A flexible PLED with in-situ thermally induced double cross-linking enhanced interfacial adhesion and a preparation method thereof

Abstract

This invention relates to the field of semiconductor device technology, specifically to a flexible PLED with enhanced interfacial adhesion through in-situ thermally induced double crosslinking and its fabrication method. This invention is simple to operate and has good process compatibility. Crosslinking monomers PEGDMA and PUA are introduced into the HTL layer and EML layer, respectively. An in-situ thermally induced double crosslinking network is used, and by introducing covalent bonds at the interface, the interfacial shear strength is improved, mitigating the interlayer delamination problem that easily occurs in flexible devices under dynamic deformation. The PLED device provided by this invention exhibits excellent photoelectric performance stability while maintaining high photoelectric conversion efficiency, and also possesses mechanical fatigue resistance, maintaining stable light emission characteristics even under tensile strain.

Description

Technical Field

[0001] This invention relates to the field of semiconductor device technology, specifically to a flexible PLED with enhanced interfacial adhesion through in-situ thermally induced double crosslinking and its preparation method. Background Technology

[0002] Flexible polymer light-emitting diodes (PLEDs) are a type of semiconductor device with flexibility and stretchability, and have broad application prospects in the fields of display and solid-state lighting. However, traditional flexible PLEDs typically employ a multilayer heterogeneous thin-film stacked structure, relying mainly on weak van der Waals forces for connection. Due to the mismatch in the intrinsic properties of organic and inorganic layers (or different organic layers), the interfacial adhesion between functional layers is insufficient, and stress concentration easily occurs after long-term bending or stretching, leading to device failure. For example, the flexibility of organic functional layers and the brittleness of inorganic electrodes, as well as the significant differences in the thermal expansion coefficients of the materials in each layer, all make the interface a stress concentration zone under mechanical loads. In dynamic usage scenarios, the device must withstand complex stresses such as periodic bending, stretching, or torsion. These stresses act directly on the weak physical stacked interfaces, inducing microcrack initiation, interlayer slippage, and even macroscopic delamination, leading to device structural failure and causing significant degradation of photoelectric performance and a sharp decrease in energy conversion efficiency. Furthermore, the infiltration of water and oxygen through interfacial gaps can further erode interfacial chemical bonds, accelerating the degradation process of the device under the "mechanical-environment" coupling effect.

[0003] Currently, existing technologies often enhance the interfacial bonding between functional layers by introducing additional bonding intermediate layers or performing plasma surface treatment. However, introducing additional bonding intermediate layers often interferes with the effective injection and transport of charge carriers, and may even introduce non-radiative recombination centers. Furthermore, these technologies are complex and have poor compatibility. Plasma surface treatment requires precision equipment, is complex to operate, and can easily damage multilayer structures, leading to impaired charge transport and degraded device performance. Therefore, developing a technical solution that does not compromise the electrical performance of the device and can achieve in-situ interface enhancement has broad application prospects. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a flexible PLED with enhanced interfacial adhesion through in-situ thermally induced double crosslinking and its preparation method. The invention employs a heat treatment technique to induce in-situ crosslinking between the hole transport layer and the light-emitting layer. By introducing covalent chemical bonding to replace physical stacking, the interlayer adhesion is enhanced, thereby improving the luminescent performance and stability of the device and solving the technical problems mentioned in the background art.

[0005] This invention is achieved through the following technical solution:

[0006] A method for preparing flexible PLEDs with enhanced interfacial adhesion through in-situ thermally induced double crosslinking includes the following steps:

[0007] S1. Introduce a first crosslinking monomer containing unsaturated acrylate double bonds into the hole transport layer (HTL layer) to obtain a modified HTL layer, and deposit the modified HTL layer on a flexible substrate with an etched anode.

[0008] A second crosslinking monomer containing unsaturated acrylate double bonds is introduced into the light-emitting layer (EML layer) to obtain a modified EML layer. The modified EML layer is then deposited on the modified HTL layer to form a stacked structure with a heterojunction interface.

[0009] The first and second crosslinking monomers are used for thermally initiated free radical polymerization reactions;

[0010] S2. Heat treatment is performed on the laminated structure obtained in step S1 to induce in-situ free radical copolymerization of the first crosslinking monomer and the second crosslinking monomer at the heterojunction interface to form a covalent crosslinking network, which can be used to enhance interfacial adhesion.

