A method for semi-transparent encapsulation of light emitting devices with self-cleaning function

Abstract

This invention discloses a semi-transparent encapsulation technology with self-cleaning function for light-emitting devices. Self-cleaning and semi-transparency are products of display technology development. Currently, there are no reports of simultaneously achieving both functions and applying them to light-emitting devices. We specifically introduce a functionalized encapsulation technology. First, polymer PDMS and a curing agent are mixed at a volume ratio of 10:1 and stirred thoroughly. Then, a certain amount of PDMS gel solution is taken and poured into a mold containing rose petals, ensuring full contact between the solution and the petal surface. After curing, a PDMS film with the reverse structure of the petal surface is obtained. This film is then combined with a Para sealing film for encapsulating the light-emitting device. Light-emitting devices based on this encapsulation technology exhibit excellent photoelectric performance and multifunctional characteristics such as self-cleaning and semi-transparency. This encapsulation technology is simple, efficient, low-cost, and widely applicable, laying a solid foundation for emerging applications of electroluminescent devices.

Description

Technical Field

[0001] This invention belongs to the field of quantum dot light-emitting diode packaging technology, specifically relating to a semi-transparent packaging method with self-cleaning function and its application in semi-transparent quantum dot light-emitting diodes. Background Technology

[0002] With the rapid development of the optoelectronic technology industry, semi-transparent quantum dot light-emitting diodes (LEDs) have shown great application prospects and unique technological charm in emerging display fields such as automotive / window displays, architectural media, and technology exhibitions. Although semi-transparent quantum dot LEDs exhibit significant advantages in performance and functionality, their application in various outdoor products remains significantly hampered. This is because outdoor environmental factors affect the lifespan and quality of outdoor products, and cleaning them, in particular, significantly increases costs. Encapsulation, a common method for protecting optoelectronic devices, can effectively improve device quality and stability; however, currently, encapsulation technologies with high light transmittance for light-emitting devices are still relatively lacking, and the cost of device cleaning remains unresolved. Polydimethylsiloxane (PDMS), due to its excellent plasticity and light transmittance, can be used as a substrate and encapsulation layer for semi-transparent devices. However, existing technologies using PDMS as an encapsulation material typically employ multilayer thin-film encapsulation methods, which makes the encapsulation process complex, costly, and affects the device's light transmittance. In addition, inspired by the rich and amazing biological species in nature, it has been found that micro- and nano-structures on biological surfaces can effectively achieve self-cleaning functions. However, the manufacturing process of these microstructures is currently mostly based on rigid photolithography, which cannot be used for flexible films. Summary of the Invention

[0003] To overcome the aforementioned difficulties, this invention provides a semi-transparent encapsulation method with self-cleaning function suitable for electroluminescent devices. By preparing a PDMS film with rose petal microstructures and combining it with PM-996, a sealing film material with excellent flexibility and light transmittance, semi-transparent quantum dot LEDs are encapsulated, increasing their stability and giving them multiple functions such as self-cleaning and semi-transparency. The introduction of this encapsulation method not only increases the stability of semi-transparent quantum dot LEDs but also paves a practical path for the self-cleaning function of future outdoor transparent electronic products.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] The preparation of PDMS films based on rose petal microstructures and their application in semi-transparent quantum dot light-emitting diodes includes the following steps:

[0006] (1) Pretreatment of rose petals: Fix fresh rose petals between two clean glass slides and flatten them by physical pressing.

[0007] Furthermore, the time used for physical flattening in step (1) is more than 8 hours.

[0008] Gel solution preparation: Mix the polymer PDMS and the curing agent in a certain proportion and stir thoroughly to form a gel solution. Then place the gel solution in a vacuum chamber to make the air bubbles disappear.

[0009] Furthermore, in step (2), the volume ratio of the PDMS polymer to the curing agent is 10:1.

[0010] Furthermore, in step (2), the PDMS polymer and curing agent are stirred for at least 20 minutes.

[0011] Furthermore, in step (2), the vacuuming time is more than 20 minutes.

[0012] (3) Preparation of biomimetic PDMS film: The pretreated rose petals were taken out and fixed on a glass slide. Then, the glass mold was fixed to the surface of the rose with tape. The prepared PDMS gel solution was poured into the mold to ensure full contact with the surface of the rose. Then, the mold was removed and placed on a baking tray for annealing and curing. After that, the rose petals were removed from the cured PDMS film. The cured PDMS film was then washed with deionized water and dried with N2 before being packaged for use.

