₁ (101) as it is, whereas the phosphorescence (108) has an emission level of T ₁ (103). Therefore, S ₁ (101) of the phosphorescent material is located at a higher energy level. Even with the same luminescent color, the delayed fluorescent material is significantly different in that both S ₁ (101) and T ₁ (103) have lower energy levels than the phosphorescent material.

In an organic EL device, if the Eg ^S1 (104) of the luminescent material is small, the energy difference between the work function of the electrodes used for the anode and the cathode, the HOMO of the hole transport layer, and the LUMO of the electron transport layer becomes small, and hole injection The barrier and electron injection barrier are reduced. As a result, the driving voltage of the organic EL element is lowered. Therefore, at the same emission wavelength, since the delayed fluorescent material has a smaller Eg ^S1 (104) and Eg ^T1 (105) than the phosphorescent material, the hole injection barrier and the electron injection barrier become smaller. The drive voltage of the EL element is lowered. Therefore, by using the delayed fluorescent material, it is possible to increase the film thickness within a range in which the driving voltage is not significantly increased. Thereby, the thickness of the light emitting layer can be designed in a wide range.

The delayed fluorescent material used in the present invention can be identified from the light emission characteristics that the emission process is delayed fluorescence (107). The delayed emission of the compound used in the present invention has the following characteristics.
(1) The emission lifetime at room temperature (298K) is about microseconds (2) The emission wavelength at room temperature (298K) is shorter than the emission wavelength at low temperature (77K) (3) The emission lifetime at room temperature (298K) , Significantly shorter than the light emission lifetime at low temperature (77K) (4) The emission intensity is improved by the increase in temperature

Compared with the emission wavelength at room temperature and the emission wavelength at low temperature, normal fluorescence emission and phosphorescence emission (108), while the emission wavelength at the same wavelength or low temperature becomes shorter, the delayed fluorescence emission (107) The emission wavelength at low temperature becomes longer. This is because light emission from a singlet is observed at room temperature, but light is emitted from T ₁ (103), which is lower in energy than S ₁ (101) at low temperature. The emission wavelength here refers to the maximum emission wavelength or the emission start wavelength.

In addition, normal fluorescence emission is emission from S ₁ (101) and thus has a lifetime of about nanoseconds, whereas phosphorescence emission (108) in which T ₁ (103) is involved in emission is generally emission lifetime. Is from microseconds to milliseconds. Similarly, in the delayed fluorescence emission (107), since T ₁ (103) is involved in the emission, the emission lifetime is about microseconds. The light emission lifetime of the light emitting material used in the present invention is preferably 0.1 microsecond or more and less than 1 millisecond in a solid state or a solution state.

Regarding the emission lifetime, the emission lifetimes of delayed fluorescence (107) and phosphorescence (108) are on the order of microseconds, but as a feature of delayed fluorescence (107), the emission lifetime at low temperature is significantly higher than the emission lifetime at room temperature. It becomes long. For example, when it is considered that non-radiation deactivation is suppressed at a low temperature, when considering a phosphorescent compound having a quantum yield of 0.1 at room temperature, the low-temperature emission lifetime is at most 10 times the emission lifetime at room temperature. It is. In the case of delayed fluorescence, light emission is strongly dependent on temperature because light is emitted from different excited states at low temperature and room temperature. At room temperature, light is emitted from S ₁ (101), but at low temperature, light is emitted from T ₁ (103). Therefore, the light emission life at low temperature is more than 10 times the light emission life at room temperature, and depending on the compound, it is two or more orders of magnitude longer. Is also observed. The light emission life of the light emitting material used in the present invention is preferably 10 times or more, more preferably 50 times or more, and still more preferably 100 times or more of the light emission life at low temperature in the solid state or solution state. It is.

Furthermore, the phosphorescence emission (108) increases in the non-radiation deactivation rate as the temperature increases, so the emission intensity decreases. In the case of delayed fluorescence emission (107), the emission intensity increases as the temperature increases. improves. This is because the external temperature energy, T ₁ increases the probability of intersection (106) between terms from (103) S ₁ to (101), T ₁ (103) intersystem crossing to the S ₁ (101) from (106 This is because it becomes easier to emit light.

