JP4631490B2 - Light emitting device - Google Patents

Description

  The present invention relates to a light emitting device in which a white light emitting element and a color filter of each color are combined.

  An organic electroluminescence (EL / Electroluminescence) device, etc. as an exposure head in a display device used in an electronic device such as a mobile phone, a personal computer or a PDA (Personal Digital Assistants), or an image forming device such as a digital copying machine or a printer The light emitting device has attracted attention.

In constructing this type of light emitting device, a light emitting device that combines a light emitting element that emits light corresponding to each color to each of a plurality of pixels and a white light emitting element and a color filter of each color in recent years have been proposed. (For example, see Patent Documents 1, 2, and 3).
JP-A-8-162269 Japanese Patent Laid-Open No. 2004-220871 JP 2004-227854 A

  However, in any of the above-mentioned patent documents, an attempt has been made to improve color purity with respect to the emission spectrum of light emitted from the white light-emitting element and the spectrum after passing through the color filter. Since no consideration is given to the utilization efficiency of light emitted from the light emitting element, there is a problem that the amount of light cut by the color filter is large and the utilization efficiency of light is low.

  In view of the above problems, an object of the present invention is to provide a light emitting device capable of improving the utilization efficiency of light emitted from a white light emitting element.

In order to solve the above problems, in the present invention, a red pixel including a white light emitting element and a red color filter, a green pixel including a white light emitting element and a green color filter, and a white light emitting element and a blue color are provided. In the light emitting device including a blue pixel including the color filter, the white light emitting element emits light having only two peaks in the emission spectrum, and the emitted light has a wavelength of 500 nm ± 5 nm in the emission spectrum. It has a local minimum value, has a first emission peak in the wavelength range of 400 nm to 500 nm, and a second emission peak in the wavelength range of 500 nm to 600 nm, and the wavelength of the first emission peak is the blue color filter. The wavelength of the second light emission peak is approximately the same as the peak wavelength of the transmitted light, and the wavelength of the light transmitted through the green color filter , Characterized in that present between the peak wavelength of light transmitted through the red color filter.

  In the present invention, the white light emitting element has a first minimum value in the wavelength range of 500 nm ± 5 nm in the emission spectrum, and the minimum value in such a wavelength range adds the transmission characteristics of the XYZ filter used for chromaticity measurement. In view of the spectrum and the transmission characteristics of the color filter, the light does not contribute to the color specification of the three primary colors. Therefore, the use efficiency of the light emitted from the white light emitting element can be increased by suppressing unnecessary light emission. Further, since the emission spectrum has the first minimum value in the wavelength range of 500 nm ± 5 nm, the chromaticity y value is small and the chromaticity can be improved because the tailing on the long wavelength side of blue light is small. .

In another embodiment of the present invention, a red pixel including a white light emitting element and a red color filter, a green pixel including a white light emitting element and a green color filter, and a white light emitting element and a blue color filter are provided. The white light emitting element emits light having only three peaks in the emission spectrum, and the emitted light has a first minimum value of 580 ± within a wavelength range of 500 ± 5 nm in the emission spectrum. Each has a second minimum value in the wavelength range of 5 nm, the first emission peak in the wavelength range of 400 nm to 500 nm, the second emission peak in the wavelength range of 500 nm to 600 nm, and the third emission in the wavelength range of 600 nm or more. Each has a peak, and the wavelength of the first emission peak is substantially the same as the peak wavelength of the light that has passed through the blue color filter, and the second emission peak. The difference between the peak wavelength and the peak wavelength of the light transmitted through the green color filter is within ± 5 nm, and the peak values of the first emission peak, the second emission peak, and the third emission peak are The spectrum of the light emitted from the white light emitting element is multiplied by the transmittance of each color filter to set the white balance in the light of each color, and the peak value of the first light emission peak and the second light emission peak are set. The peak value of the first emission peak is set to the maximum among the peak value of the second peak and the peak value of the third emission peak .

  In the present invention, the white light emitting element has a second minimum value in the wavelength range of 580 nm ± 5 nm in the emission spectrum, and the minimum value in such a wavelength range is represented by the three primary colors in terms of the transmission characteristics of the color filter. It does not contribute to the light. Therefore, the use efficiency of the light emitted from the white light emitting element can be increased by suppressing unnecessary light emission.