[0011] S3. After heat treatment in step S2, 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi) as the electron transport layer, LiF as the electron injection layer, and Al electrode as the cathode are sequentially thermally vapor-deposited onto the surface of the stacked structure to prepare the target flexible PLED.

[0012] As a further aspect of the present invention, in step S1, the first crosslinking monomer is polyethylene glycol dimethacrylate (PEGDMA), and the second crosslinking monomer is polyurethane acrylate (PUA).

[0013] As a further embodiment of the present invention, step S1 specifically involves: dissolving PEGDMA in deionized water and stirring magnetically until completely dissolved; mixing the PEGDMA aqueous solution with a PEDOT:PSS aqueous solution to obtain a modified HTL layer solution; spin-coating the solution onto a flexible substrate with an etched anode at 3000 rpm; pre-drying at 100°C for 10 minutes; and obtaining a modified HTL layer after film formation. Additionally, dissolving PUA in toluene solvent and mixing the toluene solution of PUA with a chlorobenzene solution of Super Yellow (SY) to obtain a modified EML layer solution; spin-coating the solution onto the modified HTL layer at 1500 rpm; and obtaining a modified EML layer after film formation.

[0014] In a further embodiment of the present invention, the modified HTL layer is a PEDOT:PSS film doped with PEGDMA, wherein the mass fraction of PEGDMA in the solid component is 15~50 wt%.

[0015] In a further embodiment of the present invention, the modified EML layer is a SY thin film doped with PUA, wherein the mass fraction of PUA in the solid component is 15~50 wt%.

[0016] In a further embodiment of the present invention, in step S2, the heat treatment is a heat annealing treatment performed under an inert atmosphere, with the temperature set to 120~160℃ and the time set to 2~20 minutes.

[0017] Preferably, the heat treatment temperature is 140℃ and the time is 10 minutes.

[0018] The present invention also provides a flexible PLED device, the structure of which comprises, in sequence: a substrate, an anode, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, and a cathode, and is prepared by any of the above-described preparation methods.

[0019] As a further aspect of the present invention, the structure of the flexible PLED device comprises, in sequence: a PET substrate, an ITO anode, a modified hole transport layer, a modified light-emitting layer, an electron transport layer TPBi, an electron injection layer LiF, and a metal cathode Al.

[0020] As a further embodiment of the present invention, the structure of the flexible PLED device comprises, in sequence: a PET substrate (0.1 mm), an ITO anode (50 nm), a modified HTL layer (20~35 nm), a modified EML layer (40~50 nm), an electron transport layer TPBi (20 nm), an electron injection layer LiF (1 nm), and a metal cathode Al (100 nm).

[0021] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0022] 1. The present invention introduces crosslinking monomers PEGDMA and PUA into the HTL layer and EML layer respectively. By introducing covalent bonds at the interface, the interfacial shear strength is improved, thus mitigating the interlayer delamination problem that easily occurs in flexible devices under dynamic deformation.

[0023] 2. This invention is simple to operate and has good process compatibility. It adopts an in-situ thermally induced double cross-linked network, which maintains high photoelectric conversion efficiency while exhibiting excellent photoelectric performance stability.

[0024] 3. The PLED device provided by the present invention has mechanical fatigue resistance characteristics compared with the unmodified reference device, and can still maintain stable light emission characteristics when subjected to tensile strain. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This invention provides a schematic diagram of the interface microstructure of a flexible PLED device under bending deformation and a corresponding physical deformation model.

[0027] Figure 2 This is a comparison chart of the fluorescence quantum yield of luminescent systems doped with different proportions of PUA;

[0028] Figure 3 This is a bar chart comparing the effects of PEGDMA and PUA doping ratios on the maximum brightness of the flexible PLED device of this invention.

[0029] Figure 4 The images show a comparison of the Fourier transform infrared (FTIR) spectra of the functional layers of the flexible PLED device. From top to bottom, the images are the spectra of the films obtained after heat treatment in Example 1, before heat treatment in Example 1, single PUA crosslinking (15 wt%) in Control Group 1, and single PEGDMA crosslinking (50 wt%) in Control Group 2.

[0030] Figure 5 These are comparison images of X-ray photoelectron spectroscopy (XPS) of the functional layers of flexible PLED devices. (a) is the C1s spectrum, and (b) is the S2p spectrum. From top to bottom, the images show the uncrosslinked group of Comparative Example 1 and the double-crosslinked group of Example 1, respectively.

