CN110492009B

CN110492009B - Electroluminescent device based on exciplex system matched with boron-containing organic compound

Info

Publication number: CN110492009B
Application number: CN201810457084.XA
Authority: CN
Inventors: 叶中华; 李崇; 张兆超
Original assignee: Jiangsu Sunera Technology Co Ltd
Current assignee: Jiangsu Sunera Technology Co Ltd
Priority date: 2018-05-14
Filing date: 2018-05-14
Publication date: 2020-11-10
Anticipated expiration: 2038-05-14
Also published as: CN110492009A; WO2019218969A1

Abstract

The invention relates to an electroluminescent device based on an exciplex system and matched with a boron-containing organic compound, wherein a host material comprises a first organic compound and a second organic compound, the difference between the HOMO energy level of the first organic compound and the HOMO energy level of the second organic compound is more than 0.2eV, and the difference between the LUMO energy level of the first organic compound and the LUMO energy level of the second organic compound is more than 0.2 eV. The mixture or interface formed by the two generates exciplex under the excitation of light or electric field. The singlet state energy level of the exciplex is higher than that of the guest material, and the triplet state energy level is higher than that of the guest material; the first organic compound and the second organic compound have different carrier transport characteristics; the guest material is an organic compound containing a boron atom. The organic electroluminescent device prepared by the method has the characteristics of high efficiency and long service life.

Description

Electroluminescent device based on exciplex system matched with boron-containing organic compound

Technical Field

The invention relates to the technical field of semiconductors, in particular to an organic electroluminescent device with high efficiency and long service life,

Background

Organic electroluminescent diodes (OLEDs) have been actively researched and developed. The simplest basic structure of an organic electroluminescent device comprises a light-emitting layer sandwiched between opposing cathodes and anodes. The organic electroluminescent device is considered to be a next-generation flat panel display material and receives much attention because it can realize ultra-thin and ultra-light weight, has a fast response speed to an input signal, and can realize low-voltage dc driving.

The organic electroluminescent device is generally considered to have the following light emission mechanism: when a voltage is applied between electrodes sandwiching a light-emitting layer, electrons injected from an anode and holes injected from a cathode are recombined in the light-emitting layer to form excitons, and the excitons relax to a ground state to release energy to form photons. In an organic electroluminescent device, a light-emitting layer generally requires a host material doped with a guest material to obtain higher energy transfer efficiency, and the light-emitting potential of the guest material is fully exerted. In order to obtain higher host-guest energy transfer efficiency, the collocation of host-guest materials and the balance degree of electrons and holes in the host materials are key factors for obtaining high-efficiency devices. The carrier mobility of electrons and holes in the existing main body material often has large difference, so that an exciton recombination region deviates from a light emitting layer, and the existing device has low efficiency and poor stability.

The use of Organic Light Emitting Diodes (OLEDs) for large area flat panel displays and lighting has attracted considerable attention in the industry and academia. However, the conventional organic fluorescent material can emit light only by using 25% singlet excitons formed by electric excitation, and the internal quantum efficiency of the device is low (up to 25%). External quantum efficiencies are generally below 5%, and are far from the efficiencies of phosphorescent devices. Although the phosphorescence material enhances the intersystem crossing due to the strong spin-orbit coupling of the heavy atom center, the singlet excitons and the triplet excitons formed by the effective electric excitation can emit light, so that the internal quantum efficiency of the device reaches 100%, the phosphorescence material has the problems of high price, poor material stability, serious device efficiency roll-off and the like, and the application of the phosphorescence material in OLEDs is limited.

A Thermally Activated Delayed Fluorescence (TADF) material is a third generation organic light emitting material that has been developed following organic fluorescent materials and organic phosphorescent materials. Such materials generally have a small singlet-triplet energy level difference (Δ EST), and triplet excitons can be converted into singlet excitons for emission by intersystem crossing. This can make full use of singlet excitons and triplet excitons formed under electrical excitation, and the internal quantum efficiency of the device can reach 100%. Meanwhile, the material has controllable structure, stable property, low price and no need of precious metal, and has wide application prospect in the field of OLEDs.

Although TADF materials can theoretically achieve 100% exciton utilization, there are actually the following problems: (1) the T1 and S1 states of the designed molecule have strong CT characteristics, and a very small energy gap of S1-T1 state can realize high conversion rate of T1 → S1 state excitons through a TADF process, but simultaneously lead to low radiation transition rate of S1 state, so that the high exciton utilization rate and the high fluorescence radiation efficiency are difficult to realize at the same time;

(2) due to the fact that the TADF material adopting the D-A, D-A-D or A-D-A structure has large molecular flexibility, the configuration of molecules in a ground state and an excited state is changed greatly, the half-peak width (FWHM) of a spectrum of the material is too large, and the color purity of the material is reduced;

(3) even though doped devices have been employed to mitigate the T exciton concentration quenching effect, most devices of TADF materials suffer from severe roll-off in efficiency at high current densities.

(4) In a traditional host-guest collocation mode, due to the fact that the electron and hole transmission rates of a host material are different, the carrier recombination rate is reduced, and the device efficiency is reduced; meanwhile, the carrier compound region is close to one side of the main body material, so that the carrier compound region is too concentrated, the density of triplet state base carriers is too concentrated, the carrier quenching phenomenon is obvious, and the efficiency and the service life of the device are reduced.

In order to improve the efficiency and stability of the organic electroluminescent device, the improvement of the device structure and the development of materials are necessary to meet the requirements of panel enterprises and lighting enterprises in the future.

Disclosure of Invention

In view of the above problems in the prior art, the present application provides a high efficiency organic electroluminescent device. On one hand, the charge carriers in the device can be effectively balanced, and the exciton quenching effect is reduced; the other side can effectively improve and reduce the FWHM of the spectrum; the efficiency, the service life and the color purity of the organic light-emitting device are effectively improved.

The technical scheme of the invention is as follows:

the present applicant provides an organic electroluminescent device comprising a cathode, an anode, and a light-emitting layer located between the cathode and the anode; the light emitting layer includes: a host material and a guest material; a hole transport region is arranged between the anode and the light-emitting layer, and an electron transport region is arranged between the cathode and the light-emitting layer;

the host material includes a first organic compound and a second organic compound, a difference between a HOMO level of the first organic compound and a HOMO level of the second organic compound is 0.2eV or more, and a difference between a LUMO level of the first organic compound and a LUMO level of the second organic compound is 0.2eV or more;

a mixture or an interface formed by the first organic compound and the second organic compound generates an exciplex under the condition of optical excitation or electric field excitation; the emission spectrum of the exciplex formed and the absorption spectrum of the guest material have overlap; the singlet state energy level of the formed exciplex is higher than that of the guest material, and the triplet state energy level is higher than that of the guest material; and the first organic compound and the second organic compound have different carrier transport characteristics.

