Light-emitting device and display device

Abstract

The embodiment of the invention discloses a light-emitting device and a display device, at least a charge generation unit with an NPNP structure is formed, at least three charge depletion regions are formed on an interface where an N-type charge generation layer and a P-type charge generation layer are stacked, and charges capable of freely moving do not exist in the charge depletion regions. Therefore, large resistance can be generated in a charge depletion region, the transverse transmission capacity of charges is further reduced, and pixel crosstalk generated by transverse charge flow can be reduced. Meanwhile, in a non-charge depletion region, charges can flow normally, namely transverse and longitudinal transmission of the charges can be carried out normally, the charge depletion regions of the N-type charge generation layers and the P-type charge generation layers which are alternately stacked are narrower, injection of generated electrons and holes is quicker, the voltage of the device can be reduced, and the performance of the device is improved. And meanwhile, the electric leakage problem of the charge generation unit caused by PN junctions is reduced, the current efficiency is improved, and the power efficiency is improved.

Description

Technical Field

[0001] The present disclosure relates to the field of display technologies, and particularly to a light-emitting device and a display device. Background Art

[0002] With the development of display technologies, people's requirements for display devices are also getting higher and higher. Compared with the relatively mature liquid crystal display (LCD), the organic electroluminescence display (OLED) has the advantages of high color saturation, low driving voltage, wide viewing angle display, flexibility, fast response speed, and simple manufacturing process. Therefore, in the small-size display field (such as electronic products like mobile phones and watches), it has gradually replaced the mainstream position of LCD displays, and its product development trend is rapidly concentrating on the medium and large-size fields.

[0003] The stacked OLED is an OLED in which multiple light-emitting units are connected in series through a charge generation layer and are controlled by only one external power source. At the same voltage, compared with the single-layer OLED, the stacked OLED has higher luminous brightness and current efficiency, and the luminous brightness and current efficiency increase exponentially with the increase in the number of series-connected light-emitting units. Also, at the same current density, the stacked OLED has a longer lifespan compared with the single-layer OLED. However, since the stacked OLED has multiple light-emitting units, it has a higher operating voltage and lower power efficiency compared with the single-layer OLED. The higher operating voltage and lower power efficiency will affect the power consumption of the stacked OLED and reduce the performance of the stacked OLED light-emitting device. Summary of the Invention

[0004] The light-emitting device and the display device provided by the embodiments of the present disclosure are used to solve the problems of higher operating voltage and lower power efficiency of the stacked OLED.

[0005] On the one hand, the embodiments of the present disclosure provide a light-emitting device, including: an anode and a cathode disposed opposite to each other, at least two light-emitting units stacked between the anode and the cathode, and a charge generation and separation unit disposed between two adjacent light-emitting units; the charge generation and separation unit includes an N-type charge transport unit, a charge generation unit, and a P-type charge transport unit stacked in sequence in a direction from the anode to the cathode, and the charge generation unit includes at least two N-type charge generation layers and at least two P-type charge generation layers alternately disposed in a direction from the anode to the cathode.

[0006] In a possible implementation, in the above-mentioned light-emitting device provided by the embodiments of the present disclosure, the light-emitting unit located between the anode and the charge generation separation unit includes: a hole injection layer, a first hole transport layer, a first electron blocking layer, and a first light-emitting layer that are sequentially stacked; the hole injection layer is close to the anode;

[0007] The light-emitting unit located between the cathode and the charge generation separation unit includes: an electron injection layer, a first electron transport layer, a first hole blocking layer, a second light-emitting layer, and a second electron blocking layer that are sequentially stacked; the electron injection layer is close to the cathode;

[0008] Wherein, the thickness of the charge generation separation unit is less than or equal to the sum of the thicknesses of the hole injection layer and the first hole transport layer, and the ratio of the sum of the thicknesses of the hole injection layer and the first hole transport layer to the thickness of the charge generation separation unit is less than or equal to 5.

[0009] In a possible implementation, in the above-mentioned light-emitting device provided by the embodiments of the present disclosure, the percentage of the thickness of the charge generation separation unit in the thickness of the light-emitting device is less than or equal to 25%, and the percentage of the sum of the thicknesses of the hole injection layer and the first hole transport layer in the thickness of the light-emitting device is less than or equal to 55%.

[0010] In a possible implementation, in the above-mentioned light-emitting device provided by the embodiments of the present disclosure, the N-type charge transport unit includes: a second hole blocking layer located between the first light-emitting layer and the charge generation unit, and a second electron transport layer located between the second hole blocking layer and the charge generation unit; the P-type charge transport unit includes a second hole transport layer located between the second electron blocking layer and the charge generation unit;

[0011] Wherein, the sum of the thicknesses of the second hole blocking layer and the second electron transport layer is less than or equal to the sum of the thicknesses of the first electron transport layer and the first hole blocking layer, and the ratio of the sum of the thicknesses of the first electron transport layer and the first hole blocking layer to the sum of the thicknesses of the second hole blocking layer and the second electron transport layer is greater than or equal to 3.

[0012] In a possible implementation, in the above-mentioned light-emitting device provided by the embodiments of the present disclosure, the thickness of the first hole transport layer is greater than the thickness of the second hole transport layer, and the mobility of the first hole transport layer is less than the mobility of the second hole transport layer;

[0013] The thickness of the first electron transport layer is less than the thickness of the second electron transport layer, and the mobility of the first electron transport layer is less than the mobility of the second electron transport layer.

[0014] In a possible implementation, in the above-mentioned light-emitting device provided by the embodiments of the present disclosure, the N-type charge generation layer includes a first host material and a first guest material doped in the first host material, and the doping concentration of the first guest material is between 0.4% and 2%.

[0015] In a possible implementation, in the above-mentioned light-emitting device provided by the embodiments of the present disclosure, the P-type charge generation layer includes a second host material and a second guest material doped in the second host material, and the doping concentration of the second guest material is greater than or equal to 5%.

