Method for improving the performance of OLED devices based on multiple quantum well structures of exciplexes

Abstract

The present invention discloses a method for improving the performance of OLED devices based on a multi-quantum well structure of an exciplex. By alternately inserting CBP and B3PyMPM thin layers into adjacent layers of fac‑Ir(ppy)3, a multi-quantum well structure is formed between the CBP / B3PyMPM heterojunction to prepare an undoped ultra-thin green phosphorescent OLED device. The thickness of each CBP or B3PyMPM layer is set to 2 nm to ensure effective exciton tunneling. Therefore, carriers can be effectively distributed at each interface, and increasing the number of quantum well structures can make the distribution of excitons more uniform, thereby avoiding exciton quenching caused by a large number of excitons. The synergistic effect of the exciplex and the quantum well structure is used to broaden the exciton recombination area and improve the exciton utilization rate. It can provide a new idea for improving the efficiency of green phosphorescent OLED devices and reducing efficiency roll-off.

Description

Technical Field

[0001] The present invention relates to the technical field of green phosphorescent OLED devices, and in particular to a method for improving the performance of OLED devices based on a multi-quantum well structure of an exciplex. Background Art

[0002] While traditional phosphorescent OLED devices utilize triplet energy to improve their luminous efficiency, they still have drawbacks. Their efficiency rapidly decreases with increasing brightness and current density (known as efficiency roll-off), a common problem in most phosphorescent devices. Consequently, there is a strong expectation that OLEDs will be used in a variety of applications requiring high brightness in the future.

[0003] The higher hole mobility in the hole transport layer than in the electron transport layer results in highly unbalanced carrier transport within the device, affecting the device's external quantum efficiency (EQE). This unbalanced carrier transport can also lead to device efficiency roll-off. The size of the carrier recombination zone directly affects the exciton concentration within the device. Expanding the carrier recombination zone can effectively reduce the exciton concentration, thereby minimizing exciton quenching and suppressing device efficiency roll-off. Therefore, researchers are committed to developing more balanced carrier transport systems, expanding the carrier recombination zone, improving exciton utilization, and manipulating the exciton distribution within the light-emitting layer to enhance the efficiency of OLED devices. Summary of the Invention

[0004] The purpose of the present invention is to remedy the defects of the existing technology and provide a method for improving the performance of OLED devices based on a multi-quantum well structure of an exciplex, thereby further improving the luminous brightness and efficiency of phosphorescent OLED devices.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for improving the performance of OLED devices using a multi-quantum well structure based on an exciplex. The OLED device comprises an exciplex formed by a hole-transport material, CBP, and an electron-transport material, B3PyMPM. Thin layers of CBP and B3PyMPM are alternately inserted into adjacent layers of fac-Ir(ppy)3, forming a multi-quantum well structure at the CBP / B3PyMPM heterojunction. The light-emitting layer of the phosphorescent OLED device is divided into several sublayers, creating a multi-quantum well structure with varying periods, resulting in more balanced carrier transport. This invention improves the efficiency of green phosphorescent OLED devices through an exciplex-based multi-quantum well structure.

[0007] The OLED device includes multiple ultra-thin undoped light-emitting layers, wherein the light-emitting layer material is composed of the green phosphorescent material fac-Ir(ppy)3. 4,4-bis(9-carbazolyl)biphenyl (4,4'-Bis(N-carbazolyl)-1,1'-biphenyl, CBP) and 4,6-bis(3,5-di(pyridin-3-yl)phenyl)-2-methylpyrimidine (4,6-Bis(3,5-di(pyridin-3-yl)phenyl)-2-methylpyrimidine, B3PYMPM) are alternately inserted into adjacent layers of the light-emitting fac-Ir(ppy)3 of the green phosphorescent OLED device.

[0008] The OLED device forms an interface exciplex through the hole transport material CBP and the electron transport material B3PYMPM, and inserts 0.2 nm fac-Ir(ppy)3 at the interface.

