U.S. patent application number 16/761667 was filed with the patent office on 2021-06-17 for organic-inorganic perovskite, film, light-emitting film, delayed fluorescence-emitting film, light-emitting element, and method for producing light-emitting element.
The applicant listed for this patent is KYULUX, INC.. Invention is credited to Chihaya ADACHI, Toshinori MATSUSHIMA, Chuanjiang QIN.
Application Number | 20210184138 16/761667 |
Document ID | / |
Family ID | 1000005460554 |
Filed Date | 2021-06-17 |
United States Patent
Application |
20210184138 |
Kind Code |
A1 |
QIN; Chuanjiang ; et
al. |
June 17, 2021 |
ORGANIC-INORGANIC PEROVSKITE, FILM, LIGHT-EMITTING FILM, DELAYED
FLUORESCENCE-EMITTING FILM, LIGHT-EMITTING ELEMENT, AND METHOD FOR
PRODUCING LIGHT-EMITTING ELEMENT
Abstract
An organic-inorganic perovskite satisfying E.sub.T<E.sub.T1
and E.sub.S-E.sub.T.ltoreq.0.1 eV has a high emission efficiency.
E.sub.S represents the excited singlet energy level in emission of
an inorganic component, E.sub.T represents the excited triplet
energy level in emission of an inorganic component, E.sub.T1
represents the excited triplet energy level in emission of an
organic component.
Inventors: |
QIN; Chuanjiang;
(Fukuoka-shi, Fukuoka, JP) ; MATSUSHIMA; Toshinori;
(Fukuoka-shi, Fukuoka, JP) ; ADACHI; Chihaya;
(Fukuoka-shi, Fukuoka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KYULUX, INC. |
Fukuoka-shi, Fukuoka |
|
JP |
|
|
Family ID: |
1000005460554 |
Appl. No.: |
16/761667 |
Filed: |
November 1, 2018 |
PCT Filed: |
November 1, 2018 |
PCT NO: |
PCT/JP2018/040758 |
371 Date: |
May 5, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09K 2211/1007 20130101;
H01L 51/5012 20130101; H01L 51/0077 20130101; C07F 7/24 20130101;
C09K 11/06 20130101; C09K 2211/1011 20130101; H01L 2251/558
20130101 |
International
Class: |
H01L 51/00 20060101
H01L051/00; C09K 11/06 20060101 C09K011/06; C07F 7/24 20060101
C07F007/24 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 6, 2017 |
JP |
2017-213911 |
Claims
1. An organic-inorganic perovskite satisfying the following
requirements (1) and (2): E.sub.T<E.sub.T1 (1)
E.sub.S-E.sub.T.ltoreq.0.1 eV (2) wherein E.sub.S represents an
excited singlet energy level in emission of an inorganic component
constituting the organic-inorganic perovskite, E.sub.T represents
an excited triplet energy level in emission of an inorganic
component constituting the organic-inorganic perovskite, E.sub.T1
represents an excited triplet energy level in emission of an
organic component constituting the organic-inorganic
perovskite.
2. The organic-inorganic perovskite according to claim 1, which
emits delayed fluorescence.
3. The organic-inorganic perovskite according to claim 1, which is
a quasi-two-dimensional perovskite.
4. The organic-inorganic perovskite according to claim 1, which is
represented by the following formula (10):
R.sub.2A.sub.n-1B.sub.nX.sub.3+1 (10) wherein R represents a
monovalent organic cation, A represents a monovalent cation, B
represents a divalent metal ion, X represents a halide ion, and n
represents an integer of 2 or more, and wherein an inorganic layer
having a composition represented by BX.sub.4n in the formula (10)
constitutes the inorganic component, and the organic cation
represented by R in the formula (10) constitutes the organic
component.
5. The organic-inorganic perovskite according to claim 4, wherein R
in the formula (10) is an ammonium represented by the following
formula (11): Ar(CH.sub.2).sub.n1NH.sub.3.sup.+ (11) wherein Ar
represents an aromatic ring, and n1 represents an integer of 1 to
20.
6. The organic-inorganic perovskite according to claim 4, wherein A
in the formula (10) is a formamidinium or a methylammonium.
7. The organic-inorganic perovskite according to claim 4, wherein B
in the formula (10) is Pb.sup.2+.
8. The organic-inorganic perovskite according to claim 4, wherein X
in the formula (10) is Br.sup.-.
9. An organic-inorganic perovskite represented by the following
formula (A) or the following formula (B):
PEA.sub.2FA.sub.n-1Pb.sub.nBr.sub.3n+1 (A)
PEA.sub.2MA.sub.n-1Pb.sub.nBr.sub.3n+1 (B) wherein PEA represents a
phenylethylammonium, FA represents a formamidinium, MA represents a
methylammonium, and n represents an integer of 2 or more.
10. A film comprising an organic-inorganic perovskite of claim
1.
11. A light-emitting film comprising an organic-inorganic
perovskite of claim 1.
12. A delayed fluorescence-emitting film comprising an
organic-inorganic perovskite of claim 1.
13. A light-emitting device having a film of claim 10.
14. The light-emitting device according to claim 13, which emits
delayed fluorescence at 300 K.
15. A method for producing a light-emitting device wherein an
organic-inorganic perovskite is so planned as to satisfy the
following requirements (1) and (2), and a light-emitting device is
produced using an organic-inorganic perovskite satisfying the
following requirements: E.sub.T<E.sub.T1 (1)
E.sub.S-E.sub.T.ltoreq.0.1 eV (2) wherein E.sub.S represents an
excited singlet energy level in emission of an inorganic component
constituting the organic-inorganic perovskite, E.sub.T represents
an excited triplet energy level in emission of an inorganic
component constituting the organic-inorganic perovskite, E.sub.T1
represents an excited triplet energy level in emission of an
organic component constituting the organic-inorganic perovskite.
Description
TECHNICAL FIELD
[0001] The present invention relates to an organic-inorganic
perovskite useful as a material for light-emitting films for
light-emitting devices.
BACKGROUND ART
[0002] An organic-inorganic perovskite is an ion compound composed
of a monovalent cation such as an organic cation, a divalent metal
ion such as Sn.sup.2+ or Pb.sup.2+, and a halide ion, in which
these ions are regularly aligned so as to form a same crystal
structure as that of a perovskite (perovskite structure). An
organic-inorganic perovskite has semiconductor characteristics of
inorganic substances along with flexibility and molecular planning
diversity of organic substances, and is therefore expected as
various functional materials, and development of devices using it
is being actively promoted. Among them, there are found studies
relating to light-emitting devices utilizing a film of an
organic-inorganic perovskite as a light-emitting film.
[0003] For example, NPL 1 reports observation of near-IR emission
in a light-emitting device using a film of
(C.sub.6H.sub.5C.sub.2H.sub.4NH.sub.3).sub.2(CH.sub.3NH.sub.3).sub.n-1Pb.-
sub.nI.sub.3n+1 (PEA-MA perovskite). NPL 2 reports observation of
green emission in a light-emitting device using a film of PEA-MA
perovskite. Here, a film of PEA-MA perovskite used in these
literatures corresponds to a so-called quasi-2D
(quasi-two-dimensional) perovskite which is composed of crystal
lattices of a composition represented by
(CH.sub.3NH.sub.3).sub.n-1Pb.sub.nI.sub.3n+1 and in which, on both
sides of the inorganic layer having two or more layers of a
two-dimensional array structure of a unit lattice, an organic layer
is aligned with a cationic group of an organic cation represented
by C.sub.6H.sub.5C.sub.2H.sub.4NH.sub.3 facing the organic layer
side. In these literatures, the number n of the layers having the
two-dimensional array structure is varied to measure the emission
efficiency of the devices, and among them, it is confirmed that a
relatively high emission efficiency can be realized when n is
5.
CITATION LIST
Non-Patent Literature
[0004] Non-Patent Literature 1: Nature Nanotech. 2016, 11, 872
[0005] Non-Patent Literature 2: Nano Lett. 2017,
DOI:10.1021/acs.nanolett.7b00976
SUMMARY OF INVENTION
Technical Problem
[0006] As described above, NPLs 1 and 2 use a film of a PEA-MA
perovskite in a light-emitting device, in which the number n of the
inorganic layers having a two-dimensional array structure is
controlled so as to attain a high emission efficiency. With that,
the present inventors investigated the emission efficiency of the
PEA-MA perovskite according to the same method, but have found
that, even when only the number n of the inorganic layers is
controlled in any manner, the emission efficiency peaks out at a
certain level, and is not expected to be exponentially
increased.
[0007] Given the situation, the present inventors have promoted
studies of controlling the physical properties of an
organic-inorganic perovskite from an innovative viewpoint different
from conventional ones so as to improve the emission efficiency of
the organic-inorganic perovskite.
Solution to Problem
[0008] As a result of further promoting assiduous investigations,
the present inventors have reached findings that, when an
organic-inorganic perovskite is so constituted that the excited
singlet energy level (E.sub.S) and excited triplet energy level
(E.sub.T) in emission of an inorganic component to constitute the
organic-inorganic perovskite and the excited triplet energy level
(E.sub.T1) in emission of an organic component to constitute the
organic-inorganic perovskite satisfy a predetermined relationship,
then a dramatically high emission efficiency can be attained. The
present invention is proposed here on the basis of these findings
and specifically has the following constitution.