[0016] In a possible implementation, in the above-mentioned light-emitting device provided by the embodiments of the present disclosure, the material of the P-type charge generation layer is an organic electronic material or an inorganic metal oxide material. The organic electronic material includes HATCN, and the inorganic metal oxide material includes molybdenum oxide. The thickness of the P-type charge generation layer is less than or equal to 20 nm.

[0017] In a possible implementation, in the above-mentioned light-emitting device provided by the embodiments of the present disclosure, the charge generation and separation unit has a transmittance greater than 68% in the visible light wavelength range of 380 nm to 480 nm; the charge generation and separation unit has a transmittance greater than 85% in the visible light wavelength range of 480 nm to 580 nm; the charge generation and separation unit has a transmittance greater than 86% in the visible light wavelength range of 580 nm to 680 nm.

[0018] On the other hand, the embodiments of the present disclosure also provide a display device, including the above-mentioned light-emitting device provided by the embodiments of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic structural diagram of a light-emitting device provided by an embodiment of the present disclosure;

[0020] Figure 2 It is a schematic structural diagram of a blue light-emitting device provided in the related art;

[0021] Figure 3 It is a schematic structural diagram of a blue light-emitting device provided by an embodiment of the present disclosure;

[0022] Figure 4 It is a schematic structural diagram of another blue light-emitting device provided by an embodiment of the present disclosure;

[0023] Figure 5 It is for Figure 2 corresponding charge generation unit for IV test at 20 V voltage

[0024] Figure 6 A structural schematic diagram for performing an IV test on the corresponding charge generation unit at a voltage of 20V; Figure 3

[0025] Figure 7 A structural schematic diagram for performing an IV test on the corresponding charge generation unit at a voltage of 20V; Figure 4

[0026] Figure 8 A structural schematic diagram of a blue light-emitting device provided in the related art;

[0027] Figure 9 A structural schematic diagram of another blue light-emitting device provided in an embodiment of the present disclosure;

[0028] Figure 10 A structural schematic diagram of another blue light-emitting device provided in an embodiment of the present disclosure;

[0029] Figure 11 For Figure 8 A structural schematic diagram of the corresponding charge generation unit;

[0030] Figure 12 For Figure 9 A structural schematic diagram of the corresponding charge generation unit;

[0031] Figure 13 For Figure 10 A structural schematic diagram of the corresponding charge generation unit. Detailed implementation manners

[0032] To make the objectives, technical solutions and advantages of the embodiments of the present disclosure clearer, the technical solutions of the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present disclosure. Obviously, the described embodiments are some but not all of the embodiments of the present disclosure. And without conflict, the embodiments in the present disclosure and the features in the embodiments can be combined with each other. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present disclosure without creative efforts fall within the scope of protection of the present disclosure.

[0033] ​​Unless otherwise defined, technical terms or scientific terms used in this disclosure shall have the ordinary meanings as understood by those of ordinary skill in the art to which this disclosure pertains. The words such as "including" or "comprising" used in this disclosure mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects. The words such as "connected" or "coupled" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The terms such as "inside", "outside", "above", and "below" are only used to indicate relative positional relationships, and when the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0034] It should be noted that the sizes and shapes of the figures in the drawings do not reflect the true proportions, and the purpose is only to schematically illustrate the content of this disclosure. Throughout the drawings, the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions.

[0035] Traditional OLED light-emitting devices are composed of a hole transport layer, a light-emitting layer, and an electron transport layer, which are sandwiched between an anode and a cathode electrode. Later, in order to improve the performance of OLED light-emitting devices, multiple-layer light-emitting units were successively designed, and functional layers including a hole injection layer, an electron injection layer, an electron blocking layer, and a hole blocking layer were continuously added. Then, the concept of a doped light-emitting layer OLED was also proposed and applied in actual production and manufacturing. Through the optimization of the thickness of the functional layers, the improvement of the preparation process, and the application of each functional layer, the light-emitting performance of OLED light-emitting devices has been steadily improved.

[0036] In order to further improve the performance of OLED light-emitting devices, the concept of stacked OLEDs emerged. A stacked OLED is an OLED in which multiple light-emitting units are connected in series through a charge generation layer and are controlled by only one external power source. At the same voltage, compared with a single-layer OLED light-emitting device, a stacked OLED light-emitting device has higher luminous brightness and current efficiency. The luminous brightness and current efficiency increase exponentially with the increase in the number of series-connected light-emitting units. And at the same current density, compared with a single-layer OLED, a stacked OLED has a longer lifespan. The key reason why a stacked OLED has better device performance than a single-layer OLED is that there is a charge generation layer inside it, and the charge generation layer is the most important factor affecting the performance of a stacked OLED light-emitting device.

[0037] However, since there are multiple light-emitting units in a stacked OLED, the operating voltage used is higher than that of a single-layer OLED, and there is a problem of low power efficiency. The higher operating voltage and lower power efficiency will affect the power consumption of the stacked OLED light-emitting device and reduce the performance of the stacked OLED light-emitting device.

[0038] In view of this, embodiments of the present disclosure provide a light-emitting device. By optimizing the structure of the charge generation and separation unit that affects the performance of the stacked device, it is beneficial to the generation and separation of charges, which can significantly reduce the operating voltage of the stacked device and improve the current efficiency and power efficiency of the stacked device. As Figure 1 shown, the light-emitting device provided by the embodiments of the present disclosure includes: an anode 1 and a cathode 2 arranged opposite to each other, at least two light-emitting units 3 stacked between the anode 1 and the cathode 2, and a charge generation and separation unit 4 arranged between two adjacent light-emitting units 3; the charge generation and separation unit 4 includes an N-type charge transport unit 41, a charge generation unit 42, and a P-type charge transport unit 43 stacked in sequence along the direction from the anode 1 to the cathode 2, and the charge generation unit 42 includes at least two N-type charge generation layers 421 (N-CGL) and at least two P-type charge generation layers 422 (P-CGL) arranged alternately along the direction from the anode 1 to the cathode 2.