  A light-emitting device to which the present invention is applied is used as a display device in an electronic apparatus such as a mobile phone, a personal computer, or a PDA. A light emitting device to which the present invention is applied is used as an exposure head in an image forming apparatus such as a digital copying machine or a printer.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings used for the following description, the scales are different for each layer and each member in order to make each layer and each member large enough to be recognized on the drawing.

[Embodiment 1]
(Pixel configuration)
FIGS. 1A and 1B are explanatory diagrams schematically showing the configuration of each pixel of an organic EL device (light emitting device) to which the present invention is applied.

  The organic EL device 1 shown in FIG. 1A is a bottom emission type that emits display light toward the substrate 11 side, and any one of red (R), green (G), and blue (B) pixels 100 ( A white organic EL element 10 is also formed in R), (G), and (B), and when viewed from the white organic EL element 10, for example, between the substrate 11 and the white organic EL element 10. Are formed with color filters 19 (R), (G), and (B) corresponding to the respective colors of red (R), green (G), and blue (B). The white organic EL element 10 includes a light-transmissive first electrode 12 (anode) made of ITO or the like, a hole injection layer 13, a light-emitting layer 14, a light-reflective second electrode 15 (cathode). Are stacked in this order.

  In such an organic EL display device 1, in the organic EL element 10, when a current flows to the second electrode 15 through the hole injection layer 13 and the light emitting layer 14, the light emitting layer 14 emits light according to the amount of current at that time. To do. The light emitted from the light emitting layer 14 passes through the first electrode 12 and the substrate 11 and is emitted to the observer side, while the light emitted from the light emitting layer 14 toward the second electrode 15. Is reflected by the second electrode 15, passes through the first electrode 12, the color filter, and the substrate 11 and is emitted to the observer side. At this time, the light emitted from the light emitting layer 14 is white light, but is colored by the color filters 19 (R), (G), and (B), so that each pixel 100 (R), (G), ( A predetermined color light can be emitted from B). The color filters 19 (R), (G), and (B) may be formed on the side opposite to the white organic EL element 10 when viewed from the substrate 11.

  The organic EL device 1 shown in FIG. 1B is a top emission type that emits display light toward the side opposite to the substrate 11 side, and is similar to the organic EL device 1 shown in FIG. The white organic EL element 10 is formed in any of the pixels 100 (R), (G), and (B) of R, green (G), and blue (B). However, in this embodiment, red (R), green (G), and blue (B) are formed on the light emission side as viewed from the white organic EL element 10, for example, on the side opposite to the substrate 11 as viewed from the white organic EL element 10. Color filters 19 (R), (G), and (B) corresponding to the respective colors are formed. The white organic EL element 10 includes a light reflecting layer 16 such as silver or aluminum, a transparent first electrode 12 (anode) made of ITO, a hole injection layer 13, a light emitting layer 14, a thin layer on the upper side of the substrate 11. A light transmissive second electrode 17 (cathode) on which an electrode layer such as aluminum is formed is laminated in this order. Here, the substrate 11 may be either a light transmissive substrate or a light transmissive substrate. In the organic EL display device 1 configured as described above, when a current flows from the first electrode 12 to the second electrode 15 through the hole injection layer 13 and the light emitting layer 14, the light emitting layer 14 according to the current amount at that time. Emits light. The light emitted from the light emitting layer 14 is transmitted through the second electrode 17 and emitted to the observer side, while the light emitted from the light emitting layer 14 toward the substrate 20 is emitted from the first electrode 12. The light is reflected by the light reflecting layer 16 formed in the lower layer, passes through the second electrode 17 and is emitted to the observer side. At this time, the light emitted from the light emitting layer 14 is white light, but is colored by the color filters 19 (R), (G), and (B), so that each pixel 100 (R), (G), ( A predetermined color light can be emitted from B).

