Organic electroluminescent device and preparation method thereof, and display device

Abstract

An organic electroluminescent device and a preparation method thereof, and a display device. The organic electroluminescent device includes an anode, a cathode, and a light-emitting layer and an electron transport layer arranged between the anode and the cathode, wherein the electron transport layer is arranged between the light-emitting layer and the cathode; the electron transport layer includes a first host material and a second host material, and the mixing ratio of the first host material and the second host material on the side of the electron transport layer close to the light-emitting layer is different from the mixing ratio of the first host material and the second host material on the side of the electron transport layer far from the light-emitting layer.

Description

Technical Field

[0001] The present disclosure relates to but is not limited to the field of display technology, and in particular to an organic electroluminescent device and a preparation method thereof, and a display device. Background Art

[0002] Organic light emitting devices (OLED) are active light emitting devices with the advantages of light emission, ultra-thinness, wide viewing angle, high brightness, high contrast, low power consumption, and extremely high response speed. They have gradually become the next generation display technology with great development prospects. With the continuous development of display technology, display devices with OLED as the light emitting device and thin film transistor (TFT) for signal control have become the mainstream products in the current display field.

[0003] OLED includes an anode, a cathode, and a light-emitting layer disposed between the anode and the cathode. The principle of its light emission is to inject holes and electrons from the anode and cathode into the light-emitting layer respectively. When the electrons and holes meet in the light-emitting layer, the electrons and holes recombine to generate excitons. These excitons emit light while changing from an excited state to a ground state. In order to allow electrons and holes to be smoothly injected from the electrode into the light-emitting layer at a lower driving voltage, a hole injection layer and a hole transport layer are disposed between the anode and the light-emitting layer, and an electron injection layer and an electron transport layer are disposed between the cathode and the light-emitting layer. In order for OLED to achieve better light-emitting efficiency, the design of the electron transport layer is relatively important. Summary of the invention

[0004] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0005] On the one hand, exemplary embodiments of the present disclosure provide an organic electroluminescent device, comprising an anode, a cathode, and a light-emitting layer and an electron transport layer arranged between the anode and the cathode, wherein the electron transport layer is arranged between the light-emitting layer and the cathode; the electron transport layer comprises a first host material and a second host material, and the mixing ratio of the first host material and the second host material on a side of the electron transport layer close to the light-emitting layer is different from the mixing ratio of the first host material and the second host material on a side of the electron transport layer far from the light-emitting layer.

[0006] In an exemplary embodiment, the first host material has a refractive index greater than a refractive index of the second host material.

[0007] In an exemplary embodiment, along a direction from close to the light-emitting layer to far from the light-emitting layer, the mass percentage of the first host material in the electron transport layer gradually decreases, and the mass percentage of the second host material in the electron transport layer gradually increases.

[0008] In an exemplary embodiment, on a side of the electron transport layer close to the light emitting layer, the mass percentage of the first host material in the electron transport layer is 60% to 80%, and the mass percentage of the second host material in the electron transport layer is 20% to 40%.

[0009] In an exemplary embodiment, on a side of the electron transport layer away from the light emitting layer, the mass percentage of the first host material in the electron transport layer is 0 to 10%, and the mass percentage of the second host material in the electron transport layer is 90 to 100%.

[0010] In an exemplary embodiment, the thickness of the light emitting layer is 10 nm to 25 nm, the thickness of the electron transport layer is 20 nm to 50 nm, and the refractive index of the electron transport layer on the side of the electron transport layer close to the light emitting layer is 1.80 to 2.00.

[0011] In an exemplary embodiment, the thickness of the electron transport layer is 20 nm to 50 nm, the thickness of the cathode is 10 nm to 20 nm, and the refractive index of the electron transport layer on a side of the electron transport layer close to the cathode is 1.55 to 1.70.

[0012] In an exemplary embodiment, a hole injection layer, a hole transport layer and an electron blocking layer are further arranged between the anode and the light-emitting layer, a hole blocking layer is further arranged between the light-emitting layer and the electron transport layer, and an electron injection layer is further arranged between the electron transport layer and the cathode; the hole injection layer has a thickness of 5nm to 20nm, the hole transport layer has a thickness of 100nm to 150nm, the electron blocking layer has a thickness of 5nm to 20nm, the light-emitting layer has a thickness of 10nm to 25nm, the hole blocking layer has a thickness of 5nm to 15nm, and the electron injection layer has a thickness of 0.5nm to 2nm; on the side of the electron transport layer close to the hole blocking layer, the refractive index of the electron transport layer is 1.80 to 2.00, and on the side of the electron transport layer close to the electron injection layer, the refractive index of the electron transport layer is 1.55 to 1.70.

[0013] In an exemplary embodiment, the electron transport layer has a maximum red light refractive index n in the wavelength range of 600 nm to 640 nm. RMAX , with a maximum green light refractive index n in the wavelength range of 510nm to 550nm GMAX, with a maximum blue light refractive index n in the wavelength range of 440nm to 480nm BMAX ; The electron transport layer satisfies:

[0014] │n BMAX -n GMAX │≤0.4,│n BMAX -n RMAX │≤0.8.

[0015] In an exemplary embodiment, the maximum red light refractive index n RMAX is 1.81 to 1.91, the maximum green light refractive index n GMAX is 1.86 to 1.96, the maximum blue light refractive index n BMAX It is between 1.90 and 2.00.

[0016] In an exemplary embodiment, the electron transport layer has a minimum red light refractive index n in the wavelength range of 600 nm to 640 nm. RMIN , with a minimum green light refractive index n in the wavelength range of 510nm to 550nm GMIN , with a minimum blue light refractive index n in the wavelength range of 440nm to 480nm BMIN ; The electron transport layer satisfies:

[0017] │n BMIN -n GMIN │≤0.5,│n BMIN -n RMIN │≤1.0.

[0018] In an exemplary embodiment, the minimum red light refractive index n RMIN is 1.55 to 1.65, the minimum green light refractive index n GMIN is 1.57 to 1.67, the minimum blue light refractive index n BMIN It is 1.60 to 1.70.

[0019] On the other hand, an exemplary embodiment of the present disclosure further provides a display device including the aforementioned organic electroluminescent device.

[0020] In another aspect, the exemplary embodiments of the present disclosure further provide a method for preparing an organic electroluminescent device, comprising:

[0021] forming an anode;

[0022] forming a light-emitting layer;

[0023] forming an electron transport layer, wherein the electron transport layer includes a first host material and a second host material, wherein a mixing ratio of the first host material and the second host material on a side of the electron transport layer close to the light-emitting layer is different from a mixing ratio of the first host material and the second host material on a side of the electron transport layer far from the light-emitting layer;

[0024] A cathode is formed.

[0025] In an exemplary embodiment, forming an electron transport layer includes: adopting a co-evaporation method of a first main material source and a second main material source, and controlling the evaporation rate of the first main material to gradually decrease and the evaporation rate of the second main material to gradually increase during the process from the beginning of evaporation to the end of evaporation, so that along the direction from close to the light-emitting layer to away from the light-emitting layer, the mass percentage of the first main material in the electron transport layer gradually decreases, and the mass percentage of the second main material in the electron transport layer gradually increases.

[0026] In an exemplary embodiment, at the beginning of evaporation, the evaporation rate of the first host material is controlled to be to Control the evaporation rate of the second main material to to At the end of the evaporation, the evaporation rate of the first host material is controlled to be 0 to Control the evaporation rate of the second main material to to

[0027] Other aspects will be apparent upon reading and understanding the drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings are used to provide a further understanding of the technical solution of the present disclosure and constitute a part of the specification. Together with the embodiments of the present disclosure, they are used to explain the technical solution of the present disclosure and do not constitute a limitation on the technical solution of the present disclosure. The shapes and sizes of the components in the accompanying drawings do not reflect the actual proportions and are only intended to illustrate the contents of the present disclosure.

[0029] Figure 1 is a structural schematic diagram of a display device;

[0030] Figure 2 is a schematic diagram of a planar structure of a display device;

[0031] Figure 3 is a schematic diagram of an equivalent circuit of a pixel driving circuit;

[0032] Figure 4 is a working timing diagram of a pixel driving circuit;

[0033] Figure 5is a schematic diagram of a cross-sectional structure of a display device;

[0034] Figure 6 It is a structural schematic diagram of a light emitting device according to an exemplary embodiment of the present disclosure;

[0035] Figure 7 It is a schematic structural diagram of another light emitting device according to an exemplary embodiment of the present disclosure;

[0036] Figure 8 The light extraction efficiency comparison results of the comparative structures of the exemplary embodiments of the present disclosure are shown;

[0037] Figures 9a to 9c FIG. 4 is a mode ratio distribution diagram of a light emitting device according to an exemplary embodiment of the present disclosure.

[0038] Description of reference numerals:

[0039] 10- anode; 20- hole injection layer; 30- hole transport layer;

[0040] 40-electron blocking layer; 50-light-emitting layer; 60-hole blocking layer;

[0041] 70-electron transport layer; 80-electron injection layer; 90-cathode;

[0042] 101-substrate; 102-driving circuit layer; 103-light-emitting structure layer.

[0043] 104-encapsulation layer; 210-driving transistor; 211-storage capacitor;

[0044] 301- anode; 302- pixel definition layer; 303- organic light emitting layer;

[0045] 304- cathode; 401- first packaging layer; 402- second packaging layer;

[0046] 403-third encapsulation layer. DETAILED DESCRIPTION

[0047] The embodiments herein can be implemented in a plurality of different forms. A person skilled in the art can easily understand the fact that the implementation and content can be transformed into various forms without departing from the purpose and scope of the present disclosure. Therefore, the present disclosure should not be interpreted as being limited to the contents described in the following embodiments. In the absence of conflict, the embodiments in the present disclosure and the features in the embodiments can be combined arbitrarily with each other.