Therefore, a small Eg ^S1 (104) tends to be a highly efficient delayed fluorescent material. However, this small Eg ^S1 (104) is achieved because S ₁ (101) and T ₁ (103) are in the charge-mobility state, resulting in a very small exchange integral. Therefore, most of the delayed fluorescence (107) described here emits light from an excited state having a charge-transfer property. In general, an emission spectrum from a charge transfer state has a characteristic that it tends to be a broad spectrum. For this reason, when organic EL element light emission including a delayed fluorescent material is used for display applications, it is preferable to provide means capable of adjusting the emission spectrum width, emission peak, and the like.

  The organic EL device according to the present invention has a pair of electrodes of an anode and a cathode, a light emitting layer disposed therebetween, and a hole transport layer provided on the anode side in contact with the light emitting layer. In addition, a hole injection layer, an electron blocking layer, a hole blocking layer, an electron transport layer, and an electron injection layer may be provided between the pair of electrodes, and these may be provided as appropriate.

  FIG. 2 shows an example of the configuration of the organic EL element in the present embodiment, taking as an example a case where the light emitting layer has a delayed fluorescent material and a resonator structure between a pair of electrodes. In this figure, the organic EL element is composed of an upper electrode, a lower electrode, and an organic functional layer. In FIG. 2, 201 is a substrate, 202 is an anode (reflection electrode), 203 is an organic functional layer, 204 is a cathode (semi-transparent electrode), 205 is a reflection layer, 206 is a transparent conductive film, 207 is a hole transport layer, 208 is A light emitting layer, 209 is an electron transport layer, 210 is a protective layer, and 211 is a sealing glass.

  In FIG. 2, a configuration in which the lower electrode is a reflective electrode 202 whose anode is an anode and the upper electrode is a translucent electrode 204 whose cathode is a cathode is shown as an example.

  In the formation of the resonator, the interface between the upper electrode and the lower electrode on the organic layer side is a reflection surface. As a light emitting element, light is extracted from one of them, so that the combination is a reflective electrode and a semi-transparent electrode, but the upper and lower electrode arrangement may be arbitrarily determined depending on the light extraction surface and the element configuration. For example, in the present embodiment, a top emission element that extracts light emission from a translucent electrode opposite to the substrate 201 is shown, but the present invention can also be applied to a bottom emission type element.

  Here, the reflective electrode 202 includes a reflective layer 205 and a transparent conductive film 206.

  The reflectance at the interface with the transparent conductive film 206 as the reflective layer 205 is at least 50% or more, preferably 80% or more, and is not particularly limited. For example, silver (Ag) or aluminum (Al Or a metal such as chromium (Cr) or an alloy thereof. Further, gold (Au), platinum (Pt), tungsten (W), and the like having a high work function are effective as electrodes having high hole injection properties and reflectivity.

  As the transparent conductive film 206, an oxide conductive film, specifically, a compound film (ITO) of indium oxide and tin oxide, a compound film of indium oxide and zinc oxide (IZO), or the like can be used. The transparent conductive film can be introduced as necessary. When introducing a transparent conductive film, reduce the carrier injection barrier from the reflective layer to the organic functional layer, adjust the optical path length inside the device, or if the reflective layer is formed of an insulating member such as a dielectric multilayer film, etc. There is.

  Here, “transparent” means that the transmittance is 80% or more and 100% or less, and more specifically, the extinction coefficient κ is 0.05 from the viewpoint of suppressing attenuation due to multiple reflection. Hereinafter, it is preferably 0.01 or less.

  The translucent electrode 204 is made of a single metal material or an alloy. Since the extinction coefficient κ of the metal material is large, the amount of transmitted light decreases due to light absorption when light passes through the electrode. In order to efficiently extract light from the translucent electrode, it is necessary to suppress light absorption. For this reason, it is preferable to select one having a small real part refractive index. Examples of the metal material for that purpose include silver, aluminum, magnesium, calcium, sodium, and gold.