[0013] Furthermore, in step (3), the height of the PDMS gel solution poured into the mold is 1 mm.

[0014] Furthermore, in step (3), the annealing and curing temperature is 70°C and the time is 2 hours.

[0015] Furthermore, in step (3), the time for rinsing the cured PDMS membrane with deionized water is 20 minutes.

[0016] (4) Fabrication of semi-transparent quantum dot light-emitting diodes:

[0017] The semi-transparent quantum dot light-emitting diode includes a cathode 1, an electron injection layer 2, a quantum dot light-emitting layer 3, a hole transport layer 4, a hole injection layer 5, and an anode 6, which are stacked sequentially from bottom to top.

[0018] The ITO-coated glass substrate was cleaned and UV-treated. Then, the treated substrate was transferred to a glove box, and an electron injection layer of ZnO, a quantum dot emitting layer of CdSe-ZnS, and a hole transport layer of PVK were sequentially prepared using a spin coater. Each spin coat was followed by an appropriate annealing treatment. Next, the device was removed from the glove box and spin-coated with a PEDOT:PSS solution in an atmospheric environment, followed by annealing. Finally, the device was returned to the glove box, where a silver nanowire metal anode was spin-coated and annealed.

[0019] Furthermore, in step (4), the spin coating speed of the ZnO is 1500 r / min and the time is 35 s.

[0020] Furthermore, in step (4), the annealing temperature of the ZnO is 120°C and the annealing time is 20 min.

[0021] Furthermore, in step (4), the spin coating speed of the quantum dot light-emitting layer is 2000 r / min and the time is 40 s.

[0022] Furthermore, in step (4), the annealing temperature of the quantum dot light-emitting layer is 110°C and the time is 30 min.

[0023] Furthermore, in step (4), the spin coating speed of the PVK is 2500 r / min and the time is 40 s.

[0024] Furthermore, in step (4), the annealing temperature of the PVK is 120°C and the time is 20 min.

[0025] Furthermore, in step (4), the spin coating speed of PEDOT:PSS is 3000 r / min and the time is 40 s.

[0026] Furthermore, in step (4), the annealing temperature of PEDOT:PSS is 90°C and the time is 10 min.

[0027] Furthermore, in step (4), the spin coating speed of the silver nanowires is 2000 r / min and the time is 40 s.

[0028] Furthermore, in step (4), the annealing temperature of the silver nanowires is 90°C and the annealing time is 10 min.

[0029] (5) Packaging and testing process of semi-transparent quantum dot light-emitting diodes:

[0030] Para-996 sealing adhesive was applied to the back (unstructured side) of the prepared biomimetic PDMS film to form an encapsulation film. Then, the Para-996 sealing film side of the encapsulation film was attached to the surface of the prepared translucent quantum dot light-emitting diode device, and annealing was performed to complete the encapsulation of the translucent quantum dot light-emitting diode. After encapsulation, the device was removed from the glove box and its performance was tested in an atmospheric environment.

[0031] Furthermore, in step (5), the area of ​​the Para-996 sealing adhesive is 15mm × 15mm.

[0032] Furthermore, in step (5), the area of ​​the biomimetic PDMS film is 15mm × 15mm.

[0033] Furthermore, in step (5), the annealing temperature of the encapsulation process is 90°C and the time is 5 min.

[0034] The advantages of this invention are as follows: Using readily available biomaterials such as rose petals as templates, the microstructure of biological organisms is replicated using PDMS gel solution, and combined with inexpensive and readily available Para-996 to achieve a flexible and transparent encapsulation film. The method is simple, effective, and inexpensive to manufacture, making it suitable for flexible electroluminescent devices. The semi-transparent quantum dot LEDs based on this encapsulation layer exhibit excellent performance, while also possessing semi-transparency, anti-reflection, and self-cleaning functions, greatly enhancing the application prospects of next-generation displays outdoors. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the process for preparing the biomimetic PDMS film in Example 1.

[0036] Figure 2 Scanning electron microscope (SEM) images (a) and (b) of the rose petal material used in Example 1 at different magnifications, and scanning electron microscope (SEM) images (c) and (d) of the prepared biomimetic PDMS film at different magnifications.

