Tandem light-emitting device and manufacturing method thereof

Abstract

The present invention relates to a tandem light-emitting device and a manufacturing method thereof. The tandem light-emitting device according to the present invention and a display device comprising same have maximized color purity and luminous efficiency, improved on-off response, superb operation life, and low manufacturing costs. In addition, the method for manufacturing a tandem light-emitting device according to the present invention has low manufacturing costs, and can manufacture the tandem light-emitting device of the present invention.

Description

Tandem light-emitting device and method for manufacturing the same

[0001] The present invention relates to a tandem light-emitting device and a method for manufacturing the same, and more particularly, to a tandem light-emitting device having excellent color purity and luminous efficiency and a method for manufacturing the same.

[0002]

[0003] Meanwhile, it is disclosed that the present invention was invented with the support of the following national research and development project.

[0004] [National Research and Development Project 1 that supported this invention]

[0005] [Project ID] 2710016197 [Project ID] 2016R1A3B1908431 (1711181228)

[0006] [Ministry Name] Ministry of Science and ICT [Project Management (Specialized) Institution Name] National Research Foundation of Korea

[0007] [Research Project Name] Individual Basic Research (Ministry of Science and ICT)

[0008] [Research Project Name] Nanoparticle-Mimicking Polycrystalline Optoelectronic Device Leader Research

[0009] [Project Implementing Organization] Seoul National University [Research Period] March 1, 2024 - February 28, 2025

[0010]

[0011] [National Research and Development Project 2 that supported this invention]

[0012] [Project ID] 2710006449 [Project ID] 00422598 (2400422598)

[0013] [Ministry Name] Ministry of Science and ICT

[0014] [Name of Project Management (Specialist) Agency] Korea Institute for Science and Technology Promotion

[0015] [Research Project Name] Industry-Academia-Research Cooperation Activation Support Project - University Technology Management Promotion (IP Star Science)

[0016] Okay. Support type)

[0017] [Research Project Name] IP Advancement and Commercialization for Next-Generation Electronic Materials and Devices Using the Optical and Electrical Properties of Perovskites

[0018] [Project Implementing Organization] Seoul National University [Research Period] April 1, 2025 - December 31, 2025

[0019]

[0020] The current display industry is evolving toward lightweight and thin forms with high efficiency, low power consumption, high resolution, and high color purity.

[0021] Perovskite light-emitting diodes (PeLEDs), which contain only perovskite light-emitting units, have a small full width at half maximum (FWHM) of the peak wavelength of the electroluminescence (EL) spectrum, resulting in high color purity. They are attracting attention as promising devices for use in next-generation display devices due to their ease of synthesis and low material costs. However, they have the limitation of having lower luminous efficiency than organic light-emitting diodes (OLEDs), which contain only organic light-emitting units.

[0022] On the other hand, although organic light-emitting devices have higher luminescence efficiency than perovskite light-emitting devices, they have the disadvantage of having a large half-width of the peak wavelength of the electroluminescence spectrum, resulting in unclear colors, and relatively high material costs compared to perovskite light-emitting devices.

[0023]

[0024] In order to overcome the limitations of a single light-emitting device that includes only a single light-emitting unit, such as the perovskite light-emitting unit or organic light-emitting unit described above, a method of applying a tandem structure that simultaneously includes an organic light-emitting unit and a perovskite light-emitting unit, as disclosed in Korean Patent Publication No. 10-2168612, is emerging. When a tandem structure is used, it is theoretically expected that high light-emitting efficiency can be achieved while sufficiently lowering color purity, and that the operating life can be improved due to reduced electrical stress, compared to when a device is manufactured using individual light-emitting units. However, existing tandem structure light-emitting devices, including the invention disclosed in the aforementioned Republic of Korea Patent Publication No. 10-2168612, simply combined an organic light-emitting unit and a perovskite light-emitting unit, and each light-emitting unit had different resistance and JVL characteristics, so that the electroluminescence spectrum shifted overall, the half-width did not decrease, or charge imbalance occurred, and thus high color purity and high luminous efficiency could not be guaranteed, and the operating life was not sufficient.

[0025]

[0026] The present invention has been designed to solve the above-described problems, and its purpose is to provide a tandem light-emitting element and a display device including the same, which have maximized color purity and luminous efficiency, excellent operating life, and low manufacturing cost.

[0027] In addition, another object of the present invention is to provide a method for manufacturing a tandem light-emitting device capable of manufacturing the tandem light-emitting device of the present invention at a low manufacturing cost.

[0028]

[0029] The problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

[0030]

[0031] In order to solve the above-described problem, a tandem light-emitting device is provided, comprising: a first electrode; a perovskite light-emitting unit disposed on the first electrode and including a first hole transport layer, a perovskite light-emitting layer, and a first electron transport layer; a charge generation layer disposed on the perovskite light-emitting unit; an organic light-emitting unit disposed on the charge generation layer and including a second hole transport layer, an organic light-emitting layer, and a second electron transport layer; and a second electrode disposed on the organic light-emitting unit; wherein, by controlling the thicknesses of the second hole transport layer and the second electron transport layer, a full width at half maximum (FWHM) of the emission spectrum of the entire tandem light-emitting device satisfies the following relational expression 1.

[0032] <Relationship 1>

[0033] FWHM(PeLED) ≤ FWHM(tandem) ≤ FWHM(OLED)

[0034] At this time, the FWHM (OLED) is the half-width of a light-emitting element including an organic light-emitting unit and not including a perovskite light-emitting unit, the FWHM (tandem) is the half-width of the tandem light-emitting element, and the FWHM (PeLED) is the half-width of a light-emitting element including a perovskite light-emitting unit and not including an organic light-emitting unit.

[0035] Additionally, the refractive index of at least one selected from the group consisting of the first hole transport layer, the first electron transport layer, the second hole transport layer, and the second electron transport layer may be 1.4 to 2.2.

[0036] In addition, the perovskite light-emitting layer is composed of ABX3, A4BX6, AB2X5, A2BX4, A2BX6, A2B + B 3+ X6, A3B2X9 or A'2A k-1 B k X 3k+1 A crystal structure, wherein A is a monovalent organic cation, a monovalent inorganic cation, or a combination thereof, B is one or more types of metal ions, and X is F - , Cl - , Br - , I - , SCN - , OCN - , SeCN - , HCO 2- , CH3COO - or a combination of these, where k can be an integer between 2 and 6.

[0037] Additionally, the first electron transport layer and / or the second electron transport layer may have a multilayer structure.

[0038] In addition, in the multilayer structure, the materials included in each layer are different from each other, and the LUMO energy level of each layer in the first electron transport layer may become higher as it gets closer to the perovskite light-emitting layer, and the LUMO energy level of each layer in the second electron transport layer may become higher as it gets closer to the organic light-emitting layer.

[0039] Additionally, the charge generation layer may include an n-type charge generation layer and / or a p-type charge generation layer.

[0040] According to one embodiment of the present invention, the thickness of the second hole transport layer and the thickness of the second electron transport layer can satisfy the following relationship 2 and / or the following relationship 3.

[0041] <Relationship 2>

[0042] a ≤ x + by ≤ c

[0043] At this time, in the relational expression 2, x is the thickness of the second electron transport layer, y is the thickness of the second hole transport layer, a is -89.474×n + 265.001, b is -1.053×n + 2.931, c is -63.158×n + 243.001, and n is the refractive index of the second hole transport layer.

[0044] <Relationship 3>

[0045] d ≤ x + ey ≤ f

[0046] At this time, in the relational expression 3, x is the thickness of the second electron transport layer, y is the thickness of the second hole transport layer, d is 15.789×m + 82.95, e is 1.105×m-0.903, f is 135, and m is the refractive index of the second electron transport layer.

[0047] In addition, when the above relational expression 2 and / or the above relational expression 3 is satisfied, the thickness of the second hole transport layer may be 50 to 80 nm, and the thickness of the second electron transport layer may be 40 to 60 nm.

[0048] In addition, when the above relational expression 2 and / or the above relational expression 3 is satisfied, the perovskite light-emitting unit and the organic light-emitting unit can satisfy the following relational expression 4.

[0049] <Relationship 4>

[0050] 0.8 ≤ A / B ≤ 1.2

[0051] At this time, A is the current density of the perovskite light-emitting unit when the applied voltage to the perovskite light-emitting unit is 2.8 V, and B is the current density of the organic light-emitting unit when the applied voltage to the organic light-emitting unit is 2.8 V.

[0052] In addition, the organic light-emitting layer may include a host and / or a dopant, wherein the host may contain at least one selected from the group consisting of CBP, TCTA, mCP, DCzPPy, PCPPn, PCPN, CzTP, TCPB, and CzPA, and the dopant may contain at least one selected from the group consisting of a fluorescent organic material, a phosphorescent organic material, and a thermally activated delayed fluorescent organic material.

[0053] Additionally, the tandem light-emitting element may have a half-width of 30 nm or less.

[0054] Additionally, the tandem light-emitting device may have an external quantum efficiency (EQE) of 30% or more.

[0055]

[0056] In order to solve the above-described problem, a display device including the above-described tandem light-emitting element is provided.

[0057]

[0058] In order to solve the above-described problem, a method for manufacturing a tandem light-emitting device is provided, comprising: (1) forming a first hole transport layer, a perovskite light-emitting layer, and a first electron transport layer sequentially on a first electrode to form a perovskite light-emitting unit; (2) forming a charge generation layer on the first electron transport layer; (3) forming a second hole transport layer, an organic light-emitting layer, and a second electron transport layer sequentially on the charge generation layer to form an organic light-emitting unit; and (4) forming a second electrode on the second electron transport layer; and controlling the thicknesses of the second hole transport layer and the second electron transport layer, a method for manufacturing a tandem light-emitting device is provided in which the emission spectrum full width at half maximum (FWHM) of the entire tandem light-emitting device satisfies the following relational expression 1.

[0059] <Relationship 1>

[0060] FWHM(PeLED) ≤ FWHM(tandem) ≤ FWHM(OLED)

[0061] At this time, the FWHM (OLED) is the half-width of a light-emitting element including an organic light-emitting unit and not including a perovskite light-emitting unit, the FWHM (tandem) is the half-width of the tandem light-emitting element, and the FWHM (PeLED) is the half-width of a light-emitting element including a perovskite light-emitting unit and not including an organic light-emitting unit.

[0062] In addition, the first hole transport layer and the perovskite light-emitting layer may be deposited through a solution process, and the first electron transport layer, the charge generation layer, the second hole transport layer, the organic light-emitting layer, and the second electron transport layer may be deposited through a dry process.

[0063] According to one embodiment of the present invention, the second hole transport layer and the second electron transport layer can be deposited to a thickness satisfying the following relationship 2 and / or the following relationship 3, respectively.

[0064] <Relationship 2>

[0065] a ≤ x + by ≤ c

[0066] At this time, in the relational expression 2, x is the thickness of the second electron transport layer, y is the thickness of the second hole transport layer, a is -89.474×n + 265.001, b is -1.053×n + 2.931, c is -63.158×n + 243.001, and n is the refractive index of the second hole transport layer.

[0067] <Relationship 3>

[0068] d ≤ x + ey ≤ f

[0069] At this time, in the relational expression 3, x is the thickness of the second electron transport layer, y is the thickness of the second hole transport layer, d is 15.789×m + 82.95, e is 1.105×m-0.903, f is 135, and m is the refractive index of the second electron transport layer.

[0070] In addition, when deposited with a thickness satisfying the above relational expression 2 and / or the above relational expression 3, the thickness of the second hole transport layer may be 50 to 80 nm, and the thickness of the second electron transport layer may be 40 to 60 nm.

[0071] In addition, the method for manufacturing the above-described tandem light-emitting element can manufacture the above-described tandem light-emitting element.

[0072]

[0073] The tandem light-emitting element and the display device including the same according to the present invention have maximized color purity and luminous efficiency, improved on-off response, excellent operating life, and low manufacturing cost.

[0074] In addition, the method for manufacturing a tandem light-emitting device according to the present invention has a low manufacturing cost and can manufacture the tandem light-emitting device of the present invention.

[0075]

[0076] The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the composition of the invention described in the description or claims of the present invention.

[0077]

[0078] FIG. 1 is a graph showing the concept of a tandem light-emitting device of the present invention and the optical micro-resonance effect structure. FIG. 1a is a result of the full width at half maximum (FWHM) of the emission spectrum of a light-emitting device including only an organic light-emitting unit (hereinafter, referred to as an organic light-emitting device). FIG. 1b is a result of the full width at half maximum (FWHM) of the emission spectrum of a light-emitting device including only a perovskite light-emitting unit (hereinafter, referred to as a perovskite light-emitting device). FIG. 1c is a result of the full width at half maximum of the emission spectrum of a tandem light-emitting device according to a preferred embodiment of the present invention. FIG. 1d is a photographic image of the tandem light-emitting device of the present invention in operation. FIG. 1e is a schematic diagram of the structure of a tandem light-emitting device according to a preferred embodiment of the present invention. FIG. 1f is a three-dimensional graph showing the result of the full width at half maximum according to the thickness of the second hole transport layer and the second electron transport layer of the organic light-emitting unit included in the tandem light-emitting device through optical simulation, which shows the optical micro-resonance effect.

[0079] FIG. 2 shows electrical and optical measurement results for the tandem light-emitting device, perovskite light-emitting device, and organic light-emitting device of the present invention. FIG. 2a shows the voltage-current density measurement results for each light-emitting device. FIG. 2b shows the voltage-luminance measurement results for each light-emitting device. FIG. 2c shows the luminance-external quantum efficiency (EQE) measurement results for each light-emitting device. FIG. 2d shows the normalized electroluminescence (EL) spectra measurement results for each light-emitting device. FIG. 2e is a graph expressing the external quantum efficiency results for a conventional perovskite light-emitting device and a tandem light-emitting device according to a preferred embodiment of the present invention. FIG. 2f shows the normalized transient EL intensity measurement results for each light-emitting device. Fig. 2g is a streak camera image captured over a period of 500 μs during the turn-on process of the tandem light-emitting device of the present invention. Fig. 2h is a result of measuring a time-resolved spectra over a period of 500 μs during the turn-on process of the tandem light-emitting device of the present invention. Fig. 2i is a photographic image showing a large-area flexible display device including the tandem light-emitting device of the present invention.