[0031] Figure 6 This is a comparison diagram of the shear strength of the HTL / EML interface under different modification conditions of the present invention;

[0032] Figure 7 This is a schematic diagram of the macroscopic adhesion test using a 1 kg weight according to the present invention;

[0033] Figure 8 This is a comparison chart of the EQE curves of the flexible PLED device provided by the present invention as a function of the number of bending cycles;

[0034] Figure 9 This is a comparison graph showing the relative brightness of the flexible PLED device provided by this invention as a function of the number of bending cycles. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Unless otherwise specified, the raw materials and reagents used in the examples are readily available commercially, and the experimental methods used are all conventional methods in the art.

[0037] Example 1

[0038] This embodiment also provides a method for preparing flexible PLEDs with enhanced interfacial adhesion through in-situ thermally induced double crosslinking, which specifically includes the following steps:

[0039] S1. Dissolve 56 mg PEGDMA in 1 mL of deionized water and stir magnetically until completely dissolved. Mix the resulting PEGDMA aqueous solution with a PEDOT:PSS aqueous solution to adjust the mass fraction of PEGDMA in the solid component to 50 wt% to prepare a modified HTL layer solution. Spin-coat the solution onto a flexible PET substrate etched with an ITO anode (3000 rpm, 30 s) and pre-dry at 100°C for 10 minutes to obtain a modified HTL layer. Dissolve 4 mg PUA in 1 mL of toluene solvent. Mix the toluene solution of PUA with a chlorobenzene solution of Super Yellow (SY) to adjust the mass fraction of PUA in the solid component to 15 wt% to prepare a modified EML layer solution. Spin-coat the solution onto the modified HTL layer at 1500 rpm to obtain a modified EML layer, forming a stacked structure with a heterojunction interface.

[0040] S2. The stacked structure obtained in step S1 is placed in a nitrogen glove box for thermal annealing. The temperature is set to 140°C and the time is 10 minutes. This induces the first crosslinking monomer PEGDMA and the second crosslinking monomer PUA to undergo in-situ free radical copolymerization at the heterojunction interface, forming a covalent crosslinking network that can enhance the interfacial adhesion and tightly anchor the adjacent functional layers.

[0041] S3, in high vacuum (<1×10⁻⁶) -5 Under the condition of mbar, the surface of the stacked structure after heat treatment in step S2 is sequentially thermally deposited with TPBi as an electron transport layer, LiF as an electron injection layer, and Al electrode as a cathode to prepare the target flexible PLED.

[0042] The flexible PLED prepared in this embodiment comprises the following structure in sequence: a PET substrate (thickness of 0.1 mm), an ITO anode (thickness of 50 nm), a modified HTL layer doped with PEGDMA (thickness of 20-35 nm), a modified EML layer doped with PUA (thickness of 40-50 nm), an electron transport layer TPBi (thickness of 20 nm), an electron injection layer LiF (thickness of 1 nm), and a metal cathode Al (thickness of 100 nm).

[0043] Example 2

[0044] This embodiment provides a flexible PLED with enhanced interfacial adhesion through in-situ thermally induced double crosslinking and its preparation method. The preparation method provided in this embodiment is similar to that in Example 1, except that the mass fraction of PUA in the solid component is adjusted to 30 wt%, while the other steps remain unchanged. The structure of the flexible PLED obtained is consistent with that in Example 1.

[0045] Example 3

[0046] This embodiment provides a flexible PLED with enhanced interfacial adhesion through in-situ thermally induced double crosslinking and its preparation method. The preparation method provided in this embodiment is similar to that in Example 1, except that the mass fraction of PUA in the solid component is adjusted to 50 wt%, while the other steps remain unchanged. The structure of the flexible PLED obtained is consistent with that in Example 1.

[0047] Example 4

[0048] This embodiment provides a flexible PLED with enhanced interfacial adhesion through in-situ thermally induced double crosslinking and its preparation method. The preparation method provided in this embodiment is similar to that in Example 1, except that the mass fraction of PEGDMA in the solid component is adjusted to 30 wt%, while the other steps remain unchanged. The structure of the flexible PLED obtained is consistent with that in Example 1.

