Laminated OLED device and display panel

Abstract

The invention discloses a laminated OLED (Organic Light Emitting Diode) device and a display panel. The laminated OLED device comprises a first electrode, a first light-emitting stack layer, a first charge generation layer, a second charge generation layer, a second light-emitting stack layer and a second electrode which are sequentially laminated, the first light-emitting stack layer comprises a first electron transport layer; the first charge generation layer and the first electron transport layer are arranged adjacently; wherein the electron mobility of the first charge generation layer is greater than that of the first electron transport layer; a thickness of the first charge generation layer is smaller than a thickness of the first electron transport layer. According to the laminated OLED device and the display panel provided by the invention, the electron injection transmission efficiency of the charge generation layer is improved, the device capacitance is effectively reduced, and the display effect in low-gray-scale display is further improved.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of display technology, and in particular to a stacked OLED device and a display panel. Background Art

[0002] Organic Light-Emitting Diode (OLED) is a current-driven light-emitting element with the advantages of fast response, autonomous luminescence, wide viewing angle and wide operating temperature range, and is therefore widely used in the field of high-performance displays.

[0003] In recent years, with the development of semiconductor lighting technology, various light-emitting device structures have been proposed, and stacked OLED devices are one of them. Stacked OLED devices are two or more single-layer OLED devices connected in series through a charge generation layer. Due to the increase in device capacitance, the brightness is often uneven in low grayscale display, affecting the display effect. Summary of the invention

[0004] The present invention provides a laminated OLED device and a display panel, which improve the electron injection transmission efficiency of a charge generation layer, effectively reduce the device capacitance, and further improve the display effect in low grayscale display.

[0005] In a first aspect, an embodiment of the present invention provides a stacked OLED device, comprising a first electrode, a first light-emitting stacked layer, a first charge generation layer, a second charge generation layer, a second light-emitting stacked layer, and a second electrode stacked in sequence;

[0006] The first light-emitting stacked layer includes a first electron transport layer; the first charge generating layer is arranged adjacent to the first electron transport layer; wherein the electron mobility of the first charge generating layer is greater than the electron mobility of the first electron transport layer; and the thickness of the first charge generating layer is less than the thickness of the first electron transport layer.

[0007] Optionally, the material of the first charge generation layer includes a low work function metal or an alkali metal.

[0008] Optionally, the first light-emitting stacked layer further includes a first light-emitting layer, a first electron blocking layer, a first hole transport layer and a first hole injection layer;

[0009] The first electron transport layer, the first light emitting layer, the first electron blocking layer, the first hole transport layer and the first hole injection layer are sequentially stacked between the first charge generation layer and the first electrode.

[0010] Optionally, the second light-emitting stacked layer further includes a second electron transport layer, a second light-emitting layer, a second electron blocking layer, and a second hole transport layer;

[0011] The second hole transport layer, the second electron blocking layer, the second light emitting layer and the second electron transport layer are sequentially stacked between the second charge generation layer and the second electrode; the second charge generation layer is adjacent to the second hole transport layer.

[0012] Optionally, the first charge generating layer has a film thickness ranging from 1 to 10 nm.

[0013] Optionally, the first electron transport layer has a film thickness ranging from 30 to 50 nm.

[0014] Optionally, the second electron transport layer has a film thickness ranging from 20 to 40 nm.

[0015] Optionally, the energy level difference between the highest occupied molecular orbital energy level of the first charge generation layer and the highest occupied molecular orbital energy level of the first electron transport layer is greater than 0.3V.

[0016] Optionally, the energy level difference between the lowest unoccupied molecular orbital energy level of the first charge generation layer and the lowest unoccupied molecular orbital energy level of the second charge generation layer is less than 0.3V.

[0017] In a second aspect, an embodiment of the present invention provides a display panel, comprising a stacked OLED device as described in any embodiment of the present invention.