[0037] Figure 3 The figures show the contact angle (CA) and sliding angle (SA) of the biomimetic PDMS film cured at different temperatures in Example 1 (a), the CA and sliding angle (SA) of the biomimetic PDMS film cured at 70 degrees Celsius after being bent a different number of times at a radius of curvature of 3 mm (b) (the inset is a physical image of the biomimetic PDMS film under bending), the transmittance curve of the biomimetic PDMS film cured at different temperatures (c), and the reflectance curve of different encapsulation materials (d).

[0038] Figure 4 The diagram shows the device structure of the semi-transparent quantum dot light-emitting diode used in Example 2 (a) and the overall structure of the packaged device (b).

[0039] Figure 5 The graphs show the current density-voltage characteristic curve (a), brightness-voltage characteristic curve (b), current efficiency-brightness characteristic curve (c), and power efficiency-brightness characteristic curve (d) of the semi-transparent quantum dot light-emitting diode device used in Example 2.

[0040] Figure 6 The self-cleaning capability test process of the semi-transparent quantum dot light-emitting diode device used in Example 2 is shown in Figure (a) and (b), which compares the device with mud and sand on its surface with deionized water before and after cleaning, and the device with unstructured PDMS encapsulation film before and after cleaning with deionized water. Detailed Implementation

[0041] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0042] Example 1: A method for preparing a semi-transparent encapsulation film with self-cleaning function, comprising the following steps:

[0043] (1) Pretreatment of biological materials: Fresh rose petals were fixed between two glass slides and kept for 8 hours to make them flat.

[0044] (2) Gel solution preparation: Mix the polymer PDMS and the curing agent at a volume ratio of 10:1 and stir thoroughly for at least 20 minutes. Then transfer the solution to a vacuum chamber and heat for 10 minutes. -1 Vacuum at a pressure of pa for 20 minutes to thoroughly remove air bubbles from the solution.

[0045] (3) Microstructure replication operation: Fix the glass mold on the glass slide with rose petals, then pour the prepared PDMS gel solution into the mold to make the solution height 1mm, then place the mold containing the solution on the baking tray and anneal at 70℃ for 2h.

[0046] (4) Post-treatment of PDMS membrane: Remove the annealed and cured PDMS membrane, remove the rose petals, wash the surface of the PDMS membrane with deionized water, and then dry it with N2.

[0047] (5) Characterization of PDMS film: The treated PDMS film was characterized by various parameters, including surface morphology under scanning electron microscopy, water contact angle, sliding angle, bending resistance, transmittance and reflectance.

[0048] (6) Preparation of encapsulation film: cut out Para-996 sealing film of the same size as PDMS film, and attach it tightly to the back of biomimetic PDMS film to obtain encapsulation film;

[0049] Figure 1 This is a flowchart illustrating the process of replicating the microstructure of rose petals. Since rose petals are not perfectly flat, we pre-treated them using step 1 above before film fabrication to make them relatively flat, effectively improving the replication effect. To prevent the final biomimetic film from being too thick or too thin and affecting the encapsulation effect, we controlled the depth of the PDMS gel solution injected into the mold to 1 mm, as shown in the diagram. Figure 1 As shown. Furthermore, due to the inherent characteristics of roses, through extensive experimental comparison, we selected annealing the PDMS gel solution at 70℃ to obtain the most complete biomimetic PDMS film with the replicated surface structure. This ensured that the surface morphology largely preserved the reverse structure of the rose petal surface, as shown. Figure 2 As shown, even after magnification of 8000 times, the complete fine microstructure can still be observed. Figure 3 (a) shows the water contact angle and sliding angle of PDMS films obtained by annealing and curing at different temperatures. The results show that the biomimetic PDMS film obtained by annealing and curing at 70°C has a contact angle of 155° and a sliding angle of only 2.3°, exhibiting the best superhydrophobicity. This also indicates that the surface structure of the rose petals replicated by curing at this temperature is the most complete. Figure 3 (b) The water contact angle and sliding angle of the biomimetic PDMS membrane at different bending times are shown. The results show that after 5000 bending cycles, the water contact angle of the PDMS membrane is still above 150°, while the sliding angle only increases slightly. This indicates that the biomimetic PDMS membrane has good durability and can still maintain its superhydrophobicity after thousands of bending cycles. Figure 3 (c) The transmittance of PDMS films annealed at different temperatures is shown. The results indicate that the transmittance of PDMS films annealed at different temperatures varies. The PDMS film annealed at 70℃ has the lowest transmittance, indicating the strongest light scattering at this temperature. This further suggests that the microstructure replicated by the PDMS film annealed at this temperature is the most complete. Even so, the transmittance of the PDMS film annealed at 70℃ remains above 66% in the visible light range, ensuring the transparency of the device. Figure 3 (d) also shows the light reflectance of different encapsulation materials. The results show that the light reflectance of the PDMS film with biomimetic microstructure is significantly reduced from nearly 90% to below 50% compared with the unstructured PDMS film and glass. This indicates that the anti-reflection ability of the film is significantly improved after microstructure replication.