The guest material is an organic compound containing boron atoms, the singlet state energy level of the guest material is lower than that of the exciplex, and the triplet state energy level of the guest material is lower than that of the exciplex.

Preferably, | HOMO_{A second organic compound}The first organic compound of | - | HOMO | > is not less than 0.3 eV; l LUMO_{A second organic compound}The first organic compound | is | - | LUMO | > 0.3 eV; where | HOMO | and | LUMO | are expressed as absolute values of the energy levels of the compound.

Preferably, 0.3 eV. ltoreq. HOMO_{A second organic compound}The first organic compound I-HOMO is less than or equal to 0.8 eV; LUMO less than or equal to 0.4eV_{A second organic compound}The first organic compound I-LUMO is less than or equal to 0.8 eV.

Preferably, the difference between the triplet level and the singlet level of the exciplex formed from the first organic compound and the second organic compound is 0.2eV or less; the exciton energy is transferred from the exciplex to the guest material, which eventually causes the guest material to emit light.

Preferably, the first organic compound and the second organic compound form a mixture according to a mass ratio of 1:99 to 99:1, and an exciplex is generated under the condition of optical excitation or electric field excitation.

Preferably, the first organic compound and the second organic compound form a stacked structure having an interface, the first organic compound is located on a hole transporting side, and the second organic compound is located on an electron transporting side, and the exciplex is generated by light excitation or electric field excitation.

Preferably, the mass fraction of the first organic compound is 10% to 90% of the host material, and the mass fraction of the guest material in the light-emitting layer is 1% to 5% or 5% to 30% of the host material.

Preferably, the host material in the light-emitting layer is an interface formed by a first organic compound and a second organic compound, the guest material is doped in the first organic compound, and the mass fraction of the guest material in the light-emitting layer is 1% -5% of the host material; or the host material in the light-emitting layer is an interface formed by the first organic compound and the second organic compound, the guest material is doped in the second organic compound, and the mass fraction of the guest material in the light-emitting layer is 1-5% of that of the host material.

Preferably, the host material in the light-emitting layer is an interface formed by a first organic compound and a second organic compound, the guest material is doped in the first organic compound, and the mass fraction of the guest material in the light-emitting layer is 5% -30% of the host material; or the host material in the light-emitting layer is an interface formed by the first organic compound and the second organic compound, the guest material is doped in the second organic compound, and the mass fraction of the guest material in the light-emitting layer is 5-30% of that of the host material.

Preferably, the first organic compound has a hole mobility greater than an electron mobility, and the second organic compound has an electron mobility greater than a hole mobility; and the first organic compound is a hole transporting type material and the second organic compound is an electron transporting type material.

Preferably, the light-emitting peak wavelength of the guest material is 400-500nm, or 500-560nm, or 560-780 nm.

Preferably, the difference between the singlet and triplet energy levels of the guest material is 0.3eV or less.

Preferably, the number of boron atoms in the guest material is greater than or equal to 1, and the boron atoms are bonded with other elements in an sp2 hybrid orbital mode; the group connected with the boron is one of a hydrogen atom, a substituted or unsubstituted C1-C6 straight-chain alkyl group, a substituted or unsubstituted C3-C10 cycloalkyl group, a substituted or unsubstituted C1-C10 heterocycloalkyl group, a substituted or unsubstituted C6-C60 aryl group and a substituted or unsubstituted C3-C60 heteroaryl group; and the groups connected with the boron atoms can be independently connected, or can be directly bonded with each other to form a ring or connected with the boron through other groups to form a ring.

Preferably, the guest material contains a number of boron atoms of 1, 2, or 3.

Preferably, the guest material has a structure represented by the following general formula (1):

wherein X₁、X₂、X₃Each independently represents a nitrogen atom or a boron atom, X₁、X₂、X₃At least one atom of the boron atoms is a boron atom; z, which is the same or different at each occurrence, is represented by N or c (r);

a. b, c, d, e each independently represent 0, 1, 2, 3 or 4;

C₁and C₂，C₃And C₄，C₅And C₆，C₇And C₈，C₉And C₁₀Wherein at least one pair of carbon atoms can be connected to form a 5-7 membered ring structure;

r, which is identical or different at each occurrence, is represented by H, D, F, Cl, Br, I, C (═ O) R¹，CN，Si(R¹)₃，P(＝O)(R¹)₂，S(＝O)₂R¹A linear alkyl or alkoxy radical having C1 to C20, or a branched or cyclic alkyl or alkoxy radical having C3 to C20, or an alkenyl or alkynyl radical having C2 to C20, where the abovementioned radicals may each be substituted by one or more radicals R¹And wherein one or more CH2 groups of the above groups may be replaced by-R¹C＝CR¹-、-C≡C-、Si(R¹)₂、C(＝O)、C＝NR¹、-C(＝O)O-、C(＝O)NR¹-、NR¹、P(＝O)(R¹) O-, -S-, SO or SO2, and in which one or more H atoms in the abovementioned radicals may be replaced by D, F, Cl, Br, I or CN, or an aromatic or heteroaromatic ring system having from 5 to 30 aromatic ring atoms which may in each case be replaced by one or more R¹Substituted, or aryloxy or heteroaryl radicals having 5 to 30 aromatic ring atoms, which radicals may be substituted by one or more radicals R¹Substitution, wherein two or more groups R may be linked to each other and may form a ring:

R¹identical or different at each occurrence is represented by H, D, F, Cl, Br, I, C (═ O) R²，CN，Si(R²)₃，P(＝O)(R²)₂，N(R²)S(＝O)₂R²A linear alkyl or alkoxy radical having C1 to C20, or a branched or cyclic alkyl or alkoxy radical having C3 to C20, or an alkenyl or alkynyl radical having C2 to C20, where the abovementioned radicals may each be substituted by one or more radicals R¹And wherein one or more CH2 groups of the above groups may be replaced by-R²C＝CR²-、-C≡C-、Si(R²)₂、C(＝O)、C＝NR²、-C(＝O)O-、C(＝O)NR²-、NR²、P(＝O)(R²) O-, -S-, SO or SO2, and in which one or more H atoms in the abovementioned radicals may be replaced by D, F, Cl, Br, I or CN, or an aromatic or heteroaromatic ring system having from 5 to 30 aromatic ring atoms which may in each case be replaced by one or more R²Substituted, or aryloxy or heteroaryl radicals having 5 to 30 aromatic ring atoms, which radicals may be substituted by one or more radicals R²Substituted, in which two or more radicals R¹May be connected to each other and may form a ring:

R²identical or different at each occurrence of an aliphatic, aromatic or heteroaromatic organic radical which is denoted H, D, F or has C1-C20, where one or more H atoms may also be replaced by D or F; here two or more substituents R2 may be linked to each other and may form a ring;

ra, Rb, Rc, Rd each independently represent a linear or branched C1-C20 alkyl group, a linear or branched C1-C20 alkyl-substituted silane group, a substituted or unsubstituted C5-30 aryl group, a substituted or unsubstituted C5-C30 heteroaryl group, a substituted or unsubstituted C5-C30 arylamine group;

in the case where the Ra, Rb, Rc, Rd groups are bonded to Z, said group Z is equal to C.

Preferably, the guest material has a structure represented by the following general formula (2):

wherein X₁、X₃Each independently represents a single bond, B (R), N (R), C (R)₂、Si(R)₂、O、C＝N(R)、C＝C(R)₂P (r), P (═ O) R, S, or SO₂；X₂Independently represent a nitrogen atom or a boron atom, and X₁、X₂、X₃At least one of them is represented by a boron atom;

Z₁-Z₁₁each independently represents a nitrogen atom or C (R);

a. b, c, d, e each independently represent 0, 1, 2, 3 or 4;

ra, Rb, Rc, Rd each independently represent linear or branched C1-20 alkyl substituted alkyl, linear or branched C1-C20 alkyl substituted silyl, substituted or unsubstituted C5-C30 aryl, substituted or unsubstituted C5-C30 heteroaryl, substituted or unsubstituted C5-C30 arylamine;

Preferably, the guest material has a structure represented by the following general formula (3):

wherein X₁、X₂、X₃Each independently represents a single bond, B (R), N (R), C (R)₂、Si(R)₂、O、C＝N(R)、C＝C(R)₂P (r), P (═ O) R, S, or SO₂；

Z, Y at different positions are independently represented by C (R) or N;

K₁is represented by a single bond, B (R), N (R), C (R)₂、Si(R)₂、O、C＝N(R)、C＝C(R)₂P (r), P (═ O) R, S, or SO₂One of linear or branched C1-C20 alkyl substituted alkylene, linear or branched C1-C20 alkyl substituted silylene and C6-C20 aryl substituted alkylene;

is represented by an aromatic group with 6-20 carbon atoms or an aromatic hetero group with 3-20 carbon atoms;

m represents the

number

0, 1, 2, 3, 4 or 5; l is selected from single bond, double bond, triple bond, aromatic group with 6-40 carbon atoms or heteroaryl with 3-40 carbon atoms;

r, which is identical or different at each occurrence, is represented by H, D, F, Cl, Br, I, C (═ O) R¹，CN，Si(R¹)₃，P(＝O)(R¹)₂，S(＝O)₂R¹A linear alkyl or alkoxy radical having C1 to C20, or a branched or cyclic alkyl or alkoxy radical having C3 to C20, or an alkenyl or alkynyl radical having C2 to C20, where the abovementioned radicals may each be substituted by one or more radicals R¹And wherein one or more CH2 groups of the above groups may be replaced by-R¹C＝CR¹-、-C≡C-、Si(R¹)₂、C(＝O)、C＝NR¹、-C(＝O)O-、C(＝O)NR¹-、NR¹、P(＝O)(R¹) -O-, -S-, SO or SO2, and wherein the above radicalsOne or more H atoms in the group can be replaced by D, F, Cl, Br, I or CN, or an aromatic or heteroaromatic ring system having 5 to 30 aromatic ring atoms, which can be substituted in each case by one or more R¹Substituted, or aryloxy or heteroaryl radicals having 5 to 30 aromatic ring atoms, which radicals may be substituted by one or more radicals R¹Substitution, wherein two or more groups R may be linked to each other and may form a ring:

R_nindependently represent a linear or branched C1-C20 alkyl substituted alkyl, a linear or branched chainA substituted or unsubstituted C1-C20 alkyl-substituted silyl group, a substituted or unsubstituted C5-C30 aryl group, a substituted or unsubstituted C5-C30 heteroaryl group, a substituted or unsubstituted C5-C30 arylamine group;

ar represents linear or branched C1-C20 alkyl substituted alkyl, linear or branched C1-C20 alkyl substituted silane, substituted or unsubstituted C5-C30 aryl, substituted or unsubstituted C5-C30 heteroaryl, substituted or unsubstituted C5-C30 arylamine or a structure shown in a general formula (4):

K₂、K₃each independently represents a single bond, B (R), N (R), C (R)₂、Si(R)₂、O、C＝N(R)、C＝C(R)₂P (r), P (═ O) R, S, S ═ O or SO₂One of linear or branched C1-C20 alkyl substituted alkylene, linear or branched C1-C20 alkyl substituted silylene and C6-C20 aryl substituted alkylene;

preferably, X in the formula (3)₁、X₂、X₃May also each independently be absent, i.e. X₁、X₂、X₃The positions shown are each independently free of atoms and bonds, and X₁、X₂、X₃At least one of which indicates the presence of an atom or bond.

Preferably, the hole transport region comprises one or more of a hole injection layer, a hole transport layer, and an electron blocking layer in combination. The electron transport region comprises one or more of an electron injection layer, an electron transport layer, and a hole blocking layer.

The present application also provides a lighting or display element comprising one or more organic electroluminescent devices as described above; and in the case where a plurality of devices are included, the devices are combined in a lateral or longitudinal superposition.

In the context of the present invention, HOMO means the highest occupied orbital of a molecule, and LUMO means the lowest unoccupied orbital of a molecule, unless otherwise specified. Further, "LUMO energy level difference" referred to in the present specification means a difference in absolute value of each energy value.

In the context of the present invention, unless otherwise specified, the singlet (S1) energy level means the singlet lowest excited state energy level of the molecule, and the triplet (T1) energy level means the triplet lowest excited state energy level of the molecule. In addition, "triplet energy level difference" and "singlet and triplet energy level difference" referred to in the present specification mean a difference in absolute value of each energy. In addition, the difference between the energy levels is expressed in absolute values.