[0039] For the above light-emitting device provided by the embodiments of the present disclosure, by adopting at least two N-type charge generation layers and at least two P-type charge generation layers arranged alternately, that is, at least forming a charge generation unit with an NPNP structure. Since the N-type charge generation layer and the P-type charge generation layer are two different types of materials, a charge depletion region will be formed at the interface between the two stacks, that is, at least three charge depletion regions are formed. There are no freely movable charges in the charge depletion region, so a relatively large resistance can be generated in the charge depletion region, thereby reducing the lateral charge transport ability, that is, reducing pixel crosstalk caused by lateral charge flow; at the same time, in the non-charge depletion region, charges can flow normally, that is, the lateral and longitudinal transport of charges can proceed normally. Compared with the charge depletion region of the single-layer NP structure in the prior art, the charge depletion regions of the multi-layer alternately stacked N-type charge generation layer and P-type charge generation layer of the present disclosure are narrower, and the injection of electrons and holes is faster. Therefore, the multi-layer alternately stacked N-type charge generation layer and P-type charge generation layer adopted by the present disclosure can reduce the device voltage, at the same time reduce the leakage problem of the charge generation unit caused by the PN junction, improve the current efficiency, and improve the power efficiency.

[0040] Specifically, the N-type charge generation layer is also an N-type organic semiconductor, and the P-type charge generation layer is also a P-type organic semiconductor.

[0041] In some embodiments, in the above light-emitting device provided by the embodiments of the present disclosure, as Figure 1As shown, in the embodiments of the present disclosure, taking the light-emitting device including two light-emitting units 3 as an example, the light-emitting unit 3 located between the anode 1 and the charge generation and separation unit 4 includes: a hole injection layer 31 (HIL), a first hole transport layer 32 (HTL1), a first electron blocking layer 33 (EBL1), and a first light-emitting layer 34 (EML1) that are sequentially stacked; the hole injection layer 31 is close to the anode 1; the light-emitting unit 3 located between the cathode 2 and the charge generation and separation unit 4 includes: an electron injection layer 35 (EIL), a first electron transport layer 36 (ETL1), a first hole blocking layer 37 (HBL1), a second light-emitting layer 38 (EML2), and a second electron blocking layer 39 (EBL2) that are sequentially stacked; the electron injection layer 35 is close to the cathode 2.

[0042] Currently, in order to obtain a higher aperture ratio, OLED devices generally adopt a top-emission structure to improve the aperture ratios of the R / G / B three primary colors and thus improve the device lifetime. Therefore, the anode basically uses a relatively thick Ag electrode for total reflection. The Ag electrode can improve the light emission rate, but it has a great impact on the light extraction. The surface plasmon polariton (SPP) effect and the waveguide effect inside the device are both loss mechanisms, which suppress the light extraction efficiency of the device. Due to the SPP effect and the waveguide effect, the light extraction ratio of the OLED device can only reach about 20-25%, and the SPP effect probably causes about 30-35% of the light loss. Therefore, in order to avoid the SPP effect and improve the light extraction efficiency of the OLED device, as Figure 1 shown, the thickness S1 of the charge generation and separation unit 4 is less than or equal to the sum S2 of the thicknesses of the hole injection layer 31 and the first hole transport layer 32, and the ratio (S2 / S1) of the sum S2 of the thicknesses of the hole injection layer 31 and the first hole transport layer 32 to the thickness S1 of the charge generation and separation unit 4 is less than or equal to 5. By adopting the scheme of thickening S2, it can be ensured that the light-emitting area of the device is as far away from the anode 1 as possible, suppressing the SPP effect in the OLED device, enhancing the microcavity effect of the light-emitting device, and improving the overall optical characteristics of the light-emitting device to achieve better Panel optical characteristics such as L-decay and Color Shift.

[0043] In some embodiments, in the above-mentioned light-emitting device provided in the embodiments of the present disclosure, as Figure 1 shown, the percentage of the thickness S1 of the charge generation and separation unit 4 in the thickness of the light-emitting device is less than or equal to 25%, and the percentage of the sum S2 of the thicknesses of the hole injection layer 31 and the first hole transport layer 32 in the thickness of the light-emitting device is less than or equal to 55%. This can further ensure that the light-emitting area of the device is as far away from the anode 1 as possible, enhancing the microcavity effect of the light-emitting device and improving the overall optical characteristics of the light-emitting device.

[0044] In some embodiments, in the above-mentioned light-emitting device provided in the embodiments of the present disclosure, as Figure 1As shown, the present disclosure further optimizes the structures of the N-type charge transport unit 41 and the P-type charge transport unit 43 to improve the charge transport speed, achieve better recombination of electrons and holes, and thus improve the performance of the stacked light-emitting device. Specifically, the N-type charge transport unit 41 includes: a second hole blocking layer 411 (HBL2) located between the first light-emitting layer 34 and the charge generation unit 42, and a second electron transport layer 412 (ETL2) located between the second hole blocking layer 411 and the charge generation unit 42; the P-type charge transport unit 43 includes a second hole transport layer 431 (HTL2) located between the second electron blocking layer 39 and the charge generation unit 42.

