Light-emitting device with reflective electrode and light-emitting layer
A novel light-emitting device with high emission efficiency is provided. A light-emitting device with a high blue index (BI) is provided. A light-emitting device with low power consumption is provided. A light-emitting device including a first electrode and a second electrode which are a reflective electrode and a semi-transmissive and semi-reflective electrode, and an EL layer sandwiched between the first electrode and the second electrode, where the EL layer contains an emission center substance, where when the emission center substance in the EL layer includes only one kind of substance, photon energy of a peak wavelength of light emitted from the light-emitting device is designed from an average value of photon energy of light emitted by the emission center substance in a solution state and emission edge energy on a short wavelength side of an emission spectrum of the emission center substance in the solution state.
1. A light-emitting device comprising:
a first electrode;
a second electrode; and
an EL layer between the first electrode and the second electrode, the EL layer comprising a light-emitting layer,
wherein the light-emitting layer comprises an emission center substance,
wherein the first electrode and the second electrode overlap each other,
wherein one of the first electrode and the second electrode is a reflective electrode and the other is a semi-transmissive and semi-reflective electrode,
wherein E ave is an average of photon energy of an emission spectrum of the emission center substance,
wherein E edge is an energy at an emission edge on a short wavelength side of the emission spectrum,
wherein E em is a photon energy corresponding to a light having a wavelength λ,
wherein the wavelength λ is longer than a peak wavelength of the emission spectrum,
wherein an optical path length between the reflective electrode and the light-emitting layer is configured to (2n−1)λ/4 where n is a natural number, and
wherein the following formula (1) is satisfied:
E ave ≤E em ≤0.95 E edge (1).
2. The light-emitting device according to claim 1 , wherein the emission spectrum is an emission spectrum obtained from a solution comprising the emission center substance.
3. The light-emitting device according to claim 2 , wherein a solvent of the solution has a dielectric constant greater than or equal to 1 and less than or equal to at room temperature.
4. The light-emitting device according to claim 2 , wherein a solvent of the solution is toluene or chloroform.
5. The light-emitting device according to claim 1 , wherein the emission center substance is capable of emitting blue light.
6. The light-emitting device according to claim 1 , wherein E em is greater than or equal to 2.6 eV and less than or equal to 2.9 eV.
7. The light-emitting device according to claim 1 , wherein a difference between E em and E ave is 0.02 eV or more.
8. The light-emitting device according to claim 1 , wherein a blue index of the light-emitting device is 89.1 or more.
9. The light-emitting device according to claim 1 ,
wherein the emission spectrum is obtained by counting photons emitted from the emission center substance,
wherein E ave is estimated by the following formula (IV):
E
ave
=
∅
p
N
p
=
ch
·
∫
F
(
λ
)
/
λ
d
λ
∫
F
(
λ
)
d
λ
,
(
IV
)
wherein λ is wavelength,
wherein c is light speed,
wherein h is the Planck constant, and
wherein ∫F(λ)dλ corresponds to an integral value of the emission spectrum.
10. The light-emitting device according to claim 1 ,
wherein the emission spectrum is obtained by measuring energy itself emitted from the emission center substance or by normalized spectrum that is proportional to the energy,
wherein E ave is estimated by the following formula (VI):
E
a
v
e
=
∅
p
N
p
=
ch
·
∫
∅
p
(
λ
)
d
λ
∫
∅
p
(
λ
)
λ
d
λ
,
(
VI
)
wherein λ is wavelength,
wherein c is light speed,
wherein h is the Planck constant, and
wherein ϕ p (λ) corresponds to the energy or a proportional value to the energy.
11. The light-emitting device according to claim 1 , further comprising an organic compound layer on a first surface of the semi-transmissive and semi-reflective electrode,
wherein the organic compound layer comprises an organic compound with molecular weight greater than or equal to 300 and less than or equal to 1200,
wherein a second surface of the semi-transmissive and semi-reflective electrode and the reflective electrode face each other, and
wherein the second surface is an opposite surface to the first surface.
12. A light-emitting apparatus comprising:
the light-emitting device according to claim 1 , and
one of a transistor and a substrate.
13. An electronic device comprising:
the light-emitting apparatus according to claim 12 , and
one of a sensor, an operation button, a speaker and a microphone.
14. A lighting device comprising:
the light-emitting apparatus according to claim 12 , and
a housing.
15. A light-emitting device comprising:
a first electrode;
a second electrode; and
an EL layer between the first electrode and the second electrode,
wherein the first electrode and the second electrode overlap each other,
wherein one of the first electrode and the second electrode is a reflective electrode and the other is a semi-transmissive and semi-reflective electrode,
wherein the EL layer comprises a light-emitting layer,
wherein the light-emitting layer comprises an emission center substance,
wherein an average value of photon energy of light emitted by the emission center substance in a solution state is denoted by E ave [eV],
wherein emission edge energy on a short wavelength side of an emission spectrum of the emission center substance in the solution state is denoted by E edge [eV],
wherein photon energy corresponding to a light having a wavelength λ is denoted by E em [eV],
wherein the wavelength λ is longer than a peak wavelength of the emission spectrum of the emission center substance in the solution state,
wherein an optical path length between the reflective electrode and the light-emitting layer is configured to (2n−1)λ/4 where n is a natural number, and
wherein E em [eV] is expressed by the following formula (1):
E ave ≤E em ≤0.95 E edge (1).
16. The light-emitting device according to claim 15 , wherein the following formula (2) is satisfied:
E ave +0.02≤ E em ≤0.95 E edge (2).
17. The light-emitting device according to claim 15 , wherein a solvent forming the solution state has a dielectric constant greater than or equal to 1 and less than or equal to 10 at room temperature.
18. The light-emitting device according to claim 17 , wherein the solvent is toluene or chloroform.
19. The light-emitting device according to claim 15 , wherein the emission center substance is capable of emitting blue light.
20. The light-emitting device according to claim 15 , wherein E em is greater than or equal to 2.6 eV and less than or equal to 2.9 eV.
21. An electronic device comprising the light-emitting device according to claim 15 .