  In FIG. 2, the organic functional layer 203 is composed of, for example, three layers of a hole transport layer 207, a light emitting layer 208, and an electron transport layer 209. However, only the light emitting layer may be used. Or you may form from several layers, such as 2 layers and 4 layers.

  The light emitting layer 207 may be made of only a delayed fluorescent light emitting material, for example, but it is preferable to use the delayed fluorescent material as a light emitting dopant from the viewpoint of the light emitting efficiency and driving life of the device. The doping concentration as the light emitting dopant is not particularly specified, but is preferably 5 to 50% by weight, more preferably 10 to 30% by weight. The light emitting layer in this case refers to a layer containing a light emitting dopant.

  The hole transport layer 207 and the electron transport layer 209 have not only a transport function but also a function as a charge injection layer from each electrode, but a separate injection layer or transport layer may be additionally provided. Further, a layer having a charge blocking function, an exciton diffusion preventing function, or the like may be newly provided as a layer adjacent to the light emitting layer.

  In such an element, the interface between the reflective electrode 202 and the hole transport layer 207 on the substrate 201 or the interface between the reflective layer 205 and the transparent conductive film 206 and the interface between the semitransparent electrode 204 and the electron injection layer 209 are formed on the reflective surface. As described above, a resonating part is formed between both reflecting surfaces. It is assumed that the optical distance between the upper and lower electrodes is L, the resonance wavelength is λ, the angle at which the light emitted from the element is visually recognized is θ (0 ° when viewed directly facing the element), and the order of interference is m. Further, when the sum of the phase shifts when light emission is reflected by each electrode is φ (rad), if there is a relationship satisfying <Equation 1> between the parameters, the strengthening due to the resonance effect can be used.

  Here, the optical distance L is the sum (= n1d1 + n2d2 +...) Of the optical film thickness (= refractive index (n) × film thickness (d)) of the organic functional layer between the upper and lower electrodes. Note that when light emission is actually reflected by each electrode, the phase shift sum φ changes depending on the combination of the electrode material and the organic material constituting the reflective interface.

  The peak wavelengths of the respective emission colors are, for example, 600 to 680 nm for red, 500 to 560 nm for green, and 430 to 490 nm for blue. Therefore, in the case of an interference resonator of the same order, the emission wavelength becomes shorter in the order of R, G, and B, so the optical distance determined by the laminated film thickness of the element also becomes shorter in the order of R, G, and B.

  The distance between the reflecting surfaces depends on how many m are set. However, if the distance is too long, reinforcement by resonance does not occur. Therefore, the distance between the reflecting surfaces needs to be a coherent distance. Specifically, the distance between the reflecting surfaces is preferably 5 μm or less. More preferably, the distance between both reflecting surfaces is 1 μm or less.

  In carrying out this configuration, it is preferable that m = 1 or more and less than 7 in Formula 1. More preferably, m = 1 or 2. Further, when m = 7 or more, the organic film becomes about 1 micron, and the influence of the high voltage of the driving element occurs.

  An element having a resonator structure has a configuration in which light corresponding to the resonance wavelength of the resonator is strengthened and extracted to the outside. In general, in order to obtain a spectrum having a high peak intensity and a narrow width, it is preferable to match the peak wavelength of the internal emission spectrum with the resonance wavelength (the wavelength that is most intense by resonance).

  Since many emission spectra of delayed fluorescent materials have a wide half-value width, it is assumed that the internal emission peak wavelength of the element and the resonance wavelength shift. In this case, in order to improve chromaticity, the resonance wavelength is set so that the chromaticity is improved with respect to the internal emission peak wavelength. For example, the resonance wavelength may be set longer than the internal emission peak wavelength.

  This makes it possible to realize an element that exhibits high efficiency and excellent chromaticity.