Preferably, the first organic compound and the second organic compound constituting the host material are respectively and independently selected from H1, H2, H3, H4, H5, H6, H7, H8 and H9, but not limited to the above materials, and the structures thereof are respectively:

the difference in HOMO/LUMO levels between the first organic compound and the second organic compound is 0.2eV or more. A mixture or an interface formed by the first organic compound and the second organic compound can form an exciplex under the excitation of light, and the exciplex can also be generated under the excitation of an electric field; the exciplex cannot be generated under optical excitation, but can be generated under electric field excitation as long as the HOMO/LUMO level difference complex of the first organic compound and the second organic compound is required.

Preferably, the first organic compound and the second organic compound in the host material of the light-emitting layer form a mixture, wherein the mass fraction of the first organic compound is 10% to 90%, and in a preferred embodiment, may be, for example, 9:1 to 1:9, preferably 8:2 to 2:8, preferably 7:3 to 3:7, more preferably 1:1, and the mass fraction of the guest material in the light-emitting layer is 1% to 5%.

Preferably, the first organic compound and the second organic compound in the host material of the light-emitting layer form a mixture, wherein the mass fraction of the first organic compound is 10% to 90%, and in a preferred embodiment, may be, for example, 9:1 to 1:9, preferably 8:2 to 2:8, preferably 7:3 to 3:7, more preferably 1:1, and the mass fraction of the guest material in the light-emitting layer is 5% to 30%.

Preferably, the singlet energy level of the guest material is lower than that of the exciplex, and the triplet energy level of the guest material is lower than that of the exciplex.

Preferably, the guest material of the organic electroluminescent device may be selected from the following compounds:

more preferably, the guest material is selected from the following compounds:

preferably, the mass percentage of the guest material to the host material is 1 to 5%, preferably 1 to 3%;

preferably, the mass percentage of the guest material to the host material is 5 to 30%, preferably 5 to 10%.

In another aspect, the organic electroluminescent device of the present invention further comprises a cathode and an anode.

Preferably, the anode comprises a metal, metal oxide or a conductive polymer. For example, the anode can have a work function in the range of about 3.5 to 5.5 eV. Illustrative examples of conductive materials for the anode include carbon, aluminum, vanadium, chromium, copper, zinc, silver, gold, other metals, and alloys thereof; zinc oxide, indium oxide, tin oxide, Indium Tin Oxide (ITO), indium zinc oxide, and other similar metal oxides; and mixtures of oxides and metals, e.g. ZnO, Al and SnO₂Sb. Both transparent and non-transparent materials can be used as anode materials. For a structure emitting light to the anode, transparency can be formedOf (2) an anode. Herein, transparent means a degree to which light emitted from the organic material layer is transparent, and the transmittance of light is not particularly limited.

For example, when the organic light emitting device of the present specification is a top emission type and an anode is formed on a substrate before an organic material layer and a cathode are formed, not only a transparent material but also a non-transparent material having excellent light reflectivity may be used as an anode material. Alternatively, when the organic light emitting device of the present specification is of a bottom emission type and the anode is formed on the substrate before the organic material layer and the cathode are formed, a transparent material is required to be used as the anode material, or a non-transparent material is required to be formed as a thin film which is thin enough to be transparent.

Preferably, as for the cathode, a material having a small work function is preferable as a cathode material so that electron injection can be easily performed. For example, in the present specification, a material having a work function ranging from 2eV to 5eV may be used as the cathode material. The cathode may comprise a metal such as magnesium, calcium, sodium, potassium, titanium, indium, yttrium, lithium, gadolinium, aluminum, silver, tin, and lead or alloys thereof; materials having a multilayer structure, e.g. LiF/Al or LiO₂Al, etc., but are not limited thereto.

The cathode may be formed using the same material as the anode. In this case, the cathode may be formed using the anode material as described above. In addition, the cathode or anode may comprise a transparent material.

The organic light emitting device of the present invention may be a top emission type, a bottom emission type, or a both-side emission type, depending on the material used.

Preferably, the organic light emitting device of the present invention comprises a hole injection layer. The hole injection layer may preferably be disposed between the anode and the light emitting layer. The hole injection layer is formed of a hole injection material known to those skilled in the art. The hole injection material is a material that easily receives holes from the anode at a low voltage, and the HOMO of the hole injection material is preferably located between the work function of the anode material and the HOMO of the surrounding organic material layer. Specific examples of the hole injection material include, but are not limited to, metalloporphyrin-based organic materials, oligopolythiophene-based organic materials, arylamine-based organic materials, hexacarbonitrile hexaazabenzophenanthrene-based organic materials, quinacridone-based organic materials, perylene-based organic materials, anthraquinone-based conductive polymers, polyaniline-based conductive polymers, polythiophene-based conductive polymers, or the like.

Preferably, the organic light emitting device of the present invention comprises a hole transport layer. The hole transport layer may preferably be disposed between the hole injection layer and the light emitting layer, or between the anode and the light emitting layer. The hole transport layer is formed of a hole transport material known to those skilled in the art. The hole transport material is preferably a material having high hole mobility, which is capable of transferring holes from the anode or the hole injection layer to the light-emitting layer. Specific examples of the hole transport material include, but are not limited to, arylamine-based organic materials, conductive polymers, and block copolymers having a bonding portion and a non-bonding portion.

Preferably, the organic light emitting device of the present invention further comprises an electron blocking layer. The electron blocking layer may preferably be disposed between the hole transport layer and the light emitting layer, or between the hole injection layer and the light emitting layer, or between the anode and the light emitting layer. The electron blocking layer is formed of an electron blocking material known to those skilled in the art, such as TCTA.