[1] An organic-inorganic perovskite satisfying the following
requirements (1) and (2):
E.sub.T<E.sub.T1 (1)
E.sub.S-E.sub.T.ltoreq.0.1 eV (2)
[0009] wherein E.sub.S represents the excited singlet energy level
in emission of an inorganic component constituting the
organic-inorganic perovskite, E.sub.T represents the excited
triplet energy level in emission of an inorganic component
constituting the organic-inorganic perovskite, E.sub.T1 represents
the excited triplet energy level in emission of an organic
component constituting the organic-inorganic perovskite.
[2] The organic-inorganic perovskite according to [1], which emits
delayed fluorescence. [3] The organic-inorganic perovskite
according to [1] or [2], which is a quasi-2D perovskite. [4] The
organic-inorganic perovskite according to any one of [1] to [3],
which is represented by the following formula (10):
R.sub.2A.sub.n-1B.sub.nX.sub.3n+1 (10)
[0010] wherein R represents a monovalent organic cation, A
represents a monovalent cation, B represents a divalent metal ion,
X represents a halide ion, and n represents an integer of 2 or
more,
[0011] and wherein the inorganic layer having a composition
represented by BX.sub.4n in the formula (10) constitutes the
inorganic component, and the organic cation represented by R in the
formula (10) constitutes the organic component.
[5] The organic-inorganic perovskite according to [4], wherein R in
the formula (10) is an ammonium represented by the following
formula (11):
Ar(CH.sub.2).sub.n1NH.sub.3.sup.+ (11)
[0012] wherein Ar represents an aromatic ring, and n1 represents an
integer of 1 to 20.
[6] The organic-inorganic perovskite according to [4] or [5],
wherein A in the formula (10) is a formamidinium or a
methylammonium. [7] The organic-inorganic perovskite according to
any one of [4] to [6], wherein B in the formula (10) is Pb.sup.2+.
[8] The organic-inorganic perovskite according to any one of [4] to
[7], wherein X in the formula (10) is Br--. [9] An
organic-inorganic perovskite represented by the following formula
(A) or the following formula (B):
PEA.sub.2FA.sub.n-1Pb.sub.nBr.sub.3n+1 (A)
PEA.sub.2MA.sub.n-1Pb.sub.nBr.sub.3n+1 (B)
[0013] wherein PEA represents a phenylethylammonium, FA represents
a formamidinium, MA represents a methylammonium, and n represents
an integer of 2 or more.
[10] A film containing an organic-inorganic perovskite of any one
of [1] to [9]. [11] A light-emitting film containing an
organic-inorganic perovskite of any one of [1] to [9]. [12] A
delayed fluorescence-emitting film containing an organic-inorganic
perovskite of any one of [1] to [9]. [13] A light-emitting device
having a film of any one of [10] to [12]. [14] The light-emitting
device according to [13], which emits delayed fluorescence at 300
K. [15] A method for producing a light-emitting device wherein an
organic-inorganic perovskite is so planned as to satisfy the
following requirements, and a light-emitting device is produced
using the organic-inorganic perovskite satisfying the following
requirements (1) and (2):
E.sub.T<E.sub.T1 (1)
E.sub.S-E.sub.T.ltoreq.0.1 eV (2)
[0014] wherein E.sub.S represents the excited singlet energy level
in emission of an inorganic component constituting the
organic-inorganic perovskite, E.sub.T represents the excited
triplet energy level in emission of an inorganic component
constituting the organic-inorganic perovskite, E.sub.T1 represents
the excited triplet energy level in emission of an organic
component constituting the organic-inorganic perovskite.
Advantageous Effects of Invention
[0015] The organic-inorganic perovskite of the present invention is
useful as a material for light-emitting films. A light-emitting
device in which the light-emitting film is formed using the
organic-inorganic perovskite of the present invention can realize a
high emission efficiency.
BRIEF DESCRIPTION OF DRAWINGS
[0016] FIGS. 1A and 1B include schematic views for explaining an
emission mechanism of the organic-inorganic perovskite of the
present invention, in which FIG. 1A is a schematic view of showing
an emission process of the organic-inorganic perovskite of the
present invention, and FIG. 1B is a schematic view of showing an
emission process of an organic-inorganic perovskite not satisfying
the requirements defined in the present invention.
[0017] FIG. 2 is a schematic cross-sectional view showing a layer
configuration example of an electroluminescent device of the
present invention.
[0018] FIG. 3 shows photoabsorption spectra and emission spectra of
a PEA-EA perovskite and an NMA-FA perovskite.
[0019] FIG. 4 is a graph showing excitation light intensity
dependence of the photoluminescence quantum yield (PLQY) of a
PEA-EA perovskite and an NMA-FA perovskite.
[0020] FIG. 5 shows transient decay curves of emission, measured at
30 K and 300 K, of a PEA-EA perovskite and an NMA-FA
perovskite.
[0021] FIG. 6 shows transient decay curves of emission, measured at
100 K, 200 K and 300 K, of a PEA-EA perovskite.
[0022] FIG. 7 shows transient decay curves of emission, measured at
100 K, 200 K and 300 K, of an NMA-FA perovskite.
[0023] FIG. 8 shows emission spectra of an electroluminescent
device using a PEA-EA perovskite and an electroluminescent device
using an NMA-FA perovskite.
[0024] FIG. 9 shows graphs of current density-voltage-luminance
characteristics of an electroluminescent device using a PEA-EA
perovskite and an electroluminescent device using an NMA-FA
perovskite.
[0025] FIG. 10 shows graphs of current density-voltage-external
quantum efficiency (EQE) characteristics of an electroluminescent
device using a PEA-EA perovskite and an electroluminescent device
using an NMA-FA perovskite.
[0026] FIG. 11 shows graphs of current density-voltage-lamp
efficiency, luminance, external quantum efficiency (EQE)
characteristics of an electroluminescent device using a PEA-MA
perovskite.
[0027] FIG. 12 shows graphs of current density-voltage-lamp
efficiency, luminance, external quantum efficiency (EQE)
characteristics of an electroluminescent device using a NMA-MA
perovskite.
DESCRIPTION OF EMBODIMENTS
[0028] Hereinunder the contents of the present invention are
described in detail. The constitutional elements may be described
below with reference to representative embodiments and specific
examples of the invention, but the invention is not limited to the
embodiments and the examples. In the description herein, a
numerical range expressed as "to" means a range that includes the
numeral values before and after "to" as the lower limit and the
upper limit. Also in this description, "main component" means a
component having a largest content among the constituent
components. The hydrogen atom that is present in the molecule of
the compound used in the invention is not particularly limited in
isotope species, and for example, all the hydrogen atoms in the
molecule may be .sup.1H, and all or a part of them may be .sup.2H
(deuterium (D)).
Organic-Inorganic Perovskite
[0029] The organic-inorganic perovskite of the present invention
satisfies the following requirements (1) and (2):
E.sub.T<E.sub.T1 (1)
E.sub.S-E.sub.T.ltoreq.0.1 eV (2)
[0030] In the requirements (1) and (2), E.sub.S represents the
excited singlet energy level in emission of an inorganic component
constituting the organic-inorganic perovskite, E.sub.T represents
the excited triplet energy level in emission of an inorganic
component constituting the organic-inorganic perovskite, E.sub.T1
represents the excited triplet energy level in emission of an
organic component constituting the organic-inorganic
perovskite.
[0031] In the present invention, the "excited singlet energy level
in emission of an inorganic component constituting the
organic-inorganic perovskite" means an energy level that causes an
inorganic component to emit fluorescence via the energy level; and
the "excited triplet energy level in emission of an inorganic
component constituting the organic-inorganic perovskite" means an
energy level that causes an inorganic component to emit
phosphorescence via the energy level. Here, the "inorganic
component" indicates an inorganic layer constituting the
organic-inorganic perovskite, precisely an inorganic layer BX.sub.4
of a two-dimensional configuration of unit lattices BX.sub.6 where
a divalent metal ion B is positioned at the center of an octahedron
with sharing apexes of halide ions X.
[0032] In the present invention, the "excited triplet energy level
in emission of an organic component constituting the
organic-inorganic perovskite" means an energy level that causes an
organic component to emit phosphorescence via the energy level.
Here, the "organic component" indicates an organic cation of the
organic-inorganic perovskite.
[0033] In this description, the "excited singlet energy level in
emission of an organic component constituting the organic-inorganic
perovskite" is represented by E.sub.S1. Here, the "excited singlet
energy level in emission of an organic component constituting the
organic-inorganic perovskite" means an energy level that causes an
organic component to emit fluorescence via the energy level.
[0034] The organic-inorganic perovskite of the present invention
satisfies the above-mentioned requirements (1) and (2) and
therefore provides a high emission efficiency. This can be presumed
to be because, in the organic-inorganic perovskite satisfying the
above-mentioned requirements, the excited triplet energy formed in
the inorganic component does not transfer to the organic component
and can be efficiently utilized for emission from the
organic-inorganic perovskite. Hereinunder the mechanism is
described with reference to FIGS. 1A and 1B. FIGS. 1A and 1B show
energy level diagrams of an organic-inorganic perovskite, an
inorganic component and an organic component. .GAMMA..sub.1 and
.GAMMA..sub.2 in the inorganic component each represent an excited
triplet energy level E.sub.T in emission at a different vibration
level, and .GAMMA..sub.5 represents an excited singlet energy level
E.sub.S in emission. The number of vibration levels of the excited
triplet energy level E.sub.T and the excited singlet energy level
E.sub.S in emission of the inorganic component constituting the
organic-inorganic perovskite of the present invention, the excited
singlet energy level E.sub.S1 and the excited triplet energy level
E.sub.T1 in emission of the organic component constituting the
organic-inorganic perovskite are not limited to the number shown in
FIGS. 1A and 1B. In the present invention, of each energy level
E.sub.S, E.sub.T, and E.sub.T1, at least the energy levels at a
lowest vibration level satisfy the the requirements (1) and
(2).
