Multicolor OLED and method for regulating and controlling color through positive and negative bias polarities

Abstract

The invention relates to a multi-color OLED and a method for regulating and controlling colors through positive and negative bias polarities, which can convert a non-luminous single carrier device into a luminous device, realize a luminous function under positive and negative biases, expand the working mode and application range of the OLED device, realize independent and flexible regulation and control of colors and brightness, provide more possibilities for display and illumination application, and improve the display and illumination performance. And the charge injection balance degree of the device is improved, so that the luminous efficiency is improved, and the performance improvement of the OLED technology in practical application is promoted. The OLED comprises an ITO coated glass substrate, a Ca layer, a first Cs2CO3 layer, a Cs2CO3 and TPBI mixed layer, a first TPBI layer, a red light-emitting layer, a first TCTA layer, a MoO3 layer, a second TCTA layer, a green light-emitting layer, a second TPBI layer, a second Cs2CO3 layer and an Al electrode from bottom to top.

Description

Technical Field

[0001] The present invention relates to the technical field of optoelectronics, and in particular to a multicolor OLED whose color is regulated by positive and negative bias polarity, as well as a preparation method and an operating method of the multicolor OLED whose color is regulated by positive and negative bias polarity. Background Art

[0002] In the field of OLED (Organic Light-Emitting Diode) technology, traditional OLEDs operate by injecting holes into the anode and electrons into the cathode. These holes and electrons recombine in the light-emitting layer to generate light radiation, thereby achieving luminescence. Single-carrier devices, typified by electron-only devices (EODs), operate by injecting only one type of carrier and lack inherent luminescence. In existing technology systems, they are typically used to measure electrical transport parameters.

[0003] In recent years, researchers have conducted a series of fruitful research projects around OLED technology. Some have attempted to construct AC-driven OLEDs using electronic devices, aiming to achieve color and brightness tunability. Others have focused on hybrid intermediate connectors based on MoO3 layers and p-type doping in tandem OLEDs, hoping to optimize device performance. Meanwhile, there are also efforts to prepare high-efficiency, long-life, voltage-dependent, color-tunable OLEDs and achieve voltage-dependent color change in single-emitter, undoped OLEDs.

[0004] Although these studies have achieved certain results, from an overall perspective, existing technologies still face many challenges in practical applications. Take the application of charge generation layer (CGL) in tandem OLED as an example. Although the charge generation layer has been introduced into this field and has promoted the generation and recombination of charges to a certain extent, there are still obvious shortcomings in achieving efficient and controllable light emission. On the one hand, it is difficult to achieve independent control of color and brightness. In display and lighting application scenarios, it is impossible to flexibly and accurately present colors and adjust brightness according to diverse needs; on the other hand, some device structures have imbalance problems during the charge injection process, which not only leads to a decrease in the transfer efficiency of charges inside the device, but also greatly limits the luminous efficiency of the device, making it difficult for existing OLED technology to meet the ever-increasing high-performance requirements of the display and lighting fields. Therefore, the development of a new OLED to solve the above-mentioned deficiencies in the existing technology has become an important issue that needs to be overcome in this field. Summary of the Invention

[0005] In order to overcome the defects of the existing technology, the technical problem to be solved by the present invention is to provide a multi-color OLED with color control through positive and reverse bias polarity, which can convert non-luminous single-carrier devices into luminous devices, realize the luminous function under positive and negative bias, expand the working mode and application range of OLED devices, realize independent and flexible control of color and brightness, provide more possibilities for display and lighting applications, improve the charge injection balance of the device, and thus improve the luminous efficiency, promoting the performance improvement of OLED technology in practical applications.

