Light-emitting device and preparation method thereof, light-emitting substrate and light-emitting device

Abstract

A light-emitting device comprises: a first light-emitting layer and a second light-emitting layer which are stacked, a hole transport layer located on a side of the first light-emitting layer away from the second light-emitting layer; and an electron transport layer located on a side of the second light-emitting layer away from the first light-emitting layer; the material of the first light-emitting layer comprises a first host material A and a first TADF sensitizer B, and the material of the second light-emitting layer comprises a second host material D, a second TADF sensitizer E and a second fluorescent material F; the transport rates of the materials of the first light-emitting layer and the second light-emitting layer for holes are both greater than the transport rates of the materials of the first light-emitting layer and the second light-emitting layer for electrons, and there is a first overlapping region between the normalized electroemission spectrum of the first TADF sensitizer B and the normalized absorption spectrum of the second fluorescent material F.

Description

Technical Field

[0001] The present disclosure relates to the field of lighting and display technology, and in particular to a light-emitting device and a method for preparing the same, a light-emitting substrate and a method for preparing the same, and a light-emitting apparatus. Background Art

[0002] Organic Light Emitting Diode (OLED) has the characteristics of self-luminescence, wide viewing angle, fast response time, high luminous efficiency, low operating voltage, thin substrate thickness, large-size and flexible substrate production and simple process. It is hailed as the next generation of "star" display technology. Summary of the invention

[0003] On the one hand, a light-emitting device is provided, comprising: a first light-emitting layer and a second light-emitting layer which are stacked, a hole transport layer located on a side of the first light-emitting layer away from the second light-emitting layer; and an electron transport layer located on a side of the second light-emitting layer away from the first light-emitting layer; the material of the first light-emitting layer comprises a first host material A and a first TADF sensitizer B, and the material of the second light-emitting layer comprises a second host material D, a second TADF sensitizer E and a second fluorescent material F; the transport rates of the materials of the first light-emitting layer and the second light-emitting layer for holes are both greater than the transport rates of the materials of the first light-emitting layer and the second light-emitting layer for electrons, and there is a first overlapping region between the normalized electroemission spectrum of the first TADF sensitizer B and the normalized absorption spectrum of the second fluorescent material F.

[0004] In some embodiments, the area of ​​the first overlapping region is greater than 70% of the area of ​​the normalized absorption spectrum of the second fluorescent material F; and / or the difference between the peak position of the lowest energy absorption peak in the normalized absorption spectrum of the second fluorescent material F and the peak position of the highest energy emission peak in the electroemission spectrum of the first TADF sensitizer B is less than or equal to 25nm.

[0005] In some embodiments, the lowest singlet energy S1 of the second host material D, the second TADF sensitizer E, and the second fluorescent light-emitting material F, and the lowest triplet energy T1 of the second host material D, the second TADF sensitizer E, and the second fluorescent light-emitting material F satisfy:

[0006] S1(D)-T1(D)>0.2eV;

[0007] S1(E)-T1(E)<0.2eV;

[0008] S1(F)-T1(F)>0.2eV;

[0009] S1(D)>S1(E)>S1(F);

[0010] T1(D)>T1(E)>T1(F).

[0011] In some embodiments, the first TADF sensitizer B and the second TADF sensitizer E are the same or different; when the first TADF sensitizer B and the second TADF sensitizer E are different, there is a second overlapping region between the normalized electroemission spectrum of the second TADF sensitizer E and the normalized absorption spectrum of the second fluorescent light-emitting material F.

[0012] In some embodiments, the area of ​​the second overlapping region is greater than 70% of the area of ​​the normalized absorption spectrum of the first doping material F; and / or the difference between the peak position of the lowest energy absorption peak in the normalized absorption spectrum of the second fluorescent material F and the peak position of the highest energy emission peak in the normalized electroemission spectrum of the second TADF sensitizer E is less than or equal to 25nm.

[0013] In some embodiments, the wavelength corresponding to the peak position of the strongest emission peak of the second host material D, the second TADF sensitizer E, and the second fluorescent light-emitting material F satisfies:

[0014] λ(D)>λ(E)>λ(F).

[0015] In some embodiments, the HOMO energy level of the second host material D and the HOMO energy level of the second TADF sensitizer E, and the LUMO energy level of the second host material D and the LUMO energy level of the second TADF sensitizer E satisfy:

[0016] |HOMO|(D)-|HOMO|(E)<0.2eV;

[0017] |LUMO|(D)-|LUMO|(E)>0.3eV;

[0018] and / or,

[0019] The HOMO energy level of the first host material A and the HOMO energy level of the first TADF sensitizer B, as well as the LUMO energy level of the first host material A and the LUMO energy level of the first TADF sensitizer B satisfy:

[0020] |HOMO|(A)-|HOMO|(B)<0.2eV;

[0021] |LUMO|(B)-|LUMO|(A)>0.3eV.

[0022] In some embodiments, the second host material D and the second TADF sensitizer E satisfy the following relationship:

[0023] ||HOMO|(D)-|LUMO|(E)-S1(E)|≤0.2eV;

[0024] |HOMO|(D)-|LUMO|(E)-T1(E)|≤0.2eV;

[0025] and / or,

[0026] The first host material A and the first TADF sensitizer B satisfy the following relationship:

[0027] ||HOMO|(A)-|LUMO|(B)-S1(B)|≤0.2eV;

[0028] |HOMO|(A)-|LUMO|(B)-T1(B)|≤0.2eV.

[0029] In some embodiments, the second host material D and the first TADF sensitizer B satisfy the following relationship:

[0030] ||HOMO|(D)-|LUMO|(B)-S1(B)|≤0.2eV;

[0031] ||HOMO|(D)-|LUMO|(B)-T1(B)|≤0.2eV;

[0032] and / or,

[0033] The first host material A and the second TADF sensitizer E satisfy the following relationship:

[0034] ||HOMO|(A)-|LUMO|(E)-S1(E)|≤0.2eV;

[0035] ||HOMO|(A)-|LUMO|(E)-T1(E)|≤0.2eV.

[0036] In some embodiments, the first host material A and the second host material D are the same or different; when the first host material A and the second host material D are different, the first host material A and the second host material D satisfy the following conditions:

[0037] |HOMO(A)-HOMO(D)|<0.2eV;

[0038] |T1(A)-T1(D)|<0.1eV.

[0039] In some embodiments, the first host material A and the second host material D are the same, the first TADF sensitizer B and the second TADF sensitizer E are the same, and the mass ratio of the first TADF sensitizer B to the first host material A is consistent with the mass ratio of the second TADF sensitizer E to the second host material D.

[0040] In some embodiments, the first host material A and the second host material D are the same, the first TADF sensitizer B and the second TADF sensitizer E are the same, and the mass ratio of the first TADF sensitizer B to the first host material A is less than the mass ratio of the second TADF sensitizer E to the second host material D.

[0041] In some embodiments, the mass ratio of the first TADF sensitizer B to the first host material A is greater than or equal to 5% and less than or equal to 40%; the mass ratio of the second TADF sensitizer E to the second host material D is greater than or equal to 15% and less than or equal to 50%.

[0042] In some embodiments, the first TADF sensitizer B and the second TADF sensitizer E are different, and the lowest triplet energy of the first TADF sensitizer B and the second TADF sensitizer E, and the lowest singlet energy of the first TADF sensitizer B and the second TADF sensitizer E satisfy:

[0043] |T1(E)-T1(B)|<0.2eV;

[0044] |S1(E)-S1(B)|<0.2eV;

[0045] and / or,

[0046] Under the same test conditions, the luminescence efficiency of the light-emitting system composed of the first host material A and the first TADF sensitizer B is greater than the luminescence efficiency of the light-emitting system composed of the second host material D and the second TADF sensitizer E.

[0047] In some embodiments, the first light-emitting layer further comprises a first fluorescent light-emitting material C; the lowest singlet energy S1 of the first host material A, the first TADF sensitizer B and the first fluorescent light-emitting material C, and the lowest triplet energy T1 of the first host material A, the first TADF sensitizer B and the first fluorescent light-emitting material C satisfy:

[0048] S1(A)-T1(A)>0.2eV;

[0049] S1(B)-T1(B)<0.2eV;

[0050] S1(C)-T1(C)>0.2eV;

[0051] S1(A)>S1(B)>S1(C);

[0052] T1(A)>T1(B)>T1(C);

[0053] Wherein, the first fluorescent material C and the second fluorescent material F are the same or different;

[0054] When the first fluorescent material C and the second fluorescent material F are different, the wavelength corresponding to the strongest emission peak in the normalized electroemission spectrum of the first fluorescent material C is smaller than the wavelength corresponding to the strongest emission peak in the normalized electroemission spectrum of the second fluorescent material F, and there is a third overlapping region between the normalized electroemission spectrum of the first fluorescent material C and the normalized absorption spectrum of the second fluorescent material F.

[0055] In some embodiments, the area of ​​the third overlapping region is greater than 70% of the area of ​​the normalized absorption spectrum of the second fluorescent material F; and / or the peak position difference between the lowest energy absorption peak in the normalized absorption spectrum of the second fluorescent material F and the highest energy emission peak in the normalized electroemission spectrum of the first fluorescent material C is less than or equal to 25nm.

[0056] In some embodiments, the normalized electroemission spectrum of the first fluorescent light emitting material C and the normalized electroemission spectrum of the second fluorescent light emitting material F have a fourth overlapping region.

[0057] In some embodiments, the area of ​​the fourth overlapping region is greater than 90% of the area of ​​the normalized electroemission spectra of the first fluorescent material C and the second fluorescent material F; and / or the absolute value of the peak difference between the strongest emission peak in the normalized electroemission spectrum of the first fluorescent material C and the strongest emission peak in the normalized electroemission spectrum of the second fluorescent material F is less than 5nm.

[0058] In some embodiments, the wavelengths corresponding to the peak positions of the strongest emission peaks of the first host material A, the first TADF sensitizer B, and the first fluorescent light-emitting material C satisfy:

[0059] λ(A)>λ(B)>λ(C).

[0060] In some embodiments, when the first fluorescent luminescent material C and the second fluorescent luminescent material F are the same, the second TADF sensitizer E and the first TADF sensitizer B are the same, and the first host material A and the second host material D are the same, the mass proportion of the first fluorescent luminescent material C in the first light-emitting layer is greater than the mass proportion of the second fluorescent luminescent material F in the second light-emitting layer.

[0061] In some embodiments, a difference between a mass percentage of the first fluorescent material C in the first light-emitting layer and a mass percentage of the second fluorescent material F in the second light-emitting layer is greater than or equal to 0.1%.

[0062] In some embodiments, the mass proportion of the first fluorescent material C in the first light-emitting layer is 0.5% to 3%, and the mass proportion of the second fluorescent material F in the second light-emitting layer is 0.5% to 3%.

[0063] In some embodiments, the thickness of the first light-emitting layer is less than the thickness of the second light-emitting layer.

[0064] In some embodiments, the present invention further includes: a hole blocking layer located between the electron transport layer and the second light-emitting layer; and / or an electron blocking layer located between the hole transport layer and the first light-emitting layer.

[0065] In some embodiments, when the light-emitting device includes the electron blocking layer, the lowest triplet energy of the electron blocking layer is greater than the lowest triplet energy of the first TADF sensitizer B, and the difference between the two is greater than 0.2 eV; when the light-emitting device includes the hole blocking layer, the lowest triplet energy of the hole blocking layer is greater than the lowest triplet energy of the second TADF sensitizer E, and the difference between the two is greater than 0.2 eV.

[0066] In some embodiments, when the light-emitting device includes the hole blocking layer, the absolute value of the HOMO energy level of the hole blocking layer is 0.2 eV higher than the absolute value of the HOMO energy level of the second host material D; when the light-emitting device includes the electron blocking layer, the energy level difference between the HOMO energy level of the electron blocking layer and the HOMO energy level of the first host material A is less than or equal to 0.2 eV.

