Method for preparing spectrum continuously adjustable perovskite-polymer composite film by femtosecond laser direct writing and application thereof

Abstract

The application discloses a method for preparing a spectrum continuously adjustable perovskite-polymer composite film by femtosecond laser direct writing and application. The method comprises the following steps: preparing a perovskite precursor solution and coating to form a uniform wet film, and performing heating annealing under an inert atmosphere to obtain a perovskite precursor composite film; a femtosecond laser is used to perform focusing scanning in a line scanning mode, a spatial overlap is controlled to form a continuous and uniform heat field by adjacent pulses, perovskite nanocrystal growth is induced, and a perovskite-polymer composite film with continuously adjustable emission spectrum is obtained. Based on the quantum size effect of a single halogen system or the ion exchange mechanism of a mixed halogen system, the application realizes, for the first time, sub-nanometer precision continuous spectrum tuning in a visible light band in the composite film, and can directly write a high-resolution 2D or 3D light-emitting pattern in the film, thereby fundamentally eliminating spectrum crosstalk caused by a heterojunction, and providing a new technical platform for full-color display, information encryption and flexible optoelectronic devices.

Description

Technical Field

[0001] This invention relates to a polymer composite film, which relates to the field of micro-nano optical materials, and specifically to a method and application for preparing spectrally continuously tunable perovskite-polymer composite films by femtosecond laser direct writing. Background Technology

[0002] As the core visual interface of modern information society, full-color display technology is undergoing a profound transformation from traditional liquid crystal displays (LCDs) to self-emissive display technologies such as organic light-emitting diodes (OLEDs), quantum dot light-emitting diodes (QLEDs), and micro-light-emitting diodes (Micro-LEDs). The core driving force behind this transformation stems from the market's urgent demand for higher color gamut coverage (such as the BT.2020 standard), higher resolution (moving towards 4K / 8K and even higher), lower power consumption, and longer lifespan.

[0003] Nanocrystalline materials, due to their unique quantum confinement effect resulting from their size tunability, can achieve controllable tuning of emission in the visible to near-infrared wavelength range by adjusting particle size, making them a research hotspot in the display field. Among them, metal halide perovskite nanocrystals (PNCs) stand out for their high photoluminescence quantum yield (PLQY), narrow-band emission, and ABX3-type crystal structure (A-site cations such as Cs). + FA + MA + B-site cations such as Pb² + Halogen ions at the X-position, such as Cl... - ,Br - I - The tunable structure of PNCs makes them an ideal luminescent material for next-generation high color gamut displays. Therefore, combining the intrinsic luminescence advantages of PNCs with full-color display technology is expected to open up new research directions for high-performance display devices.

[0004] However, key technological bottlenecks remain in material preparation and device integration. While existing technologies can achieve bandgap tuning by adjusting halogen composition (Cl / Br / I) or synthesis conditions through chemical synthesis, the non-equilibrium nucleation process limits wavelength control, resulting in significant dispersion and uncontrollability. Spectral precision is typically maintained only at the nanometer to tens of nanometer level, failing to meet the precise wavelength requirements of standards such as BT.2020. In recent years, studies have utilized laser direct writing to induce localized perovskite crystallization in polymer films; however, due to uneven grain size distribution caused by localized high-gradient thermal fields, most studies remain limited to single-wavelength or a few discrete wavelengths, again hindering the achievement of highly precise control of continuous spectra.

[0005] Furthermore, current multicolor light-emitting devices generally employ a spatial arrangement strategy of discrete pixels for red, green, and blue (RGB). This architecture relies on complex photolithography or multi-step printing processes, which are not only cumbersome and costly, but also introduce numerous heterogeneous interfaces that easily lead to spectral crosstalk and material interface degradation, accelerating device performance decline. Therefore, how to achieve wide-spectrum, continuously tunable, sub-nanometer precision control, and in-situ patterned integration in a single medium has become a key challenge to overcome the bottlenecks of existing display technologies and promote the development of next-generation full-color displays and intelligent optoelectronic devices. Summary of the Invention

[0006] To address the problems existing in the background technology, this invention provides a method and application for preparing spectrally continuously tunable perovskite-polymer composite thin films using femtosecond laser direct writing. This invention addresses the difficulty of achieving wide-spectrum, continuously tunable, high-precision control, and patterned integration of existing perovskite luminescent materials in the same solid medium. By inducing a uniform thermal field in a polymer-based thin film using a femtosecond laser line scanning mode, in-situ nucleation and growth of perovskite nanocrystals are achieved. Furthermore, through the synergistic control of laser parameters and halogen components, sub-nanometer-scale continuously tunable emission spectra from blue to red light are obtained, while simultaneously enabling the construction of high-resolution luminescent patterns.

[0007] The technical solution adopted in this invention is: I. A method for preparing spectrally tunable perovskite-polymer composite thin films by femtosecond laser direct writing, comprising: Step 1) Cesium salt, lead salt and halogen salt are dissolved in a strongly polar aprotic solvent and mixed to obtain a perovskite precursor. Then, ligands and a transparent polymer matrix are added and stirred until completely dissolved to obtain a perovskite precursor solution.

[0008] Step 2) The perovskite precursor solution is coated onto a hydrophilically modified glass substrate to form a uniform wet film. Then, it is heated and annealed under an inert atmosphere to evaporate the solvent and obtain a dense perovskite precursor composite film.

