A Laser Regulation Method for the Phase Transition Process of an Organic Light-Emitting Molecular Film

Abstract

The present invention discloses a method for laser regulation of the phase transition process of an organic light-emitting molecular thin film, belonging to the technical field of optoelectronic device preparation, including Step 1: Pretreatment of a donor substrate and a target substrate; Step 2: Laser regulation of the phase transition process of the organic light-emitting molecular thin film; this method provides an instantaneous time when the molecules are in a liquid or gaseous state through the process of laser acting on the organic molecules, greatly reducing the resistance in the molecular orientation process and solving the problem of large intermolecular forces and the forces between the molecules and the substrate in the solid state environment; and after the organic molecules are deposited on the target substrate, not only can the molecular orientation be regulated, but also the final morphology of the organic molecular thin film can be regulated through laser parameters, etc., providing a new method for simultaneously realizing molecular orientation regulation in the preparation of laser-induced organic molecular thin films.

Description

Technical Field

[0001] The present invention belongs to the technical field of optoelectronic device preparation, and particularly relates to realizing a solid-liquid-solid or solid-gas-solid phase change process by using organic light-emitting molecular materials on a donor substrate through femtosecond laser-induced evaporation, transferring the materials to a target substrate to prepare an organic light-emitting molecular thin film, and regulating the phase change process and the molecular final state of the organic light-emitting molecules by changing the distance between the substrates and laser parameters, so as to provide a new strategy for the laser-induced organic molecular thin film preparation technology. Background Art

[0002] With the development of world informatization and life intelligence, flexible electronic devices with characteristics such as flexible display, flexible sensing, and flexible light emission have become one of the most promising information technologies in the world today. Their market scale is growing at an astonishing speed and they have wide applications in fields such as information, energy, medical care, and national defense. As a representative device of flexible electronics, organic light-emitting diodes (OLEDs) are widely used in fields such as solid-state lighting and flat panel displays due to their advantages of energy conservation, environmental protection, wide viewing angle, light weight, flexibility, and large-area preparation, and have great application prospects. Organic light-emitting molecules have also become a new generation of display and lighting materials. However, at present, there are still relatively large problems. The main problem is that there is a huge gap between the external quantum efficiency (about 20%) and the internal quantum efficiency (close to 100%) of organic light emission in OLEDs. This is because the dipole orientation of the organic light-emitting molecular thin film is random, and the transition dipole moment is perpendicular to the direction of photon emission, resulting in random photon emission directions and thus low external quantum efficiency.

[0003] In order to improve the external quantum efficiency, it is crucial to regulate the dipole orientation of organic light-emitting molecules. At present, there are relatively few related studies. The traditional method is chemical synthesis. During the synthesis process, the structure of specific molecules is designed, and the configuration of the molecules is regulated to be a linear structure to obtain a high molecular orientation rate, thereby obtaining the result of improving the external quantum efficiency of the device. However, this regulation is only for specific molecular configurations, which has great limitations. At the same time, the synthesis process is complicated and difficult to operate. In terms of molecular alignment regulation, there are studies on gas molecules. Some researchers have aligned nitrogen molecules using dual-beam lasers to achieve the maximum value of their orderly molecular arrangement. However, at present, this technology is limited to some gaseous molecules with simple structures, because the damping in the gaseous environment is small and it is easy to align the molecules. The organic molecular film is in a solid state, the damping in the solid state environment is large, and there is a large interaction force between molecules and molecules and between molecules and substrates, which makes it difficult to align organic molecules in a solid film state. The alignment technology of molecules in the film needs to be developed. Compared with the solid environment, the liquid and gas environments have larger spatial volumes and smaller intermolecular interactions, so it is easier to achieve molecular alignment control after the material undergoes a solid-liquid or solid-gas transition, which can provide a corresponding technical solution for the alignment control of organic molecules. In addition, separating the organic molecular film from the substrate and eliminating the influence of the interaction between the molecules and the substrate can also provide more favorable conditions for molecular alignment. Summary of the invention