[0067] In another aspect, a light-emitting substrate is provided, comprising the light-emitting device as described above.

[0068] In another aspect, a light emitting device is provided, comprising the light emitting substrate as described above.

[0069] In another aspect, a method for preparing a light-emitting device is provided, comprising:

[0070] A hole transport layer, a first light-emitting layer, a second light-emitting layer and an electron transport layer are formed which are stacked in sequence; wherein the material of the first light-emitting layer includes a first host material A and a first TADF sensitizer B; the second light-emitting layer includes a second host material D, a second TADF sensitizer E and a second fluorescent material F; the transmission rates of the materials of the first light-emitting layer and the second light-emitting layer for holes are both greater than the transmission rates of the materials of the first light-emitting layer and the second light-emitting layer for electrons, and there is a first overlapping region between the normalized electroemission spectrum of the second fluorescent material F and the normalized absorption spectrum of the first TADF sensitizer B. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] In order to more clearly illustrate the technical solutions in the present disclosure, the following briefly introduces the drawings required to be used in some embodiments of the present disclosure. Obviously, the drawings described below are only drawings of some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can also be obtained based on these drawings. In addition, the drawings described below can be regarded as schematic diagrams, and are not limitations on the actual size of the product involved in the embodiments of the present disclosure, the actual process of the method, the actual timing of the signal, etc.

[0072] Figure 1 is a cross-sectional structural diagram of a light-emitting substrate according to some embodiments;

[0073] Figure 2 is a cross-sectional structural diagram of a light-emitting substrate according to some other embodiments;

[0074] Figure 3 is a comparison diagram of normalized electroemission spectra of TH-1 and TH-2 and normalized absorption spectrum of Dopant according to some embodiments;

[0075] Figure 4 is a comparison diagram of normalized electroemission spectra of TH-2 and TH-3 and normalized absorption spectrum of Dopant according to some embodiments;

[0076] Figure 5 is a comparison diagram of the electro-emission spectra of Dopant when the first TADF sensitizer B is TH-2 and TH-3 respectively according to some embodiments;

[0077] Figure 6 is a comparison diagram of voltage-current characteristic curves of light-emitting devices according to Comparative Example 1 and Experimental Example 1 according to some embodiments;

[0078] Figure 7 is a comparison diagram of the life span of the light emitting devices of Comparative Example 1 and Experimental Example 1 according to some embodiments;

[0079] Figure 8 is a comparison diagram of voltage-current characteristic curves of light-emitting devices according to Comparative Example 2 and Experimental Example 2 according to some embodiments;

[0080] Fig. 9 A comparison chart of the lifespan of the light emitting devices according to Comparative Example 2 and Experimental Example 2, and Comparative Example 3 and Experimental Examples 3 to 6 of some embodiments;

[0081] Fig.10 is a graph showing the relationship between the distance between the second fluorescent light-emitting material F and the surface of the light-emitting layer close to the hole transport layer and the light-emitting intensity of the second fluorescent light-emitting material F at 625 nm according to some embodiments;

[0082] Fig.11 is a comparison diagram of current density-current efficiency of light-emitting devices according to Comparative Example 3 and Experimental Examples 3 to 6 of some embodiments;

[0083] Fig.12 is a cross-sectional structural diagram of a light-emitting substrate according to some other embodiments;

[0084] Fig.13 is a cross-sectional structural diagram of a light-emitting substrate according to some further embodiments;

[0085] Fig.14 is a flow chart of a method for preparing a light-emitting substrate according to some embodiments. DETAILED DESCRIPTION

[0086] The following will be combined with the accompanying drawings to clearly and completely describe the technical solutions in some embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments provided by the present disclosure, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present disclosure.

[0087] Unless the context requires otherwise, throughout the specification and claims, the term "comprise" and other forms thereof, such as the third person singular form "comprises" and the present participle form "comprising", are to be interpreted as open, inclusive, that is, "including, but not limited to". In the description of the specification, the terms "one embodiment", "some embodiments", "exemplary embodiments", "example", "specific example" or "some examples" and the like are intended to indicate that specific features, structures, materials or characteristics associated with the embodiment or example are included in at least one embodiment or example of the present disclosure. The schematic naming of the above terms does not necessarily refer to the same embodiment or example. In addition, the specific features, structures, materials or characteristics may be included in any one or more embodiments or examples in any appropriate manner.

[0088] In the following, the terms "first" and "second" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present disclosure, unless otherwise specified, "plurality" means two or more.

[0089] “At least one of A, B, and C” has the same meaning as “at least one of A, B, or C” and both include the following combinations of A, B, and C: A only, B only, C only, the combination of A and B, the combination of A and C, the combination of B and C, and the combination of A, B, and C.

[0090] “A and / or B” includes the following three combinations: A only, B only, and a combination of A and B.

[0091] The use of "adapted to" or "configured to" herein is meant to be open and inclusive language that does not exclude devices adapted or configured to perform additional tasks or steps.

[0092] Additionally, the use of “based on” is meant to be open and inclusive, as a process, step, calculation, or other action “based on” one or more stated conditions or values ​​may, in practice, be based on additional conditions or values ​​beyond those stated.

[0093] As used herein, "about" or "approximately" includes the stated value and the average value that is within an acceptable range of deviation from the particular value, where the acceptable range of deviation is determined by one of ordinary skill in the art taking into account the measurements in question and the errors associated with the measurement of the particular quantity (i.e., the limitations of the measurement system).

[0094] Exemplary embodiments are described herein with reference to cross-sectional views and / or plan views that are idealized exemplary drawings. In the drawings, the thickness of layers and regions are exaggerated for clarity. Therefore, variations in shape relative to the drawings due to, for example, manufacturing techniques and / or tolerances are conceivable. Therefore, the exemplary embodiments should not be interpreted as being limited to the shapes of the regions shown herein, but include shape deviations due to, for example, manufacturing. For example, an etched region shown as a rectangle will typically have curved features. Therefore, the regions shown in the drawings are schematic in nature, and their shapes are not intended to illustrate the actual shape of regions of the device, and are not intended to limit the scope of the exemplary embodiments.

[0095] Some embodiments of the present disclosure provide a light-emitting device, which includes a light-emitting substrate and may also include other components. For example, it may include a circuit for providing an electrical signal to the light-emitting substrate to drive the light-emitting substrate to emit light. The circuit may be called a control circuit and may include a circuit board and / or an IC (Integrate Circuit) electrically connected to the light-emitting substrate.

[0096] In some embodiments, the light emitting device may be a lighting device, in which case the light emitting device is used as a light source to achieve a lighting function. For example, the light emitting device may be a backlight module in a liquid crystal display device, a lamp for internal or external lighting, or various signal lights.

[0097] In other embodiments, the light-emitting device may be a display device, in which case the light-emitting substrate is a display substrate for realizing the function of displaying an image (i.e., a picture). The light-emitting device may include a display or a product including a display. Among them, the display may be a flat panel display (Flat Panel Display, FPD), a micro display, etc. If divided according to whether the user can see the back of the display, the display may be a transparent display or an opaque display. If divided according to whether the display can be bent or curled, the display may be a flexible display or an ordinary display (which may be called a rigid display). For example, products including displays may include: computer monitors, televisions, billboards, laser printers with display functions, telephones, mobile phones, personal digital assistants (Personal Digital Assistant, PDA), laptop computers, digital cameras, camcorders, viewfinders, vehicles, large-area walls, theater screens or stadium signs, etc.

[0098] Some embodiments of the present disclosure provide a light-emitting substrate, such as Figure 1 As shown, the light-emitting substrate 1 may include a substrate 11, a pixel defining layer 12 disposed on the substrate 11, and a plurality of light-emitting devices 13. The pixel defining layer 12 has a plurality of openings Q, and the plurality of light-emitting devices 13 may be disposed in one-to-one correspondence with the plurality of openings Q. The plurality of light-emitting devices 13 here may be all or part of the light-emitting devices 13 included in the light-emitting substrate 1; and the plurality of openings Q may be all or part of the openings on the pixel defining layer 12.

[0099] In some embodiments, the substrate 11 may be glass, sapphire (aluminum oxide), polyimide, silicon wafer, etc.

[0100] In some embodiments, Figure 1 As shown, each light emitting device 13 includes: a first electrode 131 (anode), a hole transport layer 134, a first light emitting layer 133a, a second light emitting layer 133b, an electron transport layer 135 and a second electrode 132 (cathode) stacked in sequence.

[0101] In some embodiments, the material of the anode can be selected from high work function materials, such as ITO (Indium Tin Oxides), IZO (Indium Zinc Oxide) or composite materials (such as Ag / ITO, Al / ITO, Ag / IZO or Al / IZO, where "Ag / ITO" refers to a stacked structure consisting of a metal silver electrode and an ITO electrode), and the material of the cathode can be selected from low work function materials, such as metal Al, Ag or Mg, or low work function metal alloy materials (such as magnesium-aluminum alloy, magnesium-silver alloy), etc.

[0102] In some embodiments, for each light emitting device 13, the anode is closer to the substrate 11 than the cathode, or the cathode is closer to the substrate 11 than the anode. That is, the light emitting substrate 1 can be a "upright" light emitting substrate or an "inverted" light emitting substrate.

[0103] When the anode is closer to the substrate 11 than the cathode, the light-emitting substrate 1 is a "normal" light-emitting substrate; when the cathode is closer to the substrate 11 than the anode, the light-emitting substrate 1 is an "inverted" light-emitting substrate.

[0104] According to whether the first electrode 131 and the second electrode 132 are light-transmissive, the light-emitting substrate 1 can be divided into a bottom-emitting light-emitting substrate, a top-emitting light-emitting substrate and a double-sided emission light-emitting substrate.

[0105] Taking the light-emitting substrate 1 as an "upright" light-emitting substrate as an example, when the first electrode 131 is selected from a transparent electrode, such as ITO, IZO, etc., and the second electrode 132 is selected from a thicker metal electrode (in this case, the second electrode 132 can be regarded as a reflective electrode), such as a magnesium-aluminum alloy with a thickness of more than 80nm, the light-emitting substrate 1 is a bottom-emitting light-emitting substrate. When the first electrode 131 is selected from a thicker stacked structure (in this case, the first electrode 131 can be regarded as a reflective electrode), such as Ag / ITO, Al / ITO, Ag / IZO or Al / IZO, and the second electrode 132 is selected from a thinner metal electrode, such as a magnesium-aluminum alloy with a thickness of 10nm to 20nm, the light-emitting substrate 1 is a top-emitting light-emitting substrate. Of course, when the first electrode 131 is selected from a transparent electrode and the material of the second electrode 132 is selected from a thinner metal electrode, the light-emitting substrate 1 is a double-sided emission light-emitting substrate.

[0106] Here, it should be noted that, when the light-emitting substrate 1 is a bottom-emitting light-emitting substrate, the substrate 11 can be made of a material with a light transmittance greater than 85%, such as glass.

[0107] Furthermore, in the case where the light-emitting substrate 1 described above is a top-emitting light-emitting substrate, as Figure 2 As shown, the light emitting device 13 may further include an optical capping layer (CPL) 14 disposed on the side of the second electrode 132 away from the first electrode 131, and the refractive index of the optical capping layer 14 is greater than 1.8 and the thickness is 50nm-100nm, which can improve the optical output.

[0108] In addition, when the light-emitting substrate 1 described above is a top-emitting light-emitting substrate, the thickness of the first light-emitting layer 133a and the second light-emitting layer 133b can also be adjusted so that the thickness of the first light-emitting layer 133a and the second light-emitting layer 133b can meet the optical path requirements of the optical microresonator, thereby obtaining better light output intensity and color.