[0009] 0.2 nm fac-Ir(ppy)3 was inserted into the heterojunction interface of CBP / B3PyMPM / CBP / B3PyMPM to prepare a triple quantum well structured OLED device, so that the prepared OLED device has three light-emitting layers.

[0010] 0.2 nm fac-Ir(ppy)3 was inserted into the heterointerface of CBP / B3PyMPM / CBP / B3PyMPM / CBP / B3PyMPM to prepare a five-quantum well structure OLED device, so that the prepared OLED device has five light-emitting layers.

[0011] The thickness of the light-emitting layer fac-Ir(ppy)3 of the OLED device remains unchanged at 0.2 nm, and CBP and B3PyMPM thin layers are alternately inserted into adjacent layers of fac-Ir(ppy)3. The thickness of the CBP and B3PyMPM thin layers ranges from 1 nm to 4 nm.

[0012] The thickness of the light-emitting layer fac-Ir(ppy)3 of the OLED device remains unchanged at 0.2 nm, and CBP and B3PyMPM thin layers are alternately inserted into adjacent layers of fac-Ir(ppy)3. The thickness of the CBP and B3PyMPM thin layers is preferably 2 nm.

[0013] The advantages of the present invention are: 1. Compared with traditional phosphorescent OLED devices, the structural carriers adopted by the present invention can be dispersed in the quantum well structure. The quantum well structure makes the distribution of excitons more uniform, reduces the exciton quenching caused by large-scale exciton aggregation, and improves the luminous efficiency of the OLED device.

[0014] 2. The quantum well structure of the present invention confines carriers in each potential well, thereby increasing the recombination rate of excitons and improving the efficiency of OLED devices.

[0015] 3. The present invention utilizes the synergistic effect of exciplexes and quantum well structures to increase the number of interfacial exciplexes, broaden the exciton recombination area, and effectively suppress the efficiency roll-off of OLED devices at high brightness. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the energy level diagram of the triple quantum well structure OLED device B.

[0017] Figure 2 This is the energy level diagram of the five-quantum well structure OLED device C.

[0018] Figure 3 This is the structural diagram of the triple-quantum well structure OLED device B.

[0019] Figure 4 This is a structural diagram of the OLED device C with a five-quantum well structure.

[0020] Figure 5 A diagram of the material structure used for the multi-quantum well structure of OLED devices.

[0021] Figure 6 This is the power efficiency-brightness-current efficiency diagram of the OLED device.

[0022] Figure 7 This is the external quantum efficiency-brightness diagram of OLED devices. DETAILED DESCRIPTION

[0023] The following is a detailed description of the embodiments of the present invention. This embodiment is based on the technical solution of the present invention and provides a detailed implementation method and specific operation process. The scope of protection of the present invention includes but is not limited to the following embodiments.

[0024] For the preparation of control example A:

[0025] For the device with the structure of (ITO / MoO3(10 nm) / TAPC(30 nm) / CBP(15 nm) / fac-Ir(ppy)3(0.2 nm) / B3PyMPM(50 nm) / LiF(1 nm) / Al(100 nm)), we performed the following steps:

[0026] (1) Cleaning of ITO glass substrate:

[0027] The ITO glass substrate was placed in a beaker filled with ITO cleaning solution diluted with pure water, and then placed in an ultrasonic cleaner for 30 minutes of ultrasonic treatment, and then the pure water was replaced for 10 minutes of ultrasonic treatment.

[0028] (2) Drying of ITO glass substrate:

[0029] The cleaned ITO glass substrate was blown dry with a high-purity nitrogen gun, and then placed in a constant temperature drying oven at 120°C for 0.5 h for use;

[0030] (3) UV-ozone treatment of ITO glass substrate:

[0031] The dried ITO glass substrate was taken out from the drying oven and placed in a UV ozone machine for 20 minutes to further remove organic matter adhering to the ITO glass substrate and improve the work function of the ITO surface.