Preferably, the organic light emitting device of the present invention comprises an electron injection layer. The electron injection layer may preferably be disposed between the cathode and the light emitting layer. The electron injection layer is formed of an electron injection material known to those skilled in the art. The electron injection layer may be formed using, for example, an electron accepting organic compound. Here, as the electron accepting organic compound, known optional compounds may be used without particular limitation. As such organic compounds, there can be used: polycyclic compounds, such as p-terphenyl or quaterphenyl or derivatives thereof; polycyclic hydrocarbon compounds, such as naphthalene, tetracene, perylene, coronene, chrysene, anthracene, diphenylanthracene or phenanthrene, or derivatives thereof; or a heterocyclic compound, for example, phenanthroline, bathophenanthroline, phenanthridine, acridine, quinoline, quinoxaline or phenazine, or a derivative thereof. Inorganic materials may also be used for formation, including, but not limited to, for example, magnesium, calcium, sodium, potassium, titanium, indium, yttrium, lithium, gadolinium, aluminum, silver, tin, and lead or alloys thereof; LiF, LiO₂、LiCoO₂、NaCl、MgF₂、CsF、CaF₂、BaF₂、NaF、RbF、CsCl、Ru₂CO₃、YbF₃Etc.; and materials having a multilayer structure, e.g. LiF/Al or LiO₂Al, etc.

Preferably, the organic light emitting device of the present invention comprises an electron transport layer. The electron transport layer may preferably be disposed between the electron injection layer and the light emitting layer, or between the cathode and the light emitting layer. The electron transport layer is formed of an electron transport material known to those skilled in the art. The electron transport material is a material capable of easily receiving electrons from the cathode and transferring the received electrons to the light emitting layer. Materials with high electron mobility are preferred. Specific examples of the electron transport material include, but are not limited to, 8-hydroxyquinoline aluminum complex; a complex comprising 8-hydroxyquinoline aluminum; an organic radical compound; and hydroxyflavone metal complexes; and TPBi.

Preferably, the organic light emitting device of the present invention further comprises a hole blocking layer. The hole blocking layer may preferably be disposed between the electron transport layer and the light emitting layer, or between the electron injection layer and the light emitting layer, or between the cathode and the light emitting layer. The hole blocking layer is a layer that reaches the cathode by preventing injected holes from passing through the light emitting layer, and may be generally formed under the same conditions as the hole injecting layer. Specific examples thereof include oxadiazole derivatives, triazole derivatives, phenanthroline derivatives, BCP, aluminum complexes, and the like, but are not limited thereto.

Preferably, the hole blocking layer may be the same layer as the electron transport layer.

In addition, preferably, the organic light emitting device may further include a substrate. In particular, in an organic light emitting device, an anode or a cathode may be provided on a substrate. There is no particular limitation on the substrate. The substrate may be a rigid substrate, such as a glass substrate, or may be a flexible substrate, such as a flexible film-shaped glass substrate, a plastic substrate, or a film-shaped substrate.

The organic light emitting device of the present invention can be produced using the same materials and methods known in the art. Specifically, the organic light emitting device can be produced by the following steps: depositing a metal, a conductive metal oxide, or an alloy thereof on a substrate using a Physical Vapor Deposition (PVD) process (e.g., sputtering or e-beam evaporation) to form an anode; forming an organic material layer including a hole injection layer, a hole transport layer, an electron blocking layer, a light emitting layer, and an electron transport layer on the anode; followed by deposition thereon of a material that can be used to form the cathode. In addition, an organic light emitting device may also be fabricated by sequentially depositing a cathode material, one or more organic material layers, and an anode material on a substrate. In addition, during the manufacture of the organic light emitting device, the organic light emitting composite material of the present invention may be formed into an organic material layer using a solution coating method in addition to a physical vapor deposition method. As used in this specification, the term "solution coating method" means spin coating, dip coating, blade coating, inkjet printing, screen printing, spray coating, roll coating, and the like, but is not limited thereto.

There is no particular limitation on the thickness of each layer, and those skilled in the art can determine it as needed and as the case may be.

Preferably, the thickness of the light-emitting layer and optionally of the hole-injecting layer, the hole-transporting layer, the electron-blocking layer and the electron-transporting layer, the electron-injecting layer, respectively, is from 0.5 to 150nm, preferably from 1 to 100 nm.

Preferably, the thickness of the light-emitting layer is 20 to 80nm, preferably 30 to 60 nm.

The beneficial technical effects of the invention are as follows:

the main material of the light-emitting layer of the organic electroluminescent device provided by the invention is formed by matching two materials, and a mixture or an interface formed by the two materials generates an exciplex under the conditions of optical excitation and electric excitation. The triplet state exciton concentration of the host material can be reduced, the quenching effect of the triplet state exciton is reduced, and the stability of the device is improved.

The second compound is a material with different carrier mobility from the first compound, can balance carriers in the main body material, increases an exciton recombination region, improves the efficiency of the device, can effectively solve the problem that the color of the material is deviated under high current density, and improves the stability of the luminous color of the device.

The formed exciplex has smaller difference between triplet state energy and singlet state energy level, so that triplet state excitons can be rapidly converted into singlet state excitons, the quenching effect of the triplet state excitons is reduced, and the stability of the device is improved. Meanwhile, the singlet state of the exciplex is higher than the singlet state energy level of the guest material, and the triplet state energy level is higher than the triplet state energy level of the guest material, so that the energy can be effectively prevented from being transmitted back to the host material from the guest material, and the efficiency and the stability of the device are further improved.

In the structure formed by bonding the boron-containing guest material with other atoms in an sp2 hybridization mode of boron, as boron is an electron-deficient atom, the boron can form a charge transfer state or a reverse space resonance effect with an electron donating group or a weak electron withdrawing group, so that HOMO and LUMO electron cloud orbitals are separated, and the singlet-triplet energy level difference of the material is reduced, thereby generating a delayed fluorescence phenomenon; meanwhile, the material formed by taking boron atoms as the core can obtain very small singlet state-triplet state energy level difference, and can effectively reduce the delayed fluorescence life of the material due to the high fluorescence radiation rate, thereby reducing the triplet state quenching effect of the material and improving the efficiency of the device.

In addition, due to the existence of boron atoms, the rigidity in molecules is enhanced, the flexibility of the molecules is reduced, the configuration difference between the ground state and the excited state of the material is reduced, the FWHM of the luminescent spectrum of the material is effectively reduced, the color purity of the device is favorably improved, and the color gamut of the device is improved. Therefore, the device structure matching of the invention can effectively replace the device efficiency, the service life and the color purity.

Drawings

Fig. 1 is a schematic view of an embodiment of an organic electroluminescent device of the present invention, in which: 1. a substrate layer; 2. an anode layer; 3. a hole injection layer; 4. a hole transport layer; 5. an electron blocking layer; 6. a light emitting layer; 7. a hole blocking/electron transporting layer; 8. an electron injection layer; 9. a cathode layer.

FIG. 2 is a schematic diagram of the principle of built-in electric field (1); FIG. 3 is a schematic diagram of the principle of built-in electric field (2).