[0109] In some embodiments, Figure 2 As shown, the light-emitting substrate 1 may further include an encapsulation layer 15, and the encapsulation layer 15 may be a UV (Ultraviolet Rays) encapsulation glue or an encapsulation film. Among them, the UV encapsulation glue is also called shadowless glue. The optical cover layer 14 may be arranged on a side of the encapsulation layer 15 away from the second electrode 132, or may be arranged on a side of the encapsulation layer 15 close to the second electrode 132.

[0110] In some embodiments, the material of the first light-emitting layer 133a includes a first host material A and a first TADF (Thermally Activated Delayed Fluorescence) sensitizer B, and the material of the second light-emitting layer 133b includes a second host material D, a second TADF sensitizer E, and a second fluorescent light-emitting material F. The transport rates of the first light-emitting layer 133a and the second light-emitting layer 133b to holes are both greater than the transport rates of the first light-emitting layer 133a and the second light-emitting layer 133b to electrons, and the normalized electroemission spectrum of the first TADF sensitizer B and the normalized absorption spectrum of the second fluorescent light-emitting material F have a first overlapping region.

[0111] The host material refers to the material with the largest mass proportion in the host-guest doping system. TADF sensitizer is a material with TADF characteristics. Materials with TADF characteristics are materials with a small energy gap between the singlet excited state and the triplet excited state. In this material, sufficient reverse intersystem crossing from the triplet excited state to the singlet excited state is generated through thermal excitation, and the triplet exciton is converted into a singlet exciton, which can fully utilize the energy of the triplet exciton.

[0112] Fluorescence resonance energy transfer (also known as Forster energy transfer) refers to the phenomenon that when the emission spectrum of one fluorescent group (donor) overlaps with the absorption spectrum of the other group (acceptor) between two different fluorescent groups, the two fluorescent groups will be separated by a certain distance (usually less than 1 / 2). ), the phenomenon of fluorescence energy transfer from the donor to the acceptor can be observed, that is, when excited by the excitation light of the donor, the fluorescence intensity produced by the donor is much lower than when it exists alone, while the fluorescence emitted by the acceptor is greatly enhanced, accompanied by the corresponding shortening and prolongation of their fluorescence lifetimes. Simply put, it is the process of energy transfer from the donor to the acceptor mediated by a pair of dipoles in the excited state of the donor group. This process does not involve photons, so it is non-radiative. After the donor molecule is excited, when the acceptor molecule is at a certain distance from the donor molecule, and the energy difference between the vibration energy levels of the ground state and the first electronic excited state of the donor and the acceptor is adapted to each other, the donor in the excited state will transfer part or all of the energy to the acceptor, causing the acceptor to be excited. In the entire energy transfer process, the emission and reabsorption of photons are not involved.

[0113] The electroemission spectrum of the first TADF sensitizer B is the spectrum that can be emitted when the first TADF sensitizer B is doped into the first host material A in a certain proportion (such as 20%) to prepare a light-emitting device in the power-on state. The spectrum can reflect the wavelength range (as the horizontal axis) of the light emitted by the first TADF sensitizer B and the light intensity corresponding to each wavelength within the wavelength range (as the vertical axis).

[0114] The absorption spectrum of the second fluorescent material F is the spectrum that can be absorbed when the second fluorescent material F is made into a thin sheet under the irradiation of light in the 200-800nm ​​band (including ultraviolet light and visible light). The spectrum can reflect the absorption intensity (as the vertical coordinate) of the second fluorescent material F to light of different wavelengths (as the horizontal coordinate) under the 200-800nm ​​band light.

[0115] Spectral normalization is to normalize the spectrum, that is, to set the total light intensity to 1, so that the light intensity on the ordinate becomes a decimal. The spectrum obtained in this way is the normalized spectrum.

[0116] According to the first overlapping region between the electro-emission spectrum of the first TADF sensitizer B and the absorption spectrum of the second fluorescent material F, it can be known that the energy of the singlet exciton of the first TADF sensitizer B can be transferred to the singlet exciton of the second fluorescent material F through Forster energy transfer, and the singlet exciton of the second fluorescent material F transitions back to the ground state to emit light. Therefore, the first TADF sensitizer B acts as a donor, and the second fluorescent material F acts as an acceptor, and the above Forster energy transfer conditions are met, that is, the first TADF sensitizer B and the second fluorescent material F are both fluorescent materials, and under the excitation of the emission spectrum of the first TADF sensitizer B, the fluorescence emitted by the second fluorescent material F will be greatly enhanced, and the fluorescence lifetime will be improved, while the fluorescence emitted by the first TADF sensitizer B will be reduced, and the fluorescence lifetime will be reduced.

[0117] In this embodiment, according to the above-mentioned transmission rate of the materials of the first light-emitting layer 133a and the second light-emitting layer 133b for holes is greater than the transmission rate of the materials of the first light-emitting layer 133a and the second light-emitting layer 133b for electrons, it can be known that when holes and electrons are simultaneously injected into the surfaces of the first light-emitting layer 133a and the second light-emitting layer 133b away from each other and begin to be transmitted, since the transmission rate of holes is greater than the transmission rate of electrons, holes and electrons are more likely to meet in the light-emitting layer close to the electron transport layer 135, that is, holes and electrons are more likely to meet at the location of the second light-emitting layer 133b, and therefore, relative to the first light-emitting layer 133a, holes and electrons (that is, electrons and holes) are more likely to recombine to produce excitons at the location of the second light-emitting layer 133b.

[0118] Therefore, when a small amount of holes and electrons are recombined at the location of the first light-emitting layer 133a to generate excitons and make the first TADF sensitizer B emit light, most of the holes and electrons are recombined at the location of the second light-emitting layer 133b to generate excitons and make the second fluorescent light-emitting material F emit light. In this case, assuming that the light-emitting device 13 only includes one light-emitting layer, that is, the material and composition ratio at the location of the first light-emitting layer 133a are exactly the same as the material and composition ratio at the location of the second light-emitting layer 133b, the light-emitting efficiency of the light-emitting device 13 is completely dependent on the light-emitting efficiency of the material at the location of the second light-emitting layer 133b. In this embodiment, since the material and composition ratio of the first light-emitting layer 133a are not exactly the same as the material and composition ratio of the second light-emitting layer 133b, and the normalized electroemission spectrum of the first TADF sensitizer B is the same as the normalized electroemission spectrum of the second fluorescent light-emitting material F. There is a first overlapping region between the absorption spectra. Therefore, the energy of the singlet exciton of the first TADF sensitizer B can be transferred to the singlet exciton of the second fluorescent light-emitting material F through Forster energy, so that the fluorescence emitted by the second fluorescent light-emitting material F is greatly enhanced, and the device life is improved. Compared with a single-layer light-emitting layer, the energy generated by a small amount of excitons can be used to enhance the fluorescence emitted by the second fluorescent light-emitting material F and improve the fluorescence lifetime, thereby solving the problem in the related art that a small amount of excitons contributes little to the luminescence and energy transfer cannot be achieved, thereby failing to improve the luminescence efficiency of the light-emitting device.

[0119] In some embodiments, the first host material A and the second host material D may be the same or different. Accordingly, the first TADF sensitizer B and the second TADF sensitizer E may also be the same or different.

[0120] In the case where the first host material A and the second host material D are the same, the first host material A and the second host material D may both be thermally delayed fluorescent materials or traditional fluorescent materials (different from thermally delayed fluorescent materials). In this case, the first host material A and the second host material D may both be monomer materials or materials in the form of radical-excited complexes. In the case where the first host material A and the second host material D are both monomer materials, the molecular structures of the first host material A and the second host material D are the same. In the case where the first host material A and the second host material D are both materials in the form of radical-excited complexes, the molecular structures and compositions of the first host material A and the second host material D are the same.

[0121] In the case where the first host material A and the second host material D are different, the first host material A and the second host material D satisfy the following:

[0122] |HOMO(A)-HOMO(D)|<0.2eV;

[0123] |T1(A)-T1(D)|<0.1eV.

[0124] At this time, in the case where the first host material A and the second host material D are both monomer materials, the molecular structures of the first host material A and the second host material D are different, and they can be both thermally delayed fluorescent materials or traditional fluorescent materials. Alternatively, the first host material A and the second host material D are thermally delayed fluorescent materials and traditional fluorescent materials, respectively. In the case where the first host material A and the second host material D are both materials in the form of exciplexes, the molecular structure of at least one of the electron donor molecules and the electron acceptor molecules in the first host material A and the second host material D is different, and / or the mixing ratio between the electron donor molecules and the electron acceptor molecules is different. At this time, the electron donor molecules and the electron acceptor molecules can both be thermally delayed fluorescent materials or traditional fluorescent materials, or the electron donor molecules and the electron acceptor molecules can be thermally delayed fluorescent materials and traditional fluorescent materials, respectively.

[0125] In this embodiment, the HOMO (Highest Occupied Molecular Orbital) energy levels between the first host material A and the second host material D are not much different, which facilitates the injection of holes injected into the first host material A into the second host material D, thereby facilitating the recombination of holes and electrons on the second host material D, improving the luminous efficiency of the second fluorescent material F, and avoiding the problem that holes and electrons cannot recombine normally on the second host material D.

[0126] At the same time, since the energy difference between the triplet excitons of the first host material A and the second host material D is not large, the excitons can freely migrate between the first light-emitting layer 133a and the second light-emitting layer 133b, which is beneficial to expand the light-emitting area.

[0127] It should be noted here that, for the exciplex, the HOMO (Highest Occupied Molecular Orbital) energy level of the exciplex is the HOMO energy level with a smaller absolute value of the electron donor molecule and the electron acceptor molecule (that is, the deeper HOMO energy level of the electron donor molecule and the electron acceptor molecule), and the LUMO (Lowest Unoccupied Molecular Orbital) energy level of the exciplex is the LUMO energy level with a larger absolute value of the electron donor molecule and the electron acceptor molecule (that is, the shallower LUMO energy level of the electron donor molecule and the electron acceptor molecule).

[0128] Based on this, in some embodiments, the first host material A and the second host material D can be independently selected from carbazole derivatives or aromatic silane derivatives, such as 3,3′-di(9H-carbazol-9-yl)-1,1′-biphenyl (3,3′-Di(9H-carbazol-9-yl)biphenyl), 1,3-di-9-carbazolylbenzene and 4,4-di(9-carbazolyl)biphenyl (4,4′-Bis(N-carbazolyl)-1,1′-biphenyl).

[0129] In the case where the first TADF sensitizer B and the second TADF sensitizer E are the same, the first TADF sensitizer B and the second TADF sensitizer E can also be both monomer materials or materials in the form of exciplexes. In the case where the first TADF sensitizer B and the second TADF sensitizer E are both monomer materials, the molecular structures of the first TADF sensitizer B and the second TADF sensitizer E are the same. In the case where the first TADF sensitizer B and the second TADF sensitizer E are both materials in the form of exciplexes, the molecular structures and mixing ratios of the electron donor molecules and the electron acceptor molecules in the first TADF sensitizer B and the second TADF sensitizer E are the same. At this time, the difference between the triplet energy and the singlet energy of the first TADF sensitizer B, and the difference between the triplet energy and the singlet energy of the second TADF sensitizer E are both small, and both can produce delayed fluorescence. And when the first TADF sensitizer B and the second TADF sensitizer E are the same, according to the first overlapping region between the normalized electroemission spectrum of the first TADF sensitizer B and the normalized absorption spectrum of the second fluorescent material F, it can be known that the normalized electroemission spectrum of the second TADF sensitizer E and the normalized absorption spectrum of the second fluorescent material F also have a first overlapping region, that is, the energy of the singlet exciton of the second TADF sensitizer E can also be transferred to the singlet exciton of the second fluorescent material F through Forster energy, thereby further improving the luminescence efficiency and fluorescence lifetime.