  As described above, the delayed fluorescent material has a smaller band gap than the phosphorescent material when compared at the same emission wavelength. Therefore, the band gap of the host material or other auxiliary dopant material constituting the light emitting layer 208 can be smaller than that in the case of using a phosphorescent material having the same emission wavelength. Therefore, holes and electrons are smoothly injected into the light emitting layer using the delayed fluorescent material. Therefore, the use of the delayed fluorescent material for the light emitting layer contributes to lowering of the drive voltage. An organic EL element composed of a light emitting layer using a delayed fluorescent material has a small voltage rise even when the thickness of the light emitting layer is increased.

  The thickness of the light emitting layer may be increased as one of means for satisfying the condition of Formula 1 that is the resonance condition. In order to reduce the voltage or to increase the thickness of the light emitting layer, it is preferable to include a large amount of delayed fluorescent material as a light emitting dopant. The doping concentration of the light emitting dopant in the light emitting layer is 5 to 50% by weight, more preferably 10 to 30% by weight.

  Next, the display device of the present invention will be described with reference to FIG.

  The element configuration of this display device is a reflective layer 301, a transparent conductive layer 302, an organic functional layer 303, a semitransparent electrode 304 as a cathode, hole transport layers 305 and 306, a blue light emitting layer 307, a green light emitting layer 308, and a red light emitting layer. 309, electron transport layers 310 and 311. In the present embodiment, the delayed fluorescent material is a light emitting dopant of the green light emitting layer. The light emitting layer using the delayed fluorescent material is not particularly limited to green. The light emitting dopant of the light emitting layer of other light emitting color may use a delayed fluorescent material, but a phosphorescent light emitting material is used for the light emitting dopant of the red light emitting layer, and a fluorescent material or a phosphorescent light emitting material is used for the light emitting dopant of the blue light emitting material. It is preferable to use it. The doping concentration in this case is as described above.

  In each color element, the thickness of the transparent conductive layer 302, the thickness of the hole transport layers 305 and 306, the thickness of the electron transport layers 310 and 311, and the like are adjusted so as to satisfy the RGB resonance conditions. In this embodiment, the organic EL elements of all colors have a resonator structure. However, in the present invention, at least the green organic EL element, preferably the green organic EL element and the blue organic EL element have a resonator structure. That's fine.

  In general, in a display panel in which RGB organic EL elements are mounted, changing the optical film thickness by the transparent conductive layer 302, the hole transport layers 305 and 306, the electron transport layers 310 and 311 and the like in each of RGB colors is applied to each color pixel. Accordingly, the mask deposition is performed accordingly, so that the manufacturing process of the display device is complicated.

  However, in the present invention, it is possible to increase the film thickness so as to satisfy the resonator condition by increasing the film thickness of the light emitting layer of the element including the delayed fluorescent material as compared with other organic layers. By offsetting the optical thickness corresponding to the thickness of the hole transport layer or the electron transport layer by increasing the thickness of the light emitting layer 308 containing the delayed fluorescent material, at least in the B pixel and the G pixel The hole transport layer 305 can have a common thickness. In the present embodiment, the thickness of the hole transport layer 305 is shared with that of the B pixel in the configuration in which the light emitting layer of the G pixel is the thickest. This means that the hole transport layer can be shared in the G pixel and the R pixel as well.

  For blue pixels that want to avoid a decrease in light extraction efficiency, it is necessary to consider not only the resonator conditions but also the optical interference to the reflective electrode. Therefore, in the element structure of blue and green pixels, when the hole transport layer 305 is made common, it is preferable that the optical interference between the light emission position of the blue pixel and the reflective electrode is matched to the optimum condition. As a result, the green pixel can satisfy the resonator condition by adjusting the film thickness of the light emitting layer without degrading the performance of the blue pixel due to the common layer of the hole transport layer.

  In the organic EL display device according to the present invention, a plurality of red organic EL elements, green organic EL elements, and blue organic EL elements may be provided in the plane of the substrate, and each may constitute a pixel.

  The organic EL elements of each color may be connected by signal wiring for each row and information wiring for each column.