[0032] (4) Device preparation process:

[0033] After steps (1), (2), and (3), the UV-ozone treated ITO glass substrate is placed on a custom substrate holder and then placed in the evaporation chamber of the EvoVac ultrahigh vacuum coating machine. The chamber valve is closed and the evaporation chamber is evacuated. When the vacuum level of the chamber is raised to 5.5×10-6 Torr, evaporation can begin. Then, the functional layers of the device are evaporated in sequence: MoO3 (hole injection layer), TAPC (hole transport layer), CBP (hole transport layer), fac-Ir(ppy)3 (light-emitting layer), B3PyMPM (electron transport layer), LiF (electron injection layer) and Al (cathode). The thickness of each film layer is 10 nm, 30 nm, 15 nm, 0.2 nm, 50 nm, 1 nm, and 100 nm, respectively. The evaporation rates were 1 Å / s, 0.8 Å / s, 0.8 Å / s, 0.05 Å / s, 0.9 Å / s, 0.4 Å / s, and 1.2 Å / s, respectively. After the coating was complete, the coating chamber cooled to the appropriate temperature before the device was removed from the coating machine.

[0034] (5) Device packaging process:

[0035] After the evaporation process, the device was removed and, in a glove box with water and oxygen concentrations below 1 ppm, a glass cover plate coated with UV-curable adhesive was bonded to the device substrate using a pre-made fixture. After shielding the organic layer, the device was cured under UV light for 3 minutes. This UV exposure formed a barrier that effectively prevented water and oxygen in the air from entering the device and reacting with it.

[0036] (6) Perform performance test on the packaged device:

[0037] During current-voltage-luminance characterization testing, a test system consisting of a Keithley 2400 power meter and a Topcon SR-UL1R spectroradiometer was used to collect relevant OLED device data (voltage, current, luminance, and spectrum). External quantum efficiency (EQE) for all devices was calculated using the current density, luminance, and spectrum data obtained from these tests. No device packaging was performed prior to testing. All tests were conducted at room temperature in a darkroom.

[0038] For preparation of device B:

[0039] A device with a structure of (ITO / MoO3(10 nm) / TAPC(30 nm) / CBP(15 nm) / fac-Ir(ppy)3(0.2 nm) / B3PyMPM(2 nm) / fac-Ir(ppy)3(0.2 nm) / CBP(2 nm) / fac-Ir(ppy)3(0.2 nm) / B3PyMPM(50 nm) / LiF(1 nm) / Al(100 nm)) is fabricated. The steps of the present invention are as follows:

[0040] (1) Repeat steps (1), (2), and (3) of preparing device A.

[0041] (2) Device preparation process:

[0042] After the treatment in steps (1), (2), and (3), the ITO glass substrate treated with UV ozone was placed on a custom substrate rack and then placed in the evaporation chamber of the EvoVac ultra-high vacuum coating machine. The valve of the chamber was closed and the evaporation chamber was evacuated. When the vacuum degree of the chamber was increased to 5.5×10 -6Torr can start evaporation. Then, the functional layers of the device are sequentially deposited: MoO3 (hole injection layer), TAPC (hole transport layer), CBP (hole transport layer), triple quantum well structure layer (fac-Ir(ppy)3 (0.2 nm) / B3PyMPM (2 nm) / fac-Ir(ppy)3(0.2 nm) / CBP(2 nm) / fac-Ir(ppy)3(0.2 nm)), B3PyMPM (electron transport layer), LiF (electron injection layer) and Al (cathode). The thickness of each film layer is 10 nm, 30 nm, 15 nm, 0.2 nm, 2 nm, 0.2 nm, 2 nm, 0.2 nm, 50 nm, 1 nm and 100 nm respectively. The rates outside the light-emitting layer are 1 Å / s, 0.8 Å / s, 0.8 Å / s, 0.05 Å / s, 0.5 Å / s, 0.05 Å / s, 0.5 Å / s, 0.05 Å / s, 0.5 Å / s, 0.4 Å / s, and 1.2 Å / s, respectively. After coating, wait for the chamber to cool to the appropriate temperature before opening the coating machine and removing the device.