[0045] In some embodiments, the optical effect near the cathode side is also affected by the SPP effect, but it is weaker than that on the anode side. Therefore, in order to further improve the light extraction efficiency of the OLED device and reduce the optical loss caused by the SPP effect, in the above-mentioned light-emitting device provided in the embodiments of the present disclosure, as Figure 1 shown, the sum S4 of the thicknesses of the second hole blocking layer 411 and the second electron transport layer 412 is less than or equal to the sum S3 of the thicknesses of the first electron transport layer 36 and the first hole blocking layer 37, and the ratio (S3 / S4) of the sum S3 of the thicknesses of the first electron transport layer 36 and the first hole blocking layer 37 to the sum S4 of the thicknesses of the second hole blocking layer 411 and the second electron transport layer 412 is greater than or equal to 3. By adopting the scheme of thickening S3, it can ensure that the light-emitting area of the device is as far away from the cathode 2 as possible, weaken the SPP effect on the cathode side, enhance the microcavity effect of the light-emitting device, and improve the overall optical characteristics of the light-emitting device.

[0046] In some embodiments, in the above-mentioned light-emitting device provided in the embodiments of the present disclosure, as Figure 1 shown, the thickness of the first hole transport layer 32 is greater than the thickness of the second hole transport layer 431, and the mobility of the first hole transport layer 32 is less than the mobility of the second hole transport layer 431. This can improve the overall optical characteristics of the light-emitting device.

[0047] In some embodiments, in the above-mentioned light-emitting device provided in the embodiments of the present disclosure, as Figure 1 shown, the thickness of the first electron transport layer 36 is less than the thickness of the second electron transport layer 412, and the mobility of the first electron transport layer 36 is less than the mobility of the second electron transport layer 412. This can improve the overall optical characteristics of the light-emitting device.

[0048] In some embodiments, in the above-mentioned light-emitting device provided in the embodiments of the present disclosure, as Figure 1As shown, the N-type charge generation layer 421 includes a first host material and a first guest material doped in the first host material, and the doping concentration of the first guest material is between 0.4% and 2%. Specifically, the first host material, the first guest material, and the doping concentration of the first guest material are all factors affecting the transmittance of the N-type charge generation layer 421. Therefore, the N-type charge generation layer 421 can further change the transmittance by adjusting the first host material, the first guest material, or the doping concentration of the first guest material.

[0049] In some embodiments, the first guest material may be a metal or metal salt with a work function in the range of 2 to 3 eV, that is, a low work function metal or low work function metal salt, for example, including at least one of ytterbium (Yb), lithium (Li), cesium (Cs), lithium carbonate, or cesium carbonate.

[0050] In some embodiments, the first host material may include any one selected from pyridine, pyrazine ring, and imidazole substances.

[0051] In some embodiments, in the above-mentioned light-emitting device provided by the embodiments of the present disclosure, as Figure 1 shown, the P-type charge generation layer 422 includes a second host material and a second guest material doped in the second host material, and the doping concentration of the second guest material is greater than or equal to 5%. Specifically, the second host material, the second guest material, and the doping concentration of the second guest material are all factors affecting the transmittance of the P-type charge generation layer 422. Therefore, the P-type charge generation layer 421 can further change the transmittance by adjusting the first host material, the first guest material, or the doping concentration of the first guest material.

[0052] In some embodiments, the second guest material may include an organic electronic type material and / or an inorganic metal oxide material. Among them, the organic electronic type material may include HATCN (2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene), and the inorganic metal oxide material may include molybdenum oxide (MoO).

[0053] Specifically, the chemical structural formula of HATCN is:

[0054] In some embodiments, the second host material is generally a hole transport material of a derivative type such as m-MTDATA (4,4',4'-tris(N-3-methylphenyl-N-phenylamino)triphenylamine) or NPB (N,N'-diphenyl-N,N'-(1-naphthyl)-1,1'-biphenyl-4,4'-diamine).

[0055] Specifically, the chemical structural formula of m-MTDATA is: The chemical structural formula of NPB is:

[0056] In some embodiments, in the above-mentioned light-emitting device provided by the embodiments of the present disclosure, as Figure 1 shown, the material of the P-type charge generation layer 422 can be an undoped organic electron-type material or an inorganic metal oxide material. Specifically, the organic electron-type material includes HATCN, and the inorganic metal oxide material includes molybdenum oxide.

[0057] In some embodiments, in the above-mentioned light-emitting device provided by the embodiments of the present disclosure, as Figure 1 shown, when the material of the P-type charge generation layer 422 is an undoped organic electron-type material or an inorganic metal oxide material, the P-type charge generation layer 422 has a strong ability to transport holes, but also has strong absorption and low transmittance. Therefore, the thickness of the P-type charge generation layer 422 needs to be less than or equal to 20 nm to improve the transmittance of the P-type charge generation layer 422.

[0058] In some embodiments, in the above-mentioned light-emitting device provided by the embodiments of the present disclosure, as Figure 1 shown, the first light-emitting layer 34 can include a first red light-emitting layer REML1, a first green light-emitting layer GEML1, and a first blue light-emitting layer BEML1, and the second light-emitting layer 38 can include a second red light-emitting layer REML2, a second green light-emitting layer GEML2, and a second blue light-emitting layer BEML2.

[0059] In some embodiments, the first blue light-emitting layer BEML1 and the second blue light-emitting layer BEML2 include: an electron-type host material (BH) and a blue light-emitting guest material (BD).

[0060] In some embodiments, in the above-mentioned light-emitting device provided by the embodiments of the present disclosure, as Figure 1 shown, the thickness of the first electron blocking layer 33 (REBL1) below the first red light-emitting layer REML1, the thickness of the first electron blocking layer 33 (GEBL1) below the first green light-emitting layer GEML1, and the thickness of the first electron blocking layer 33 (BEBL1) below the first blue light-emitting layer BEML1 decrease in sequence. Setting the first electron blocking layer 33 below the first red light-emitting layer REML1 to be relatively thicker than the first electron blocking layer 33 corresponding to other color light-emitting layers is beneficial to enhancing the microcavity effect and can improve the light extraction efficiency.