FIG. 4 is an angle dependent spectrum of a single film.

Fig. 5 shows the lifetime of the organic electroluminescent device prepared in the example when it is operated at different temperatures.

Detailed Description

The present invention will be described in detail with reference to the accompanying FIG. 1 and examples, but the scope of the present invention is not limited by these preparation examples. In the context of the present invention, HOMO means the highest occupied orbital of a molecule, and LUMO means the lowest unoccupied orbital of a molecule, unless otherwise specified. Further, "LUMO energy level difference" referred to in the present specification means a difference in absolute value of each energy value.

Example 1

The structure of the organic electroluminescent device prepared in example 1 is shown in fig. 1, and the specific preparation process of the device is as follows:

cleaning an ITO anode layer 2 on a transparent glass substrate layer 1, respectively ultrasonically cleaning the ITO anode layer 2 with deionized water, acetone and ethanol for 30 minutes, and then treating the ITO anode layer 2 in a plasma cleaner for 2 minutes; drying the ITO glass substrate, placing the ITO glass substrate in a vacuum cavity until the vacuum degree is less than 1 x 10^-6Torr, evaporating a mixture of HT1 and P1 with the film thickness of 10nm on the ITO anode layer 2, the mass ratio of HT1 and P1 is 97:3, and the layer is a hole injection layer 3; next, 50nm thick HT1 was evaporated to form a hole transport layer 4; then evaporating EB1 with the thickness of 20nm, wherein the layer is used as an electron blocking layer 5; further, a light-emitting layer 6 with the thickness of 25nm is evaporated, wherein the light-emitting layer comprises a host material and a guest doping dye, the selection of specific materials is shown in table 1, and the rate is controlled by a film thickness meter according to the mass percentage of the host material and the doping dye; ET1 and Liq with a thickness of 40nm are further evaporated on the luminescent layer 6, and the mass ratio of ET1 to Liq is1:1, the organic material layer serves as a hole blocking/electron transporting layer 7; vacuum evaporating LiF with the thickness of 1nm on the hole blocking/electron transporting layer 7, wherein the layer is an electron injection layer 8; on the electron injection layer 8, a cathode Al (80nm) was vacuum-evaporated, which was a cathode electrode layer 9. The thickness of the evaporated film is different for different devices. The selection of specific materials for example 1 is shown in table 1:

the structures of the organic electroluminescent devices obtained in comparative examples 1 to 14 and examples 2 to 21 are similar to those of example 1, and the preparation method adopts the method of example 1; specific materials used are shown in table 1.

TABLE 1

It should be noted that the dual body of the present invention has two expressions: one dual host form is where the first and second organic compounds are co-evaporated by a dual source to form a mixture with a proportion of guest material doped in the mixture, for example H2: h1: DG-4 ═ 50: 50:12(40 nm); another dual host type is to evaporate the first organic compound or the second organic compound first), and then evaporate the second organic compound or the first organic compound, where the two form a stacked structure of an interface, and a guest material is doped in the first organic compound or the second organic compound, such as H3(20 nm)/H9: DR-1 ═ 100:10(20nm) or H3: DR-1 ═ 100:10(20nm)/H9(20 nm).

The starting materials H1-H9 referred to in Table 1 are as indicated above, and the structural formulae of the remaining materials are as follows:

wherein the energy level relation of the host-guest material is as follows:

h1: HOMO is-5.82 eV, LUMO is-2.80 eV, S1 is 2.92eV, and T1 is 2.77 eV;

h2: HOMO is-5.60 eV, LUMO is-2.17 eV, S1 is 3.23eV, and T1 is 2.76 eV;

h3: HOMO is-6.01 eV, LUMO is-2.58 eV, S1 is 3.53eV, and T1 is 2.86 eV;

h4: HOMO is-6.23 eV, LUMO is-2.64 eV, S1 is 3.46eV, and T1 is 2.63 eV;

h5: HOMO is-5.64 eV, LUMO is-2.27 eV, S1 is 3.28eV, and T1 is 2.71 eV;

h6: HOMO is-5.78 eV, LUMO is-2.50 eV, S1 is 3.40eV, and T1 is 2.77 eV;

h7: HOMO is-6.48 eV, LUMO is-2.89 eV, S1 is 3.54eV, and T1 is 2.72 eV;

h8: HOMO is-5.57 eV, LUMO is-2.25 eV, S1 is 3.19eV, and T1 is 2.62 eV;

h9: HOMO is-6.52 eV, LUMO is-3.43 eV, S1 is 3.22eV, and T1 is 2.50 eV;

BD-1: HOMO was 5.48eV, LUMO was 2.78eV, S1 was 2.73eV, and T1 was 2.63 eV;

BD-2: HOMO was 5.70eV, LUMO was 2.85eV, S1 was 2.80eV, and T1 was 2.65 eV;

DG-1: HOMO was 5.90eV, LUMO was 3.40eV, S1 was 2.40eV, and T1 was 2.30 eV;

DG-2: HOMO was 5.50eV, LUMO was 2.85eV, S1 was 2.40eV, and T1 was 2.30 eV;

DG-3: HOMO was 5.40eV, LUMO was 2.76eV, S1 was 2.38eV, and T1 was 2.33 eV;

5.58eV for HOMO, 2.77eV for LUMO, 2.44eV for S1, and 2.37eV for T1;

DR-1: HOMO was 5.30eV, LUMO was 3.35eV, S1 was 2.15eV, and T1 was 2.04 eV;

a-1: HOMO was 5.90eV, LUMO was 3.00eV, S1 was 3.0eV, and T1 was 2.75 eV;

a-2: HOMO was 5.70eV, LUMO was 3.10eV, S1 was 2.40eV, and T1 was 1.70 eV.

The carrier mobility of the selected materials described above is shown in table 2 below:

TABLE 2

Name of Material	Hole mobility (cm)²/V·S)	Electron mobility (cm)²/V·S)
			H1	2.01*10^-4	1.56*10^-2
H2	5.44*10^-3	1.09*10^-4
			H3	5.31*10^-3	2.08*10^-4
H4	2.18*10^-4	2.10*10^-2
			H5	8.76*10^-3	1.24*10^-4
H6	7.12*10^-3	2.35*10^-4
			H7	3.12*10^-4	4.52*10^-3
H8	4.11*10^-4	1.01*10^-2
			H9	2.50*10^-4	6.78*10^-3

The energy levels of the host material and the exciplex-forming energy levels are shown in table 3 below:

TABLE 3

Note: wherein H2: h3(50:50) is expressed as a mixture of a first organic compound and a second organic compound with the mass percentage of 50:50 in the main material; H2/H3 indicates that the first organic compound and the second organic compound form an interface in the host material. Where PL represents the optical excitation spectrum and EL represents the electric field excitation spectrum.