[0004] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is: to provide an organic luminescent molecular material evaporating on a donor substrate by femtosecond laser induction to realize a solid-liquid-solid or solid-gas-solid phase change process, and transfer it to a target substrate to prepare an organic luminescent molecular film. The method provides an instantaneous time for the molecule to be in a liquid or gaseous state through the process of laser acting on the organic molecule, greatly reducing the resistance of the molecular orientation process, and solving the problem of large intermolecular forces and forces between molecules and substrates in a solid environment; and after the organic molecules are deposited on the target substrate, not only the molecular orientation can be regulated, but also the final morphology of the organic molecular film can be regulated by laser parameters, etc., providing a new method for laser-induced organic molecular film preparation and simultaneous molecular orientation regulation. Generally, when a femtosecond laser acts on a substance, there are mainly photothermal processes and photomechanical processes. Under different mechanisms, the process of organic molecules leaving the donor substrate is significantly different, resulting in the obvious morphological differences in the properties of the organic molecular film formed on the target substrate. By observing the morphology of the organic molecular film on the target substrate, the solid-liquid-solid and solid-gas-solid phase change processes of organic molecules under the action of femtosecond laser can be inferred.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for laser regulation of the phase transition process of an organic light-emitting molecular thin film, the specific steps are as follows:

[0007] Step 1: Pretreatment of the donor substrate and the target substrate;

[0008] The donor substrate and the target substrate are pretreated with acetone, absolute ethanol, and deionized water respectively. The pretreated donor substrate is placed in a vacuum coater for evaporation of the organic light-emitting material thin film;

[0009] Step 2: Laser regulation of the phase transition process of the organic light-emitting molecular thin film;

[0010] First, the side of the donor substrate coated with the organic light-emitting material thin film in Step 1 is oriented towards the target substrate, and a certain distance is maintained between the two substrates to control the flight distance of the organic molecules from the donor substrate to the target substrate; then, the entire sample is fixed on the displacement platform with the donor substrate on top and the target substrate on the bottom. Finally, the laser is focused on the organic light-emitting material thin film of the donor substrate, and then the organic light-emitting material thin film is scanned with the laser to induce the transfer of organic molecules to the target substrate and undergo solid-liquid-solid and solid-gas-solid phase transition processes during this process. Femtosecond laser can induce non-linear absorption of organic molecules. After the organic molecules absorb energy, solid-liquid or solid-gas phase transition occurs, and the volume expansion provides a driving force for the molecules to break away from the donor substrate. Different transferred organic thin films can be obtained on the target substrate by changing the thickness of the thin film on the donor substrate, the distance between the donor substrate and the target substrate, and the single-pulse energy of the laser.

[0011] Furthermore, both the donor substrate and the target substrate described in Step 1 are clean glass slides.

[0012] Furthermore, the pretreatment process described in Step 1 is specifically as follows:

[0013] First, the donor substrate and the target substrate are wiped with acetone, then wiped with absolute ethanol, and then cleaned with deionized water. The wiping process uses clean medical absorbent cotton balls, and then air-dries naturally in a closed space.

[0014] Furthermore, the size of the glass slide described in Step 1 is 50*25*0.2 mm; the absorbent cotton balls used are medical absorbent cotton balls; the organic light-emitting material is the green light material tris(8-hydroxyquinoline)aluminum (Alq 3 , C 27 H 18 AlN 3 O 3 ), purchased from Sigma-Aldrich (Shanghai) Trading Co., Ltd.

[0015] Further, the thickness of the organic light-emitting material thin film on the donor substrate is 20 nm, 40 nm, 60 nm, or 80 nm; the distance between the donor substrate and the target substrate is 1 - 200 μm.

