JP2009211868A - Structure for extracting light from light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve efficiency of a light emitting element by arranging a diffraction structure different from a conventional diffraction structure on a light extraction surface side of the light emitting element such as an organic electroluminescent element. <P>SOLUTION: In this structure for extracting light, a slant structural body having a slant structure in which high-refractive-index regions 2 and low-refractive-index regions 3 are repeated at a certain cycle in a one-dimensional direction along a flat plate 1, and the high-refractive-index regions 2 and the low-refractive-index regions 3 are inclined at a certain slant angle with respect to the normal of the flat plate 1 is arranged on a light extraction surface side of a luminescent layer 11 of the light emitting element. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a light extraction structure from a light emitting element, and more particularly to an optical structure for efficiently extracting light from a light emitting element.

  In a light-emitting element, for example, an organic electroluminescence element, light having an emission angle greater than a critical angle is totally reflected and cannot be taken out due to the influence of the refractive index of the light-emitting body. For this reason, if the refractive index of the light emitter is 1.6, only about 20% of the total amount of light emission can be used effectively.

  As a technique for improving the light extraction efficiency, as disclosed in Patent Document 1, a technique is proposed in which a diffraction grating or a zone plate is arranged on the light extraction surface side to improve the light extraction efficiency.

  Furthermore, as shown in Patent Document 2 and Non-Patent Document 1, there has been proposed a technique in which a high refractive index layer and a nanoporous layer or a photonic crystal are arranged on the light extraction surface side to improve the light extraction efficiency. .

Further, as shown in Patent Document 3, a prism lens sheet is arranged on the light extraction surface side to improve the light extraction efficiency.
Japanese Patent Laid-Open No. 11-283951 JP 2006-12826 A JP-A-9-73983 Appl.Phys.Lett, 82,3779-3781 (2003) “SPIE” Vol. 883 (1988), p. 8-11

  The present invention has been made in view of such a situation in the prior art, and its purpose is to arrange a diffractive structure different from the conventional diffractive structure on the light extraction surface side of a light emitting element such as an organic electroluminescent element. This is to increase the efficiency of the light emitting element.

  The light extraction structure from the light emitting device of the present invention that achieves the above object has a high refractive index region and a low refractive index region that repeat at a constant period in a one-dimensional direction along the flat plate. Is characterized in that a slant structure having a slant structure inclined at a constant slant angle with respect to the normal line of the flat plate is disposed on the light extraction surface side of the light emitting layer of the light emitting element.

  In this case, in the slant structure, it is desirable that the slant structure is arranged in an integer number of rotational symmetry around the normal of the plane of the flat plate.

  In the slant structure, a high refractive index region or a portion where the high refractive index region and the low refractive index region are spatially overlapped is a high refractive index region, and a portion where the low refractive index region is spatially overlapped is a low refractive index. It is desirable to be an area.

  In addition, a high refractive index layer larger than the refractive index on the light emitting layer side is disposed between the light emitting layer and the slant structure, or a square pyramid or roof type microscopic array is formed on the emission side of the light emitting layer. It is more desirable that a prism array in which a large number of prisms are arranged is arranged.

  According to the present invention, by using the slant structure as described above, the light extraction efficiency is improved, and a highly efficient light emitting device can be obtained.

  Hereinafter, the principle and examples of the light extraction structure from the light emitting device of the present invention will be described.

  The basic structure of the light extraction structure of the present invention is a high refractive index space region 2 and a low refractive index space region 3 (hereinafter, the space region is simply referred to as a region) in the flat plate 1 as shown in a sectional view in FIG. Is repeated with a period between the wavelength of light used in the one-dimensional direction along the flat plate 1 and about twice the wavelength, and the high refractive index region 2 and the low refractive index region 3 are in relation to the normal of the flat plate 1. A slant structure 10 having a slant structure inclined at a constant slant angle α (α ≠ 0 °, 90 °) is used, and this structure 10 is placed on the light extraction surface side of the light-emitting layer 11 of the light-emitting body on the transparent substrate 12. The amount of light taken out from the light emitting layer 11 through the transparent substrate 12 is increased (higher efficiency). The high refractive index region 2 and the low refractive index region 3 are spatially flat and are arranged in parallel to each other.

  Further, as shown in a cross-sectional view in FIG. 2, the slant structure 10 has a repetitive slant structure of a high refractive index region 2 and a low refractive index region 3 inclined at a slant angle α as shown in FIG. Arranged rotationally symmetrical integer times (2 times in FIG. 2) with respect to the normal (high refractive index region 2 mutually or a portion where the high refractive index region 2 and the low refractive index region 3 spatially overlap each other has a high refractive index. The portion where the region and the low refractive index region 3 spatially overlap each other is a low refractive index region.) However, it is possible to increase the amount of light extracted from the light emitting layer 11 through the transparent substrate 12. By increasing the number of times of rotational symmetry, the uniformity around the normal of extraction efficiency is improved.

