Preparation method and application of polymer light extraction film based on random wrinkles for organic electroluminescent device

Abstract

The invention discloses a preparation method and application of a polymer light extraction film based on random wrinkles for an organic electroluminescent device, and belongs to the technical field of light extraction films, and the preparation method comprises the following steps: treating a pre-cleaned silicon wafer with OTS steam to prepare a hydrophobic surface; the preparation method comprises the following steps: dripping a mixed PDMS prepolymer on a pre-cleaned silicon wafer, uniformly spin-coating PDMS on the surface of the silicon wafer on a spin coater at a rotating speed of 3000rpm, heating in a drying oven to cure the PDMS into a film, putting into a vacuum thermal deposition system, weighing parylene precursor drug tetrachloro-p-xylene ring dimer, depositing parylene through the vacuum thermal deposition system, and drying to obtain the parylene film. And after surface random wrinkles are spontaneously formed, stripping from the surface of the silicon wafer to prepare the PDMS / parylene light extraction film with a random wrinkle structure on the surface. According to the preparation method and application of the random wrinkle-based polymer light extraction film for the organic electroluminescent device, the preparation process of the random wrinkle-based polymer light extraction film is simple, and the random wrinkle-based polymer light extraction film can be repeatedly used.

Description

Technical Field

[0001] The present invention relates to the technical field of light extraction thin films, and in particular to a preparation method and application of a polymer light extraction thin film based on random wrinkles for organic light-emitting diodes. Background Art

[0002] Organic light-emitting diodes (OLEDs) have attracted extensive attention from global researchers due to their broad application prospects in the fields of solid-state lighting and full-color displays, as well as their flexibility, self-luminescence, simple preparation, and easy large-area production, and are widely used in the fields of lighting and display. Currently, the internal quantum efficiency of OLEDs has reached nearly perfection, about 100%, but their external quantum efficiency only remains at about 20%. This gap is mainly attributed to a large number of photons generated in the light-emitting layer being captured by non-radiative modes, including surface plasmon polariton (SPP) modes at the metal electrode interface, waveguide modes between the ITO (indium tin oxide) electrode and the organic layer, and energy loss modes in the glass substrate. These non-radiative modes significantly hinder the improvement of the external quantum efficiency of OLEDs.

[0003] To solve the above problems, researchers have adopted various strategies: (1) For SPP modes, by introducing periodic micro-nano structures between the metal electrode and the organic layer, SPP modes can be effectively excited and guided to couple out, thereby recovering the energy lost in this mode. (2) For waveguide modes, replacing the ITO electrode has become an effective solution. Since the high refractive index of the ITO thin film easily causes energy loss in waveguide modes, alternative materials such as carbon nanotube electrodes, conductive polymers, or metal mesh electrodes can significantly reduce this loss. (3) For the energy loss caused by the glass substrate, by treating the substrate surface, such as introducing patterned structures, surface roughening, fabricating microlens arrays, or adding scattering media, total reflection at the substrate-air interface can be effectively suppressed, thereby reducing energy loss. However, the implementation of these solutions is not easy. They require the introduction of complex micro-nano structure processing techniques during the preparation of OLEDs, and these light extraction structures often do not have reusability, thus increasing the production cost. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method and application of a polymer light extraction thin film based on random wrinkles for organic light-emitting diodes. By preparing a polymer light extraction thin film with random wrinkles on the surface to externally modify OLEDs, without changing the electrical properties of the device itself, the light in the substrate mode is extracted to increase the light extraction efficiency of OLEDs and thus increase the external quantum efficiency of the device itself.

[0005] To achieve the above object, the present invention provides a method for preparing a polymer light extraction film based on random wrinkles for an organic electroluminescent device, comprising the following steps:

[0006] Step 1: Prepare a silicon substrate with a hydrophobic surface;

[0007] Step 2: Prepare a PDMS film;

[0008] Step 3: Prepare a PDMS / parylene composite polymer light extraction film.

[0009] Preferably, the specific operation of Step 1 is: treating the polished silicon wafer with an ultrasonic cleaner, then wiping the surface of the silicon wafer in sequence with ethanol - acetone - ethanol, and then drying. The dried silicon wafer is treated with octadecyltrichlorosilane (OTS) vapor to prepare a hydrophobic surface on the silicon wafer surface to obtain a silicon wafer with a hydrophobic surface.