[0048] In the drawings, the size of the constituent elements, the thickness of the layer, or the area may be exaggerated for the sake of clarity. Therefore, any implementation of the present disclosure is not necessarily limited to the dimensions shown in the drawings, and the shapes and sizes of the components in the drawings do not reflect the true proportions. In addition, the drawings schematically show ideal examples, and any implementation of the present disclosure is not limited to the shapes or values ​​shown in the drawings.

[0049] The ordinal numbers such as "first", "second", and "third" in this article are set to avoid confusion among constituent elements rather than to limit the quantity.

[0050] In this document, for the sake of convenience, the words and phrases indicating the orientation or positional relationship such as "middle", "upper", "lower", "front", "back", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like are used to illustrate the positional relationship of the constituent elements with reference to the drawings. This is only for the convenience of describing the implementation methods and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as a limitation of the present disclosure. The positional relationship of the constituent elements can be appropriately changed according to the direction of the constituent elements being described. Therefore, it is not limited to the words and phrases described in the text and can be appropriately replaced according to the circumstances.

[0051] In this document, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate, or the internal communication of two elements. For ordinary technicians in this field, the meanings of the above terms in this disclosure can be understood according to the circumstances.

[0052] In this article, a transistor refers to a component including at least three terminals: a gate electrode, a drain electrode, and a source electrode. A transistor has a channel region between a drain electrode (or drain electrode terminal, drain region, or drain electrode) and a source electrode (or source electrode terminal, source region, or source electrode), and current can flow through the drain electrode, the channel region, and the source electrode. In this article, the channel region refers to the region where the current mainly flows.

[0053] In this article, the first electrode may be a drain electrode and the second electrode may be a source electrode, or the first electrode may be a source electrode and the second electrode may be a drain electrode. In the case of using transistors with opposite polarities or when the current direction changes during circuit operation, the functions of the "source electrode" and the "drain electrode" may sometimes be interchanged. Therefore, in this article, the "source electrode" and the "drain electrode" may be interchanged.

[0054] In this article, "electrical connection" includes the situation where the components are connected together through an element having some electrical function. There is no particular limitation on the "element having some electrical function" as long as it can transmit and receive electrical signals between the connected components. The "element having some electrical function" can be, for example, an electrode or wiring, or a switching element such as a transistor, or other functional elements such as a resistor, inductor or capacitor.

[0055] In this article, "parallel" means that the angle formed by two straight lines is greater than -10° and less than 10°, and therefore, also includes the state where the angle is greater than -5° and less than 5°. In addition, "perpendicular" means that the angle formed by two straight lines is greater than 80° and less than 100°, and therefore, also includes the state where the angle is greater than 85° and less than 95°.

[0056] In this document, "film" and "layer" can be interchanged. For example, "conductive layer" can sometimes be replaced by "conductive film". Similarly, "insulating film" can sometimes be replaced by "insulating layer".

[0057] The term "about" as used herein refers to values ​​that are not strictly limited and allow for process and measurement errors.

[0058] Figure 1 FIG. 1 is a schematic diagram of the structure of a display device. Figure 1As shown, the OLED display device may include a timing controller, a data signal driver, a scan signal driver, a light emitting signal driver, and a pixel array, and the pixel array may include a plurality of scan signal lines (S1 to Sm), a plurality of data signal lines (D1 to Dn), a plurality of light emitting signal lines (E1 to Eo), and a plurality of sub-pixels Pxij. In an exemplary embodiment, the timing controller may provide a grayscale value and a control signal suitable for the specification of the data signal driver to the data signal driver, a clock signal suitable for the specification of the scan signal driver, a scan start signal, etc. to the scan signal driver, and a clock signal suitable for the specification of the light emitting signal driver, an emission stop signal, etc. to the light emitting signal driver. The data signal driver may generate a data voltage to be provided to the data signal lines D1, D2, D3, ... and Dn using the grayscale value and the control signal received from the timing controller. For example, the data signal driver may sample the grayscale value using the clock signal, and apply the data voltage corresponding to the grayscale value to the data signal lines D1 to Dn in units of pixel rows, where n may be a natural number. The scan signal driver may generate a scan signal to be provided to the scan signal lines S1, S2, S3, ... and Sm by receiving a clock signal, a scan start signal, etc. from a timing controller. For example, the scan signal driver may sequentially provide a scan signal having an on-level pulse to the scan signal lines S1 to Sm. For example, the scan signal driver may be constructed in the form of a shift register, and may sequentially transmit a scan start signal provided in the form of an on-level pulse to a next-level circuit under the control of a clock signal to generate a scan signal, and m may be a natural number. The luminous signal driver may generate an emission signal to be provided to the luminous signal lines E1, E2, E3, ... and Eo by receiving a clock signal, an emission stop signal, etc. from a timing controller. For example, the luminous signal driver may sequentially provide an emission signal having an off-level pulse to the luminous signal lines E1 to Eo. For example, the luminous signal driver may be constructed in the form of a shift register, and may sequentially transmit a luminous stop signal provided in the form of an off-level pulse to a next-level circuit under the control of a clock signal to generate a luminous signal, and o may be a natural number. The pixel array may include a plurality of sub-pixels Pxij. Each subpixel Pxij may be connected to a corresponding data signal line, a corresponding scan signal line, and a corresponding light emitting signal line, and i and j may be natural numbers. Subpixel Pxij may refer to a subpixel in which a transistor is connected to the i-th scan signal line and to the j-th data signal line.

[0059] Figure 2 FIG. 1 is a schematic diagram of a planar structure of a display device. Figure 2As shown, in a plane parallel to the display device, the display device may include a plurality of pixel units P arranged in a matrix, at least one of the plurality of pixel units P includes a first sub-pixel P1 emitting a first color light, a second sub-pixel P2 emitting a second color light, and a third sub-pixel P3 emitting a third color light, and the first sub-pixel P1, the second sub-pixel P2, and the third sub-pixel P3 each include a pixel driving circuit and a light-emitting device. The pixel driving circuits in the first sub-pixel P1, the second sub-pixel P2, and the third sub-pixel P3 are respectively connected to the scanning signal line, the data signal line, and the light-emitting signal line, and the pixel driving circuit is configured to receive the data voltage transmitted by the data signal line under the control of the scanning signal line and the light-emitting signal line, and output a corresponding current to the light-emitting device. The light-emitting devices in the first sub-pixel P1, the second sub-pixel P2, and the third sub-pixel P3 are respectively connected to the pixel driving circuits of the sub-pixels in which they are located, and the light-emitting devices are configured to emit light of corresponding brightness in response to the current output by the pixel driving circuit of the sub-pixel in which they are located.

[0060] In an exemplary embodiment, the pixel unit P may include a red (R) sub-pixel, a green (G) sub-pixel, and a blue (B) sub-pixel, or may include a red sub-pixel, a green sub-pixel, a blue sub-pixel, and a white sub-pixel, which is not limited in the present disclosure. In an exemplary embodiment, the shape of the sub-pixel in the pixel unit may be rectangular, rhombus, pentagonal, or hexagonal. When the pixel unit includes three sub-pixels, the three sub-pixels may be arranged in horizontal parallel, vertical parallel, or in a herringbone manner. When the pixel unit includes four sub-pixels, the four sub-pixels may be arranged in horizontal parallel, vertical parallel, or in a square manner, which is not limited in the present disclosure.

[0061] In exemplary embodiments, the pixel driving circuit may be a 3T1C, 4T1C, 5T1C, 5T2C, 6T1C, or 7T1C structure. Figure 3 FIG. 1 is a schematic diagram of an equivalent circuit of a pixel driving circuit. Figure 3 As shown, the pixel driving circuit may include 7 transistors (first transistor T1 to seventh transistor T7), 1 storage capacitor C and 7 signal lines (data signal line D, first scanning signal line S1, second scanning signal line S2, light emitting signal line E, initial signal line INIT, first power line VDD and second power line VSS).

[0062] In an exemplary embodiment, a first end of the storage capacitor C is connected to the first power line VDD, and a second end of the storage capacitor C is connected to the second node N2 , ie, the second end of the storage capacitor C is connected to the control electrode of the third transistor T3 .

[0063] The control electrode of the first transistor T1 is connected to the second scan signal line S2, the first electrode of the first transistor T1 is connected to the initial signal line INIT, and the second electrode of the first transistor is connected to the second node N2. When the on-level scan signal is applied to the second scan signal line S2, the first transistor T1 transmits the initialization voltage to the control electrode of the third transistor T3, so that the charge amount of the control electrode of the third transistor T3 is initialized.

[0064] The control electrode of the second transistor T2 is connected to the first scan signal line S1, the first electrode of the second transistor T2 is connected to the second node N2, and the second electrode of the second transistor T2 is connected to the third node N3. When the on-level scan signal is applied to the first scan signal line S1, the second transistor T2 connects the control electrode of the third transistor T3 to the second electrode.

[0065] The control electrode of the third transistor T3 is connected to the second node N2, that is, the control electrode of the third transistor T3 is connected to the second end of the storage capacitor C, the first electrode of the third transistor T3 is connected to the first node N1, and the second electrode of the third transistor T3 is connected to the third node N3. The third transistor T3 can be called a driving transistor, and the third transistor T3 determines the amount of driving current flowing between the first power line VDD and the second power line VSS according to the potential difference between its control electrode and the first electrode.