[0006] The technical solution of the present invention is: This multi-color OLED that controls color by forward and reverse bias polarity includes, from bottom to top: an ITO-coated glass substrate, a Ca layer, a first Cs2CO3 layer, a Cs2CO3 and TPBI mixed layer, a first TPBI layer, a red light-emitting layer, a first TCTA layer, a MoO3 layer, a second TCTA layer, a green light-emitting layer, a second TPBI layer, a second Cs2CO3 layer, and an Al electrode;

[0007] The Ca layer, the first Cs2CO3 layer, and the second Cs2CO3 layer reduce the electron injection barrier. The Cs2CO3 and TPBI mixed layer, the first TPBI layer, and the second TPBI layer transport electrons to the light-emitting layer. The red light-emitting layer is a red phosphor film, and the green light-emitting layer is a green phosphor film. The MoO3 layer serves as a charge generation layer and forms p-doped regions with the first TCTA layer and the second TCTA layer, respectively, and together with the structures on both sides constitute a nipin symmetrical structure.

[0008] This invention converts non-luminescent single-carrier devices (such as EODs) into luminescent devices and utilizes a specific structure to achieve luminescence under positive and negative bias voltages, expanding the operating modes and application range of OLED devices. By providing different color luminescent layers at different PIN junctions and combining them with AC drive, independent and flexible control of color and brightness is achieved, overcoming the limitations of traditional OLEDs in this regard and providing more possibilities for display and lighting applications. This improves the device's charge injection balance, thereby increasing luminous efficiency and overcoming the low efficiency of existing similar devices, thereby promoting the performance of OLED technology in practical applications.

[0009] A method for preparing a multicolor OLED by controlling the color by positive and negative bias polarity is also provided, which comprises the following steps:

[0010] (1) Configuration of luminescent materials: The red luminescent material is composed of CBP and red phosphor according to 1:

[0011] The green luminescent material is configured with a ratio of CBP and green phosphor at a ratio of 1:0.8, and a mixture of Cs2CO3 and TPBI at a ratio of 1:0.3;

[0012] (2) The ITO-coated glass substrate was ultrasonically cleaned with detergent for 10 min, then ultrasonically cleaned with water for 10 min each, and then ultrasonically cleaned with alcohol for 10 min each, and then dried with nitrogen;

[0013] (3) Turn on the cooling machine, then turn on the evaporation machine, enter the device structure in the process menu, set the evaporation source, place the materials in four batches, and place the evaporation source materials in the order of the menu. The bulk material is placed in a tungsten boat, and the powder material is placed in a tungsten basket. After placing the mask plate, perform evaporation to ensure that each layer is accurately deposited in the corresponding position according to the design requirements.

[0014] A method for operating a multi-color OLED by controlling the color by forward and reverse bias polarity is also provided, which comprises the following steps:

[0015] (I) Under positive bias, electrons are injected from the negative bias electrode and pass through the second TPBI layer (11)

[0016] Transport, the electrons in the second TCTA layer (9) are transferred to its valence band, thereby realizing electron-hole recombination luminescence at the pin junction, and the nip junction is in a closed state that does not participate in luminescence;

[0017] (II) Under negative bias, the flow direction of electrons and holes is opposite to that under positive bias. Electrons are injected from the positive bias electrode, transported through the Cs2CO3 and TPBI mixed layer (4) and the first TPBI layer (5), and charge transfer occurs between the MoO3 layer (8) and the first TCTA layer (7). Electron-hole recombination is achieved at another pin junction, and the pin junction that previously emitted light under positive bias is now in the closed state.

[0018] (III) Under AC voltage drive, the luminous intensity ratio of the two pin junctions is adjusted by changing the amplitude of the applied positive and negative voltages, thereby achieving color and brightness control. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 3 is a schematic structural diagram of a multi-color OLED in which colors are controlled by forward and reverse bias polarities according to the present invention.

[0020] Figure 2 There are five different sets of square waves and their corresponding emission spectra. Figure 2 In (a), Vn is zero, and only positive voltage is applied to the OLED device. Correspondingly, Figure 2 In the emission spectrum shown in (f), only the green spectrum curve is presented. When Vp is kept constant and Vn is moved toward the negative direction, as shown in Figure 2 (b) with Figure 2 (c) shows that Figure 2 (g) and Figure 2(h) In the corresponding emission spectrum, the red light spectrum curve is apparent, and the greater the absolute value of Vn, the higher the intensity of the red light spectrum curve. If Vn is kept constant and Vp is moved toward the negative direction, such as Figure 2 (d) and Figure 2 (e) shows the corresponding Figure 2 (i) and Figure 2 (j) In the emission spectrum, the intensity of the green light spectrum curve decreases. In particular, when Vp is zero, as Figure 2 (e) Figure 2 (j) The corresponding emission spectrum only contains the red light spectrum curve. Therefore, by adjusting the forward and reverse bias voltages, the color change of the OLED can be controlled.