  In the organic EL device 1 configured as described above, the hole injection layer 13 and the light emitting layer 14 can be formed by a vapor deposition method, a spin coating method, a printing method, an ink jet method (liquid ejection method), or the like. Since the white light emitting layer can be formed in common for each of the RGB pixels, it is not always necessary to pattern each pixel. Therefore, even if a hole injection layer, a light emitting layer, and an electron injection layer are formed on the entire surface of the light emitting region, No problem.

  In this case, the hole injection layer 13 may be formed by depositing a low molecular weight hole injection material such as m-MTDATA, TPD, or copper phthalocyanine by a vapor deposition method, or 3, 4-polyethylene which is a polyolefin derivative. It can be formed by using dioxythiophene / polystyrene sulfonic acid (PEDOT / PSS) as a hole injecting material, discharging a dispersion containing water / alcohol as a main solvent to a predetermined region, and then drying. In addition, the material for forming the hole injection layer 13 is not limited to the above-mentioned materials, and materials well known in low molecular weight systems, triphenylamine polymers, and the like can also be used.

  As for the material for forming the light emitting layer 14, in the case of a low molecular system, a well-known material such as DPVBi (blue light emitting material), Alq3 (green light emitting material) manufactured by Idemitsu Kosan Co., Ltd., or yellow light is emitted. Can be used by doping with quinacridone, coumarin 6 or the like, and in the case of emitting red light, Nile red may be doped at the time of vapor deposition. When a printing method or an inkjet method is used, a polymer material, for example, a polymer material having a molecular weight of 1000 or more can be used. Specifically, a polyfluorene derivative, a polyphenylene derivative, polyvinylcarbazole, a polythiophene derivative, or a polymer material thereof, a perylene dye, a coumarin dye, a rhodamine dye, such as rubrene, perylene, 9,10-diphenylanthracene, What doped tetraphenyl butadiene, Nile red, coumarin 6, quinacridone, etc. is used. As such a polymer material, a π-conjugated polymer material in which π electrons of a double bond are non-polarized on a polymer chain is also a conductive polymer, and thus has excellent light emitting performance. Preferably used. In particular, a compound having a fluorene skeleton in the molecule, that is, a polyfluorene compound is more preferably used. In addition to such materials, for example, a composition for an organic EL device disclosed in JP-A-11-40358, that is, a precursor of a conjugated polymer organic compound, and at least one kind for changing light emission characteristics A composition for an organic EL device comprising the above fluorescent dye can also be used as a light emitting layer forming material. When a low molecular material is used, it is better to insert an electron injection layer, and Alq3 or the like is preferably used.

  In configuring the white organic EL element 10, a hole transport layer, an electron injection layer, an electron transport layer, or the like may be formed.

(Configuration of white organic EL element 10)
Before describing the configuration of the white organic EL element 10 of this embodiment, the characteristics required for the white organic EL element 10 will be described with reference to FIGS. 2 (a), (b), (c), and (d).

  2A, 2B, 2C, and 2D are explanatory diagrams showing transmission characteristics of an X filter used for chromaticity measurement, and explanatory diagrams showing transmission characteristics of a Y filter used for chromaticity measurement. FIG. 5 is an explanatory diagram showing transmission characteristics of a Z filter used for chromaticity measurement, and a spectrum diagram when the spectra of these color filters are added. FIG. 3 shows a spectrum diagram of light emitted from the white organic EL element used in the light emitting device according to Embodiment 1 of the present invention, and transmitted through the color filters 19 (R), (G), and (B). FIG.

  Since each of the XYZ filters used for chromaticity measurement has the sensitivity characteristics shown in FIGS. 2A, 2B, and 2C, the light having the sensitivity characteristics shown in FIG. If the organic EL element 10 emits, sufficient image quality can be obtained for human eyes. Here, in the sensitivity characteristic shown in FIG. 2D, the first minimum value B1 is in the wavelength region of 500 nm ± 5 nm. In addition, the first emission peak A1 exists in the wavelength range of 400 nm to 500 nm, and the second emission peak A2 exists in the wavelength range of 500 nm to 600 nm.