[0066] The control electrode of the fourth transistor T4 is connected to the first scan signal line S1, the first electrode of the fourth transistor T4 is connected to the data signal line D, and the second electrode of the fourth transistor T4 is connected to the first node N1. The fourth transistor T4 can be called a switching transistor, a scan transistor, etc. When the on-level scan signal is applied to the first scan signal line S1, the fourth transistor T4 enables the data voltage of the data signal line D to be input to the pixel driving circuit.

[0067] The control electrode of the fifth transistor T5 is connected to the light emitting signal line E, the first electrode of the fifth transistor T5 is connected to the first power line VDD, and the second electrode of the fifth transistor T5 is connected to the first node N1. The control electrode of the sixth transistor T6 is connected to the light emitting signal line E, the first electrode of the sixth transistor T6 is connected to the third node N3, and the second electrode of the sixth transistor T6 is connected to the first electrode of the light emitting device. The fifth transistor T5 and the sixth transistor T6 can be called light emitting transistors. When the on-level light emitting signal is applied to the light emitting signal line E, the fifth transistor T5 and the sixth transistor T6 form a driving current path between the first power line VDD and the second power line VSS to make the light emitting device emit light.

[0068] The control electrode of the seventh transistor T7 is connected to the first scan signal line S1, the first electrode of the seventh transistor T7 is connected to the initial signal line INIT, and the second electrode of the seventh transistor T7 is connected to the first electrode of the light emitting device. When the on-level scan signal is applied to the first scan signal line S1, the seventh transistor T7 transmits the initialization voltage to the first electrode of the light emitting device to initialize or release the charge accumulated in the first electrode of the light emitting device.

[0069] In an exemplary embodiment, the second electrode of the light emitting device is connected to the second power line VSS, the signal of the second power line VSS is a low level signal, and the signal of the first power line VDD is a continuously provided high level signal. The first scanning signal line S1 is a scanning signal line in the pixel driving circuit of the current display row, and the second scanning signal line S2 is a scanning signal line in the pixel driving circuit of the previous display row, that is, for the nth display row, the first scanning signal line S1 is S(n), and the second scanning signal line S2 is S(n-1), and the second scanning signal line S2 of the current display row is the same as the first scanning signal line S1 in the pixel driving circuit of the previous display row, which can reduce the signal lines of the display panel and realize the narrow frame of the display panel.

[0070] In an exemplary embodiment, the first transistor T1 to the seventh transistor T7 may be a P-type transistor, or may be an N-type transistor. Using the same type of transistors in the pixel driving circuit can simplify the process flow, reduce the process difficulty of the display panel, and improve the yield of the product. In some possible implementations, the first transistor T1 to the seventh transistor T7 may include a P-type transistor and an N-type transistor.

[0071] In an exemplary embodiment, the first scan signal line S1, the second scan signal line S2, the emission signal line E, and the initial signal line INIT extend in a horizontal direction, and the second power line VSS, the first power line VDD, and the data signal line D extend in a vertical direction.

[0072] In an exemplary embodiment, the light emitting device may be an organic light emitting diode (OLED) including a first electrode (anode), an organic light emitting layer, and a second electrode (cathode) stacked.

[0073] Figure 4 This is a working timing diagram of a pixel driving circuit. Figure 3 The operation process of the pixel driving circuit of the example is described in detail. Figure 3The pixel driving circuit includes 7 transistors (first transistor T1 to sixth transistor T7), 1 storage capacitor C and 7 signal lines (data signal line D, first scanning signal line S1, second scanning signal line S2, light emitting signal line E, initial signal line INIT, first power line VDD and second power line VSS), and all 7 transistors are P-type transistors.

[0074] In an exemplary embodiment, the operation process of the pixel driving circuit may include:

[0075] The first stage A1 is called the reset stage. The signal of the second scanning signal line S2 is a low-level signal, and the signals of the first scanning signal line S1 and the light-emitting signal line E are high-level signals. The signal of the second scanning signal line S2 is a low-level signal, which turns on the first transistor T1. The signal of the initial signal line INIT is provided to the second node N2 to initialize the storage capacitor C and clear the original data voltage in the storage capacitor. The signals of the first scanning signal line S1 and the light-emitting signal line E are high-level signals, which turns off the second transistor T2, the fourth transistor T4, the fifth transistor T5, the sixth transistor T6 and the seventh transistor T7. In this stage, the OLED does not emit light.

[0076] The second stage A2 is called the data writing stage or the threshold compensation stage. The signal of the first scanning signal line S1 is a low level signal, the signals of the second scanning signal line S2 and the light emitting signal line E are high level signals, and the data signal line D outputs the data voltage. In this stage, since the second end of the storage capacitor C is at a low level, the third transistor T3 is turned on. The signal of the first scanning signal line S1 is a low level signal, which turns on the second transistor T2, the fourth transistor T4 and the seventh transistor T7. The second transistor T2 and the fourth transistor T4 are turned on so that the data voltage output by the data signal line D is provided to the second node N2 through the first node N1, the turned-on third transistor T3, the third node N3, and the turned-on second transistor T2, and the difference between the data voltage output by the data signal line D and the threshold voltage of the third transistor T3 is charged into the storage capacitor C. The voltage of the second end (the second node N2) of the storage capacitor C is Vd-|Vth|, Vd is the data voltage output by the data signal line D, and Vth is the threshold voltage of the third transistor T3. The seventh transistor T7 is turned on so that the initial voltage of the initial signal line INIT is provided to the first electrode of the OLED, the first electrode of the OLED is initialized (reset), the pre-stored voltage inside it is cleared, the initialization is completed, and the OLED is ensured not to emit light. The signal of the second scanning signal line S2 is a high-level signal, which turns off the first transistor T1. The signal of the light-emitting signal line E is a high-level signal, which turns off the fifth transistor T5 and the sixth transistor T6.

[0077] The third stage A3 is called the light-emitting stage, the signal of the light-emitting signal line E is a low-level signal, and the signals of the first scanning signal line S1 and the second scanning signal line S2 are high-level signals. The signal of the light-emitting signal line E is a low-level signal, which turns on the fifth transistor T5 and the sixth transistor T6, and the power supply voltage output by the first power supply line VDD provides a driving voltage to the first electrode of the OLED through the turned-on fifth transistor T5, the third transistor T3 and the sixth transistor T6, driving the OLED to emit light.

[0078] During the driving process of the pixel driving circuit, the driving current flowing through the third transistor T3 (driving transistor) is determined by the voltage difference between its gate electrode and the first electrode. Since the voltage of the second node N2 is Vdata-|Vth|, the driving current of the third transistor T3 is:

[0079] I=K*(Vgs-Vth) 2 =K*[(Vdd-Vd+|Vth|)-Vth] 2 =K*[(Vdd-Vd] 2

[0080] Among them, I is the driving current flowing through the third transistor T3, that is, the driving current driving the OLED, K is a constant, Vgs is the voltage difference between the gate electrode and the first electrode of the third transistor T3, Vth is the threshold voltage of the third transistor T3, Vd is the data voltage output by the data signal line D, and Vdd is the power supply voltage output by the first power supply line VDD.

[0081] Figure 5 FIG. 1 is a schematic diagram of a cross-sectional structure of a display device, illustrating the structure of three sub-pixels of an OLED display device. Figure 5 As shown, on a plane perpendicular to the display device, the display device may include a driving circuit layer 102 disposed on a substrate 101, a light emitting structure layer 103 disposed on a side of the driving circuit layer 102 away from the substrate 101, and an encapsulation layer 104 disposed on a side of the light emitting structure layer 103 away from the substrate 101. In some possible implementations, the display device may include other film layers, such as spacers, etc., which are not limited in the present disclosure.

[0082] In an exemplary embodiment, the substrate may be a flexible substrate or a rigid substrate. The flexible substrate may include a first flexible material layer, a first inorganic material layer, a semiconductor layer, a second flexible material layer, and a second inorganic material layer stacked together. The materials of the first flexible material layer and the second flexible material layer may be polyimide (PI), polyethylene terephthalate (PET), or a surface-treated polymer soft film, etc. The materials of the first inorganic material layer and the second inorganic material layer may be silicon nitride (SiNx) or silicon oxide (SiOx), etc., for improving the water and oxygen resistance of the substrate. The material of the semiconductor layer may be amorphous silicon (a-si), polycrystalline silicon (p-si), or oxide (Oxide).

[0083] In an exemplary embodiment, the driving circuit layer 102 of each sub-pixel may include a plurality of transistors and storage capacitors constituting a pixel driving circuit. Figure 5 Only one driving transistor and one storage capacitor are used as examples for illustration. In some possible implementations, the driving circuit layer 102 of each sub-pixel may include: a first insulating layer disposed on a substrate; an active layer disposed on the first insulating layer; a second insulating layer covering the active layer; a gate electrode and a first capacitor electrode disposed on the second insulating layer; a third insulating layer covering the gate electrode and the first capacitor electrode; a second capacitor electrode disposed on the third insulating layer; a fourth insulating layer covering the second capacitor electrode, the second insulating layer, the third insulating layer and the fourth insulating layer having vias, the vias exposing the active layer; a source electrode and a drain electrode disposed on the fourth insulating layer, the source electrode and the drain electrode being connected to the active layer through the vias respectively; a flat layer covering the aforementioned structure, the flat layer having vias, the vias exposing the drain electrode. The active layer, the gate electrode, the source electrode and the drain electrode constitute a transistor 210, and the first capacitor electrode and the second capacitor electrode constitute a storage capacitor 211.