[0018] The embodiment of the present invention provides a stacked OLED device and a display panel. By setting a first charge generation layer and a second charge generation layer in the stacked OLED device, the electron mobility of the first charge generation layer is greater than the electron mobility of the adjacent first electron transport layer, thereby effectively providing the electrons of the first charge generation layer to the first electron transport layer. The thickness of the first charge generation layer is set to be less than the thickness of the first electron transport layer, so that the electrons can quickly pass through the first charge generation layer, and the accumulation of charges on the surface of the first electron transport layer is also avoided, thereby avoiding the voltage increase of the device caused by the accumulation of charges, and the holes and electrons in the first light-emitting layer are more likely to recombine. The electron injection and transmission are faster at low brightness, which improves the electron injection and transmission efficiency of the charge generation layer, effectively reduces the device capacitance, and thus improves the display effect in low grayscale display. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A structural schematic diagram of a stacked OLED device is provided for an embodiment of the present invention;

[0020] Figure 2 A structural schematic diagram of another stacked OLED device is provided for an embodiment of the present invention;

[0021] Figure 3 A structural schematic diagram of another stacked OLED device is provided for an embodiment of the present invention;

[0022] Figure 4 A structural schematic diagram of another stacked OLED device is provided for an embodiment of the present invention. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] The stacked OLED device is two or more single-layer OLED devices connected in series through the charge generation layer, so the self-capacitance of the OLED device increases. And according to the fact that the capacitance is equal to the product of the charge amount and the charging time, it can be known that the charging time will increase accordingly, which leads to inconsistent charging time of the RGB light-emitting units. In low-brightness images, the short charging time causes insufficient charging, resulting in uneven brightness of the image, which affects the display effect.

[0025] In view of this, Figure 1 A schematic diagram of the structure of a stacked OLED device is provided for an embodiment of the present invention. Figure 1 , including a first electrode 110, a first light-emitting stacked layer 120, a first charge generation layer 130, a second charge generation layer 140, a second light-emitting stacked layer 150 and a second electrode 160 which are sequentially stacked;

[0026] The first light-emitting stacked layer 120 includes a first electron transport layer 121; the first charge generation layer 130 is arranged adjacent to the first electron transport layer 121; wherein the electron mobility of the first charge generation layer 130 is greater than the electron mobility of the first electron transport layer 121; the thickness of the first charge generation layer 130 is less than the thickness of the first electron transport layer 121.

[0027] Specifically, the first electrode 110, as an anode for injecting holes, may include a conductive material with a high work function, such as ITO, IZO or ZnO. The second electrode 160, as a cathode for injecting electrons, may include a conductive material with a low work function, such as Al, Mg or Al-Mg alloy. When the OLED device is bottom-emitting, the second electrode 160 is used as a reflective electrode. When the OLED device is top-emitting, the first electrode 110 may include a reflective layer or a reflective electrode, and the second electrode 160 is a transparent electrode.

[0028] The first light-emitting stacking layer 120 is arranged on the first electrode 110, the first charge generating layer 130 is arranged on the side of the first light-emitting stacking layer 120 away from the first electrode 110, the second charge generating layer 140 is arranged on the side of the first charge generating layer 130 away from the first electrode 110, and the second light-emitting stacking layer 150 is arranged on the side of the second charge generating layer 140 away from the first electrode 110. The first light-emitting stacking layer 120 includes a first electron transport layer 121, and the first electron transport layer 121 is arranged adjacent to the first charge generating layer 130.