The organic electroluminescent devices prepared in examples 1 to 21 and comparative examples 1 to 14 were subjected to performance tests, and the results are shown in Table 4.

TABLE 4

As can be seen from the data in table 4, in examples 1 to 21, compared with comparative examples 1 to 14, when the host material and the boron-containing material are adopted as the guest material in the above-mentioned combination, the device efficiency and the device lifetime are significantly improved, and at the same time, the FWHM of the device spectrum is reduced and the color purity of the device is improved, compared with the conventional material as the host material. The device efficiency and service life of the device adopting double-host matching DB-1, DB-2 and other boron-containing materials are obviously improved, the main reason is that the host material of the luminescent layer is formed by matching two materials, and a mixture or an interface formed by the two materials generates an exciplex under the conditions of light excitation and electric excitation, so that the exciplex can improve the efficiency of energy transfer to a guest material, reduce the triplet exciton concentration of the host material, reduce the triplet exciton quenching effect and prolong the service life of the device. The structure matching not only tries blue light devices, but also tries green light and red light devices, and shows the universality of the device structure.

In addition, the second compound is a material with different carrier mobility from the first compound, so that carriers in the main body material can be balanced, an exciton recombination region is increased, the efficiency of the device is improved, the problem of material color shift under high current density can be effectively solved, and the stability of the light-emitting color of the device is improved. The formed exciplex has smaller difference between triplet state energy and singlet state energy level, so that triplet state excitons can be rapidly converted into singlet state excitons, the quenching effect of the triplet state excitons is reduced, and the stability of the device is improved.

The singlet state of the exciplex is higher than the singlet state energy level of the guest material, and the triplet state energy level is higher than the triplet state energy level of the guest material, so that the energy can be effectively prevented from returning to the host material from the guest material, and the efficiency and the stability of the device are further improved.

Further, the applicant found that a mixture or an interface formed by the first organic compound of the electron-transporting type and the second organic compound of the hole-transporting type forms a stable built-in electric field at the mixture or the interface of the two due to different carrier transport characteristics of the two. Meanwhile, due to the electron deficiency of boron, when the boron-containing compound is doped into an interface or a mixture formed by the first organic compound and the second organic compound, a molecular directional combined arrangement can be generated under the interaction of an internal electric field and boron atoms, so that the molecular arrangement of the boron-containing compound tends to horizontal arrangement, the light extraction rate of the material is improved, and the light emitting efficiency of the device is improved. However, the interface or mixture formed by the single host material and the first organic substance and the second organic substance with the same carrier property and the boron-containing compound cannot produce the above effect because the interface or mixture cannot form a stable built-in electric field. In addition, the boron-containing compound can generate strong action force with a built-in electric field due to the very strong electron-deficient induction action of boron atoms, so that the boron-containing compound generates molecular oriented rearrangement. The specific principle is shown in fig. 2 and 3.

To further validate the above principle, one can test the angle-dependent spectrum of a single film (shown in FIG. 4). The results of the horizontal dipole test are shown in table 5 below.

TABLE 5 horizontal dipole ratio test results

Numbering	Single film	Horizontal dipole ratio
			1	H3:BD-1＝100:3(60nm)	0.60
2	H7:BD-1＝100:3(60nm)	0.62
			3	H3:H7:BD-1＝50:50:3(60nm)	0.85
4	H3(30nm)/H7:BD-1＝100:3(30nm)	0.87
			5	H3:H7:A-1＝50:50:3(60nm)	0.63
6	H2:DG-1＝100:12(60nm)	0.60
			7	H2：H1：DG-1＝50：50:12(60nm)	0.88
8	H2(30nm)/H1：DG-1＝100:12(30nm)	0.90
			9	H2：H1：A-2＝50：50:12(60nm)	0.61

As can be seen from fig. 4 and table 5, the ratio of horizontal molecular arrangement of the mixture formed by the first organic compound of electron-transporting type and the second organic compound of hole-transporting type or the interface matched with the boron-containing compound is significantly increased. And other collocation types have lower proportion of horizontal molecular arrangement.

Furthermore, the service life of the OLED device prepared by the invention is stable when the device works at different temperatures, and the efficiency of the device is tested at-10-80 ℃ in comparative example 1, comparative example 3, example 6, comparative example 5, example 8, comparative example 13 and example 20, and the obtained results are shown in Table 6 and FIG. 5.

TABLE 6

Note: the above test data shows that the device is at 10mA/cm²The device data of (1).

As shown in table 6 and fig. 5, it can be found that the EQE of the device collocated with the host material and the guest material adopted in the structure of the present application changes less at different temperatures compared with the traditional device collocation, and the EQE of the device is almost unchanged at higher temperatures, which indicates that the device collocated with the structure of the present application has better device stability.

Claims

1. An organic electroluminescent device comprising a cathode, an anode, and a light-emitting layer between the cathode and the anode; the light emitting layer includes: a host material and a guest material; a hole transport region is arranged between the anode and the light-emitting layer, and an electron transport region is arranged between the cathode and the light-emitting layer;

characterized in that the host material comprises a first organic compound and a second organic compound, 0.3eV ≦ HOMO_{A second organic compound}The first organic compound I-HOMO is less than or equal to 0.8 eV; LUMO less than or equal to 0.4eV_{A second organic compound}The first organic compound I-LUMO is less than or equal to 0.8 eV;

a mixture or an interface formed by the first organic compound and the second organic compound generates an exciplex under the condition of optical excitation or electric field excitation; the emission spectrum of the exciplex formed and the absorption spectrum of the guest material have overlap; the singlet state energy level of the formed exciplex is higher than that of the guest material, and the triplet state energy level is higher than that of the guest material; the first organic compound and the second organic compound have different carrier transport characteristics;

2. The organic electroluminescent device according to claim 1, wherein the difference between the triplet level and the singlet level of the exciplex formed from the first organic compound and the second organic compound is 0.2eV or less; the exciton energy is transferred from the exciplex to the guest material, which eventually causes the guest material to emit light.