[0021] Figure 3 It is the EL spectrum corresponding to AC driving and the normalized EL spectrum under different Vp and Vn combinations. DETAILED DESCRIPTION

[0022] First, the following terminology is explained.

[0023] OLED: Organic Light-Emitting Diode is an electronic device that uses organic semiconductor materials to emit light under the action of an electric field.

[0024] ITO: Indium Tin Oxide, a metal oxide with good transparency and conductivity, is used as a substrate material in the OLED device of the present invention to provide a conductive and transparent base for the preparation of subsequent functional layers.

[0025] JV: Current density-voltage is an important parameter for measuring the electrical performance of OLED devices. By measuring the current density at different voltages, the charge injection and transfer characteristics of the device can be evaluated.

[0026] LV: Luminance-Voltage, used to characterize the luminance of OLED devices at different voltages. It reflects the luminous efficiency and performance of the device and is one of the key indicators for evaluating the luminous performance of the device.

[0027] EL: Electroluminescence refers to the luminescence phenomenon produced by a substance under the action of an electric field. It is the core luminescence principle of OLED devices. The color and intensity distribution of the device's luminescence can be analyzed through the EL spectrum.

[0028] PIN: A structure composed of a p-type semiconductor, an intrinsic semiconductor, and an n-type semiconductor. In the OLED device of the present invention, different PIN junctions work in conjunction with the light-emitting layer, the charge-generating layer, etc. to achieve light emission under positive and negative bias voltages and color and brightness control.

[0029] EOD: Electron Only Device, a device structure that only injects electrons as carriers, is usually used to study electrical transport characteristics.

[0030] CGL: Charge Generation Layer, a functional layer used to generate additional charge carriers in the device and promote electron-hole recombination luminescence. In the present invention, its function is achieved based on materials such as MoO3.

[0031] ETL: Electron Transport Layer, which is responsible for transporting electrons in OLED devices, allowing electrons to move smoothly from the electrode to the light-emitting layer. In the present invention, it is composed of Cs2CO3-doped TPBi and TPBI layers, and plays a key role in the luminescence performance of the device.

[0032] EML: Emitting Layer, a functional layer in OLED devices that realizes electroluminescence, generating photons through the recombination of electrons and holes. The present invention uses green phosphor (Ir(ppy)3) and red phosphor (Ir(piq)3) films as the emissive layer materials.

[0033] Ir(ppy)3: tris(2-phenylpyridine)iridium(III), a metal-organic complex. The ppy ligand represents the 2-phenylpyridine ligand, which coordinates to the central iridium atom via the nitrogen atom on the pyridine ring and the carbon atom on the benzene ring, forming a complex with specific structure and properties. In fields such as organic electroluminescent devices, Ir(ppy)3 is often used as a luminescent material due to its excellent luminescent properties, producing efficient phosphorescence.

[0034] Ir(piq)3: Tris(1-phenylisoquinolinate)iridium(III), also a metallo-organic complex. The piq ligand here refers to the 1-phenylisoquinoline ligand, with the iridium atom coordinated by the nitrogen atom on the isoquinoline ring. Ir(piq)3 also has important applications in organic optoelectronic devices, particularly as a phosphorescent material that can emit light at a specific wavelength, playing a crucial role in display technology and other fields.

[0035] TPBI: 1,3,5-Tri(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl, an organic semiconductor material used as an electron transport layer (ETL) or its component in devices.

[0036] TCTA: 4,40,400-Tri(9-carbazoyl)triphenylamine, plays an important role in the device structure, interacting with the layers and participating in the charge transport and recombination processes.