[0061] In some embodiments, in the above-mentioned light-emitting device provided by the embodiments of the present disclosure, as Figure 1As shown, the thickness of the second electron blocking layer 39 (REBL2) under the second red emission layer REML2, the thickness of the second electron blocking layer 39 (GEBL2) under the second green emission layer GEML2, and the thickness of the second electron blocking layer 39 (BEBL2) under the second blue emission layer BEML2 decrease in sequence. Setting the second electron blocking layer 39 under the second red emission layer REML2 to be thicker than the second electron blocking layers 39 corresponding to other color emission layers is conducive to enhancing the microcavity effect and can improve the light extraction efficiency.

[0062] It should be noted that in the present disclosure Figure 1 the charge generation unit 42 includes two N-type charge generation layers 421 (N-CGL) and two P-type charge generation layers 422 (P-CGL) arranged alternately as an example. Of course, the charge generation unit 42 can also include three N-type charge generation layers 421 (N-CGL) and three P-type charge generation layers 422 (P-CGL) arranged alternately, and is not limited thereto.

[0063] In some embodiments, in the above-mentioned light-emitting device provided by the embodiments of the present disclosure, as Figure 1 shown, by optimizing the structure of the charge generation and separation unit 4 and restricting parameters such as thickness and mobility in the embodiments of the present disclosure, the charge generation and separation unit 4 is made to satisfy that the transmittance is greater than 68% in the visible light wavelength range of 380 nm to 480 nm; the charge generation and separation unit 4 is made to satisfy that the transmittance is greater than 85% in the visible light wavelength range of 480 nm to 580 nm; the charge generation and separation unit 4 is made to satisfy that the transmittance is greater than 86% in the visible light wavelength range of 580 nm to 680 nm. When the charge generation and separation unit 4 satisfies the above transmittances in different visible light wavelength ranges, it can improve the speed of charge generation by the charge generation unit 42, the speed of charge separation, and the speed of charge injection into other film layers, and improve the speed of charge transmission by the N-type charge transport unit 41 and the P-type charge transport unit 43 and the speed of charge injection into other film layers, thereby improving the performance of the light-emitting device, reducing the working voltage, and enhancing the current efficiency and power efficiency.

[0064] The following makes a detailed introduction to the recombination of electrons and holes in the emission layer:

[0065] Transfer the electrons generated at the interface between the N-type charge generation layer 421 and the P-type charge generation layer 422 to the first light-emitting layer 34. Specifically, electrons and holes are generated at the interface between the N-type charge generation layer 421 and the P-type charge generation layer 422. The N-type charge generation layer 421 and the P-type charge generation layer 422 work together to separate the electrons and holes. Among them, the N-type charge generation layer 421 acquires electrons and injects them into the second electron transport layer 412. The second electron transport layer ETL2 transports the electrons to the second hole blocking layer 411. The second hole blocking layer 411 is configured to block holes and transport the received electrons to the first light-emitting layer 34.

[0066] Transfer the holes generated by the anode 1 to the first light-emitting layer 34. Specifically, the hole injection layer 31 injects the holes generated by the anode 1 into the first hole transport layer 32. The first hole transport layer 32 transports the holes to the first electron blocking layer 33. The first electron blocking layer 33 is configured to block electrons and transport the received holes to the first light-emitting layer 34.

[0067] Transfer the holes generated at the interface between the N-type charge generation layer 421 and the P-type charge generation layer 422 to the second light-emitting layer 38. Specifically, the N-type charge generation layer 421 and the P-type charge generation layer 422 work together to separate the electrons and holes. Among them, the P-type charge generation layer 422 acquires holes and injects them into the second hole transport layer 431. The second hole transport layer 431 transports the holes to the second electron blocking layer 39. The second electron blocking layer 39 is configured to block electrons and transport the received holes to the second light-emitting layer 38.

[0068] Transfer the electrons generated by the cathode 2 to the second light-emitting layer 38. Specifically, the electron injection layer 35 injects the electrons generated by the cathode 2 into the first electron transport layer 36. The first electron transport layer 36 transports the electrons to the first hole blocking layer 37. The first hole blocking layer 37 is configured to block holes and transport the received electrons to the second light-emitting layer 38.

[0069] Taking the blue light-emitting device structure as an example, the light-emitting device provided by the embodiments of the present disclosure can reduce the device voltage and the leakage problem of the charge generation unit caused by the PN junction will be described.

[0070] Solution 1:

[0071] Comparative example: As Figure 2 shown, the charge generation unit 42 includes a blue light-emitting device structure with an N-type charge generation layer 421 (N-CGL) and a P-type charge generation layer 422 (P-CGL):

[0072] ITO / HTL1: NDP9 (10 nm, 3%) / m-MTDATA (34 nm) / NPB (10 nm) / BH: BD (20 nm, 1%) / TPBI (3 nm) / BCP: Liq (5 nm, 50%) / BCP: Yb (12 nm, 1%) / m-MTDATA: NDP9 (7 nm, 6%) / m-MTDATA (15 nm) / NPB (3 nm) / BH: BD (20 nm, 1%) / TPBI (5 nm) / BCP: Liq (30 nm, 50%) / Yb (1 nm) / Mg: Ag (13 nm, 1:9) / NPB (60 nm), from the first to the last in sequence are Figure 2 The material, thickness, and doping concentration parameters of each layer from anode 1 to cathode 2.

[0073] Example 1 of the present disclosure: As Figure 3 shown, the charge generation unit 42 includes a blue light-emitting device structure with two N-type charge generation layers 421 (N-CGL) and two P-type charge generation layers 422 (P-CGL) arranged alternately:

[0074] ITO / HTL1: NDP9 (10 nm, 3%) / m-MTDATA (34 nm) / NPB (10 nm) / BH: BD (20 nm, 1%) / TPBI (3 nm) / BCP: Liq (5 nm, 50%) / BCP: Yb (6 nm, 1%) / m-MTDATA: NDP9 (3.5 nm, 6%) / BCP: Yb (6 nm, 1%) / m-MTDATA: NDP9 (3.5 nm, 6%) / m-MTDATA (15 nm) / NPB (3 nm) / BH: BD (20 nm, 1%) / TPBI (5 nm) / BCP: Liq (30 nm, 50%) / Yb (1 nm) / Mg: Ag (13 nm, 1:9) / NPB (60 nm), from the first to the last in sequence are Figure 3 The material, thickness, and doping concentration parameters of each layer from anode 1 to cathode 2.