[0080] Fig. 3 shows the results of electrical optimization according to the presence or absence of a multilayer structure in the electron transport layer included in a tandem light-emitting device. Fig. 3a shows a schematic structure of a valley-center tandem light-emitting device (an optimized light-emitting device, a light-emitting device in which the first and second electron transport layers have a multilayer structure). Fig. 3b shows the results of voltage-current density measurements for each of the organic light-emitting unit and the perovskite light-emitting unit included in the valley-center tandem light-emitting device and the unbalanced tandem light-emitting device 1 (a non-optimized light-emitting device, a tandem light-emitting device in which the first and second electron transport layers do not have a multilayer structure). Fig. 3c shows the results of voltage-current density measurements for the valley-center tandem light-emitting device and the unbalanced tandem light-emitting device 1. Fig. 3d shows the results of voltage-external quantum efficiency measurements for the valley-center tandem light-emitting device and the unbalanced tandem light-emitting device 1. Fig. 3e shows the results of normalized electroluminescence spectra measurements for valley-center tandem light-emitting devices and unbalanced tandem light-emitting devices 1. Fig. 3f shows the results of external quantum efficiencies obtained through optical simulation and actually measured external quantum efficiencies for valley-center tandem light-emitting devices and unbalanced tandem light-emitting devices 1. Fig. 3g shows the results of peak shifts in normalized electroluminescence spectra according to driving voltage in unbalanced tandem light-emitting devices 1. Fig. 3h shows the results of peak shifts in normalized electroluminescence spectra according to driving voltage in valley-center tandem light-emitting devices. Fig. 3i shows the results of normalized electroluminescence spectra obtained through optical simulation and actually measured normalized electroluminescence spectra for valley-center tandem light-emitting devices, perovskite light-emitting devices, and organic light-emitting devices.

[0081] Fig. 4 shows the results of electrical optimization depending on the presence or absence of a multilayer structure in the electron transport layer included in the tandem light-emitting device. Fig. 4a and Fig. 4e show the schematic structure of an unbalanced tandem light-emitting device 1 and the voltage-current density measurement results for each of an organic light-emitting unit and a perovskite light-emitting unit included in the unbalanced tandem light-emitting device. Fig. 4b and Fig. 4f show the schematic structure of an unbalanced tandem light-emitting device 2 and the voltage-current density measurement results for each of an organic light-emitting unit and a perovskite light-emitting unit included in the unbalanced tandem light-emitting device. Fig. 4c and Fig. 4g show the schematic structure of an unbalanced tandem light-emitting device 3 and the voltage-current density measurement results for each of an organic light-emitting unit and a perovskite light-emitting unit included in the unbalanced tandem light-emitting device. FIG. 4d and FIG. 4h are schematic diagrams of a valley-center tandem light-emitting device and voltage-current density measurement results for each of an organic light-emitting unit and a perovskite light-emitting unit included in the tandem light-emitting device. FIG. 4i shows current density and luminance measurement results according to voltage for an unbalanced light-emitting device and a valley-center tandem light-emitting device. FIG. 4j shows voltage and external quantum efficiency results for an unbalanced light-emitting device and a valley-center tandem light-emitting device. FIG. 4k shows normalized electroluminescence spectrum measurement results for an unbalanced light-emitting device and a valley-center tandem light-emitting device. FIG. 4l shows results showing external quantum efficiency through optical simulation and actually measured external quantum efficiency.

[0082] Figure 5 shows the results of peak shifts in the electroluminescence spectrum according to driving voltage in an unbalanced light-emitting element and a valley-center tandem light-emitting element.

[0083] Figure 6 shows the results of transient electroluminescence intensity measurements for an unbalanced light-emitting element and a valley-center tandem light-emitting element. Figure 6a shows the entire turn-on and turn-off processes, Figure 6b is an enlarged view of the turn-on process, and Figure 6c is an enlarged view of the turn-off process.

[0084] Figure 7 is a two-dimensional graph showing the results of the half-width according to the thickness of the second hole transport layer and the second electron transport layer of the organic light-emitting unit included in the tandem light-emitting device through optical simulation, and shows the optical micro-resonance effect.

[0085] Figure 8 shows the electrical and optical measurement results for the valley-center tandem light-emitting devices, valley tandem light-emitting devices (valley 1 and valley 2), and off-valley tandem light-emitting devices (off-valley 1 and off-valley 2) shown in Figure 7. Figure 7a shows the voltage-current density measurement results of each light-emitting device. Figure 7b shows the voltage-external quantum efficiency measurement results of each light-emitting device. Figure 7c shows the voltage-luminance measurement results. Figure 7d shows the normalized electroluminescence spectrum measurement results of each light-emitting device. Figure 7e shows the electroluminescence intensity measurement results according to the angle in each light-emitting device.

[0086] Fig. 9 shows optical simulation results and actual measurement results for a valley-center tandem light-emitting device and a thick tandem light-emitting device. Fig. 9a shows an optical simulation result for the external quantum efficiency of the entire device according to the thickness of the second hole transport layer and the second electron transport layer of the organic light-emitting unit included in the tandem light-emitting device. Fig. 9b shows an optical simulation result for the external quantum efficiency of the perovskite light-emitting unit included in the tandem light-emitting device according to the thickness of the second hole transport layer and the second electron transport layer of the organic light-emitting unit included in the tandem light-emitting device. Fig. 9c shows an optical simulation result for the external quantum efficiency of the organic light-emitting unit included in the tandem light-emitting device according to the thickness of the second hole transport layer and the second electron transport layer of the organic light-emitting unit included in the tandem light-emitting device. Fig. 9d shows the voltage-external quantum efficiency measurement results for each tandem light-emitting device. Figure 9e shows the results of external quantum efficiency through optical simulation and actual measured external quantum efficiency for each tandem light-emitting device. Figure 9f shows the results of normalized electroluminescence spectra and half-width measurements for each tandem light-emitting device. Figures 9g to 9i show the results of normalized electroluminescence spectra and half-width measurements for the entire light-emitting device, perovskite light-emitting unit, and organic light-emitting unit in each tandem light-emitting device through optical simulation.

[0087] Fig. 10 shows the results of an analysis of the emission area of ​​a valley-center tandem light-emitting device. Fig. 10a illustrates a schematic structure and the position of the emission area of ​​a valley-center tandem light-emitting device. Fig. 10b shows the results of an optical simulation and actual measurement according to the position of the emission area of ​​a valley-center tandem light-emitting device, and is an electroluminescence spectrum according to the angle.

[0088] Figure 11 shows the angle-dependent electroluminescence spectra for valley-center tandem light-emitting devices and thick tandem light-emitting devices, and the optical simulation results and actual measurement results of the perovskite light-emitting unit and organic light-emitting unit included in each light-emitting device. Figure 11a shows the results for the valley-center tandem light-emitting device, and Figure 11b shows the results for the thick tandem light-emitting device.

[0089] Figure 12 shows the results of simulating the relative electroluminescence spectra according to angle for a valley-center tandem light-emitting device, a thick tandem light-emitting device, and an off-valley tandem light-emitting device.

[0090] Fig. 13 shows the results of electrical and optical optimization according to the thickness of ZADN (2-[4-(9,10-Di-naphthalen-2-yl-anthracen-2-yl)-phenyl]-1-phenyl-1H-benzoimidazole) among the first electron transport layers of the perovskite light-emitting unit included in the tandem light-emitting device of the present invention. Fig. 13a shows a schematic structure of the tandem light-emitting device of the present invention and the thickness (X nm) of the ZADN. Fig. 13b shows the results showing the half-width of the electroluminescence spectrum according to the thickness of the ZADN. Fig. 13c shows the results showing the external quantum efficiency through optical simulation and the actually measured external quantum efficiency with respect to the change in the thickness of the ZADN.

[0091] Fig. 14 shows the results of electrical and optical measurements according to the thickness of ZADN among the first electron transport layers of the perovskite light-emitting units included in the tandem light-emitting device of the present invention. Fig. 14a shows the results of voltage-current density measurements for tandem light-emitting devices with various ZADN thicknesses, Fig. 14b shows the results of voltage-luminance measurements, and Fig. 14c shows the results of voltage-external quantum efficiency measurements. In addition, Fig. 14d shows the results of voltage-current efficiency measurements, and Fig. 14e shows the results of normalized electroluminescence spectrum measurements.

[0092] Figure 15 shows the results of measuring the lifespan of the tandem light-emitting device and perovskite light-emitting device of the present invention. Figure 15a shows the lifespan of the tandem light-emitting device and the perovskite light-emitting device when the initial luminance (L0) is 1000 cd / m. 2 When , the result shows the change in luminance over time of each element, and Fig. 15b is the result of the electroluminescence spectrum showing the luminance change and operating time from the initial luminance of the tandem light-emitting element.

[0093]

[0094] Hereinafter, the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily practice the present invention. The present invention can be implemented in various forms and is not limited to the embodiments described herein. In the drawings, parts not directly related to the description have been omitted for clarity.

[0095] The terminology used in this specification is only used to describe specific embodiments and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, it should be understood that the terms “comprise” or “have” indicate the presence of features, numbers, steps, operations, components, or combinations thereof described in the specification, but do not preclude the possibility that one or more other features, numbers, steps, operations, components, or combinations thereof may be present or added.

[0096] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries should be interpreted in a way consistent with their meaning within the context of the relevant technology, and will not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0097]

[0098] As described above, Fig. 1a is a result of the full width at half maximum (FWHM) of the emission spectrum of a light-emitting device (hereinafter, referred to as an organic light-emitting device) including only an organic light-emitting unit, and Fig. 1b is a result of the full width at half maximum (FWHM) of the emission spectrum of a light-emitting device (hereinafter, referred to as a perovskite light-emitting device) including only a perovskite light-emitting unit. As can be seen from these, perovskite light-emitting devices (Perovskite Light-Emitting Diodes; PeLEDs) have a problem of low luminous efficiency, and organic light-emitting devices (Organic Light-Emitting Diodes; OLEDs) have a problem of low color purity and high material costs. To solve this problem, there was an attempt to manufacture a tandem light-emitting device including both of the above units, but the conventional tandem light-emitting devices were simply a combination of an organic light-emitting unit and a perovskite light-emitting unit, and each light-emitting unit had different resistance and JVL characteristics, so that the light-emitting spectrum shifted overall, the half-width did not decrease, or a charge imbalance occurred, and thus high color purity and high light-emitting efficiency could not be guaranteed, and the operating life was not sufficient.

[0099]

[0100] Accordingly, the present invention seeks to solve the above-described problem by providing a tandem light-emitting device including a first electrode; a perovskite light-emitting unit disposed on the first electrode and including a first hole transport layer, a perovskite light-emitting layer, and a first electron transport layer; a charge generation layer disposed on the perovskite light-emitting unit; an organic light-emitting unit disposed on the charge generation layer and including a second hole transport layer, an organic light-emitting layer, and a second electron transport layer; and a second electrode disposed on the organic light-emitting unit, wherein, by controlling the thicknesses of the second hole transport layer and the second electron transport layer, the emission spectrum half maximum (FWHM) of the entire tandem light-emitting device satisfies the following relational expression 1.

[0101] <Relationship 1>

[0102] FWHM(PeLED) ≤ FWHM(tandem) ≤ FWHM(OLED)

[0103] At this time, the FWHM (OLED) is the half-width of a light-emitting element including an organic light-emitting unit and not including a perovskite light-emitting unit, the FWHM (tandem) is the half-width of the tandem light-emitting element, and the FWHM (PeLED) is the half-width of a light-emitting element including a perovskite light-emitting unit and not including an organic light-emitting unit.

[0104] This allows for maximizing luminous efficiency, such as color purity and external quantum efficiency, while increasing the operating lifespan. High efficiency can be achieved with only two units, thereby reducing manufacturing costs, as shown in FIGS. 1C and 1D. FIG. 1C is a result of the half-width of the luminous spectrum of a tandem light-emitting device according to a preferred embodiment of the present invention, and FIG. 1D is a photographic image of the tandem light-emitting device of the present invention in operation.

[0105] FIG. 1e is a schematic diagram of the structure of a tandem light-emitting device according to a preferred embodiment of the present invention, which will be described below with reference to FIG. 1e.

[0106]

[0107] First, the first electrode and the second electrode included in the tandem light-emitting device of the present invention will be described.

[0108] The first electrode may be an anode or a cathode, and the second electrode may also be an anode or a cathode. The second electrode may be the opposite electrode of the first electrode, and specifically, when the first electrode is an anode, the second electrode may be a cathode, and when the first electrode is a cathode, the second electrode may be an anode.

[0109] The first electrode or the second electrode is not particularly limited as long as it is a type that can be commonly used in the art. For example, the first electrode or the second electrode may be a reflective electrode, a semi-transmissive electrode, or a transmissive electrode. Preferably, the first electrode and / or the second electrode may include lithium (Li), silver (Ag), magnesium (Mg), aluminum (Al), aluminum-lithium (Al-Li), calcium (Ca), magnesium-indium (Mg-In), magnesium-silver (Mg-Ag), ytterbium (Yb), silver-ytterbium (Ag-Yb), indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide (SnO2), zinc oxide (ZnO), carbon nanotubes, graphene, nanowires, polymers, or any combination thereof. If the first electrode is a reflective electrode, the second electrode, which is the opposite electrode, may be a semi-transmissive electrode or a transmissive electrode, but is not limited thereto.

[0110] The first electrode or the second electrode may be formed through a method commonly used in the art, and the present invention is not particularly limited thereto. For example, it may be formed through a dry process and a solution (wet) process, and the dry process may be any general dry process used in the art, such as a thermal evaporation process, a vacuum deposition process, an atomic layer deposition (ALD) process, a chemical vapor deposition (CVD) process, a physical vapor deposition (PVD) process, an air jet process, etc., and the solution process may be any general solution process used in the art, such as a spin coating process, a slot die coating process, a blade coating process, a printing coating process, a gravure coating process, a spray coating process, etc.

[0111] The above first electrode or the above second electrode may have a single-layer structure or a multi-layer structure. In this case, a multi-layer structure means that the materials, crystals, or physical properties contained in each layer are different and the number of layers is two or more. Hereinafter, the meaning of a multi-layer structure is the same.