[0043] (3) Device packaging process:

[0044] After the evaporation process, the device was removed and, in a glove box with water and oxygen concentrations below 1 ppm, a glass cover plate coated with UV-curable adhesive was bonded to the device substrate using a pre-made fixture. After shielding the organic layer, the device was cured under UV light for 3 minutes. This UV exposure formed a barrier that effectively prevented water and oxygen in the air from entering the device and reacting with it.

[0045] (4) Perform performance test on the packaged device:

[0046] During current-voltage-luminance characterization testing, a test system consisting of a Keithley 2400 power meter and a Topcon SR-UL1R spectroradiometer was used to collect relevant OLED device data (voltage, current, luminance, and spectrum). External quantum efficiency (EQE) for all devices was calculated using the current density, luminance, and spectrum data obtained from these tests. No device packaging was performed prior to testing. All tests were conducted at room temperature in a darkroom.

[0047] For preparation of device C:

[0048] A device with a structure of (ITO / MoO3(10 nm) / TAPC(30 nm) / CBP(15 nm) / fac-Ir(ppy)3(0.2 nm) / B3PyMPM(2 nm) / fac-Ir(ppy)3(0.2 nm) / CBP(2 nm) / fac-Ir(ppy)3(0.2 nm) / B3PyMPM(2 nm) / fac-Ir(ppy)3(0.2 nm) / CBP(2 nm) / fac-Ir(ppy)3(0.2 nm) / B3PyMPM(50 nm) / LiF(1 nm) / Al(100 nm)) is fabricated. The steps of the present invention are as follows:

[0049] (1) Repeat steps (1), (2), and (3) of preparing device A.

[0050] (2) Device preparation process:

[0051] After the treatment in steps (1), (2), and (3), the ITO glass substrate treated with UV ozone was placed on a custom substrate rack and then placed in the evaporation chamber of the EvoVac ultra-high vacuum coating machine. The valve of the chamber was closed and the evaporation chamber was evacuated. When the vacuum degree of the chamber was increased to 5.5×10 -6 Torr can start evaporation. Then, the functional layers of the device were evaporated in sequence: MoO3 (hole injection layer), TAPC (hole transport layer), CBP (hole transport layer), five-quantum well structure layer (fac-Ir(ppy)3(0.2 nm) / B3PyMPM(2 nm) / fac-Ir(ppy)3(0.2 nm) / CBP(2 nm) / fac-Ir(ppy)3(0.2 nm) / B3PyMPM(2 nm) / fac-Ir(ppy)3(0.2 nm) / CBP(2 nm) / fac-Ir(ppy)3(0.2 nm)), B3PyMPM (electron transport layer), LiF (electron injection layer) and Al (cathode). The thickness of each film layer is 10 nm, 30 nm, 15 nm, 0.2 nm, 2 nm, 0.2 nm, 2 nm, 0.2 nm, 2 nm, 0.2 nm, 2 nm, 0.2 nm, 50 nm, 1 nm The speeds outside the light-emitting layer are 1 Å / s, 0.8 Å / s, 0.8 Å / s, 0.05 Å / s, 0.5 Å / s, 0.05 Å / s, 0.5 Å / s, 0.05 Å / s, 0.5 Å / s, 0.05 Å / s, 0.5 Å / s, 0.05 Å / s, 0.5 Å / s, 0.4 Å / s, and 1.2 Å / s, respectively. After coating, wait until the chamber cools to the appropriate temperature before removing the device from the coating machine.

[0052] (3) Device packaging process:

[0053] After the evaporation process, the device was removed and, in a glove box with water and oxygen concentrations below 1 ppm, a glass cover plate coated with UV-curable adhesive was bonded to the device substrate using a pre-made fixture. After shielding the organic layer, the device was cured under UV light for 3 minutes. This UV exposure formed a barrier that effectively prevented water and oxygen in the air from entering the device and reacting with it.