[0009] Step 3) A femtosecond laser is used to focus and scan the perovskite precursor composite film in a line scanning mode along a preset scanning path. By controlling the laser parameters, the scanning speed, repetition frequency and laser power are precisely controlled to control the spatial overlap of adjacent pulses of the femtosecond laser to form a continuous and uniform thermal field. This induces the perovskite precursor to decompose, nucleate and grow into perovskite nanocrystals. The thermal field environment overcomes the thermal gradient dispersion problem of the traditional point scanning mode and can induce uniform nucleation and controllable growth of perovskite nanocrystals, thereby obtaining a perovskite-polymer composite film with continuously tunable emission spectrum.

[0010] In step 1), the cesium salt, lead salt, and halogen salt are dissolved in a strongly polar aprotic solvent in a molar ratio of 1:1:3, and the total mass fraction of the cesium salt, lead salt, and halogen salt is 10.9%; the strongly polar aprotic solvent is one of N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone.

[0011] In step 1), the halogen salt can be a single halogen system or a mixed halogen system. The single halogen system can be CsPbBr3 or CsPbI3. When using CsPbBr3, the emission wavelength of the perovskite-polymer composite film continuously varies within the range of 500-520 nm. When using CsPbI3, the emission wavelength of the perovskite-polymer composite film is between 640-670 nm. The halogen content varies continuously within the nm range; the mixed halogen system uses CsPb(Cl / Br)3, CsPb(Br / I)3, or CsPb(Cl / Br / I)3. When using CsPb(Cl / Br)3, the molar ratio of Cl:Br is 2:1, 1.5:1.5, or 0.5:2.5; when using CsPb(Br / I)3, the molar ratio of Br:I is 1:2, 1.25:1.75, 1.5:1.5, 1.75:1.25, or 2:1, to achieve continuous spectral coverage of the perovskite-polymer composite film in the visible light band from 430 nm to 670 nm. By adjusting the molar ratio of Cl, Br, and I and combining it with fine-tuning of laser parameters, continuous spectral coverage of the entire visible light band from blue light (430 nm) to red light (670 nm) is achieved. The tuning accuracy of both the single halogen system and the mixed halogen system using femtosecond lasers is 0.05~0.1. nm, by changing the laser scanning speed, repetition frequency or single pulse energy, the emission wavelength can be continuously tuned using the quantum size effect.

[0012] In step 1), when CsPb(Cl / Br / I)3 is used, and the molar ratio of Cl:Br:I is 1.0~1.2:0.7~0.9:1.0~1.2, the perovskite-polymer composite film is focused under the laser parameters of a femtosecond laser with a repetition frequency of 200 kHz, a scanning speed of 3 mm / s, and a single pulse energy of 2 μJ, to induce nanocrystal luminescence and obtain near-ideal white light emission with color coordinates (0.32, 0.32) in the CIE 1931 color space.

[0013] The femtosecond laser has a wavelength of 800 nm or 1030 nm, a pulse width of 240 fs⁻¹ ps, a repetition rate adjustable in the range of 5 kHz to 1 MHz, a single pulse energy of 1–3 μJ, and a scanning speed of 1–10 mm / s. By adjusting these parameters, the thermal field temperature and the growth kinetics of the nanocrystals can be precisely controlled.

[0014] In step 1), the perovskite precursor has the general formula ABX3, where the A-site ion is Cs. + FA + MA + PEA + One or more of them, with the B-site ion being Pb². + Sn² + Cu² + One or more of them, with the X-position ion being Cl. - ,Br - I - One or more of the following; the ligand is 18-crown-6, and the molar ratio of the ligand to the B-site ion in the perovskite precursor is 0.02~0.05:1; the ligand can suppress the spontaneous crystallization of the precursor and ensure that the precursor is uniformly distributed in the film before laser direct writing.

[0015] In step 1), the transparent polymer matrix is ​​one of polymethyl methacrylate, polyvinylidene fluoride, polyethylene terephthalate, polystyrene, or polydimethylsiloxane. The molecular weight range of the transparent polymer matrix is ​​90W~120W, and the mass ratio of the transparent polymer matrix to the perovskite precursor is 0.09~0.18:1.

[0016] In step 2), the perovskite precursor solution is coated by spin coating, blade coating, or drop coating. When spin coating, the spin coating speed is 500~2000 r / min, the spin coating time is 200~360 s, and the wet film thickness is 3~5 μm. When blade coating, the blade coating speed is 1 cm / s, and the wet film thickness is 10~50 μm. When drop coating, the wet film thickness is 50~200 μm.

[0017] In step 2), the heating annealing process is carried out under nitrogen protection, with a heating rate of 30~60℃ / min, an annealing temperature of 60~120℃, and an annealing time of 1~3h.

[0018] II. A spectrally tunable perovskite-polymer composite film: The spectrally tunable perovskite-polymer composite film is prepared by the method described above.

[0019] III. Application of a spectrally continuously tunable perovskite-polymer composite thin film: The application includes its use as a high-resolution two-dimensional luminescent pattern or three-dimensional micro / nano structure prepared by femtosecond laser on the surface of optoelectronic smart devices.

[0020] By controlling the scanning path and parameters of the femtosecond laser through computer programming, high-resolution two-dimensional luminescent patterns (such as micro QR codes with line widths up to 1 μm) or three-dimensional micro / nano structures (such as spirals) can be directly written onto thin films, enabling custom programming of luminescent patterns. Perovskite-polymer composite thin films can be applied in full-color displays, information encryption, flexible sensing, piezoelectric devices, or three-dimensional photonic integration.