[0112] The thickness of each of the first electrode or the second electrode is not limited as long as it is a thickness that can be applied to a light-emitting element, and thus the present invention does not limit it. Preferably, it may be 50 to 200 nm. For example, each thickness is 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 102, 104, 106, 108, 110, 112, It can be 114, 116, 118, 120, 122, 124, 126, 128, 130, 132, 134, 136, 138, 140, 142, 144, 146, 148, 150, 152, 154, 156, 158, 160, 162, 164, 166, 168, 170, 172, 174, 176, 178, 180, 182, 184, 186, 188, 190, 192, 194, 196, 198 or 200.

[0113]

[0114] Next, the perovskite light-emitting unit included in the tandem light-emitting device according to the present invention will be described. The perovskite light-emitting unit is disposed on the first electrode and includes a first hole transport layer, a perovskite light-emitting layer, and a first electron transport layer. Here, the meaning of being disposed does not mean that any configuration is excluded between the first electrode and the perovskite light-emitting unit, and hereinafter, the meaning of being disposed is as follows.

[0115]

[0116] The refractive index of the first hole transport layer may be, but is not limited to, 1.4 to 2.2. For example, based on 531 nm, the refractive index of the first hole transport layer is 1.40, 1.41, 1.42, 1.43, 1.44, 1.45, 1.46, 1.47, 1.48, 1.49, 1.50, 1.51, 1.52, 1.53, 1.54, 1.55, 1.56, 1.57, 1.58, 1.59, 1.60, 1.61, 1.62, 1.63, 1.64, 1.65, 1.66, 1.67, 1.68, 1.69, 1.70, 1.71, 1.72, 1.73, 1.74, 1.75, 1.76, 1.77, 1.78, 1.79, 1.80, 1.81, 1.82, 1.83, 1.84, 1.85, 1.86, 1.87, 1.88, 1.89, 1.90, 1.91, 1.92, 1.93, 1.94, 1.95, 1.96, 1.97, 1.98, 1.99, 2.00, 2.01, 2.02, 2.03, 2.04, 2.05, 2.06, 2.07, 2.08, 2.09, 2.10, 2.11, 2.12, 2.13, 2.14, 2.15, 2.16, 2.17, It can be 2.18, 2.19 or 2.20. If the refractive index of the first hole transport layer is outside the above range, the optimal optical micro-resonance effect cannot be achieved, so the luminous efficiency of the device may decrease and the half-width of the luminous spectrum may widen, resulting in a decrease in color purity.

[0117] Preferably, the refractive index of the first hole transport layer may be 1.4 to 1.8, and more preferably, the refractive index of the first hole transport layer may be 1.45 to 1.75. For example, the refractive index of Buf-HIL that may be used in the first hole transport layer is 1.49.

[0118]

[0119] In addition, the first hole transport layer may be applied without limitation to any material commonly used in the art, but preferably may be a material satisfying the above-described refractive index. For example, the first hole transport layer may include at least one selected from the group consisting of compounds containing an aryl group and / or a heteroaryl group, polymers and derivatives of the compounds, and specifically, 4,4′-Cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine](TAPC), 4,4',4"-Tris(carbazol-9-yl)triphenylamine(TCTA), N,N′-Di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine(NPB), 4,4′-Bis(9-carbazolyl)-1,1′-biphenyl (CBP), Poly[N,N'-bis(4-butylphenyl)-N,N'-bisphenylbenzidine](Poly-TPD), polyaniline(PANI), Poly(n-vinylcarbazole)(PVK), It may include at least one selected from the group consisting of poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine(PTAA) and Buf-HIL.

[0120] The above first hole transport layer may have a single-layer structure or a multi-layer structure, and the present invention is not particularly limited thereto.

[0121] Additionally, the first hole transport layer may be a hole injection layer.

[0122] The thickness of the first hole transport layer is not particularly limited, but may preferably be 20 to 100 nm. Specifically, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, It can be 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 or 100 nm.

[0123]

[0124] The above perovskite light-emitting layer is ABX3, A4BX6, AB2X5, A2BX4, A2BX6, A2B + B 3+ X6, A3B2X9 or A'2A k-1 B k X 3k+1 A crystal structure, wherein A is a monovalent organic cation, a monovalent inorganic cation, or a combination thereof, B is one or more types of metal ions, and X is F - , Cl - , Br - , I - , SCN - , OCN - , SeCN - , HCO 2- , CH3COO - or a combination thereof, and k can be an integer between 2 and 6. For example, A is formamidinium (NH2CH=NH + ) ion, acetamidinium (acetamidinium, NH2C(CH)=NH2 +) ion or guamidinium (Guamidinium, NHC(NH)=NH + ) ions such as amidinium group organic cations; or organic ammonium (RNH3) cations, for example CH3NH3 + , HC(NH2)2 + , C4H9NH3 + , (CH3NH3) n , ((C x H 2x+1 ) n NH3)2(CH3NH3) n , (RNH3)2, (C n H 2n+1 NH3)2, (CF3NH3), (CF3NH3) n , ((C x F 2x+1 ) n NH3)2(CF3NH3) n , ((C x F 2x+1 ) n NH3)2 or (C n F 2n+1 NH3)2 (where n is an integer greater than or equal to 1), an organic phosphonium (RPH3) cation, or a monovalent alkali metal cation (e.g., Cs + ) may be.

[0125] Preferably, the perovskite light-emitting layer comprises an ABX3 crystal structure, wherein A is a monovalent organic cation or a combination thereof, B is one or more types of metal ions, and F is F - , Cl - , Br - , I - Or it could be a combination of these.

[0126] More preferably, the perovskite light-emitting layer comprises an APbBr3 crystal structure, and A may be FA (formamidinium), GA (guanidinium), or a combination thereof.

[0127]

[0128] The above perovskite light-emitting layer may have a single-layer structure or a multi-layer structure, and the present invention is not particularly limited thereto.

[0129]

[0130] In tandem light-emitting devices, it is desirable for the perovskite light-emitting layer to have high transmittance, and for this purpose, it is desirable for the thickness to be thin.

[0131] The thickness of the perovskite light-emitting layer may be 1 to 100 nm, but is not particularly limited. For example, it may be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 65, 70, 75, 80, 85, 90, 95 or 100 nm. Preferably, it may be 50 nm or less, and more preferably, it may be 30 nm or less.

[0132] If it exceeds 100 nm, the transmittance of the perovskite unit decreases, absorbing the light emission of the organic light emitting unit, which may hinder the formation of an optimal resonance structure, thereby lowering the light emission efficiency of the device or lowering the color purity.

[0133]

[0134] Perovskite materials can include polycrystalline perovskite, quasi-2d perovskite, and perovskite nanocrystal.

[0135] To realize a high-efficiency tandem light-emitting device, it is preferable to use perovskite nanocrystals and quasi-2d perovskites, which can easily control the thickness of the perovskite light-emitting layer while reducing the transmittance, and the use of perovskite nanocrystals may be more preferable. Meanwhile, polycrystalline perovskites are not impossible to use, and if the thickness can be controlled to less than 100 nm, they can also be used.

[0136]

[0137] The refractive index of the first electron transport layer may be, but is not limited to, 1.4 to 2.2. For example, at 531 nm, the refractive index of the first electron transport layer is 1.40, 1.41, 1.42, 1.43, 1.44, 1.45, 1.46, 1.47, 1.48, 1.49, 1.50, 1.51, 1.52, 1.53, 1.54, 1.55, 1.56, 1.57, 1.58, 1.59, 1.60, 1.61, 1.62, 1.63, 1.64, 1.65, 1.66, 1.67, 1.68, 1.69, 1.70, 1.71, 1.72, 1.73, 1.74, 1.75, 1.76, 1.77, 1.78, 1.79, 1.80, 1.81, 1.82, 1.83, 1.84, 1.85, 1.86, 1.87, 1.88, 1.89, 1.90, 1.91, 1.92, 1.93, 1.94, 1.95, 1.96, 1.97, 1.98, 1.99, 2.00, 2.01, 2.02, 2.03, 2.04, 2.05, 2.06, 2.07, 2.08, 2.09, 2.10, 2.11, 2.12, 2.13, 2.14, 2.15, 2.16, 2.17, It can be 2.18, 2.19 or 2.20. If the refractive index of the first electron transport layer is outside the above range, the optimal optical micro-resonance effect cannot be achieved, which may lower the luminous efficiency of the device and widen the half-width of the luminous spectrum, thereby reducing the color purity.

[0138] Preferably, the refractive index of the first electron transport layer may be 1.6 to 1.9, and more preferably, 1.65 to 1.85. For example, the refractive indices of TPBi and ZADN that can be used in the first electron transport layer are 1.74 and 1.84, respectively.

[0139]

[0140] In addition, the first electron transport layer may be applied without limitation to any material commonly used in the art, but preferably may be a material satisfying the above-described refractive index.For example, the first electron transport layer may include at least one selected from the group consisting of compounds containing an aryl group and / or a heteroaryl group, polymers and derivatives of the compounds, and specifically, 2,2',2"-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)(TPBi), 1,3,5-Tri(m-pyridin-3-ylphenyl)benzene(TmPyPB), 4,6-Bis(3,5-di(pyridin-3-yl)phenyl)-2-methylpyrimidine(B3PYMPM), 2,4,6-Tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine(PO-T2T), 3′,3′′′,3′′′′′-(1,3,5-triazine-2,4,6-triyl) tris(([1,1′-biphenyl]-3-carbonitrile))(CN-T2T), 2-[4-(9,10-Di-naphthalen-2-yl-anthracen-2-yl)-phenyl]-1-phenyl-1H-benzoimidazole(ZADN), Tris(2,4,6-trimethyl-3-(pyridin-3-yl)phenyl)borane(3TPYMB), Alq3, 3-(Biphenyl-4-yl)-5-(4-tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole(TAZ), 4,7-Diphenyl-1,10-phenanthroline(Bphen), 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), Bis(10-hydroxybenzo[h]quinolinato)beryllium(BeBq2), It may include at least one selected from the group consisting of 1,3,5-Tri(p-pyrid-3-yl-phenyl)benzene (TpPyPB) and Bis(8-hydroxy-2-methylquinoline)-(4-phenylphenoxy)aluminum (BAlq).

[0141]

[0142] FIG. 1f is a three-dimensional graph obtained by optical simulation of the half width of the electroluminescence spectrum according to the thickness of the second hole transport layer and the second electron transport layer of the organic light-emitting unit included in the tandem light-emitting device, which can be calculated using a multilayer thin-film OLED optical simulation method based on the classical dipole model described in papers (Phys. Rev. B 85, ​​115205 (2012), Opt. Express 23, A279-A291 (2015), Nat. Commun. 5, 4769 (2014), Nat. Commun. 7, 11791 (2016)), etc., or an optical simulation software package based on this method (e.g., J-OSTD (JooAm), SETFOS (FLUXim)).

[0143] The input parameters of the above optical simulation include the light-emitting device structure and the refractive index and thickness of each layer, the photoluminescence quantum efficiency (absolute luminous efficiency, Photoluminescence Quantum Yield, PLQY) of the light-emitting layer, the photoluminescence spectrum of the light-emitting layer, the emitting dipole orientations of the light-emitting layer, and the emission-zone distribution of the light-emitting layer, and each parameter can be obtained experimentally.

[0144] At this time, the refractive index of each layer can be obtained by measuring the thin film layer formed on the silicon substrate using a variable-angle spectroscopic ellipsometry using an ellipsometer (e.g., JA Woollam M-2000) or by analyzing the UV-Vis absorbance of the thin film layer formed on the quartz substrate by fitting it to an optical simulation. In addition, the PLQY of the emitting layer can be obtained by exciting each emitting-side thin film formed on the quartz substrate with a laser that generates appropriate absorption and then measuring the luminescence generated using an integrating sphere and a spectrometer connected to it. In addition, the luminescence dipole alignment of the emitting layer can be analyzed by optical simulation of the p-polarized angle-dependent photoluminescence generated by attaching each emitting layer formed on the quartz substrate to a half cylinder lens and then exciting it with a laser, thereby obtaining the horizontal dipole alignment ratio and the vertical dipole alignment ratio through the optical simulation software package. Furthermore, the location of the EMZ in an actual light-emitting device can be determined by finding a matching point by comparing the angle-dependent photoluminescence measurements with the optical simulation results for each EMZ.

[0145] Based on the input parameters derived above, optical simulation can be performed through the following process. 1) The light-emitting body inside the emitting layer is modeled using a classical dipole model to generate electromagnetic waves, and the emitting dipole is set to generate light reflecting the experimentally measured dipole orientation ratio. The effective PLQY of the emitting dipole is calculated by applying the Purcell factor of the cavity where the emitting dipole is located to the experimentally measured PLQY of the thin film. 2) The reflection, transmission, and refraction phenomena that occur when the electromagnetic wave generated from the emitting dipole reaches the thin film interface can be calculated using the Fresnel equation, and these can be calculated using the experimentally measured refractive index of each layer. 3) The multiple reflection, transmission, refraction, and interference effects caused by the multilayer structure of the actual device are calculated using the transfer matrix method (TMM). This allows for the calculation of light propagation in a multilayered emitting device, which in turn allows for the calculation of the final spectrum. For reference, the perovskite light-emitting layer of the present invention may be so thin that photon recycling may not be considered.

[0146]

[0147] Fig. 3a schematically illustrates the structure of a valley-center tandem light-emitting device (an optimized light-emitting device, a light-emitting device in which the first and second electron transport layers have a multilayer structure). Referring to Fig. 3a, the first electron transport layer may have a single-layer structure or a multilayer structure, and preferably, a multilayer structure. Compared to a single-layer structure, a multilayer structure provides more options for selecting the thickness and material of each layer, which may be advantageous in achieving excellent micro-resonance effects and charge balance.

[0148] In the above multilayer structure, the materials contained in each layer are different from each other, and the LUMO energy level of each layer in the first electron transport layer may increase as it approaches the perovskite light-emitting layer. Through this, electrons generated in the charge generation layer can be effectively injected into the electron transport layer, thereby facilitating electron transport more smoothly, thereby increasing the current density and enhancing the light-emitting efficiency.