[0130] When the first TADF sensitizer B and the second TADF sensitizer E are different, the normalized electroemission spectrum of the second TADF sensitizer E and the normalized absorption spectrum of the second fluorescent light emitting material F have a second overlapping region.

[0131] In this case, when the first TADF sensitizer B and the second fluorescent luminescent material F are both materials in the form of an exciplex, similar to the first host material A and the second host material D above, the molecular structure of at least one of the electron donor molecule and the electron acceptor molecule in the first TADF sensitizer B and the second fluorescent luminescent material F is different, and / or the mixing ratio between the electron donor molecule and the electron acceptor molecule is different. At this time, the difference between the triplet energy and the singlet energy of the first TADF sensitizer B, and the difference between the triplet energy and the singlet energy of the second TADF sensitizer E are both small, and delayed fluorescence can be generated. And in this case, there is a second overlapping region between the normalized electroemission spectrum of the second TADF sensitizer E and the normalized absorption spectrum of the second fluorescent luminescent material F. The energy of the singlet exciton of the second TADF sensitizer E can also be transferred to the singlet exciton of the second fluorescent luminescent material F through the Forster energy, which can also improve the fluorescence intensity and life of the second fluorescent luminescent material F.

[0132] Based on this, in some embodiments, the first TADF sensitizer B and the second TADF sensitizer E can be independently selected from triazines, pyridines, ketones, quinones, furans and other derivatives having one or more DA structures, such as 3,4,5,6-tetrakis(3,6-di-tert-butyl-9-carbazolyl)-terephthalonitrile (3,4,5,6-tetrakis(3,6-di-t-Butylcarbazol-9-yl)-1,2-dicyanobenzene) and 2,3,5,6-tetrakis(9-carbazolyl)-terephthalonitrile (2,3,5,6-tetrakis(carbazol-9-yl)-1,4-dicyanobenzene).

[0133] In some embodiments, the area of ​​the second overlapping region is greater than 70% of the area of ​​the normalized absorption spectrum of the second fluorescent material F. And / or, the difference between the peak position of the absorption peak with the lowest energy in the normalized absorption spectrum of the second fluorescent material F and the peak position of the emission peak with the highest energy in the normalized electro-emission spectrum of the second TADF sensitizer E is less than or equal to 25 nm. In this embodiment, the Forster energy transfer from the second TADF sensitizer E to the second fluorescent material F can be sufficient, so that the color purity of the light emitted by the second fluorescent material F can be improved.

[0134] Here, taking the first host material A and the second host material D as the same, both are TM, TM is selected from 3,3′-di(9H-carbazol-9-yl)-1,1′-biphenyl (3,3′-Di(9H-carbazol-9-yl)biphenyl) as an example, when the first TADF sensitizer B and the second TADF sensitizer E are the same, for example, the first TADF sensitizer B and the second TADF sensitizer E can be TH-1, TH-1 can be selected from 3,4,5,6-tetrakis(3,6-di-t-Butylcarbazol-9-yl)-1,2-dicyanobenzene, at this time, the normalized electroemission spectrum of TH-1 and the normalized absorption spectrum of the second fluorescent light-emitting material F (Dopant) (using Dopant-Abs) are as follows: Figure 3 As shown, the second overlapping region satisfies the above conditions. And the difference between the peak position of the absorption peak with the lowest energy in the normalized absorption spectrum of the second fluorescent luminescent material F and the peak position of the emission peak with the highest energy in the normalized electro-emission spectrum of the second TADF sensitizer E is less than or equal to 20nm. Therefore, the energy transfer between the second TADF sensitizer E and the second fluorescent luminescent material F is sufficient, which can improve the color purity of the light emitted by the second fluorescent luminescent material F. At the same time, according to the first TADF sensitizer B and the second TADF sensitizer E being the same, the above relationship also exists between the first TADF sensitizer B and the second fluorescent luminescent material F. Compared with a single-layer light-emitting layer, it is possible to use the energy generated by a small amount of excitons to enhance the fluorescence emitted by the second fluorescent luminescent material F and improve the fluorescence lifetime, thereby solving the problem in the related art that a small amount of excitons contribute little to the luminescence and cannot achieve energy transfer, thereby failing to improve the luminescence efficiency of the light-emitting device.

[0135] When the first TADF sensitizer B and the second TADF sensitizer E are different, Forster energy transfer can also occur from the first TADF sensitizer B to the second fluorescent light-emitting material F. It can be seen that, compared with a single-layer light-emitting layer, the energy generated by a small amount of excitons can be utilized to enhance the fluorescence emitted by the second fluorescent light-emitting material F and increase the fluorescence lifetime, thereby solving the problem in the related art that a small amount of excitons contributes little to the luminescence and cannot achieve energy transfer, thereby failing to improve the luminescence efficiency of the light-emitting device.

[0136] In some embodiments, the area of ​​the first overlapping region is greater than 70% of the area of ​​the normalized absorption spectrum of the second fluorescent material F. And / or, the difference between the peak position of the lowest energy absorption peak in the normalized absorption spectrum of the second fluorescent material F and the peak position of the highest energy emission peak in the electro-emission spectrum of the first TADF sensitizer B is less than or equal to 25 nm. In this embodiment, the energy transfer from the first TADF sensitizer B to the second fluorescent material F can be sufficient, and the color purity of the light emitted by the second fluorescent material F can be improved.

[0137] Among them, according to the above that the first TADF sensitizer B and the second TADF sensitizer E can be the same or different, it can be known that when the first TADF sensitizer B and the second TADF sensitizer E are the same, the area of ​​the second overlapping region can be referred to as being greater than 70% of the area of ​​the normalized absorption spectrum of the first doping material F. And / or, the difference between the peak position of the lowest energy absorption peak in the normalized absorption spectrum of the second fluorescent light-emitting material F and the peak position of the highest energy emission peak in the normalized electro-emission spectrum of the second TADF sensitizer E is less than or equal to 25nm.

[0138] In the case where the first TADF sensitizer B and the second TADF sensitizer E are different, since the area of ​​the second overlapping region is greater than 70% of the area of ​​the normalized absorption spectrum of the first doping material F. And / or, the difference between the peak position of the lowest energy absorption peak in the normalized absorption spectrum of the second fluorescent luminescent material F and the peak position of the highest energy emission peak in the normalized electro-emission spectrum of the second TADF sensitizer E is less than or equal to 25nm, on the basis that the area of ​​the first overlapping region is greater than 70% of the area of ​​the normalized absorption spectrum of the second fluorescent luminescent material F. And / or, the difference between the peak position of the lowest energy absorption peak in the normalized absorption spectrum of the second fluorescent luminescent material F and the peak position of the highest energy emission peak in the electro-emission spectrum of the first TADF sensitizer B is less than or equal to 25nm, the luminescence intensity, fluorescence lifetime and color purity of the second fluorescent luminescent material F can be further improved.

[0139] For example, the first host material A and the second host material are both selected from TM, TM is selected from 3,3′-di(9H-carbazol-9-yl)-1,1′-biphenyl, the second TADF sensitizer E is selected from TH-1, TH-1 is selected from 3,4,5,6-tetrakis(3,6-di-t-Buty Taking the first TADF sensitizer B as an example, the first TADF sensitizer B is selected from TH-2, and TH-2 is selected from 2,3,5,6-tetrakis(carbazol-9-yl)-1,4-dicyanobenzene, the normalized electroemission spectrum of TH-2 and the normalized absorption spectrum of the second fluorescent material F (Dopant) are as follows: Figure 3 As shown in FIG. 1 , it can be seen that the area of ​​the first overlapping region is greater than the area of ​​the second overlapping region. Using TH-3 as a comparative example, by measuring the normalized electro-emission spectrum of TH-3 and the normalized absorption spectrum of the second fluorescent material F (Dopant), Figure 4 As shown, the overlap area between the normalized electroemission spectrum of TH-3 and the normalized absorption spectrum of the second fluorescent luminescent material F (Dopant) is smaller than the overlap area between the normalized electroemission spectrum of TH-2 and the normalized absorption spectrum of the second fluorescent luminescent material F (Dopant), and correspondingly, as Figure 5 As shown, the emission peak of the second fluorescent material F of the light-emitting device made in this way clearly has the EL characteristic emission from TH-3, and the color purity is poor, while the emission peak of the second fluorescent material F of the light-emitting device made with TH-2 as the first TADF sensitizer B does not have the EL characteristic emission from TH-2, and the color purity is better.

[0140] In some embodiments, the lowest singlet energy S1 of the second host material D, the second TADF sensitizer E, and the second fluorescent light-emitting material F, and the lowest triplet energy T1 of the second host material D, the second TADF sensitizer E, and the second fluorescent light-emitting material F satisfy:

[0141] S1(D)-T1(D)>0.2eV;

[0142] S1(E)-T1(E)<0.2eV;

[0143] S1(F)-T1(F)>0.2eV;

[0144] S1(D)>S1(E)>S1(F);

[0145] T1(D)>T1(E)>T1(F).

[0146] In this embodiment, holes and electrons are recombined on the second host material D to form a large number of singlet excitons and triplet excitons. The energy of the singlet excitons of the second host material D can be transferred to the singlet excitons of the second TADF sensitizer E through Forster energy transfer, and the triplet excitons of the second host material D can be transferred to the triplet excitons of the second TADF sensitizer E through Dexter energy transfer. The triplet excitons of the second TADF sensitizer E can transition to their own singlet state through anti-intersystem crossing. Therefore, the Dexter energy transfer from the triplet excitons of the second TADF sensitizer E to the triplet T1 excitons of the second fluorescent light-emitting material F can be suppressed, thereby improving the luminous efficiency. In addition, S1(D)>S1(E)>S1(F), T1(D)>T1(E)>T1(F), which can effectively avoid the energy from the second fluorescent light-emitting material F to the second TADF sensitizer E and the second host material D in reverse, and achieve sufficient host-guest energy transfer.

[0147] In some embodiments, the wavelength corresponding to the peak position of the strongest emission peak of the second host material D, the second TADF sensitizer E, and the second fluorescent light-emitting material F satisfies:

[0148] λ(D)>λ(E)>λ(F).

[0149] In this embodiment, the transfer of energy from a high energy state to a low energy state can be ensured, the reverse transfer of energy can be prevented, and full utilization of energy can be achieved.

[0150] In some embodiments, the HOMO energy level of the second host material D and the HOMO energy level of the second TADF sensitizer E, and the LUMO energy level of the second host material D and the LUMO energy level of the second TADF sensitizer E satisfy:

[0151] |HOMO|(D)-|HOMO|(E)<0.2eV;

[0152] |LUMO|(D)-|LUMO|(E)>0.3eV;

[0153] and / or,

[0154] The HOMO energy level of the first host material A and the HOMO energy level of the first TADF sensitizer B, as well as the LUMO energy level of the first host material A and the LUMO energy level of the first TADF sensitizer B satisfy:

[0155] |HOMO|(A)-|HOMO|(B)<0.2eV;

[0156] |LUMO|(B)-|LUMO|(A)>0.3eV.

[0157] In this embodiment, in the second light-emitting layer 133b, the HOMO energy level of the second host material D and the HOMO energy level of the second TADF sensitizer E are not much different, which is convenient for holes to jump into the HOMO energy level of the second TADF sensitizer E, and the LUMO energy level of the second TADF sensitizer E is deeper than the LUMO energy level of the second host material D, which is conducive to electrons falling into the LUMO energy level of the second TADF sensitizer E, so that electrons and holes are mainly recombined on the second TADF sensitizer E, so that electrons and holes tend to form excitons of the second TADF sensitizer E and emit light, avoiding the formation of electron-hole pairs between the host and guest luminescent bodies, which is not conducive to luminescence. And / or, in the first light-emitting layer 133a, the HOMO energy level of the first host material A and the HOMO energy level of the first TADF sensitizer B are not much different, which is convenient for holes to transition to the HOMO energy level of the first TADF sensitizer B, while the LUMO energy level of the first TADF sensitizer B is deeper than the LUMO energy level of the first host material A, which is conducive to electrons falling into the LUMO energy level of the first TADF sensitizer B, so that electrons and holes are mainly recombined on the first TADF sensitizer B, so that electrons and holes tend to form excitons of the first TADF sensitizer B and emit light, avoiding the formation of electron-hole pairs between the host and guest luminescent bodies, which is not conducive to luminescence.

