Foldable organic light-emitting device based on preset creases and preparation method of foldable organic light-emitting device

Abstract

The invention belongs to the technical field of flexible light-emitting devices, and particularly discloses a foldable organic light-emitting device based on preset creases and a preparation method thereof, and the preparation method comprises the steps: S1, preparing a glass substrate; s2, a poly-p-xylylene-C thin film is obtained through a chemical vapor deposition method; s3, performing hydrophobic treatment on the substrate; s4, obtaining a patterned template through a photoetching method; s5, a patterned polydimethylsiloxane template is cast; s6, evaporating the OLED by adopting a vacuum thermal evaporation system; and S7, obtaining the foldable OLED through an imprinting method. According to the foldable organic light-emitting device based on the preset crease and the preparation method of the foldable organic light-emitting device, the crease is manufactured through a vertical imprinting method, operation is easy, cost is low, large-area design can be achieved, after imprinting is conducted through a prepared patterned PDMS template, an OLED shows excellent folding performance, and the OLED can be applied to the field of light emitting devices. Meanwhile, the photoelectric property of the device is not influenced.

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 developed rapidly, and people's demand for a better life has increased. As a medium for human-computer interaction, display technology is closely related to our lives. From the initial bulky cathode ray tube display to flat-panel liquid crystal displays and flexible OLED displays, display technology has achieved rapid development. In particular, flexible display technology has made the form of the display no longer limited to a flat structure, and has begun to develop towards a deformable display. Foldable screens have shown great application potential in foldable mobile phones. By folding, the size of the mobile phone screen can be doubled or tripled, breaking the size boundary between mobile phones and tablets, greatly expanding the functions of mobile phones, and providing users with functions and conveniences that small-sized mobile phones cannot achieve. It has become a research hotspot for high-end mobile phones and displays. We have reason to believe that flexible and bendable displays will play an increasingly important role in future life.

[0003] Folding is a unique deformation mode with typical characteristics of a folding angle with a small radius of curvature, a fixed bending position and a designable folding structure. Among the developed folding processes, one is an intrinsic 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 will be produced, 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 are the main components of current display technology. However, organic electroluminescent devices have a multi-layer structure. If the intrinsic folding scheme is adopted, the bending radius gradually decreases during the folding process, the interlayer interaction force is complex, and the gradually increasing bending strain has a significant negative impact on the device performance. The crease preset scheme can better control the folding structure of the device and the bending strain at the crease, which is conducive to obtaining foldable organic electroluminescent devices and foldable displays with high luminescence performance and complex folding 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 made by using a vertical imprinting method, which is simple to operate, low in cost, and can be designed over a large area. After imprinting with 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: Standardized cleaning treatment of the glass substrate: ultrasonic cleaning for 60 minutes in the order of acetone, anhydrous ethanol and deionized water, then wiping with medical sterile cotton balls containing anhydrous ethanol, then rinsing with deionized water, finally drying the water droplets on the surface of the glass substrate with a nitrogen gun, and placing it in a constant temperature oven at 95°C for 20 minutes, and then taking it out for use;

[0008] S2, obtaining a poly(p-xylene)-C 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 poly(p-xylene)-C film on the surface of the glass substrate;

[0009] S3, performing 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 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 turn, 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 OLED, depositing a layer of parylene-C film on the hydrophobic surface of the glass substrate obtained in step S3 by the method of step S2, and then spin coating a layer of UV-curable optical adhesive film, exposing and curing in a UV light box, and transferring to the vacuum thermal evaporation system to evaporate the OLED device;

[0013] S7. Obtain a foldable OLED by a stamping method. Spin-coat a layer of UV-curable optical adhesive on the surface of the OLED obtained in step S6. Align the PDMS template obtained in step S5 with the OLED device for stamping. Put it into a transition chamber of a glove box and evacuate for 2 minutes to remove bubbles. Then, expose and cure it in a UV light box. After that, remove the PDMS template and peel off the entire multilayer structure 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 polyparaxylene-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 fluorination 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 stage; 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 developing 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 a 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 folds 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 its performance is relatively stable after multiple folding.

[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 is a flow chart of preparing an imprinting mold in an embodiment of the present invention;

[0030] Figure 2 The flowchart of the preparation and vertical imprinting of a 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 diagram and ii is a cross-sectional diagram, iv is a surface diagram of NOA63 after imprinting, v is a cross-sectional diagram of NOA63 after imprinting, and iii is a schematic diagram of the structure of NOA63 after imprinting;

[0033] Figure 5 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) is a diagram showing the device structure in an outward folding state and the deformation process from unfolding to being completely folded in half, and (b) is a diagram showing the device structure in an inward folding state and the deformation process from unfolding to being completely folded in half;

[0035] Figure 7 3 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 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 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 through the accompanying drawings and embodiments.