[0084] In an exemplary embodiment, the light emitting structure layer 103 includes a light emitting device that makes an organic material emit light under the action of an electric field, and the light emitting structure layer 103 may include an anode 301, a pixel definition layer 302, an organic light emitting layer 303, and a cathode 304. The anode 301 is disposed on the planar layer 205, and is connected to the drain electrode of the driving transistor 210 through a via hole opened on the planar layer 205; the pixel definition layer 302 is disposed on the anode 301 and the planar layer 205, and a pixel opening is disposed on the pixel definition layer 302, and the pixel opening exposes the anode 301; the organic light emitting layer 303 is at least partially disposed in the pixel opening, and the organic light emitting layer 303 is connected to the anode 301; the cathode 304 is disposed on the organic light emitting layer 303, and the cathode 304 is connected to the organic light emitting layer 303; the organic light emitting layer 303 emits light of corresponding colors under the drive of the anode 301 and the cathode 304.

[0085] In an exemplary embodiment, the encapsulation layer 104 may include a stacked first encapsulation layer 401, a second encapsulation layer 402 and a third encapsulation layer 403. The first encapsulation layer 401 and the third encapsulation layer 403 may be made of inorganic materials, the second encapsulation layer 402 may be made of organic materials, and the second encapsulation layer 402 is arranged between the first encapsulation layer 401 and the third encapsulation layer 403 to ensure that external water vapor cannot enter the light-emitting structure layer 103.

[0086] In an exemplary embodiment, the organic light-emitting layer of the OLED light-emitting device may include an emitting layer (Emitting Layer, referred to as EML), and any one or more of the following: a hole injection layer (HIL), a hole transport layer (HTL), a hole blocking layer (HBL), an electron blocking layer (EBL), an electron injection layer (EIL), and an electron transport layer (ETL). Under the voltage drive of the anode and the cathode, the light-emitting properties of the organic material are used to emit light as needed.

[0087] In an exemplary embodiment, the light-emitting layers of OLED light-emitting devices of different colors are different. For example, a red light-emitting device includes a red light-emitting layer, a green light-emitting device includes a green light-emitting layer, and a blue light-emitting device includes a blue light-emitting layer. In order to reduce the process difficulty and improve the yield, the hole injection layer and the hole transport layer on one side of the light-emitting layer can use a common layer, and the electron injection layer and the electron transport layer on the other side of the light-emitting layer can use a common layer. In an exemplary embodiment, any one or more of the hole injection layer, the hole transport layer, the electron injection layer, and the electron transport layer can be made by a single process (a single evaporation process or a single inkjet printing process), but isolation is achieved by means of a surface step difference of the formed film layer or by surface treatment. For example, any one or more of the hole injection layer, the hole transport layer, the electron injection layer, and the electron transport layer corresponding to adjacent sub-pixels can be isolated. In an exemplary embodiment, the organic light-emitting layer can be prepared by an evaporation process or an inkjet process.

[0088] As the market requires products with higher and higher resolutions, higher and higher brightness of independent sub-pixels, and lower and lower power consumption, higher requirements are placed on the light extraction efficiency and brightness of the light-emitting devices in the display device. According to the different light-emitting positions, OLED display devices can be divided into bottom-emitting OLED and top-emitting OLED. Although top-emitting OLED has the characteristics of improved luminous efficiency and increased color purity, and has a significant enhancement effect on the display effect, it also has losses such as internal optical waveguides, surface plasmons, and non-radiative dissipation, which reduce the light extraction efficiency. In an OLED display device, in order to enhance the light extraction efficiency of the device, an external light extraction structure is usually provided, for example, a light output coupling layer is provided on the translucent cathode, or a layer of high refractive index dielectric is provided on the surface of the translucent cathode.

[0089] Figure 6 FIG. 1 is a schematic diagram of a light emitting device according to an exemplary embodiment of the present disclosure. Figure 6 As shown, the light emitting device is an organic electroluminescent device, which may include an anode 10, a cathode 90, and an organic light emitting layer disposed between the anode 10 and the cathode 90. In an exemplary embodiment, the organic light emitting layer may include a stacked light emitting layer (EML) 50 and an electron transport layer (ETL) 70, and the electron transport layer 70 is disposed between the light emitting layer 50 and the cathode 90. In an exemplary embodiment, the light emitting layer 50 is configured to cause electrons and holes to recombine and emit light, and the electron transport layer 70 is configured to achieve directional and orderly controllable migration of injected electrons.

[0090] In an exemplary embodiment, the electron transport layer may include at least a first host material and a second host material, and along the direction from the light emitting layer 50 to the cathode 90, the mass percentage of the first host material in the electron transport layer gradually decreases, and the mass percentage of the second host material in the electron transport layer gradually increases. In an exemplary embodiment, the first host material and the second host material may satisfy:

[0091] N1>N2;

[0092] Wherein, N1 is the refractive index of the first host material, and N2 is the refractive index of the second host material. For example, the refractive index N1 of the first host material may be approximately 1.8 (@460 nm), and the refractive index N2 of the second host material may be approximately 1.6 (@460 nm).

[0093] In an exemplary embodiment, the refractive index of a material may be measured using an ellipsometer, and @460nm represents the refractive index measured at a wavelength of 460nm.

[0094] In exemplary embodiments, the electron transport layer may have a refractive index of about 1.80 to about 2.00 at a first side of the electron transport layer close to the light emitting layer.

[0095] In exemplary embodiments, at a second side of the electron transport layer away from the light emitting layer (close to the cathode), the refractive index of the electron transport layer may be about 1.55 to 1.70.

[0096] In exemplary embodiments, the electron transport layer may have a thickness of about 20 nm to 50 nm.

[0097] In an exemplary embodiment, the first host material and the second host material may include, but are not limited to, the following materials: 8-hydroxyquinoline aluminum (Alq3), 4,7-diphenyl-1,10-phenanthroline (BPhen), 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBI).

[0098] In an exemplary embodiment, the first host material and the second host material can be co-evaporated so that the first host material and the second host material are uniformly dispersed in the electron transport layer, and the mixing ratio can be regulated by controlling the evaporation rate of the first host material and the evaporation rate of the second host material during the evaporation process. For example, during the evaporation process, the evaporation rate of the first host material is controlled to be about Control the evaporation rate of the second host material to be approximately The mass percentage of the first main material in the electron transport layer is about 30%, and the mass percentage of the second main material in the electron transport layer is about 70%.

[0099] In an OLED structure, the refractive index of the electron transport layer is usually fixed. When a light wave (electromagnetic wave) is incident on the interface between the metal and the dielectric, the free electrons on the metal surface collectively oscillate, and the electromagnetic wave couples with the free electrons on the metal surface to form a near-field electromagnetic wave that propagates along the metal surface. If the oscillation frequency of the electrons is consistent with the frequency of the incident light wave, resonance will occur. In the resonant state, the energy of the electromagnetic field is effectively converted into the collective vibration energy of the free electrons on the metal surface. At this time, a special electromagnetic mode is formed: the electromagnetic field is confined to a very small range on the metal surface and is enhanced. This phenomenon is called the surface plasmon polariton (SPP) effect, which will lead to a decrease in the efficiency of the emitted light. In order to reduce the surface plasmon phenomenon between the electron transport layer and the cathode to reduce light loss, the electron transport layer needs to use a material with a smaller refractive index. However, the reflection effect of the film layer between the electron transport layer and the light-emitting layer with a smaller refractive index is low, which reduces the microcavity effect of the overall device and reduces the light extraction efficiency of the light-emitting device. In order to improve the reflection effect of the film layer between the electron transport layer and the light-emitting layer, the electron transport layer needs to use a material with a larger refractive index. However, the surface plasmon phenomenon between the electron transport layer with a larger refractive index and the cathode is serious, the light loss increases, and the light extraction efficiency of the light-emitting device is reduced. The electron transport layer of the exemplary embodiment of the present disclosure is formed by mixing the first main material and the second main material with different refractive indices, and the mixing ratio of the first main material and the second main material at different positions is different. The refractive index of the electron transport layer close to the light-emitting layer is greater than the refractive index of the electron transport layer far from the light-emitting layer, which maximizes the reasonable matching of the refractive index in the multi-film layer system, optimizes the optical performance of the light-emitting device, effectively improves the coupling light extraction efficiency inside the light-emitting device, and is more conducive to exerting the light extraction characteristics of the device.

[0100] In the exemplary embodiments of the present disclosure, by reducing the refractive index of the electron transport layer on the side away from the light-emitting layer, the surface plasmon phenomenon between the electron transport layer and the cathode is effectively reduced, and the light loss is reduced. By increasing the refractive index of the electron transport layer on the side close to the light-emitting layer, the film reflection effect between the electron transport layer and the light-emitting layer is effectively improved, and the microcavity effect of the overall device is enhanced. Therefore, the exemplary embodiments of the present disclosure maximize the reasonable matching of the refractive index in the multi-film system, optimize the optical performance of the light-emitting device, effectively improve the coupling light extraction efficiency inside the light-emitting device, and are more conducive to the light extraction characteristics of the device.

[0101] In an exemplary embodiment, the light emitting layer may be a red light emitting layer, a green light emitting layer, or a blue light emitting layer. By improving the light emitting efficiency of the red light emitting layer, the green light emitting layer, and the blue light emitting layer, the overall performance of the light emitting device may be improved.