[0016] Further, the laser in step two is a femtosecond laser. The wavelength of the femtosecond laser is 343 - 1030 nm, the laser power is 10 - 2000 mW, the pulse frequency is 1 - 500 kHz, the single-pulse energy of the laser is 0.02 - 2000 μJ, the scanning speed is 0.1 - 2 mm / s, and a 40x objective lens is used for focusing with a numerical aperture of 0.65; the laser optical path is as follows: First, the femtosecond laser emitted by the laser passes through the first convex lens and the shutter and then is expanded by the second convex lens to enlarge the light spot. Then, it passes through the first total reflection mirror, the second total reflection mirror, the third convex lens, and the fourth convex lens for beam shaping, and successively passes through the attenuation sheet, the first half-reflection and half-transmission lens, and the objective lens for focusing and then is incident on the sample to be processed.

[0017] Further, in step two, the scanning direction of the laser adopts a point-by-point scanning method for laser transfer; First, according to the size of the designed thin film transfer area, it is converted into a program recognizable by the laser, and the line spacing is set to 0.1 - 1 mm. The laser scanning speed in the horizontal direction is 0.1×10 -3 -2×10 -3 m / s.

[0018] Compared with the prior art, the advantages of the present invention are as follows:

[0019] (1) By using the method of laser-induced phase change, it is possible to quickly regulate the solid-liquid-solid and solid-gas-solid phase changes of organic molecules. The operation is simple, and the applicable materials are extensive, which can meet the requirements of commercial applications;

[0020] (2) By using laser-induced phase change, the transfer of the organic thin film from the donor substrate to the target substrate can be realized simultaneously during the phase change regulation process, thereby realizing the preparation process of the organic molecular thin film;

[0021] (3) By using the laser-induced phase change technology, instantaneous liquid and gaseous organic molecules can be provided, greatly reducing the intermolecular force, and the force between the molecules and the substrate is also avoided during the transfer process, which is beneficial to the orientation regulation of organic molecules. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0023] Figure 1 Schematic diagram of a method for laser regulation of the phase change process of an organic light-emitting molecular thin film according to the present invention;

[0024] Figure 2 Fluorescence micrographs of organic molecules on a target substrate at different substrate spacing distances and femtosecond laser single-pulse energies according to the present invention;

[0025] Figure 3 Scanning electron micrographs of organic molecules on a target substrate at different substrate spacing distances and femtosecond laser single-pulse energies according to the present invention;

[0026] Figure 4 Morphologies of organic molecules after energy transfer by different femtosecond laser single-pulse energies when the spacing distance between two substrates is 1 - 10 μm in the present invention;

[0027] Wherein: a is a scanning electron micrograph of organic molecules on a target substrate when the laser single-pulse energy is 1.2 μJ, b is a scanning electron micrograph of organic molecules on a target substrate when the laser single-pulse energy is 9.7 μJ, c is a scanning electron micrograph of organic molecules on a target substrate when the laser single-pulse energy is 43.3 μJ, d is a magnified scanning electron micrograph of organic molecules on a target substrate at different organic molecular thin film thicknesses when the laser single-pulse energy is 1.2 μJ. Among them, the diameters of the nanoparticles from small to large correspond to the thicknesses of the organic molecular thin films evaporated on the donor substrate being 20 nm, 40 nm, 60 nm, 80 nm respectively. e is a magnified scanning electron micrograph of organic molecules on a target substrate when the laser single-pulse energy is 9.7 μJ, and f is a magnified scanning electron micrograph of organic molecules on a target substrate when the laser single-pulse energy is 43.3 μJ.

[0028] Figure 5 XRD characterization diagram of the evaporated thin film and the laser-transferred thin film in the present invention. Detailed implementation manners

[0029] To clearly and completely describe the technical solutions and their specific working processes of the present invention, in combination with the accompanying drawings of the specification, the detailed implementation manners of the present invention are as follows:

[0030] Example 1 A method for regulating the phase change process of an organic light-emitting molecular thin film using a laser.