[0021] The beneficial effects of this invention are:

[0022] 1. This invention achieves, for the first time, sub-nanometer precision continuous spectral tuning across the entire visible light band from 430 nm to 670 nm in solid composite films through the quantum size effect of a single halogen system or the ion exchange mechanism of a mixed halogen system, overcoming the shortcomings of discrete and low precision spectral control in traditional chemical synthesis methods.

[0023] 2. The continuous and uniform thermal field generated by the femtosecond laser line scanning mode proposed in this invention can precisely control the nucleation and growth of nanocrystals, with a spectral tuning accuracy of 0.05~0.1 nm at the sub-nanometer level, meeting the fine-tuning requirements of high-standard displays such as BT.2020 for specific wavelengths.

[0024] 3. This invention does not require a complex spatial arrangement of three primary color pixels. By synergistically controlling the laser parameters and halogen ratio in the same thin film, full-color output from blue light to red light can be achieved, and ideal white light emission can be obtained, fundamentally eliminating spectral crosstalk and material degradation caused by heterogeneous interfaces.

[0025] 4. This invention utilizes the spatial selectivity of femtosecond laser direct writing to directly write high-precision micron-level two-dimensional luminescent patterns and three-dimensional microstructures into thin films. Combined with the flexible properties of the polymer matrix, it fundamentally eliminates spectral crosstalk caused by heterogeneous interfaces, providing a new technology platform for applications such as full-color displays, high-density data storage, information encryption, flexible wearable sensing, and optoelectronic devices. Attached Figure Description

[0026] Figure 1 A schematic diagram illustrating the effect of pulse overlap on perovskite nanocrystals in two scanning modes of a femtosecond laser line on the single-halogen perovskite composite film prepared in Example 1.

[0027] Figure 2 This is a schematic diagram illustrating the regulation of the luminescence properties of the monohalogen perovskite composite film prepared in Example 1 induced by different femtosecond laser parameters (laser power, scanning speed, repetition frequency) to generate nanocrystals.

[0028] Figure 3 This is a schematic diagram illustrating the sub-nanometer-scale full visible light continuous spectrum tuning of the single-halogen and dihalogen perovskite composite thin films prepared in Examples 1 and 2.

[0029] Figure 4 The images show physical examples of the single-halogen and dihalogen perovskite composite films prepared in Examples 1 and 2, which achieve a full-color gradient display of the Great Wall.

[0030] Figure 5 The phase evolution process and photoluminescence (PL) spectrum of the trihalomethane perovskite composite thin film prepared in Example 2 under laser power driving are shown.

[0031] Figure 6 The photoluminescence PL spectrum and color coordinate diagram of the trihalomethane perovskite composite thin film prepared in Example 2, which achieves near-ideal white light emission;

[0032] Figure 7 A schematic diagram of the time-dependent fluorescence behavior of the miniature QR (Quick Response Code) prepared according to the present invention;

[0033] Figure 8 The CsPbBr3- sample prepared for this invention was photographed under ultraviolet light. x I x Schematic diagram of a spiral pattern composed of nanocrystals;

[0034] Figure 9 This is a schematic diagram of the multifunctional sensing application prepared according to the present invention, wherein, Figure 9 Figure A shows a schematic diagram of the piezoelectric output performance of the prepared CsPbBr3 / PVDF nanofibers under different pressures. Figure 9 B is a schematic diagram of the piezoelectric properties with different contents of perovskite nanocrystals. Figure 9 C represents a schematic diagram of the triboelectric properties with different amounts of perovskite nanocrystals added. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] There are no particular restrictions on the source of any raw materials used in this invention; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0037] The purity of the raw materials used in this invention is not particularly limited. Preferably, the purity is analytical grade or conventional in the field of perovskite material preparation.

[0038] All materials of this invention are conventional in the field, and each designation and abbreviation is clear and distinct in its relevant application. Those skilled in the art can purchase them from the market or prepare them by conventional methods based on the designation, abbreviation, and corresponding application.

[0039] All processes in this invention are referred to by abbreviations that are common abbreviations in the field. Each abbreviation is clear and specific in its relevant application area, and those skilled in the art can understand its conventional process steps based on the abbreviation.

[0040] In the following embodiments, unless otherwise specified, the methods used are conventional methods in the art, and the materials, reagents, detection devices, etc. used are all commercially available.

[0041] Specific embodiments of the present invention are as follows: Example 1:

[0042] This embodiment describes the evolution process of nanocrystals in perovskite thin films under femtosecond laser direct writing line scanning mode and a method for preparing spectrally continuously tunable composite thin films in a single halogen system. The specific steps are as follows: Step 1: Cesium salt, lead salt, and halide salt were dissolved in a strongly polar aprotic solvent at a molar ratio of 1:1:3 to obtain a perovskite precursor. The strongly polar aprotic solvent was N,N-dimethylformamide, and the total mass fraction of cesium salt, lead salt, and halide salt was 10.9%. Then, ligands to inhibit the self-crystallization process of perovskite were added to obtain a mixed solution. The mixed solution was placed on a magnetic stirrer and heated and stirred thoroughly at 60°C and 600 rpm for 6 hours to obtain a homogeneous and transparent initial perovskite precursor solution. The general formula of perovskite in the perovskite precursor is ABX3, where the A-site ion is a cesium ion (Cs). + Formamidinium ion (FA) + methylamine ion MA + Phenylethylamine ions (PEA) + One or more of them, with the B-site ion being lead ion Pb². + Tin ions Sn² + Copper ions Cu² + One or more of them, where the ion at the X site is a chloride ion (Cl). - Bromide ions (Br) - Iodide ions -One or more of the following; the ligand is 18-crown-6, and the molar ratio of the ligand to the B-site ion in the perovskite precursor is 0.05:1; the ligand can suppress the spontaneous crystallization of the precursor and ensure that the precursor is uniformly distributed in the film before laser direct writing.