  FIG. 3 is a plan view of the flat plate 1 showing the relationship between the number of rotational symmetry and the slant structure as viewed from the + z-axis (FIGS. 1 and 2) direction, FIG. 3 (a) is three times, and FIG. Is 4 times, FIG. 3 (c) is 5 times, FIG. 3 (d) is 6 times, and FIG. 3 (e) is 8 times. In the case of the three-fold rotational symmetry in FIG. 3A, the arrangement structure of the high refractive index region 2 and the low refractive index region 3 is the same as that in FIG. The high refractive index regions 2 are arranged obliquely in a stripe pattern (in the figure, this is indicated by “/////”). In the case of the four-fold rotational symmetry in FIG. 3B, the arrangement structure of the high refractive index region 2 and the low refractive index region 3 is the same as in FIG. The high refractive index regions 2 are arranged side by side in a crossed lattice pattern (in the figure, this is indicated by “XXXX”). In the case of the five-fold rotational symmetry in FIG. 3C, in the cross-sectional view along the five dot-and-dash lines in the figure, the arrangement structure of the high refractive index region 2 and the low refractive index region 3 is the same as in FIG. The high refractive index regions 2 are arranged obliquely in a stripe pattern. In the case of the six-fold rotational symmetry in FIG. 3D, in the cross-sectional view along the three-dot chain line in the figure, the arrangement structure of the high refractive index region 2 and the low refractive index region 3 is the same as in FIG. The high refractive index regions 2 are arranged side by side in a cross grid pattern. In the case of the eight-fold rotational symmetry in FIG. 3 (e), in the cross-sectional view along the four-dot chain lines in the figure, the arrangement structure of the high refractive index region 2 and the low refractive index region 3 is the same as in FIG. The high refractive index regions 2 are arranged side by side in a cross grid pattern. The same applies to other integer times. When the number of rotational symmetry is an odd number, the high refractive index regions 2 are arranged obliquely in stripes in the rotationally symmetric direction as in FIG. When the number of rotational symmetry is an even number, the high refractive index regions 2 are arranged side by side in a crossed lattice pattern in the rotationally symmetric direction as in FIG.

  Further, as shown in FIG. 4, a high refractive index layer 13 larger than the refractive index of the transparent substrate 12 is disposed on the light emitting layer 11 side of the slant structure 10 of FIGS. The amount of light taken out can be increased by reducing the divergence angle of the luminous flux and making the light within the divergence angle incident on the slant structure 10.

  Further, as shown in FIG. 5, a high-refractive-index prism array 14 in which a large number of square pyramid or roof-shaped minute prisms are arranged in an array on the emission side of the light emitting layer 11 is arranged. Is embedded in the transparent substrate 12 having a relatively low refractive index, the divergence angle of the light beam emitted from the light emitting layer 11 is reduced by the prism array 14 and the light within the divergence angle is slanted. By making the light incident on the structure 10, the amount of light taken out can be increased.

  Next, numerical examples of the light extraction structure from the light emitting element of the present invention will be shown. The utilization efficiency of the slant structure 10 can be determined strictly by vector diffraction theory (Non-Patent Document 2). In the following description, parameters such as pitch / wavelength, duty ratio, pitch direction shift amount indicating slant, slant angle, groove depth / wavelength, and the like are as shown in FIG. Here, to add a little explanation, the wavelength λ is a used wavelength, the pitch Λ is a repetitive pitch in the direction along the surface of the flat plate 1 of the high refractive index region 2 (low refractive index region 3), and the duty ratio w / Λ is a ratio per pitch of the high refractive index region 2, and the slant angle α is an angle with respect to the normal of the flat plate 1 of the high refractive index region 2 and the low refractive index region 3 as described above, and indicates a slant. The shift amount s in the pitch direction is the shift amount between the front and back surfaces of the flat plate 1 of the high refractive index region 2 or the low refractive index region 3, and the groove depth d is provided by the high refractive index region 2 and the low refractive index region 3. The thickness of the obtained flat plate 1.

FIG. 3B shows a four-fold rotationally symmetric slant structure 10 in which TE and TM polarized light are equal from the light emitting layer 11, and an incident angle of 0 to 90 ° and an azimuth angle of 0 to 90 ° (azimuth angle). Is actually 0 to 360 °, but calculation is performed at 0 to 90 ° in consideration of symmetry.) When isotropically radiated and incident on the slant structure 10, the high refractive index region For Examples 1 to 8 in which the refractive index of 2 is 1.5 and the refractive index of the low refractive index region 3 is 1 (air), the parameters of the slant structure 10 and the light extraction efficiency are shown below. The wavelength λ was normalized to 1.