[0037] CBP: 4,4'-N,N'-dicarbazol biphenyl (4,4'-Bis(carbazol-9-yl)biphenyl), a commonly used organic hole transport material, is used as a matrix material in the luminescent material configuration of the present invention and is mixed with a phosphorescent dye to form a luminescent layer, which helps to improve luminous efficiency and stability.

[0038] CIE: International Commission on Illumination (Commission Internationale de l'Eclairage), which developed the CIE coordinates, a standard colorimetric system for describing colors, used to characterize changes in the color of light emitted by a device.

[0039] like Figure 1 As shown, this multi-color OLED that controls color by forward and reverse bias polarity includes, from bottom to top: an ITO (Indium Tin Oxide)-coated glass substrate 1, a Ca layer 2, a first Cs2CO3 layer 3, a Cs2CO3 and TPBI mixed layer 4, a first TPBI layer 5, a red light-emitting layer 6, a first TCTA layer 7, a MoO3 layer 8, a second TCTA layer 9, a green light-emitting layer 10, a second TPBI layer 11, a second Cs2CO3 layer 12, and an Al electrode 13;

[0040] The Ca layer, the first Cs2CO3 layer, and the second Cs2CO3 layer reduce the electron injection barrier. The Cs2CO3 and TPBI mixed layer, the first TPBI layer, and the second TPBI layer transport electrons to the light-emitting layer. The red light-emitting layer is a red phosphor film, and the green light-emitting layer is a green phosphor film. The MoO3 layer serves as a charge generation layer and forms p-doped regions with the first TCTA layer and the second TCTA layer, respectively, and together with the structures on both sides constitute a nipin symmetrical structure.

[0041] This invention converts non-luminescent single-carrier devices (such as EODs) into luminescent devices and utilizes a specific structure to achieve luminescence under positive and negative bias voltages, expanding the operating modes and application range of OLED devices. By providing different color luminescent layers at different PIN junctions and combining them with AC drive, independent and flexible control of color and brightness is achieved, overcoming the limitations of traditional OLEDs in this regard and providing more possibilities for display and lighting applications. This improves the device's charge injection balance, thereby increasing luminous efficiency and overcoming the low efficiency of existing similar devices, thereby promoting the performance of OLED technology in practical applications.

[0042] Preferably, the thicknesses of the Ca layer, the first Cs2CO3 layer, the Cs2CO3 and TPBI mixed layer, the first TPBI layer, the red light-emitting layer, the first TCTA layer, the MoO3 layer, the second TCTA layer, the green light-emitting layer, the second TPBI layer, the second Cs2CO3 layer, and the Al electrode are 1nm, 1nm, 30nm, 10nm, 10nm, 10nm, 3nm, 10nm, 20nm, 30nm, 1nm, and 100nm, respectively.

[0043] A method for preparing a multicolor OLED by controlling the color by positive and negative bias polarity is also provided, which comprises the following steps:

[0044] (1) Configuration of luminescent materials: The red luminescent material is composed of CBP and red phosphor according to 1:

[0045] The green luminescent material is configured with a ratio of CBP and green phosphor at a ratio of 1:0.8, and a mixture of Cs2CO3 and TPBI at a ratio of 1:0.3;

[0046] (2) The ITO-coated glass substrate was ultrasonically cleaned with detergent for 10 min, then ultrasonically cleaned with water twice for 10 min each, and then ultrasonically cleaned with alcohol twice for 10 min each, and then dried with nitrogen;

[0047] (3) Turn on the cooling machine, then turn on the evaporation machine, enter the device structure in the process menu, set the evaporation source, place the materials in four batches, and place the evaporation source materials in the order of the menu. The bulk material is placed in a tungsten boat, and the powder material is placed in a tungsten basket. After placing the mask plate, perform evaporation to ensure that each layer is accurately deposited in the corresponding position according to the design requirements.

[0048] Preferably, in step (3), the -4 Pa in a vacuum environment.