[0043] Then, transparent polymer matrix powder, which is polyvinylidene fluoride, is added to the initial perovskite precursor solution. The molecular weight range of the transparent polymer matrix is ​​120W, and the mass ratio of the transparent polymer matrix to the perovskite precursor is 0.18:1, to obtain the final perovskite precursor solution. In this embodiment, the mass concentration of the transparent polymer matrix in the final perovskite precursor solution is 13%wt.

[0044] In this embodiment, an electronic balance was used to weigh the perovskite precursor, ligands, and transparent polymer matrix. The perovskite precursor included cesium bromide (CsBr, Xi'an Baolai, 99.99%) and lead bromide (PbBr2, Xi'an Baolai, 99.99%). The ligand used was 18-Crown-6 (C 12 H 24 O6, Aladdin, 99%; the transparent polymer is polyvinylidene fluoride (PVDF, average MW ~ 534,000, Alfa Aesar), whose cross-linked network can effectively restrict ion migration, which is beneficial for achieving localized crystallization under subsequent laser irradiation. In this embodiment, the mass ratio of cesium bromide, lead bromide, and 18-Crown-6 is 0.02 mmol: 0.02 mmol: 0.038 mmol, and the strongly polar aprotic solvent used is N,N-dimethylformamide (DMF, AR, Sigma-Aldrich).

[0045] The halogen salt adopts a single halogen system, which is either CsPbBr3 or CsPbI3. The tuning accuracy of the single halogen system and the mixed halogen system in femtosecond laser is 0.05~0.1 nm. By changing the laser scanning speed, repetition frequency or single pulse energy, the emission wavelength can be continuously tuned by utilizing the quantum size effect.

[0046] It is understandable that the aforementioned ligands contain functional groups such as amino and carboxyl groups, which can interact with B-site metal ions (such as Pb) in perovskites. 2+ Coordination bonds are formed. This coordination can stabilize the perovskite structure and reduce its internal defect state density.

[0047] Understandably, PVDF is a fluoropolymer, in which the high electronegativity (4.0) of fluorine atoms forms strongly polar sites in the polymer chain. This electrostatic anchoring effect stabilizes the perovskite nuclei and inhibits disordered growth in the early stages of crystallization. The polymer matrix ultimately exists at the grain boundaries of the perovskite film, which can confine the growth of perovskite grains and improve the film formation properties, ultimately resulting in a perovskite film with uniform grain size and no pinholes.

[0048] Step 2: Clean the substrate and perform plasma hydrophilic modification on its surface. A 2×2cm soda-lime glass substrate was selected and ultrasonically cleaned sequentially in acetone, ethanol, and deionized water for 15 minutes each, then dried with high-purity nitrogen. The cleaned substrate was placed in the plasma cleaning chamber, and the program was started to enhance the hydrophilicity of the substrate surface and its wettability with the solution. It should be noted that the above plasma program includes vacuuming, oxygen flow of 50 sccm, and treatment at 100W RF power for 10 minutes.

[0049] Step 3: Use a pipette to draw up the perovskite precursor solution and spin-coat it onto the hydrophilically modified glass substrate to form a uniform wet film. Then, drop it onto the substrate to form a liquid film. It should be noted that the above film formation process in this embodiment adopts the spin-coating method. The modified substrate is quickly placed in the center of the spin coater rotor, vacuum adsorption is turned on for fixation, the spin coater speed is set to 500 r / min (which can be adjusted according to the required film thickness), the spin coating time is 360s, the spin coating program is started, and the solution is evenly spread under the action of centrifugal force to form a wet film with a thickness of 3 μm.

[0050] Step 4: Anneal the wet film containing the precursor. The spin-coated substrate is quickly transferred to a heating platform, and the heating program is started. Under a nitrogen atmosphere (oxygen content <0.1ppm, water content <0.1ppm), the film is heated from room temperature at a rate of 50℃ / min, with an annealing temperature of 80℃ and an annealing time of 2 hours. The temperature is then slowly reduced to room temperature at a rate of 20℃ / min, ultimately obtaining a dense perovskite precursor composite film containing the precursor. It is understood that in this embodiment, the solvent in the composite film evaporates rapidly after heating, making the film more dense and stable. Simultaneously, due to the inhibitory effect of ligand 18-Crown-6 on the crystallization process of the perovskite precursor, the precursor does not reach a supersaturated state in the polymer network to form initial nanocrystal nuclei, thus maintaining a uniform distribution of the precursor in the film.

[0051] Step 5: Add a small amount of grease to the center of the glass slide, and firmly attach the back of the prepared composite film sample to the glass slide to prevent displacement during laser scanning. Place the glass slide with the sample fixed on a high-precision 3D displacement platform; use a femtosecond laser in line scanning mode to focus and scan the perovskite precursor composite film along a preset scanning path. By controlling the laser parameters, the scanning speed, repetition frequency, laser power, and displacement platform position are precisely controlled to control the spatial overlap of adjacent femtosecond laser pulses to form a continuous and uniform thermal field, inducing the decomposition, nucleation, and growth of the perovskite precursor into perovskite nanocrystals. The thermal field environment overcomes the thermal gradient dispersion problem of the traditional point scanning mode, and can induce uniform nucleation and controllable growth of perovskite nanocrystals, thereby obtaining a perovskite-polymer composite film with continuously tunable emission spectra.