[0158] In some embodiments, the second host material D and the second TADF sensitizer E satisfy the following relationship:

[0159] ||HOMO|(D)-|LUMO|(E)-S1(E)|≤0.2eV;

[0160] |HOMO|(D)-|LUMO|(E)-T1(E)|≤0.2eV.

[0161] That is, the second host material D and the second TADF sensitizer E do not form an exciplex.

[0162] And / or, the first host material A and the first TADF sensitizer B satisfy the following relationship:

[0163] ||HOMO|(A)-|LUMO|(B)-S1(B)|≤0.2eV;

[0164] |HOMO|(A)-|LUMO|(B)-T1(B)|≤0.2eV.

[0165] That is, the first host material A and the first TADF sensitizer B do not form an exciplex.

[0166] An exciplex is an aggregate of two molecules or atoms of different species. In the excited state, the two molecules or atoms interact strongly, producing new energy levels. The emission spectrum is different from that of a single species and there is no fine structure.

[0167] In this embodiment, when the second host material D and the second TADF sensitizer E do not form an exciplex, the second host material D and the second TADF sensitizer E do not produce a spectrum different from their own intrinsic spectrum. When the first host material A and the first TADF sensitizer B do not form an exciplex, the first host material A and the first TADF sensitizer B do not produce a spectrum different from their own intrinsic spectrum, so that the luminescent properties of the second host material D and the second TADF sensitizer E change, and / or the luminescent properties of the first host material A and the first TADF sensitizer B change, making the performance unreliable. Thereby, the color purity of the luminescence can be further improved.

[0168] In order to further prevent the problem of unreliable performance caused by the formation of exciplexes and further improve the color purity of luminescence, the second host material D and the first TADF sensitizer B satisfy the following relationship:

[0169] ||HOMO|(D)-|LUMO|(B)-S1(B)|≤0.2eV;

[0170] ||HOMO|(D)-|LUMO|(B)-T1(B)|≤0.2eV.

[0171] That is, no exciplex is formed between the second host material D and the first TADF sensitizer B.

[0172] And / or, the first host material A and the second TADF sensitizer E satisfy the following relationship:

[0173] ||HOMO|(A)-|LUMO|(E)-S1(E)|≤0.2eV;

[0174] ||HOMO|(A)-|LUMO|(E)-T1(E)|≤0.2eV.

[0175] That is, no exciplex is formed between the first host material A and the second TADF sensitizer E.

[0176] The specific principle can refer to the above description of no excited complex formed between the second host material D and the second TADF sensitizer E, and / or no excited complex formed between the first host material A and the first TADF sensitizer B, which will not be repeated here.

[0177] In some embodiments, the first host material A and the second host material D are the same, the first TADF sensitizer B and the second TADF sensitizer E are the same, and the mass ratio of the first TADF sensitizer B and the first host material A is consistent with the mass ratio of the second TADF sensitizer E and the second host material D.

[0178] In this embodiment, by providing the first light-emitting layer 133a, utilizing the singlet excitons and triplet excitons generated at the position of the first light-emitting layer 133a, and utilizing the first TADF sensitizer B to generate sufficient antisystem crossing from the triplet excited state to the singlet excited state through thermal excitation, the triplet excitons are converted into singlet excitons, and then the energy of the singlet excitons is transferred to the singlet excitons of the second fluorescent material F through Forster energy transfer. Only by the singlet excitons of the second fluorescent material F transitioning back to the ground state to emit light, the energy from the first light-emitting layer 133a to the second light-emitting layer 133b can be fully transferred, thereby improving the luminescence efficiency and the fluorescence lifetime.

[0179] In some embodiments, the first host material A and the second host material D are the same, the first TADF sensitizer B and the second TADF sensitizer E are the same, and the mass ratio of the first TADF sensitizer B to the first host material A is less than the mass ratio of the second TADF sensitizer E to the second host material D.

[0180] In this embodiment, when the doping concentration of the second TADF sensitizer E in the second host material D is constant, by reducing the doping concentration of the first TADF sensitizer B in the first host material A, the excited state density of a single first TADF sensitizer B molecule can be effectively increased, the probability of antisystem crossing is improved, and the excitons generated at the position of the first light-emitting layer 133a can be fully utilized, thereby avoiding the problem in the related art that the exciton contribution at the position of the first light-emitting layer 133a is small due to the imbalance of hole transport, and the exciton utilization rate is low, which is not conducive to the energy transfer of the singlet excitons of the first TADF sensitizer B to the singlet excitons of the second fluorescent light-emitting material F through Forster energy, thereby making the energy utilization rate higher.

[0181] In some embodiments, the mass ratio of the first TADF sensitizer B to the first host material A is greater than or equal to 5% and less than or equal to 40%. The mass ratio of the second TADF sensitizer E to the second host material D is greater than or equal to 15% and less than or equal to 50%.

[0182] For example, when the mass ratio of the first TADF sensitizer B and the first main material A is equal to 5%, the mass ratio of the second TADF sensitizer E and the second main material D can be equal to 15%; when the mass ratio of the first TADF sensitizer B and the first main material A is equal to 15%, the mass ratio of the second TADF sensitizer E and the second main material D can be equal to 25%.

[0183] The first host material A and the second host material are both selected from TM, TM is selected from 3,3′-di(9H-carbazol-9-yl)-1,1′-biphenyl (3,3′-Di(9H-carbazol-9-yl)biphenyl), the first TADF sensitizer B and the second TADF sensitizer E are selected from TH-1, TH-1 is selected from 3,4,5,6-tetrakis(3,6-di-tert-butyl-9-carbazol-9-yl)-terephthalonitrile (3,4,5,6-tetrakis(3,6- di-t-Butylcarbazol-9-yl)-1,2-dicyanobenzene) is taken as an example, by setting up comparative example 1 and experimental example 1, in comparative example 1, the mass ratio of the first TADF sensitizer B and the first main material A is equal to the mass ratio of the second TADF sensitizer E and the second main material D, both of which are 70%:29.3%, that is, the material composition of the first light-emitting layer 133a and the material composition of the second light-emitting layer 133b in the comparative example are the same, that is, the case of a single-layer light-emitting layer. At this time, the mass percentage of Dopant in the light-emitting layer can be 0.7%. In experimental example 1, the mass ratio of the first TADF sensitizer B and the first main material A is 80%:20%, and the first light-emitting layer 133a does not contain Dopant. After being made into a light-emitting device, the luminous efficiency, voltage, color coordinates and life of the light-emitting device are tested by passing the same current density through the light-emitting device, and the following Table 1, Figure 6 and Figure 7 Results shown.

[0184] Table 1

[0185]

[0186] From Table 1, Figure 6 and Figure 7 It can be seen that by reducing the doping concentration of the first TADF sensitizer B in the first light-emitting layer 133a, a more balanced carrier distribution can be achieved, and excitons can be used more efficiently, so that the device has higher efficiency, lower efficiency roll-off, and correspondingly, longer life.

[0187] Among them, Figure 7 In the vertical axis, L refers to the brightness of the device at a certain moment, L0 refers to the initial brightness of the device, and L / L0 refers to the decay rate of the device brightness over time.

[0188] In Table 1, the life of the device in Comparative Example 1 is 100%, and the life of the device in Experimental Example 1 is 115%, which means that the life of the device in Comparative Example 1 is used as a comparison benchmark, and the life of the device in Experimental Example 1 is 15% higher than that of the device in Comparative Example 1.

[0189] In some embodiments, the first TADF sensitizer B and the second TADF sensitizer E are different, and the lowest triplet energy of the first TADF sensitizer B and the second TADF sensitizer E, and the lowest singlet energy of the first TADF sensitizer B and the second TADF sensitizer E satisfy:

[0190] |T1(E)-T1(B)|<0.2eV;

[0191] |S1(E)-S1(B)|<0.2eV.

[0192] and / or,

[0193] Under the same test conditions, the luminescence efficiency of the luminescence system composed of the first host material A and the first TADF sensitizer B is greater than the luminescence efficiency of the luminescence system composed of the second host material D and the second TADF sensitizer E.

[0194] Among them, in the light-emitting system composed of the first host material A and the first TADF sensitizer B and the light-emitting system composed of the second host material D and the second TADF sensitizer E, the mass ratio of the first TADF sensitizer B and the first host material A is the same or different from the mass ratio of the second TADF sensitizer E and the second host material D.

[0195] The same test conditions refer to the conditions that a light-emitting system composed of a first main material A and a first TADF sensitizer B and a light-emitting system composed of a second main material D and a second TADF sensitizer E are used as light-emitting layers respectively, and then assembled into a light-emitting device 13 with the same hole transport layer 134, electron transport layer 135, first electrode 131 and second electrode 132, and the same current is passed for testing.

[0196] In these embodiments, when the first TADF sensitizer B and the second TADF sensitizer E are different, the lowest triplet energy of the first TADF sensitizer B and the second TADF sensitizer E, and the lowest singlet energy of the first TADF sensitizer B and the second TADF sensitizer E satisfy the above relationship, which can realize the energy transfer between the first TADF sensitizer B and the second TADF sensitizer E, and avoid energy loss. In addition, under the same test conditions, when the luminous efficiency of the light-emitting system composed of the first host material A and the first TADF sensitizer B is greater than the luminous efficiency of the light-emitting system composed of the second host material D and the second TADF sensitizer E, it can also solve the problem in the related art that the exciton contribution at the first light-emitting layer position is small due to the imbalance of hole transport, which is not conducive to the energy transfer of the singlet exciton of the first TADF sensitizer B to the singlet exciton of the second fluorescent light-emitting material F through Forster energy.

[0197] In some embodiments, the first light-emitting layer 133a further includes a first fluorescent light-emitting material C. The lowest singlet energy S1 of the first host material A, the first TADF sensitizer B and the first fluorescent light-emitting material C, and the lowest triplet energy T1 of the first host material A, the first TADF sensitizer B and the first fluorescent light-emitting material C satisfy:

[0198] S1(A)-T1(A)>0.2eV;

[0199] S1(B)-T1(B)<0.2eV;

[0200] S1(C)-T1(C)>0.2eV;

[0201] S1(A)>S1(B)>S1(C);

[0202] T1(A)>T1(B)>T1(C).

[0203] That is, the first host material A, the first TADF sensitizer B and the first fluorescent material C have the same energy transfer process as the second host material D, the second TADF sensitizer E and the second fluorescent material F described above, which will not be repeated here. For details, please refer to the above description of the energy transfer process of the second host material D, the second TADF sensitizer E and the second fluorescent material F.

[0204] The first fluorescent material C and the second fluorescent material F are the same or different. That is, since both the first fluorescent material C and the second fluorescent material F are monomer materials, the molecular structures of the first fluorescent material C and the second fluorescent material F are the same or different.

[0205] In the case where the first fluorescent material C and the second fluorescent material F are different, the wavelength corresponding to the emission peak in the normalized electro-emission spectrum of the first fluorescent material C is smaller than the wavelength corresponding to the emission peak in the normalized electro-emission spectrum of the second fluorescent material F, and there is a third overlapping region between the normalized electro-emission spectrum of the first fluorescent material C and the normalized absorption spectrum of the second fluorescent material F. The first fluorescent material C and the second fluorescent material F satisfy the above spectral characteristics, and the energy of the singlet exciton of the first fluorescent material C can be transferred to the singlet exciton of the second fluorescent material F through Forster energy, thereby further improving the luminous efficiency of the second fluorescent material F.