[0050] Example 2: Fabrication, packaging, and testing of a semi-transparent quantum dot light-emitting diode, such as... Figure 4As shown in (a), the device includes a cathode 1, an electron injection layer 2, a quantum dot light-emitting layer 3, a hole transport layer 4, a hole injection layer 5, and an anode 6, which are stacked sequentially from bottom to top.

[0051] In this embodiment, the cathode 1 is made of ITO, the electron injection layer 2 is made of ZnO solution, the quantum dot light-emitting layer 3 is made of CdSe-ZnS solution, the hole transport layer 4 is made of PVK solution, the hole injection layer 5 is made of PEDOT:PSS solution, and the anode 6 is made of a solution containing silver nanowires. The specific implementation includes the following steps:

[0052] (1) Mix the organic polymer PEDOT:PSS (Heraeus-Clevios, 4083) aqueous solution with isopropanol IPA at a volume ratio of 1:1 and stir for 12 h to obtain the PEDOT:PSS solution of this scheme.

[0053] (2) The substrate with ITO is cleaned, and the electron injection layer 2, quantum dot light-emitting layer 3, hole transport layer 4, hole injection layer 5, and anode 6 are prepared sequentially by solution spin coating and annealing at different temperatures on the prepared cathode substrate.

[0054] (3) The encapsulation process is carried out in the glove box. The Para-996 sealing film side of the encapsulation film is attached to the surface of the quantum dot light-emitting diode and annealed at 90°C for 5 minutes to achieve perfect bonding between the encapsulation film and the device.

[0055] Figure 4 (a) is a structural diagram of the translucent quantum dot light-emitting diode in the example. All functional layers, including the anode, are fabricated using a solution method, which significantly reduces the device fabrication cost. Furthermore, it should be noted that because the substrate, functional layer materials, and encapsulation materials all possess good transparency, the silver nanowires used as the anode material also exhibit good light transmittance after being formed into a thin film. Therefore, after device encapsulation, the entire device appears translucent. When the device is turned on, light can pass through the encapsulation material from the top anode side or pass through the substrate from the bottom. Figure 4 (b) is a schematic diagram of the overall structure after the device is packaged. Due to the good light transmittance of the packaging material, the semi-transparent quantum dot light-emitting diode was successfully packaged and the transparency of the device was well maintained. Figure 5 (a) shows the current density-voltage characteristic curve of a semi-transparent quantum dot light-emitting diode. It can be seen that the current density curves measured at the top and bottom of the device basically overlap. Figure 5 (b) shows the luminance-voltage characteristic curve of the semi-transparent quantum dot light-emitting diode, with the total luminance of the device reaching 28637 cd / m². 2Its maximum luminous intensity at the top and bottom reaches 11439 and 17198 cd / m², respectively. 2 Although the brightness of the light emitted from the top is slightly weaker than that emitted from the bottom, it can still reach 10. 4 cd / m 2 The above fully meets the standards for practical application. Figure 5 (c) and 5(d) are the current efficiency-luminance characteristic curves and power efficiency-luminance characteristic curves of the semi-transparent quantum dot light-emitting diode device, respectively. The maximum current efficiency measured from the top and bottom of the device is 2.17 and 3.31 cd / A, respectively, and the maximum power efficiency is 0.98 and 1.46 lm / W, respectively. The measured efficiencies are all on the same order of magnitude, indicating that the device has good transparency. Figure 6 (a)-(d) demonstrate the self-cleaning effect of a semi-transparent quantum dot LED encapsulated with a biomimetic PDMS film in the on-state. Two emitting quantum dot LED devices were simultaneously covered with mud and sand, as shown in the figures. Figure 6 (a) and (c), and then the surfaces of the two light-emitting devices were cleaned with deionized water. The results are as follows: Figure 6 As shown in (b) and (d), after rinsing with deionized water, the device surface encapsulated with the biomimetic PDMS film showed almost no residue of mud or sand. Conversely, for devices encapsulated with PDMS without a biomimetic structure, mud and water accumulated on the device surface, partially obscuring and blocking the light-emitting area. This indicates that the biomimetic PDMS film has a significant self-cleaning function. This self-cleaning characteristic provides better environmental adaptability for the device in special outdoor environments, such as rainy days and hazy weather.