[0052] Specifically, this embodiment uses a femtosecond laser source with a wavelength of 1030nm, a pulse width of 240fs, and a repetition frequency adjustable within the range of 5kHz to 1MHz (specifically set to 1MHz, 500kHz, 200kHz, 100kHz, 50kHz, 20kHz, and 5kHz). The femtosecond laser is precisely focused onto the surface of the composite thin film using a 100X objective lens (numerical aperture NA=0.8). The laser power is adjusted by a program-controlled variable attenuator, and the single-pulse energy can be precisely controlled within the range of 1 to 3μJ (specifically set to 1μJ, 1.5μJ, 2μJ, 2.5μJ, and 3μJ). The scanning speed of the 3D displacement platform is controlled by a program, and the scanning speed is set to 1 to 10mm / s (specifically set to 1mm / s, 3mm / s, 5mm / s, 7mm / s, and 10mm / s). By adjusting the above parameters, the thermal field temperature and the growth kinetics of the nanocrystals can be precisely controlled, and then the surface morphology of the thin film is monitored in real time using a CCD camera.

[0053] Understandably, during femtosecond laser scanning, a Gaussian beam is focused on the scanning path to form a continuous and uniform thermal field. This thermal field induces thermal decomposition in the polymer network, inducing the nucleation of perovskite precursors and their growth into nanocrystal nuclei. By changing the laser parameters (single pulse energy, repetition frequency, and scanning speed), the thermal field temperature and nanocrystal nucleation kinetics can be precisely controlled to regulate the growth size of the nanocrystals, thereby achieving continuous tunability of the emission spectrum.

[0054] like Figure 1 As shown, this illustrates the influence mechanism of pulse overlap on perovskite nanocrystals in femtosecond laser line scanning mode on monohalogen perovskite composite films. Precise spectral modulation benefits from a self-reinforcing thermal cycling mechanism, an inherent characteristic of line scanning mode, fundamentally different from traditional point-by-point writing methods. Specifically, in line scanning mode M2, continuous pulses generate a continuous and uniform thermal field, with spatial overlap as follows:

[0055]

[0056] in, The center distance between two adjacent light spots. For scanning speed, The repetition frequency, Spot size

[0057] Each subsequent pulse reheats the region preheated by the previous pulse, thus spatially confining thermal energy and delaying cooling. This environment enables uniform nucleation through reduced energy input. (To promote grain growth) the grain size—and therefore the emission wavelength—can be continuously adjusted.

[0058] Conversely, the dot pattern M1 produces discrete thermal radiation with a high gradient. , (where is the thermal diffusion length), which leads to non-uniform nucleation and dispersion of grain size, resulting in discrete emission spectra.

[0059] like Figure 2 The figure illustrates the regulation of the luminescence properties of the monohalogen perovskite CsPbBr3 composite film induced by different femtosecond laser parameters (laser power, scanning speed, and repetition frequency). In a preferred embodiment, the emission spectrum of the CsPbBr3 composite film is continuously regulated by adjusting the laser parameters using the quantum size effect. Specifically, with a fixed repetition frequency of 200 kHz and a single pulse energy of 1-3 μJ, when the scanning speed is gradually increased from 3 mm / s to 12 mm / s, the emission wavelength of the prepared perovskite nanocrystals continuously red-shifts from 505 nm to 520 nm, with a tuning accuracy of 0.05~0.1 nm, achieving sub-nanometer-level continuous spectral regulation. As shown in Table 1, the study found that increasing the laser power, single pulse energy, or repetition frequency can enhance the intensity of PL, while causing a red-shift of the emission peak and reducing the full width at half maximum (FWHM). These effects are directly related to the scanning speed: slower speeds increase the number of pulses irradiated per unit volume, thereby increasing spatial overlap and promoting heat accumulation. This helps to uniformly induce nucleation and growth of high-density PNCs, thereby achieving a systematic redshift and a narrower FWHM.

[0060] Table 1

[0061] 1 10 505.324249 2 14 505.436066 1 7 505.547852 2 12 505.615485

[0062] In another preferred embodiment, cesium lead iodide (CsPbI3) can be tuned from 640 nm to 670 nm with a tuning precision of 0.05–0.1 nm. Compared to CsPbBr3, laser-induced nanocrystallization of CsPbI3 requires higher laser energy, primarily due to the complex phase transition behavior induced by iodine ions (I). Specifically, CsPbI3 exhibits a transition from a metastable perovskite phase (such as the cubic α phase) to a photoinert non-perovskite phase (δ phase), accompanied by an extremely high kinetic barrier and significant lattice strain.

[0063] Example 2:

[0064] This embodiment describes a method for preparing a composite thin film that achieves full-color tuning and white light emission by mixing halogens. The specific steps are as follows:

[0065] Unlike Example 1, the transparent polymer matrix of polyvinylidene fluoride (PVDF) was replaced with polymethyl methacrylate (PMMA, average MW ~120,000, Alfa Aesar), and the perovskite precursors included cesium chloride (CsCl, Xi'an Baolai, 99.99%), cesium bromide (CsBr, Xi'an Baolai, 99.99%), cesium iodide (CsI, Xi'an Baolai, 99.99%), lead chloride (PbCl2, Xi'an Baolai, 99.99%), lead bromide (PbBr2, Xi'an Baolai, 99.99%), and lead iodide (PbI2, Xi'an Baolai, 99.99%).