[0149]

[0150] FIG. 13 is an electrical and optical optimization result according to the thickness of ZADN (2-[4-(9,10-Di-naphthalen-2-yl-anthracen-2-yl)-phenyl]-1-phenyl-1H-benzoimidazole) among the first electron transport layers of the perovskite light-emitting unit included in the tandem light-emitting device of the present invention, and FIG. 14 is an electrical and optical measurement result according to the thickness of ZADN among the first electron transport layers of the perovskite light-emitting unit included in the tandem light-emitting device of the present invention, and the thickness of the first electron transport layer will be described with reference to FIGS. 13 and 14.

[0151] The thickness of the first electron transport layer may be, but is not limited to, 21 to 29 nm, and any thickness that can maximize the micro-resonance effect and balance the charge may be applied without limitation. For example, it may be 21.0, 21.5, 22.0, 22.5, 23.0, 23.5, 24.0, 24.5, 25.0, 25.5, 26.0, 26.5, 27.0, 27.5, 28.0, 28.5, or 29.0 nm.

[0152] Specifically, since the first electron transport layer is arranged close to the n-type charge generation layer, its thickness control may be very important in terms of external quantum efficiency and color purity. If the thickness of the first electron transport layer is less than 21 nm or more than 29 nm, a charge imbalance may occur throughout the light-emitting device, or the optimal micro-resonance effect may not be achieved, resulting in insufficient color purity or disadvantages in external quantum efficiency. In particular, when the thickness exceeds 29 nm, although excellent external quantum efficiency is predicted in optical simulations, very low external quantum efficiency may be exhibited due to charge imbalance.

[0153] In addition, when the first electron transport layer has a two-layer structure, the thickness of the layer having a lower LUMO energy level may be 17 to 23 nm, and the thickness of the layer having a higher LUMO energy level may be 4 to 6 nm. Specifically, the thickness of the layer having a lower LUMO energy level may be 17.0, 17.5, 18.0, 18.5, 19.0, 19.5, 20.0, 20.5, 21.0, 21.5, 22.0, 22.5, or 23.0 nm, and the thickness of the layer having a higher LUMO energy level may be 4.0, 4.5, 5.0, 5.5, or 6.0. For example, in the first electron transport layer, the layer with a lower LUMO energy level may include ZADN, and the layer with a higher LUMO energy level may include TPBi.

[0154]

[0155] Next, the charge generation layer included in the tandem light-emitting device of the present invention will be described.

[0156] The charge generation layer may include an n-type charge generation layer that generates and injects electrons and / or a p-type charge generation layer that generates and injects holes, and due to such a charge generation layer, electrons or holes can be injected into an adjacent light-emitting unit without resistance. In addition, the charge generation layer may electrically connect the perovskite light-emitting unit and the organic light-emitting unit, and may serve to supply electrons and holes to each unit.

[0157] The above n-type charge generation layer or the above p-type charge generation layer may have a single-layer structure or a multi-layer structure, and the present invention does not specifically limit the number of layers.

[0158]

[0159] The above n-type charge generation layer may be an organic material alone as an electron transport material or an organic material doped with an n-type dopant at a content of 5 to 40%. For example, the n-type dopant may be doped at a content of 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39 or 40%.

[0160] The electron transport material may be TPBI, TmPyPB, 3TPYMB, PO-T2T, BCP, etc. The n-type dopant may be an alkali metal such as Li, Na, K, Rb, Cs, Mg, Ca, an alkaline earth metal, or a carbonate series compound, an azide series compound, a nitride series compound, a nitrate series compound, a phosphate series compound, or a quinolate series compound based thereon. Examples of compounds based on alkali metals or alkaline earth metals include, but are not limited to, Li2CO3, LiNO3, RbNO3, Rb2CO3, AgNO3, Ba(NO3)2, Mn(NO3)2, Zn(NO3)2, CsNO3, Cs2CO3, CsF, CsN3, FePo4, and NaN3.

[0161] The thickness of the above n-type charge generation layer is not particularly limited, but may be 5 to 30 nm. For example, the thickness is 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0, 10.5, 11.0, 11.5, 12.0, 12.5, 13.0, 13.5, 14.0, 14.5, 15.0, 15.5, 16.0, 16.5, 17.0, 17.5, 18.0, 18.5, 19.0, 19.5, 20.0, 20.5, 21.0, 21.5, 22.0, 22.5, 23.0, 23.5, 24.0, 24.5, 25.0, It can be 25.5, 26.0, 26.5, 27.0, 27.5, 28.0, 28.5, 29.0, 29.5 or 30.0 nm.

[0162]

[0163] The above p-type charge generation layer may be an organic material alone as a hole transport material or an organic material doped with a p-type dopant in an amount of 5 to 40%. For example, the p-type dopant may be doped in an amount of 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39 or 40%.

[0164] As the above hole transport material, TAPC, TCTA, TPD, NPB, and CuPC can be used. The p-type dopant can be F4-TCNQ, FeCl3, WO3, MoO3, ReO3, Fe3O4, MnO2, SnO2, CoO2, CuPC, a metal oxide, or a hole injection organic material having a deep LUMO level. Specifically, the p-type hole injection layer can be, but is not limited to, PEDOT:PSS, MoO3, WO3, and V2O5.

[0165] The thickness of the above p-type charge generation layer is not particularly limited, but may be 5 to 30 nm. For example, the thickness is 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0, 10.5, 11.0, 11.5, 12.0, 12.5, 13.0, 13.5, 14.0, 14.5, 15.0, 15.5, 16.0, 16.5, 17.0, 17.5, 18.0, 18.5, 19.0, 19.5, 20.0, 20.5, 21.0, 21.5, 22.0, 22.5, 23.0, 23.5, 24.0, 24.5, 25.0, It can be 25.5, 26.0, 26.5, 27.0, 27.5, 28.0, 28.5, 29.0, 29.5 or 30.0 nm.

[0166]

[0167] An organic light-emitting unit included in a tandem light-emitting device according to the present invention is specifically described. The organic light-emitting unit is disposed on the charge generation layer and includes a second hole transport layer, an organic light-emitting layer, and a second electron transport layer.

[0168]

[0169] The refractive index of the second hole transport layer may be, but is not limited to, 1.4 to 2.2. For example, based on 531 nm, the refractive index of the second hole transport layer is 1.40, 1.41, 1.42, 1.43, 1.44, 1.45, 1.46, 1.47, 1.48, 1.49, 1.50, 1.51, 1.52, 1.53, 1.54, 1.55, 1.56, 1.57, 1.58, 1.59, 1.60, 1.61, 1.62, 1.63, 1.64, 1.65, 1.66, 1.67, 1.68, 1.69, 1.70, 1.71, 1.72, 1.73, 1.74, 1.75, 1.76, 1.77, 1.78, 1.79, 1.80, 1.81, 1.82, 1.83, 1.84, 1.85, 1.86, 1.87, 1.88, 1.89, 1.90, 1.91, 1.92, 1.93, 1.94, 1.95, 1.96, 1.97, 1.98, 1.99, 2.00, 2.01, 2.02, 2.03, 2.04, 2.05, 2.06, 2.07, 2.08, 2.09, 2.10, 2.11, 2.12, 2.13, 2.14, 2.15, 2.16, 2.17, It can be 2.18, 2.19 or 2.20. If the refractive index of the second hole transport layer is outside the above range, the optimal optical micro-resonance effect cannot be achieved, which may lower the luminous efficiency of the device and widen the half-width of the luminous spectrum, thereby reducing the color purity.

[0170] Preferably, the refractive index of the second hole transport layer may be 1.6 to 1.9, and more preferably, 1.65 to 1.85. For example, the refractive index of TAPC that may be used in the second hole transport layer is 1.71.

[0171]

[0172] In addition, the second hole transport layer may be applied without limitation to any material commonly used in the art, but preferably may be a material satisfying the above-described refractive index. For example, the second hole transport layer may include at least one selected from the group consisting of compounds containing an aryl group and / or a heteroaryl group, polymers and derivatives of the compounds, and specifically, 4,4′-Cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine](TAPC), 4,4',4"-Tris(carbazol-9-yl)triphenylamine(TCTA), N,N′-Di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine(NPB), 4,4′-Bis(9-carbazolyl)-1,1′-biphenyl (CBP), Poly[N,N'-bis(4-butylphenyl)-N,N'-bisphenylbenzidine](Poly-TPD), polyaniline(PANI), Poly(n-vinylcarbazole)(PVK), It may include at least one selected from the group consisting of poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine(PTAA) and Buf-HIL.

[0173] The second hole transport layer may have a single-layer structure or a multi-layer structure, and the present invention is not particularly limited thereto.

[0174] Additionally, the second hole transport layer may be a hole injection layer.

[0175]

[0176] The organic light-emitting layer comprises a host and / or a dopant, wherein the host contains at least one selected from the group consisting of CBP, TCTA, mCP, DCzPPy, PCPPn, PCPN, CzTP, TCPB, and CzPA, and the dopant may contain at least one selected from the group consisting of a fluorescent organic material, a phosphorescent organic material, and a thermally activated delayed fluorescent organic material.

[0177] The fluorescent organic material may be at least one of 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4Hpyran (DCJTB), (E)-2-(2-(4-(Dimethylamino)styryl)-6-methyl-4H-pyran-4-ylidene)malononitrile (DCM), and 5,6-bis(4-(9,9-dimethylacridin-10(9H)-yl)phenyl)pyrazine-2,3-dicarbonitrile (Ac-CNP).

[0178] 상기 인광 유기물은 Bt2Ir(acac), tris(1-phenylisoquinoline) iridium(III) (Ir(piq)3), Bis(2-(3,5-dimethylphenyl)-4-phenylpyridine)(2,2,6,6-tetramethylheptane-3,5-diketonate)iridium(III) (Ir(dmppyph)2tmd), Bis(2-benzo[b ]thiophen-2-yl-pyridine)(acetyridium(III)) (Ir(btp)2(acac)), Bis[1-(9,9-dimethyl-9H-fluorene-2-yl)-isoquinoline](acetylacetonate)iridium(III) (Ir(fliq)2(acac)), Bis[2-(9,9-dimethyl-9H-fluoren-2-linequinoquinolineace) (Ir(flq)2(acac)), Bis[2-(4-nhexylphenyl)quinoline](acetylacetonate)iridium(III) (Hex-Ir(phq)2(acac)), Tris[2-(4-nhexylphenyl)quinoline]iridium(III) (Hex-Ir(phq)3, Bis(2-phenylquinoline)(2-(3-methylphenyl)pyridinate)iridium(III) (Ir(phq)2tpy) 중 적어도 하나일 수 있다.

[0179] Thermal activated delayed fluorescence (TADF) organics include Dibenzo{[f,f']-4,4',7,7'-tetraphenyl}diindeno[1,2,3-cd:1',2',3'-lm]perylene (DBP); 2,3,5,6-Tetrakis[3,6-bis(1,1-dimethylethyl)-9H-carbazol-9-yl]benzonitrile(4CzBN), 7,10-Bis(4-(diphenylamino)phenyl)-2,3-dicyanopyrazino phenanthrene(TPA-DCPP), 2,8-Di-tert -butyl-5,11-bis(4-tert-butylphenyl)-6,12-diphenyltetracene(TBRb), It may be at least one of 2-(9-phenyl-9H-carbazol-3-yl)-10,10-dioxide-9H-thioxanthen-9-one (TXO-PhCz).

[0180]

[0181] The organic light-emitting layer may have a single-layer structure or a multi-layer structure, and the present invention does not specifically limit this. Preferably, it may have a multi-layer structure, and more preferably, the HOMO energy level of each layer in the organic light-emitting layer may increase as it approaches the second hole transport layer, and the LUMO energy level of each layer may decrease as it approaches the second electron transport layer.

[0182] The thickness of the organic light-emitting layer may be 1 to 100 nm, but is not particularly limited. For example, it may be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 65, 70, 75, 80, 85, 90, 95 or 100 nm.

[0183]

[0184] The refractive index of the second electron transport layer may be, but is not limited to, 1.4 to 2.2. For example, at 531 nm, the refractive index of the second electron transport layer is 1.40, 1.41, 1.42, 1.43, 1.44, 1.45, 1.46, 1.47, 1.48, 1.49, 1.50, 1.51, 1.52, 1.53, 1.54, 1.55, 1.56, 1.57, 1.58, 1.59, 1.60, 1.61, 1.62, 1.63, 1.64, 1.65, 1.66, 1.67, 1.68, 1.69, 1.70, 1.71, 1.72, 1.73, 1.74, 1.75, 1.76, 1.77, 1.78, 1.79, 1.80, 1.81, 1.82, 1.83, 1.84, 1.85, 1.86, 1.87, 1.88, 1.89, 1.90, 1.91, 1.92, 1.93, 1.94, 1.95, 1.96, 1.97, 1.98, 1.99, 2.00, 2.01, 2.02, 2.03, 2.04, 2.05, 2.06, 2.07, 2.08, 2.09, 2.10, 2.11, 2.12, 2.13, 2.14, 2.15, 2.16, 2.17, It can be 2.18, 2.19 or 2.20. If the refractive index of the second electron transport layer is outside the above range, the optimal optical micro-resonance effect cannot be achieved, which may lower the luminous efficiency of the device and widen the half-width of the luminous spectrum, thereby reducing the color purity.

[0185] Preferably, the refractive index of the second electron transport layer may be 1.6 to 1.9, and more preferably, 1.65 to 1.85. For example, the refractive indices of TPBi and ZADN that can be used in the second electron transport layer are 1.74 and 1.84, respectively.

[0186]

[0187] In addition, the second electron transport layer may be applied without limitation to any material commonly used in the art, but preferably may be a material satisfying the above-described refractive index.For example, the second electron transport layer may include at least one selected from the group consisting of compounds containing an aryl group and / or a heteroaryl group, polymers of the compounds, and derivatives thereof, and specifically, 2,2',2"-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi), 1,3,5-Tri(m-pyridin-3-ylphenyl)benzene(TmPyPB), 4,6-Bis(3,5-di(pyridin-3-yl)phenyl)-2-methylpyrimidine(B3PYMPM), 2,4,6-Tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine (PO-T2T), 3′,3′′′,3′′′′′-(1,3,5-triazine-2,4,6-triyl) tris(([1,1′-biphenyl]-3-carbonitrile)) (CN-T2T), 2-[4-(9,10-Di-naphthalen-2-yl-anthracen-2-yl)-phenyl]-1-phenyl-1H-benzoimidazole(ZADN), Tris(2,4,6-trimethyl-3-(pyridin-3-yl)phenyl)borane (3TPYMB), Alq3, 3-(Biphenyl-4-yl)-5-(4-tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole (TAZ), 4,7-Diphenyl-1,10-phenanthroline(Bphen), 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), Bis(10-hydroxybenzo[h]quinolinato)beryllium (BeBq2), It may include at least one selected from the group consisting of 1,3,5-Tri(p-pyrid-3-yl-phenyl)benzene (TpPyPB) and Bis(8-hydroxy-2-methylquinoline)-(4-phenylphenoxy)aluminum (BAlq).