[0206] In some embodiments, the area of ​​the third overlapping region is greater than 70% of the area of ​​the normalized absorption spectrum of the second fluorescent material F, and / or the peak position difference between the lowest energy absorption peak in the normalized absorption spectrum of the second fluorescent material F and the highest energy emission peak in the normalized electro-emission spectrum of the first fluorescent material C is less than or equal to 25 nm. The energy of the singlet exciton of the first fluorescent material C can be more fully transferred to the singlet exciton of the second fluorescent material F through Forster energy, thereby further improving the luminous efficiency of the second fluorescent material F and improving the color purity.

[0207] Based on the above, in some embodiments, there is a fourth overlapping region between the normalized electroemission spectrum of the first fluorescent material C and the normalized electroemission spectrum of the second fluorescent material F. This can further make the energy transfer from the first fluorescent material C to the second fluorescent material F sufficient, and further improve the luminous efficiency of the second fluorescent material F.

[0208] In some embodiments, the area of ​​the fourth overlapping region is greater than 90% of the area of ​​the respective normalized electroemission spectra of the first fluorescent material C and the second fluorescent material F, and / or the absolute value of the peak difference between the emission peak of the normalized electroemission spectrum of the first fluorescent material C and the emission peak of the normalized electroemission spectrum of the second fluorescent material F is less than 5 nm.

[0209] In some embodiments, the wavelength corresponding to the peak position of the strongest emission peak of the first host material A, the first TADF sensitizer B, and the first fluorescent light-emitting material C satisfies:

[0210] λ(A)>λ(B)>λ(C).

[0211] In this embodiment, the transfer of energy from a high energy state to a low energy state can be ensured, the reverse transfer of energy can be prevented, and full utilization of energy can be achieved.

[0212] In some embodiments, when the first fluorescent material C and the second fluorescent material F are the same, the first TADF sensitizer B and the second TADF sensitizer E are the same, and the first host material A and the second host material D are the same, the mass proportion of the first fluorescent material C in the first light-emitting layer 133a is greater than the mass proportion of the second fluorescent material F in the second light-emitting layer 133b.

[0213] That is, in the first light-emitting layer 133a and the second light-emitting layer 133b, only the mass proportion of the first fluorescent material C in the first light-emitting layer 133a and the mass proportion of the second fluorescent material F in the second light-emitting layer 133b are different.

[0214] In some embodiments, the difference between the mass percentage of the first fluorescent material C in the first light-emitting layer 133 a and the mass percentage of the second fluorescent material F in the second light-emitting layer 133 b is at least greater than or equal to 0.1%.

[0215] In some embodiments, the mass proportion of the first fluorescent material C in the first light-emitting layer 133 a is 0.5% to 3%, and the mass proportion of the second fluorescent material F in the second light-emitting layer 133 b is 0.5% to 3%.

[0216] Here, the first host material A and the second host material are still selected from TM, TM is selected from 3,3′-di(9H-carbazol-9-yl)-1,1′-biphenyl (3,3′-Di(9H-carbazol-9-yl)biphenyl), the first TADF sensitizer B and the second TADF sensitizer E are selected from TH-1, TH-1 is selected from 3,4,5,6-tetrakis(3,6-di-t-Butylcarbazol -9-yl)-1,2-dicyanobenzene), and the first fluorescent material C and the second fluorescent material F are both selected from Dopant, and Dopant is selected from Difluoro{3-ethyl-5-[1-(4-ethyl-3,5-dimethyl-2H-pyrrol-2-methylene-N)ethyl]-2,4-dimethyl-1H-pyrrolo-N}borane thyl]-2,4-dimethyl-1H-pyrrolato-N}boron) is taken as an example, by setting Comparative Example 2 and Experimental Example 2, in Comparative Example 2, the mass ratio of the first TADF sensitizer B and the first host material A is equal to the mass ratio of the second TADF sensitizer E and the second host material D, both of which are 70%:29.3%, the mass percentage of the first fluorescent material C in the first light-emitting layer and the mass percentage of the second fluorescent material F in the second light-emitting layer are the same, both of which are 0.7%, that is, the material composition of the first light-emitting layer 133a is the same as the material composition of the second light-emitting layer 133b, which is the case of a single-layer light-emitting layer. In Experimental Example 2, the mass ratio of the first TADF sensitizer B to the first host material A (80%:19%) is less than the mass ratio of the second TADF sensitizer E to the second host material D (70%:29.3%), and the mass percentage of the first fluorescent material C in the first light-emitting layer (1.2%) is greater than the mass percentage of the second fluorescent material F in the second light-emitting layer 133b (0.7%). After being made into a top-emitting light-emitting device, the voltage, luminous efficiency, color coordinates and life of the light-emitting device are tested by passing the same current density through the light-emitting device, and the following Table 2, Figure 8 and Fig. 9 Results shown.

[0217] Table 2

[0218]

[0219] From Table 2, Figure 8 and Fig. 9It can be seen that by reducing the doping concentration of the first TADF sensitizer B in the first light-emitting layer 133a and increasing the doping concentration of Dopant in the first light-emitting layer 133a, the light-emitting device has higher efficiency, lower voltage and longer life.

[0220] Among them, Fig. 9 In the vertical axis, L refers to the brightness of the device at a certain moment, L0 refers to the initial brightness of the device, and L / L0 refers to the degree of attenuation of the device brightness over time.

[0221] In Table 2, the life of the device in Comparative Example 2 is 100%, and the life of the device in Experimental Example 2 is 115%, which means that the life of the device in Comparative Example 2 is used as a comparison benchmark, and the life of the device in Experimental Example 2 is 30% higher than that of the device in Comparative Example 2.

[0222] In some embodiments, the thickness of the first light emitting layer 133a is less than the thickness of the second light emitting layer 133b.

[0223] That is, when the total thickness of the first light-emitting layer 133a and the second light-emitting layer 133b is regarded as being consistent with the thickness of the entire light-emitting layer, due to the imbalance in the transmission of holes and electrons, the recombination position is close to the electron transport layer 135. Therefore, the thickness of the first light-emitting layer 133a is smaller than the thickness of the second light-emitting layer 133b, so that the energy of the excitons at the position where the exciton contribution is small can be transferred to the second light-emitting layer 133b, avoiding the problem that the thickness of the first light-emitting layer 133a is too large, causing the holes and electrons that should have recombined in the second light-emitting layer 133b to recombined in the first light-emitting layer 133a to generate excitons, thereby causing the excitons that should have radiated light to become excitons that transfer energy, resulting in reduced luminous efficiency.

[0224] The second main material D, the second TADF sensitizer E and the second fluorescent material F are used as the constituent materials of the light-emitting layer. The second fluorescent material F is doped in the second main material D and the second TADF sensitizer E, and the luminous intensity of the second fluorescent material F at different positions in the light-emitting layer is tested, and the following can be obtained: Fig.10 As shown, a curve diagram showing the relationship between the distance between the second fluorescent light-emitting material F and the surface of the light-emitting layer close to the hole transport layer and the light-emitting intensity of the second fluorescent light-emitting material F.

[0225] Wherein, the second host material D is selected from TM, TM is selected from 3,3′-di(9H-carbazol-9-yl)-1,1′-biphenyl (3,3′-Di(9H-carbazol-9-yl)biphenyl), the second TADF sensitizer E is selected from TH-1, TH-1 is selected from 3,4,5,6-tetrakis(3,6-di-t-Butylcarbazol-9-yl)-1,2-dicyanobenzene The second fluorescent light-emitting material F is selected from Dopant, and Dopant is selected from Difluoro{3-ethyl-5-[1-(4-ethyl-3,5-dimethyl-2H-pyrrol-2-methylene-N)ethyl]-2,4-dimethyl-1H-pyrrolato-N}boron.

[0226] Depend on Fig.10 It can be seen that when the thickness of the light-emitting layer is Lnm, as the doping position of the second fluorescent material F in the light-emitting layer changes from the surface close to the hole transport layer to the surface far from the hole transport layer, the luminous intensity of the electroluminescent spectrum of the second fluorescent material F shows a regular change, and when the distance between the second fluorescent material F and the surface of the light-emitting layer close to the hole transport layer is in the thickness range of 0 to 1 / 3Lnm, the luminous intensity of the electroluminescent spectrum of the second fluorescent material F gradually increases, when the distance between the second fluorescent material F and the surface of the light-emitting layer close to the hole transport layer is in the thickness range of 1 / 3Lnm to 2 / 3Lnm, the luminous intensity of the electroluminescent spectrum of the second fluorescent material F is basically stable, and when the distance between the second fluorescent material F and the surface of the light-emitting layer close to the hole transport layer is in the thickness range of 2 / 3Lnm to Lnm, the luminous intensity of the electroluminescent spectrum of the second fluorescent material F continues to increase. It can be shown that at the position close to the electron transport layer 134, that is, the area occupying about 1 / 3 of the entire light-emitting area, the number of excitons is small and the contribution to the device light emission is small.

[0227] Based on this, by setting different material compositions in different light-emitting areas, that is, dividing the light-emitting layer in the prior art into a first light-emitting layer 133a and a second light-emitting layer 133b with different material compositions, and making the material composition of the second light-emitting layer 133b follow the material composition of the light-emitting layer in the prior art, while making the material composition of the first light-emitting layer 133a different from that of the second light-emitting layer 133b, according to the structural characteristics of the exciton distribution in the above light-emitting device, the thickness ratio of the first light-emitting layer 133a and the second light-emitting layer 133b is adjusted, and under the same current density, the voltage, luminous efficiency, color coordinates and life of each light-emitting device with different thickness ratios of the first light-emitting layer 133a and the second light-emitting layer 133b are tested, and the voltage, luminous efficiency, color coordinates and life of each light-emitting device with different thickness ratios of the first light-emitting layer 133a and the second light-emitting layer 133b are evaluated. The results are shown in Table 3. Figure 8 and Fig. 9 shown.

[0228] In the above test, the first host material A and the second host material D are the same, both selected from TM, TM is selected from 3,3′-di(9H-carbazol-9-yl)-1,1′-biphenyl (3,3′-Di(9H-carbazol-9-yl)biphenyl), the second TADF sensitizer E is selected from TH-1, the first TADF sensitizer B is different from the second TADF sensitizer E, and is selected from TH-2, TH-2 is selected from 2,3,5,6-tetrakis(carbazol-9-yl)-1,4-dicyanobenzene ), the first light-emitting layer 133a does not contain the first fluorescent material C, the second fluorescent material F is selected from Dopant, and Dopant is selected from Difluoro{3-ethyl-5-[1-(4-ethyl-3,5-dimethyl-2H-pyrrol-2-methylene-N)ethyl]-2,4-dimethyl-1H-pyrrolato-N}boron as an example. Comparative Example 3 and Experimental Examples 3, 4, 5 and 6 are set. In Comparative Example 3, the material composition of the first light-emitting layer 133a is the same as the material composition of the second light-emitting layer 133b, that is, the case of a single-layer light-emitting layer. In Experimental Examples 4 to 6, the material composition of the first light-emitting layer 133a and the material composition of the second light-emitting layer 133b are the same, but the ratio of the thickness of the first light-emitting layer 133a to the second light-emitting layer 133b is different. For example, the mass ratio of the first TADF sensitizer B to the first host material A in the first light-emitting layer 133a is 80%:19%, the mass percentage of the first fluorescent material C in the first light-emitting layer is 0.7%, the mass ratio of the second TADF sensitizer E to the second host material D in the second light-emitting layer 133b is 60%:40%, and the mass percentage of the second fluorescent material F in the second light-emitting layer 133b is 0.7%. The thickness ratios of the first light-emitting layer 133a and the second light-emitting layer 133b are 3:22, 6:19, 9:16 and 12:13, respectively. That is, taking the sum of the thicknesses of the first light-emitting layer 133a and the second light-emitting layer 133b as 25 nm as an example, when the ratio of the thicknesses of the first light-emitting layer 133a and the second light-emitting layer 133b is 3:22, the thickness of the first light-emitting layer 133a is 3 nm, and the thickness of the second light-emitting layer 133b is 22 nm. When the ratio of the thicknesses of the first light-emitting layer 133a and the second light-emitting layer 133b is 6:19, the thickness of the first light-emitting layer 133a is 6 nm, and the thickness of the second light-emitting layer 133b is 19 nm.When the thickness ratio of the first light-emitting layer 133a to the second light-emitting layer 133b is 9:16, the thickness of the first light-emitting layer 133a is 9 nm, and the thickness of the second light-emitting layer 133b is 16 nm. When the thickness ratio of the first light-emitting layer 133a to the second light-emitting layer 133b is 12:13, the thickness of the first light-emitting layer 133a is 12 nm, and the thickness of the second light-emitting layer 133b is 13 nm.