[0010] Preferably, the specific operation of Step 2 is: mixing the PDMS base material with a curing agent and performing a centrifugation operation to obtain a PDMS prepolymer. Then, the prepared PDMS prepolymer is dropped onto the silicon wafer with a hydrophobic surface obtained in Step 1, and the PDMS prepolymer is uniformly spin - coated on the silicon wafer with a hydrophobic surface on a spin coater. Then, it is heated in an oven to cure into a film to obtain a PDMS film.

[0011] Preferably, the specific operation of Step 3 is: putting the prepared PDMS film into a vacuum thermal deposition system, weighing the parylene precursor drug p - xylylene tetrachloride dimer, and sublimating the p - xylylene dichloride dimer into a gas through the vacuum thermal deposition system and cracking it to produce parylene monomers. The monomers further polymerize to form parylene. Subsequently, parylene combines with the porous PDMS. After spontaneous formation of random wrinkles on the surface, it is peeled off from the silicon wafer surface to prepare a PDMS / parylene composite polymer light extraction film with a random wrinkle structure on the surface.

[0012] Preferably, in Step 1, the ultrasonic cleaning time is 10 - 30 min, the drying process is divided into two processes of drying with nitrogen and heating and drying in an oven, and the OTS vapor treatment time is 3 - 5 h.

[0013] Preferably, in Step 2, the mass ratio of the PDMS base material to the curing agent in the PDMS prepolymer is (8 - 12):1, the centrifugation operation conditions are: the centrifuge speed is 5000 - 10000 rpm, the centrifugation time is 1 - 5 min, it is horizontally placed for 5 - 10 h after spin - coating, and the heating and curing temperature is 50 - 100 °C and the time is 1 - 3 h.

[0014] Preferably, in step three, the single - use amount of parylene precursor drug is 3 - 5 g, and the working time of the vacuum thermal deposition system is 8 - 10 h.

[0015] The present invention provides an application of a polymer light - extraction film based on random wrinkles for an organic light - emitting device. A polymer light - extraction film based on random wrinkles for an organic light - emitting device prepared by the above - mentioned preparation method of a polymer light - extraction film based on random wrinkles for an organic light - emitting device is applied to the preparation of OLEDs devices.

[0016] Therefore, by adopting the above - mentioned preparation method and application of a polymer light - extraction film based on random wrinkles for an organic light - emitting device, the present invention has the following beneficial effects:

[0017] (1) The prepared random - wrinkle light - extraction film is applied to the back of the glass substrate of the OLEDs device. Without changing the structure of the OLEDs device, on the premise of not affecting the electrical properties of the OLEDs, the random - wrinkle structure on the film surface scatters the photons emitted inside the device, effectively suppressing the total reflection phenomenon at the air - substrate interface, enhancing the light extraction of the substrate mode, and can effectively improve the light - extraction efficiency of the OLEDs, thereby increasing the external quantum efficiency of the device itself.

[0018] (2) The preparation process of the random - wrinkle light - extraction film is simple and can be reused.

[0019] The technical solution of the present invention will be further described in detail below through the drawings and embodiments. Description of the Drawings

[0020] Figure 1 It is the preparation flow chart of Embodiment 1 of the preparation method and application of a polymer light - extraction film based on random wrinkles for an organic light - emitting device of the present invention;

[0021] Figure 2 It is the surface topography map, confocal contour map and three - dimensional depth - of - field schematic diagram of the light - extraction film prepared in Embodiment 1 of the preparation method and application of a polymer light - extraction film based on random wrinkles for an organic light - emitting device of the present invention;

[0022] Figure 3 It is the schematic diagram of the OLEDs device structure of Embodiment 2 of the preparation method and application of a polymer light - extraction film based on random wrinkles for an organic light - emitting device of the present invention;

[0023] Figure 4It is the current density-voltage curve of the OLEDs with a random-crease light extraction film and the reference device (the original OLED device without the random-crease light extraction film) in Example 2 of the preparation method and application of a polymer light extraction film based on random creases for an organic electroluminescent device according to the present invention;

[0024] Figure 5 It is the luminance-current density curve of the OLEDs with a random-crease light extraction film and the reference device (the original OLED device without the random-crease light extraction film) in Example 2 of the preparation method and application of a polymer light extraction film based on random creases for an organic electroluminescent device according to the present invention;

[0025] Figure 6 It is the current efficiency-current density curve of the OLEDs with a random-crease light extraction film and the reference device (the original OLED device without the random-crease light extraction film) in Example 2 of the preparation method and application of a polymer light extraction film based on random creases for an organic electroluminescent device according to the present invention;

[0026] Figure 7 It is the CIE coordinate comparison curve of the OLEDs with a random-crease light extraction film and the reference device (the original OLED device without the random-crease light extraction film) in Example 2 of the preparation method and application of a polymer light extraction film based on random creases for an organic electroluminescent device according to the present invention. Detailed implementation manners

[0027] The technical solutions of the present invention will be further described below with reference to the drawings and examples.

