Foldable organic electroluminescent device based on preset crease and preparation method thereof

Abstract

The present invention belongs to the technical field of flexible light-emitting devices, and specifically discloses a foldable organic electroluminescent device based on preset creases and a preparation method thereof. The preparation method includes S1, preparing a glass substrate; S2, obtaining a poly(p-xylene-C) film by chemical vapor deposition; S3, performing a hydrophobic treatment on the substrate; S4, obtaining a patterned template by photolithography; S5, casting a patterned polydimethylsiloxane template; S6, vapor-depositing an OLED using a vacuum thermal evaporation system; S7, obtaining a foldable OLED by a stamping method. The present invention adopts the above-mentioned foldable organic electroluminescent device based on preset creases and a preparation method thereof. By using a vertical stamping method to make the creases, the operation is simple, the cost is low, and a large-area design can be designed. After stamping with the prepared patterned PDMS template, the OLED exhibits excellent folding performance without affecting the photoelectric performance of the device.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible light-emitting devices, and in particular to a foldable organic electroluminescent device based on a preset crease and a preparation method thereof. Background Art

[0002] In recent years, various information technologies, such as AR, VR, and 5G communications, have rapidly developed, increasing people's demand for a better life. Display technology, as a medium for human-computer interaction, has become increasingly relevant to our lives. From the initial bulky cathode ray tube displays to flat-panel LCDs and flexible OLED displays, display technology has experienced rapid advancements. Flexible display technology, in particular, has expanded the form factor of displays beyond flat panels and is now evolving towards deformable displays. Foldable screens have shown tremendous potential for applications in foldable phones. By folding, the screen size can be doubled or tripled, breaking the size barrier between phones and tablets, greatly expanding the functionality of phones and providing users with features and conveniences unavailable on smaller phones. This has become a research hotspot for high-end mobile phones and displays. We believe that flexible and bendable displays will play an increasingly important role in our lives in the future.

[0003] Folding, as a unique deformation mode, is typically characterized by a folding angle with a small radius of curvature, a fixed bending position, and a designable folding structure. Among the folding processes that have been developed, one is an intrinsically foldable device made of an ultra-thin flexible or elastic substrate. Its characteristic is that the device can be folded at any position by applying pressure. During the folding process, a crease is generated, and the device will show significant morphological changes such as wrinkling, delamination, and fracture at the crease. Another method is based on origami technology. The crease position and crease structure are pre-designed on the flat device. During the compression and buckling process, the device is folded strictly according to the preset crease. This method is simple and effective. Unlike intrinsic folding, the device obtained by this method has a strong initiative in shape design.

[0004] Organic electroluminescent devices (OLEDs) are a key component of current display technology. However, their multilayered structures, if implemented with intrinsic folding schemes, result in a gradual decrease in the bending radius during the folding process, complex interlayer interactions, and increasing bending strain, which can significantly negatively impact device performance. The crease-preset scheme provides better control over the device's folding structure and the bending strain at the crease, facilitating the development of foldable OLEDs and displays with high luminescence performance and complex folding and deformation capabilities. Summary of the Invention

[0005] The purpose of the present invention is to provide a foldable organic electroluminescent device based on preset creases and a preparation method thereof. The creases are produced by using a vertical imprinting method, which is simple to operate, low in cost, and can be designed over a large area. After imprinting the prepared patterned PDMS template, the OLED exhibits excellent folding performance without affecting the photoelectric performance of the device.

[0006] To achieve the above object, the present invention provides a method for preparing a foldable organic electroluminescent device based on a preset crease, comprising the following steps:

[0007] S1. Preparation of glass substrate: Perform standardized cleaning on the glass substrate by ultrasonic cleaning in acetone, anhydrous ethanol, and deionized water for 60 minutes, respectively. Then, wipe it with a medical sterile cotton ball containing anhydrous ethanol, rinse it with deionized water, and finally blow dry the water droplets on the surface of the glass substrate with a nitrogen gun. Then, place it in a constant temperature oven at 95°C for 20 minutes and remove it for use.