[0049] Example 5

[0050] This embodiment provides a flexible PLED with enhanced interfacial adhesion through in-situ thermally induced double crosslinking and its preparation method. The preparation method provided in this embodiment is similar to that in Example 1, except that the mass fraction of PEGDMA in the solid component is adjusted to 10 wt%, while the other steps remain unchanged. The structure of the flexible PLED obtained is consistent with that in Example 1.

[0051] Comparative Example 1

[0052] The preparation method provided in Comparative Example 1 is similar to that in Example 1, except that no annealing treatment is performed. Instead, the TPBi electrode, used as an electron transport layer, LiF electrode, used as an electron injection layer, and Al electrode, used as a cathode, are directly thermally deposited on the surface of the stacked structure obtained in Step 1 by physical stacking. This process yields an uncrosslinked target PLED, and the resulting flexible PLED structure is consistent with that in Example 1.

[0053] Blank control group

[0054] The corresponding PLED device was prepared by using a thin film made of PEDOT:PSS aqueous solution as the HTL layer and a thin film made of chlorobenzene solution of Super Yellow (SY) as the EML layer, using a preparation method similar to that in Example 1.

[0055] Control group 1

[0056] Control group 1 prepared PLEDs based on single PUA crosslinking. PEDOT:PSS aqueous solution was spin-coated onto a flexible PET substrate etched with an ITO anode (3000 rpm, 30 s), and pre-dried at 100℃ for 10 minutes to obtain an HTL layer. 4 mg of PUA was dissolved in 1 mL of toluene solvent. The toluene solution of PUA was mixed with a chlorobenzene solution of Super Yellow (SY) to adjust the mass fraction of PUA in the solid component to 15, 30, and 50 wt%, respectively, to prepare a modified EML layer solution. This solution was spin-coated onto the modified HTL layer at 1500 rpm to obtain a modified EML layer. TPBi as an electron transport layer, LiF as an electron injection layer, and an Al electrode as a cathode were sequentially thermally deposited on the surface of the modified EML layer to prepare the target PLED.

[0057] The prepared PLED sequentially comprises the following structure: PET substrate (0.1 mm thick), ITO anode (50 nm thick), HTL layer (20-35 nm thick), modified EML layer doped with PUA (40-50 nm thick), electron transport layer TPBi (20 nm thick), electron injection layer LiF (1 nm thick), and metal cathode Al (100 nm thick).

[0058] like Figure 1As shown, the mechanism of enhancing interfacial adhesion in flexible PLEDs through in-situ thermally induced double crosslinking provided by the present invention is as follows: crosslinking monomers containing acrylate double bonds are doped into the HTL layer and EML layer respectively. The "molecular stitching" interface is constructed by utilizing the in-situ thermal crosslinking effect. Under heat treatment conditions, the unsaturated double bonds in the acrylate monomers can break through thermal initiation to generate free radicals, and free radical polymerization reaction occurs at the interface to form a covalent crosslinked network structure. No additional initiator is needed. By replacing van der Waals forces with covalent bonds, the bonding strength of the HTL / EML interface can be enhanced, thereby improving the stability of the flexible PLED device.

[0059] The fluorescence quantum yield (PLQY) of PLEDs provided by the blank control group and control group 1 were measured respectively, and the results are as follows: Figure 2 As shown, the fluorescence quantum yield (PLQY) of the blank control group (PUA content of 0) was 33%; after introducing 15 wt% PUA, the PLQY significantly increased to 44%; when the PUA doping ratio was 30 wt%, the PLQY was 45%; and when the PUA doping ratio was 50 wt%, the PLQY was 48%. The tests show that the PLQY of the PLED increases with the increase of the PUA doping ratio. Within the 15~50 wt% range provided in Example 1, the introduction of PUA can effectively improve the optical performance of the light-emitting device.

[0060] Control group 2

[0061] Control group 2 prepared PLEDs based on single PEGDMA crosslinking. 56 mg of PEGDMA was dissolved in 1 mL of deionized water and magnetically stirred until completely dissolved. The resulting PEGDMA aqueous solution was mixed with PEDOT:PSS aqueous solution, and the mass fraction of PEGDMA in the solid component was adjusted to 15, 30, and 50 wt% respectively to prepare a modified HTL layer solution. This solution was spin-coated onto a flexible PET substrate etched with an ITO anode (3000 rpm, 30 s) and pre-dried at 100°C for 10 minutes to obtain the modified HTL layer. At 1500 rpm, a chlorobenzene solution of Super Yellow (SY) was spin-coated onto the modified HTL layer to obtain an EML layer. TPBi as an electron transport layer, LiF as an electron injection layer, and an Al electrode as a cathode were sequentially thermally deposited on the surface of the EML layer to prepare the target PLED.