  Each color organic EL element may be connected to a TFT in order to control luminance.

  In the organic EL display device according to the present invention, the red organic EL element, the green organic EL element, and the blue organic EL element may be of a so-called bottom emission type in which light is extracted to the outside through the base, or the light is externally passed through the base. It may be a so-called top emission type that is taken out.

  The organic EL display device according to the present invention may be in any embodiment as long as it is a display device for a television or a PC, or a device having a part for displaying an image. For example, a portable display device on which the display device of the present invention is mounted may be used. Alternatively, the display device of the present invention can be used for an electronic imaging device such as a digital camera or a display unit of a mobile phone.

<Green organic EL element example 1 (reference example) >
In this example, a green organic EL element having the configuration shown in FIG. 2 was produced with the following configuration.

  A silver alloy (AgCuNd) as a reflective electrode is formed to a thickness of 100 nm by sputtering on a glass substrate as a support and patterned, and IZO as a transparent electrode is formed to a thickness of 10 nm by sputtering. Then, patterning was performed to form an anode.

  Next, an organic functional layer was provided by the following procedure.

As a hole transport layer, PF01 was formed to a thickness of 15 nm by vacuum deposition. The degree of vacuum during vapor deposition was 5 × 10 ⁻⁵ Pa.

Next, CBP was used as the host material as the light emitting layer, and the exemplified compound 1 was used as the light emitting dopant material, and the film was formed to a thickness of 42 nm by co-evaporation (weight ratio 9: 1) by vacuum deposition. The degree of vacuum during vapor deposition was 5 × 10 ⁻⁵ Pa.

As the electron transport layer, Bphen was deposited to a thickness of 10 nm by vacuum deposition. The degree of vacuum during vapor deposition was 5 × 10 ⁻⁵ Pa.

Furthermore, as an electron transport layer, Bphen and Cs ₂ CO ₃ were co-deposited (weight ratio 9: 1) to form a film with a thickness of 14 nm by vacuum deposition. The degree of vacuum during vapor deposition was 5 × 10 ⁻⁵ Pa.

Silver (Ag) was deposited as a cathode to a film thickness of 15 nm by vacuum deposition. The degree of vacuum during vapor deposition was 8 × 10 ⁻⁵ Pa.

  The substrate on which the film was formed up to the cathode was moved to a sputtering apparatus, and silicon nitride oxide was formed into a film thickness of 1500 nm as a protective layer to obtain an organic EL element.

The organic EL element was evaluated by the following method. A DC constant current power supply (manufactured by ADC Corporation, trade name: R6243) was used as the drive power supply. The luminance was a luminance meter (trade name: BM-7FAST, manufactured by Topcon Corporation). For the measurement of CIE chromaticity, an instantaneous multi-photometry system (manufactured by Otsuka Electronics Co., Ltd., MCPD-7000) was used. As an evaluation of the organic EL device produced in this example, the evaluation was performed from the values of CIE chromaticity, driving voltage, and luminous efficiency at 100 cd / m ² luminance.

When the organic EL device produced in this example was made to emit light with a luminance of 100 cd / m ² , it emitted green light, and the chromaticity (x, y) in the CIE color system was (0.22, 0.70). . The drive voltage at that time was 4 V, and the light emission efficiency was 22 cd / A. In this example, an organic EL element having a low voltage and excellent chromaticity as compared with the comparative element 1 could be obtained.

<Green Organic EL Element Example 1-1 (Comparative Element 1)>
An element similar to the green organic EL element example 1 was prepared. However, when forming the light emitting layer, a phosphorescent material Ir (ppy) 3 shown below was used as a light emitting dopant material, and an IZO electrode of a transparent conductive film was formed on the cathode by sputtering.

When the organic EL device produced in this example was made to emit light with a luminance of 100 cd / m ² , it emitted green light, and the chromaticity (x, y) in the CIE color system was (0.33, 0.67). . The drive voltage at that time was 8 V, and the light emission efficiency was 16 cd / A.