[0031] The method described in this embodiment is as follows: First, on a pre-prepared glass donor substrate, an organic light-emitting molecular material thin film is deposited by a vacuum coater, and the thickness of the thin film is adjustable; then, the side of the donor substrate coated with the organic material thin film is oriented towards a clean glass target substrate that has been processed and aligned, and the two substrates are spaced a certain distance apart. The entire sample is fixed on the sample stage for laser processing with the donor substrate on top and the target substrate below; the focusing position of the laser is adjusted so that the laser is focused on the organic thin film on the donor substrate, and then the organic thin film is scanned with the laser. Under the action of the laser, the organic molecules in the organic material thin film undergo solid-liquid-solid and solid-gas-solid phase transitions under the action of the strong laser field and are transferred from the thin film on the donor substrate to the target substrate; during the process of the laser action, experiments need to be carried out under different substrate spacings, single-pulse laser energies, and thin film thickness conditions on the donor substrate. Under the optimal experimental conditions, the phase-transformed organic molecular thin film will be obtained on the target substrate.

[0032] As Figure 1 shown, the method for using a laser to control the solid-liquid-solid and solid-gas-solid phase transitions of organic molecules described in this embodiment is as follows:

[0033] (1) Preparation of substrates: The substrates used are glass with a size of 50*25*0.2 mm; the clean glass substrate is first wiped with acetone and then with absolute ethanol. During the wiping process, clean medical degreasing cotton balls are used. After that, it is washed clean with deionized water and naturally air-dried in a closed space; the glass substrate is placed in a vacuum coater for the deposition of an organic light-emitting material thin film as the donor substrate. Among them, the thicknesses of the deposited organic light-emitting material thin films are 20 nm, 40 nm, 60 nm, and 80 nm respectively, and the target substrate is a clean glass sheet treated with acetone, absolute ethanol, and deionized water.

[0034] (2) Laser control of the phase transition process of the organic light-emitting molecular thin film;

[0035] The specific steps are as follows: Align the side of the prepared donor substrate coated with the organic material thin film towards the target substrate, and maintain a certain spacing distance between the two substrates. The spacing distance between the donor substrate and the target substrate is 1 - 10 μm, 40 μm, 80 μm, and 190 μm. Then, fix the entire sample in the structure with the donor substrate on top and the target substrate below on the laser processing displacement platform. By adjusting the focusing position of the laser, make the laser focus on the organic thin film on the donor substrate. First, scan the organic thin film according to the designed structure, with a scanning speed of 0.2 mm / s and a line spacing of 0.1 mm. The femtosecond laser wavelength used in this process is 1030 nm, the laser power is 50 mW, the pulse frequency is 1 kHz, and the single pulse energies required for the experiment are 1.2 μJ, 9.7 μJ, 43.3 μJ, and 174.6 μJ respectively. During the processing, ensure that the glass substrate is perpendicular to the laser optical axis position. Change the film thickness of the donor substrate, the spacing distance between the donor substrate and the target substrate, and the single pulse energy of the laser to carry out the laser-induced phase change process under different conditions. Finally, phase-changed organic thin films under different conditions can be obtained on the target substrate, and a continuous and uniform thin film can be obtained under the optimal operating conditions.

[0036] It can be seen from Figure 1 that when femtosecond laser acts on the organic light-emitting molecule thin film, its ultrashort pulse and ultra-high peak power can induce non-linear absorption of organic molecules, enabling the electrons in the molecules to be excited to high energy states. Most organic molecules can absorb the energy of femtosecond laser photons through non-linear means, ensuring the wide applicability of this technology. After absorbing energy, the organic molecules undergo solid-liquid or solid-gas phase changes, and the volume expansion provides a driving force for the molecules to detach from the donor substrate. At the same time, the structure of the entire sample with the donor substrate on top and the target substrate below can also cause the thin film to transfer under its own gravity. When the organic molecules encounter the target substrate, they cool and adhere, and finally stay on the target substrate in different forms. In addition, during the flight of the organic light-emitting molecules from the donor substrate to the target substrate, they may rotate under the action of the strong femtosecond laser field to achieve the regulation of the orientation of organic molecules, so that phase change regulation, thin film preparation, and orientation regulation can be realized during the transfer process.