[0062] The prepared PLED sequentially comprises the following structure: PET substrate (thickness 0.1 mm), ITO anode (thickness 50 nm), PEGDMA-doped HTL layer (thickness 20-35 nm), EML layer (thickness 40-50 nm), electron transport layer TPBi (thickness 20 nm), electron injection layer LiF (thickness 1 nm), and metal cathode Al (thickness 100 nm).

[0063] The maximum brightness of the PLEDs provided by the blank control group, control group 1, and control group 2 were measured respectively, and the test results are as follows: Figure 3 As shown. By Figure 3 (a) It can be seen that the maximum brightness of a single PUA crosslinked device first increases and then decreases with the increase of PUA doping amount. The brightness reaches its peak when the PUA ratio is 15 wt%, while the brightness decreases sharply to 10 wt% and 50 wt% when the PUA ratio increases. 3 The cd / m² level indicates that excessive PUA severely affects the charge transport of the emissive layer.

[0064] As Figure 3 (b) It can be seen that the maximum brightness of the single PEGDMA crosslinked device shows a stable trend with the increase of PEGDMA doping amount. When the PEGDMA ratio increases from 0 to 50 wt%, the maximum brightness of the device does not show obvious quenching and remains stable at 10 wt%. 4 The cd / m² is above 2, and it reaches its maximum at 50 wt% (>2×10). 4 (cd / m²), exhibiting excellent photoelectric performance stability.

[0065] Therefore, taking the maximum brightness of the device as the first preferred criterion, the flexible PLED device provided in Example 1, which enhances the interfacial adhesion through in-situ thermally induced double crosslinking, can maintain high photoelectric conversion efficiency while exhibiting excellent photoelectric performance stability, making it the embodiment with the best technical effect in this application.

[0066] Fourier transform infrared spectroscopy (FTIR) was used to detect the heterojunction interfaces before and after heat treatment in Example 1, the single PUA crosslinked (15 wt%) in Control Group 1, and the single PEGDMA crosslinked (50 wt%) in Control Group 2. The detection results are as follows: Figure 4 As shown. By Figure 4 It can be seen that after annealing, the temperature is located at 1630 cm. -1The characteristic peak (-C=C- tensile vibration peak) at the point of origin was significantly weakened, proving that the crosslinked network was successfully constructed. The double bond conversion rate (DBC) of the heterojunction interface before and after the heat annealing treatment in Example 1 was calculated by integrating the peak area of ​​FT-IR, quantitatively assessing the degree of in-situ crosslinking at the interface. Using the carbonyl group (-C=O) as an internal standard reference peak, the relative characteristic peak area ratio of the acrylate double bond (-C=C-) was calculated, and the results are shown in Table 1. The double bond conversion rate (DBC) was calculated using the following formula: DBC = (A0 - A1) / A0 × 100%, where A0 is the characteristic peak area of ​​the acrylate double bond before annealing, and A1 is the corresponding peak area after annealing. The characteristic peak area was obtained by integrating the corresponding absorption peak in the infrared spectrum.

[0067] Table 1:

[0068]

[0069] As shown in Table 1, the peak area ratio of the film before annealing was 0.08372, while after annealing at 140℃ for 10 minutes, the peak area ratio decreased significantly to 0.03079. The double bond conversion rate (DBC) of the thermally induced in-situ crosslinking reaction at the interface reached 63.2%, which fully demonstrates that the preparation method provided in this application can successfully construct a dense covalent crosslinked network at the interface.