<Green organic EL element example 2>
A silver alloy (AgCuNd) as a reflective electrode is formed to a thickness of 100 nm by sputtering on a glass substrate as a support and patterned, and ITO as a transparent electrode is formed to a thickness of 77 nm by sputtering. Then, patterning was performed to form an anode.
Next, an organic functional layer was provided by the following procedure.

As a hole transport layer, PF01 was formed to a thickness of 35 nm by vacuum deposition. The degree of vacuum during vapor deposition was 5 × 10 ⁻⁵ Pa.

Next, CBP was used as the host material for the light emitting layer, Example Compound 1 was used as the light emitting dopant material, and a film having a thickness of 105 nm was formed by co-evaporation (weight ratio 4: 1) by vacuum evaporation. The degree of vacuum during vapor deposition was 5 × 10 ⁻⁵ Pa.

As the electron transport layer, the following compounds were formed to a thickness of 20 nm by vacuum deposition. The degree of vacuum during vapor deposition was 5 × 10 ⁻⁵ Pa.

Further, as an electron transporting layer, a compound shown in Chemical Formula 7 and Cs ₂ CO ₃ were co-deposited (weight ratio 9: 1) to form a film with a thickness of 60 nm by vacuum deposition. The degree of vacuum during vapor deposition was 5 × 10 ⁻⁵ Pa.

Silver (Ag) was deposited as a cathode to a film thickness of 15 nm by vacuum deposition. The degree of vacuum during vapor deposition was 1 × 10 ⁻⁴ Pa.

  The substrate on which the film was formed up to the cathode was moved to a sputtering apparatus, and silicon nitride oxide was formed into a film thickness of 1500 nm as a protective layer to obtain an organic EL element.

When the organic EL device produced in this example was made to emit light with a luminance of 100 cd / m ² , it emitted green light, and the chromaticity (x, y) in the CIE color system was (0.22, 0.70). . The total film thickness of the transparent anode electrode and the total organic layer of this element is 297 nm. From Equation 1, the resonance condition is 297 nm in total film thickness at a center wavelength of 535 nm, a refractive index of 1.8, m = 2, and Φ = 0 radians, and this element satisfies the resonance condition. The drive voltage at that time was 4.5 V, and the light emission efficiency was 20 cd / A. Met. In this example, an organic EL element having a lower voltage than that of the comparative element 2 could be obtained.

<Green Organic EL Element Example 2-1 (Comparative Element 2)>
An element similar to the green organic EL element example 2 was prepared. However, a phosphorescent material Ir (ppy) 3 was used as a light emitting dopant material, and a transparent IZO electrode was formed by a sputtering method instead of a silver (Ag) electrode and used as a cathode.

When the organic EL device produced in this example was made to emit light at a luminance of 100 cd / m ² , it emitted green light, and the chromaticity (x, y) in the CIE color system was (0.33, 0.63). . The driving voltage at that time was 10 V, and the light emission efficiency was 10 cd / A.

<Example 1>
An organic EL display device composed of three colors of red (R), green (G), and blue (B) was produced by the method described below. The panel size of the panel portion where the organic EL elements are arranged as pixels is 3 inches diagonally, the number of pixels is 240 vertical and 320 horizontal QVGA, and the aperture ratio of the pixels for each color, that is, each color organic EL element relative to the area of the panel portion The total area of each was 30%.

  First, a TFT drive circuit made of low-temperature polysilicon was formed on a glass substrate as a support, and a planarizing film made of acrylic resin was formed thereon. On this, a silver alloy (AgCuNd) is formed as a reflective electrode to a thickness of 100 nm by sputtering and patterned, and ITO as a transparent electrode is patterned to a thickness of 77 nm by sputtering, An anode was formed. Further, an element separation film was formed from an acrylic resin to prepare an anode side transparent electrode substrate. This was ultrasonically cleaned with isopropyl alcohol, then boiled and dried. Then, after UV / ozone cleaning, an organic compound and a cathode material were formed by vacuum deposition.