  Therefore, in this embodiment, the white organic EL element 10 is configured to have an emission spectrum indicated by a solid line L in FIG. That is, similar to the spectrum shown in FIG. 2D, the white light emitting element 10 emits light having the first minimum value B1 within the wavelength range of 500 nm ± 5 nm in the emission spectrum. Further, the white light emitting element 10 emits light having the first emission peak A1 in the wavelength range of 400 nm to 500 nm and the second emission peak A2 in the wavelength range of 500 nm to 600 nm in the emission spectrum.

  In FIG. 3, the spectrum of the light emitted from the white light emitting element 10 after passing through the red (R) color filter 19 (R) is indicated by a dotted line LR, and the light emitted from the white light emitting element 10 is The spectrum after passing through the green (G) color filter 19 (G) is indicated by a one-dot chain line LG, and the light emitted from the white light emitting element 10 is transmitted through the blue (B) color filter 19 (B). The spectrum is indicated by a two-dot chain LB.

(Effect of this embodiment)
As described above, in this embodiment, the white organic EL element 10 emits light having an emission spectrum similar to the spectrum obtained by adding the spectra of the XYZ filters used for chromaticity measurement. When considered, it can be regarded as emitting white light. Therefore, as shown in Table 1, the results of comparison with the case of using a flat light source having no wavelength dispersion are higher in the extraction efficiency when the flat light source is used, but the organic EL device of this embodiment is also sufficient. High extraction efficiency can be obtained. In Table 1, the spectrum of the light emitted from the white organic EL element 10 is multiplied by the transmission characteristics of the color filters 19 (R), (G), and (B), and light of each color is extracted. A chromaticity, a luminance ratio, and an NTSC ratio (a value indicating a color reproduction range defined by the National Television Standard Committee) by an area ratio are shown.

  Further, in the organic EL device of the present embodiment, since the light having the first minimum value B1 is emitted in the wavelength range of 500 nm ± 5 nm, the chromaticity y value is small because the tailing on the long wavelength side of the blue light is small. The chromaticity can be improved.

  Further, in the present embodiment, since the light having the first minimum value B1 is emitted in the wavelength range of 500 nm ± 5 nm which is not necessary in consideration of human vision, the light emission is not wasted and is emitted from the white light emitting element. The utilization efficiency of the emitted light is high.

  In addition, about the peak value of the short wavelength side (for example, 450 nm) and long wavelength side (for example, 580 nm), the spectrum radiate | emitted from the white organic EL element 10, and each color filter 19 (R), (G), What is necessary is just to adjust so that white balance may be taken in the chromaticity and brightness | luminance calculated from the value (extracted spectrum in each color) which multiplied the transmittance | permeability of (B). Alternatively, the white balance may be secured by optimizing the driving conditions for the white organic EL element 10 in each of the pixels 100 (R), (G), and (B). In order to realize the illustrated EL spectrum, a blue light emitting material may be added with an appropriate amount of red light emitting dopant, or a blue light emitting layer and a yellow light emitting layer may be laminated. The low molecular vapor deposition method may be a method of depositing a dopant from another vapor deposition source or a method of laminating a blue light emitting layer and a yellow light emitting layer at the time of blue material vapor deposition. A red light emitting material, or a blue light emitting material + red dopant ink can be prepared and formed by a printing method, a spin coating method, or an ink jet method.

[Embodiment 2]
FIG. 4 is a spectrum diagram of light emitted from the white organic EL element used in the light emitting device according to Embodiment 2 of the present invention, and transmitted through the color filters 19 (R), (G), and (B). FIG. Note that the basic structure of the light-emitting device of this embodiment is the same as that of Embodiment 1, and thus parts having common functions are denoted by the same reference numerals and description thereof is omitted.

  As described with reference to FIGS. 1A and 1B, the organic EL device of this embodiment also has a red pixel 100 (R) including the white light emitting element 10 and the red color filter 19 (R). ), A green pixel 100 (G) including the white light emitting element 10 and the green color filter 19 (G), and a blue pixel 100 (including the white light emitting element 10 and the blue color filter 19 (B)). B).

