DESCRIPTION
LIGHT-EMITTING ELEMENT
TECHNICAL FIELD
[0001] The present invention relates to a light emitting element usable in a display, an
illumination device, etc.
BACKGROUND ART
[0002] Light emitting elements expected as next-generation of displays or illumination
devices include an organic light emitting diode referred to as an organic EL element
(organic Electro-Luminescence element). In an organic EL element, a hole injected from a
hole injecting layer and electron injected from an electron injecting layer are each carried
to a light emitting layer, then the hole and electron are recombined on an organic molecule
in the light emitting layer to excite the organic molecule, thereby generating light emission
or radiation. Therefore, in order that the organic EL element is used as the display device
or the illumination device, the light from the light emitting layer is required to be
efficiently extracted from the surface of the organic EL element. For this purpose, a
configuration wherein a semispherical lens is provided on an organic EL element is known
by Patent Literature 1.
[Citation List]
[Patent Literature]
[0003] PATENT LITERATURE 1: Japanese Patent Application Laid-open No. 201 1 -
054407
PATENT LITERATURE 2: PCT International Publication No. W020121147759
SUMMARY OF INVENTION
Problem to be Solved by the Invention:
[0004] However, as described in Patent Literature 2 by the Applicant of the present
application, such a light emitting element provided with the semispherical lens is found to
have a problem that the angle dependency of chromaticity (chromaticity angle dependency;
the change in color due to the field angle) is great in the light emitting element. In order
that the organic EL element can be practically used in a wide variety of applications
including displays, illumination, etc., the organic EL element is required to have a low
chromaticity angle dependency while having a sufficient light emission efficiency
(luminous efficacy), and there is a demand to develop such an organic EL element.
[0005] In view of the above situations, an object of the present invention it to provide a
light emitting element having a sufficient light emission efficiency, as well as a small
change in the color due to the field angle.
Solution to the Problem:
(00061 According to an aspect of the present invention, there is provided a light emitting
element, including:
a concave-convex structure layer, a first electrode, an organic layer, and a second
electrode which are provided on a surface of a base member in this order; and
a lens member arranged on an opposite surface of the base member on a side
opposite to the surface,
wherein a center of the lens member and a center of a light emitting portion are
coincident to each other in a plane view, the light emitting portion being an area of the
organic layer sandwiched between the first and second electrodes in a thickness direction
of the base member;
a ratio of a diameter D2 of the light emitting portion to a diameter Dl of the lens
member satisfies D2/D1 10.7; and
a ratio of a distance d to the diameter Dl of the lens member satisfies d/Dl < 0.25,
the distance d being a distance between the opposite surface of the base member and the
center of the light emitting portion.
[0007] In the light emitting element, the lens member may be a semispherical lens.
[0008] In the light emitting element, the concave-convex structure layer may be formed
of a sol-gel material.
[0009] The light emitting element may include a covering layer covering a surface of the
concave-convex structure layer and arranged between the concave-convex structure layer
and the first electrode.
[0010] In the light emitting element, the base member may be a glass base member.
[0011] In the light emitting element, refractive index of the lens member may be not less
than 1.4.
[0012] In the light emitting element, the concave-convex structure layer may have a
concave-convex pattern in which an average pitch of concavities and convexities is in a
range of 100 nm to 1500 nm, and a standard deviation of depth of the concavities and
convexities is in a range of 10 nm to 100 nm.
[0013] In the light emitting element, the diameter Dl of the lens member may be in a
range of 1 mm to 100 mm; the diameter D2 of the light emitting portion may be in a range
of 0.5 mm to 70 mm; and the distance d between the opposite surface of the base member
and the center of the light emitting portion may be in a range of 0.04 mm to 5 mm.
EFFECT OF INVENTION
[0014] The light emitting element of the present invention is provided with the lens
member and the concave-convex structure layer, wherein the ratio rl of the diameter of the
light emitting portion to the diameter of the lens member satisfies rl 5 0.7; and the ratio r2
of the distance between the surface of the base member having the lens member arranged
thereon and the center of the light emitting portion to the diameter of the lens member
satisfies r2 5 0.25. With this, the light emitting element of the present invention is capable
of efficiently extracting the light, emitted in the light emitting portion, to the outside
thereof, and thus the light emitting element has a high light emitting efficiency (current
efficiency). Further, in the light emitting element of the present invention, the change in
color due to the field angle (chromaticity angle dependency) is small. Accordingly, the
light emitting element of the present invention is quite effective for a variety of kinds of
light emitting devices such as displays, illumination devices, etc.