[0035] First, when a singlet exciton and a triplet exciton form in
the inorganic component constituting the organic-inorganic
perovskite through excitation light irradiation or current
injection, the energy of the singlet exciton transfers to the
excited singlet energy level EP of the organic-inorganic perovskite
according to a Dexter transfer mechanism or a Forster transfer
mechanism, as shown in FIG. 1A, and via an energy transfer toward a
lower excited singlet energy level, the energy transfers to a
ground singlet energy level S.sub.0 and deactivates with emitting
fluorescence. Here, in the case where in the requirement (2)
defined in the present invention, E.sub.S-E.sub.T.ltoreq.0.1 eV is
satisfied, the energy level difference between the excited single
energy level E.sub.S in emission of the inorganic component and the
excited triplet energy level E.sub.T in emission thereof is small,
and therefore reverse intersystem crossing from the excited triplet
state to the excited singlet state may readily occur, and the
energy of the singlet exciton thereby formed may transfer to the
excited single energy level E.sub.P of the organic-inorganic
perovskite, and through energy transfer to a lower excited singlet
energy level, the energy transfers to a ground singlet energy level
S.sub.0 and deactivates with emitting fluorescence. The
fluorescence to be emitted at that time is observed as a delayed
fluorescence having a longer emission lifetime than that of the
fluorescence to be derived from the singlet exciton formed directly
in the inorganic component through current injection. In that
manner, in the system satisfying the requirement (2), from both the
singlet exciton directly formed in the inorganic component through
current injection and the singlet exciton formed via the reverse
intersystem crossing from the excited triplet state to the excited
singlet state, energy is supplied to the excited single energy
level E.sub.P of the organic-inorganic perovskite, and therefore
the system emits efficiently as compared with a system not
satisfying the requirement (2).
[0036] However, as shown in FIG. 1B, in the case where the
requirement (1) defined in the present invention
E.sub.T<E.sub.T1 is not satisfied, that is, in the case where
E.sub.T.gtoreq.E.sub.T1, the excited triplet energy level E.sub.T1
in emission of the organic component is smaller than the excited
triplet energy level E.sub.T in emission of the inorganic
component, and therefore the energy of the triplet exciton formed
in the inorganic component transfers to the excited triplet energy
level E.sub.T1 in emission of the organic component, and conversion
from the triplet exciton to the singlet exciton through reverse
intersystem crossing does not occur sufficiently. Consequently, the
energy of the triplet exciton formed in the inorganic component
could not be efficiently utilized for fluorescence emission of the
organic-inorganic perovskite.
[0037] As opposed to this, the organic-inorganic perovskite of the
present invention satisfies the above-mentioned requirement (1) and
additionally the requirement (2) E.sub.T<E.sub.T1, and therefore
in this, the energy of the triplet exciton formed in the inorganic
component does not transfer to the excited triplet energy level
E.sub.T1 in emission of the organic component, and conversion from
the triplet exciton to the singlet exciton through reverse
intersystem crossing occurs at a high probability. Consequently,
both the singlet exciton and the triplet exciton formed in the
inorganic component can be efficiently utilized for fluorescence
emission and delayed fluorescence emission of the organic-inorganic
perovskite, and the perovskite secures a high emission efficiency.
For example, the probability of formation of a singlet exciton and
a triplet exciton to form through current excitation is 25%/75%,
and according to this mechanism, in principle, all the excitons can
be singlet excitons and it is possible to attain an internal
quantum yield of 100%.
[0038] Here, from the viewpoint of realizing a higher emission
efficiency, E.sub.S-E.sub.T in the requirement (2) is preferably
0.5 eV or less, more preferably 0.2 eV or less, and even more
preferably 0.1 eV or less. In addition, in the requirement (1), the
difference (E.sub.T1-E.sub.T) between the excited triplet energy
level (E.sub.T1) in emission of the organic component and the
excited triplet energy level (E.sub.T) in emission of the inorganic
component is preferably 0.01 eV or more. The relationship between
the excited singlet energy level (E.sub.S1) in emission of the
organic component and the excited singlet energy level (E.sub.S) in
emission of the inorganic component is preferably
E.sub.S<E.sub.S1, and the difference therebetween
(E.sub.S1-E.sub.S) is preferably 0.01 eV or more.
[0039] The excited singlet energy level (E.sub.S) and the excited
triplet energy level (E.sub.T) in emission of the inorganic
component constituting the organic-inorganic perovskite of the
present invention, the energy difference therebetween
(E.sub.S-E.sub.T), and the excited singlet energy level (E.sub.S1)
and the excited triplet energy level (E.sub.T1) in emission of the
organic component constituting the organic-inorganic perovskite are
measured as follows. Here, the compound to be analyzed in measuring
E.sub.S and E.sub.T thereof is the inorganic component constituting
the organic-inorganic perovskite, and the compound to be analyzed
in measuring E.sub.S1 and E.sub.T1 thereof is the organic cation
constituting the organic-inorganic perovskite.
(1) Excited Singlet Energy Level (E.sub.S) in Emission of Organic
Component and Excited Singlet Energy Level (E.sub.S1) in Emission
of Organic Component
[0040] A solution of an organic-inorganic perovskite, that is, a
compound to be analyzed is applied onto an Si substrate and dried
to form thereon a sample of an organic-inorganic perovskite film
having a thickness of 160 nm. At 30 K, the fluorescence spectrum
with a 337 nm excitation light of the sample is measured. Here,
emission immediately after excitation light incidence up to 100
nanoseconds after the light incidence is integrated to plot a
fluorescence spectrum on a graph where the vertical axis indicates
emission intensity and the horizontal axis indicates wavelength. A
tangent line is drawn to the rising on the short wavelength side of
the fluorescence spectrum, and a wavelength value .lamda.edge [nm]
at the intersection between the tangent line and the horizontal
axis is read. The wavelength value is converted into an energy
value according to the following conversion expression to calculate
the excited singlet energy level E.sub.S or E.sub.S1 in
emission.
Conversion Expression: Excited singlet energy level in emission
[eV]=1239.85/.lamda.edge
[0041] For the measurement of the fluorescence spectrum, for
example, a nitrogen laser (Lasertechnik Berlin's MNL200) can be
used as an excitation light source and a streak camera (Hamamatsu
Photonics' C4334) can be used as a detector.
(2) Excited Triplet Energy Level (E.sub.T) in Emission of Inorganic
Component and Excited Triplet Energy Level (E.sub.T1) in Emission
of Inorganic Component
[0042] The same sample as that for measurement of the excited
singlet energy level in emission is cooled to 30 K, and the sample
is irradiated with a 337 nm excitation light, and using a streak
camera, the phosphorescence intensity from the sample is measured.
The emission from 1 millisecond after irradiation with the
excitation light to 20 milliseconds after the irradiation is
integrated to plot a phosphorescence spectrum on a graph where the
vertical axis indicates emission intensity and the horizontal axis
indicates wavelength. A tangent line is drawn to the rising on the
short wavelength side of the phosphorescence spectrum, and a
wavelength value .lamda.edge [nm] at the intersection between the
tangent line and the horizontal axis is read. The wavelength value
is converted into an energy value according to the following
conversion expression to calculate the excited triplet energy level
E.sub.T or E.sub.T1 in emission.
Conversion Expression: Excited triplet energy level in emission
[eV]=1239.85/.lamda.edge
[0043] The tangent line to the rising of the phosphorescence
spectrum on the short wavelength side is drawn as follows. While
moving on the spectral curve from the short wavelength side of the
phosphorescence spectrum toward the maximum value on the shortest
wavelength side among the maximum values of the spectrum, a tangent
line at each point on the curve toward the long wavelength side is
taken into consideration. With rising thereof (that is, with
increase in the vertical axis), the inclination of the tangent line
increases. The tangent line drawn at the point at which the
inclination value has a maximum value is referred to as the tangent
line to the rising on the short wavelength side of the
phosphorescence spectrum.
[0044] The maximum point having a peak intensity of 10% or less of
the maximum peak intensity of the spectrum is not included in the
maximum value on the above-mentioned shortest wavelength side, and
the tangent line drawn at the point which is closest to the maximum
value on the shortest wavelength side and at which the inclination
value has a maximum value is referred to as the tangent line to the
rising on the short wavelength side of the phosphorescence
spectrum.
(3) Difference (E.sub.S-E.sub.T) Between Excited Singlet Energy
Level (E.sub.S) and the Excited Triplet Energy Level (E.sub.T) in
Emission of Inorganic Component
[0045] (E.sub.S-E.sub.T) can be determined by subtracting the
measured value of the excited triplet energy level (E.sub.T) in
emission according to the method (2) from the measured value of the
excited singlet energy level (E.sub.S) in emission according to the
method (1).