[0188] Fig. 3a schematically illustrates the structure of a valley-center tandem light-emitting device (an optimized light-emitting device, a light-emitting device in which the first and second electron transport layers have a multilayer structure). Referring to Fig. 3a, the second electron transport layer may have a single-layer structure or a multilayer structure, and preferably, a multilayer structure. Compared to a single-layer structure, a multilayer structure provides more options for selecting the thickness and material of each layer, which may be advantageous in achieving excellent micro-resonance effects and charge balance.

[0189] In the above multilayer structure, the materials included in each layer are different from each other, and the LUMO energy level of each layer in the second electron transport layer can increase as it approaches the perovskite light-emitting layer, thereby making electron transport smoother and increasing the current density and light-emitting efficiency.

[0190]

[0191] And, more preferably, both the first and second electron transport layers may have a multilayer structure. In the case where both have a multilayer structure, the color purity and external quantum efficiency may be superior compared to when at least one layer has a single layer structure.

[0192] Specifically, a tandem light-emitting device in which the first and second electron transport layers are all multilayer structures and a tandem light-emitting device in which the first and second electron transport layers are not all multilayer structures are compared and explained.

[0193] FIG. 3b shows the voltage-current density measurement results for each of the organic light-emitting unit and the perovskite light-emitting unit included in the valley-center tandem light-emitting device and the unbalanced tandem light-emitting device 1 (a non-optimized light-emitting device, a tandem light-emitting device in which the first and second electron transport layers are not multilayer structures), FIG. 3d shows the voltage-external quantum efficiency measurement results for the valley-center tandem light-emitting device and the unbalanced tandem light-emitting device 1, FIG. 3f shows the results showing the external quantum efficiency through optical simulation and the actually measured external quantum efficiency for the valley-center tandem light-emitting device and the unbalanced tandem light-emitting device 1, and FIG. 3i shows the normalized electroluminescence spectrum results through optical simulation and the actually measured normalized electroluminescence spectrum results for the valley-center tandem light-emitting device, the perovskite light-emitting device, and the organic light-emitting device.

[0194] As can be seen from FIGS. 3b, 3d, 3f, and 3i, a tandem light-emitting device in which the first and second electron transport layers are all multilayer structures can exhibit high external quantum efficiency as predicted by the optical simulation because the current densities of the perovskite light-emitting unit and the organic light-emitting unit are completely matched at the applied voltage of 2.6 to 3.2 V for each unit. On the other hand, a tandem light-emitting device in which the first and second electron transport layers are not all multilayer structures can exhibit lower external quantum efficiency than the optical simulation prediction because the current densities of the perovskite light-emitting unit and the organic light-emitting unit are mismatched at the applied voltage of 2.6 to 3.2 V for each unit, and can exhibit less external quantum efficiency than a light-emitting device having a multilayer structure.

[0195] In addition, FIG. 3e is a normalized electroluminescence spectrum measurement result for a valley-center tandem light-emitting device and an unbalanced tandem light-emitting device 1, wherein the tandem light-emitting device in which both the first and second electron transport layers have a multilayer structure can have a smaller full width at half maximum and thus superior color purity compared to a tandem light-emitting device in which the first and second electron transport layers are not all multilayer structures, even if the thicknesses of the first electron transport layer, the second hole transport layer, and the second electron transport layer are the same. This is because the electroluminescence spectrum is shifted and expanded in the case of a tandem light-emitting device that is not a multilayer structure.

[0196] In addition, FIG. 3g is a result of the peak shift of the normalized electroluminescence spectrum according to the driving voltage in the unbalanced tandem light-emitting device 1, and FIG. 3h is a result of the peak shift of the normalized electroluminescence spectrum according to the driving voltage in the valley-center tandem light-emitting device. Referring to FIGS. 3g and 3h, the tandem light-emitting device in which both the first and second electron transport layers have a multilayer structure does not have a shift in the electroluminescence spectrum peak even when the applied voltage changes, but the tandem light-emitting device in which both the first and second electron transport layers do not have a multilayer structure exhibits a shift and expansion of the electroluminescence spectrum peak according to the applied voltage change. This may be a phenomenon caused by charge imbalance in the tandem light-emitting device that does not have a multilayer structure.

[0197]

[0198] A tandem light-emitting device in which the first and second electron transport layers are all multilayer structures and a tandem light-emitting device in which at least one layer is a single-layer structure are compared and explained.

[0199] FIG. 4 is a result of electrical optimization according to the presence or absence of a multilayer structure in the electron transport layer included in the tandem light-emitting device. Referring to this, a tandem light-emitting device having a single-layer structure may have a lower external quantum efficiency than an optical simulation prediction due to a mismatch in the current densities of the perovskite light-emitting unit and the organic light-emitting unit at the applied voltage of 2.6 to 3.2 V of each unit, and may have a lower external quantum efficiency than a light-emitting device having a multilayer structure. The half-width may also be small, resulting in insufficient color purity.

[0200] Figure 5 shows the results of peak shifts in the electroluminescence spectrum according to the driving voltage in an unbalanced light-emitting element and a valley-center tandem light-emitting element. Referring to this, in a tandem light-emitting element with a single-layer structure at any one layer, the peak of the electroluminescence spectrum shifts and expands according to changes in the applied voltage, and this may be a phenomenon caused by charge imbalance in a tandem light-emitting element with a single-layer structure at any one layer.

[0201] Furthermore, Fig. 6 shows the results of transient electroluminescence intensity measurements for an asymmetric light-emitting device (a tandem light-emitting device in which at least one of the first and second electron transport layers is not a multilayer structure) and a valley-center tandem light-emitting device. As shown in Fig. 6, a tandem light-emitting device in which all of the first and second electron transport layers are a multilayer structure can exhibit a faster turn-on response than a tandem light-emitting device in which at least one of the first and second electron transport layers is not a multilayer structure. This may be because, due to the multilayer structure and the optimized thickness, charge carrier injection of the tandem light-emitting device in which all of the multilayer structures are improved and the charge balance is very excellent.

[0202]

[0203] Referring to FIG. 1 and FIG. 7 to FIG. 11, the tandem light-emitting device of the present invention satisfies the following relational expression 1 in which the half-width of the emission spectrum of the entire tandem light-emitting device satisfies the following relational expression 1 by controlling the thickness of the second hole transport layer and the second electron transport layer, where the half-width means the width of the spectrum at a height corresponding to half the wavelength of the maximum wavelength of the emission spectrum.

[0204] <Relationship 1>

[0205] FWHM(PeLED) ≤ FWHM(tandem) ≤ FWHM(OLED)

[0206] At this time, the FWHM (OLED) is the half-width of a light-emitting element including an organic light-emitting unit and not including a perovskite light-emitting unit, the FWHM (tandem) is the half-width of the tandem light-emitting element, and the FWHM (PeLED) is the half-width of a light-emitting element including a perovskite light-emitting unit and not including an organic light-emitting unit.

[0207] Since the light-emitting device of the present invention is of a tandem type and includes both an organic light-emitting unit and a perovskite light-emitting unit, the FWHM (tandem) has a value between the FWHM (OLED) and the FWHM (PeLED). Through this, the tandem light-emitting device can have both the advantages of an organic light-emitting unit having high light-emitting efficiency and the advantages of a perovskite light-emitting unit having high color purity.

[0208] In addition, the tandem light-emitting device can satisfy FWHM(tandem) ≤ (FWHM(OLED)+FWHM(PeLED)) / 2. Preferably, while satisfying the above relationship 1, FWHM(tandem) ≤ (FWHM(OLED)+FWHM(PeLED)) / 2 can be satisfied. Through this, the tandem light-emitting device of the present invention does not simply have a midpoint value between the half-width of the perovskite light-emitting layer and the half-width of the organic light-emitting layer, but can have a half-width close to that of a perovskite light-emitting device with excellent half-width, so that high color purity can be ensured.

[0209] The above tandem light-emitting device can have all of the above-described advantages by controlling the thickness of the second hole transport layer and the second electron transport layer. If the thickness is not controlled, the micro-resonance effect may not occur effectively or a charge imbalance may occur, resulting in insufficient color purity, reduced luminous efficiency, and a reduced operating life compared to when the thickness is controlled.

[0210]

[0211] The thickness of the second hole transport layer and the thickness of the second electron transport layer may satisfy the following relationship 2 and / or the following relationship 3.

[0212] <Relationship 2>

[0213] a ≤ x + by ≤ c

[0214] At this time, in the relational expression 2, x is the thickness of the second electron transport layer, y is the thickness of the second hole transport layer, a is -89.474×n + 265.001, b is -1.053×n + 2.931, c is -63.158×n + 243.001, and n is the refractive index of the second hole transport layer. Here, n may be preferably 1.4 to 2.2 corresponding to the refractive index range of the second hole transport layer described above, thereby maximizing the luminous efficiency or color purity.

[0215] <Relationship 3>

[0216] d ≤ x + ey ≤ f

[0217] At this time, in relational expression 3, x is the thickness of the second electron transport layer, y is the thickness of the second hole transport layer,

[0218] d is 15.789×m + 82.95, e is 1.105×m-0.903, f is 135, and m is the refractive index of the second electron transport layer. Here, m may preferably be 1.4 to 2.2, which corresponds to the refractive index range of the second electron transport layer described above, thereby maximizing luminous efficiency or color purity.

[0219] When the above relational expression 2 and / or the above relational expression 3 is satisfied, the micro-resonance effect is maximized and charge balance can be achieved, so that the half-width of the electroluminescence spectrum of the entire device is reduced, so that the color purity can be very excellent, and the luminous efficiency such as the external quantum efficiency can be maximized.

[0220] Specifically, FIG. 1f and FIG. 7 are examples showing the results of half-width according to changes in the thickness of the second hole transport layer and the thickness of the second electron transport layer in a tandem light-emitting device through optical simulation. When the range of the above relational expression 2 and / or the above relational expression 3 is satisfied, the half-width can be maintained low.

[0221] More specifically, FIG. 8 shows electrical and optical measurement results for tandem light-emitting devices (Valley 1, Vally 2, and Vally-center tandem) that satisfy the above-described relational expression 2 and / or the above-described relational expression 3 and tandem light-emitting devices (Off-Valley 1 and Off-Valley 2) that do not satisfy the above-described relational expression 2 and / or the above-described relational expression 3. The devices that satisfy the above-described relational expression 2 and / or the above-described relational expression 3 may have superior luminance according to voltage, may have superior color purity due to a low half-width, and may be close to Lambertian reflectance compared to the devices that do not satisfy the above-described relational expression 2 and / or the above-described relational expression 3.

[0222] In addition, FIG. 9a is an optical simulation result for the external quantum efficiency of the entire device according to the thickness of the second hole transport layer and the second electron transport layer of the organic light-emitting unit included in the tandem light-emitting device, and FIGS. 9g to 9i are normalized electroluminescence spectra and half-width results through optical simulation of the entire light-emitting device, the perovskite light-emitting unit, and the organic light-emitting unit in the valley-center tandem light-emitting device and the thick tandem light-emitting device. Considering this, it is predicted that the thick tandem light-emitting device that deviates from the above-mentioned relational expression 2 and / or the above-mentioned relational expression 3 will have a larger half-width but higher external quantum efficiency than the valley-center tandem light-emitting device that does not deviate from the above-mentioned relational expression 2 and / or 3.

[0223] However, FIGS. 9d - 9f are measurement results of external quantum efficiency and electroluminescence spectra of a valley-center tandem light-emitting device and a thick tandem light-emitting device, and it was measured that the valley-center tandem light-emitting device had a higher external quantum efficiency and a smaller half-width. In addition, FIGS. 10 and 11 are analysis results of a light-emitting region of a valley-center tandem light-emitting device and electroluminescence spectra depending on an angle for a valley-center tandem light-emitting device and a thick tandem light-emitting device, and it is shown that the valley-center tandem light-emitting device may be closer to Lambertian reflection than the thick tandem light-emitting device. Thus, the reason why valley-center tandem light-emitting devices have a better full width at half maximum than thick tandem light-emitting devices, are closer to Lambertian reflection, and have better external quantum efficiency than optical simulation predictions is that valley-center tandem light-emitting devices can achieve charge balance close to 100%, whereas thick tandem light-emitting devices incur a large amount of electrical loss due to charge imbalance.

[0224] Meanwhile, FIG. 12 is a simulation result of relative electroluminescence spectra according to angle for a valley-center tandem light-emitting device, a thick tandem light-emitting device, and an off-valley tandem light-emitting device. In this case, a tandem light-emitting device (e.g., a valley-center tandem light-emitting device) that does not deviate from the above-mentioned relational expression 2 and / or relational expression 3 can exhibit the most intense light emission at a viewing angle of 0°, and the change in color purity according to the viewing angle can be most suppressed, unlike a tandem light-emitting device (e.g., a thick tandem light-emitting device and an off-valley tandem light-emitting device) that deviates from the above-mentioned relational expression 2 and / or relational expression 3. Accordingly, a tandem light-emitting device that satisfies the above-mentioned relational expression 2 and / or relational expression 3 can achieve high color purity and brightness, etc., at a viewing angle of 0°, which is the most important when used in a display device.

[0225] As a result, a tandem light-emitting device satisfying the above relational expression 2 and / or the above relational expression 3 may be superior to a device that does not satisfy the above relational expression 2 in terms of not only the half-width but also the external quantum efficiency, and when used in a display device, may be superior at 0°, which is the most important viewing angle, and may have less change in color purity depending on the viewing angle.