[0037] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field 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 size of the glass substrate used is 19.8*17.8*1.1mm. First, the glass substrate is subjected to standardized cleaning treatment, and ultrasonic cleaning is performed in the order of acetone, anhydrous ethanol, and deionized water for 60 minutes, then wiped with a medical sterile cotton ball containing anhydrous ethanol, and then rinsed with deionized water. Finally, the water droplets on the surface of the glass substrate are blown dry with a nitrogen gun and placed in a constant temperature oven at 95°C for 20 minutes, and then taken out for use.

[0042] (2) Preparation of PDMS imprinting 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, 2.5 g of dimer is added, the dimer is vaporized and cracked, and finally a 1 μm 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, and then annealed at 65°C for 3 minutes and 95°C for 10 minutes on a hot stage. Then the photomask was exposed (exposure energy 170 mJ / cm 2 ), annealed at 65°C for 3 minutes and 95°C for 8 minutes on a hot stage. Finally, it was placed in SU8 developer for 1 minute, rinsed with isopropanol and deionized water, dried with a nitrogen gun, and annealed at 100°C for 10 minutes on a hot stage 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 thickness of the PDMS imprinted area was ∼40 μm and the width was 120 μm.

[0046] (3) Preparation of foldable OLEDs.

[0047] The specific steps are as follows: after cleaning and drying in (1), a hydrophobic coating is spin-coated at 3000 rpm for 30 seconds. The hydrophobic coating is 3M NOVEC 1700 electronic fluoride liquid, and then 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 layer of 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. The film was then placed in a UV light box for curing, with 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 by electrodes using a PDMS film, and then a 20 μm layer of NOA63 was spin-coated at 4000 rpm for 40 seconds. The PDMS template obtained in (2) was used for imprinting. After degassing, it was exposed to a UV light box 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 preparation flow chart of the imprint mold is as follows. After the pattern is photolithographically formed on SU82025, the PDMS imprint mold with the pattern structure is obtained by casting with PDMS.

[0053] Figure 2 The preparation and vertical imprinting process flow chart of planar OLED. Planar OLED is prepared on a glass surface with reduced surface energy, and then peeled off from the glass after vertical imprinting.

[0054] Figure 3 (a) and (b) show the cross-sectional schematic diagram and OLED structure of the foldable OLED. The entire 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 part 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 convex thickness and width of the PDMS mold are approximately 40 μm and 120 μm, respectively, and the concave thickness and width of NOA63 are approximately 20 μm and 120 μm. The convex thickness of the PDMS mold is higher than that of NOA63, which is conducive to deeper imprinting.

[0056] Figure 5 Two bending modes are shown: inner bending and outer bending. The outer bending is when the indentation is outward and the inner bending is when the indentation is inward.

[0057] Figure 6 (a) and (b) show the device structure in the outward and inward folding cases. The light emission 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 the cathode, the light emission direction in both the inward and outward folding modes is ensured to be upward; and the deformation process from unfolding to completely folded in 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 when folded inward and outward respectively are shown ( Figure 7 The middle (a) is the outer 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) is folded inwards). Whether folded inwards or outwards, the current is stable when unfolded and folded. In the case of outward folding, after 1000 cycles of bending, the current efficiency and brightness of the OLED remain stable. In the case of inward folding, after 1000 cycles of bending, the brightness changes little and the current efficiency decays 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 printing method to make the creases. The operation is simple, the cost is low, and a large area can be designed. After printing with 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 solution of the present invention rather than to limit it. 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 solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution 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: Standardized cleaning treatment of the glass substrate: ultrasonic cleaning for 60 minutes in the order of acetone, anhydrous ethanol and deionized water, then wiping with medical sterile cotton balls containing anhydrous ethanol, then rinsing with deionized water, finally drying the water droplets on the surface of the glass substrate with a nitrogen gun, and placing it in a constant temperature oven at 95°C for 20 minutes, and then taking it out for use; S2, obtaining a poly(p-xylene)-C 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 poly(p-xylene)-C film on the surface of the glass substrate; S3, performing 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 polyparaxylene-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 turn, 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 OLED, depositing a layer of polyparaxylene-C film on the hydrophobic surface of the glass substrate obtained in step S3 by the method of step S2, and then spin-coating a layer of UV-curable optical adhesive film, exposing and curing in a UV light box, and transferring to the vacuum thermal evaporation system to evaporate the OLED device; S7. Obtain a foldable OLED by a stamping method. Spin-coat a layer of UV-curable optical adhesive on the surface of the OLED obtained in step S6. Align the polydimethylsiloxane template obtained in step S5 with the OLED device for stamping. Put it into a transition chamber of a glove box and evacuate for 2 minutes to remove bubbles. Then, expose and cure it in a UV light box. After that, remove the polydimethylsiloxane template and peel off the entire multilayer structure 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 polyparaxylene-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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