[0046] The organic-inorganic perovskite of the present invention is
an ion compound containing at least an organic cation, a divalent
metal ion and a halide ion, and may additionally contain any other
ion such as a monovalent cation. The other ion may be an organic
ion or an inorganic ion. The organic-inorganic perovskite of the
present invention contains an inorganic semiconductor layer and an
organic component, and may be any of a two-dimensional perovskite,
a quasi-two-dimensional perovskite or a three-dimensional
perovskite, but a two-dimensional perovskite and a
quasi-two-dimensional perovskite are preferred, and a
quasi-two-dimensional perovskite is more preferred. Here, a
two-dimensional perovskite has an inorganic semiconductor layer
such that the inorganic skeleton corresponding to the octahedral
part of a perovskite-type structure is formed in two-dimensional
alignment, and an organic layer such that the cationic group of an
organic cation is aligned facing the inorganic semiconductor layer
side, and a quasi-two-dimensional perovskite has layers
corresponding to the inorganic semiconductor layer and the organic
layer of the two-dimensional perovskite in which, however, the
inorganic semiconductor layer has two or more layers of a
two-dimensional alignment structure and a monovalent cation is
arranged at the position corresponding to each apex of the cubic
crystal of the perovskite-type structure.
[0047] Preferred examples of the organic-inorganic perovskite are
described below with reference to a quasi-two-dimensional
perovskite.
Quasi-Two-Dimensional Perovskite
[0048] A quasi-two-dimensional perovskite of the organic-inorganic
perovskite of the present invention is preferably a compound
represented by the following formula (10).
R.sub.2A.sub.n-1B.sub.nX.sub.3n+1 (10)
[0049] In the formula (10), R represents a monovalent organic
cation, A represents a monovalent cation, B represents a divalent
metal ion, X represents a halide ion, and n represents an integer
of 2 or more. Two R's, plural B's and plural X's each may be the
same as or different from each other. Plural A's, if any, may be
the same as or different from each other.
[0050] In the compound represented by the formula (10), a crystal
lattice having the composition represented by
A.sub.n-1B.sub.nX.sub.3n+1 constitutes an inorganic semiconductor
layer, and the monovalent organic cation represented by R
constitutes an organic component. n corresponds to the number of
layers having a two-dimensional alignment structure in the
inorganic semiconductor layer, and is preferably an integer of 2 to
100.
[0051] The monovalent organic cation represented by R preferably
has an aromatic ring, more preferably has an alkylene group and an
aromatic ring, even more preferably has a structure of an alkylene
group and an aromatic ring linking to each other, even more
preferably is an ammonium having a structure of an alkylene group
and an aromatic ring linking to each other, and is especially
preferably an ammonium represented by the following formula
(11).
Ar(CH.sub.2).sub.n1NH.sub.3.sup.+ (11)
[0052] In the formula (11), Ar represents an aromatic ring, and n1
represents an integer of 1 to 20.
[0053] The aromatic ring that the organic cation has may be an
aromatic hydrocarbon or an aromatic hetero ring, but is preferably
an aromatic hydrocarbon. The hetero atom of the aromatic hetero
ring includes a nitrogen atom, an oxygen atom and a sulfur atom.
The aromatic hydrocarbon is preferably a benzene ring or a
condensed polycyclic hydrocarbon having a structure of condensed
plural benzene rings, and a benzene ring; a naphthalene ring, a
phenanthrene ring, an anthracene ring, a chrysene ring, a tetracene
ring, and a perylene ring are preferred, a benzene ring, and a
naphthalene ring are more preferred, and a benzene ring is even
more preferred. The aromatic hetero ring is preferably a pyridine
ring, a pyrazine ring, a pyrimidine ring, a pyridazine ring, a
pyrrole ring, a thiophene ring, a furan ring, a carbazole ring, or
a triazine ring; and a pyridine ring, a pyrazine ring, a pyrimidine
ring, and a pyridazine ring are more preferred, and a pyridine ring
is even more preferred. The aromatic ring that the organic cation
has may have a substituent such as, for example, an alkyl group, an
aryl group or a halogen atom (preferably a fluorine atom). The
hydrogen atom existing in the aromatic ring or in the substituent
bonding to the aromatic ring may be a deuterium atom.
[0054] The monovalent cation represented by A may be an organic
cation or an inorganic cation. The monovalent cation includes a
formamidinium, an ammonium and a cesium, and is preferably a
formamidinium.
[0055] The divalent metal ion represented by B includes Cu.sup.2+,
Ni.sup.2+, Mn.sup.2+, Fe.sup.2+, Co.sup.2+, Pd.sup.2+, Ge.sup.2+,
Sn.sup.2+, Pb.sup.2+, and Eu.sup.2+; and Sn.sup.2+, and Pb.sup.2+
are preferred, and Pb.sup.2+ is more preferred.
[0056] The halide ion represented by X includes ions of fluorine,
chlorine, bromine and iodine. The halide ions represented by plural
X's may be all the same, or may be a combination of 2 or 3 kinds of
halide ions. Preferably, plural X's are the same halide ions, and
more preferably plural X's are all bromide ions.
[0057] Preferred examples of the compound represented by the
formula (10) include compounds represented by the following formula
(A) and compounds represented by the following formula (B).
However, the organic-inorganic perovskite of the present invention
is not limitatively interpreted by these examples.
PEA.sub.2FA.sub.n-1Pb.sub.nBr.sub.3n+1 (A)
PEA.sub.2MA.sub.n-1Pb.sub.nBr.sub.3n+1 (B)
[0058] In the formulae (A) and (B), PEA represents a
phenylethylammonium, FA represents a formamidinium, MA represents a
methylammonium, and n is an integer of 2 or more.
[0059] The compounds represented by the formulae (A) and (B) are
novel compounds. For a method for synthesizing the compounds,
reference may be made to the description in the section of [Film
Formation Method] and (Example 1) to be given hereinunder.
Film
[0060] Next, the film of the present invention is described. The
film of the present invention contains the organic-inorganic
perovskite of the present invention. For the description, the
preferred range and the specific examples of the organic-inorganic
perovskite, reference may be made to the corresponding description
in the section of <Organic-Inorganic Perovskite>. As
described above, the organic-inorganic perovskite of the present
invention satisfies the requirements (1) and (2) and therefore can
secure a high emission efficiency. Consequently, the film of the
present invention can be effectively used as a light-emitting film.
In particular, as satisfying the requirement (2),
E.sub.S-E.sub.T.ltoreq.0.1 eV, the organic-inorganic perovskite of
the present invention can readily undergo reverse intersystem
crossing from an excited triplet state to an excited singlet state
in the organic component therein. Consequently, the
organic-inorganic perovskite can emit light through both radiation
deactivation from the excited singlet state derived from the
singlet exciton directly formed in the inorganic component by
excitation light irradiation or current injection, and radiation
deactivation from the excited singlet state derived from the
singlet exciton formed via reverse intersystem crossing. At that
time, the radiation deactivation from the excited singlet state
derived from the singlet exciton formed via reverse intersystem
crossing is later than the radiation deactivation from the excited
singlet state derived from the singlet exciton directly formed by
current injection, and therefore the resultant light emission is
observed as delayed fluorescence emission having a long emission
lifetime. Accordingly, the film of the present invention can also
be effectively used as a delayed fluorescence emitting film. The
delayed fluorescence emitting film can be confirmed by the
transient decay curve of emission at 300 K, in which both a
fluorescent component having a short emission lifetime and a
fluorescent component having a long emission lifetime (delayed
fluorescent component) are seen.
Film Formation Method
[0061] The method for forming the film of the present invention is
not specifically limited, and may be a dry process such as a vacuum
evaporation method, or a wet process such as a solution coating
method. Here, a solution coating method is advantageous in that
film formation can be attained using a simple apparatus and for a
short period of time, and production cost can be reduced and
mass-production is easy. A vacuum evaporation method is
advantageous in that a film having a better surface condition can
be formed.
[0062] For example, for forming a film containing an
organic-inorganic perovskite represented by
PEA.sub.2FA.sub.n-1Pb.sub.nBr.sub.3n+1 according to a vacuum
evaporation method, employable is a co-evaporation method of
co-evaporating lead bromide (PbBr.sub.2), phenylethylammonium
bromide (PEABr) and formamidinium bromide (FABr) from different
evaporation sources. Films containing any other type of
organic-inorganic perovskite can also be formed according to the
method by co-evaporating a metal halide compound, a compound of a
monovalent organic cation and a halide ion and a compound of any
other monovalent cation and a halide ion.
[0063] For forming a film containing an organic-inorganic
perovskite represented by PEA.sub.2FA.sub.n-1Pb.sub.nBr.sub.3n+1
according to a solution coating method, lead bromide (PbBr.sub.2),
phenylethylammonium bromide (PEABr) and formamidinium bromide
(FABr) are reacted in a solvent to prepare an organic-inorganic
perovskite or a precursor thereof, and a coating liquid containing
the organic-inorganic perovskite is applied onto the surface of
support and dried to form a film thereon. Films containing any
other perovskite compound represented by the formula and an organic
light-emitting material can also be formed according to the method
by synthesizing an organic-inorganic perovskite in a solvent, then
applying a coating liquid that contains the organic-inorganic
perovskite and an organic light-emitting material onto the surface
of a support and drying the liquid thereon. If desired, coating
with the coating liquid may be followed by baking treatment.
[0064] The coating method with a coating liquid is not specifically
limited, and any conventionally-known coating method is employable,
such as a gravure coating method, a bar coating method, a printing
method, a spraying method, a spin coating method, a dipping method,
or a die coating method. A spin coating method is preferred since a
relatively thin coating film can be formed uniformly.