[0008] S2. Obtaining a parylene-C thin film by chemical vapor deposition: placing the glass substrate cleaned and dried in step S1 into a chemical vapor deposition system, adding a dimer, vaporizing and cracking the dimer, and finally depositing a layer of parylene-C thin film on the surface of the glass substrate;

[0009] S3, performing a hydrophobic treatment on the substrate to reduce the surface energy of the substrate, and spin-coating a hydrophobic coating on the surface of the glass substrate after cleaning and drying in step S1;

[0010] S4, obtaining a patterned template by photolithography, spin-coating photoresist on the surface of the parylene-C film deposited in step S2, exposing it with a photomask after pre-baking, and then post-baking it, and then developing it in a photoresist developer, and then rinsing it with isopropyl alcohol and deionized water in sequence, blowing off the water droplets with a nitrogen gun, and finally hardening the film on a hot stage;

[0011] S5, casting a patterned polydimethylsiloxane (PDMS) template, casting the mixed PDMS prepolymer on the patterned template in step S4, annealing and curing, and finally cutting out the cured PDMS template using a blade;

[0012] S6. Using a vacuum thermal evaporation system to evaporate the OLED, a layer of parylene-C film is deposited on the hydrophobic surface of the glass substrate obtained in step S3 using the method of step S2, and then a layer of UV-curable optical adhesive film is spin-coated. The film is exposed and cured in a UV light box, and then transferred to the vacuum thermal evaporation system to evaporate the OLED device;

[0013] S7. A foldable OLED is obtained by an imprinting method. A layer of UV-curable optical adhesive is spin-coated on the surface of the OLED obtained in step S6. The PDMS template obtained in step S5 is aligned with the OLED device for imprinting. The device is placed in a transition chamber of a glove box and evacuated for 2 minutes to remove bubbles. The device is then exposed and cured in an UV light box. The PDMS template is then removed, and the entire multilayer structure is peeled off from the surface of the glass substrate.

[0014] Preferably, in step S1 , the size of the glass substrate is 19.8 mm*17.8 mm*1.1 mm.

[0015] Preferably, in step S2, the deposition thickness of the parylene-C film is ≤1 μm, and the mass of the added dimer is 2.5 g.

[0016] Preferably, in step S3, the hydrophobic coating is 3M NOVEC 1700 electronic fluorine liquid, the rotation speed is 3000 rpm, the time is 30 s; the annealing temperature is 100° C., and the time is 10 minutes.

[0017] Preferably, in step S4, the photoresist is SU82025, the spin coating speed is 2000 rpm, and the time is 40 s; the pre-baking operation is annealing at 65°C for 3 minutes and 95°C for 10 minutes on a hot plate; the exposure energy is 170 mJ / cm 2 ; The post-baking operation is annealing at 65°C for 3 minutes and 95°C for 8 minutes on a hot stage; the development time is 1 minute; the hardening operation is annealing at 100°C for 10 minutes on a hot stage.

[0018] Preferably, in step S5, the polydimethylsiloxane (PDMS) is SYLGARD 184, the annealing temperature is 80° C., and the annealing time is 2 hours.

[0019] Preferably, in step S6, the UV-curable optical adhesive layer is NOA61, the spin coating speed is 8000 rpm, the time is 40 s, and the thickness is 2 μm; the exposure power is 100 W, the time is 1 minute, and the vacuum degree in the vacuum thermal evaporation system cavity is <5×10 -4 Pa, evaporation begins. During the evaporation process, the glass substrate is kept rotating to ensure the uniformity of the film. The metal film is obtained by monitoring the deposition thickness and deposition rate.

[0020] Preferably, in step S7, the thickness of the spin-coated UV-curable optical adhesive layer is greater than the thickness of the spin-coated UV-curable optical adhesive layer in step S6, reflecting a thickness difference.

[0021] Preferably, in step S7, the spin-coated UV-curable optical adhesive layer is NOA63, the rotation speed is 4000 rpm, the time is 40 s, the thickness is 20 μm, and the exposure power is 100 W, and the time is 5 minutes.

[0022] A foldable organic electroluminescent device based on a preset crease is prepared according to a preparation method of a foldable organic electroluminescent device based on a preset crease.

[0023] Preferably, the device structure is Ag / MoO3 / N,N′-diphenyl-N,N′-bis(1,1′-biphenyl)-4,4′-diamine(NPB) / 2,3,5,6-tet-rakis(3,6-diphenylcarbazol-9-yl)-1,4-dicyan obenzene(Ir(BT)2(acac))doped4,4′-bis(N-carbazolyl)-1,1′-biphenyl(CBP) / 1,3,5-tris(Nphenyl-ben-zimidazol-2-yl)benzene(TPBi) / Ca / Ag.