[0075] Example 2 of the present disclosure: As Figure 4 shown, the charge generation unit 42 includes a blue light-emitting device structure with three N-type charge generation layers 421 (N-CGL) and three P-type charge generation layers 422 (P-CGL) arranged alternately:

[0076] ITO / HTL1:NDP9(10nm, 3%) / m-MTDATA(34nm) / NPB(10nm) / BH:BD(20nm, 1%) / TPBI(3nm) / BCP:Liq(5nm, 50%) / BCP:Yb(4nm, 1%) / m-MTDATA:NDP9(2nm, 7%) / BCP:Yb(4nm, 1%) / m-MTDATA:NDP9(3nm, 7%) / BCP:Yb(4nm, 1%) / m-MTDATA:NDP9(2nm, 7%)m-MTDATA(15nm) / NPB(3nm) / BH:BD(20nm, 1%) / TPBI(5nm) / BCP:Liq(30nm, 50%) / Yb(1nm) / Mg:Ag(13nm, 1:9) / NPB(60nm), from the first to the last in sequence are Figure 4 The material, thickness, and doping concentration parameters of each layer from anode 1 to cathode 2.

[0077] First, test the leakage of the PN junction. N-CGL and P-CGL can be evaporated on two electrodes (ITO), and planarization is performed between the two electrodes using an organic glue to reduce the influence of underlying impurities on the test results. Apply a voltage to the electrodes for current testing, and compare the current magnitudes. The smaller the current, the larger the resistance can be considered, that is, the smaller the lateral leakage. As Figures 5 - 7 shown, at a voltage of 20V, Figures 2 - 4 IV tests were performed on the corresponding three charge generation units 42 to determine the leakage situation, record the current data at this voltage, and make a lateral comparison. The specific test data are shown in Table 1 below. It can be seen that Figure 3 the leakage of the charge generation unit 42 shown in Figure 1 is reduced by ~14% relative to the overall leakage current of the charge generation unit 42 shown in Figure 4 the leakage of the charge generation unit 42 shown in Figure 1 is reduced by ~22% relative to the overall leakage current of the charge generation unit 42 shown in

[0078] Table 1

[0079] Current Figure 2 charge generation unit 42 100％ Figure 3 charge generation unit 42 86％ Figure 4 charge generation unit 42 78％

[0080] The embodiments of the present disclosure also Figure 1 and Figure 2 shown blue light-emitting devices at 10 mA / cm 2Optical tests (voltage and EQE) were carried out under certain conditions, and lifetime tests were carried out at 15 mA / cm 2 , 25 °C. The specific test data are shown in Table 2 below.

[0081] Table 2

[0082] Voltage EQE Lifetime LT95@25℃ Figure 2 charge generation unit 42 100％ 100％ 100％ Figure 3 charge generation unit 42 98％ 103％ 112％

[0083] From the data in Table 2, it can be seen that when comparing Figure 2 the single-layer N-CGL and P-CGL and Figure 3 the double-layer N-CGL and P-CGL structures, in the charge generation and separation unit 4, the N-CGL and P-CGL are stacked in multiple layers, which can reduce the voltage of the device, improve the charge separation and transport performance, improve the device efficiency and brightness, and at the same time can effectively reduce the lateral electron transport and improve the crosstalk between pixels. Compared with the single-layer N-CGL and P-CGL structures, the double-layer N-CGL and P-CGL structures can reduce the device voltage by ~2%, improve the external quantum efficiency (EQE) of the device by ~3%, and improve the device lifetime by ~12%; the inventors of this case also synchronously tested the monochromatic spectrum of the device. Taking the Blue test spectrum as an example, it can be seen that for the double-layer N-CGL and P-CGL devices compared with the single-layer N-CGL and P-CGL devices in the green and red regions, the G / R spectral peaks generated by crosstalk are significantly reduced. It can be concluded that the double-layer N-CGL and P-CGL structures reduce the lateral transport of electrons from blue light to R / G during the blue light illumination process, thereby reducing the measured R / G spectrum and improving the blue light emission efficiency.

[0084] Solution 2:

[0085] Comparative example: As Figure 8 shown, the charge generation unit 42 includes a blue light-emitting device structure with an N-type charge generation layer 421 (N-CGL) and a P-type charge generation layer 422 (P-CGL):

[0086] ITO / HTL1:NDP9(10nm, 3%) / m-MTDATA(34nm) / NPB(10nm) / BH:BD(20nm, 1%) / TPBI(3nm) / BCP:Liq(5nm, 50%) / BCP:Yb(12nm, 1%) / m-MTDATA:NDP9(7nm, 6%) / m-MTDATA(15nm) / NPB(3nm) / BH:BD(20nm, 1%) / TPBI(5nm) / BCP:Liq(30nm, 50%) / Yb(1nm) / Mg:Ag(13nm, 1:9) / NPB(60nm), from the first to the last in sequence are Figure 9The parameters of the material, thickness, and doping concentration of each layer from the anode 1 to the cathode 2.