[0065] Not specifically limited, the solvent for the coating liquid
may be any one capable of dissolving a perovskite compound.
Specifically, examples thereof include esters (e.g., methyl
formate, ethyl formate, propyl formate, pentyl formate, methyl
acetate, ethyl acetate, pentyl acetate), ketones (e.g.,
.gamma.-butyrolactone, N-methyl-2-pyrrolidone, acetone, dimethyl
ketone, diisobutyl ketone, cyclopentanone, cyclohexanone,
methylcyclohexanone), ethers (e.g., diethyl ether,
methyl-tert-butyl ether, diisopropyl ether, dimethoxymethane,
dimethoxyethane, 1,4-dioxane, 1,3-dioxolan, 4-methyldioxolan,
tetrahydrofuran, methyltetrahydrofuran, anisole, phenetole),
alcohols (e.g., methanol, ethanol, 1-propanol, 2-propanol,
1-butanol, 2-butanol, tert-butanol, 1-pentanol, 2-methyl-2-butanol,
methoxypropanol, diacetone alcohol, cyclohexanol, 2-fluoroethanol,
2,2,2-trifluoroethanol, 2,2,3,3-tetrafluoro-1-propanol), glycol
ether (cellosolves) (e.g., ethylene glycol monomethyl ether,
ethylene glycol monoethyl ether, ethylene glycol monobutyl ether,
ethylene glycol monoethyl ether acetate, triethylene glycol
dimethyl ether), amide solvents (e.g., N,N-dimethylformamide,
acetamide, N,N-dimethylacetamide), nitrile solvents (e.g.,
acetonitrile, isobutyronitrile, propionitrile,
methoxyacetonitrile), carbonate solvents (e.g., ethylene carbonate,
propylene carbonate), halogenohydrocarbons (e.g., methylene
chloride, dichloromethane, chloroform), hydrocarbons (e.g.,
n-pentane, cyclohexane, n-hexane, benzene, toluene, xylene), and
dimethyl sulfoxide. In addition, also usable herein are those
having any two or more functional groups of esters, ketones, ethers
and alcohols (i.e., --O--, --CO--, --COO--, --OH), as well as those
derived from esters, ketones, ethers and alcohols by substituting
the hydrogen atom in the hydrocarbon moiety therein with a halogen
atom (especially a fluorine atom).
[0066] The content of the perovskite compound in the coating liquid
is preferably 1 to 50% by mass relative to the total amount of the
coating liquid, more preferably 2 to 30% by mass, even more
preferably 5 to 20% by mass. The content of the organic
light-emitting material in the coating liquid is preferably 0.001%
by mass or more and less than 50% by mass relative to the total
amount of the perovskite compound and the organic light-emitting
material.
[0067] Preferably, the coating liquid applied onto the surface of a
support is dried spontaneously or by heating in an atmosphere
purged with an inert gas such as nitrogen.
Light-Emitting Device
[0068] Next, the light-emitting device of the present invention is
described.
[0069] The light-emitting device of the present invention has a
film containing the organic-inorganic perovskite of the present
invention. For the description, the preferred range and the
specific examples of the film containing the organic-inorganic
perovskite of the present invention, reference may be made to the
description in the section of <Film>. The film of the present
invention that the light-emitting device has may have any function
and, for example, may be a light-emitting layer, or a delayed
fluorescence-emitting layer, or may be used as both a
light-emitting layer and a delayed fluorescence-emitting layer. The
light-emitting device may have only one layer of a film containing
the organic-inorganic perovskite of the present invention, or may
have two or more layers of the film. In the case where the
light-emitting device has two or more layers of a film containing
the organic-inorganic perovskite of the present invention, the
organic-inorganic perovskite that the films contain may be the same
or different.
[0070] As described above, the organic-inorganic perovskite that
the film of the present invention contains has a high emission
efficiency, and therefore the light-emitting device containing the
film can realize a high emission efficiency. In particular, the
light-emitting device that emits delayed fluorescence at 300 K can
secure an extremely high emission efficiency at room temperature.
In addition, the organic-inorganic perovskite is inexpensive, and
therefore using the film containing the perovskite, the material
cost for the light-emitting device can be reduced.
Layer Configuration of Light-Emitting Device
[0071] The light-emitting device to which the present invention is
applied may be a photoluminescent device (also expressed as a PL
device) or may also be an electroluminescent device (also expressed
as an EL device, and in the present invention, it is a perovskite
electroluminescent device). The photoluminescent device has a
structure having at least a light-emitting layer formed on a
substrate. The electroluminescent device includes at least an
anode, a cathode, and a light-emitting layer between the anode and
the cathode. The film containing the organic-inorganic perovskite
of the present invention can be favorably used as the
light-emitting layer in these light-emitting devices. The film
containing the organic-inorganic perovskite of the present
invention attains an effect that realizes a high emission
efficiency especially when applied to an electroluminescent device
among such light-emitting devices.
[0072] The electroluminescent device includes a light-emitting
layer that contains at least the organic-inorganic perovskite, and
may be formed of such a light-emitting layer alone, or may include
any other one or more organic layers in addition to the
light-emitting layer. Such other organic layers may be selected, if
desired, from among organic layers that constitute an organic
electroluminescent device, including, for example, a hole transport
layer, a hole injection layer, an electron blocking layer, a hole
blocking layer, an electron injection layer, an electron transport
layer, and an exciton blocking layer. The hole transport layer may
be a hole injection transport layer that has a hole injection
function, and the electron transport layer may be an electron
injection transport layer that has an electron injection function.
A configuration example of an electroluminescent device is shown in
FIG. 2. In FIG. 2, 1 is a substrate, 2 is an anode, 3 is a hole
injection layer, 4 is a hole transport layer, 5 is a light-emitting
layer, 6 is an electron transport layer, and 7 is a cathode.
[0073] In the following, the constituent members and the layers of
the electroluminescent device are described. The description of the
substrate and the light-emitting layer given below may apply to the
substrate and the light-emitting layer of a photoluminescent
device.
Substrate
[0074] The electroluminescent device of the invention is preferably
supported by a substrate. The substrate is not particularly limited
and may be those that have been commonly used in an organic
electroluminescent device, and examples thereof used include those
formed of glass, transparent plastics, quartz and silicon.
Anode
[0075] The anode of the electroluminescent device used is
preferably formed of, as an electrode material, a metal, an alloy,
or an electroconductive compound each having a large work function
(4 eV or more), or a mixture thereof. Specific examples of the
electrode material include a metal, such as Au, and an
electroconductive transparent material, such as CuI, indium tin
oxide (ITO), SnO.sub.2 and ZnO. A material that is amorphous and is
capable of forming a transparent electroconductive film, such as
IDIXO (In.sub.2O.sub.3--ZnO), may also be used. The anode may be
formed in such a manner that the electrode material is formed into
a thin film by such a method as vapor deposition or sputtering, and
the film is patterned into a desired pattern by a photolithography
method, or in the case where the pattern may not require high
accuracy (for example, approximately 100 .mu.m or more), the
pattern may be formed with a mask having a desired shape on vapor
deposition or sputtering of the electrode material. In alternative,
in the case where a material capable of being coated, such as an
organic electroconductive compound, is used, a wet film forming
method, such as a printing method and a coating method, may be
used. In the case where emitted light is to be taken out through
the anode, the anode preferably has a transmittance of more than
10%, and the anode preferably has a sheet resistance of several
hundred ohm per square or less. The thickness of the anode may be
generally selected from a range of from 10 to 1,000 nm, and
preferably from 10 to 200 nm, while depending on the material
used.
Cathode
[0076] The cathode is preferably formed of as an electrode material
a metal (which is referred to as an electron injection metal), an
alloy, or an electroconductive compound, having a small work
function (4 eV or less), or a mixture thereof. Specific examples of
the electrode material include sodium, a sodium-potassium alloy,
magnesium, lithium, a magnesium-cupper mixture, a magnesium-silver
mixture, a magnesium-aluminum mixture, a magnesium-indium mixture,
an aluminum-aluminum oxide (Al.sub.2O.sub.3) mixture, indium, a
lithium-aluminum mixture, and a rare earth metal. Among these, a
mixture of an electron injection metal and a second metal that is a
stable metal having a larger work function than the electron
injection metal, for example, a magnesium-silver mixture, a
magnesium-aluminum mixture, a magnesium-indium mixture, an
aluminum-aluminum oxide (Al.sub.2O.sub.3) mixture, a
lithium-aluminum mixture, and aluminum, is preferred from the
standpoint of the electron injection property and the durability
against oxidation and the like. The cathode may be produced by
forming the electrode material into a thin film by such a method as
vapor deposition or sputtering. The cathode preferably has a sheet
resistance of several hundred ohm per square or less, and the
thickness thereof may be generally selected from a range of from 10
nm to 5 .mu.m, and preferably from 50 to 200 nm. For transmitting
the emitted light, any one of the anode and the cathode of the
electroluminescent device is preferably transparent or translucent,
thereby enhancing the light emission luminance
[0077] The cathode may be formed with the electroconductive
transparent materials described for the anode, thereby forming a
transparent or translucent cathode, and by applying the cathode, a
device having an anode and a cathode, both of which have
transmittance, may be produced.