[0102] Figure 7 FIG. 1 is a schematic diagram of another light emitting device according to an exemplary embodiment of the present disclosure. Figure 7 As shown, the light emitting device is an organic electroluminescent device, which may include an anode 10, a cathode 90, and an organic light emitting layer disposed between the anode 10 and the cathode 90. In an exemplary embodiment, the organic light emitting layer may include a stacked hole injection layer 20, a hole transport layer 30, an electron blocking layer 40, a light emitting layer 50, a hole blocking layer 60, an electron transport layer 70, and an electron injection layer 80. The hole injection layer 20, the hole transport layer 30, and the electron blocking layer 40 are disposed between the anode 10 and the light emitting layer 50, the hole injection layer 20 is connected to the anode 10, the electron blocking layer 40 is connected to the light emitting layer 50, and the hole transport layer 30 is disposed between the hole injection layer 20 and the electron blocking layer 40. The hole blocking layer 60, the electron transport layer 70, and the electron injection layer 80 are disposed between the light emitting layer 50 and the cathode 90, the hole blocking layer 60 is connected to the light emitting layer 50, the electron injection layer 80 is connected to the cathode 90, and the electron transport layer 70 is disposed between the electron injection layer 80. In an exemplary embodiment, the hole injection layer 20 is configured to reduce the barrier for injecting holes from the anode so that the holes can be effectively injected from the anode into the light-emitting layer 50. The hole transport layer 30 is configured to achieve a directional, orderly, and controllable migration of the injected holes. The electron blocking layer 40 is configured to form a migration barrier for the electrons, preventing the electrons from migrating out of the light-emitting layer 50. The light-emitting layer 50 is configured to emit light by allowing electrons and holes to recombine. The hole blocking layer 60 is configured to form a migration barrier for the holes, preventing the holes from migrating out of the light-emitting layer 50. The electron transport layer 70 is configured to achieve a directional, orderly, and controllable migration of the injected electrons. The electron injection layer 80 is configured to reduce the barrier for injecting electrons from the cathode so that the electrons can be effectively injected from the cathode into the light-emitting layer 50.

[0103] In an exemplary embodiment, the material and structure of the electron transport layer 70 are the same as or similar to those of the aforementioned embodiments, and the refractive index of the electron transport layer 70 on the side of the electron transport layer 70 close to the hole blocking layer 60 may be approximately 1.80 to 2.00, and the refractive index of the electron transport layer 70 on the side of the electron transport layer 70 close to the electron injection layer 80 may be approximately 1.55 to 1.70.

[0104] In an exemplary embodiment, the anode may be made of a metal or metal oxide material with a high work function. For a bottom emission type, the anode may be made of a transparent oxide material, such as indium tin oxide (ITO) or indium zinc oxide (IZO), and the thickness of the anode may be about 80nm to 200nm. For a top emission type, the anode may be made of a metal material, such as silver (Ag), gold (Au) or their alloys, or a composite structure of a metal and a transparent oxide, such as Ag / ITO, Ag / IZO or ITO / Ag / ITO, etc., the thickness of the metal layer in the anode may be about 80nm to 100nm, and the thickness of the transparent oxide in the anode may be about 5nm to 20nm, so that the average reflectivity of the anode in the visible light region is about 85% to 95%, playing the role of a fully reflective anode.

[0105] In an exemplary embodiment, for a top-emitting OLED, the cathode may be made of a metal material formed by an evaporation process, and the metal material may be magnesium (Mg), silver (Ag) or aluminum (Al), or an alloy material, such as an alloy of Mg:Ag, with a ratio of Mg:Ag of about 9:1 to 1:9, and the thickness of the cathode may be about 10 nm to 20 nm, so that the average transmittance of the cathode at a wavelength of 530 nm is about 50% to 60%, playing a semi-transparent and semi-reflective role. For a bottom-emitting OLED, the cathode may be made of magnesium (Mg), silver (Ag), aluminum (Al) or an alloy of Mg:Ag, and the thickness of the cathode may be about greater than 80 nm, so that the cathode has good reflectivity and plays a role of a fully reflective cathode.

[0106] In an exemplary embodiment, the hole injection layer may be made of an inorganic oxide, such as molybdenum oxide, titanium oxide, vanadium oxide, rhenium oxide, ruthenium oxide, chromium oxide, zirconium oxide, hafnium oxide, tantalum oxide, silver oxide, tungsten oxide or manganese oxide, or may be made of a p-type dopant of a strong electron-withdrawing system and a dopant of a hole transport material, such as hexacyanohexaazatriphenylene, 2,3,5,6-tetrafluoro-7,7',8,8'-tetracyanoquinodimethane (F4-TCNQ), or 1,2,3-tris[(cyano)(4-cyano-2,3,5,6-tetrafluorophenyl)methylene]cyclopropane, etc.

[0107] In exemplary embodiments, the hole injection layer may have a thickness of about 5 nm to 20 nm.

[0108] In an exemplary embodiment, the hole transport layer and the electron blocking layer may be made of aromatic amine or carbazole materials having a relatively high hole mobility, such as 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB), N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (TPD), 4-phenyl-4'-(9-phenylfluorene-9-yl)triphenylamine (BAFLP), 4,4'-bis[N-(9,9-dimethylfluorene-2-yl)-N-phenylamino]biphenyl (DFLDPBi), 4,4'-di(9-carbazolyl)biphenyl (CBP), or 9-phenyl-3-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (PCzPA).

[0109] In an exemplary embodiment, the thickness of the hole transport layer may be about 100 nm to 150 nm, and the thickness of the electron blocking layer may be about 5 nm to 20 nm, which play a role in adjusting the length of the microcavity and improving the light extraction performance of the light emitting device.

[0110] In an exemplary embodiment, the light-emitting layer material can be an organic small molecule material or a quantum dot material, including but not limited to oxadiazole and its derivatives, triazole and its derivatives, rhodamine and its derivatives, 1,8-naphthalimide derivatives, pyrazoline derivatives, triphenylamine derivatives, CdSe / ZnS, PbS quantum dots, etc.

[0111] In an exemplary embodiment, the light-emitting layer material may include one material, or may include a mixture of two or more materials. The light-emitting material is divided into a blue light-emitting material, a green light-emitting material, and a red light-emitting material. The blue light-emitting material may be selected from pyrene derivatives, anthracene derivatives, fluorene derivatives, perylene derivatives, styrylamine derivatives, or metal complexes. For example, N1,N6-di([1,1'-biphenyl]-2-yl)-N1,N6-di([1,1'-biphenyl]-4-yl)pyrene-1,6-diamine, 9,10-di-(2-naphthyl)anthracene (ADN), 2-methyl-9,10-di-2-naphthylanthracene (MADN), 2,5,8,11-tetra-tert-butylperylene (TBPe), 4,4'-bis[4-(diphenylamino)phenylvinyl]biphenyl (BDAV Bi), 4,4'-bis[4-(di-p-tolylamino)phenylvinyl]biphenyl (DPAVBi), and bis(4,6-difluorophenylpyridine-C2,N)picolinyliridium (FIrpic).

[0112] Green luminescent materials can be selected from coumarin dyes, quinacridone copper derivatives, polycyclic aromatic hydrocarbons, diamine anthracene derivatives, carbazole derivatives or metal complexes. For example, coumarin 6 (C-6), coumarin 545T (C-525T), quinacridone copper (QA), N, N'-dimethylquinacridone (DMQA), 5,12-diphenylnaphthonaphthalene (DPT), N10, N10'-diphenyl-N10, N10'-diphthaloyl-9,9'-dianthracene-10,10'-diamine (referred to as BA-NPB), tris (8-hydroxyquinoline) aluminum (III) (referred to as Alq3), tris (2-phenylpyridine) iridium (Ir (ppy) 3), acetylacetonate di (2-phenylpyridine) iridium (Ir (ppy) 2 (acac)). Red luminescent materials can be selected from DCM series materials or metal complexes. For example, 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminophenylvinyl)-4H-pyran (DCM), 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidine-9-enyl)-4H-pyran (DCJTB), bis(1-phenylisoquinoline)(acetylacetonate)iridium(III) (Ir(piq)2(acac)), octaethylporphyrin platinum (PtOEP for short), bis(2-(2'-benzothienyl)pyridine-N,C3')(acetylacetonate)iridium (Ir(btp)2(acac for short), etc.

[0113] In an exemplary embodiment, the light-emitting layer including two or more mixed materials may include a host material and a guest material, and the doping ratio of the guest material is 1% to 20%. Within the doping ratio range, the host material can effectively transfer the exciton energy to the guest material to excite the guest material to emit light, and the host material "dilutes" the guest material, which can effectively improve the mutual collision between guest material molecules and the fluorescence quenching caused by the mutual collision between energy, thereby improving the luminous efficiency and device life.

[0114] In the exemplary embodiments of the present disclosure, the doping ratio refers to the ratio of the mass of the guest material to the mass of the light-emitting layer, that is, the mass percentage. In the exemplary embodiment, the host material and the guest material can be co-evaporated by a multi-source evaporation process so that the host material and the guest material are uniformly dispersed in the light-emitting layer, and the doping ratio can be regulated by controlling the evaporation rate of the guest material during the evaporation process, or by controlling the evaporation rate ratio of the host material to the guest material.

[0115] In an exemplary embodiment, the thickness of the light emitting layer 50 may be about 10 nm to 25 nm.