[0229] Table 3

[0230]

[0231] From Table 3, Fig.11 and Fig. 9 It can be seen that, compared with Comparative Example 3, the first TADF sensitizer B in Experimental Examples 3 to 6 is different from the second TADF sensitizer E, and the overlapping area of ​​the emission peak and the absorption peak of Dopant is larger, so that Experimental Examples 3 to 6 have higher efficiency and lower voltage. As the ratio of the thickness of the first light-emitting layer 133a to the second light-emitting layer 133b gradually increases, the life of the device shows a downward trend. The life of Experimental Examples 3 and 4 is higher than that of Comparative Example 3, and the life of Experimental Examples 5 and 6 is lower than that of Comparative Example 3.

[0232] In Table 3, the life of the device in Comparative Example 3 is 100%, and the life of the device in Experimental Example 3 is 110%, which means that the life of the device in Comparative Example 3 is used as a comparison benchmark, and the life of the device in Experimental Example 3 is 10% higher than the life of the device in Comparative Example 3. The life of the device in Experimental Example 4 is 105%, which means that the life of the device in Comparative Example 3 is used as a comparison benchmark, and the life of the device in Experimental Example 4 is 5% higher than the life of the device in Comparative Example 3. The life of the device in Experimental Example 5 is 86%, which means that the life of the device in Comparative Example 3 is used as a comparison benchmark, and the life of the device in Experimental Example 5 is 14% lower than the life of the device in Comparative Example 3. The life of the device in Experimental Example 6 is 68%, which means that the life of the device in Comparative Example 3 is used as a comparison benchmark, and the life of the device in Experimental Example 6 is 32% lower than the life of the device in Comparative Example 3.

[0233] In the above experimental examples and comparative examples, the energy levels and excited state energy information of the materials used are shown in Table 4 below.

[0234] Table 4

[0235] HOMO LUMO T1 S1 TM 5.8 2.6 2.70 3.48 TH-1 5.8 3.5 2.35 2.42 TH-2 5.9 3.6 2.32 2.40 TH-3 5.8 3.1 2.44 2.49 Dopant 5.6 3.6 ND 2.03 EBL 5.7 / 2.61 / HBL 6.4 / 2.59 /

[0236] In some embodiments, Fig.12As shown, the light emitting device 13 further includes: an electron blocking layer (EBL) 136 located between the hole transport layer 134 and the first light emitting layer 133a, and / or a hole blocking layer (HIL) 137 located between the electron transport layer 135 and the second light emitting layer 133b.

[0237] In some embodiments, when the light-emitting device 13 includes an electron blocking layer 136, the lowest triplet energy of the electron blocking layer 136 is greater than the lowest triplet energy of the first TADF sensitizer B in the first light-emitting layer 133a, and the difference between the two is greater than 0.2 eV. When the light-emitting device 13 includes a hole blocking layer 137, the lowest triplet energy of the hole blocking layer 137 is greater than the lowest triplet energy of the second TADF sensitizer E in the second light-emitting layer 133b, and the difference between the two is greater than 0.2 eV. The electron blocking layer 136 and / or the hole blocking layer 137 have good triplet exciton blocking ability and can confine triplet excitons in the light-emitting layer.

[0238] In some embodiments, when the light-emitting device 1 includes a hole blocking layer 137, the absolute value of the HOMO energy level of the hole blocking layer 137 is 0.2 eV higher than the absolute value of the HOMO energy level of the second host material D; when the light-emitting device 1 includes an electron blocking layer 136, the energy level difference between the HOMO energy level of the electron blocking layer 136 and the HOMO energy level of the first host material A is less than or equal to 0.2 eV.

[0239] In this embodiment, the hole blocking layer 137 has good hole blocking ability, and the electron blocking layer 136 does not affect hole transmission. In the above light-emitting device, the hole mobility can be made higher than the electron mobility by at least one order of magnitude.

[0240] It should be noted that, for a light-emitting substrate having light-emitting devices of the same light-emitting color, the electron transport layer 135, the hole transport layer 134, the electron blocking layer 136 and the hole blocking layer 137 can be uniformly covered. For a light-emitting substrate having light-emitting devices of different light-emitting colors, the hole blocking layers 137 of light-emitting devices of different light-emitting colors are different and can be respectively arranged in different openings. Fig.13 FIG. 1 shows an example in which the light-emitting substrate includes light-emitting devices of three different colors.

[0241] Among them, in the above embodiments, the electron transport layer 136 can be selected from organic materials with good electron transport properties, and LiQ3, Li and Ca can be doped into the organic material, and the thickness can be 10 to 70 nm. The hole transport layer may be selected from any one of N,N'-diphenyl-N,N'-(1-naphthalenyl)-1,1'-biphenyl-4,4'-diamine, N,N'-di(naphthalen-1-yl)-N,N'-bis-phenyl-(1,1'-biphenyl)-4,4'-diamine, and 4,4'-cyclohexylbis[N,N-bis(p-tolyl)aniline]. The material of the electron blocking layer may be selected from any one of 4,4′-cyclohexylidenebis[N,N-bis(p-tolyl)aniline] and 4,4′,4″-Tris(carbazol-9-yl)triphenylamine.

[0242] The material of the hole blocking layer (EBL) may be selected from 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline.

[0243] In other embodiments, Fig.14 As shown, the light emitting device 13 may further include a hole injection layer 138 and an electron injection layer (Electron Injection Layer, EIL) 139. The material of the electron injection layer may be selected from low work function metals, such as Li, Ca and Yb, or metal salts LiF, LiQ3, etc., and the thickness may be 0.5 to 2 nm. The material of the hole injection layer may be selected from CuPc (Copper (II) phthalocyanine, copper phthalocyanine), HATCN (2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylenehexacabonitrile), MnO3, etc., or may be a material after P-type doping of these materials, and the thickness may be 5 to 30 nm.

[0244] The embodiment of the present disclosure provides a method for preparing a light emitting device 13, comprising:

[0245] A first electrode 131, a hole transport layer 134, a first light-emitting layer 133a, a second light-emitting layer 133b, an electron transport layer 135 and a second electrode 132 are formed in sequence;

[0246] The material of the first light-emitting layer 133a includes a first host material A and a first TADF sensitizer B; the second light-emitting layer 133b includes a second host material D, a second TADF sensitizer E and a second fluorescent light-emitting material F;

[0247] The hole transmission rates of the material of the first light-emitting layer 133a and the material of the second light-emitting layer 133b are both greater than the electron transmission rates of the material of the first light-emitting layer 133a and the material of the second light-emitting layer 133b, and there is a first overlapping region between the normalized electroemission spectrum of the first TADF sensitizer B and the normalized absorption spectrum of the second fluorescent material F.

[0248] The method for preparing the light-emitting device provided in the embodiment of the present disclosure has the same technical effect as the light-emitting device described above, and will not be described in detail here.

[0249] An embodiment of the present disclosure provides a method for preparing a light-emitting substrate, comprising:

[0250] A plurality of light emitting devices 13 are formed on the substrate 11 , and each of the light emitting devices 13 is a light emitting device as described above.

[0251] A plurality of light emitting devices 13 are formed on the substrate 11, such as Fig.14 As shown, including:

[0252] S1. Form a plurality of first electrodes 131 on a substrate 11.

[0253] The material of the first electrode may be a high work function material. At this time, a plurality of first electrodes may be formed by depositing a conductive layer, and performing exposure, photolithography and etching processes.

[0254] S2 . Form a pixel defining layer 12 on the substrate 11 on which the plurality of first electrodes 131 are formed. The pixel defining layer 12 defines a plurality of openings Q. Each opening Q exposes a first electrode 131 .

[0255] S3 . Forming a hole transport film 100 , a first light emitting layer 133 a , a second light emitting layer 133 b , and an electron transport film 200 stacked in sequence on the substrate 11 having the pixel defining layer 12 .

[0256] And S4, forming the second electrode 132 on the substrate on which the hole transport film 100, the first light emitting layer 133a, the second light emitting layer 133b and the electron transport film 200 are formed.

[0257] Among them, the first light-emitting layer 133a and the second light-emitting layer 133b are both located in each opening Q, the hole transport film 100 and the electron transport film 200 both include parts located at corresponding positions of each opening Q, the part of the hole transport film 100 located at the corresponding position of each opening Q constitutes the hole transport layer 134, and the part of the electron transport film 200 located at the corresponding position of each opening Q constitutes the electron transport layer 135.

[0258] The first light-emitting layer 133a and the second light-emitting layer 133b can be formed by evaporation using a refined metal mask, and the hole transport film 100 and the electron transport film 200 can be covered in an entire layer. In this case, the hole transport film 100 and the electron transport film 200 can be formed by evaporation.

[0259] Here, it should be noted that, when the first light-emitting layer 133a includes the first host material A, the first TADF sensitizer B and the first fluorescent light-emitting material C, the first host material A, the first TADF sensitizer B and the first fluorescent light-emitting material C can be formed by multi-source evaporation. Similarly, the second host material D, the second fluorescent light-emitting material F and the second TADF sensitizer E included in the second light-emitting layer 133b can also be formed by multi-source evaporation.

[0260] In some embodiments, when the light-emitting device 13 further includes a hole blocking layer 137 and an electron blocking layer 136, the method for preparing the light-emitting substrate further includes:

[0261] Before forming the first light emitting layer 133a, the electron blocking layer 136 is formed, and before forming the electron transport layer 135, the hole blocking layer 137 is formed. The hole blocking layer 137 and the electron blocking layer 136 may also be formed by evaporation to cover the entire layer.

[0262] In some embodiments, the method for preparing the light-emitting substrate 13 further includes: forming an encapsulation layer 15 on the substrate 11 on which the second electrode 132 is formed.

[0263] In some embodiments, when the light-emitting substrate 13 is a top-emitting light-emitting substrate, the preparation method of the light-emitting substrate 1 further includes: before forming the encapsulation layer 15, or after forming the encapsulation layer 15, forming an optical cover layer 14. The refractive index of the optical cover layer 14 is greater than 1.8, and the thickness is 50-100 nm.

[0264] The above is only a specific embodiment of the present disclosure, but the protection scope of the present disclosure is not limited thereto. Any changes or substitutions that can be thought of by any person skilled in the art within the technical scope disclosed in the present disclosure should be included in the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure should be based on the protection scope of the claims.