Light-Emitting Layer
[0078] The light-emitting layer is a layer in which holes and
electrons injected from an anode and a cathode are recombined to
give excitons for light emission, and the layer is formed of a film
(light-emitting film) containing the organic-inorganic perovskite
of the present invention.
[0079] The light-emitting film for use for the light-emitting layer
of the electroluminescent device preferably has a thickness of 20
to 500 nm, more preferably 50 to 300 nm.
Injection Layer
[0080] The injection layer is a layer that is provided between the
electrode and the organic layer, for decreasing the driving voltage
and enhancing the light emission luminance, and includes a hole
injection layer and an electron injection layer, which may be
provided between the anode and the light-emitting layer or the hole
transport layer and between the cathode and the light emitting
layer or the electron transport layer. The injection layer may be
provided depending on necessity.
Blocking Layer
[0081] The blocking layer is a layer that is capable of inhibiting
charges (electrons or holes) and/or excitons present in the
light-emitting layer from being diffused outside the light-emitting
layer. The electron blocking layer may be disposed between the
light-emitting layer and the hole transport layer, and inhibits
electrons from passing through the light-emitting layer toward the
hole transport layer. Similarly, the hole blocking layer may be
disposed between the light-emitting layer and the electron
transport layer, and inhibits holes from passing through the
light-emitting layer toward the electron transport layer. The
blocking layer may also be used for inhibiting excitons from being
diffused outside the light-emitting layer. Thus, the electron
blocking layer and the hole blocking layer each may also have a
function as an exciton blocking layer. The term "the electron
blocking layer" or "the exciton blocking layer" referred to herein
is intended to include a layer that has both the functions of an
electron blocking layer and an exciton blocking layer by one
layer.
Hole Blocking Layer
[0082] The hole blocking layer has the function of an electron
transport layer in a broad sense. The hole blocking layer has a
function of inhibiting holes from reaching the electron transport
layer while transporting electrons, and thereby enhances the
recombination probability of electrons and holes in the
light-emitting layer. As the material for the hole blocking layer,
the material for the electron transport layer to be mentioned below
may be used optionally.
Electron Blocking Layer
[0083] The electron blocking layer has the function of transporting
holes in a broad sense. The electron blocking layer has a function
of inhibiting electrons from reaching the hole transport layer
while transporting holes, and thereby enhances the recombination
probability of electrons and holes in the light-emitting layer.
Exciton Blocking Layer
[0084] The exciton blocking layer is a layer for inhibiting
excitons generated through recombination of holes and electrons in
the light-emitting layer from being diffused to the charge
transporting layer, and the use of the layer inserted enables
effective confinement of excitons in the light-emitting layer, and
thereby enhances the light emission efficiency of the device. The
exciton blocking layer may be inserted adjacent to the
light-emitting layer on any of the side of the anode and the side
of the cathode, and on both the sides. Specifically, in the case
where the exciton blocking layer is present on the side of the
anode, the layer may be inserted between the hole transport layer
and the light-emitting layer and adjacent to the light-emitting
layer, and in the case where the layer is inserted on the side of
the cathode, the layer may be inserted between the light-emitting
layer and the cathode and adjacent to the light-emitting layer.
Between the anode and the exciton blocking layer that is adjacent
to the light-emitting layer on the side of the anode, a hole
injection layer, an electron blocking layer and the like may be
provided, and between the cathode and the exciton blocking layer
that is adjacent to the light-emitting layer on the side of the
cathode, an electron injection layer, an electron transport layer,
a hole blocking layer and the like may be provided. In the case
where the blocking layer is provided, preferably, at least one of
the excited singlet energy and the excited triplet energy of the
material used as the blocking layer is higher than the excited
singlet energy and the excited triplet energy of the light-emitting
layer, respectively, of the light-emitting material.
Hole Transport Layer
[0085] The hole transport layer is formed of a hole transport
material having a function of transporting holes, and the hole
transport layer may be provided as a single layer or plural
layers.
[0086] The hole transport material has one of injection or
transporting property of holes and blocking property of electrons,
and may be any of an organic material and an inorganic material.
Examples of known hole transport materials that may be used herein
include a triazole derivative, an oxadiazole derivative, an
imidazole derivative, a carbazole derivative, an indolocarbazole
derivative, a polyarylalkane derivative, a pyrazoline derivative, a
pyrazolone derivative, a phenylenediamine derivative, an arylamine
derivative, an amino-substituted chalcone derivative, an oxazole
derivative, a styrylanthracene derivative, a fluorenone derivative,
a hydrazone derivative, a stilbene derivative, a silazane
derivative, an aniline copolymer and an electroconductive polymer
oligomer, particularly a thiophene oligomer. Among these, a
porphyrin compound, an aromatic tertiary amine compound and a
styrylamine compound are preferably used, and an aromatic tertiary
amine compound is more preferably used.
Electron Transport Layer
[0087] The electron transport layer is formed of a material having
a function of transporting electrons, and the electron transport
layer may be a single layer or may be formed of plural layers.
[0088] The electron transport material (often also acting as a hole
blocking material) may have a function of transmitting the
electrons injected from a cathode to a light-emitting layer. The
electron transport layer usable here includes, for example,
nitro-substituted fluorene derivatives, diphenylquinone
derivatives, thiopyran dioxide derivatives, carbodiimides,
fluorenylidenemethane derivatives, anthraquinodimethane and
anthrone derivatives, oxadiazole derivatives, etc. Further,
thiadiazole derivatives derived from the above-mentioned oxadiazole
derivatives by substituting the oxygen atom in the oxadiazole ring
with a sulfur atom, and quinoxaline derivatives having a
quinoxaline ring known as an electron-attractive group are also
usable as the electron transport material. Further, polymer
materials prepared by introducing these materials into the polymer
chain, or having these material in the polymer main chain are also
usable.
[0089] The electroluminescent device may use the film containing
the organic-inorganic perovskite of the present invention as any
other layer than the light-emitting layer therein. For example, the
film containing the organic-inorganic perovskite may be used as the
above-mentioned hole transport layer or electron transport layer.
In that case, the organic-inorganic perovskite of the film for use
as the light-emitting layer and the organic-inorganic perovskite of
the film for use as the other layer than the light-emitting layer
may be the same or different.
[0090] In producing the electroluminescent device, the organic
layers constituting the electroluminescent device are sequentially
layered on the support. The film formation method for forming these
layers is not specifically limited, and the layers may be formed
according to any of a dry process or a wet process. For the film
formation method for forming the light-emitting layer, reference
may be made to the contents of the section of [Film Formation
Method] given hereinabove.
[0091] Preferred materials for use for the electroluminescent
device are concretely exemplified below. However, the materials for
use in the present invention are not limitatively interpreted by
the following exemplary compounds. Compounds, even though
exemplified as materials having a specific function, can also be
used as other materials having any other function.
[0092] First, preferred examples of compounds for use as a host
material in the light-emitting layer are mentioned below.
##STR00001## ##STR00002## ##STR00003## ##STR00004## ##STR00005##
##STR00006##
[0093] Next, preferred examples of compounds for use as a hole
injection material are mentioned below.
MoO.sub.x where x is 1.5 to 3.0.
##STR00007## ##STR00008##
[0094] Next, preferred examples of compounds for use as a hole
transport material are mentioned below.
##STR00009## ##STR00010## ##STR00011## ##STR00012## ##STR00013##
##STR00014## ##STR00015## ##STR00016##
[0095] Next, preferred examples of compounds for use as an electron
blocking material are mentioned below.
##STR00017## ##STR00018##
[0096] Next, preferred examples of compounds for use as a hole
blocking material are mentioned below.
##STR00019## ##STR00020## ##STR00021##
[0097] Next, preferred examples of compounds for use as an electron
transport material are mentioned below.
##STR00022## ##STR00023## ##STR00024## ##STR00025##
[0098] Next, preferred examples of compounds for use as an electron
injection material are mentioned below.
##STR00026##
[0099] Further, preferred examples of compounds for use as
additional materials are mentioned below. For example, these are
considered to be added as a stabilization material.
##STR00027##
[0100] The electroluminescent device thus produced by the
aforementioned method emits light on application of an electric
field between the anode and the cathode of the device. In this
case, when the light emission is caused by the excited singlet
energy, light having a wavelength that corresponds to the energy
level thereof may be confirmed as fluorescent light and delayed
fluorescent light. When the light emission is caused by the excited
triplet energy, light having a wavelength that corresponds to the
energy level thereof may be confirmed as phosphorescent light. The
normal fluorescent light has a shorter light emission lifetime than
the delayed fluorescent light, and thus the light emission lifetime
may be distinguished between the fluorescent light and the delayed
fluorescent light.
[0101] On the other hand, the phosphorescent light may
substantially not be observed with the organic-inorganic perovskite
of the present invention at room temperature since the excited
triplet energy is converted to heat or the like due to the
instability thereof. The excited triplet energy of the
organic-inorganic perovskite may be measured by observing light
emission under an extremely low temperature condition.
Production Method for Light-Emitting Device
[0102] The method for producing a light-emitting device of the
present invention is characterized in that an organic-inorganic
perovskite is so planned as to satisfy the following requirements,
and a light-emitting device is produced using the organic-inorganic
perovskite satisfying the following requirements (1) and (2):
E.sub.T<E.sub.T1 (1)
E.sub.S-E.sub.T.ltoreq.0.1 eV (2)
[0103] wherein E.sub.S represents the excited singlet energy level
in emission of an inorganic component constituting the
organic-inorganic perovskite, E.sub.T represents the excited
triplet energy level in emission of an inorganic component
constituting the organic-inorganic perovskite, E.sub.S1 represents
the excited singlet energy level in emission of an organic
component constituting the organic-inorganic perovskite and
E.sub.T1 represents the excited triplet energy level in emission of
an organic component constituting the organic-inorganic
perovskite.