[0024] The advantages and beneficial effects of the foldable organic electroluminescent device based on the preset crease and the preparation method thereof in the present invention are:

[0025] 1. The present invention adopts the photolithography method to prepare the mold, which has the advantages of simple operation, low cost, and large-area pattern design.

[0026] 2. The present invention can achieve preset creases by changing the pattern to meet different requirements in actual situations.

[0027] 3. The orange light OLED device used in the present invention has very good photoelectric performance and is relatively stable after being folded multiple times.

[0028] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Flow chart of the preparation of the imprint mold in an embodiment of the present invention;

[0030] Figure 2 Flowchart of preparation and vertical imprinting of planar OLED in an embodiment of the present invention;

[0031] Figure 3 Schematic diagram of a foldable OLED shown in an embodiment of the present invention, wherein A is a cross-sectional schematic diagram and B is an OLED structure diagram;

[0032] Figure 4 is a diagram of the PDMS imprint mold shown in an embodiment of the present invention, wherein i is a surface image and ii is a cross-sectional image, iv is a surface image of NOA63 after imprinting, v is a cross-sectional image of NOA63 after imprinting, and iii is a schematic diagram of the structure of NOA63 after imprinting;

[0033] Figure 5 1. This is a model diagram of two bending modes of the foldable OLED shown in an embodiment of the present invention;

[0034] Figure 6 1 is a foldable OLED shown in an embodiment of the present invention, wherein (a) shows the device structure when folded outward and the deformation process from unfolding to completely folding in half, and (b) shows the device structure when folded inward and the deformation process from unfolding to completely folding in half;

[0035] Figure 7 : This is a current curve diagram of the foldable OLED shown in an embodiment of the present invention, wherein (a) is a current curve diagram when the horizontal spacing is strained from 0% to 100% when folded outward, (b) is a normalized curve diagram of the brightness and current density after 1000 cycles (measured every 100 times) at a strain of 20%-70% when folded outward, (c) is a current curve diagram when the horizontal spacing is strained from 0% to 100% when folded inward, and (d) is a normalized curve diagram of the brightness and current density after 1000 cycles (measured every 100 times) at a strain of 20%-70% when folded inward. DETAILED DESCRIPTION

[0036] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0037] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0038] Example

[0039] A method for preparing a foldable organic electroluminescent device based on a preset crease comprises the following steps:

[0040] (1) Preparation of glass substrate.

[0041] The specific steps are as follows: The glass substrate used is 19.8 x 17.8 x 1.1 mm in size. First, the glass substrate undergoes a standardized cleaning process, ultrasonically cleaning it in acetone, anhydrous ethanol, and deionized water for 60 minutes each. It is then wiped with a sterile medical cotton ball containing anhydrous ethanol and rinsed with deionized water. Finally, a nitrogen gun is used to blow away any water droplets on the surface of the glass substrate. The substrate is then placed in a constant temperature oven at 95°C for 20 minutes and removed for later use.

[0042] (2) Preparation of PDMS imprint template.

[0043] The specific steps are as follows: the glass substrate cleaned and dried in (1) is placed in a chemical vapor deposition (CVD) system, 2.5g of dimer is added, the dimer is vaporized and cracked, and finally a 1μm parylene-C film is deposited on the surface of the glass substrate.

[0044] After the parylene was deposited, a layer of photoresist SU82025 was spin-coated at 2000 rpm on the substrate surface. The substrate was annealed at 65°C for 3 minutes and 95°C for 10 minutes on a hot plate. The photomask was then exposed (exposure energy 170 mJ / cm 2 ), annealed on a hot stage at 65°C for 3 minutes and 95°C for 8 minutes. Finally, it was placed in SU8 developer for 1 minute. Finally, it was rinsed with isopropyl alcohol and deionized water, dried with a nitrogen gun, and annealed on a hot stage at 100°C for 10 minutes to obtain a patterned SU8 template.

[0045] The mixed PDMS prepolymer (SYLGARD 184, a mixture of silicone elastomer and curing agent in a mass ratio of 10:1) was cast on the patterned SU8 template and heated in vacuum at 80°C for 2 hours. Finally, the cured PDMS template was cut out using a blade. The PDMS imprinting area had a thickness of ~40 μm and a width of 120 μm.

