Bottom emission type electroluminescent display with partially reflecting electrodes
View Patent ↗A bottom emission type electroluminescent display in which light emitted from a light emitting layer undergoes constructive interference between a first electrode and a second electrode. The bottom emission type electroluminescent display has a transparent substrate, a first electrode and a second electrode. The first electrode and the second electrode are formed on the same side of the transparent substrate. The electroluminescent display also has a medium layer interposed between the first electrode and the second electrode and includes a light emission layer that emits light when the first electrode and the second electrode are electrically driven. The first electrode is formed as a translucent conductive layer that partially reflects the light emitted from the light emission layer and the second electrode is formed as a reflection layer that reflects the light emitted from the light emission layer.
1. A bottom emission type electroluminescent display, comprising:
a transparent substrate;
a first electrode and a second electrode formed on a same side of the transparent substrate; and
a medium layer interposed between the first electrode and the second electrode and comprising a light emitting layer that emits light when the first electrode and the second electrode are electrically driven,
wherein the first electrode is formed as a translucent conductive layer that partially reflects the light emitted from the light emitting layer and the second electrode is formed as a reflection layer that reflects the light emitted from the light emitting layer, and the first electrode is formed as a single layer.
2. The bottom emission type electroluminescent display of claim 1 , wherein the medium layer interposed between the first electrode and the second electrode is formed so that light reflected by the first electrode and the second electrode undergoes constructive interference.
3. The bottom emission type electroluminescent display of claim 2 , wherein the medium layer interposed between the first electrode and the second electrode has a thickness and a refractive index which substantially maximize the value of E t in the following formula:
(
E
t
E
o
)
=
t
ⅇ
ⅈ
2
π
λ
n
2
d
[
1
+
r
′
r
ⅇ
ⅈ
2
λ
n
2
(
4
d
)
+
{
r
′
r
ⅇ
ⅈ
2
λ
n
2
(
4
d
)
}
2
+
…
]
+
tr
′
ⅇ
ⅈ
2
π
λ
n
2
(
3
d
)
[
1
+
r
′
r
ⅇ
ⅈ
2
λ
n
2
(
4
d
)
+
{
r
′
r
ⅇ
ⅈ
2
λ
n
2
(
4
d
)
}
2
+
…
]
=
t
ⅇ
ⅈ
2
π
λ
n
2
d
1
+
r
′
ⅇ
ⅈ
2
π
λ
n
2
(
2
d
)
1
-
rr
′
ⅇ
ⅈ
2
π
λ
n
2
(
4
d
)
.
wherein E t is a luminance of light discharged from the bottom emission type electroluminescent display, E o is a luminance of light emitted from the light emitting layer, t is a light transmittance of the first layer, λ is a wavelength of light emitted from the light emitting layer, n 2 is a refractive index of the medium layer, 2 d is a thickness of the medium layer, r is a light reflectivity of the first layer, r′ is a light reflectivity of the second layer, e represents an exponential function, and i represents an imaginary number.
4. The bottom emission type electroluminescent display according to claim 1 , wherein the first electrode is made of a composite material comprising a transparent material and a partially reflective material.
5. The bottom emission type electroluminescent display according to claim 4 , wherein the transparent material is selected from the group consisting of indium zinc oxide (IZO), aluminum tin oxide (ATO), and zinc oxide (ZnO), an reflective material selected from the group consisting of Ag, Mg, Al, Pt, Pd, Au, Ni, Ir, and Cr.
6. The bottom emission type electroluminescent display of claim 1 , wherein the first electrode has a light transmittance of about 20% to about 80%.