BRIEF DESCRIPTION OF DRAWINGS
[0015] Figs. I (a) and 1 (b) schematically depict a light emitting element according to an
embodiment of the present invention, wherein Fig. 1 (a) is a schematic top view and Fig.
1 (b) is a schematic cross-sectional view as viewed in a 1-1 direction of Fig. 1 (a).
Figs. 2(a) and 2(b) schematically depict a light emitting element according to
another embodiment of the present invention, wherein Fig. 2(a) is a schematic top view
and Fig. 2(b) is a schematic cross-sectional view as viewed in a 1-1 direction of Fig. 2(a).
Fig. 3 conceptually depicts an exemplary transfer step in a manufacturing method
for manufacturing the light emitting element of the embodiment.
Fig. 4 is a schematic cross-sectional view of a light emitting element of each of
Comparative Examples l,4,6, 8, 1 1, 13, 15, 18 and 2 1.
Fig. 5 is a schematic cross-sectional view of a light emitting element of each of
Comparative Examples 2, 5, 7, 9, 12, 14, 16, 19 and 22.
Fig. 6 is a table showing the results of evaluation of chromaticity angle
dependency in light emitting elements in Example 1 and Comparative Examples 1 to 3.
Fig. 7 is a table showing the results of evaluation of current efficiency in light
emitting elements in Examples 2 to 6 and Comparative Examples 4 to 22.
Figs. 8(a) and 8(b) schematically depict a light emitting element according to still
another embodiment of the present invention and having an adhesive layer directly formed
on a base member, wherein Fig. 8(a) is a schematic top view and Fig. 8(b) is a schematic
cross-sectional view as viewed in a 1-1 direction of Fig. 8(a).
Figs. 9(a) and 9(b) schematically depict a light emitting element according to yet
another embodiment of the present invention and having an adhesive layer contacting both
of a concave-convex structure layer and a base member, wherein Fig. 9(a) is a schematic
top view and Fig. 9(b) is a schematic cross-sectional view as viewed in a 1-1 direction of
Fig. 9(a).
DESCRIPTION OF EMBODIMENTS
[0016] In the following, an embodiment of a light emitting element (optical element) and
a method for manufacturing the light emitting element according to the present invention
will be explained with reference to the drawings.
[0017] The schematic top view and schematic cross-sectional view of a light emitting
element 100 of the embodiment are depicted respectively in Figs. 1 (a) and 1 (b). The light
emitting element 100 mainly includes a plate-shaped base member 40, a concave-convex
structure layer 142, a first electrode 92, an organic layer 94, a second electrode 98 and a
lens member 20. The concave-convex structure layer 142, the first electrode 92, the
organic layer 94 and the second electrode 98 are formed in this order on one surface of the
base member, and the lens member 20 is arranged on the other surface (opposite surface),
of the base member, opposite to the one surface.
[0018] As depicted in Figs. l(a) and 1 (b), provided that an in-plain direction of the base
member 40 is defined as an XY direction, and a direction perpendicular to the XY
direction, namely, a height direction of the light emitting element 100 (thickness direction
of the base member) is defined as a Z direction, an area in the organic layer 94 which is
sandwiched between the first electrode 92 and the second electrode 98 in the Z direction (a
hatched portion in Fig. l(b)) becomes a portion which emits light under a condition that the
light emitting element is electrified or energized, namely becomes a light emitting portion
94a. In the light emitting element 100, the light emitting portion 94a and the lens member
20 are arranged such that the centers of the light emitting portion 94a and the lens member
20 are coincident to each other in a plane view. The term "the centers ... are coincident to
each other in a plane view" means that when the light emitting element 100 is viewed from
a direction parallel to the optical axis of the lens member 20 (Z direction), one piece of the
light emitting portion 94a is overlapped only with one piece of the lens member 20 and the
position of the optical axis of the lens member 20 is substantially coincident with the
position of the center of the light emitting portion 94a in the in-plane (XY) direction.