[0029] Exemplarily, the first light-emitting stacked layer 120 may further include a first hole injection layer 122, a first hole transport layer 123, and a first light-emitting layer 124 sequentially stacked on the first electrode 110. The second light-emitting stacked layer 150 includes a second hole transport layer 151, a second light-emitting layer 152, and a second electron transport layer 153 sequentially stacked on the second charge generation layer 140. The first charge generation layer 130 and the second charge generation layer 140 are used to generate charges or separate holes and electrons, so that electrons and holes are respectively transferred to the first light-emitting stacked layer 120 and the second light-emitting stacked layer 150. The first charge generation layer 130 transfers electrons to the first electron transport layer 121 of the first light-emitting stacked layer 120, and then transfers them to the first light-emitting layer 124 through the first electron transport layer 121. The second charge generation layer 140 transfers holes to the second hole transport layer 151, and then the second hole transport layer 151 provides holes to the second light-emitting layer 152. In order to effectively provide the electrons of the first charge generation layer 130 to the first electron transport layer 121, the electron mobility of the first charge generation layer 130 is greater than the electron mobility of the first electron transport layer 121. Thus, the charges generated by the second charge generation layer 140 are quickly transferred to the first light-emitting layer 124, avoiding the increase of device voltage and poor stability caused by charge accumulation, thereby ensuring that the electrons are transferred to the first light-emitting layer 124 faster to achieve composite light emission. In order to facilitate the rapid transmission of electrons, the thickness of the first charge generation layer 130 is less than the thickness of the first electron transport layer 121. Since the thickness of the first charge generation layer 130 is thin, the electrons pass through the first charge generation layer 130 quickly. By increasing the thickness of the first electron transport layer 121, the accumulation on the surface of the first electron transport layer 121 is avoided, and the electrons continue to be transmitted to the first light-emitting layer 124, thereby avoiding the increase of device voltage caused by charge accumulation. Holes and electrons in the first light-emitting layer 124 are more likely to recombine. At low brightness, due to faster electron injection and transmission, the electron injection and transmission capacity of the charge generation layer is improved, thereby reducing the device capacitance. In normal display, due to the improved electron transfer efficiency, the exciton concentration of the light-emitting layer is increased, thereby improving the luminous efficiency. Exemplarily, the first charge generation layer 130 has a thickness ranging from 1 to 10 nm, preferably 8 nm, and optionally, the first electron transport layer 121 has a thickness ranging from 30 to 50 nm.

[0030] The embodiment of the present invention provides a stacked OLED device and a display panel. By setting a first charge generation layer and a second charge generation layer in the stacked OLED device, the electron mobility of the first charge generation layer is greater than the electron mobility of the adjacent first electron transport layer, thereby effectively providing the electrons of the first charge generation layer to the first electron transport layer. The thickness of the first charge generation layer is set to be less than the thickness of the first electron transport layer, so that the electrons can quickly pass through the first charge generation layer, and the accumulation of charges on the surface of the first electron transport layer is also avoided, thereby avoiding the voltage increase of the device caused by the accumulation of charges, and the holes and electrons in the first light-emitting layer are more likely to recombine. The electron injection and transmission are faster at low brightness, which improves the electron injection and transmission efficiency of the charge generation layer, effectively reduces the device capacitance, and thus improves the display effect in low grayscale display.

[0031] Optionally, the material of the first charge generation layer 130 includes a low work function metal or an alkali metal.

[0032] Specifically, the first charge generation layer 130 is N-type doped, the second charge generation layer 140 is P-type doped, and the first charge generation layer 130 and the second charge generation layer 140 constitute a charge generation layer with a PN junction. The material of the first charge generation layer 130 includes a low work function metal or an alkali metal, such as Li, Na, K, Cs and / or Ca, doped into an electron transport material, and the electron transport material doped with the low work function metal or alkali metal is evaporated to form the second charge transport layer. Due to the formation of the space charge effect, the energy barrier between the first charge generation layer 130 and the first electron transport layer 121 can be greatly reduced, the driving voltage is reduced, and electrons are more easily injected into the adjacent first light-emitting layer 124.

[0033] Based on the above embodiments, Figure 2 A structural schematic diagram of another stacked OLED device is provided for an embodiment of the present invention, see Figure 2 , the first light-emitting stacked layer 120 further includes a first light-emitting layer 124, a first electron blocking layer 125, a first hole transport layer 123 and a first hole injection layer 122;

[0034] A first electron transport layer 121 , a first light emitting layer 124 , a first electron blocking layer 125 , a first hole transport layer 123 and a first hole injection layer 122 are sequentially stacked between the first charge generation layer 130 and the first electrode 110 .

[0035] Specifically, when electrons are transferred from the first electron transport layer 121 to the interface of the first hole transport layer 123, since the lowest unoccupied molecular orbital (LUMO) of the first electron transport layer 121 is much higher than the LUMO of the first hole transport layer 123, it is not easy for the electrons to cross into the first hole transport layer 123, and thus they are blocked at this interface. A first electron blocking layer 125 is further provided between the first light-emitting layer 124 and the first hole transport layer 123 to prevent electrons from entering the hole transport layer. At this time, holes are transferred from the first hole injection layer 122 and the first hole transport layer 123 to the vicinity of the interface of the first light-emitting layer 124, where they recombine with electrons to generate excitons, and the excitons release energy in the form of light emission and non-light emission.