[0116] In an exemplary embodiment, the hole blocking layer can be made of aromatic heterocyclic compounds, such as imidazole derivatives such as benzimidazole derivatives, imidazopyridine derivatives, and benzimidazolephenanthridine derivatives; oxazine derivatives such as pyrimidine derivatives and triazine derivatives; quinoline derivatives, isoquinoline derivatives, phenanthroline derivatives, and the like containing nitrogen-containing six-membered ring structures (including compounds having phosphine oxide-based substituents on the heterocyclic ring), etc. For example, 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene (OXD-7), 3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenyl)-1,2,4-triazole (TAZ), 3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenyl)-1,2,4-triazole (p-EtTAZ), bathophenanthroline (BPhen), bathocuproin (BCP) or 4,4'-bis(5-methylbenzoxazol-2-yl)stilbene (BzOs), etc.

[0117] In exemplary embodiments, the hole blocking layer may have a thickness of about 5 nm to about 15 nm.

[0118] In an exemplary embodiment, the electron injection layer may be made of an alkali metal or metal, such as lithium fluoride (LiF), ytterbium (Yb), magnesium (Mg), or calcium (Ca), or a compound of these alkali metals or metals.

[0119] In exemplary embodiments, the electron injection layer may have a thickness of about 0.5 nm to 2 nm.

[0120] In an exemplary embodiment, for a top emission type OLED, the thickness of the organic light emitting layer between the cathode and the anode can be designed to meet the optical path requirement of the optical microresonant cavity to obtain the optimal light output intensity and color.

[0121] In an exemplary embodiment, the organic electroluminescent device can be applied to a display substrate in which an OLED is used as a light emitting device and a thin film transistor (TFT) is used for signal control. In an exemplary embodiment, the display substrate including the OLED can be prepared by the following preparation method.

[0122] First, a driving circuit layer is formed on a substrate through a patterning process. The driving circuit layer of each sub-pixel may include a driving transistor and a storage capacitor constituting a pixel driving circuit.

[0123] Subsequently, a planar layer is formed on the substrate having the aforementioned structure, and a via hole exposing the drain electrode of the driving transistor is formed on the planar layer of each sub-pixel.

[0124] Subsequently, an anode is formed on the substrate having the aforementioned structure by a patterning process, and the anode of each sub-pixel is connected to the drain electrode of the driving transistor through a via hole on the planar layer.

[0125] Subsequently, a pixel definition layer is formed on the substrate having the aforementioned structure by a patterning process, and a pixel opening exposing the anode is formed on the pixel definition layer of each sub-pixel, and each pixel opening serves as a light emitting region of each sub-pixel.

[0126] Subsequently, on the substrate formed with the aforementioned structure, an open mask is first used to sequentially evaporate a hole injection layer and a hole transport layer, and a common layer of the hole injection layer and the hole transport layer is formed on the organic electroluminescent device, that is, the hole injection layers of all sub-pixels are connected, and the hole transport layers of all sub-pixels are connected. For example, the areas of the hole injection layer and the hole transport layer are roughly the same, but the thicknesses are different.

[0127] Subsequently, a fine metal mask (FMM) is used to evaporate the electron blocking layer and the red light-emitting layer, the electron blocking layer and the green light-emitting layer, and the electron blocking layer and the blue light-emitting layer on different sub-pixels respectively. The electron blocking layer and the light-emitting layer of adjacent sub-pixels may have a small amount of overlap (for example, the overlapping portion occupies less than 10% of the area of ​​the respective light-emitting layer patterns), or may be isolated.

[0128] Subsequently, an open mask is used to sequentially evaporate a hole blocking layer, an electron transport layer, an electron injection layer and a cathode to form a common layer of the hole blocking layer, the electron transport layer, the electron injection layer and the cathode on the organic electroluminescent device, that is, the hole blocking layers of all sub-pixels are connected, the electron transport layers of all sub-pixels are connected, the electron injection layers of all sub-pixels are connected, and the cathodes of all sub-pixels are connected.

[0129] In an exemplary embodiment, since the electron transport layer is a common layer and the light emitting layers of different sub-pixels are isolated, the orthographic projection of the electron transport layer on the substrate includes the orthographic projection of the light emitting layer on the substrate, and the area of ​​the electron transport layer is larger than that of the light emitting layer.

[0130] In an exemplary embodiment, since the electron transport layer is a common layer, the orthographic projection of the electron transport layer on the substrate includes at least the orthographic projections of the light emitting regions of the two sub-pixels on the substrate.

[0131] In an exemplary embodiment, the positive projection of one or more layers of the hole injection layer, the hole transport layer, the hole blocking layer, the electron transport layer, the electron injection layer, and the cathode on the substrate is continuous. In some examples, at least one layer of the hole injection layer, the hole transport layer, the hole blocking layer, the electron transport layer, the electron injection layer, and the cathode of at least one row or column of sub-pixels is connected. In some examples, at least one layer of the hole injection layer, the hole transport layer, the hole blocking layer, the electron transport layer, the electron injection layer, and the cathode of multiple sub-pixels is connected.

[0132] In an exemplary embodiment, the organic light-emitting layer may include a microcavity adjustment layer between the hole transport layer and the light-emitting layer. For example, after forming the hole transport layer, a fine metal mask may be used to evaporate a red microcavity adjustment layer and a red light-emitting layer, a green microcavity adjustment layer and a green light-emitting layer, and a blue microcavity adjustment layer and a blue light-emitting layer in different sub-pixels. In an exemplary embodiment, the red microcavity adjustment layer, the green microcavity adjustment layer, and the blue microcavity adjustment layer may include an electron blocking layer.

[0133] In an exemplary embodiment, the orthographic projection of the light emitting layer of at least part of the sub-pixels on the substrate overlaps with the orthographic projection of the light emitting layer driven by the pixel driving circuit on the substrate.

[0134] In an exemplary embodiment, the electron transport layer can be evaporated by multi-source co-evaporation to form an electron transport layer including a first main material and a second main material. The mixing ratio can be regulated by controlling the evaporation rate of the first main material and the evaporation rate of the second main material during the evaporation process.

[0135] In an exemplary embodiment, on the side of the electron transport layer close to the light-emitting layer, the mass percentage of the first host material in the electron transport layer is 60% to 80%, and the mass percentage of the second host material in the electron transport layer is 20% to 40%. For example, on the side of the electron transport layer close to the light-emitting layer, the mass percentage of the first host material in the electron transport layer is 70%, and the mass percentage of the second host material in the electron transport layer is 30%.

[0136] In an exemplary embodiment, on the side of the electron transport layer away from the light-emitting layer, the mass percentage of the first host material in the electron transport layer is 0 to 10%, and the mass percentage of the second host material in the electron transport layer is 90 to 100%. For example, on the side of the electron transport layer away from the light-emitting layer, the mass percentage of the second host material in the electron transport layer is 100%.

[0137] In an exemplary embodiment, the electron transport layer may be evaporated in the following manner: from the beginning of evaporation to the end of evaporation, the evaporation rate of the first host material gradually decreases, and the evaporation rate of the second host material gradually increases. For example, at the beginning of evaporation, the evaporation rate of the first host material is Then the evaporation rate gradually decreased. At the end of the evaporation, the evaporation rate was When the evaporation starts, the evaporation rate of the second main material is Then the evaporation rate gradually increased. At the end of the evaporation, the evaporation rate was Thus, on the side close to the light-emitting layer, the mass percentage of the first host material in the electron transport layer is about 60%, and the mass percentage of the second host material is about 40%; on the side away from the light-emitting layer, the mass percentage of the first host material in the electron transport layer is about 10%, and the mass percentage of the second host material is about 90%. For another example, at the beginning of evaporation, the evaporation rate of the first host material is Then the evaporation rate gradually decreased, and at the end of evaporation, the evaporation rate was 0. At the beginning of evaporation, the evaporation rate of the second main material was Then the evaporation rate gradually increased. At the end of the evaporation, the evaporation rate was In this way, on the side close to the light-emitting layer, the mass percentage of the first host material in the electron transport layer is about 80%, and the mass percentage of the second host material is about 20%; on the side away from the light-emitting layer, the mass percentage of the first host material in the electron transport layer is about 0, and the mass percentage of the second host material is about 100%.

[0138] In an exemplary embodiment, the decreasing method and degree of the evaporation rate of the first main material, and the increasing method and degree of the evaporation rate of the second main material can be set according to actual conditions, such as using continuous decrease or continuous increase, or using step decrease or step increase, which is not limited in the present disclosure.

[0139] Table 1 shows the refractive index of the electron transport layer at different mixing ratios at a wavelength of 460nm. As shown in Table 1, when the electron transport layer only contains the second main material (the ratio of the first main material to the second main material is approximately 0%:100%), the refractive index of the electron transport layer is low, only about 1.65. By mixing with the first main material with a high refractive index, the refractive index of the electron transport layer can be increased. As the mass percentage of the first main material increases, the refractive index of the electron transport layer gradually increases. When the ratio of the first main material to the second main material in the electron transport layer is approximately 70%:30%, the refractive index of the electron transport layer can reach 1.95, and the refractive index of the electron transport layer increases by about 18%. Among them, at a wavelength of 460nm, the refractive index of the first main material is about 2.05.

[0140] Table 1: Refractive index of the electron transport layer with different mixing ratios at a wavelength of 460nm

[0141] First main material: Second main material Refractive index (wavelength 460nm) 0％:100％ 1.65 30％:70％ 1.79 50％:50％ 1.87 70％:30％ 1.95

[0142] Table 2 shows the refractive index of the electron transport layer at different mixing ratios at a wavelength of 530nm. As shown in Table 2, when the electron transport layer only contains the second main material, the refractive index of the electron transport layer is low, only about 1.62. By mixing with the first main material with a high refractive index, the refractive index of the electron transport layer can be increased. As the mass percentage of the first main material increases, the refractive index of the electron transport layer gradually increases. When the ratio of the first main material to the second main material in the electron transport layer is about 70%:30%, the refractive index of the electron transport layer can reach 1.91, and the refractive index of the electron transport layer increases by about 18%. Among them, at a wavelength of 530nm, the refractive index of the first main material is about 2.0.