[0046] (3) Preparation of foldable OLEDs.

[0047] The specific steps are as follows: the surface of the glass substrate cleaned and dried in (1) is spin-coated with a hydrophobic coating at 3000 rpm for 30 s. The hydrophobic coating is 3M NOVEC 1700 electronic fluoride liquid, and annealed on a hot stage at 100°C for 10 minutes to serve as a hydrophobic layer for peeling off the substrate.

[0048] Then, the glass substrate was placed in a chemical vapor deposition (CVD) system, 2.5 g of dimer was added, and after the dimer was vaporized and cracked, a parylene-C film was deposited on the surface of the glass substrate.

[0049] A layer of UV-curable optical adhesive NOA61 was spin-coated on the surface of the parylene-C film at a spin-coating speed of 8000 rpm and a time of 40 s, and then placed in a UV light box for curing to a thickness of 2 μm.

[0050] OLED was deposited on the surface of NOA61 film using a vacuum thermal evaporation system. The device structure was Ag(xnm) / MoO3(3nm) / NPB(40nm) / CBP:Ir(BT)2(acac) (the rate of the doping material Ir(BT)2(acac) was 5% of the rate of the main material CBP, 30nm) / TPBi(30nm) / Ca(3nm) / Ag(ynm), where the evaporation rates of Ag, NPB, TPBi, and Ca were The evaporation rate of MoO3 is The evaporation rate of CBP is The evaporation rate of Ir(BT)2(acac) is Top emission OLED x=80, y=18, bottom emission OLED x=18, y=80.

[0051] The OLED was shielded with electrodes using a PDMS film. A 20 μm layer of NOA63 was then spin-coated at 4000 rpm for 40 seconds. The PDMS template obtained in (2) was used for imprinting. After degassing, the OLED was exposed to UV light for 5 minutes for curing. Finally, the PDMS template was removed and the entire structure was peeled off from the glass surface to obtain a foldable OLED.

[0052] Figure 1 The following is a flow chart of the preparation of the imprint mold. After patterning SU82025, PDMS is cast to obtain a PDMS imprint mold with a patterned structure.

[0053] Figure 2 This is a flow chart for the fabrication and vertical imprinting of planar OLEDs. A planar OLED is fabricated on a glass surface with reduced surface energy, then vertically imprinted and peeled off the glass.

[0054] Figure 3 (a) and (b) show the cross-sectional schematics and OLED structure of the foldable OLED. The overall structure is glass / parylene (1μm) / NOA61 (2μm) / OLED / NOA63 (20μm), and the device structure is Ag / MoO3 / NPB / CBP:Ir(BT)2(acac) / TPBi / Ca / Ag.

[0055] Figure 4 The surface of the indented portion of the PDMS imprint mold is shown ( Figure 4 i) and cross section ( Figure 4 ii), and the NOA63 surface after stamping ( Figure 4 iv) and cross section ( Figure 4 v) and structural diagram ( Figure 4 In (iii), the scale bar is 40 μm. The PDMS mold's protrusions have a thickness and width of approximately 40 μm and 120 μm, respectively, while the NOA63's depressions have a thickness and width of approximately 20 μm and 120 μm. The PDMS mold's protrusions have a greater thickness than the NOA63, facilitating deeper imprinting.

[0056] Figure 5 Two bending modes are shown: inward fold and outward fold. The indentation is outward for outward fold and inward for inward fold.

[0057] Figure 6 (a) and (b) show the device structure in the outward and inward folding cases. The light direction can be changed by changing the electrode thickness, such as Figure 6 As shown in the figure, by swapping the electrode thickness of the anode and cathode, the light output direction in both the inward and outward bending modes is guaranteed to be upward; and the deformation process from unfolding to completely folding in both the outward and inward folding cases is also shown (each process has 10 illustrations).

[0058] Figure 7 The current curves of the prepared foldable OLED under the horizontal spacing from 0% to 100% strain are shown in the inward and outward folding cases ( Figure 7 The middle (a) is the outward fold. Figure 7 (c) is inward fold) and the normalized curves of brightness and current density after 1000 cycles (measured every 100 times) under 20%-70% strain ( Figure 7 The middle (b) is the outward fold. Figure 7 (d) shows the folded-in display. Whether folded inward or outward, the current remains stable when unfolded and folded. For the outward-folded display, the OLED's current efficiency and brightness remain stable after 1,000 bending cycles. For the inward-folded display, the brightness changes minimally after 1,000 bending cycles, while the current efficiency decreases by 10%.