[0066] The mixed halogen system specifically uses CsPb(Br / Cl)3 and CsPb(Br / I)3. In this example, the molar ratio of cesium bromide, lead bromide, and 18-Crown-6 in the dihalogen system is 0.02 mmol:0.02 mmol:0.038 mmol, which is typical for preparing CsPbBr in bromine-iodine doped polymers. 3-x I x Br nanocrystals - :I - The ratios were 1:2, 1.25:1.75, 1.5:1.5, 1.75:1.25, and 2:1, respectively. In typical chlorobromine-doped polymers, CsPbBr... 3-x Cl x Cl nanocrystals - Br⁻ - The ratios were 2:1, 1:1, and 0.5:2.5, respectively; in typical chlorobromine-iodine triple-doped polymers, the mixed halogen system used was CsPb(Cl / Br / I)3, Cl - Br - :I -The ratios were 1.1:0.8:1.1 to achieve continuous spectral coverage of the visible light band from 430 nm to 670 nm for the perovskite-polymer composite film. By adjusting the molar ratio of Cl, Br, and I and combining it with fine control of laser parameters, continuous spectral coverage of the entire visible light band from blue light (430 nm) to red light (670 nm) was achieved. The tuning accuracy of the single halogen system and the mixed halogen system in the femtosecond laser was 0.05~0.1 nm. By changing the laser scanning speed, repetition frequency, or single pulse energy, the quantum size effect was used to achieve continuous tuning of the emission wavelength.

[0067] like Figure 3 As shown, sub-nanometer full visible light continuous spectral tuning is achieved for monohalogen and dihalogen perovskite composite thin films. A direct comparison of key performance indicators (tuning accuracy and range) highlights the superiority of our method over traditional chemical synthesis and standard laser-induced methods. Traditional chemical synthesis adjusts luminescence properties by regulating reaction parameters (such as time, temperature, and precursor composition); however, its tuning accuracy is limited, with emission peak shifts spanning several nanometers even within the same batch. Conversely, laser direct writing methods offer high tuning accuracy, with intervals of approximately 1 nm, but are limited by a narrow tuning range, restricting their spectral coverage. In contrast, our method achieves both broad spectral coverage and unprecedented tuning accuracy. By optimizing precursor composition, laser parameters, and processing techniques, continuous photoluminescence PL tuning from 430 nm to 670 nm is achieved with high accuracy. Reaching the sub-nanometer level, and further refined to 0.05 to 0.1 nm, this capability enables the fabrication of flexible composite films with full-color display functionality, such as... Figure 4 As shown in the image, a real-world image of the Great Wall is displayed using a single-halogen and double-halogen perovskite composite thin film, exhibiting excellent spatial resolution and color fidelity.

[0068] like Figure 5 The figure shows the phase evolution process and PL spectrum of the trihalomethane perovskite composite film under laser power driving. In a preferred embodiment, by introducing mixed halogens (Cl, Br, I) into the precursor and using a femtosecond laser thermal field to promote the dynamic exchange of halide ions, a broad spectrum of emission wavelengths can be continuously covered. Specifically, a CsPb(Cl / Br / I)3 mixed halogen system is used in the precursor. With a fixed scan speed of 10 mm / s and a repetition frequency of 200 kHz, when the power increases from 10% to 50%, the emission peak position of the film continuously redshifts from 470 nm in the blue region to 620 nm in the red region, achieving full-color continuous tuning across the entire visible light band. Through photo-induced mixed halogen phase separation reaction, the internal structure of the film is induced to evolve, thereby precisely constructing perovskite nanocrystal patterns with multiple colors on the composite film.

[0069] like Figure 6 The figure shows the PL spectrum and color coordinates of a trihalomethane perovskite composite thin film achieving near-ideal white light emission. In another preferred embodiment, by optimizing the molar ratio of Cl:Br:I in the precursor and combining it with fine adjustment of laser parameters, near-ideal white light emission can be achieved in a single thin film. This is an achievement never before realized by the FsLDW method. Unlike traditional rare-earth doped phosphors, which require a multi-step doping process, specifically, when the stoichiometric ratio of CsBr, PbCl2, PbBr2, and PbI2 in the precursor is controlled at Cl:Br:I = 1.1:0.8:1.1, under laser parameters of 200kHz repetition frequency, 3mm / s scanning speed, and 2μJ single-pulse energy, the emission spectrum of the prepared region is close to ideal white light, with CIE color coordinates of (0.32, 0.32), achieving high-quality white light emission.

[0070] In application, this invention specifically refers to a method for creating a miniature QR code with time-dependent fluorescence behavior using a laser path. The specific steps are as follows:

[0071] Similar to Example 1, the same precursor formulation is used, except that the 18-Crown-6 ligand is not added in step 1. Both methods utilize software programming in a computer control module to modify parameters such as the target focal position, movement speed, and laser parameters, allowing for the direct writing of high-resolution luminescent patterns onto the thin film. Specifically, by setting the repetition frequency to 200 kHz, single-pulse energy to 2.0 μJ, and scanning speed to 10 mm / s, and designing patterns using AI and converting them into scanning paths, micron-scale QR code patterns with a linewidth of 1 μm can be fabricated on the thin film. Furthermore, through layer-by-layer scanning, three-dimensional micro / nano structures (such as spirals and photonic crystal structures) can also be fabricated, enabling customized programming of luminescent patterns and high-density data storage.