[0226]

[0227] In addition, referring to FIGS. 7 and 8, when the above-described relational expression 2 and / or the above-described relational expression 3 is satisfied, the thickness of the second hole transport layer may be 50 to 80 nm, and the thickness of the second electron transport layer may be 40 to 60 nm. For example, the thickness of the second hole transport layer may be 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79 or 80 nm, and the thickness of the second electron transport layer may be 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59 or 60 nm. If the thickness of the second hole transport layer and the thickness of the second electron transport layer are out of the range, the microcavity effect, which is advantageous for implementing a narrow half-width, may be distorted, resulting in a half-width exceeding 30 nm and low color purity.

[0228]

[0229] In addition, referring to FIG. 3b, when the above relational expression 2 and / or the above relational expression 3 is satisfied, the perovskite light-emitting unit and the organic light-emitting unit can satisfy the following relational expression 4.

[0230] <Relationship 4>

[0231] 0.8 ≤ A / B ≤ 1.2

[0232] At this time, A is the current density of the perovskite light-emitting unit when the applied voltage to the perovskite light-emitting unit is 2.8 V, and B is the current density of the organic light-emitting unit when the applied voltage to the organic light-emitting unit is 2.8 V.

[0233] If relation 4 is not satisfied, a charge imbalance may occur in the tandem light-emitting element, which may reduce color purity and luminous efficiency. This can be confirmed through FIGS. 3 to 5, as described above.

[0234]

[0235] The above-described tandem light-emitting device may further include at least one of an electron injection layer, a hole injection layer, and an insulating intermediate layer.

[0236] The above electron injection layer may be LiF and / or Liq, but is not limited thereto, and its thickness is not limited as long as it can be commonly applied in the art, but is not particularly limited in the present invention.

[0237] Likewise, there is no limitation on the type and thickness of the hole injection layer and insulating intermediate layer as long as they are used in the art.

[0238] Furthermore, the electron injection layer, hole injection layer, and insulating intermediate layer may have a single-layer structure or a multi-layer structure, and the present invention is not particularly limited thereto.

[0239]

[0240] FIG. 2a shows the voltage-current density measurement results for a tandem light-emitting device, a perovskite light-emitting device, and an organic light-emitting device, and FIG. 2b shows the voltage-luminance measurement results. As shown in FIGS. 2a and 2b, the tandem light-emitting device may have a current efficiency (CE) of 100 cd / A or more. For example, when the current efficiency is calculated through the luminance and current density of each device shown in FIGS. 2a and 2b, the current efficiency of the tandem light-emitting device according to a preferred embodiment of the present invention may be 151.8 cd / A, the perovskite light-emitting device may be 66.2 cd / A, and the organic light-emitting device may be 76.5 cd / A.

[0241]

[0242] FIG. 2c is a result of luminance-external quantum efficiency (EQE) measurement for a tandem light-emitting device, a perovskite light-emitting device, and an organic light-emitting device, and FIG. 2e is a graph expressing the result of external quantum efficiency for a conventional perovskite light-emitting device and a tandem light-emitting device according to a preferred embodiment of the present invention. As shown in FIGS. 2c and 2e, the tandem light-emitting device can have an external quantum efficiency of 30% or more. For example, the external quantum efficiency can be 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98 or 100%. Preferably, the external quantum efficiency can be 35% or greater.

[0243]

[0244] FIG. 2d is a normalized electroluminescence (EL) spectra measurement result for a tandem light-emitting device, a perovskite light-emitting device, and an organic light-emitting device. As shown in FIG. 2d, the tandem light-emitting device may have a half-width of 30 nm or less. For example, it may be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30 nm. Preferably, the half-width may be 28 nm or less. If the half-width can be maintained at 30 nm or less, color purity may be excellent.

[0245]

[0246] FIG. 2f shows the normalized transient EL intensity measurement results for a tandem light-emitting device, a perovskite light-emitting device, and an organic light-emitting device. Referring to FIG. 2f, the tandem light-emitting device can have an improved turn-off or turn-on response (response) time compared to the perovskite light-emitting device or the organic light-emitting device, respectively. The perovskite light-emitting layer has higher charge carrier mobility than the organic light-emitting layer, and thus has an improved turn-on response time compared to the organic light-emitting layer. However, due to ion mobility and charge carrier trapping, it has an inferior turn-off response time compared to the organic light-emitting layer. In a tandem light-emitting device including all of the light-emitting layers, the turn-on response time is improved to be close to the level of the perovskite light-emitting device, and the turn-off response time is improved to be close to the level of the organic light-emitting device, and thus, the turn-on and turn-off responses can be greatly improved compared to a single unit device.

[0247] FIG. 2g is a streak camera image captured over a period of 500 μs during the turn-on process of the tandem light-emitting device of the present invention, and FIG. 2h is a result of a time-resolved spectra measurement over a period of 500 μs during the turn-on process of the tandem light-emitting device of the present invention. Referring to FIGS. 2g and 2h, the tandem light-emitting device can stably exhibit an emission spectrum when the operating time is 400 μs or longer.

[0248] Finally, as can be seen from FIGS. 2f to 2h, the perovskite light-emitting layer and the organic light-emitting layer included in the tandem light-emitting device of the present invention uniformly contribute to electroluminescence while simultaneously responding to voltage pulses, so that the tandem light-emitting device can have excellent turn-on and turn-off characteristics.

[0249]

[0250] Meanwhile, Fig. 15 shows the results of measuring the lifespan of the tandem light-emitting device and perovskite light-emitting device of the present invention. Considering this, the tandem light-emitting device has an operating lifespan of L0 = 100 cd / m. 2 The operating life can be more than 3000 hours under electrical stress. Preferably, it can be more than 5000 hours. Since the tandem light-emitting device includes multiple light-emitting layers, as the voltage applied to each light-emitting layer decreases, the electrical stress required to achieve the same brightness as a single light-emitting device decreases, so that the operating life can be improved.

[0251]

[0252] Additionally, the tandem light-emitting device may have a peak in the 500-550 nm wavelength range of the emission spectrum, but is not limited thereto. If it has a peak in the above wavelength range, the tandem light-emitting device may emit light in the green visible light region.

[0253] By appropriately changing the material type and thickness of each layer of the above tandem light-emitting device, a light-emitting device having high color purity and high luminous efficiency while having a luminous spectrum peak in a wavelength range different from the above range can be implemented.

[0254]

[0255] In order to solve the above-described problem, a display device including the above-described tandem light-emitting element is provided.

[0256] The above display device can be large-area and flexible. In addition, the display device can include the above-described tandem light-emitting element, thereby maximizing color purity and luminous efficiency, improving on-off response, exhibiting excellent operating life, and having low manufacturing costs.

[0257]

[0258] In order to solve the above-described problem, a method for manufacturing a tandem light-emitting device is provided, comprising: (1) forming a first hole transport layer, a perovskite light-emitting layer, and a first electron transport layer sequentially on a first electrode to form a perovskite light-emitting unit; (2) forming a charge generation layer on the first electron transport layer; (3) forming a second hole transport layer, an organic light-emitting layer, and a second electron transport layer sequentially on the charge generation layer to form an organic light-emitting unit; and (4) forming a second electrode on the second electron transport layer; and controlling the thicknesses of the second hole transport layer and the second electron transport layer, a method for manufacturing a tandem light-emitting device is provided in which the emission spectrum full width at half maximum (FWHM) of the entire tandem light-emitting device satisfies the following relational expression 1.

[0259] <Relationship 1>

[0260] FWHM(PeLED) ≤ FWHM(tandem) ≤ FWHM(OLED)

[0261] At this time, the FWHM (OLED) is the half-width of a light-emitting element including an organic light-emitting unit and not including a perovskite light-emitting unit, the FWHM (tandem) is the half-width of the tandem light-emitting element, and the FWHM (PeLED) is the half-width of a light-emitting element including a perovskite light-emitting unit and not including an organic light-emitting unit.

[0262] The above-described method for manufacturing a tandem light-emitting device can manufacture the above-described tandem light-emitting device. Therefore, any content that overlaps with the content regarding the above-described tandem light-emitting device will be omitted.

[0263]

[0264] First, as step (1), a first hole transport layer, a perovskite light-emitting layer, and a first electron transport layer are sequentially formed on a first electrode to form a perovskite light-emitting unit.

[0265] The above first electrode may be prepared on a substrate, and since the first electrode is as described above, it is omitted.

[0266] The substrate may be any substrate commonly used in the art, and is not particularly limited thereto in the present invention. For example, the substrate may be a flexible material or a rigid material. Preferably, the substrate may be a metal substrate such as carbon (C), iron (Fe), chromium (Cr), manganese (Mn), nickel (Ni), titanium (Ti), molybdenum (Mo), or stainless steel (SUS); a plastic substrate such as polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polyphenylene sulfide (PPS), polyallylate, polyimide, polyetherimide (PEI), polyacrylate (PAR), or polycarbonate; a glass substrate; a sapphire substrate, a quartz substrate, a silicon substrate, or any combination thereof.

[0267]

[0268] Since the first hole transport layer and the perovskite light-emitting layer are as described above, specific details are omitted.

[0269] The above first hole transport layer and / or the perovskite light emitting layer may be deposited through a solution process, but is not limited thereto. In this case, the solution process may be any common solution process used in the art, such as a spin coating process, a slot die coating process, a blade coating process, a printing coating process, a gravure coating process, or a spray coating process.

[0270]

[0271] Since the first electron transport layer is as described above, specific details are omitted.

[0272] The above first electron transport layer may be deposited through a dry process, but is not limited thereto. In this case, the dry process may be any general dry process used in the art, such as a thermal evaporation process, a vacuum deposition process, an atomic layer deposition (ALD) process, a chemical vapor deposition (CVD) process, a physical vapor deposition (PVD) process, or an air jet process.

[0273]

[0274] Next, as step (2), a charge generation layer is formed on the first electron transport layer formed in step (1).

[0275] Since the charge generation layer is as described above, specific details are omitted.

[0276] The above charge generation layer may be deposited through a dry process, but is not limited thereto. In this case, the dry process may be any general dry process used in the art, such as a thermal evaporation process, a vacuum deposition process, an atomic layer deposition (ALD) process, a chemical vapor deposition (CVD) process, a physical vapor deposition (PVD) process, or an air jet process.

[0277]

[0278] Next, as a step (3), a second hole transport layer, an organic light-emitting layer, and a second electron transport layer are sequentially formed on the charge generation layer formed in step (2) to form an organic light-emitting unit.

[0279] Since the second hole transport layer, the organic light-emitting layer, and the second electron transport layer are as described above, specific details are omitted.

[0280] At least one of the second hole transport layer, the organic light-emitting layer, and the second electron transport layer may be deposited through a dry process, but is not limited thereto. In this case, the dry process may be any general dry process used in the art, such as a thermal evaporation process, a vacuum deposition process, an atomic layer deposition (ALD) process, a chemical vapor deposition (CVD) process, a physical vapor deposition (PVD) process, or an air jet process.

[0281]

[0282] Next, as a step (4), a second electrode is formed on the second electron transport layer formed in step (3).

[0283] Since the second electrode is as described above, specific details are omitted.

[0284] The above second electrode may be deposited through a dry process, but is not limited thereto. In this case, the dry process may be any general dry process used in the art, such as a thermal evaporation process, a vacuum deposition process, an atomic layer deposition (ALD) process, a chemical vapor deposition (CVD) process, a physical vapor deposition (PVD) process, or an air jet process.

[0285]

[0286] Meanwhile, the method for manufacturing a tandem light-emitting device of the present invention can be manufactured at a low cost by using only two units while also using a perovskite light-emitting body that is cheaper than an organic light-emitting body.

[0287]

[0288] The present invention will be described in more detail through the following examples, but the following examples do not limit the scope of the present invention, and should be interpreted as helping to understand the present invention.

[0289]

[0290] <Example>

[0291] Example 1

[0292] Oleic acid (90.0%, Alfa Aesar), n-decylamine (98.0%, TCI), guanidinium bromide (GABr, >99%, GreatCell Solar), formamidinium bromide (FABr, >99.99%, GreatCell Solar), lead(II) bromide (PbBr2, 99.999%, Sigma-Aldrich), toluene (99.5%, Samchun Chemicals), 1-butyl alcohol (99.0%, Samchun Chemicals), and N,N-dimethylformamide (>99.8%, Sigma-Aldrich) were prepared as synthetic materials. The synthetic materials described above were used without any treatment.

[0293] Molybdenum oxide (MoO3, 99.97%, Sigma-Aldrich), lithium nitride (Li3N, ≥99.50%, Sigma-Aldrich), ZADN (2-[4-(9,10-di-naphthalen-2-yl-anthracen-2-yl)-phenyl]-1-phenyl-1H-benzoimidazole, >99%, Suzhou Geao New Material), BCP (Bathocuproine, OSM), TPBi (2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1H-benzimidazole, >99.9%, OSM), TAPC (1,1-bis[(di-4-tolylamino)phenyl]cyclohexane, >99.9%, OSM), TCTA (tris(4-carbazoyl-9-ylphenyl)amine, >99.9%, OSM), CBP (4,4′-bis(N-carbazolyl)-1,1′-biphenyl, >99.9%, OSM), Ir(ppy)2acac (bis(2-phenylpyridine)iridium(iii) acetylacetonate, >99.5%, OSM), and lithium fluoride (Foosung) were prepared as materials for thermal deposition.

[0294] FA 0.9 GA 0.1PbBr3 perovskite nanocrystals were synthesized at room temperature (17-19 °C) in normal air. A precursor solution was formed by dissolving FABr, GABr, and PbBr2 in 0.5 mL of anhydrous N,N-dimethylformamide (the molar ratio of FABr:GABr was 9:1, and FABr+GABr and PbBr2 were 0.2 and 0.1 mmol, respectively). The precursor solution was then added to a crystallization-inducing solution containing 5.0 mL of toluene, 2.00 mL of 1-butanol, 0.30 mL of oleic acid, and 24.2 μL of n-decylamine, which was stirred vigorously for 10 min. The resulting colloidal perovskite nanocrystals were then sequentially centrifuged, washed, and collected in toluene.