[0104] For the description of the requirements (1) and (2), the
definitions of E.sub.S, E.sub.T, E.sub.S1, and E.sub.T1, and the
measurement methods and the preferred ranges thereof, reference may
be made to the corresponding description on the section of
"Organic-Inorganic Perovskite> given hereinabove; and for the
configuration of the light-emitting device to be produced and the
other step than the planning step for the organic-inorganic
perovskite, reference may be made to the corresponding description
in the section of <Light-Emitting Device>.
[0105] The organic-inorganic perovskite can be planned, for
example, by selecting and combining the ions and the number of n
for R, A, B and X in the formula (10) so as to satisfy the
requirements (1) and (2). As described above, the organic-inorganic
perovskite satisfying the requirements (1) and (2) have a high
emission efficiency, and therefore according to the production
method, a light-emitting device using the organic-inorganic
perovskite having a high emission efficiency can be produced at a
low cost.
[0106] The electroluminescent device of the invention may be
applied to any of a single device, a structure with plural devices
disposed in an array, and a structure having anodes and cathodes
disposed in an X-Y matrix. According to the present invention using
a film containing the organic-inorganic perovskite of the present
invention as a light-emitting layer, a light-emitting device having
a markedly improved light emission efficiency can be obtained. The
light-emitting device such as the electroluminescent device of the
present invention may be applied to a further wide range of
purposes. For example, an electroluminescent display apparatus may
be produced with the electroluminescent device of the invention,
and for the details thereof, reference may be made to S. Tokito, C.
Adachi and H. Murata, "Yuki EL Display" (Organic EL Display)
(Ohmsha, Ltd.). In particular, the electroluminescent device of the
invention may be applied to electroluminescent illumination and
backlight which are highly demanded.
EXAMPLES
[0107] The features of the present invention will be described more
specifically with reference to Examples given below. The materials,
processes, procedures and the like shown below may be appropriately
modified unless they deviate from the substance of the invention.
Accordingly, the scope of the invention is not construed as being
limited to the specific examples shown below. For measurement of
photoabsorption spectra, used was a UV-visible-near IR
spectrophotometer (Lambda 950-PKA, Perkin Elmer); for measurement
of emission spectra, used was a measurement device (Fluoromax-4,
Horiba Jobin, Yvon); for measurement of transient decay curves of
emission, used was a streak camera (C4334, Hamamatsu Photonics);
for X-ray diffraction analysis, used was an X-ray diffractometer
(RINT-2500, Rigaku); for measurement of electroluminescent device
characteristics, used were an external quantum efficiency
measurement device (C9920-12, Hamamatsu Photonics), Source Meter
(2400 series, Keithley Instruments), and a multichannel analyzer
(PMA-12, Hamamatsu Photonics); and for measurement of film
thickness, used was a profile meter (DektakXT, Bruker).
[0108] The organic-inorganic perovskite used in the following
Examples 1 and 2 is PEA.sub.2FA.sub.n-1Pb.sub.nBr.sub.3n+1 (n=8).
Here, PEA represents a phenylethylammonium, and FA represents a
formamidinium. The organic-inorganic perovskite used in the
Comparative Examples 1 and 2 is
NMA.sub.2FA.sub.n-1Pb.sub.nBr.sub.3n+1 (n=8). Here, NMA represents
a 1-naphthylmethylammonium, and FA represents a formamidinium. The
excited singlet energy level E.sub.S and the excited triplet energy
level E.sub.T in emission of the inorganic component constituting
each perovskite and the excited singlet energy level E.sub.S1 and
the excited triplet energy level E.sub.T1 in emission of the
organic component constituting each perovskite are shown in Table
1.
TABLE-US-00001 TABLE 1 Inorganic Component Organic Component
Organic-Inorganic excited singlet energy excited triplet energy
excited singlet energy excited triplet energy Perovskite level in
emission E.sub.S level in emission E.sub.T level in emission
E.sub.S1 level in emission E.sub.T1
PEA.sub.2FA.sub.n-1Pb.sub.nBr.sub.3n+1 (n = 8) 3.01 eV 2.99 eV 4.4
eV 3.3 eV NMA.sub.2MA.sub.n-1Pb.sub.nBr.sub.3n+1 (n = 8) 3.01 eV
2.99 eV 4.1 eV 2.6 eV
(Example 1) Production of Photoluminescent Device Using PEA-FA
Perovskite Film
[0109] In a glove box in a nitrogen atmosphere, a film of
PEA.sub.2FA.sub.n-1Pb.sub.nBr.sub.3n+1 (where n=8) was formed
(hereinafter referred to as "PEA-FA perovskite film"). First, to an
N,N-dimethylformamide solution of formamidinium bromide
(HC(NH.sub.2).sub.2Br) and lead bromide (PbBr.sub.2) dissolved
therein at a molar ratio of 1/1, 25 mol % of phenylethylammonium
bromide (C.sub.6H.sub.5CH.sub.2CH.sub.2NH.sub.3Br) was added to
prepare a precursor solution having a PEA-FA perovskite
concentration of 0.4 M. 50 .mu.L of the PEA-FA perovskite precursor
solution was dropwise applied onto a quartz glass substrate, and
spin-coated at 4500 rpm for 30 seconds to form a PEA-FA perovskite
precursor film. During the spin-coating, 0.3 mL of toluene was
dropwise applied onto the film. Subsequently, the PEA-FA perovskite
precursor film was baked at 70.degree. C. for 15 minutes, and
further baked at 100.degree. C. for 5 minutes to form a PEA-FA
perovskite film having a thickness of 150 nm, thereby providing a
photoluminescent device.
(Comparative Example 1) Production of Photoluminescent Device Using
NMA-FA Perovskite Film
[0110] A photoluminescent device was produced in the same manner as
in Example 1, except that, in forming the perovskite film, a film
of NMA.sub.2FA.sub.n-1Pb.sub.nBr.sub.3+1 was formed (hereinafter
referred to a "NMA-FA perovskite film) using
1-naphthylmethylammonium bromide
(C.sub.10H.sub.7CH.sub.2NH.sub.3Br) in place of phenylethylammonium
bromide.
[0111] Each perovskite formed in Example 1 and Comparative Example
1 was analyzed to measure the X-ray diffraction spectrum thereof,
and was confirmed to have a quasi-2D perovskite crystal
structure.
[0112] FIG. 3 shows photoabsorption spectra measured at 300 K and
emission spectra measured with a 450 nm excitation light of the
perovskite films formed in Example 1 and Comparative Example 1;
FIG. 4 is a graph showing excitation light intensity dependence of
the photoluminescence quantum yield (PLQY) thereof; FIG. 5 shows
transient decay curves of emission thereof with a 337 nm excitation
light, measured at 30 K and 300 K; FIG. 6 shows transient decay
curves of emission with a 337 nm excitation light, measured at 100
K, 200 K and 300 K, of the PEA-EA perovskite film formed in Example
1; FIG. 7 shows transient decay curves of emission with a 337 nm
excitation light, measured at 100 K, 200 K and 300 K, of the NMA-FA
perovskite film formed in Comparative Example 1.
[0113] As in FIG. 3, the PEA-FA perovskite film formed in Example 1
and the NMA-FA perovskite film formed in Comparative Example 1 have
the same absorption characteristic with no absorption peak derived
from low-dimensional perovskite particles, from which it is known
that the two films mostly have a quasi-2D perovskite structure. The
emission maximum wavelength of the PEA-FA perovskite film was 527
nm, that of the NMA-FA perovskite film was 530 nm, the PL quantum
yield of the PEA-FA perovskite film was 64%, and that of the NMA-FA
perovskite film was 60%. Apart from these, the emission spectra of
the films were measured at 30 K, and the full-width at half-maximum
of the emission peak of the PEA-FA perovskite film was 9 nm and
that of the NMA-FA perovskite film was 8 nm. Thus, a sharp emission
peak was observed in these. This indicates that each perovskite
film has few crystal defects and has a high crystallinity.
[0114] In the transient decay curves of emission at 30 K shown in
FIG. 5, no difference is seen between the PEA-FA perovskite film
and the NMA-FA perovskite film, and the emission lifetime of the
films was 120 ns. On the other hand, regarding the transient decay
curves of emission at 300 K, the NMA-FA perovskite film has a decay
pattern not differing from that at 30 K, while the PEA-FA
perovskite film is seen to have a short lifetime component having
an emission lifetime of 155 ns and a long lifetime component having
an emission lifetime of 853 nm. In FIG. 7, no change is seen in the
transient decay curve of emission of the NMA-FA perovskite film
even when the temperature was elevated from 100 K up to 300 K. As
opposed to this, as in FIG. 6, the long lifetime component tends to
gradually increase in the PEA-FA perovskite film with increase in
the temperature from 100 K up to 300 K. Here, the behavior of the
excited triplet energy formed in the inorganic component is
analyzed based on the transient decay curves of emission, and
first, it is considered that the short lifetime emission observed
in the NMA-FA perovskite film may be an emission based on the
excited singlet energy level E.sub.S of the inorganic component.