  Next, the film thickness of each layer was set as follows as an example satisfying the resonator condition of each RGB pixel. Here, in Equation 1, m = 2 and Φ = 0 radians.

  Next, an organic functional layer was provided according to the following procedure according to Table 1.

As a common layer, PF01 was formed as a hole transport layer by vacuum deposition to a thickness of 35 nm for the B and G pixel portions and to a thickness of 170 nm for the red pixels. The degree of vacuum during vapor deposition was 5 × 10 ⁻⁵ Pa. At this time, in order to simplify the process, a hole transport layer was simultaneously formed on the B and G pixel portions. A portion where the B and G pixel portions are aligned with each other straddles between the pixels, and more specifically, a hole transport layer is formed also on the element isolation film.

  In this embodiment, the hole transport layer in the R pixel portion is thicker than the other pixel portions. For example, the material constituting the hole transport layer is formed with a thickness of 35 nm over the entire panel, that is, between the pixels. After that, a material for forming the hole transport layer is provided in only the R pixel portion with a thickness of 135 nm, and as a result, the R pixel portion is provided with a 170 nm hole transport layer. Also good.

CBP was used as the host light-emitting material for the blue light-emitting layer, and the blue fluorescent material shown below was used as the light-emitting dopant material, and a film having a thickness of 45 nm was formed by co-evaporation (weight ratio 9: 1). The degree of vacuum during vapor deposition was 5 × 10 ⁻⁵ Pa.

CBP was used as a host material for the green light-emitting layer, and Exemplified Compound 1 was deposited as a light-emitting dopant material to a film thickness of 105 nm by co-evaporation (weight ratio 4: 1). The degree of vacuum during vapor deposition was 5 × 10 ⁻⁵ Pa.

CBP was used as the host material for the red light-emitting layer, and the following red phosphorescent material was used as the light-emitting dopant material, and a film having a thickness of 30 nm was formed by co-evaporation (weight ratio 9: 1). The degree of vacuum during vapor deposition was 5 × 10 ⁻⁵ Pa.

  During film formation, a mask corresponding to the light emission pattern was used to separate vapor deposition on the same substrate, thereby obtaining an organic EL element in which RGB pixels were arranged in a matrix.

A compound shown in Chemical Formula 7 as a common electron transport layer is formed on these light emitting layers by vacuum deposition on the entire panel region in which the pixel portion is arranged to a thickness of 20 nm, and further the compound shown in Chemical Formula 7 and Cs ₂ CO ₃ was deposited to a film thickness of 60 nm by co-evaporation (weight ratio 9: 1). The degree of vacuum during vapor deposition was 5 × 10 ⁻⁵ Pa.

  Silver (Ag) was deposited to a thickness of 15 nm as a cathode.

  Furthermore, as a protective film, silicon nitride oxide was formed to a thickness of 700 nm to obtain an organic EL display device.

In this organic EL display device, power consumption at white 200 cd / m ² was 400 mW. The chromaticity (x, y) of the RGB light emitting pixels in the CIE color system is B (0.15, 0.08), G (0.22, 0.67), R (0.67, 0.31). The NTSC ratio was 93%, and a display device having an excellent color reproduction range was obtained.

  In this embodiment, mask vapor deposition is required for the hole transport layer and the light emitting layer, and the other layers are common layers. Therefore, the mask deposition required for forming the organic functional layer was five times. In this example, an organic EL display device having a wider color reproduction range and lower power consumption than that of Comparative Example 1 and a reduced number of mask vapor deposition times as compared with Comparative Example 2 could be obtained.

<Comparative example 1>
An organic EL display device was produced in the same manner as in the above example of producing an organic EL display device. However, Ir (ppy) 3 was used as a light-emitting dopant material for the green light-emitting layer, and a transparent IZO electrode was formed by a sputtering method instead of the silver (Ag) electrode and used as a cathode.

In this organic EL display device, the power consumption at white 200 cd / m ² was 600 mW. The chromaticity (x, y) of the RGB light emitting pixels in the CIE color system is B (0.15, 0.11), G (0.27, 0.65), R (0.67, 0.31). The NTSC ratio was 80.7%.