[0087] Embodiment 3 of the present disclosure: As Figure 9 shown, the charge generation unit 42 includes a blue light-emitting device structure with two N-type charge generation layers 421 (N-CGL) and two P-type charge generation layers 422 (P-CGL) arranged alternately:

[0088] ITO / HTL1:NDP9(10nm, 3%) / m-MTDATA(36nm) / NPB(10nm) / BH:BD(20nm, 1%) / TPBI(3nm) / BCP:Liq(5nm, 50%) / BCP:Yb(6nm, 1%) / HATCN(2nm) / BCP:Yb(6nm, 1%) / HATCN(2nm) / m-MTDATA(16nm) / NPB(3nm) / BH:BD(20nm, 1%) / TPBI(5nm) / BCP:Liq(30nm, 50%) / Yb(1nm) / Mg:Ag(13nm, 1:9) / NPB(60nm), from the first to the last in sequence are Figure 9 The parameters of the material, thickness, and doping concentration of each layer from the anode 1 to the cathode 2.

[0089] Embodiment 4 of the present disclosure: As Figure 10 shown, the charge generation unit 42 includes a blue light-emitting device structure with three N-type charge generation layers 421 (N-CGL) and three P-type charge generation layers 422 (P-CGL) arranged alternately:

[0090] ITO / HTL1:NDP9(10nm, 3%) / m-MTDATA(34nm) / NPB(10nm) / BH:BD(20nm, 1%) / TPBI(3nm) / BCP:Liq(5nm, 50%) / BCP:Yb(4nm, 1%) / HATCN(2nm) / BCP:Yb(4nm, 1%) / HATCN(2nm) / BCP:Yb(4nm, 1%) / HATCN(2nm, 7%)m-MTDATA(16nm) / NPB(3nm) / BH:BD(20nm, 1%) / TPBI(5nm) / BCP:Liq(30nm, 50%) / Yb(1nm) / Mg:Ag(13nm, 1:9) / NPB(60nm), from the first to the last in sequence are Figure 4 The parameters of the material, thickness, and doping concentration of each layer from the anode 1 to the cathode 2.

[0091] The currently more commonly used structure of the charge generation unit 42 is Figure 8The single-layer N-CGL and P-CGL stacked structure shown forms a charge depletion region, i.e., a space charge depletion region, at the stacked interface because N-CGL and P-CGL are two different types of materials, as Figure 11 shown. In the charge depletion region P1, there are no freely movable charges. Therefore, within the charge depletion region P1, a relatively large resistance can be generated, thereby reducing the lateral charge transport ability. That is, it can be simply considered that the existence of the charge depletion region P1 can reduce the crosstalk effect of the R / G / B light-emitting layers on the Panel. The wider the width of the charge depletion region P1, the weaker the crosstalk effect, but it is not conducive to charge transport, resulting in a sharp increase in the voltage of the device. To reduce the operating voltage of the device, the Figure 9 and Figure 10 shown multi-layer N-CGL and P-CGL stacked structures are adopted, so that the charge depletion region P1 between adjacent N-CGL and P-CGL becomes narrower, as Figure 12 and Figure 13 shown. Figure 12 Schematic Figure 9 of the charge depletion region P1, Figure 13 Schematic Figure 10 of the charge depletion region P1, the injection of electrons and holes is more rapid. Therefore, the multi-layer alternating stacked N-type charge generation layer and P-type charge generation layer adopted in the present disclosure can reduce the device voltage and at the same time improve the crosstalk effect of the device. To further reduce the device power consumption, in Embodiment 3 and Embodiment 4 of Solution 2 on the basis of satisfying Solution 1, the material of the P-type charge generation layer 422 in Embodiment 3 and Embodiment 4 is an undoped material (such as HATCN). HATCN has a strong charge transport ability. In this way, the P-CGL can further reduce the device voltage while ensuring crosstalk. Since the film thickness of the P-CGL is less than or equal to 20 nm, its light absorption does not have a great impact on the device efficiency due to the use of the undoped material method.

[0092] We calculated the comparison between the width of the charge depletion region and the lateral leakage current caused by the PN junction through the Mott-Schottky equation. The multi-layer N-CGL and P-CGL stacked structure adopts the method of superimposing the widths of the charge depletion regions, and the data in Table 3 below are obtained.

[0093] Table 3

[0094] Charge depletion region width Figure 8 charge generation unit 42 100％ Figure 9 charge generation unit 42 109％ Figure 10 charge generation unit 42 116％

[0095] As can be seen from Table 3 Figure 10 The comparison of the total widths of the corresponding charge depletion regions P1 Figure 8The structure is improved by 16%, so that the present disclosure can further reduce the crosstalk problem caused by the charge generation unit 42, and the width of a single charge depletion region P1 becomes narrower, which can reduce the operating voltage of the device.

[0096] The present disclosure for the above Figures 8 - 10 shown blue light emitting device, under the condition of 10 mA / cm 2 the device was optically tested, and under the condition of 15 mA / cm 2 , at 25 °C, the device was subjected to a lifetime test, and the specific test data are shown in Table 4 below.

[0097] Table 4

[0098] Voltage EQE Lifetime LT95@25℃ Figure 8 charge generation unit 42 100％ 100％ 100％ Figure 9 charge generation unit 42 97％ 99％ 96％ Figure 10 charge generation unit 42 95％ 99％ 95％

[0099] It can be seen from the data in Table 4 that in the stacked structure of multi-layer N-CGL and P-CGL, the P-CGL uses an undoped material (HATCN). Compared with Figure 3 where the P-CGL in Figure 3 uses a doped material (m-MTDATA:NDP9), this embodiment can significantly reduce the operating voltage of the stacked device. At the same time, the efficiency and lifetime of the device are not greatly lost compared with

[0100] the structure shown, so the gain in power consumption can well make up for the loss of device lifetime.

[0101] Based on the same inventive concept, embodiments of the present disclosure further provide a display device, including the above-mentioned light-emitting device provided by the embodiments of the present disclosure. The display device provided by the embodiments of the present disclosure has great advantages in applications for products with small and medium-sized display panels, such as mobile phones, tablet computers, in-vehicle devices, wearable devices, etc. Since the stacked light-emitting devices in the display device have improved power efficiency and current efficiency compared with traditional stacked light-emitting devices, and the operating voltage is reduced, the display effects of the stacked light-emitting devices on the display device can be better optimized, such as light-emitting brightness, color and other effects.