  The white organic EL element 10 of the present embodiment is configured to have an emission spectrum indicated by a solid line L in FIG. 4. Like the spectrum shown in FIG. 2D, the white light emitting element 10 has an emission spectrum of 500 nm. Light having a first minimum value B1 is emitted within a wavelength range of ± 5 nm. Further, the white light emitting element 10 emits light having the first emission peak A1 in the wavelength range of 400 nm to 500 nm and the second emission peak A2 in the wavelength range of 500 nm to 600 nm in the emission spectrum.

  Furthermore, in the emission spectrum of the light emitted from the white light emitting element 10, the second minimum value B2 exists in the wavelength range of 580 nm ± 5 nm, and the third emission peak A3 exists in the wavelength range of 600 nm or more.

  Here, in FIG. 4, the spectrum after the light emitted from the white light emitting element 10 passes through the red (R) color filter 19 (R) is indicated by a dotted line LR, and the light emitted from the white light emitting element 10 is shown. Shows the spectrum after passing through the green (G) color filter 19 (G), and the light emitted from the white light emitting element 10 passes through the blue (B) color filter 19 (B). Is shown by a two-dot chain LB, and the difference between the wavelength of the second emission peak A2 and the transmission maximum wavelength of the green color filter 19 (G) is within ± 5 nm.

  In the organic EL device 1 configured in this manner, as shown in Table 2, the comparison result with the case of using a flat light source having no wavelength dispersion is higher in terms of extraction efficiency when the flat light source is used. Even in the organic EL device 1 of the present embodiment, sufficiently high extraction efficiency can be obtained.

  Further, in the organic EL device of the present embodiment, since the light having the first minimum value B1 is emitted in the wavelength range of 500 nm ± 5 nm, the chromaticity y value is small because the tailing on the long wavelength side of the blue light is small. The chromaticity can be improved.

  Furthermore, in the present embodiment, since the light having the first minimum value B1 is emitted in the wavelength range of 500 nm ± 5 nm which is not necessary in consideration of human vision, the light emission is not wasted and the white light emitting element 10 Use efficiency of emitted light is high.

  Furthermore, in the present embodiment, the second minimum value B2 exists in the wavelength range of 580 nm ± 5 nm that is wasted in view of the transmission characteristics of the red color filter 19 (R) and the green color filter 19 (G). Therefore, the utilization efficiency of the light emitted from the white light emitting element 10 is high.

  In order to achieve the illustrated EL spectrum, appropriate amounts of green and red light emitting dopants are added to the blue light emitting material, or in the case of low molecular vapor deposition, blue, green and red light emitting layers are stacked, or A combination of a doping method and a lamination method may be used. In the low molecular vapor deposition method, at the time of blue material vapor deposition, a method of depositing green light emission and red light emission dopants from different vapor deposition sources, or a layer of blue, green, and red light emission materials may be vapor deposited and laminated, In the case of using a polymer material, an ink of a blue light emitting material, a green light emitting material, and a red light emitting material, or a blue light emitting material + green dopant + red dopant, or a combination thereof is created, and a printing method, a spin coating method, Or it can form by the inkjet method.

(Example of application to display devices)
The organic EL device 1 to which the present invention is applied can be used as a passive matrix display device or an active matrix display device. Among these display devices, the active matrix display device is configured to have the electrical configuration shown in FIG.

  FIG. 5 is a block diagram showing an electrical configuration of the organic EL display device. In FIG. 1, in the organic EL device 1, a plurality of scanning lines 63, a plurality of data lines 64 extending in a direction intersecting with the extending direction of the scanning lines 63, and the data lines 64 are arranged in parallel. A plurality of common power supply lines 65 and pixels 100 (light emitting areas) corresponding to the intersections of the data lines 64 and the scanning lines 63 are configured, and the pixels 100 are arranged in a matrix in the image display area. A data line driving circuit 51 including a shift register, a level shifter, a video line, and an analog switch is configured for the data line 64. A scanning line driving circuit 54 including a shift register and a level shifter is configured for the scanning line 63. Each pixel 100 holds a pixel switching thin film transistor 6 to which a scanning signal is supplied to the gate electrode via the scanning line 63 and an image signal supplied from the data line 64 via the thin film transistor 6. The storage capacitor 33, the current control thin film transistor 7 to which the image signal held by the storage capacitor 33 is supplied to the gate electrode 43, and the common supply line 65 when electrically connected to the common power supply line 65 through the thin film transistor 7 The white organic EL element 10 into which a drive current flows from the electric wire 65 is configured. In the organic EL display device 1, each pixel 100 is red (R), green (G), or blue depending on which color filter 19 (R), (G), or (B) is configured for each pixel 100. It corresponds to one of (B).