[0295] A glass substrate patterned with indium tin oxide (ITO), corresponding to the first electrode layer, was sequentially cleaned by ultrasonic treatment in acetone and 2-propanol for 15 minutes each. The glass substrate was then boiled in 2-isopropanol for 5 minutes, then transferred to an ultraviolet-ozone cleaner and treated with ultraviolet-ozone for 10 minutes to remove residual organic substances. Next, a buffered hole injection layer (Buf-HIL) composed of poly(3,4-ethylenedioxythiophene) / poly(styrene sulfonate) (PEDOT:PSS) and a perfluorinated ionomer was spin-coated on the substrate in air as the first hole transport layer to a thickness of 60 nm, and then annealed at 150 °C for 30 min to ensure effective self-organization of PEDOT:PSS and the perfluorinated ionomer. Considering the low glass transition temperature (Tg: ~85 °C) of the polyethylene terephthalate (PET) substrate used in the fabrication of flexible devices, Buf-HIL was annealed at 80 °C for 30 min. Afterwards, it was transferred to a glove box and spin-coated with the perovskite nanocrystal solution at 500 rpm for 60 s to form a perovskite light-emitting layer. Next, a solution of 1,3,5-tris(bromomethyl)-2,4,6-triethylbenzene in toluene was spin-coated at 3000 rpm for 60 s to form an insulating interlayer that can improve charge balance.After that, it was transferred to a vacuum deposition equipment, and a 5 nm thick TPBi layer was deposited as one layer included in the first electron transport layer corresponding to the multilayer structure, and a 20 nm thick ZADN layer was deposited as another layer included in the first electron transport layer. Then, a 20 nm thick BCL:Li (volume ratio 9:1) co-deposition layer was deposited as an n-type charge generation layer, a 5 nm thick MoO3 layer was deposited as a p-type charge generation layer, and a 65 nm thick TAPC layer was deposited as a second hole transport layer. After that, a 5 nm thick TCTA:Ir(ppy)2acac (volume ratio 97:3) co-deposition layer was deposited as one layer included in the organic light-emitting layer corresponding to the multilayer structure, and a CBP:Ir(ppy)2acac (volume ratio 96:4) co-deposition layer was deposited as another layer included in the organic light-emitting layer. Next, a 5 nm thick TPBi layer was deposited as one layer included in the second electron transport layer corresponding to the multilayer structure, a 50 nm thick ZADN layer was deposited as another layer included in the second electron transport layer, and a 1 nm thick LiF (lithium fluoride) layer was deposited as an electron injection layer. After that, a 100 nm thick aluminum layer was deposited as the second electrode, thereby manufacturing a tandem light-emitting device. Meanwhile, the device was encapsulated before the experiment.

[0296]

[0297] Example 2

[0298] A tandem light-emitting device was manufactured in the same manner as in Example 1, except that a 25 nm thick TPBi layer was deposited as the first electron transport layer corresponding to the single-layer structure, and a 55 nm thick TPBi layer was deposited as the second electron transport layer corresponding to the single-layer structure.

[0299]

[0300] Example 3

[0301] A tandem light-emitting device was manufactured in the same manner as in Example 1, except that a 25 nm thick TPBi layer was deposited as the first electron transport layer corresponding to the single-layer structure.

[0302]

[0303] Example 4

[0304] A tandem light-emitting device was manufactured in the same manner as in Example 1, except that a 55 nm thick TPBi layer was deposited as the second electron transport layer corresponding to the single-layer structure.

[0305]

[0306] Example 5

[0307] A tandem light-emitting device was manufactured in the same manner as in Example 1, except that a 90 nm thick TAPC layer was deposited as a second hole transport layer and a 30 nm thick ZADN layer was deposited as another layer included in the second electron transport layer.

[0308]

[0309] Example 6

[0310] A tandem light-emitting device was manufactured in the same manner as in Example 1, except that a 40 nm thick TAPC layer was deposited as a second hole transport layer and a 70 nm thick ZADN layer was deposited as another layer included in the second electron transport layer.

[0311]

[0312] Example 7

[0313] A tandem light-emitting device was manufactured in the same manner as in Example 1, except that a 30 nm thick TAPC layer was deposited as a second hole transport layer and a 30 nm thick ZADN layer was deposited as another layer included in the second electron transport layer.

[0314]

[0315] Example 8

[0316] A tandem light-emitting device was manufactured in the same manner as in Example 1, except that a 90 nm thick TAPC layer was deposited as a second hole transport layer and a 70 nm thick ZADN layer was deposited as another layer included in the second electron transport layer.

[0317]

[0318] Example 9

[0319] A tandem light-emitting device was manufactured in the same manner as in Example 1, except that a 95 nm thick TAPC layer was deposited as a second hole transport layer and a 55 nm thick ZADN layer was deposited as another layer included in the second electron transport layer.

[0320]

[0321] Example 10

[0322] A tandem light-emitting device was manufactured in the same manner as in Example 1, except that a 5 nm thick ZADN layer was deposited as another layer included in the first electron transport layer.

[0323]

[0324] Example 11

[0325] A tandem light-emitting device was manufactured in the same manner as in Example 1, except that a 10 nm thick ZADN layer was deposited as another layer included in the first electron transport layer.

[0326]

[0327] Example 12

[0328] A tandem light-emitting device was manufactured in the same manner as in Example 1, except that a 15 nm thick ZADN layer was deposited as another layer included in the first electron transport layer.

[0329]

[0330] Example 13

[0331] A tandem light-emitting device was manufactured in the same manner as in Example 1, except that a 40 nm thick ZADN layer was deposited as another layer included in the first electron transport layer.

[0332]

[0333] <Comparative Example>

[0334] Comparative Example 1

[0335] A perovskite light-emitting device was manufactured in the same manner as in Example 1, except that the n-type charge generation layer, the p-type charge generation layer, the second hole transport layer, the organic light-emitting layer, and the second electron transport layer were not deposited.

[0336]

[0337] Comparative Example 2

[0338] An organic light-emitting device was manufactured in the same manner as in Example 1, except that the first hole transport layer, perovskite light-emitting layer, insulating intermediate layer, first electron transport layer, and n-type charge generation layer were not deposited.

[0339]

[0340] <Experimental Example>

[0341] Experimental Example 1: Optical Simulation

[0342] Optical simulations were performed using a multilayer thin-film OLED optical simulation method based on the classical dipole model and an optical simulation software package (J-OSTD, JooAm) developed based on this method.

[0343] The input parameters of the simulation included the refractive index of each layer, the photoluminescence quantum yield (PLQY) of the emitting layer, the photoluminescence spectrum of the emitting layer, the emitting dipole orientations of the emitting layer, and the experimental emission-zone distribution of the emitting layer. The refractive indices of the organic emitting layers were obtained by optically fitting variable-angle spectroscopic ellipsometry (VASE) data, which were measured using a variable-angle spectroscopic ellipsometer (JA Woollam M-2000) in the angular range of 50-70°. Photon recycling of the perovskite emitting layer was not considered because the perovskite emitting layer is very thin, 30 nm.

[0344] The emission area of ​​each unit was determined by comparing the experimentally measured angle-dependent electroluminescence intensity with the optical simulation results. As a result, the emission areas of the perovskite emission unit and the organic emission unit were 30 nm (the edge of the perovskite emission layer) and 5 nm (the center of the organic emission layer), respectively (Fig. 10). The PLQYs for the films of Ir(ppy)2acac and perovskite nanocrystals were measured to be 86% and 77%, respectively. In addition, the emission dipole orientations of Ir(ppy)2acac and perovskite nanocrystals were confirmed to be 74.0% and 66.7% (isotropic), respectively, through angle-dependent photoluminescence intensity analysis. For PLQY measurements, the perovskite emission layer and the organic emission layer were prepared on untreated quartz substrates through spin coating and vacuum deposition, respectively. For the optical simulation of tandem light-emitting devices, perovskite light-emitting layers and organic light-emitting layers were inserted into the light-emitting device model. All simulations were performed assuming perfect charge balance in both the perovskite light-emitting unit and the organic light-emitting unit, which means that the number of electrically generated excitons is the same in both units. The simulated electroluminescence spectrum and full width at half maximum (FWHM) of the tandem light-emitting device are the simulated electroluminescence spectra at the forward viewing angle (0°), which is the simulation at the forward viewing angle because it best represents the spectrum of the tandem light-emitting device. The optical simulation itself takes into account the Purcell effect, so the external quantum efficiency (EQE) calculated from the optical simulation is EQE sim = ∫PLQY eff (λ)×η out It can be expressed as (λ)dλ, where PLQY eff (λ) is the effective PLQY determined by the Purcell effect and η out (λ) is the outcoupling efficiency at a given wavelength λ.

[0345]

[0346] Optical simulations were performed on the examples and comparative examples using the above-described method, and the results are expressed in FIGS. 1f, 3f, 3i, 4l, 7, 9a - 9c, 9e, 9g - 9i, 10b, 11, 12, and 13c.

[0347] Specifically, the optical simulation of the tandem light-emitting device (valley-center tandem light-emitting device) of Example 1 is shown in FIG. 1f, FIG. 3i, and FIG. 10b.

[0348] Additionally, the optical simulation of the tandem light-emitting device of Example 1 and the tandem light-emitting device of Example 2 (unbalanced tandem light-emitting device 1) is shown in FIG. 3f.

[0349] In addition, the optical simulations of the tandem light-emitting device of Example 1, the tandem light-emitting device of Example 5 (valley 1 tandem light-emitting device), the tandem light-emitting device of Example 6 (valley 2 tandem light-emitting device), the tandem light-emitting device of Example 7 (off-valley 1 tandem light-emitting device), the tandem light-emitting device of Example 8 (off-valley 2 tandem light-emitting device), and the tandem light-emitting device of Example 9 (thick tandem light-emitting device) are shown in FIG. 7.

[0350] Additionally, optical simulations of the tandem light-emitting devices of Example 1 (valley-centre) and Example 9 (thick) are shown in FIGS. 9a - 9c, 9e, 9g - 9i, and 11.

[0351] Additionally, optical simulations of the tandem light-emitting devices of Example 1 (valley-center), Example 7 (off-valley 1), and Example 9 (thick) are shown in Fig. 12.

[0352] Additionally, optical simulations of the tandem light-emitting devices of Examples 1, 10 to 13 are shown in Fig. 13.

[0353]

[0354] Experimental Example 2: Image of the light-emitting device in operation

[0355] The results of operating the tandem light-emitting device of Example 1 were photographed and shown in Fig. 1d. The results of operating the tandem light-emitting device of Example 1 by applying it to a large-area flexible display device were photographed and shown in Fig. 2i.

[0356]

[0357] Experimental Example 3: Measurement of electroluminescence spectrum and half-width

[0358] The electroluminescence spectrum of the light-emitting device was measured using a Keithley 236 source measure unit and a Minolta CS 2000 spectroradiometer, and the full width at half maximum was obtained from this.

[0359]

[0360] The electroluminescence spectrum was measured and the half-width was obtained for the light-emitting devices of Comparative Example 1, Comparative Example 2, and Example 1 using the above-described method, and the results are shown in Figs. 1a to 1c and Fig. 2d.

[0361] In addition, the electroluminescence spectra of the light-emitting devices of Examples 1 and 2 were measured using the above-described method, and the results are shown in FIGS. 3e, 3g, and 3i.

[0362] In addition, the electroluminescence spectra of the light-emitting devices of Examples 1 to 4 were measured using the above-described method, and the results are shown in FIG. 4k and FIG. 5.

[0363] In addition, the electroluminescence spectra of the light-emitting devices of Examples 1, 5 to 8 were measured using the above-described method, and the results are shown in FIGS. 8d and 8e.

[0364] In addition, the electroluminescence spectrum was measured and the half-width was obtained for the light-emitting devices of Examples 1 and 9 using the above-described method, and the results are shown in Fig. 9f.

[0365] In addition, the electroluminescence spectrum of the light-emitting element of Example 1 was measured using the method described above, and the results are shown in Fig. 10b.

[0366] In addition, the electroluminescence spectra of the light-emitting devices of Examples 1 and 9 were measured using the above-described method, and the results are shown in FIGS. 11a and 11b, respectively.

[0367] In addition, the electroluminescence spectra of the light-emitting devices of Examples 1, 10, and 13 were measured using the above-described method, and the results are shown in Fig. 14e. Using this, the half-width was obtained, and the results are shown in Fig. 13b.

[0368] In addition, the electroluminescence spectrum was measured for the light-emitting element of Example 1 and the half-width was obtained, and the results are shown in Fig. 15b.

[0369]

[0370] Experimental Example 4: Current Density-Voltage-Luminance (JVL) Measurement

[0371] The current density-voltage-luminance of the light-emitting device was measured using a Keithley 236 source measure unit and a Minolta CS 2000 spectroradiometer. The voltage-current efficiency was also measured.

[0372]

[0373] The current density-voltage-luminance of the light-emitting elements of Comparative Example 1, Comparative Example 2, and Example 1 were measured using the above-described method, and the results are shown in FIGS. 2a and 2b.

[0374] In addition, the current density-voltage-luminance of the light-emitting devices of Examples 1 and 2 were measured using the above-described method, and the results are shown in Figs. 3b and 3c. Here, the Bottom unit of Fig. 3b represents a perovskite light-emitting unit, and the Top unit represents an organic light-emitting unit.

[0375] In addition, the current density-voltage-luminance of the light-emitting devices of Examples 1 to 4 were measured using the above-described method, and the results are shown in Figs. 4e to 4i. Here, the Bottom unit of Figs. 4e to 4i represents a perovskite light-emitting unit, and the Top unit represents an organic light-emitting unit.

[0376] In addition, the current density-voltage-luminance was measured for the light-emitting devices of Examples 1, 5, and 8 using the above-described method, and the results are shown in FIGS. 8a and 8c.

[0377] In addition, the current density-voltage-luminance and voltage-current efficiency were measured for the light-emitting devices of Examples 1, 10 to 13 using the above-described method, and the results are shown in FIGS. 14a, 14b, and 14d.

[0378]

[0379] Experimental Example 5: Measurement of External Quantum Efficiency (EQE)

[0380] The external quantum efficiency of the light-emitting device was measured using a Keithley 236 source measure unit and a Minolta CS 2000 spectroradiometer.

[0381]

[0382] The external quantum efficiency of the light-emitting device of Example 1 was measured using the above-described method, and the results were compared with those of a conventional light-emitting device, and are shown in Fig. 2e.

[0383] In addition, the external quantum efficiency was measured for the light-emitting devices of Comparative Example 1, Comparative Example 2, and Example 1 using the above-described method, and the results are shown in Fig. 2c.