[0070] The heterojunction interfaces of Example 1 (double crosslinked group) and Comparative Example 1 (uncrosslinked group) after in-situ thermal induction were rinsed with solvent, respectively, and compared by X-ray photoelectron spectroscopy (XPS). The detection results are as follows: Figure 5 As shown. By Figure 5 (a) C1s energy dispersive spectroscopy shows that after solvent washing, the surface of the double cross-linked group provided in Example 1 still retains strong OC=O ester group characteristic peaks, proving that the top cross-linked luminescent network was not eluted; Figure 5 (b) S2p energy dispersive spectroscopy shows that in Comparative Example 1 (uncrosslinked group), the surface material was eluted and a strong sulfur characteristic peak of the underlying PEDOT:PSS was exposed, while no sulfur signal was detected in the double-crosslinked group of Example 1. The "retention of ester groups" in the top layer and the "complete shielding of sulfur signal" in the bottom layer both prove that a dense PUA / PEGDMA network was formed at the interface due to crosslinking, and the interface "molecular stitching" was successfully achieved.

[0071] Shear tests were used to determine the interfacial strength of heterostructures in Comparative Example 1 (unmodified), Control Group 1 (single PUA crosslinking 15 wt%), Control Group 2 (single PEGDMA crosslinking 50 wt%), and Example 1 (in-situ thermally induced double crosslinking). The test results are as follows: Figure 6 As shown. By Figure 6It can be seen that the shear strength of the interface of the blank control group is lower than the detection limit of the test equipment, while the shear strength of the double cross-linked interface after annealing at 140℃ in Example 1 is increased to 382.3 kPa. This indicates that the double cross-linked network provided in Example 1 has a very strong suturing effect on the interface, which is significantly better than the blank control group and the single cross-linked group. From the perspective of macroscopic mechanics, this strongly confirms that in-situ covalent cross-linking can significantly enhance the interfacial adhesion of flexible device PLED.

[0072] Performance tests were conducted on PLED devices prepared within the annealing temperature range of 120–160°C provided in this application. Comparison with in-situ crosslinking parameters revealed that when the annealing temperature was below 120°C, the interfacial crosslinking degree was insufficient, and the shear strength was below 100 kPa. When the annealing temperature exceeded 160°C, although the crosslinking degree increased, the thermal stability of the functional layer light-emitting material decreased, leading to a reduction in device efficiency. Within the annealing temperature range of 120–160°C provided in this application, treatment at 140°C for 10 minutes balanced material stability and device photoelectric efficiency, and the device interfacial strength reached 382.3 kPa. This demonstrates that the in-situ crosslinking parameters have a significant impact on the overall performance improvement of flexible PLED devices.

[0073] Macroscopic adhesion tests were performed on the in-situ thermally induced double crosslinked heterojunction interface provided in Example 1 using a 1 kg weight. The detection method is as follows: Figure 7 As shown in the figure. During the test, relying solely on the centimeter-scale in-situ cross-linked contact surface formed between the modified HTL layer and the modified EML layer, a 1 kg weight could be stably suspended in the direction of vertical gravity without interlayer delamination. This intuitively and fully demonstrates the strength of the interfacial adhesion, proving that the in-situ covalent double cross-linked network formed by thermal induction can greatly enhance the adhesion between adjacent functional layers of flexible devices.

[0074] The flexible PLED devices provided in Example 1 and Comparative Example 1 were fixed on a cyclic stretching machine and subjected to 200 consecutive cyclic bends under ambient air conditions and a bending radius of 2 mm. The device performance was recorded using a spectrometer, and the test results are as follows: Figure 8 As shown. By Figure 8 It can be seen that the relative external quantum efficiency (EQE) of the double-crosslinked modified device provided in Example 1 shows almost no decay, with a retention rate close to 95%, while the EQE of the unmodified PLED device in Comparative Example 1 decays to less than 60% of its initial value. Figure 9It can be seen that the unmodified PLED device provided in Comparative Example 1 can only maintain 10% of its initial brightness after 200 cycles of cyclic stretching; while the flexible PLED device provided in Example 1 can maintain 40% of its initial brightness after 200 cycles of cyclic stretching, and can still maintain stable light-emitting performance, showing extremely strong mechanical fatigue resistance characteristics. This indicates that the covalent network, as a mechanical energy dissipation center, can effectively resist and dissipate interlayer shear stress when the device undergoes macroscopic bending deformation, fundamentally avoiding interlayer physical peeling and deformation failure, improving the stability of the flexible device, and confirming the key role of the covalent cross-linked network in improving the mechanical life of the device.