[0037] It can be seen from Figure 2 that the laser-regulated phase change process of the organic light-emitting molecule thin film can realize the transfer of the organic thin film from the donor substrate to the target substrate, without damaging its fluorescence characteristics, can maintain the photophysical characteristics of the material itself, and can obtain a thin film with clear boundaries under appropriate operating conditions, realizing the preparation of the organic molecule thin film. Figure 2Among them, the intervals between the donor substrate and the target substrate are 1 - 10 μm, 40 μm, 80 μm, and 190 μm respectively, and the single-pulse energies of the laser used are 1.2 μJ, 9.7 μJ, 43.3 μJ, and 174.6 μJ respectively. It can be seen from the figure that the larger the interval between the two substrates, the more dispersed the formed molecular thin film is, indicating that the flight direction of the molecules has divergence during the material transfer process; if a uniform molecular thin film is to be prepared, experiments need to be carried out under the condition that the donor substrate and the target substrate are relatively close; in addition, with the increase of the single-pulse energy of the femtosecond laser, the fluorescence of the organic molecular thin film first increases and then decreases. When the single-pulse energy of the laser is 9.7 μJ, the fluorescence properties of the organic molecular thin film are the best.

[0038] It can be seen from Figure 3 that it is consistent with the fluorescence characteristics of Figure 2 . The condition with the best fluorescence properties also corresponds to obtaining a more uniform thin film, while larger laser energy and substrate spacing are not conducive to the formation of a complete and uniform organic molecular thin film.

[0039] It can be seen from Figure 4 that organic molecular thin films with different aggregation morphologies will be obtained under the action of different laser energies, and different aggregation morphologies correspond to different phase transition processes. When the single-pulse energy of the laser is relatively low (1.2 μJ), spherical nanoparticles that have experienced a solid-liquid-solid phase transition process are obtained, that is, the organic molecules in the laser action area absorb the laser energy and change from the solid state to the molten state, and then form spheres with low interfacial energy under the action of surface tension. When the laser action stops, nanoparticles are obtained by cooling. When the laser energy increases to 9.7 μJ, a continuous thin film with a small amount of aggregation and nanoparticles is obtained. This continuous thin film has experienced a solid-gas-solid phase transition process. This is because some molecules at the substrate and molecule interface are ionized after absorbing high-energy laser to form a plasma with properties similar to gas, and the plasma expansion provides a driving force to push the molecules at the corresponding position towards the target substrate. When the laser energy continues to increase to 43.3 μJ, a thin film with poor continuity, rough surface and obvious holes is formed. This is because the organic molecules have undergone Coulomb explosion, which further changes the molecular structure. Through the above analysis, it can be seen that femtosecond laser can induce solid-liquid-solid and solid-gas-solid phase transition processes at different single-pulse energies, and can simultaneously provide instantaneous liquid and gaseous organic molecules, reducing the intermolecular force and the force between the molecule and the substrate, which is beneficial to the orientation regulation of organic molecules. And a continuous and uniform thin film can be obtained on the target substrate under appropriate conditions.

[0040] It can be seen from Figure 5It can be seen that the organic thin film after laser regulation still presents an amorphous state similar to that of the evaporated thin film. Combining the fluorescence microscope photos and scanning electron microscope photos can prove the process of laser-induced phase change and transfer of the organic thin film, and the non-destructive transfer and thin film preparation of the organic light-emitting molecular thin film can be realized.