However, since the excited triplet energy level E.sub.T1 of the
organic component (NMA) is lower than the excited triplet energy
level E.sub.T of the inorganic component, energy transfer occurs
from the excited triplet energy level E.sub.T of the inorganic
component to the excited triplet energy level E.sub.T1 of the
organic component (NMA), and therefore delayed fluorescence of a
long lifetime component cannot be observed. Also in the PEA-FA
perovskite film, it is considered that the short lifetime emission
may be an emission based on the excited singlet energy level
E.sub.S of the inorganic component. Since the excited triplet
energy level E.sub.T1 of the organic component (PEA) is higher than
the excited triplet energy level E.sub.T of the inorganic
component, energy transfer from E.sub.T to E.sub.T1 does not occur.
Namely, the observed emission of the long lifetime component is
presumed to be a thermal activation type delayed fluorescence owing
to radiation deactivation in transfer of the excited singlet energy
to the excited singlet energy level of the organic-inorganic
perovskite through reverse intersystem crossing from the excited
triplet state to the excited singlet state. This process is a
thermal activation process, and therefore the proportion of the
long lifetime component increases with the increase in the sample
temperature. Specifically, from the transient decay curves of
emission in FIGS. 5 and 6, it is known that, when the difference
between the excited singlet energy level E.sub.S and the excited
triplet energy level E.sub.T in emission of the inorganic component
is reduced to make the excited triplet energy level E.sub.T1 of the
organic component (PEA) higher than the excited triplet energy
level E.sub.T of the inorganic component, then reverse intersystem
crossing from the excited triplet state to the excited singlet
state comes to be easier in the inorganic component and the excited
triplet energy can be used as delayed fluorescence.
(Example 2) Production of Electroluminescent Device Using PEA-FA
Perovskite Film
[0115] A glass substrate having, as formed thereon, an anode of
indium tin oxide (ITO) having a thickness of 100 nm (sheet
resistance 12 .OMEGA./sq) was prepared. On the ITO film, PVK was
dropwise applied, spin-coated at 1000 rpm for 45 seconds, and baked
at 120.degree. C. for 30 minutes to form a PVK film having a
thickness of 40 nm.
[0116] Next, in the same manner as in Example 1, a PEA-FA
perovskite precursor solution having a concentration of 0.4 M was
prepared, and using this, a PEA-FA perovskite film having a
thickness of 150 nm was formed.
[0117] Subsequently, on the PEA-FA perovskite film, thin films were
layered at a vacuum degree of 10.sup.-4 Pa according to a vacuum
evaporation method. First, on the PEA-FA perovskite film, TPBi was
formed in a thickness of 40 nm. Next, lithium fluoride (LiF) was
formed in a thickness of 0.8 nm, and then aluminum (Al) was
vapor-deposited in a thickness of 100 nm to form a cathode, and
further a glass substrate was put thereon and sealed up with a
UV-curable resin to produce an electroluminescent device.
(Comparative Example 2) Production of Electroluminescent Device
Using NMA-FA Perovskite Film
[0118] In the same manner as in Example 1, a PVK film was formed on
an ITO film formed on a glass substrate. In the same manner as in
Comparative Example 1, an NMA-FE perovskite film having a thickness
of 150 nm was formed on the PVK film. Subsequently, in the same
manner as in Example 2, TPBi, lithium fluoride and aluminum were
vapor-deposited in sequence on the NMA-FA perovskite film, and on
the aluminum cathode, a glass substrate was put and sealed up with
a UV-curable resin to produce an electroluminescent device.
[0119] FIG. 8 shows emission spectra of the electroluminescent
devices produced in Example 2 and Comparative Example 2; FIG. 9
shows current density-voltage-luminance characteristics thereof;
and FIG. 10 shows current density-voltage-external quantum
efficiency (EQE) characteristics thereof. Table 2 shows the
emission characteristics of the electroluminescent devices. In
FIGS. 9 and 10, "PEA-FA Perovskite Film" shows the
electroluminescent device of Example 2 using a PEA-FA perovskite
film; and "NMA-FA Perovskite Film" shows the electroluminescent
device of Comparative Example 2 using an NMA-FA perovskite
film.
TABLE-US-00002 TABLE 2 Maximum Maximum Emission Full-Width at CIE
External Euminance Current Maximum Half-Maximum of Chromaticity
Quantum Yield (at 6 V) Efficiency Wavelength Emission Peak
Coordinate Perovskite Film (%) (cd/m.sup.2) (cd/A) (nm) (nm) (x, y)
Example 2 PEA-FA Perovskite 12.4 5200 52.1 527 21 (0.18, 0.76) Film
Comparative NMA-FA Perovskite 3.4 500 16.3 531 21 (0.20, 0.75)
Example 2 Film
[0120] Each electroluminescent device was driven, and all the
devices gave green color emission. As in Table 2, the
electroluminescent device using a PEA-FA perovskite film of Example
2 had an external quantum yield nearly 4 times higher than that of
the electroluminescent device using an NMA-FA perovskite film of
Comparative Example 2, and the former was excellent also in
luminance and current efficiency. Regarding the exciton forming
factor .beta. presumed from the external quantum efficiency, the
factor of the electroluminescent device of Example 2 was 97%, and
that of the electroluminescent device of Comparative Example 2 was
27%. The data suggest that in the electroluminescent device using a
PEA-FA perovskite film, both the singlet excitons and the triplet
excitons were converted into photons, but in the electroluminescent
device using an NMA-FA perovskite film, only a part of the singlet
excitons were converted into photons.
(Example 3) Production of Electroluminescent Device Using PEA-MA
Perovskite Film
[0121] A PEA-MA perovskite precursor solution was prepared in the
same manner as in Example 1 except that an equimolar amount of
methylammonium bromide (CH.sub.3NH.sub.3Br) was used in place of
phenylethylammonium bromide
(C.sub.6H.sub.5CH.sub.2CH.sub.2NH.sub.3Br) in Example 1. Then in
the same manner as in Example 2 except that the PEA-MA perovskite
precursor solution was used in place of the PEA-FA perovskite
precursor solution in Example 2, an electroluminescent device using
a PEA-MA perovskite film was produced.
(Comparative Example 3) Production of Electroluminescent Device
Using NMA-MA Perovskite Film
[0122] An NMA-MA perovskite precursor solution was prepared in the
same manner as in Comparative Example 1 except that an equimolar
amount of methylammonium bromide (CH.sub.3NH.sub.3Br) was used in
place of phenylethylammonium bromide
(C.sub.6H.sub.5CH.sub.2CH.sub.2NH.sub.3Br) in Comparative Example
1. Then in the same manner as in Comparative Example 2 except that
the NMA-MA perovskite precursor solution was used in place of the
NMA-FA perovskite precursor solution in Comparative Example 2, an
electroluminescent device using an NMA-MA perovskite film was
produced.
[0123] Each electroluminescent device produced in Example 3 and
Comparative Example 3 was driven, and all the devices gave green
color emission, and delayed fluorescence emission was confirmed in
these. FIG. 11 shows current density-voltage-lamp efficiency,
luminance, external quantum efficiency (EQE) characteristics of the
electroluminescent device produced in Example 3; and FIG. 12 shows
current density-voltage-lamp efficiency, luminance, external
quantum efficiency (EQE) characteristics of the electroluminescent
device produced in Comparative Example 3. Table 3 shows emission
characteristics of the electroluminescence devices. The
electroluminescent device using a PEA-MA perovskite film of Example
3 had an external quantum yield nearly 9 times higher than that of
the electroluminescent device using an NMA-MA perovskite film of
Comparative Example 3, and the former was excellent also in
luminance and current efficiency.
TABLE-US-00003 TABLE 3 Maximum Maximum Emission Full-Width at CIE
External Luminance Current Maximum Half-Maximum of Chromaticity
Quantum Yield (at 6 V) Efficiency Wavelength Emission Peak
Coordinate Perovskite Film (%) (cd/m.sup.2) (cd/A) (nm) (nm) (x, y)
Example 3 PEA-MA Perovskite 4.88 1545 15.2 528 20 (0.15, 0.77) Film
Comparative NMA-MA Perovskite 0.55 8 1.96 522 21 (0.13, 0.76)
Example 3 Film
[0124] From the above, it is known that, using an organic-inorganic
perovskite film in which the difference between the excited singlet
energy level E.sub.S and the excited triplet energy level E.sub.T
in emission of the inorganic component is small (not more than 0.1
eV) and in which the excited triplet energy level E.sub.T1 of the
organic component (PEA) is higher than the excited triplet energy
level E.sub.T of the inorganic component, both the singlet excitons
and the triplet excitons are utilized for light emission, and
accordingly, an electroluminescent device having an extremely high
emission efficiency can be realized.
##STR00028##
INDUSTRIAL APPLICABILITY
[0125] The organic-inorganic perovskite of the present invention
has a high emission efficiency and is inexpensive. Accordingly,
using the organic-inorganic perovskite of the present invention as
a light-emitting film of a light-emitting device, an inexpensive
light-emitting device having a high emission efficiency can be
provided. Consequently, the industrial applicability of the present
invention is great.
REFERENCE SIGNS LIST
[0126] 1 Substrate
[0127] 2 Anode
[0128] 3 Hole Injection Layer
[0129] 4 Hole Transport Layer
[0130] 5 Light-Emitting Layer
[0131] 6 Electron Transport Layer
[0132] 7 Cathode
* * * * *