  In this embodiment, mask vapor deposition is required for the hole transport layer and the light emitting layer, and the other layers are common layers. Therefore, the mask deposition required for forming the organic functional layer was five times.

<Comparative example 2>
A display device in which the organic functional layer in the above-described organic EL display device preparation example was changed as follows was manufactured.

As a hole transporting layer, PF01 was formed by vacuum deposition using a mask with a thickness of 35 nm on the B pixel, 95 nm on the G pixel, and 170 nm on the R pixel. The degree of vacuum during vapor deposition was 5 × 10 ⁻⁵ Pa.

CBP was used as the host light-emitting material for the blue light-emitting layer, and the same blue fluorescent material as in Example 1 was used as the light-emitting dopant material, and a film having a thickness of 35 nm was formed by co-evaporation (weight ratio 9: 1). The degree of vacuum during vapor deposition was 5 × 10 ⁻⁵ Pa. CBP was used as the host material for the green light-emitting layer, and Exemplified Compound 1 was deposited as a light-emitting dopant material to a film thickness of 45 nm by co-evaporation (weight ratio 9: 1). The degree of vacuum during vapor deposition was 5 × 10 ⁻⁵ Pa. CBP was used as the host material for the red light-emitting layer, and the same red phosphorescent material as in Example 1 was used as the light-emitting dopant material, and a film having a thickness of 30 nm was formed by co-evaporation (weight ratio 9: 1). The degree of vacuum during vapor deposition was 5 × 10 ⁻⁵ Pa.

In this organic EL display device, power consumption at white 200 cd / m ² was 400 mW. The chromaticity (x, y) of the RGB light emitting pixels in the CIE color system is B (0.15, 0.08), G (0.22, 0.67), R (0.67, 0.31). The NTSC ratio was 93%, and a display device having an excellent color reproduction range was obtained.

  In this comparative example, mask vapor deposition is required for the hole transport layer and the light emitting layer, and the other layers are common layers. However, as compared with Example 1, one more mask deposition of the hole transport layer was required. Therefore, the mask deposition required for forming the organic functional layer was six times.

101: lowest excited singlet state (S ₁ ), 102: ground state (S ₀ ), 103: lowest excited triplet state, 104: energy in S ₁ state (Eg ^S1 ), 105: energy in T ₁ state (Eg ^T1 ), 106: Intersystem crossing, 107: Delayed fluorescence, 108: Phosphorescence

Claims (5)

Each of the organic EL elements has a red organic EL element, a green organic EL element, and a blue organic EL element as a pixel, and each of the organic EL elements includes a pair of electrodes, a hole transport layer, and a light emitting layer,
The light emitting layer of the green organic EL element has a thermally excited delayed fluorescent material, the green organic EL element and the blue organic EL element have a resonator structure between the pair of electrodes, and the green organic The order of interference of the resonator structure of the EL element and the blue organic EL element is secondary, and the hole transport layers of the green organic EL element and the blue organic EL element are provided with the same film thickness in common. An organic EL display device. The hole transport layer of the red organic EL element is thicker than the hole transport layer of the green organic EL element and the blue organic EL element, and the red organic EL element has a resonator structure between the pair of electrodes. 2. The organic EL display device according to claim 1, wherein the order of interference of the resonator structure of the red organic EL element is second order.   3. The organic EL display device according to claim 1, wherein the organic EL element having the resonator structure has a peak wavelength of an internal emission spectrum and a wavelength that is strengthened most by resonance coincide with each other. The organic EL display device according to any one of claims 1 to 3 , wherein the thickest layer among the layers provided between the pair of electrodes of the green organic EL element is the light emitting layer. Each of the organic EL elements has a pair of electrodes, a hole transport layer, and a light emitting layer in the order of a reflective electrode, a hole transport layer, and a light emitting layer of the pair of electrodes. 5. The organic EL display device according to any one of 1 to 4 .

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