Claims

1. A light emitting device, comprising: A first light-emitting layer and a second light-emitting layer are stacked, wherein the material of the first light-emitting layer includes a first host material A and a first TADF sensitizer B, and the material of the second light-emitting layer includes a second host material D, a second TADF sensitizer E and a second fluorescent light-emitting material F; a hole transport layer located on a side of the first light-emitting layer away from the second light-emitting layer; as well as, an electron transport layer located on a side of the second light-emitting layer away from the first light-emitting layer; The transport rates of holes by the material of the first light-emitting layer and the material of the second light-emitting layer are both greater than the transport rates of electrons by the material of the first light-emitting layer and the material of the second light-emitting layer, and there is a first overlapping region between the normalized electroemission spectrum of the first TADF sensitizer B and the normalized absorption spectrum of the second fluorescent light-emitting material F; The second host material D and the second TADF sensitizer E satisfy the following relationship: ||HOMO|(D)-|LUMO|(E) -S1(E)|≤0.2eV; |HOMO|(D)-|LUMO|(E) -T1(E)|≤0.2eV; The first host material A and the second TADF sensitizer E satisfy the following relationship: ||HOMO|(A)-|LUMO|(E) -S1(E)|≤0.2eV; |HOMO|(A)-|LUMO|(E) -T1(E)|≤0.2eV.

2. The light emitting device according to claim 1, wherein: The area of ​​the first overlapping region is greater than 70% of the area of ​​the normalized absorption spectrum of the second fluorescent light-emitting material F; and / or, The difference between the peak position of the lowest energy absorption peak in the normalized absorption spectrum of the second fluorescent light-emitting material F and the peak position of the highest energy emission peak in the electroemission spectrum of the first TADF sensitizer B is less than or equal to 25 nm.

3. The light emitting device according to claim 1 or 2, wherein: The lowest singlet energy S1 of the second host material D, the second TADF sensitizer E and the second fluorescent light-emitting material F, and the lowest triplet energy T1 of the second host material D, the second TADF sensitizer E and the second fluorescent light-emitting material F satisfy: S1(D)-T1(D)>0.2eV; S1(E)-T1(E)<0.2eV; S1(F)-T1(F)>0.2eV; S1(D)>S1(E)>S1(F); T1(D)>T1(E)>T1(F).

4. The light emitting device according to claim 3, wherein: The first TADF sensitizer B and the second TADF sensitizer E are the same or different; When the first TADF sensitizer B and the second TADF sensitizer E are different, a normalized electroemission spectrum of the second TADF sensitizer E and a normalized absorption spectrum of the second fluorescent light-emitting material F have a second overlapping region.

5. The light emitting device according to claim 4, wherein: The area of ​​the second overlapping region is greater than 70% of the area of ​​the normalized absorption spectrum of the second fluorescent light-emitting material F; and / or, The difference between the peak position of the lowest energy absorption peak in the normalized absorption spectrum of the second fluorescent light-emitting material F and the peak position of the highest energy emission peak in the normalized electroemission spectrum of the second TADF sensitizer E is less than or equal to 25 nm.

6. The light emitting device according to claim 1 or 2, wherein: The wavelength corresponding to the peak position of the strongest emission peak of the second host material D, the second TADF sensitizer E and the second fluorescent luminescent material F satisfies: λ(D)>λ(E)>λ(F).

7. The light emitting device according to claim 1 or 2, wherein: The HOMO energy level of the second host material D and the HOMO energy level of the second TADF sensitizer E, as well as the LUMO energy level of the second host material D and the LUMO energy level of the second TADF sensitizer E satisfy: |HOMO|(D)-|HOMO|(E)<0.2eV; |LUMO|(D)-|LUMO|(E)>0.3 eV; and / or, The HOMO energy level of the first host material A and the HOMO energy level of the first TADF sensitizer B, as well as the LUMO energy level of the first host material A and the LUMO energy level of the first TADF sensitizer B satisfy: |HOMO|(A)-|HOMO|(B)<0.2eV; |LUMO|(B)-|LUMO|(A)>0.3 eV.

8. The light emitting device according to claim 1 or 2, wherein: The first host material A and the first TADF sensitizer B satisfy the following relationship: |HOMO|(A)-|LUMO|(B) -S1(B)|≤0.2eV; |HOMO|(A)-|LUMO|(B) -T1(B)|≤0.2eV.

9. The light emitting device according to claim 1 or 2, wherein: The second host material D and the first TADF sensitizer B satisfy the following relationship: |HOMO|(D)-|LUMO|(B) -S1(B)|≤0.2eV; |HOMO|(D)-|LUMO|(B) -T1(B)|≤0.2eV.

10. The light emitting device according to claim 1 or 2, wherein: The first host material A and the second host material D are the same or different; In the case where the first host material A and the second host material D are different, the first host material A and the second host material D satisfy the following conditions: |HOMO(A)-HOMO(D)|<0.2eV; |T1(A)-T1(D)|<0.1eV.

11. The light emitting device according to claim 1 or 2, wherein: The first host material A and the second host material D are the same, the first TADF sensitizer B and the second TADF sensitizer E are the same, and the mass ratio of the first TADF sensitizer B to the first host material A is consistent with the mass ratio of the second TADF sensitizer E to the second host material D.

12. The light emitting device according to claim 1 or 2, wherein: The first host material A and the second host material D are the same, the first TADF sensitizer B and the second TADF sensitizer E are the same, and the mass ratio of the first TADF sensitizer B to the first host material A is less than the mass ratio of the second TADF sensitizer E to the second host material D.

13. The light emitting device according to claim 12, wherein: The mass ratio of the first TADF sensitizer B to the first host material A is greater than or equal to 5% and less than or equal to 40%; The mass ratio of the second TADF sensitizer E to the second main material D is greater than or equal to 15% and less than or equal to 50%.

14. The light emitting device according to claim 1 or 2, wherein: The first TADF sensitizer B and the second TADF sensitizer E are different, and the lowest triplet energy of the first TADF sensitizer B and the second TADF sensitizer E, and the lowest singlet energy of the first TADF sensitizer B and the second TADF sensitizer E satisfy: |T1(E)-T1(B)|<0.2eV; |S1(E)-S1(B)|<0.2eV; and / or, Under the same test conditions, the luminescence efficiency of the light-emitting system composed of the first host material A and the first TADF sensitizer B is greater than the luminescence efficiency of the light-emitting system composed of the second host material D and the second TADF sensitizer E.

15. The light emitting device according to claim 1 or 2, wherein: The first light-emitting layer further includes a first fluorescent light-emitting material C; The lowest singlet energy S1 of the first host material A, the first TADF sensitizer B and the first fluorescent light-emitting material C, and the lowest triplet energy T1 of the first host material A, the first TADF sensitizer B and the first fluorescent light-emitting material C satisfy: S1(A)-T1(A)>0.2eV; S1(B)-T1(B)<0.2eV; S1(C)-T1(C)>0.2eV; S1(A)>S1(B)>S1(C); T1(A)>T1(B)>T1(C); Wherein, the first fluorescent material C and the second fluorescent material F are the same or different; When the first fluorescent material C and the second fluorescent material F are different, the wavelength corresponding to the strongest emission peak in the normalized electroemission spectrum of the first fluorescent material C is smaller than the wavelength corresponding to the strongest emission peak in the normalized electroemission spectrum of the second fluorescent material F, and there is a third overlapping region between the normalized electroemission spectrum of the first fluorescent material C and the normalized absorption spectrum of the second fluorescent material F.

16. The light emitting device according to claim 15, wherein: The area of ​​the third overlapping region is greater than 70% of the area of ​​the normalized absorption spectrum of the second fluorescent material F; and / or the peak position difference between the lowest energy absorption peak in the normalized absorption spectrum of the second fluorescent material F and the highest energy emission peak in the normalized electroemission spectrum of the first fluorescent material C is less than or equal to 25nm.

17. The light emitting device according to claim 15, wherein: The normalized electroemission spectrum of the first fluorescent light-emitting material C and the normalized electroemission spectrum of the second fluorescent light-emitting material F have a fourth overlapping region.

18. The light emitting device according to claim 17, wherein: The area of ​​the fourth overlapping region is greater than 90% of the area of ​​the normalized electroemission spectrum of each of the first fluorescent material C and the second fluorescent material F; and / or the absolute value of the peak position difference between the strongest emission peak in the normalized electroemission spectrum of the first fluorescent material C and the strongest emission peak in the normalized electroemission spectrum of the second fluorescent material F is less than 5nm.

19. The light emitting device according to claim 15, wherein: The wavelengths corresponding to the peak positions of the strongest emission peaks of the first host material A, the first TADF sensitizer B and the first fluorescent luminescent material C satisfy: λ(A)>λ(B)>λ(C).

20. The light emitting device according to claim 15, wherein: When the first fluorescent luminescent material C and the second fluorescent luminescent material F are the same, the second TADF sensitizer E and the first TADF sensitizer B are the same, and the first host material A and the second host material D are the same, the mass proportion of the first fluorescent luminescent material C in the first light-emitting layer is greater than the mass proportion of the second fluorescent luminescent material F in the second light-emitting layer.

21. The light emitting device according to claim 20, wherein: The difference between the mass proportion of the first fluorescent material C in the first light-emitting layer and the mass proportion of the second fluorescent material F in the second light-emitting layer is greater than or equal to 0.1%.

22. The light emitting device according to claim 20, wherein: The mass proportion of the first fluorescent material C in the first light-emitting layer is 0.5% to 3%, and the mass proportion of the second fluorescent material F in the second light-emitting layer is 0.5% to 3%.

23. The light emitting device according to claim 1 or 2, wherein: The thickness of the first light-emitting layer is smaller than the thickness of the second light-emitting layer.

24. The light emitting device according to claim 1, wherein: Also includes: a hole blocking layer located between the electron transport layer and the second light emitting layer; and / or, An electron blocking layer is located between the hole transport layer and the first light emitting layer.

25. The light emitting device according to claim 24, wherein: In the case where the light-emitting device includes the electron blocking layer, the lowest triplet energy of the electron blocking layer is greater than the lowest triplet energy of the first TADF sensitizer B, and the difference between the two is greater than 0.2 eV; In the case where the light-emitting device includes the hole blocking layer, the lowest triplet energy of the hole blocking layer is greater than the lowest triplet energy of the second TADF sensitizer E, and the difference between the two is greater than 0.2 eV.

26. The light emitting device according to claim 24 or 25, wherein: In the case where the light-emitting device includes the hole blocking layer, the absolute value of the HOMO energy level of the hole blocking layer is 0.2 eV higher than the absolute value of the HOMO energy level of the second host material D; In the case where the light-emitting device includes the electron blocking layer, an energy level difference between a HOMO energy level of the electron blocking layer and a HOMO energy level of the first host material A is less than or equal to 0.2 eV.

27. A light-emitting substrate, comprising the light-emitting device according to any one of claims 1 to 26.

28. A light emitting device comprising the light emitting substrate according to claim 27.

29. A method for preparing a light emitting device, comprising: forming a hole transport layer, a first light-emitting layer, a second light-emitting layer and an electron transport layer stacked in sequence; The material of the first light-emitting layer includes a first host material A and a first TADF sensitizer B; the second light-emitting layer includes a second host material D, a second TADF sensitizer E and a second fluorescent light-emitting material F; The transport rates of holes by the material of the first light-emitting layer and the material of the second light-emitting layer are both greater than the transport rates of electrons by the material of the first light-emitting layer and the material of the second light-emitting layer, and there is a first overlapping region between the normalized electroemission spectrum of the second fluorescent material F and the normalized absorption spectrum of the first TADF sensitizer B; The second host material D and the second TADF sensitizer E satisfy the following relationship: ||HOMO|(D)-|LUMO|(E) -S1(E)|≤0.2eV; |HOMO|(D)-|LUMO|(E) -T1(E)|≤0.2eV; The first host material A and the second TADF sensitizer E satisfy the following relationship: ||HOMO|(A)-|LUMO|(E) -S1(E)|≤0.2eV; |HOMO|(A)-|LUMO|(E) -T1(E)|≤0.2eV.

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