[0019] As depicted in Figs. 1 (a) and 1 (b), provided that the diameter of the lens member
20 is defined as "Dl ", the dimeter of the light emitting portion 94a is defined as "D2", and
the distance in the Z direction between the surface of the base member 40 on which the
lens member 20 is arranged (an adhesion surface of the base member 40 at which the lens
member 20 is adhered to the base member 40) and the center of the light emitting portion
94a in the Z direction is defined as "d", then in the light emitting element 100 of the
present embodiment, a ratio rl of D2 to Dl satisfies rl 5 0.7 and a ratio r2 of d to Dl
satisfies r2 5 0.25. In a case that the ratio rl and the ratio r2 both exceed the upper limit
values thereof, respectively, the efficiency of extracting the light emitted in the light
emitting portion 94a therefrom is lowered and the light emission efficiency (current
efficiency) of the light emitting element becomes insufficient in some cases, as appreciated
from examples and comparative examples (to be described later on). From the viewpoint
of improving the light extracting efficiency by the lens member, the values of the ratio rl
and the ratio r2 preferably become closer to 0 (zero) as much as possible. Therefore, it is
preferred that the ratio rl and the ratio r2 are respectively within a range of 0 < rl 50.7
and a range of 0 < r2 5 0.25. On the other hand, as will be described later on, in view of
the handleability (ease of handling) and the mechanical strength, etc., the diameter Dl is
preferably within a range of 1 mm to 100 mm and the diameter D2 is preferably within a
range of 0.5 mm to 70 mm. Further, as will be described later on, since the thickness of
the base member 40 is preferably in a range of 40 pm to 3000 pm, the distance d is
preferably in a range of 0.04 mm to 5 mm.
[0020]
The base member 40 is not particularly limited, and it is possible to appropriately
use any publicly known transparent substrate which can be used for the light emitting
element. Those usable as the base member 40 include, for example, a substrate made of a
transparent inorganic material such as glass; substrates made of resins such as polyester
(polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate,
polyarylate, and the like), an acrylic-based resin (polymethyl methacrylate and the like),
polycarbonate, polyvinyl chloride, a styrene-based resin (ABS resin and the like), a
cellulose-based resin (triacetyl cellulose and the like), a polyimide-based resin (polyimide
resin, polyimideamide resin, and the like) and cycloolefin polymer; a stacked substrate
obtained by forming, on the surface of a substrate made of any one of the foregoing resins,
a gas barrier layer made of an inorganic material such as SiN, SiO2, Sic, SiOxNy, Ti02, or
A1203 and/or a gas barrier layer made of a resin material; and a stacked substrate obtained
by alternately stacking, on a substrate made of any one of the foregoing resins, the gas
barrier layer made of the inorganic material and the gas barrier layer made of the resin
material. In terms of uses (application purpose) of the light emitting element, the base
member 40 desirably has the heat resistance and the weather resistance to UV light and the
like. In view of these points, thus, base members made of inorganic materials such as glass
and quarts substrates are more preferably used. In particular, in a case that the base
member 40 is made of the inorganic material and that the concave-convex structure layer
142 is made of an inorganic material such as a sol-gel material, then the difference between
the refractive index of the base member 40 and the refractive index of the concave-convex
structure layer 142 is small, which in turn makes it possible to prevent any unintended
refraction and/or reflection in the light emitting element 100. Thus, the base member 40 is
preferably made of any inorganic material. It is allowable to perform a surface treatment
for the base member 40 or to provide an easy-adhesion layer on the base member 40 so as
to improve the adhesion property of the base member 40; and/or it is also allowable to
provide a gas barrier layer in order to keep out moisture and/or gas such as oxygen. The
thickness of the base member 40 is preferably to be thin in order to improve the light
extracting efficiency, and is preferably within a range of 40 pm to 3000 pm. In a case that
the thickness of the base member 40 is less than the lower limit as described above, the
handling of the base member 40 becomes difficult in some cases, and a base member with
such a thickness is hard to obtain.
[0021]
The concave-convex structure layer 142 is a layer having a minute concaveconvex
pattern formed on a surface thereof. The minute concave-convex pattern may be
any pattern such as a lens structure or a structure having the light diffusion function, light
diffraction function, etc. Among the above-described concave-convex patterns, an
irregular concave-convex pattern in which pitches of concavities and convexities are nonuniform
and orientations of concavities and convexities have no directionality. In order
that the concave-convex structure layer 142 functions as the diffraction grating, the
average pitch of concavities and convexities is preferably in a range of 100 nm to 1500 nm.