[0054] (4) Perform performance test on the packaged device:

[0055] During current-voltage-luminance characterization testing, a test system consisting of a Keithley 2400 power meter and a Topcon SR-UL1R spectroradiometer was used to collect relevant OLED device data (voltage, current, luminance, and spectrum). External quantum efficiency (EQE) for all devices was calculated using the current density, luminance, and spectrum data obtained from these tests. No device packaging was performed prior to testing. All tests were conducted at room temperature in a darkroom.

[0056] The principle of the present invention is:

[0057] The OLED utilizes an exciplex formed by the hole-transporting material CBP and the electron-transporting material B3PYMPM. The green phosphorescent material fac-Ir(ppy)3 serves as the emitting layer. A quantum well structure within the emitting layer ensures a more balanced charge carrier distribution within the emitting layer. By alternating thin layers of CBP and B3PyMPM between adjacent layers of fac-Ir(ppy)3, a multi-quantum well structure is formed at the CBP / B3PyMPM heterointerface. The thickness of each CBP or B3PyMPM layer is set at 2 nm to ensure efficient exciton tunneling. This effectively disperses charge carriers at each interface, increasing the number of quantum wells and achieving a more uniform exciton distribution, thereby preventing exciton quenching caused by excessive exciton aggregation. The synergistic effect of the exciplex and quantum well structure broadens the exciton recombination zone, resulting in a more balanced charge carrier distribution within the emitting layer and a more uniform exciton distribution throughout the emitting layer. This reduces exciton quenching and improves OLED device performance.

Claims

1. A method for improving the performance of an OLED device based on a multi-quantum well structure of an exciplex, wherein the OLED device comprises multiple ultrathin undoped light-emitting layers, wherein the light-emitting layers are made of the green phosphorescent material fac-Ir(ppy)3, and wherein: The hole transport material 4,4-bis(9-carbazolyl)-biphenyl (4,4'-Bis(N-carbazolyl)-1,1'-biphenyl, CBP) and the electron transport material 4,6-bis(3,5-di(3-pyridin-3-yl)phenyl)-2-methylpyrimidine (4,6-Bis(3,5-di(pyridin-3-yl)phenyl)-2-methylpyrimidine, B3PYMPM) are alternately inserted between adjacent layers of multiple light-emitting layers fac-Ir(ppy)3 of the OLED device. The OLED device forms an interfacial exciplex through the hole transport material CBP and the electron transport material B3PYMPM, and inserts 0.2 nm fac-Ir(ppy)3 at the interface; The thickness of the light-emitting layer fac-Ir(ppy)3 of the OLED device remains unchanged at 0.2 nm, and thin layers of hole transport material CBP and electron transport material B3PyMPM are alternately inserted into adjacent layers of the light-emitting layer fac-Ir(ppy)3. The film thickness of the hole transport material CBP and electron transport material B3PyMPM thin layers is 1 to 4 nm.

2. The method for improving the performance of OLED devices based on a multi-quantum well structure of an exciplex according to claim 1, characterized in that: 0.2 nm fac-Ir(ppy)3 was inserted into the heterojunction interface of CBP / B3PyMPM / CBP / B3PyMPM to prepare a triple quantum well structured OLED device, so that the prepared OLED device has three light-emitting layers.

3. The method for improving the performance of OLED devices based on a multi-quantum well structure of an exciplex according to claim 1, characterized in that: 0.2 nm fac-Ir(ppy)3 was inserted into the heterointerface of CBP / B3PyMPM / CBP / B3PyMPM / CBP / B3PyMPM to prepare a five-quantum well structure OLED device, so that the prepared OLED device has five light-emitting layers.

4. The method for improving the performance of OLED devices based on a multi-quantum well structure of an exciplex according to claim 1, characterized in that: The thickness of the thin layer of hole transport material CBP and electron transport material B3PyMPM is 2 nm.

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