[0072] The miniature QR code pattern was photographed every 600 seconds using a microscope. Figure 7 As shown, a miniature QR code exhibits time-dependent fluorescence behavior. Under continuous ultraviolet irradiation, the pattern dynamically changes color from red to yellow, and then to green. In contrast, the miniature QR code prepared using 18-Crown-6 as a ligand emits stable red fluorescence over time. This is because 18-Crown-6 effectively suppresses the phase transition during femtosecond laser direct writing.

[0073] like Figure 8 As shown, this is an example of the process of using FsLOS technology to synthesize CsPbBr in mixed halides. 3-x I xA three-dimensional helical structure was constructed within an organic-inorganic hybrid perovskite-polymer matrix to enable higher-dimensional information storage. Under ultraviolet irradiation, this three-dimensional structure exhibits gradual color transitions and time-varying microluminescence patterns, significantly improving data storage capacity and security.

[0074] The present invention also prepares a polyvinylidene fluoride-coated perovskite nanocrystal luminescent spun film for piezoelectric performance testing according to the following steps:

[0075] Step 1: Dissolve 0.0213g cesium bromide, 0.0367g lead bromide, a halide salt, and 1.5g polyvinylidene fluoride in 10mL of N,N-dimethylformamide to obtain a perovskite precursor. The molar ratio of cesium bromide to lead bromide is 1:1. The halide salt used is CsPbBr3, and the amount of halide salt added to the perovskite is 0.03-0.18% of the total mass of the perovskite precursor. The mass percentage of polyvinylidene fluoride in the perovskite precursor is 20wt%. This ratio is beneficial for uniform solution spraying and smooth spinning during electrospinning.

[0076] Step 2: Place the perovskite precursor obtained in Step 1 on a stirrer and stir at room temperature for 12 hours to clarify the solution and obtain the spinning solution.

[0077] Step 3: Electrospinning the spinning solution obtained in Step 2: The spinning solution is loaded into an electrospinning device. During the electrospinning process, an electrospinning device with a roller collecting device is used. The receiving distance is 15cm, the roller speed is 800rpm, the positive voltage is 14kV, the negative voltage is -5KV, and the spinning solution flow rate is 30μL / min. The electrospinning environmental conditions are controlled as follows: temperature is 22~25℃, humidity is 30~40%. After spinning is completed, a preliminary luminescent textile film is obtained.

[0078] Understandably, the polyvinylidene fluoride fibers are arranged in an interlaced pattern, forming a continuous and irregular three-dimensional network, with nanocrystals successfully embedded within the polyacrylonitrile fibers. This dense encapsulation structure provides a protective effect for the nanocrystals, effectively blocking moisture and oxygen from the air, thereby significantly inhibiting the decomposition of the nanocrystals.

[0079] Step 4: Transfer the preliminary luminescent textile film obtained in Step 3 to a high-temperature heating stage for thermal cross-linking treatment at a temperature of 160°C for 1 hour, and finally obtain a perovskite nanocrystal luminescent textile film coated with polyvinylidene fluoride.

[0080] The piezoelectric properties of the nanofiber membrane prepared above were tested, and the process is as follows:

[0081] Fabrication of piezoelectric devices. The prepared CsPbBr3 nanofiber membrane was cut into 2cm×2cm square samples. 100nm silver was deposited on the upper and lower surfaces of the fiber membrane as electrodes to form the basic piezoelectric unit. The electrodes were circles with a radius of 0.5mm. The electrodes on both sides were led out by conductive adhesive polished at both ends to obtain a nanofiber piezoelectric device based on flexible PVDF.

[0082] Piezoelectric performance testing. A mechanical excitation-electric signal synchronous acquisition system was used for testing, and all tests were conducted at room temperature. The piezoelectric device was fixed on the test platform, and periodic pressure was applied to the device surface via a microcomputer-controlled linear actuator. Standard test conditions were set as follows: applied compressive force of 2~21N, and operating frequency of 1kHz. The open-circuit voltage signal between the two electrodes of the device was directly measured and recorded using an oscilloscope. The external circuit current signal flowing through the device was measured using an electrochemical workstation in short-circuit mode. The peak open-circuit voltage and peak short-circuit current were extracted from the recorded periodic signals as key indicators for evaluating the piezoelectric output performance.

[0083] like Figure 9 Figure A shows the piezoelectric output performance of the prepared CsPbBr3 / PVDF nanofibers under different pressures (2 to 21 N), indicating that the composite fiber membrane has an excellent response process. With the generation of periodic pressure, the CsPbBr3 / PVDF nanofiber membrane stably outputs a signal, demonstrating excellent piezoelectric properties. Direct electrospinning of the spinning solution can yield a luminescent textile film that emits bright green light under ultraviolet light. Figure 9 As shown in Figure B, after adding different amounts of perovskite nanocrystals (CsPbBr3 = 3, 6, 9, 12, 15, 18 wt%), the peak voltage initially increased significantly with increasing CsPbBr3 concentration (the peak charge was close to 0.5 V at a concentration of around 12%), and then gradually decreased. Both excessively high and low concentrations are detrimental to improving piezoelectric performance. Furthermore, as... Figure 9 As shown in Figure C, this hybrid thin film exhibits great potential in triboelectric sensing, achieving a maximum voltage output VOC of 13.7 V with a doping concentration of approximately 12%, a value significantly higher than... Figure 9 The pressure response value in B indicates that the hybrid film has excellent sensing capabilities in contact sensing applications.