In a case that the average pitch of concavities and convexities is less than the lower limit,
pitches are so small relative to the wavelengths of the visible light that the diffraction of
the light by concavities and convexities is less likely to occur. On the other hand, in a case
that the average pitch exceeds the upper limit, the diffraction angle is so small that
functions as the diffraction grating are more likely to be lost. The average pitch of
concavities and convexities is more preferably in a range of 200 nm to 1200 nm. The
average value of the depth distribution of concavities and convexities is preferably in a
range of 20 nm to 200 nm. In a case that the average value of the depth distribution of
concavities and convexities is less than the lower limit, the depth is so small relative to the
wavelengths of the visible light that the required diffraction is less likely to occur. On the
other hand, in a case that the average value exceeds the upper limit, the intensity of
diffracted light becomes non-uniform, which in turn results in the following tendency.
Namely, for example, the electric field distribution in the organic layer 94 of the light
emitting element 100 becomes non-uniform, thereby causing the electric field to
concentrate on a certain position or area in the organic layer 94 and thus causing any leak
current to be easily generated, and/or shortening the service life of the light emitting
element 100. The average value of the depth distribution of concavities and convexities is
more preferably in a range of 30 nm to 150 nm. The standard deviation of the depth of
convexities and concavities is preferably in a range of 10 nm to 100 nm. In a case that the
standard deviation of depth of convexities and concavities is less than the lower limit, the
depth is so small relative to the wavelengths of the visible light that the required diffraction
is less likely to occur. On the other hand, in a case that the standard deviation exceeds the
upper limit, the intensity of diffracted light becomes non-uniform, which in turn results in
the following tendency. Namely, for example, the electric field distribution in the organic
layer 94 of the light emitting element 100 becomes non-uniform, thereby causing the
electric field to concentrate on a certain position or area in the organic layer 94 and thus
causing any leak current to be easily generated, and/or shortening the service life of the
light emitting element 100. The standard deviation of depth of convexities and concavities
is preferably within a range of 15 nm to 75 nm.
[0022] Note that the term "average pitch of concavities and convexities" in the present
application means an average value of the pitch of concavities and convexities in a case of
measuring the pitch of concavities and convexities (spacing distance between adjacent
convex portions or spacing distance between adjacent concave portions) in a surface on
which the convexities and concavities are formed. Such an average value of the pitch of
concavities and convexities is obtained as follows. Namely, a concavity and convexity
analysis image is obtained by measuring the shape of concavities and convexities on the
surface by using a scanning probe microscope (for example, a scanning probe microscope
manufactured by HITACHI HIGH-TECH SCIENCE CORPORATION, under the product
name of "E-sweep", etc.), under the following measurement conditions, then the distances
between randomly selected concave portions or convex portions adjacent to each other are
measured at not less than 100 points in the concavity and convexity analysis image, and
then the average of the distances is calculated and is determined as the average value of the
pitch of concavities and convexities. The measurement conditions are as follows:
Measurement mode: cantilever intermittent contact mode
Material of the cantilever: silicon
Lever width of the cantilever: 40 pm
Diameter of tip of chip of the cantilever: 10 nm
[0023] Further, in the present application, the average value of the depth distribution of
concavities and convexities and the standard deviation of the depth of concavities and
convexities can be calculated by the following manner. Namely, a concavity and
convexity analysis image is obtained by measuring the shape of concavities and
convexities on the surface by using a scanning probe microscope (for example, a scanning
probe microscope manufactured by HITACHI HIGH-TECH SCIENCE CORPORATION,
under the product name of "E-sweep", etc.), in a randomly selected measurement region of
3 pm square (vertical: 3 pm, horizontal: 3 pin) or in a randomly selected measurement
region of 10 pm square (vertical: 10 pm, horizontal: 10 pm) under the above-described
conditions. When doing so, data of height of concavities and convexities at not less than
16,384 points (vertical: 128 points x horizontal: 128 points) are obtained within the
measurement region, each in nanometer scale. Note that although the number of
measurement points is different depending on the kind and setting of the measuring device
which is used, for example in a case of using the above-described scanning probe
microscope manufactured by HITACHI HIGH-TECH SCIENCE CORPORATION, under
the product name of "E-sweep", it is possible to perform the measurement at measurement
points of 65,536 points (vertical: 256 points x horizontal: 256 points; namely, the