[0102] For the above-mentioned light-emitting device and display device provided by the embodiments of the present disclosure, by adopting at least two N-type charge generation layers and at least two P-type charge generation layers arranged alternately, that is, at least forming a charge generation unit with an NPNP structure. Since the N-type charge generation layer and the P-type charge generation layer are two different types of materials, a charge depletion region will be formed at the interface where they are stacked. That is, at least three charge depletion regions are formed. There are no freely movable charges in the charge depletion region. Therefore, a relatively large resistance can be generated in the charge depletion region, thereby reducing the lateral charge transfer ability, that is, pixel crosstalk caused by lateral charge flow can be reduced. At the same time, in the non-charge depletion region, charges can flow normally, that is, the lateral and longitudinal transfer of charges can proceed normally. Compared with the charge depletion region of a single-layer NP structure in the prior art, each charge depletion region of the multi-layer alternately stacked N-type charge generation layer and P-type charge generation layer of the present disclosure is narrower, and the injection of electrons and holes is more rapid. Therefore, the multi-layer alternately stacked N-type charge generation layer and P-type charge generation layer adopted by the present disclosure can reduce the device voltage, and at the same time reduce the leakage problem of the charge generation unit caused by the PN junction, improve the current efficiency, and improve the power efficiency.

[0103] Although the preferred embodiments of the present disclosure have been described, those skilled in the art can make additional changes and modifications to these embodiments once they learn the basic creative concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications falling within the scope of the present disclosure.

[0104] Obviously, those skilled in the art can make various changes and modifications to the embodiments of the present disclosure without departing from the spirit and scope of the embodiments of the present disclosure. Thus, if these modifications and variations of the embodiments of the present disclosure fall within the scope of the claims of the present disclosure and their equivalent technologies, the present disclosure also intends to include these changes and modifications.

Claims

1. A light-emitting device, characterized in that, Comprising: An anode and a cathode which are oppositely arranged, at least two light-emitting units arranged in a stacked manner between the anode and the cathode, and a charge generation and separation unit arranged between two adjacent light-emitting units; the charge generation and separation unit includes an N-type charge transport unit, a charge generation unit, and a P-type charge transport unit which are sequentially arranged in a stacked manner in the direction from the anode to the cathode, and the charge generation unit includes at least two N-type charge generation layers and at least two P-type charge generation layers which are alternately arranged in the direction from the anode to the cathode.

2. The light-emitting device according to claim 1, wherein The light-emitting unit located between the anode and the charge generation and separation unit includes: a hole injection layer, a first hole transport layer, a first electron blocking layer, and a first light-emitting layer which are sequentially arranged in a stacked manner; the hole injection layer is close to the anode. The light-emitting unit located between the cathode and the charge generation and separation unit includes: an electron injection layer, a first electron transport layer, a first hole blocking layer, a second light-emitting layer, and a second electron blocking layer which are sequentially arranged in a stacked manner; the electron injection layer is close to the cathode. Wherein, the thickness of the charge generation and separation unit is less than or equal to the sum of the thicknesses of the hole injection layer and the first hole transport layer, and the ratio of the sum of the thicknesses of the hole injection layer and the first hole transport layer to the thickness of the charge generation and separation unit is less than or equal to 5.

3. The light-emitting device according to claim 2, wherein, The percentage of the thickness of the charge generation and separation unit in the thickness of the light-emitting device is less than or equal to 25%, and the percentage of the sum of the thicknesses of the hole injection layer and the first hole transport layer in the thickness of the light-emitting device is less than or equal to 55%.

4. The light-emitting device according to claim 2, wherein, The N-type charge transport unit includes: a second hole blocking layer located between the first light-emitting layer and the charge generation unit, and a second electron transport layer located between the second hole blocking layer and the charge generation unit; the P-type charge transport unit includes a second hole transport layer located between the second electron blocking layer and the charge generation unit. Wherein, the sum of the thicknesses of the second hole blocking layer and the second electron transport layer is less than or equal to the sum of the thicknesses of the first electron transport layer and the first hole blocking layer, and the ratio of the sum of the thicknesses of the first electron transport layer and the first hole blocking layer to the sum of the thicknesses of the second hole blocking layer and the second electron transport layer is greater than or equal to 3.

5. The light-emitting device according to claim 4, characterized in that, The thickness of the first hole transport layer is greater than the thickness of the second hole transport layer, and the mobility of the first hole transport layer is less than the mobility of the second hole transport layer. The thickness of the first electron transport layer is less than the thickness of the second electron transport layer, and the mobility of the first electron transport layer is less than the mobility of the second electron transport layer.

6. The light-emitting device according to claim 1, characterized in that, The N-type charge generation layer includes a first host material and a first guest material doped in the first host material, and the doping concentration of the first guest material is between 0.4% and 2%.

7. The light-emitting device according to claim 1, wherein, The P-type charge generation layer includes a second host material and a second guest material doped in the second host material, and the doping concentration of the second guest material is greater than or equal to 5%.

8. The light-emitting device according to claim 1, characterized in that, The material of the P-type charge generation layer is an organic electronic material or an inorganic metal oxide material. The organic electronic material includes HATCN, and the inorganic metal oxide material includes molybdenum oxide. The thickness of the P-type charge generation layer is less than or equal to 20 nm.

9. The light-emitting device according to claim 1, characterized in that, The charge generation and separation unit has a transmittance greater than 68% in the visible light wavelength range of 380 nm to 480 nm; the charge generation and separation unit has a transmittance greater than 85% in the visible light wavelength range of 480 nm to 580 nm; the charge generation and separation unit has a transmittance greater than 86% in the visible light wavelength range of 580 nm to 680 nm.

10. A display device, characterized in that, It includes the light-emitting device according to any one of claims 1-9.

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