[0028] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the field to which the present invention belongs.

[0029] The present invention provides a preparation method of a polymer light extraction film based on random creases for an organic electroluminescent device, including the following steps:

[0030] Step 1: Prepare a silicon substrate with a hydrophobic surface in advance: Treat the polished silicon wafer with an ultrasonic cleaner, then wipe the surface of the silicon wafer in the order of ethanol-acetone-ethanol, and then dry it. The dried silicon wafer is treated with octadecyltrichlorosilane (OTS) vapor to prepare a hydrophobic surface on the silicon wafer surface to obtain a silicon wafer with a hydrophobic surface.

[0031] The time for ultrasonic cleaning is 10 - 30 min. The drying process is divided into two processes: drying with nitrogen and heating and drying in an oven. The time for OTS vapor treatment is 3 - 5 h.

[0032] Step 2: Prepare the PDMS film: Mix the PDMS substrate with the curing agent and perform a centrifugation operation to obtain the PDMS prepolymer. Then, drop the prepared PDMS prepolymer onto the silicon wafer with a hydrophobic surface obtained in Step 1, and spin-coat the PDMS prepolymer evenly on the silicon wafer with a hydrophobic surface on a spin coater. After that, heat it in an oven to cure it into a film to obtain the PDMS film.

[0033] The mass ratio of the PDMS substrate to the curing agent in the PDMS prepolymer is (8 - 12):1. The centrifugation operation conditions are: the centrifuge speed is 5000 - 10000 rpm, the centrifugation time is 1 - 5 min, it is placed horizontally for 5 - 10 h after spin-coating, the heating and curing temperature is 50 - 100 °C, and the time is 1 - 3 h.

[0034] Step 3: Prepare the PDMS / parylene composite polymer light extraction film: Put the prepared PDMS film into a vacuum thermal deposition system, weigh the parylene precursor drug p - xylylene tetrachloride dimer, and sublime the p - xylylene dichloride dimer into a gas through the vacuum thermal deposition system, and it undergoes pyrolysis to produce parylene monomers. The monomers further polymerize to form parylene. Subsequently, parylene combines with the porous PDMS. After spontaneous formation of random surface wrinkles, it is peeled off from the silicon wafer surface to prepare a PDMS / parylene composite polymer light extraction film with a random wrinkle structure on the surface.

[0035] Among them, the single - use amount of the parylene precursor drug is 3 - 5 g, and the working time of the vacuum thermal deposition system is 8 - 10 h.

[0036] The present invention provides an application of a polymer light extraction film based on random wrinkles for an organic electroluminescent device. A polymer light extraction film based on random wrinkles for an organic electroluminescent device prepared by the above - mentioned preparation method of a polymer light extraction film based on random wrinkles for an organic electroluminescent device is applied to the preparation of OLEDs devices.

[0037] Example 1

[0038] As Figure 1 shown, the present invention provides a preparation method of a polymer light extraction film based on random wrinkles for an organic electroluminescent device, including the following steps:

[0039] Step 1. Prepare a silicon substrate with a hydrophobic surface in advance: Treat the purchased polished 2 cm × 2 cm silicon wafer with an ultrasonic cleaner for 10 min. Then wipe the surface in the order of ethanol - acetone - ethanol, and then dry it. The drying process includes two processes: blowing dry with nitrogen and drying in an oven. Treat the pre - cleaned silicon wafer with octadecyltrichlorosilane (OTS) vapor to prepare a hydrophobic surface on the silicon wafer, which is convenient for the subsequent peeling of the film. The vapor treatment time is 4 h. The OTS reagent, ethanol, and acetone are all purchased from Sigma - Aldrich (Shanghai) Trading Co., Ltd.