[0036] Optionally, the second light-emitting stacked layer 150 further includes a second electron transport layer 153, a second light-emitting layer 152, a second electron blocking layer 154, and a second hole transport layer 151;

[0037] A second hole transport layer 151 , a second electron blocking layer 154 , a second light emitting layer 152 and a second electron transport layer 153 are sequentially stacked between the second charge generation layer 140 and the second electrode 160 ; the second charge generation layer 140 is adjacent to the second hole transport layer 151 .

[0038] Specifically, the second electrode 160 generates electrons that are transported from the second electron transport layer 153 to the interface of the second hole transport layer 151. The LUMO of the second electron transport layer 153 is greater than the LUMO of the second hole transport layer 151, so it is not easy for the electrons to cross into the second hole transport layer 151 and are blocked at this interface. A second electron blocking layer 154 is further provided between the second light-emitting layer 152 and the second hole transport layer 151 to prevent electrons from entering the hole transport layer. The second charge generation layer 140 transports holes to the second hole transport layer 151, and the second hole transport layer 151 provides holes to the vicinity of the interface of the second light-emitting layer 152 to recombine with electrons to generate excitons, and the excitons release energy in the form of light emission and non-light emission.

[0039] Based on the above embodiments, Figure 3 A structural schematic diagram of another stacked OLED device is provided for an embodiment of the present invention, see Figure 3, the first light-emitting layer 124 and the second light-emitting layer 152 each include a first color light-emitting layer 210, a second color light-emitting layer 220 and a third color light-emitting layer 230. The first color, the second color and the third color may be blue, green and red, respectively. The first color light-emitting layer 210, the second color light-emitting layer 220 and the third color light-emitting layer 230 in the first light-emitting layer 124 are arranged in the same layer, and the first color light-emitting layer 210, the second color light-emitting layer 220 and the third color light-emitting layer 230 in the second light-emitting layer 152 are arranged in the same layer. Exemplarily, the attached Figure 3 In the figure, the first color light-emitting layer 210, the second color light-emitting layer 220 and the third color light-emitting layer 230 are arranged in sequence, but there is no specific limitation. The first color light-emitting layer 210, the second color light-emitting layer 220 and the third color light-emitting layer 230 can be arranged in other arrangement orders.

[0040] Figure 4 A structural schematic diagram of another stacked OLED device is provided for an embodiment of the present invention, see Figure 4 The stacked OLED device also includes an optical adjustment layer 410, which is arranged between the second hole transport layer 151 and the second electron blocking layer. The light from each light-emitting layer is transmitted and reflected at different interfaces inside the OLED device, and complex interference phenomena will occur at this time. These reflected lights interfere with each other, causing constructive interference and generating resonance phenomena. In order to form a resonance frequency with the same number of inherent vibrations as the luminescent substance, the optical properties of the luminescent material should be considered, and the corresponding resonance thickness is formed according to the wavelength of the light. The resonance thickness can be formed by using the thickness of the OLED and the various stacked films outside. For example, in the second light-emitting layer 152, when the thickness of the red light color luminescent layer (the third color luminescent layer 230) and the green light color luminescent layer (the second color luminescent layer 220) are the same, the thickness of the optical adjustment layer facing the red light color luminescent layer can be greater than the thickness of the optical adjustment layer facing the green light color luminescent layer to meet the corresponding resonance thickness. In this way, the light efficiency can be effectively improved.

[0041] Optionally, the second electron transport layer 153 has a thickness ranging from 20 to 40 nm. The second electron transport layer 153 is close to the second electrode 160. The electrons generated by the second electron are transported from the second electron transport layer 153 to the next layer. The second electron transport layer 153 has an appropriate thickness so that the generated charges can be quickly transferred to the next layer to avoid the accumulation of charges causing the device voltage to increase, thereby reducing the device capacitance, increasing the probability of compound luminescence of holes and electrons, and improving the luminescence efficiency of the stacked OLED device.