[0041] The preferred embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0042] In addition, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without conflict. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0043] Furthermore, any combination can be made between various different embodiments of the present invention as long as it does not violate the idea of the present invention, and it should also be regarded as the content disclosed by the present invention.

Claims

1. A method for laser regulation of the phase transition process of an organic light-emitting molecular thin film, characterized in that, the specific steps are as follows: Step 1: Pretreatment of the donor substrate and the target substrate; The donor substrate and the target substrate are pretreated with acetone, absolute ethanol, and deionized water respectively. After pretreatment, the donor substrate is placed in a vacuum coating instrument for evaporation coating of the organic light-emitting material thin film; Step 2: Laser regulation of the phase transition process of the organic light-emitting molecular thin film; First, the side of the donor substrate coated with the organic light-emitting material thin film in Step 1 is oriented towards the target substrate, and a certain distance is maintained between the two substrates to control the flight distance of the organic molecules from the donor substrate to the target substrate; Then, the entire sample is fixed on a displacement platform with the structure of the donor substrate on top and the target substrate below. Finally, the laser is controlled to focus on the organic light-emitting material thin film of the donor substrate, and then the organic light-emitting material thin film is scanned with the laser to induce the transfer of organic molecules to the target substrate and undergo solid-liquid-solid and solid-gas-solid phase transition processes during this process. Femtosecond laser can induce non-linear absorption of organic molecules. After the organic molecules absorb energy, they undergo solid-liquid or solid-gas phase transitions, and the volume expansion provides a driving force for the molecules to break away from the donor substrate; The laser described in Step 2 is a femtosecond laser. The wavelength of the femtosecond laser is 343 - 1030 nm, the laser power is 10 - 2000 mW, the pulse frequency is 1 - 500 kHz, the single pulse energy of the laser is 0.02 - 2000 μJ, the scanning speed is 0.1 - 2 mm / s, and a 40x objective lens is used for focusing with a numerical aperture of 0.65; The laser optical path is as follows: First, the femtosecond laser emitted by the laser passes through the first convex lens and the shutter and then is expanded by the second convex lens to expand the light spot. Then, it undergoes beam shaping through the first total reflector, the second total reflector, the third convex lens, and the fourth convex lens in sequence, and is incident on the sample to be processed after passing through the attenuation sheet, the first semi-reflective semi-transmissive lens, and the objective lens for focusing in sequence; In Step 1, the thickness of the organic light-emitting material thin film on the donor substrate is 20 nm, 40 nm, 60 nm, or 80 nm; The distance between the donor substrate and the target substrate is 1 - 200 μm.

2. A method for laser regulation of the phase transition process of an organic light-emitting molecular thin film as described in claim 1, characterized in that, both the donor substrate and the target substrate described in Step 1 are clean glass slides.

3. A method for laser regulation of the phase transition process of an organic light-emitting molecular thin film as described in claim 1, characterized in that, the pretreatment process described in Step 1 is specifically as follows: First, the donor substrate and the target substrate are wiped with acetone, then wiped with absolute ethanol, and then cleaned with deionized water. The wiping process uses clean medical degreasing cotton balls, and then air-dries naturally in a closed space.

4. A method for laser regulation of the phase transition process of an organic light-emitting molecular thin film as described in claim 2, characterized in that, The size of the glass sheet in Step 1 is 50*25*0.2 mm; the degreasing cotton balls used are medical degreasing cotton balls; the organic light-emitting material is the green light material tris(8-hydroxyquinoline) aluminum (Alq 3 , C 27 H 18 AlN 3 O 3 ).

5. A method for laser regulation of the phase transition process of an organic light-emitting molecular thin film as described in claim 1, characterized in that, In Step 2, the laser scanning direction uses a point-by-point scanning method for laser transfer; first, according to the size of the designed film transfer area, it is converted into a program recognizable by the laser, the line spacing is set to 0.1 - 1 mm, and the laser scanning speed is 0.1×10 -3 -2×10 -3 m / s.

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