[0049] A method for operating a multi-color OLED by controlling the color by forward and reverse bias polarity is also provided, which comprises the following steps:

[0050] (I) Under positive bias, electrons are injected from the negative bias electrode and pass through the second TPBI layer (11)

[0051] Transport, the electrons in the second TCTA layer (9) are transferred to its valence band, thereby realizing electron-hole recombination luminescence at the pin junction, and the nip junction is in a closed state that does not participate in luminescence;

[0052] (II) Under negative bias, the flow direction of electrons and holes is opposite to that under positive bias. Electrons are injected from the positive bias electrode, transported through the Cs2CO3 and TPBI mixed layer (4) and the first TPBI layer (5), and charge transfer occurs between the MoO3 layer (8) and the first TCTA layer (7). Electron-hole recombination is achieved at another pin junction, and the pin junction that previously emitted light under positive bias is now in the closed state.

[0053] (III) Under AC voltage drive, the luminous intensity ratio of the two pin junctions is adjusted by changing the amplitude of the applied positive and negative voltages, thereby achieving color and brightness control.

[0054] Preferably, in step (III), when the positive amplitude Vp is fixed and the negative amplitude Vn is changed, as Vn decreases, the red emission gradually increases, and the CIE coordinates move from the green area to the red area, achieving color change adjustment from green to yellow to red.

[0055] Preferably, in step (III), when Vn is fixed and Vp is changed, as Vp increases, green emission gradually increases, and the CIE coordinates move from the red region to the green region, achieving color change adjustment from red to yellow to green.

[0056] Specifically, an AC source meter was used to output a square wave to drive the OLED device. When the Vp amplitude was fixed at 18V and the Vn amplitude was subsequently varied, the spectrum exhibited significant changes. When Vn was set to 0V, the measured spectrum of the OLED device contained only a green component. As the absolute value of Vn gradually increased to -24V, -28V, -30V, and -32V, the red component in the spectrum gradually emerged and became increasingly prominent. Similar spectral changes were observed when the experimental conditions were changed to a fixed Vn of -30V and Vp was varied. Initially, with Vp at 0V, only red was observed in the spectrum of the OLED device. However, as the amplitude was gradually increased from 0V to 14V, 16V, 18V, and 20V, the green component in the spectrum gradually emerged and became increasingly prominent. This achieved color control of the OLED device.

[0057] The beneficial technical effects of the present invention are as follows:

[0058] 1. Innovative application expansion: This invention innovatively transforms non-luminescent single-carrier devices into luminescent devices that can operate under positive and negative bias voltages, opening up new ideas for the design and application of OLED devices and expanding the application scenarios of the devices. For example, it has potential value in special display requirements (such as dual-mode display) or new lighting applications.

[0059] 2. Independent Control: The company successfully achieved independent control of color and brightness, overcoming the limitations of traditional OLEDs, which struggle to adjust both simultaneously. This feature enables OLEDs to produce richer, more realistic colors in displays and flexibly adjust light color and brightness to suit different scenarios in lighting, providing greater flexibility and competitive advantages for OLED applications in both display and lighting.

[0060] 3. Laying a Research Foundation: Although the efficiency and brightness of the current device still need to be improved, this invention provides an important foundation and direction for subsequent research to improve charge injection balance and luminous efficiency. Through in-depth research on the device structure and operating principles, further optimization of material selection, layer structure design, and preparation process can be achieved, showing potential for technological improvement and broad application prospects.

[0061] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of protection of the technical solution of the present invention.

Claims

1. A multi-color OLED that controls color by forward and reverse bias polarity, characterized by: From bottom to top, it includes: an ITO-coated glass substrate (1), a Ca layer (2), a first Cs2CO3 layer (3), a Cs2CO3 and TPBI mixed layer (4), a first TPBI layer (5), a red light-emitting layer (6), a first TCTA layer (7), a MoO3 layer (8), a second TCTA layer (9), a green light-emitting layer (10), a second TPBI layer (11), a second Cs2CO3 layer (12), and an Al electrode (13); The Ca layer, the first Cs2CO3 layer, and the second Cs2CO3 layer reduce the electron injection barrier. The Cs2CO3 and TPBI mixed layer, the first TPBI layer, and the second TPBI layer transport electrons to the light-emitting layer. The red light-emitting layer is a red phosphor film, and the green light-emitting layer is a green phosphor film. The MoO3 layer serves as a charge generation layer and forms p-doped regions with the first TCTA layer and the second TCTA layer, respectively, and together with the structures on both sides constitute a nipin symmetrical structure.