Example 1 Example 2 Example 3 Example 4
Pitch / wavelength (both x and y directions) 1.8 1.6 1.8 1.6
Duty ratio (both x and y directions) 0.4 0.5 0.4 0.5
Amount of deviation in the pitch direction indicating slant 2.0 2.0 1.0 2.5
Slant angle 38.7 ° 42.4 ° 24.2 ° 41.6 °
Groove depth / wavelength 4.5 3.5 4.0 4.5
Light extraction efficiency 29.5% 29.5% 29.0% 28.8%

Example 5 Example 6 Example 7 Example 8
Pitch / wavelength (both x and y directions) 1.8 1.8 1.2 1.8
Duty ratio (both x and y directions) 0.6 0.3 0.3 0.4
Amount of deviation in the pitch direction indicating slant 2.0 1.0 2.0 1.5
Slant angle 35.8 ° 35.8 ° 34.4 ° 42.0 °
Groove depth / wavelength 5.0 2.5 3.5 3.0
Light extraction efficiency 28.7% 28.7% 28.6% 28.5%.

  As a comparative example, the light extraction efficiency in the case of only a flat plate having a refractive index of 1.5 and no slant structure is about 23%.

  The incident angle dependency and the azimuth angle dependency of the utilization efficiency in Examples 1 to 8 are shown in FIGS. 7 to 14 also show the incident angle dependency in the case of a flat plate.

  The light extraction structure from the light emitting device of the present invention has been described based on the embodiments. However, the present invention is not limited to these embodiments, and various modifications can be made.

It is sectional drawing which shows the slant structure which is the basic structure in the light extraction structure of this invention. It is sectional drawing in the case of assuming that a slant structure is arrange | positioned by the rotational symmetry of even number of times. It is a top view which shows the relationship between the frequency | count of rotational symmetry, and a slant structure. It is sectional drawing which shows the modification of the light extraction structure of this invention. It is sectional drawing which shows the modification of another light extraction structure of this invention. It is a figure for demonstrating the various parameters of a slant structure. It is a figure which shows the incident angle and azimuth angle dependence of the utilization efficiency of Example 1. FIG. It is a figure which shows the incident angle and azimuth angle dependence of the utilization efficiency of Example 2. FIG. It is a figure which shows the incident angle and azimuth angle dependence of the utilization efficiency of Example 3. It is a figure which shows the incident angle and azimuth angle dependence of the utilization efficiency of Example 4. It is a figure which shows the incident angle and azimuth angle dependence of the utilization efficiency of Example 5. It is a figure which shows the incident angle and azimuth | direction angle dependence of the utilization efficiency of Example 6. FIG. It is a figure which shows the incident angle and azimuth angle dependence of the utilization efficiency of Example 7. FIG. It is a figure which shows the incident angle and azimuth angle dependence of the utilization efficiency of Example 8. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Flat plate 2 ... High refractive index space area (high refractive index area)
3. Low refractive index space region (low refractive index region)
DESCRIPTION OF SYMBOLS 10 ... Slant structure 11 ... Light emitting layer 12 ... Transparent substrate 13 ... High refractive index layer 14 ... Prism array

Claims (5)

A slant in which a high-refractive index region and a low-refractive index region repeat in a one-dimensional direction along a flat plate at a constant period, and the high-refractive index region and low-refractive index region are inclined at a constant slant angle with respect to the normal line of the flat plate. A light extraction structure from a light emitting element, wherein a slant structure having a structure is disposed on a light extraction surface side of a light emitting layer of the light emitting element. 2. The light extraction structure from a light emitting device according to claim 1, wherein in the slant structure, the slant structure is arranged in an integer number of rotational symmetry around a normal line of the surface of the flat plate. In the slant structure, a high refractive index region or a portion where the high refractive index region and the low refractive index region are spatially overlapped is a high refractive index region, and a portion where the low refractive index region is spatially overlapped is a low refractive index region. The light extraction structure from the light emitting device according to claim 2, wherein The high-refractive-index layer larger than the refractive index by the side of the said light emitting layer is arrange | positioned between the said light emitting layer and the said slant structure, The light emitting element from any one of Claim 1 to 3 characterized by the above-mentioned. Light extraction structure. 4. The prism array according to claim 1, wherein a prism array having a large number of quadrangular pyramid or roof-shaped prisms arranged in an array is disposed on the emission side of the light emitting layer. Light extraction structure from light emitting element.

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