[0143] Table 2: Refractive index of the electron transport layer with different mixing ratios at a wavelength of 530nm

[0144]

[0145]

[0146] Table 3 shows the refractive index of the electron transport layer at different mixing ratios at a wavelength of 620nm. As shown in Table 3, when the electron transport layer only contains the second main material, the refractive index of the electron transport layer is low, only about 1.60. By mixing with the first main material with a high refractive index, the refractive index of the electron transport layer can be increased. As the mass percentage of the first main material increases, the refractive index of the electron transport layer gradually increases. When the ratio of the first main material to the second main material in the electron transport layer is about 70%:30%, the refractive index of the electron transport layer can reach 1.86, and the refractive index of the electron transport layer increases by about 16%. Among them, at a wavelength of 620nm, the refractive index of the first main material is about 1.96.

[0147] Table 3: Refractive index of the electron transport layer with different mixing ratios at a wavelength of 620nm

[0148] First main material: Second main material Refractive index (wavelength 620nm) 0％:100％ 1.60 30％:70％ 1.69 50％:50％ 1.81 70％:30％ 1.86

[0149] In an exemplary embodiment, when the electron transport layer is first evaporated, the evaporation rate of the first host material may be set to 70% E MAX , the evaporation rate of the second host material is set to 30%E MAX The ratio of the first host material to the second host material in the evaporated electron transport layer is about 70%:30%, so that the side of the electron transport layer close to the light-emitting layer has a higher refractive index. Subsequently, the evaporation rate of the first host material can be gradually reduced, and the evaporation rate of the second host material can be gradually increased. When the evaporation of the electron transport layer is completed, the evaporation rate of the first host material becomes 0, and the evaporation rate of the second host material becomes E MAXThe ratio of the first main material to the second main material in the evaporated electron transport layer is approximately 0%:100%, so that the electron transport layer has a lower refractive index on the side close to the cathode.

[0150] In an exemplary embodiment, the display substrate may include a red sub-pixel emitting red light, a green sub-pixel emitting green light, and a blue sub-pixel emitting blue light. Since the electron transport layer is a common layer, the electron transport layer has different refractive indices in the regions where the red sub-pixel, the green sub-pixel, and the blue sub-pixel are located.

[0151] In an exemplary embodiment, the electron transport layer has a maximum red light refractive index n in the wavelength range of 600 nm to 640 nm. RMAX , with a maximum green light refractive index n in the wavelength range of 510nm to 550nm GMAX , with a maximum blue light refractive index n in the wavelength range of 440nm to 480nm BMAX In an exemplary embodiment, the electron transport layer may satisfy:

[0152] │n BMAX -n GMAX │≤0.4,│n BMAX -n RMAX │≤0.8.

[0153] In an exemplary embodiment, the electron transport layer has a minimum red light refractive index n in the wavelength range of 600 nm to 640 nm. RMIN , with a minimum green light refractive index n in the wavelength range of 510nm to 550nm GMIN , with a minimum blue light refractive index n in the wavelength range of 440nm to 480nm BMIN In an exemplary embodiment, the electron transport layer may satisfy:

[0154] │n BMIN -n GMIN │≤0.5,│n BMIN -n RMIN │≤1.0.

[0155] In an exemplary embodiment, the maximum refractive index position in the electron transport layer is located on the side of the electron transport layer close to the light emitting layer, and the minimum refractive index position in the electron transport layer is located on the side of the electron transport layer far from the light emitting layer.

[0156] The exemplary embodiment of the present disclosure sets the refractive index relationship of the electron transport layer at different wavelengths so that the refractive index difference of the electron transport layer within the range of the red sub-pixel, the green sub-pixel and the blue sub-pixel is small. At the same thickness, the difference in the electron transport layer's influence on the microcavity effect is small, and the influence of the electron transport layer on the red light output efficiency, the green light output efficiency and the blue light output efficiency can be relatively balanced. The three colors of red, green and blue light can be optimized at the same time, thereby maximizing the overall light output efficiency and light output quality.

[0157] Tables 4 and 5 are the results of comparative experiments. In the comparative experiments, the organic light-emitting layers of comparative structures 1 to 3 are all HIL / HTL / EBL / EML / HBL / ETL / EIL, the hole injection layer HIL, the hole transport layer HTL, the electron blocking layer EBL, the light-emitting layer EML, the hole blocking layer HBL and the hole injection layer EIL in the above structures are of the same material and thickness, and the thickness of the electron transport layer ETL in the above structures is the same.

[0158] Table 4 shows the mixing conditions of the electron transport layer in each comparative structure of the exemplary embodiment of the present disclosure. As shown in Table 4, in the electron transport layer of comparative structure 1, the proportion of the second host material in the electron transport layer is 100%, and the refractive index in the electron transport layer is constant along the direction from the light-emitting layer to the cathode. In the electron transport layer of comparative structure 2, on the side close to the light-emitting layer, the proportion of the first host material in the electron transport layer is 30%, and the proportion of the second host material in the electron transport layer is 70%; on the side away from the light-emitting layer, the proportion of the second host material in the electron transport layer is 100%. In the electron transport layer of comparative structure 3, on the side close to the light-emitting layer, the proportion of the first host material in the electron transport layer is 70%, and the proportion of the second host material in the electron transport layer is 30%; on the side away from the light-emitting layer, the proportion of the second host material in the electron transport layer is 100%.

[0159] Table 4: Electron transport layers in comparative structures

[0160]

[0161] Table 5 is a comparison result of light extraction efficiency of comparative structures of exemplary embodiments of the present disclosure. Figure 8 The light extraction efficiency comparison results of the comparative structures of the exemplary embodiments of the present disclosure are shown in Table 5, where the horizontal axis is the mixing ratio of the two materials and the vertical axis is the light extraction efficiency. Figure 8As shown, compared with Comparative Structure 1, since the side of the electron transport layer close to the light-emitting layer in Comparative Structure 2 and Comparative Structure 3 is mixed with the first host material with a higher refractive index, the refractive index increases, which improves the film reflection effect between the electron transport layer and the light-emitting layer, which is beneficial to the light-emitting characteristics of the light-emitting device, and thus the light extraction efficiency of Comparative Structure 2 and Comparative Structure 3 is improved. Compared with Comparative Structure 2, since the proportion of the first host material mixed on the side of the electron transport layer close to the light-emitting layer in Comparative Structure 3 is higher than the proportion of the first host material mixed on the side of the electron transport layer close to the light-emitting layer in Comparative Structure 2, the refractive index of the side of the electron transport layer close to the light-emitting layer in Comparative Structure 3 is greater than the refractive index of the side of the electron transport layer close to the light-emitting layer in Comparative Structure 2, which further improves the film reflection effect between the electron transport layer and the light-emitting layer, and thus the light extraction efficiency of Comparative Structure 3 is higher than the light extraction efficiency of Comparative Structure 2.

[0162] Table 5: Comparison results of light extraction efficiency of contrast structures

[0163] Light output efficiency Contrast structure 1 15.80％ Contrast structure 2 16.90％ Contrast structure 3 18.20％

[0164] Figures 9a to 9c This is a mode share distribution diagram of the light-emitting device of the exemplary embodiment of the present disclosure. According to Maxwell's equations and boundary conditions, 100% of the total light output energy of the light-emitting device can be decomposed into different forms of energy mode distribution. Generally, OLED light-emitting devices can include four energy mode distributions, namely: SPP mode, waveguide mode, absorption mode and coupled light mode, among which only the coupled light mode is effective in improving the efficiency of the light-emitting device. Therefore, in the design of the light-emitting device, various optical structures are needed to increase the share of the coupled light mode and to suppress the share of other modes to a certain extent, so as to achieve the purpose of improving the efficiency of the light-emitting device. Figure 9a This is the stacked average contribution distribution diagram for comparison structure 1. Figure 9b This is the distribution diagram of the mode ratio of the comparison structure 2. Fig.9c To compare the mode share distribution diagram of structure 3, the mode shares from top to bottom are: SPP mode, waveguide mode, absorption mode and coupled light mode, and the vertical axis represents the relative average contribution.

[0165] like Figures 9a to 9cAs shown, compared with the comparative structure 1, since the electron transport layer in the comparative structure 2 and the comparative structure 3 is mixed with the first main material with a higher refractive index on the side close to the light-emitting layer, the refractive index increases, thereby improving the film reflection effect between the electron transport layer and the light-emitting layer, so that the proportion of the SPP loss mode in the comparative structure 2 and the comparative structure 3 is reduced, and the proportion of the waveguide mode is increased, but the degree of reduction in the proportion of the SPP loss mode is greater than the degree of increase in the proportion of the waveguide mode, so that the proportion of the coupled light mode increases, thereby improving the efficiency of the light-emitting device. Compared with Comparative Structure 2, since the proportion of the first host material mixed on the side of the electron transport layer close to the light-emitting layer in Comparative Structure 3 is higher than that on the side of the electron transport layer close to the light-emitting layer in Comparative Structure 2, the refractive index of the electron transport layer close to the light-emitting layer in Comparative Structure 3 is greater than the refractive index of the electron transport layer close to the light-emitting layer in Comparative Structure 2, which further improves the film reflection effect between the electron transport layer and the light-emitting layer, thereby increasing the proportion of the SPP loss mode and reducing the proportion of the waveguide mode in Comparative Structure 3, but the degree of decrease in the proportion of the waveguide mode is greater than the degree of increase in the proportion of the SPP loss mode, and thus the proportion of the coupled light-emitting mode of Comparative Structure 3 increases, further improving the efficiency of the light-emitting device.