[Other embodiments]
In the above embodiment, an organic EL element is used as a light emitting element, but the present invention may be applied to a light emitting device using another light emitting element. In any case, the technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

[Example of mounting on electronic devices]
A light-emitting device to which the present invention is applied can be used as a display device in various electronic devices such as a mobile phone, a personal computer, and a PDA. The light emitting device to which the present invention is applied can also be used as an exposure head in an image forming apparatus such as a digital copying machine or a printer.

(A), (b) is explanatory drawing which shows typically the structure of each pixel of the organic electroluminescent apparatus (light-emitting device) to which this invention is applied. (A), (b), (c), (d) is explanatory drawing which shows the transmission characteristic of X filter used for chromaticity measurement, explanatory drawing which shows the transmission characteristic of Y filter used for chromaticity measurement, color It is explanatory drawing which shows the permeation | transmission characteristic of Z filter used for a degree measurement, and a spectrum figure when the spectrum of these color filters is added. It is the spectrum figure of the light radiate | emitted from the white organic EL element used for the light-emitting device concerning Embodiment 1 of this invention, and the spectrum figure after permeate | transmitting each color filter. It is the spectrum figure of the light radiate | emitted from the white organic EL element used for the light-emitting device concerning Embodiment 1 of this invention, and the spectrum figure after permeate | transmitting each color filter. It is a block diagram which shows the electrical structure of an organic electroluminescence display (light-emitting device).

Explanation of symbols

1 ... Organic EL display device (light emitting device) 10 ... White organic EL device (white light emitting device) 11 ... Substrate 12 ... First electrode 13 ... Hole injection layer 14 ... Light emission Layer, 15, 17... Second electrode, 16 .. light reflecting layer, 19 (R), (G), (B) .. color filter

Claims (2)

A red pixel having a white light emitting element and a red color filter, a green pixel having a white light emitting element and a green color filter, and a blue pixel having a white light emitting element and a blue color filter In the light emitting device
The white light emitting element emits light having only two peaks in the emission spectrum ,
The emitted light has a minimum value in the wavelength range of 500 nm ± 5 nm in the emission spectrum, a first emission peak in the wavelength range of 400 nm to 500 nm, and a second emission peak in the wavelength range of 500 nm to 600 nm,
The wavelength of the first emission peak substantially coincides with the peak wavelength of the light transmitted through the blue color filter,
The wavelength of the second emission peak exists between the peak wavelength of the light transmitted through the green color filter and the peak wavelength of the light transmitted through the red color filter.
A light emitting device characterized by that. In a red pixel having a white light emitting element and a red color filter, a green pixel having a white light emitting element and a green color filter, and a light emitting device having a white light emitting element and a blue color filter,
The white light emitting element emits light having only three peaks in the emission spectrum ,
The emitted light has a first minimum value in the wavelength range of 500 ± 5 nm and a second minimum value in the wavelength range of 580 ± 5 nm in the emission spectrum, respectively, and a first emission peak in the wavelength range of 400 nm to 500 nm, Having a second emission peak in the wavelength range of 500 nm to 600 nm, a third emission peak in the wavelength range of 600 nm or more,
The wavelength of the first emission peak substantially coincides with the peak wavelength of the light transmitted through the blue color filter,
The difference between the wavelength of the second emission peak and the peak wavelength of the light transmitted through the green color filter is within ± 5 nm,
The peak value of each of the first emission peak, the second emission peak, and the third emission peak was extracted by multiplying the spectrum of the emitted light from the white light emitting element by the transmittance of each color filter. The white balance is set for each color light,
Of the peak value of the first emission peak, the peak value of the second emission peak, and the peak value of the third emission peak, the peak value of the first emission peak is set to be maximum. ,
A light emitting device characterized by that.

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