measurement in a resolution of 256 x 256 pixels) within the measurement region of 10 pm
square. With respect to the height of concavities and convexities (unit: nm) measured in
such a manner, at first, a measurement point "P" is determined, among all the measurement
points, which is the highest from the surface of a base member. Then, a plane which
includes the measurement point P and which is parallel to the surface of the base member
is determined as a reference plane (horizontal plane), and a depth value from the reference
plane (difference obtained by subtracting, from the value of height from the base member
at the measurement point P, the height from the base member at each of the measurement
points) is obtained as the data of depth of concavities and convexities. Note that such a
depth data of concavities and convexities can be obtained, for example, by performing
automatic calculation with software in the measurement device (for example, the abovedescribed
scanning probe microscope manufactured by HITACHI HIGH-TECH SCIENCE
CORPORATION, under the product name of "E-sweep"), and the value obtained by the
automatic calculation in such a manner can be utilized as the data of depth of concavities
and convexities. After obtaining the data of depth of concavity and convexity at each of
the measurement points in this manner, the values, which can be calculated by obtaining
the arithmetic average value and the standard deviation of the obtained data of depth of
concavity and convexity, are adopted as the average value of the depth distribution of
concavities and convexities and the standard deviation of the depth of concavities and
convexities. In this specification, the average pitch of concavities and convexities and the
average value of the depth distribution of concavities and convexities can be obtained via
the above-described measuring method, regardless of the material of the surface on which
concavities and convexities are formed.
[0024] Note that, however, the term "irregular concave-convex pattern" includes such a
quasi-periodic structure in which a Fourier-transformed image, obtained by performing a
two-dimensional fast Fourier-transform processing on a concavity and convexity analysis
image obtained by analyzing a concave-convex shape on the surface, shows a circular or
annular pattern, namely, such a quasi-periodic structure in which, although concavities and
convexities have no particular orientation (directionality), the structure has the distribution
of pitches of concavities and convexities (pitches of concavities and convexities vary).
Therefore, the substrate having such a quasi-periodic structure is suitable for a diffraction
substrate used in a surface-emitting element, such as the organic EL element, provided that
the substrate has concavities and convexities of which pitch distribution or pitch variability
enables the substrate to diffract visible light.

We claim:
1 . A light emitting element, comprising:
a concave-convex structure layer, a first electrode, an organic layer, and a second
electrode which are provided on a surface of a base member in this order; and
a lens member arranged on an opposite surface of the base member on a side
opposite to the surface,
wherein a center of the lens member and a center of a light emitting portion are
coincident to each other in a plane view, the light emitting portion being an area of the
organic layer sandwiched between the first and second electrodes in a thickness direction
of the base member;
a ratio of a diameter D2 of the light emitting portion to a diameter Dl of the lens
member satisfies D2/D I 5 0.7; and
a ratio of a distance d to the diameter D 1 of the lens member satisfies d/D 1 5 0.25,
the distance d being a distance between the opposite surface of the base member and the
center of the light emitting portion.
2. The light emitting element according to claim I, wherein the lens
member is a semispherical lens.
3. The light emitting element according to claim 1 or 2, wherein the
concave-convex structure layer is formed of a sol-gel material.
4. The light emitting element according to any one of claims 1 to 3, further
comprising a covering layer covering a surface of the concave-convex structure layer and
arranged between the concave-convex structure layer and the first electrode.
5. The light emitting element according to any one of claims 1 to 4, wherein
the base member is a glass base member.
6. The light emitting element according to any one of claims 1 to 5, wherein
refractive index of the lens member is not less than 1.4.
7. The light emitting element according to any one of claims 1 to 6, wherein
the concave-convex structure layer has a concave-convex pattern in which an average pitch
of concavities and convexities is in a range of 100 nm to 1500 nm, and a standard deviation
of depth of the concavities and convexities is in a range of 10 nm to 100 nm.
8. The light emitting element according to any one of claims 1 to 7, wherein
the diameter Dl of the lens member is in a range of 1 mm to 100 mm.
9. The light emitting element according to any one of claims 1 to 8, wherein
the diameter D2 of the light emitting portion is in a range of 0.5 mm to 70 mm.
10. The light emitting element according to any one of claims 1 to 9, wherein
the distance d between the opposite surface of the base member and the center of the light
emitting portion is in a range of 0.04 mm to 5 mm.