[0166] The exemplary embodiment of the present disclosure adopts a mixed structure of a first main material and a second main material in the electron transport layer, and the refractive index of the electron transport layer close to the light-emitting layer is greater than the refractive index of the electron transport layer away from the light-emitting layer, thereby maximizing the reasonable matching of the refractive index in the multi-film layer system, optimizing the optical performance of the light-emitting device, effectively improving the coupling light output efficiency inside the light-emitting device, and correspondingly suppressing other undesirable mode effects, which is more conducive to exerting the light output characteristics of the device.

[0167] The present disclosure also provides a method for preparing an organic electroluminescent device, comprising:

[0168] forming an anode;

[0169] forming a light-emitting layer;

[0170] forming an electron transport layer, wherein the electron transport layer includes a first host material and a second host material, wherein a mixing ratio of the first host material and the second host material on a side of the electron transport layer close to the light-emitting layer is different from a mixing ratio of the first host material and the second host material on a side of the electron transport layer far from the light-emitting layer;

[0171] A cathode is formed.

[0172] In an exemplary embodiment, forming an electron transport layer includes: adopting a co-evaporation method of a first main material source and a second main material source, and controlling the evaporation rate of the first main material to gradually decrease and the evaporation rate of the second main material to gradually increase during the process from the beginning of evaporation to the end of evaporation, so that along the direction from close to the light-emitting layer to away from the light-emitting layer, the mass percentage of the first main material in the electron transport layer gradually decreases, and the mass percentage of the second main material in the electron transport layer gradually increases.

[0173] In an exemplary embodiment, at the beginning of evaporation, the evaporation rate of the first host material is controlled to be to Control the evaporation rate of the second main material to to At the end of the evaporation, the evaporation rate of the first host material is controlled to be 0 to Control the evaporation rate of the second main material to to On the side close to the light-emitting layer, the mass percentage of the first main material in the electron transport layer is 60% to 80%, and the mass percentage of the second main material in the electron transport layer is 20% to 40%; on the side away from the light-emitting layer, the mass percentage of the first main material in the electron transport layer is approximately 0 to 10%, and the mass percentage of the second main material in the electron transport layer is approximately 90% to 100%.

[0174] The present disclosure also provides a display device, including the aforementioned organic electroluminescent device. The display device can be any product or component with a display function, such as a mobile phone, a tablet computer, a television, a monitor, a laptop computer, a digital photo frame, a navigator, a car display, a smart watch, a smart bracelet, etc.

[0175] Although the embodiments disclosed in the present disclosure are as above, the contents described are only embodiments adopted to facilitate understanding of the present disclosure and are not intended to limit the present disclosure. Any technician in the relevant field can make any modifications and changes in the form and details of implementation without departing from the spirit and scope disclosed in the present disclosure, but the scope of patent protection of this application shall still be based on the scope defined by the attached claims.

Claims

1. An organic electroluminescent device, comprising an anode, a cathode, and a light-emitting layer and an electron transport layer arranged between the anode and the cathode, wherein the electron transport layer is arranged between the light-emitting layer and the cathode; the electron transport layer comprises a first host material and a second host material, and the mixing ratio of the first host material and the second host material on the side of the electron transport layer close to the light-emitting layer is different from the mixing ratio of the first host material and the second host material on the side of the electron transport layer far from the light-emitting layer; the refractive index of the side of the electron transport layer close to the light-emitting layer is greater than the refractive index of the side of the electron transport layer far from the light-emitting layer; The electron transport layer has a maximum red light refractive index n in the wavelength range of 600nm to 640nm. RMAX , with a maximum green light refractive index n in the wavelength range of 510nm to 550nm GMAX , with a maximum blue light refractive index n in the wavelength range of 440nm to 480nm BMAX ; The electron transport layer satisfies: │n BMAX -n GMAX │≤0.4,│n BMAX -n RMAX │≤0.8。 2. The organic electroluminescent device according to claim 1, wherein: The first host material has a refractive index greater than a refractive index of the second host material.

3. The organic electroluminescent device according to claim 1, wherein: Along the direction from close to the light-emitting layer to far from the light-emitting layer, the mass percentage of the first host material in the electron transport layer gradually decreases, and the mass percentage of the second host material in the electron transport layer gradually increases.

4. The organic electroluminescent device according to claim 3, wherein: On a side of the electron transport layer close to the light-emitting layer, the mass percentage of the first host material in the electron transport layer is 60% to 80%, and the mass percentage of the second host material in the electron transport layer is 20% to 40%.

5. The organic electroluminescent device according to claim 3, wherein: On a side of the electron transport layer away from the light-emitting layer, the mass percentage of the first host material in the electron transport layer is 0 to 10%, and the mass percentage of the second host material in the electron transport layer is 90 to 100%.

6. The organic electroluminescent device according to claim 1, wherein: The thickness of the light-emitting layer is 10 nm to 25 nm, the thickness of the electron transport layer is 20 nm to 50 nm, and the refractive index of the electron transport layer on a side of the electron transport layer close to the light-emitting layer is 1.80 to 2.

00.

7. The organic electroluminescent device according to claim 1, wherein: The thickness of the electron transport layer is 20 nm to 50 nm, the thickness of the cathode is 10 nm to 20 nm, and the refractive index of the electron transport layer on a side of the electron transport layer close to the cathode is 1.55 to 1.

70.

8. The organic electroluminescent device according to claim 1, wherein: A hole injection layer, a hole transport layer and an electron blocking layer are also arranged between the anode and the light-emitting layer, a hole blocking layer is also arranged between the light-emitting layer and the electron transport layer, and an electron injection layer is also arranged between the electron transport layer and the cathode; the thickness of the hole injection layer is 5nm to 20nm, the thickness of the hole transport layer is 100nm to 150nm, the thickness of the electron blocking layer is 5nm to 20nm, the thickness of the light-emitting layer is 10nm to 25nm, the thickness of the hole blocking layer is 5nm to 15nm, and the thickness of the electron injection layer is 0.5nm to 2nm; on the side of the electron transport layer close to the hole blocking layer, the refractive index of the electron transport layer is 1.80 to 2.00, and on the side of the electron transport layer close to the electron injection layer, the refractive index of the electron transport layer is 1.55 to 1.

70.

9. The organic electroluminescent device according to any one of claims 1 to 8, wherein: The maximum red light refractive index n RMAX is 1.81 to 1.91, the maximum green light refractive index n GMAX is 1.86 to 1.96, the maximum blue light refractive index n BMAX It is between 1.90 and 2.

00.

10. The organic electroluminescent device according to any one of claims 1 to 8, wherein the electron transport layer has a minimum red light refractive index n in the wavelength range of 600 nm to 640 nm. RMIN , with a minimum green light refractive index n in the wavelength range of 510nm to 550nm GMIN , with a minimum blue light refractive index n in the wavelength range of 440nm to 480nm BMIN ; The electron transport layer satisfies: │n BMIN -n GMIN │≤0.5,│n BMIN -n RMIN │≤1.0。 11. The organic electroluminescent device according to claim 10, wherein: The minimum red light refractive index n RMIN is 1.55 to 1.65, the minimum green light refractive index n GMIN is 1.57 to 1.67, the minimum blue light refractive index n BMIN It is 1.60 to 1.

70.

12. A display device comprising the organic electroluminescent device according to any one of claims 1 to 11.

13. A method for preparing an organic electroluminescent device, comprising: forming an anode; forming a light-emitting layer; An electron transport layer is formed, wherein the electron transport layer includes a first main material and a second main material, wherein the mixing ratio of the first main material and the second main material on a side of the electron transport layer close to the light-emitting layer is different from the mixing ratio of the first main material and the second main material on a side of the electron transport layer far from the light-emitting layer; the refractive index of the side of the electron transport layer close to the light-emitting layer is greater than the refractive index of the side of the electron transport layer far from the light-emitting layer; and the electron transport layer has a maximum red light refractive index n in a wavelength range of 600 nm to 640 nm. RMAX , with a maximum green light refractive index n in the wavelength range of 510nm to 550nm GMAX , with a maximum blue light refractive index n in the wavelength range of 440nm to 480nm BMAX ; The electron transport layer satisfies: │n BMAX -n GMAX │≤0.4,│n BMAX -n RMAX │≤0.8; A cathode is formed.

14. The preparation method according to claim 13, wherein: Forming an electron transport layer includes: adopting a co-evaporation method of a first main material source and a second main material source, and controlling the evaporation rate of the first main material to gradually decrease and the evaporation rate of the second main material to gradually increase during the process from the beginning of evaporation to the end of evaporation, so that along the direction from close to the light-emitting layer to away from the light-emitting layer, the mass percentage of the first main material in the electron transport layer gradually decreases, and the mass percentage of the second main material in the electron transport layer gradually increases.

15. The preparation method according to claim 14, wherein: At the beginning of evaporation, the evaporation rate of the first main material is controlled to be 6Å / s to 8Å / s, and the evaporation rate of the second main material is controlled to be 2Å / s to 4Å / s; at the end of evaporation, the evaporation rate of the first main material is controlled to be 0 to 1Å / s, and the evaporation rate of the second main material is controlled to be 9Å / s to 10Å / s.

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