[0084] The above specific embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A method for preparing spectrally tunable perovskite-polymer composite thin films by femtosecond laser direct writing, characterized in that, include: Step 1) Cesium salt, lead salt and halide salt are dissolved in a strongly polar aprotic solvent and mixed to obtain a perovskite precursor. Then, ligands and a transparent polymer matrix are added and stirred until completely dissolved to obtain a perovskite precursor solution. Step 2) The perovskite precursor solution is coated onto a hydrophilically modified glass substrate to form a uniform wet film, and then heated and annealed under an inert atmosphere to obtain a dense perovskite precursor composite film. Step 3) A femtosecond laser is used to focus and scan the perovskite precursor composite film in a line scanning mode along a preset scanning path. The adjacent pulses of the femtosecond laser are controlled to generate spatial overlap to form a continuous and uniform thermal field, which induces the perovskite precursor to decompose, nucleate and grow into perovskite nanocrystals, thereby obtaining a perovskite-polymer composite film with continuously tunable emission spectrum.

2. The method for preparing spectrally tunable perovskite-polymer composite thin films by femtosecond laser direct writing according to claim 1, characterized in that: In step 1), the cesium salt, lead salt, and halogen salt are dissolved in a strongly polar aprotic solvent in a molar ratio of 1:1:3, and the total mass fraction of the cesium salt, lead salt, and halogen salt is 10.9%; the strongly polar aprotic solvent is one of N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone.

3. The method for preparing spectrally tunable perovskite-polymer composite thin films by femtosecond laser direct writing according to claim 1, characterized in that: In step 1), the halogen salt can be a single halogen system or a mixed halogen system. The single halogen system can be CsPbBr3 or CsPbI3. When using CsPbBr3, the emission wavelength of the perovskite-polymer composite film continuously varies within the range of 500-520 nm. When using CsPbI3, the emission wavelength of the perovskite-polymer composite film is between 640-670 nm. The halogen content varies continuously within the nm range; the mixed halogen system uses CsPb(Cl / Br)3, CsPb(Br / I)3, or CsPb(Cl / Br / I)3. When using CsPb(Cl / Br)3, the molar ratio of Cl:Br is 2:1, 1.5:1.5, or 0.5:2.

5. When using CsPb(Br / I)3, the molar ratio of Br:I is 1:2, 1.25:1.75, 1.5:1.5, 1.75:1.25, or 2:1, to achieve continuous spectral coverage of the visible light band from 430 nm to 670 nm for the perovskite-polymer composite film. The tuning accuracy of both the single halogen system and the mixed halogen system under femtosecond laser conditions is 0.05–0.1 nm.

4. The method for preparing spectrally tunable perovskite-polymer composite thin films by femtosecond laser direct writing according to claim 3, characterized in that: In step 1), when CsPb(Cl / Br / I)3 is used, the molar ratio of Cl:Br:I is 1.0~1.2:0.7~0.9:1.0~1.

2. The perovskite-polymer composite film is focused under the laser parameters of a femtosecond laser with a repetition frequency of 200 kHz, a scanning speed of 3 mm / s, and a single pulse energy of 2 μJ, inducing nanocrystal luminescence and obtaining white light emission with color coordinates (0.32, 0.32) in the CIE 1931 color space.

5. The method for preparing spectrally tunable perovskite-polymer composite thin films by femtosecond laser direct writing according to claim 1, characterized in that: In step 1), the perovskite precursor has the general formula ABX3, where the A-site ion is Cs. + FA + MA + PEA + One or more of them, with the B-site ion being Pb². + Sn² + Cu² + One or more of them, with the X-position ion being Cl. - ,Br - I - One or more of the following; the ligand is 18-crown ether-6, and the molar ratio of the ligand to the B-site ion in the perovskite precursor is 0.02~0.05:

1.

6. The method for preparing spectrally tunable perovskite-polymer composite thin films by femtosecond laser direct writing according to claim 1, characterized in that: In step 1), the transparent polymer matrix is ​​one of polymethyl methacrylate, polyvinylidene fluoride, polyethylene terephthalate, polystyrene, or polydimethylsiloxane. The molecular weight range of the transparent polymer matrix is ​​90W~120W, and the mass ratio of the transparent polymer matrix to the perovskite precursor is 0.09~0.18:

1.

7. The method for preparing spectrally tunable perovskite-polymer composite thin films by femtosecond laser direct writing according to claim 1, characterized in that: In step 2), the perovskite precursor solution is coated by spin coating, blade coating, or drop coating. When spin coating, the spin coating speed is 500~2000 r / min, the spin coating time is 200~360 s, and the wet film thickness is 3~5 μm. When blade coating, the blade coating speed is 1 cm / s, and the wet film thickness is 10~50 μm. When drop coating, the wet film thickness is 50~200 μm.

8. The method for preparing spectrally tunable perovskite-polymer composite thin films by femtosecond laser direct writing according to claim 1, characterized in that: In step 2), the heating annealing process is carried out under nitrogen protection, with a heating rate of 30~60℃ / min, an annealing temperature of 60~120℃, and an annealing time of 1~3h.

9. A perovskite-polymer composite thin film with continuously tunable spectrum, characterized in that: The spectrally tunable perovskite-polymer composite film is prepared by the method described in any one of claims 1-8.

10. The application of the spectrally tunable perovskite-polymer composite thin film according to claim 9, characterized in that: The applications include using femtosecond laser-fabricated two-dimensional luminescent patterns or three-dimensional micro / nano structures on the surface of optoelectronic smart devices.

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