3. The organic electroluminescent device according to claim 1, wherein the first organic compound and the second organic compound are mixed in a mass ratio of 1:99 to 99:1, and an exciplex is generated under optical excitation or electric field excitation.

4. The organic electroluminescent device according to claim 1, wherein the first organic compound and the second organic compound form a stacked structure having an interface, the first organic compound is located on a hole transporting side, and the second organic compound is located on an electron transporting side, and an exciplex is generated under light excitation or electric field excitation.

5. The organic electroluminescent device according to claim 1, wherein the mass fraction of the first organic compound is 10% to 90% of the host material, and the mass fraction of the guest material in the light-emitting layer is 1% to 5% or 5% to 30% of the host material.

6. The organic electroluminescent device according to claim 1, wherein the host material in the light-emitting layer is an interface formed by a first organic compound and a second organic compound, the guest material is doped in the first organic compound, and the mass fraction of the guest material in the light-emitting layer is 1% to 5% of the host material; or the host material in the light-emitting layer is an interface formed by the first organic compound and the second organic compound, the guest material is doped in the second organic compound, and the mass fraction of the guest material in the light-emitting layer is 1-5% of that of the host material.

7. The organic electroluminescent device according to claim 1, wherein the host material in the light-emitting layer is an interface formed by a first organic compound and a second organic compound, the guest material is doped in the first organic compound, and the mass fraction of the guest material in the light-emitting layer is 5% to 30% of the host material; or the host material in the light-emitting layer is an interface formed by the first organic compound and the second organic compound, the guest material is doped in the second organic compound, and the mass fraction of the guest material in the light-emitting layer is 5-30% of that of the host material.

8. The organic electroluminescent device according to claim 1, wherein the first organic compound has a hole mobility greater than an electron mobility, and the second organic compound has an electron mobility greater than a hole mobility; and the first organic compound is a hole transporting type material and the second organic compound is an electron transporting type material.

9. The organic electroluminescent device as claimed in claim 1, wherein the guest material has a peak wavelength of 400-500nm, or 500-560nm, or 560-780 nm.

10. The organic electroluminescent device according to claim 1, wherein the difference between the singlet and triplet energy levels of the guest material is 0.3eV or less.

11. The organic electroluminescent device according to claim 1, wherein the guest material contains boron atoms in an amount of 1 or more, the boron atoms being bonded to other elements by sp2 hybrid orbital mode; the group connected with the boron is one of a hydrogen atom, a substituted or unsubstituted C1-C6 straight-chain alkyl group, a substituted or unsubstituted C3-C10 cycloalkyl group, a substituted or unsubstituted C1-C10 heterocycloalkyl group, a substituted or unsubstituted C6-C60 aryl group and a substituted or unsubstituted C3-C60 heteroaryl group; and the groups connected with the boron atoms can be independently connected, or can be directly bonded with each other to form a ring or connected with the boron through other groups to form a ring.

12. The organic electroluminescent device of claim 1, wherein the guest material comprises a number of boron atoms of 1, 2, or 3.

13. The organic electroluminescent device according to claim 1, wherein the guest material has a structure represented by the following general formula (1):

a. b, c, d, e each independently represent 0, 1, 2, 3 or 4;

in the case where Ra, Rb, Rc, Rd groups are bonded to Z, Z is equal to C.

14. The organic electroluminescent device according to claim 1, wherein the guest material has a structure represented by the following general formula (2):

Z₁-Z₁₁each independently represents a nitrogen atom or C (R);

a. b, c, d, e each independently represent 0, 1, 2, 3 or 4;

in the case where Ra, Rb, Rc, Rd groups are bonded to Z, Z is equal to C.

15. The organic electroluminescent device according to claim 1, wherein the guest material has a structure represented by the following general formula (3):

Z, Y at different positions are independently represented by C (R) or N;

m represents the number 0, 1, 2, 3, 4 or 5; l is selected from single bond, double bond, triple bond, aromatic group with 6-40 carbon atoms or heteroaryl with 3-40 carbon atoms;

R¹identical or different at each occurrence is represented by H, D, F, Cl, Br, I, C (═ O) R²，CN，Si(R²)₃，P(＝O)(R²)₂，N(R²)S(＝O)₂R²A linear alkyl or alkoxy radical having C1 to C20, or a branched or cyclic alkyl or alkoxy radical having C3 to C20, or an alkenyl or alkynyl radical having C2 to C20, where the abovementioned radicals may each be substituted by one or more radicals R¹And wherein one or more CH2 groups of the above groups may be replaced by-R²C＝CR²-、-C≡C-、Si(R²)₂、C(＝O)、C＝NR²、-C(＝O)O-、C(＝O)NR²-、NR²、P(＝O)(R²) O-, -S-, SO or SO2, and in which one or more H atoms in the abovementioned radicals may be replaced by D, F, Cl, Br, I or CN, or an aromatic or heteroaromatic ring system having from 5 to 30 aromatic ring atoms which may in each case be replaced by one or more R²Substituted, or having 5 to 30 aryl radicalsAryloxy or heteroaryl radical of a ring member of the family, which radical may be substituted by one or more radicals R²Substituted, in which two or more radicals R¹May be connected to each other and may form a ring:

R_nindependently represent a linear or branched C1-C20 alkyl substituted alkyl group, a linear or branched C1-C20 alkyl substituted silyl group, a substituted or unsubstituted C5-C30 aryl group, a substituted or unsubstituted C5-C30 heteroaryl group and a substituted or unsubstituted C5-C30 arylamine group;

K₂、K₃each independently represents a single bond, B (R), N (R), C (R)₂、Si(R)₂、O、C＝N(R)、C＝C(R)₂P (r), P (═ O) R, S, S ═ O or SO₂Linear or branched C1-C20 alkyl substituted alkylene, linear or branched C1-C20 alkyl substituted silylene and C6-C20 aryl substituted alkylene.

16. The organic electroluminescent device as claimed in claim 15, wherein X in the general formula (3)₁、X₂、X₃May also each independently be absent, i.e. X₁、X₂、X₃The positions shown are each independently free of atoms and bonds, and X₁、X₂、X₃At least one of which indicates the presence of an atom or bond.

17. The organic electroluminescent device of claim 1, wherein the hole transport region comprises one or more of a combination of a hole injection layer, a hole transport layer, and an electron blocking layer; the electron transport region comprises one or more of an electron injection layer, an electron transport layer, and a hole blocking layer.