2. The multi-color OLED with color control by forward and reverse bias polarity according to claim 1, characterized in that: The thicknesses of the Ca layer, the first Cs2CO3 layer, the Cs2CO3 and TPBI mixed layer, the first TPBI layer, the red light-emitting layer, the first TCTA layer, the MoO3 layer, the second TCTA layer, the green light-emitting layer, the second TPBI layer, the second Cs2CO3 layer, and the Al electrode are 1nm, 1nm, 30nm, 10nm, 10nm, 10nm, 3nm, 10nm, 20nm, 30nm, 1nm, and 100nm, respectively.

3. The method for preparing a multi-color OLED by controlling the color by positive and negative bias polarity according to claim 2, characterized in that: It includes the following steps: (1) Preparation of luminescent materials: red luminescent material is prepared by CBP and red phosphor in a ratio of 1:0.8, green luminescent material is prepared by CBP and green phosphor in a ratio of 1:0.8, and a mixture of Cs2CO3 and TPBI in a ratio of 1:0.3; (2) The ITO-coated glass substrate was ultrasonically cleaned with detergent for 10 min, then ultrasonically cleaned with water twice for 10 min each, and then ultrasonically cleaned with alcohol twice for 10 min each, and then dried with nitrogen; (3) Turn on the cooling machine, then turn on the evaporation machine, enter the device structure in the process menu, set the evaporation source, place the materials in four batches, and place the evaporation source materials in the order of the menu. The bulk material is placed in a tungsten boat, and the powder material is placed in a tungsten basket. After placing the mask plate, perform evaporation to ensure that each layer is accurately deposited in the corresponding position according to the design requirements.

4. The method for preparing a multicolor OLED by controlling the color by positive and negative bias polarity according to claim 3, characterized in that: In the step (3), the -4 Pa in a vacuum environment.

5. The method for operating a multi-color OLED by controlling the color by forward and reverse bias polarity according to claim 2, characterized in that: It includes the following steps: (I) Under positive bias, electrons are injected from the negative bias electrode, transmitted through the second TPBI layer (11), and the electrons in the second TCTA layer (9) are transferred to its valence band, thereby realizing electron-hole recombination luminescence at the pin junction, and the nip junction is in a closed state and does not participate in luminescence; (II) Under negative bias, the flow direction of electrons and holes is opposite to that under positive bias. Electrons are injected from the positive bias electrode, transported through the Cs2CO3 and TPBI mixed layer (4) and the first TPBI layer (5), and charge transfer occurs between the MoO3 layer (8) and the first TCTA layer (7). Electron-hole recombination is achieved at another pin junction, and the pin junction that previously emitted light under positive bias is now in the closed state. (III) Under AC voltage drive, the luminous intensity ratio of the two pin junctions is adjusted by changing the amplitude of the applied positive and negative voltages, thereby achieving color and brightness control.

6. The method for operating a multi-color OLED by controlling the color by forward and reverse bias polarity according to claim 5, characterized in that: In the step (III), when the positive amplitude Vp is fixed and the negative amplitude Vn is changed, as Vn decreases, the red emission gradually increases, and the CIE coordinates move from the green area to the red area, achieving color change adjustment from green to yellow to red.

7. The method for operating a multi-color OLED by controlling the color by forward and reverse bias polarity according to claim 5, characterized in that: In the step (III), when Vn is fixed and Vp is changed, as Vp increases, green emission gradually increases, and the CIE coordinates move from the red area to the green area, achieving color change adjustment from red to yellow to green.

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