[0040] Step 2. Prepare the PDMS film: First, mix the PDMS substrate used to prepare the PDMS prepolymer with the curing agent, and then perform a centrifugation operation to make them fully and evenly mixed. The mass ratio of the PDMS substrate to the curing agent is 10:1. The conditions for the centrifugation operation are: rotation speed 8000 rpm, time 2 min. Drop the prepared PDMS prepolymer on the silicon wafer with a hydrophobic surface, and spin - coat the PDMS prepolymer evenly on the surface of the silicon wafer with a hydrophobic surface at a rotation speed of 8000 rpm and place it horizontally for 10 h. Then heat it in an oven to cure it into a PDMS film. The temperature in the oven is 90 °C, and the curing time is 2 h. The heating and curing process ensures the uniformity, strength, and toughness of the film, providing a high - quality material basis for subsequent experiments or applications.

[0041] Step 3. Prepare the PDMS / parylene composite polymer light - extraction film: First, put the prepared PDMS film into a vacuum thermal deposition system, and set the working time of the vacuum thermal deposition system to 10 h. Weigh 3 g of parylene precursor drug (tetrachlorop - xylene cyclodimer), and the parylene precursor drug is purchased from Parylene Nano Technology (Suzhou) Co., Ltd. Through the vacuum thermal deposition system, the solid material of tetrachlorop - xylene cyclodimer sublimes into a gas, cracks to produce parylene monomers, and further polymerizes to form parylene. Subsequently, it combines with the porous PDMS. After spontaneous formation of random surface wrinkles, peel it from the silicon wafer surface to prepare a PDMS / parylene light - extraction film with a random wrinkle structure on the surface.

[0042] In the process of preparing high-performance PDMS / parylene light extraction films, first, the precisely prepared PDMS film is properly placed inside an advanced vacuum thermal deposition system to ensure its position stability and structural integrity during the deposition process. Subsequently, 3 grams of parylene precursor drug (tetrachlorop-xylene cyclodimer) is accurately measured and introduced as the deposition source material. Through a precisely controlled vacuum thermal deposition system, the tetrachlorop-xylene cyclodimer is sublimated into a gaseous state and undergoes a cracking reaction at high temperature to produce highly reactive parylene monomers. These monomers then polymerize to form parylene and combine with the PDMS film with a porous structure to form a random micron-scale wrinkled structure through a self-assembly process. Finally, the PDMS film combined with parylene is peeled off from the deposition system to obtain a PDMS / parylene composite light extraction film with a unique random wrinkled morphology.

[0043] Figure 2 In (a) is the SEM image of the obtained random wrinkled light extraction film. It can be seen from the figure that the obtained random wrinkled light extraction film has a good morphology under the scanning electron microscope.

[0044] Figure 2 In (b) is the contour map of the obtained random wrinkled light extraction film measured by confocal microscopy. It can be seen from the contour map that the wrinkle height and orientation are randomly and uniformly distributed.

[0045] Figure 2 In (c) is the three-dimensional depth-of-field image of the obtained random wrinkled light extraction film. It can be observed from the figure that the PDMS / parylene composite polymer film is randomly and uniformly distributed in the horizontal and vertical directions.

[0046] Example 2

[0047] The light extraction film prepared in Example 1 is applied to the preparation of OLEDs devices. The specific operation is as follows:

[0048] (1) Wipe the ITO glass used for preparing OLEDs devices with ethanol, rinse the solvent with deionized water and put it in an oven to dry; deposit 3 nm MoO 3 , 40 nm NPB, 30 nm CBP co-evaporated with 5 wt% Ir(BT) 2 (acac), 25 nm TPBi, 3 nm Ca, 80 nm Ag on the ITO glass to prepare OLEDs with the structure: glass substrate / ITO / MoO 3 (3 nm) / NPB(40 nm) / CBP:Ir(bt) 2(acac)(5 wt%, 30 nm) / TPBi(25 nm) / Ca(3 nm) / Ag(80 nm); The schematic diagram of the obtained OLEDs device is as follows Figure 3 As shown, the random wrinkled light extraction film can be transferred and adhered to the glass substrate of the OLEDs device multiple times without using other methods for fixation.

[0049] During the test, a Keithley 2400 programmable voltage-current source was used to provide voltage and current to the OLEDs reference device and the OLEDs device with the random wrinkled light extraction film, and data was collected. A Photo Research PR-655 spectrophotometer was used to collect data such as luminance and spectrum.

[0050] It can be seen from Figure 4 that the OLEDs device with the random wrinkled light extraction film shows a similar current density-voltage curve to the reference device, and introducing the PDMS light extraction film does not affect the electrical properties of the OLEDs device.

[0051] It can be seen from Figure 5 that after introducing the random wrinkled light extraction film, the maximum luminance of the OLEDs device increases from 56820 cd / m 2 to 65353 cd / m 2 , and the luminance increases significantly.