[0384] In addition, the external quantum efficiency was measured for the light-emitting devices of Examples 1 and 2 using the above-described method, and the results are shown in FIGS. 3d and 3f.

[0385] In addition, the external quantum efficiency was measured for the light-emitting devices of Examples 1 to 4 using the above-described method, and the results are shown in FIGS. 4j and 4l.

[0386] In addition, the external quantum efficiency was measured for the light-emitting devices of Examples 1, 5 to 8 using the above-described method, and the results are shown in Fig. 8b.

[0387] In addition, the external quantum efficiency was measured for the light-emitting devices of Examples 1 and 9 using the above-described method, and the results are shown in FIGS. 9d and 9e.

[0388] In addition, the external quantum efficiency was measured for the light emitting devices of Examples 1, 10 to 13 using the above-described method, and the results are shown in FIGS. 13c and 14c.

[0389]

[0390] Experimental Example 6: Measurement of transient electroluminescence and time-resolved spectrum

[0391] Transient electroluminescence and time-resolved spectra were measured using a system consisting of a streak camera (C10627, Hamamatsu Photonics), a delay generator (DG645, Stanford Research Systems), and a function generator (Agilent 33250A). The voltage pulses used in the measurements were set to a width of 5 ms, a repetition frequency of 20 Hz, and a voltage corresponding to the turn-on voltage of each device (e.g., 3.0 V for organic light-emitting devices and perovskite light-emitting devices, and 5.9 V for tandem light-emitting devices).

[0392]

[0393] Transient electroluminescence, streak camera images, and time-resolved spectra were measured for the light-emitting devices of Comparative Example 1, Comparative Example 2, and Example 1 using the above-described method, and the results are shown in FIGS. 2f to 2h.

[0394] In addition, the transient electroluminescence intensity was measured for the light-emitting devices of Examples 1 to 4 using the above-described method, and the results are shown in Fig. 6.

[0395]

[0396] Experimental Example 7: Measurement of the operating life of a light-emitting device

[0397] Using a Keithley 236 source measure unit and a Minolta CS 2000 spectroradiometer, L0 = 100 cd / m 2 The operating life of the light-emitting device was determined by measuring the luminance and electroluminescence spectra over time under electrical stress conditions.

[0398]

[0399] The luminance and electroluminescence spectra of the light-emitting devices of Example 1 and Comparative Example 1 were measured over time using the above-described method, and the results are shown in Fig. 15.

[0400]

[0401] Experimental Example 8: Various Experimental Values

[0402] Meanwhile, the current efficiency, power efficiency, and WPE (Wall Plug Efficiency) of the light-emitting devices of Example 1, Comparative Example 1, and Comparative Example 2 were obtained using the experimental methods used in Experimental Examples 3 to 5, and are expressed in Table 1.

[0403]

[0404] In addition, the external quantum efficiency and peak and half-width of the electroluminescence spectrum predicted or measured by simulation in the experimental examples described above were organized, and the CIE color coordinates and response time were obtained and shown in Table 2.

[0405]

[0406] Referring to FIG. 2, FIG. 15, Tables 1 and 2, the tandem light-emitting device of Example 1 showed an external quantum efficiency of 30% or more, which is superior to the efficiency of the conventional perovskite light-emitting device, and a half-width of 30 nm or less, which resulted in high color purity. In contrast, the perovskite light-emitting device of Comparative Example 1 had a very low external quantum efficiency, and the organic light-emitting device of Comparative Example 2 had a large half-width, which resulted in significantly reduced color purity. In addition, the turn-on reaction time of Example 1 was close to that of Comparative Example 1, the turn-off reaction time was close to that of Comparative Example 2, and the turn-off reaction time and the turn-on reaction time were much shorter than those of Comparative Example 1 and Comparative Example 2, respectively. Furthermore, the operating lifetime of Example 1 was L0 = 1000 cd / m 2 LT under electrical stress conditions 50 113 hours (L0= 1000 cd / m 2 LT under electrical stress conditions 50 = 5596 hours) followed by LT 50 It showed an excellent operating life compared to Comparative Example 1, which lasted only 1 hour and 48 minutes.

[0407] Referring to FIGS. 3 to 6 and Tables 1 and 2, Example 1, unlike Examples 2 to 4, had both the first electron transport layer and the second electron transport layer as a multilayer structure, thereby showing almost perfect charge balance, and exhibited high external quantum efficiency and full width at half maximum as predicted by the optical simulation. In contrast, Examples 2 to 4 had at least one electron transport layer as a multilayer structure, resulting in charge imbalance. As a result, unlike what was predicted by the optical simulation, the external quantum efficiency did not exceed 30%, and the full width at half maximum did not reach 28 nm or less, resulting in lower luminescence efficiency and color purity than Example 1. In addition, Examples 2 to 4 showed a larger shift of the electroluminescence spectrum peak than Example 1, and the turn-on response time was longer than that of Example 1, resulting in lower performance.

[0408] Referring to FIGS. 7 and 8, Tables 1 and 2, Example 1, in which the thicknesses of the first and second electron transport layers were appropriately adjusted while satisfying the above-mentioned relational expressions 2 and / or 3, had superior external quantum efficiency, luminance, and full width at half maximum compared to Examples 5 to 8, and was close to Lambertian reflection. However, unlike the predicted values, Examples 5 to 8 did not have an external quantum efficiency of 30% or more, and the full width at half maximum did not reach 30 nm or less.

[0409] Referring to FIGS. 9 - 11, Tables 1 and 2, Example 9 was predicted to achieve higher external quantum efficiency than Example 1 in the optical simulation, but a charge imbalance occurred, resulting in an external quantum efficiency of less than 30%, a half-width exceeding 30 nm, resulting in insufficient color purity, and being far from Lambertian reflection, resulting in overall inferior performance to Example 1.

[0410] Referring to FIG. 12, Example 1 shows the most intense luminescence at a viewing angle of 0°, which is most consistent with the entire electroluminescence spectrum at a viewing angle of 0°, and thus, when used in a display device, it can achieve strong color purity and brightness at the most important viewing angle of 0°. However, Examples 7 and 9 have a more inconsistent overall electroluminescence spectrum at a viewing angle of 0° than Example 1, and thus, may be disadvantageous in color purity and brightness compared to Example 1 at the most important angle of 0°.

[0411] Referring to FIGS. 13-14, Tables 1 and 2, Example 1 having an appropriate first electron transport layer thickness exhibited superior current efficiency, full width at half maximum, and external quantum efficiency compared to Examples 10-13, which did not. In particular, Example 13 was predicted to achieve an external quantum efficiency of 49.2% in optical simulations, but the actual measured value was measured to be very low at less than 20% due to charge imbalance.

[0412] Finally, considering the experimental examples described above, it was confirmed that Example 1, which corresponds to a valley-center tandem light-emitting device adjusted to an appropriate thickness while satisfying the above-described relationships, achieved high color purity by showing a very excellent half-width compared to other comparative examples and examples, and that the luminous efficiency, such as the external quantum efficiency, was also maximized.

[0413]

[0414] Although the embodiments of the present invention have been described above, the spirit of the present invention is not limited to the embodiments presented in this specification, and those skilled in the art who understand the spirit of the present invention will be able to easily propose other embodiments by adding, changing, deleting, or adding components within the scope of the same spirit, but this will also be considered to fall within the spirit of the present invention.

Claims

1. First electrode; A perovskite light-emitting unit disposed on the first electrode and comprising a first hole transport layer, a perovskite light-emitting layer, and a first electron transport layer; A charge generation layer disposed on the perovskite light emitting unit; An organic light-emitting unit (unit) disposed on the charge generation layer and having a second hole transport layer, an organic light-emitting layer, and a second electron transport layer; and A second electrode disposed on the organic light emitting unit; By controlling the thickness of the second hole transport layer and the second electron transport layer, a tandem light-emitting device in which the emission spectrum half-width (FWHM) of the entire tandem light-emitting device satisfies the following relational expression 1: <Relationship 1> FWHM(PeLED) ≤ FWHM(tandem) ≤ FWHM(OLED) At this time, the FWHM (OLED) is the half-width of a light-emitting element including an organic light-emitting unit and not including a perovskite light-emitting unit, The above FWHM(tandem) is the half-width of the tandem light-emitting element, The above FWHM (PeLED) is the half-width of a light-emitting device that includes a perovskite light-emitting unit and does not include an organic light-emitting unit.

2. In paragraph 1, A tandem light-emitting device characterized in that at least one selected from the group consisting of the first hole transport layer, the first electron transport layer, the second hole transport layer, and the second electron transport layer has a refractive index of 1.4 to 2.

2.

3. In paragraph 1, The above perovskite emitting layer comprises ABX3, A4BX6, AB2X5, A2BX4, A2BX6, A2B + B 3+ X6, A3B2X9 or A'2A k-1 B k X 3k+1 Contains a crystal structure, The above A is a monovalent organic cation, a monovalent inorganic cation, or a combination thereof, The above B is one or more types of metal ions, The above X is F - , Cl - , Br - , I - , SCN - , OCN - , SeCN - , HCO 2- , CH3COO - or a combination of these, A tandem light-emitting element characterized in that k is an integer between 2 and 6.

4. In paragraph 1, A tandem light-emitting device, characterized in that the first electron transport layer and / or the second electron transport layer has a multilayer structure.

5. In paragraph 4, In the above multilayer structure, the materials contained in each layer are different from each other. In the first electron transport layer, the LUMO energy level of each layer increases as it approaches the perovskite emitting layer. A tandem light-emitting device characterized in that the LUMO energy level of each layer in the second electron transport layer becomes higher as it approaches the organic light-emitting layer.

6. In paragraph 1, A tandem light-emitting device, characterized in that the charge generation layer includes an n-type charge generation layer and / or a p-type charge generation layer.

7. In paragraph 1, A tandem light-emitting device characterized in that the thickness of the second hole transport layer and the thickness of the second electron transport layer satisfy the following relational expression 2 and / or the following relational expression 3: <Relationship 2> a ≤ x + by ≤ c At this time, in relational expression 2, x is the thickness of the second electron transport layer, y is the thickness of the second hole transport layer, a is -89.474×n + 265.001, b is -1.053×n + 2.931, c is -63.158×n + 243.001, where n is the refractive index of the second hole transport layer. <Relationship 3> d ≤ x + ey ≤ f At this time, in the relational expression 3, x is the thickness of the second electron transport layer, y is the thickness of the second hole transport layer, d is 15.789×m + 82.95, e is 1.105×m-0.903, and f is 135, where m is the refractive index of the second electron transport layer.

8. In paragraph 7, The thickness of the second hole transport layer is 50 to 80 nm, A tandem light-emitting device, characterized in that the thickness of the second electron transport layer is 40 to 60 nm.

9. In paragraph 7, A tandem light-emitting device characterized in that the perovskite light-emitting unit and the organic light-emitting unit satisfy the following relational expression 4: <Relationship 4> 0.8 ≤ A / B ≤ 1.2 At this time, A is the current density of the perovskite light-emitting unit when the applied voltage to the perovskite light-emitting unit is 2.8 V, The above B is the current density of the organic light emitting unit when the applied voltage to the organic light emitting unit is 2.8 V.

10. In paragraph 1, The above organic light-emitting layer comprises a host and / or a dopant, The above host contains at least one selected from the group consisting of CBP, TCTA, mCP, DCzPPy, PCPPn, PCPN, CzTP, TCPB, and CzPA, A tandem light-emitting device characterized in that the dopant contains at least one selected from the group consisting of a fluorescent organic material, a phosphorescent organic material, and a thermally activated delayed fluorescent organic material.

11. In paragraph 1, A tandem light-emitting device characterized by a half-width of 30 nm or less.

12. In paragraph 1, A tandem light-emitting device characterized by an external quantum efficiency (EQE) of 30% or more.

13. A display device including the tandem light-emitting element of paragraph 1. 14.(1) A step of forming a perovskite light-emitting unit by sequentially forming a first hole transport layer, a perovskite light-emitting layer, and a first electron transport layer on a first electrode; (2) a step of forming a charge generation layer on the first electron transport layer; (3) a step of forming an organic light-emitting unit by sequentially forming a second hole transport layer, an organic light-emitting layer, and a second electron transport layer on the charge generation layer; and (4) a step of forming a second electrode on the second electron transport layer; A method for manufacturing a tandem light-emitting device in which the emission spectrum half-width (FWHM) of the entire tandem light-emitting device satisfies the following relational expression 1 by controlling the thickness of the second hole transport layer and the second electron transport layer: <Relationship 1> FWHM(PeLED) ≤ FWHM(tandem) ≤ FWHM(OLED) At this time, the FWHM (OLED) is the half-width of a light-emitting element including an organic light-emitting unit and not including a perovskite light-emitting unit, The above FWHM(tandem) is the half-width of the tandem light-emitting element, The above FWHM (PeLED) is the half-width of a light-emitting device that includes a perovskite light-emitting unit and does not include an organic light-emitting unit.

15. In paragraph 14, The above first hole transport layer and the perovskite light-emitting layer are deposited through a solution process, A method for manufacturing a tandem light-emitting device, characterized in that the first electron transport layer, the charge generation layer, the second hole transport layer, the organic light-emitting layer, and the second electron transport layer are deposited through a dry process.

16. In paragraph 14, A method for manufacturing a tandem light-emitting device, characterized in that the second hole transport layer and the second electron transport layer are each deposited to a thickness satisfying the following relational expression 2 and / or the following relational expression 3: <Relationship 2> a ≤ x + by ≤ c At this time, in relational expression 2, x is the thickness of the second electron transport layer, y is the thickness of the second hole transport layer, a is -89.474×n + 265.001, b is -1.053×n + 2.931, c is -63.158×n + 243.001, where n is the refractive index of the second hole transport layer. <Relationship 3> d ≤ x + ey ≤ f At this time, in the relational expression 3, x is the thickness of the second electron transport layer, y is the thickness of the second hole transport layer, d is 15.789×m + 82.95, e is 1.105×m-0.903, and f is 135, where m is the refractive index of the second electron transport layer.

17. In paragraph 16, A method for manufacturing a tandem light-emitting device, characterized in that the thickness of the second hole transport layer is 50 to 80 nm, and the thickness of the second electron transport layer is 40 to 60 nm.

18. In paragraph 14, A method for manufacturing a tandem light-emitting device, characterized by manufacturing the tandem light-emitting device of claim 1.

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