[0042] Optionally, the energy level difference between the highest occupied molecular orbital energy level (HOMO) of the first charge generation layer 130 and the highest occupied molecular orbital energy level of the first electron transport layer 121 is greater than 0.3 V. The HOMO of the molecule has a smaller binding on its electrons, thereby improving the transmission of electrons from the first charge generation layer 130 to the first electron transport layer 121. The energy level difference between the two being greater than 0.3 V can also prevent electrons from being transported back, and at the same time, can block the holes of the first light-emitting layer 124 from being transmitted to the second light-emitting layer 152.

[0043] Optionally, the energy level difference between the lowest unoccupied molecular orbital energy level (LUMO) of the first charge generation layer 130 and the lowest unoccupied molecular orbital energy level (LUMO) of the second charge generation layer 140 is less than 0.3V, and when the first charge generation layer 130 is N-type doped and the second charge generation layer 140 is P-type doped, it is more conducive to the injection of electrons generated by the second charge generation layer 140 into the first charge generation layer 130.

[0044] The stacked OLED device provided in the above embodiment includes two light-emitting stacked layers, which is only an exemplary demonstration and not a limitation to the technical solution of the present invention. Those skilled in the art can adjust the number of light-emitting stacked layers.

[0045] The embodiment of the present invention further provides a display panel, which includes a laminated OLED device having any of the features described in the above embodiments. The type of the display panel can be any one of an organic light-emitting diode (OLED) display panel, an in-plane switching (IPS) display panel, a twisted nematic (TN) display panel, a vertical alignment (VA) display panel, an electronic paper, a QLED (Quantum Dot Light Emitting Diodes) display panel or a microLED (μLED) display panel, and the present invention does not specifically limit this.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A stacked OLED device, characterized in that: It includes a first electrode, a first light-emitting stacked layer, a first charge generating layer, a second charge generating layer, a second light-emitting stacked layer and a second electrode which are sequentially stacked; The first light-emitting stacked layer includes a first electron transport layer; the first charge generating layer is arranged adjacent to the first electron transport layer; wherein the electron mobility of the first charge generating layer is greater than the electron mobility of the first electron transport layer; and the thickness of the first charge generating layer is less than the thickness of the first electron transport layer.

2. The stacked OLED device according to claim 1, characterized in that: The material of the first charge generation layer includes a low work function metal or an alkali metal.

3. The stacked OLED device according to claim 1, characterized in that: The first light-emitting stacked layer further includes a first light-emitting layer, a first electron blocking layer, a first hole transport layer and a first hole injection layer; The first electron transport layer, the first light emitting layer, the first electron blocking layer, the first hole transport layer and the first hole injection layer are sequentially stacked between the first charge generation layer and the first electrode.

4. The stacked OLED device according to claim 1, characterized in that: The second light-emitting stacked layer further includes a second electron transport layer, a second light-emitting layer, a second electron blocking layer, and a second hole transport layer; The second hole transport layer, the second electron blocking layer, the second light emitting layer and the second electron transport layer are sequentially stacked between the second charge generation layer and the second electrode; the second charge generation layer is adjacent to the second hole transport layer.

5. The stacked OLED device according to any one of claims 1 to 4, characterized in that: The first charge generating layer has a film thickness ranging from 1 to 10 nm.

6. The stacked OLED device according to claim 5, characterized in that: The thickness of the first electron transport layer is in the range of 30-50 nm.

7. The stacked OLED device according to any one of claims 1 to 4, characterized in that: The second electron transport layer has a thickness ranging from 20 to 40 nm.

8. The stacked OLED device according to claim 1, characterized in that: The energy level difference between the highest occupied molecular orbital energy level of the first charge generation layer and the highest occupied molecular orbital energy level of the first electron transport layer is greater than 0.3V.

9. The stacked OLED device according to claim 1, characterized in that: The energy level difference between the lowest unoccupied molecular orbital energy level of the first charge generation layer and the lowest unoccupied molecular orbital energy level of the second charge generation layer is less than 0.3V.

10. A display panel, characterized in that: A stacked OLED device comprising the stacked OLED device according to any one of claims 1 to 9.

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