[0052] It can be seen from Figure 6 that after introducing the PDMS light extraction film, the maximum current efficiency of the OLEDs device increases from 32.8 cd / A to 36.9 cd / A, an increase of 12.5%, indicating that introducing the random wrinkled light extraction film is beneficial to improving the light extraction efficiency of the OLEDs device.

[0053] It can be seen from Figure 7 that the CIE coordinates of the OLEDs device with the random wrinkled light extraction film do not change significantly with the angle compared to the reference device, indicating that introducing the random wrinkled light extraction film can improve the angular dependence of the OLEDs device.

[0054] Therefore, the present invention adopts the above-mentioned preparation method and application of a random wrinkled-based polymer light extraction film for organic electroluminescent devices. The prepared random wrinkled light extraction film is applied to the back of the glass substrate of the OLEDs device. Without changing the structure of the OLEDs device, it can effectively improve the light extraction efficiency of the OLEDs without affecting the electrical properties of the OLEDs, thereby increasing the external quantum efficiency of the device itself; the preparation process of the random wrinkled light extraction film is simple and can be reused.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a random wrinkled polymer light extraction film for an organic electroluminescent device, characterized in that: The following steps are involved: Step 1: pre-preparing a silicon substrate with a hydrophobic surface; Step 2, preparing a PDMS film; Step 3: Prepare PDMS / parylene composite polymer light extraction film.

2. The method for preparing a random wrinkled polymer light extraction film for an organic electroluminescent device according to claim 1, characterized in that: The specific operation of step one is: treating the polished silicon wafer with an ultrasonic cleaner, then wiping the surface of the silicon wafer with ethanol-acetone-ethanol in sequence, and then drying it. The dried silicon wafer is treated with octadecyltrichlorosilane OTS vapor to obtain a silicon wafer with a hydrophobic surface.

3. The method for preparing a random wrinkled polymer light extraction film for an organic electroluminescent device according to claim 1, characterized in that: The specific operation of step two is: mixing the PDMS substrate and the curing agent and performing centrifugal operation to obtain a PDMS prepolymer, then dripping the prepared PDMS prepolymer on the silicon wafer with a hydrophobic surface obtained in step one, and evenly spin-coating the PDMS prepolymer on the silicon wafer with a hydrophobic surface on a spin coater, and then heating it in an oven to solidify it into a film to obtain a PDMS film.

4. The method for preparing a random wrinkled polymer light extraction film for an organic electroluminescent device according to claim 1, characterized in that: The specific operation of step three is: put the prepared PDMS film into a vacuum thermal deposition system, weigh the parylene precursor drug tetrachloroparaxylene cyclic dimer, and sublime the tetrachloroparaxylene dimer into a gas state through the vacuum thermal deposition system, and crack it to produce parylene monomers, and the monomers are further polymerized to form parylene, and then parylene is combined with loose and porous PDMS. After random wrinkles on the surface are spontaneously formed, it is peeled off from the surface of the silicon wafer to prepare a PDMS / parylene composite polymer light extraction film with a random wrinkle structure on the surface.

5. The method for preparing a random wrinkled polymer light extraction film for an organic electroluminescent device according to claim 2, characterized in that: In step 1, the ultrasonic cleaning time is 10-30 minutes, the drying process is divided into two processes: nitrogen blowing and heating and drying in an oven, and the OTS steam treatment time is 3-5 hours.

6. The method for preparing a random wrinkled polymer light extraction film for an organic electroluminescent device according to claim 3, characterized in that: In step 2, the mass ratio of PDMS substrate to curing agent in the PDMS prepolymer is (8-12):1, and the centrifugal operation conditions are: the centrifuge speed is 5000-10000rpm, the centrifugal time is 1-5min, the spin coating is placed horizontally for 5-10h, and the heating curing temperature is 50-100℃ for 1-3h.

7. The method for preparing a random wrinkled polymer light extraction film for an organic electroluminescent device according to claim 4, characterized in that: In step 3, the single usage amount of parylene precursor is 3-5g, and the working time of the vacuum thermal deposition system is 8-10h.

8. An application of a random wrinkled polymer light extraction film for an organic electroluminescent device, characterized in that: A polymer light extraction film based on random wrinkles for an organic electroluminescent device prepared by the method for preparing a polymer light extraction film based on random wrinkles for an organic electroluminescent device as described in any one of claims 1 to 7 is used in the preparation of OLEDs devices.

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