[0059] Therefore, the present invention adopts the above-mentioned foldable organic electroluminescent device based on preset creases and its preparation method, and uses a vertical imprinting method to produce creases. The operation is simple, the cost is low, and a large area design can be performed. After imprinting the prepared patterned PDMS template, the OLED exhibits excellent folding performance without affecting the photoelectric performance of the device.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a foldable organic electroluminescent device based on a preset crease, characterized in that: The steps include: S1. Preparation of glass substrate: Perform standardized cleaning on the glass substrate by ultrasonic cleaning in acetone, anhydrous ethanol, and deionized water for 60 minutes, respectively. Then, wipe it with a medical sterile cotton ball containing anhydrous ethanol, rinse it with deionized water, and finally blow dry the water droplets on the surface of the glass substrate with a nitrogen gun. Then, place it in a constant temperature oven at 95°C for 20 minutes and remove it for use. S2. Obtaining a parylene-C thin film by chemical vapor deposition: placing the glass substrate cleaned and dried in step S1 into a chemical vapor deposition system, adding a dimer, vaporizing and cracking the dimer, and finally depositing a layer of parylene-C thin film on the surface of the glass substrate; S3, performing a hydrophobic treatment on the substrate to reduce the surface energy of the substrate, and spin-coating a hydrophobic coating on the surface of the glass substrate after cleaning and drying in step S1; S4, obtaining a patterned template by photolithography, spin-coating a photoresist on the surface of the parylene-C film deposited in step S2, exposing it with a photomask after pre-baking, and then post-baking it, and then developing it in a photoresist developer, and then rinsing it with isopropyl alcohol and deionized water in sequence, blowing off the water droplets with a nitrogen gun, and finally hardening the film on a hot stage; S5, casting a patterned polydimethylsiloxane template, casting the mixed polydimethylsiloxane prepolymer on the patterned template in step S4, annealing and curing under vacuum, and finally cutting out the cured polydimethylsiloxane template using a blade; S6. Using a vacuum thermal evaporation system to evaporate the OLED, a layer of parylene-C film is deposited on the hydrophobic surface of the glass substrate obtained in step S3 using the method of step S2, and then a layer of UV-curable optical adhesive film is spin-coated. The film is exposed and cured in a UV light box, and then transferred to the vacuum thermal evaporation system to evaporate the OLED device; S7. A foldable OLED is obtained by an imprinting method. A layer of UV-curable optical adhesive is spin-coated on the surface of the OLED obtained in step S6. The polydimethylsiloxane template obtained in step S5 is aligned with the OLED device for imprinting. The device is placed in a transition chamber of a glove box and evacuated for 2 minutes to remove bubbles. The device is then exposed and cured in a UV light box. The polydimethylsiloxane template is then removed, and the entire multilayer structure is peeled off from the surface of the glass substrate.

2. The method for preparing a foldable organic electroluminescent device based on a preset crease according to claim 1, characterized in that: In step S2 , the deposition thickness of the parylene-C film is ≤1 μm.

3. The method for preparing a foldable organic electroluminescent device based on a preset crease according to claim 1, characterized in that: In step S7 , the thickness of the spin-coated UV-curable optical adhesive layer is greater than the thickness of the spin-coated UV-curable optical adhesive layer in step S6 , reflecting a thickness difference.

4. A foldable organic electroluminescent device based on a preset crease, characterized in that: It is prepared according to the preparation method according to any one of claims 1 to 3.

5. The foldable organic electroluminescent device based on a preset crease according to claim 4, characterized in that: The structure of the device is Ag / MoO3 / N,N′-diphenyl-N,N′-bis(1,1′-biphenyl)-4,4′-diamine / 2,3,5,6-tet-rakis(3,6-diphenyl carbazol-9-yl)-1,4-dicyanobenzene doped 4,4′-bis(N-carbazolyl)-1,1′-biphenyl / 1,3,5-tris(Nphenyl-ben-zimidazol-2-yl)benzene / Ca / Ag.

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