[0056] These results demonstrate that this biomimetic PDMS thin-film encapsulation method based on microstructure replication opens up possibilities for the outdoor use of display devices. Furthermore, the inherent light transmittance of the encapsulation material provides a new approach for the functional encapsulation of semi-transparent light-emitting devices, promoting the practical application of transparent displays in outdoor environments.

[0057] It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this invention, and these modifications and improvements are all within the scope of protection of this invention.

Claims

1. A method for semi-transparent encapsulation of a light emitting device with self-cleaning function, characterized in that: Includes the following steps: Step 1: Rose petal treatment: Fix fresh rose petals onto a clean glass slide, then cover the rose petals with another glass slide and place them in a drying cabinet for a period of time to ensure that the surface of the rose petals is flat. Step 2: Gel solution preparation: mix PDMS polymer and curing agent in a certain volume ratio and stir well to form a gel solution, place the gel solution in a vacuum chamber, slowly vacuum to a vacuum degree of 10 -1 pa, maintain the vacuum degree and continue to vacuum, remove the air bubbles generated in the solution due to stirring, and form a bubble-free PDMS gel solution; Step 3: Replication process: Fix the self-made glass mold onto the glass slide with rose petals attached. Then pour an appropriate amount of PDMS gel solution prepared in Step 2 into the mold, ensuring it is in full contact with the surface of the petals. Next, place the mold on a baking tray for annealing. Then, use tweezers to peel off the PDMS from the rose petals, obtaining a biomimetic PDMS film with a self-cleaning surface. The height of the PDMS gel solution poured in is 1 mm. The annealing temperature is 70℃. Step 4: Preparation of encapsulation film: Clean the surface of the PDMS film with the biomimetic self-cleaning surface obtained in Step 3 with deionized water and dry it with nitrogen gas; cut out a Para-996 sealing film of the same size as the PDMS film and attach it tightly to the back of the biomimetic PDMS film for bonding with the biomimetic PDMS film to obtain an encapsulation film with self-cleaning, anti-reflective and semi-transparent characteristics. Step 5: Fabrication and encapsulation of semi-transparent quantum dot light-emitting diodes: The substrate coated with ITO is cleaned and subjected to UV treatment. On the treated substrate, an electron injection layer, a quantum dot light-emitting layer, a hole transport layer, a hole injection layer, and a metal nanowire electrode are sequentially fabricated by solution spin coating and annealing at different temperatures. The Para-996 sealing film side of the encapsulation film prepared in Step 4 is tightly attached to the surface of the fabricated device and annealed to complete the encapsulation of the device. Step 6: Device performance testing: Place the packaged device at room temperature for various performance tests.

2. The semi-transparent encapsulating method for a light emitting device with a self-cleaning function according to claim 1, wherein the semi-transparent encapsulating method is characterized by: The rose in step 1 is a red Carola rose, and the surface in contact with PDMS is the inner surface of the petals.

3. The method of claim 1, wherein the self-cleaning function is provided by a material having a hydrophilic surface. The volume ratio of PDMS solution polymer to curing agent in step 2 is 10:1; the polymer and curing agent in step 2 are stirred thoroughly for more than 20 minutes.

4. The method of claim 1, wherein the self-cleaning function is provided by a material having a hydrophilic surface. In step 2, the PDMS gel solution is evacuated for more than 20 minutes.

5. The method of claim 1, wherein the self-cleaning function is provided by a material having a hydrophilic surface. In step 4, both the PDMS and Para-996 sealing film have an area of ​​15mm × 15mm.

6. A semi-transparent encapsulation method with self-cleaning function for a light-emitting device as described in claim 1, characterized in that, The annealing temperature during encapsulation in step 5 is 90°C.

7. A semi-transparent encapsulation method with self-cleaning function for light-emitting devices as described in claim 1, characterized in that, The electron injection layer in step 5 is ZnO, the quantum dot luminescent layer is CdSe-ZnS, the hole transport layer is PVK, and the hole injection layer is prepared by mixing PEDOT:PSS aqueous solution and isopropanol in a 1:1 volume ratio.

8. A semi-transparent encapsulation method with self-cleaning function for a light-emitting device as described in claim 1, characterized in that, The metal nanowires mentioned in step 5 are silver nanowires.

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