[0075] In summary, this invention is simple to operate and has good process compatibility. By introducing crosslinking monomers PEGDMA and PUA containing acrylate double bonds into the HTL layer and EML layer respectively, and using an in-situ thermally induced double crosslinking network, the interfacial shear strength is improved by introducing covalent bonds at the interface, thus mitigating the interlayer delamination problem that easily occurs in flexible devices under dynamic deformation. The PLED device provided by this invention exhibits excellent photoelectric performance while maintaining high photoelectric conversion efficiency, and also possesses mechanical fatigue resistance, maintaining stable light emission characteristics even when subjected to tensile strain.

[0076] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing flexible PLEDs by in-situ thermally induced double crosslinking to enhance interfacial adhesion, characterized in that, Specifically, the following steps are included: S1. Introduce a first crosslinking monomer containing unsaturated acrylate double bonds into the hole transport layer to obtain a modified hole transport layer, and deposit the modified hole transport layer on a flexible substrate etched with an anode. A second crosslinking monomer containing unsaturated acrylate double bonds is introduced into the light-emitting layer to obtain a modified light-emitting layer. The modified light-emitting layer is then deposited on the modified hole transport layer to form a stacked structure with a heterojunction interface. The first and second crosslinking monomers are used for thermally initiated free radical polymerization reactions; S2. Heat treatment is performed on the laminated structure obtained in step S1 to induce in-situ free radical copolymerization of the first crosslinking monomer and the second crosslinking monomer at the heterojunction interface, which is used to form a covalent crosslinking network and enhance the interfacial adhesion. S3. After heat treatment in step S2, the surface of the stacked structure is sequentially thermally deposited with TPBi as an electron transport layer, LiF as an electron injection layer, and Al electrode as a cathode to prepare the target flexible PLED.

2. The preparation method according to claim 1, characterized in that, In step S1, the first crosslinking monomer is polyethylene glycol dimethacrylate (PEGDMA), and the second crosslinking monomer is polyurethane acrylate (PUA).

3. The preparation method according to claim 2, characterized in that, Step S1 is as follows: Polyethylene glycol dimethacrylate is dissolved in deionized water and magnetically stirred until completely dissolved. The polyethylene glycol dimethacrylate aqueous solution is mixed with PEDOT:PSS aqueous solution to obtain a modified hole transport layer solution. The solution is spin-coated onto a flexible substrate with an etched anode at 3000 rpm and pre-dried at 100°C for 10 minutes to obtain a modified hole transport layer. Polyurethane acrylate is dissolved in toluene solvent. The polyurethane acrylate toluene solution is mixed with Super Yellow chlorobenzene solution to obtain a modified light-emitting layer solution. The solution is spin-coated onto the modified hole transport layer at 1500 rpm to obtain a modified light-emitting layer.

4. The preparation method according to claim 3, characterized in that, The modified hole transport layer is a PEDOT:PSS film doped with polyethylene glycol dimethacrylate, wherein the mass fraction of polyethylene glycol dimethacrylate is 15~50 wt%.

5. The preparation method according to claim 3, characterized in that, The modified light-emitting layer is a Super Yellow film doped with polyurethane acrylate, wherein the mass fraction of polyurethane acrylate is 15~50 wt%.

6. The preparation method according to claim 1, characterized in that, In step S2, the heat treatment is a heat annealing process performed under an inert atmosphere, with the heat treatment temperature set to 120~160℃ and the time set to 2~20 minutes.

7. The preparation method according to claim 6, characterized in that, The heat treatment temperature is 140℃ and the time is 10 minutes.

8. A flexible PLED device, the structure of which comprises, in sequence: The substrate, anode, hole transport layer, light-emitting layer, electron transport layer, electron injection layer, and cathode are characterized in that they are prepared by any one of the preparation methods described in claims 1-7.

9. The flexible PLED device according to claim 8, characterized in that, Its structure includes, in sequence: PET substrate, ITO anode, modified hole transport layer, modified light-emitting layer, electron transport layer TPBi, electron injection layer LiF, and metal cathode Al.

10. The flexible PLED device according to claim 9, characterized in that, Its structure includes, in sequence: a PET substrate with a thickness of 0.1 mm, an ITO anode with a thickness of 50 nm, a modified hole transport layer with a thickness of 20~35 nm, a modified light-emitting layer with a thickness of 40~50 nm, an electron transport layer TPBi with a thickness of 20 nm, an electron injection layer LiF with a thickness of 1 nm, and a metal cathode Al with a thickness of 100 nm.

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