A method for preparing a two-dimensional perovskite phase pure thin film
By controlling the precursor solution state through a solvent-additive synergistic strategy, the phase heterogeneity problem of two-dimensional perovskite thin films was solved, enabling the preparation of high-phase-purity thin films and improving device performance and experimental reliability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZHENGZHOU UNIV
- Filing Date
- 2026-03-13
- Publication Date
- 2026-06-09
AI Technical Summary
Existing technologies make it difficult to prepare high-phase-purity two-dimensional perovskite thin films, especially those with n≥4. Thermodynamic and kinetic competition exists during the crystallization process, leading to phase heterogeneity and affecting material properties and device efficiency.
By employing a solvent-additive synergistic strategy, the precursor solution state was controlled, and a low DMSO ratio and precise amounts of MACl additives were used to control the crystallization process, thus achieving the preparation of phase-pure thin films.
Two-dimensional perovskite thin films with narrow phase distribution and high crystallinity were obtained. They exhibited good repeatability and were suitable for large-area continuous fabrication, thereby improving device performance and the reliability of experimental data.
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Figure CN122180296A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to optoelectronic materials and thin film preparation technology, specifically to a method for preparing two-dimensional perovskite phase pure thin films. In particular, by controlling the aggregation state and crystallization kinetics of the precursor solution, a controllable preparation of a specific high-phase purity perovskite thin film with a target quantum well width n value greater than or equal to 3 can be achieved. Background Technology
[0002] Two-dimensional halide perovskite materials have become ideal candidates for next-generation optoelectronic devices due to their combination of the excellent optoelectronic properties of three-dimensional perovskites (such as high absorption coefficient, tunable band gap, and long carrier diffusion length) with the outstanding environmental stability imparted by organic layers. Their core structural feature lies in the presence of bulky organic spacer cations (such as butammonium phosphate, BA). + Separated by ) and composed of [PbX6] 4－ The inorganic layer composed of octahedrons directly determines the quantum confinement strength, exciton binding energy, and charge transport dimension of the material, thereby enabling continuous and precise control of the optoelectronic properties from wide bandgap to narrow bandgap.
[0003] However, a long-standing and unresolved scientific challenge and technological bottleneck in the preparation of two-dimensional perovskite thin films using solution methods (especially spin coating) is the difficulty in obtaining films with a single quantum well width (i.e., "phase purity"). The fundamental reason lies in the thermodynamic and kinetic competition of the crystallization process: thermodynamically, phases with lower n values (e.g., n=1,2) possess a more negative enthalpy of formation (∆H). f Therefore, they are more energy-stable and tend to preferentially nucleate in the early stages of crystallization. Once low-n-value phases form, they irreversibly consume the organic spacer cations in the system, causing the stoichiometry required for subsequent crystallization to deviate from the target ratio, thereby inducing the mixed growth of higher-n-value phases or even quasi-three-dimensional (3D) phases. The end result is that even when using precursors with a nominal stoichiometry of n=4 or 5, the resulting films are microscopically a mixture of "phase heterogeneity" composed of multiple phases with different n-values (n=1, 2, 3, 4, ∞, etc.), exhibiting a broad "phase distribution".
[0004] This inherent phase heterogeneity has a series of fatal negative impacts on material and device performance: 1) It introduces a large number of defects: the interface between phases with different n values becomes a nonradiative recombination center for charge carriers, significantly reducing carrier lifetime; 2) It causes energy disorder: the energy level differences between different phase domains form a chaotic band arrangement, hindering efficient charge extraction and transport; 3) It degrades device parameters: directly leading to a decrease in the open-circuit voltage (V) of the solar cell. OC4) It hinders fundamental research: the intrinsic photoelectric properties of materials (such as exciton dynamics and charge transport mechanisms) are obscured by complex multiphase coexistence phenomena, making it difficult to obtain reliable and reproducible experimental data, thus hindering a deeper understanding of the structure-property relationship of such materials. To address this challenge, various attempts have been made in the field, mainly categorized into the following strategies, but all have significant limitations:
[0005] Solvent engineering attempts to control the formation and conversion rate of the mesophase by adjusting the ratio of a good solvent (such as DMF) to a coordinating solvent (such as DMSO). However, these methods largely rely on empirical trial and error, have a narrow optimization window, and typically only provide limited improvement in film morphology or partial suppression of certain impurity phases. They are largely ineffective in obtaining high-phase-purity films with n≥4, and lack a mechanistic understanding of how solvent ratios precisely control the precursor solution state (such as micelle size and distribution).
[0006] Additive engineering involves introducing additives such as methylammonium chloride (MACl) and methylamine bromide (MABr) to regulate crystallization kinetics or passivate defects. While additives can improve film quality, their mechanisms of action are complex and often considered a "black box." Most studies have failed to clarify whether additives affect nucleation, growth, or phase transition processes, and systematic research on how additives synergistically affect the precursor aggregation state with solvents is lacking. For example, using MAI and MACl can produce drastically different effects, but the underlying reasons are often overlooked.
[0007] Complex fabrication processes, such as two-step methods, liquid phase epitaxy, single crystal melting-back, and spatially confined crystallization, can yield high-quality single crystals or thin films. However, these methods are often cumbersome, require stringent conditions, are difficult to scale up, and are not suitable for preparing large-area, continuous phase-pure thin films on conventional substrates.
[0008] More importantly, existing technologies generally share a common deficiency: they primarily focus on optimizing process results (such as higher device efficiency and better morphology) rather than fundamentally controlling the crystallization path. This means that there is a lack of a universal and predictable theoretical framework and design principles for the two core questions: "Why is it difficult to obtain phase-pure thin films?" and "How to rationally design to obtain a pure phase with a specific n value?". Particularly for systems with n ≥ 4, the preparation of phase-pure thin films is extremely difficult due to the thermodynamic tendency to form phases with lower n values; related reports are rare, and process reproducibility is poor.
[0009] Therefore, there is an urgent need in this field for a novel technical approach that can not only provide a method for the reproducible preparation of high-phase-purity two-dimensional perovskite thin films (especially n≥4), but also reveal and actively manipulate their crystallization path based on physicochemical principles, and establish a deterministic correlation from "precursor solution design" to "final film phase composition", thereby providing a solid scientific foundation and technical solution for the precise synthesis of two-dimensional perovskite materials and their application in high-performance devices. Summary of the Invention
[0010] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing pure two-dimensional perovskite phase thin films. By using a solvent-additive synergistic strategy to regulate the precursor state, precise control of this path is achieved, thereby obtaining thin films with narrow phase distribution and high crystallinity.
[0011] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a two-dimensional perovskite phase pure thin film, comprising the following steps:
[0012] To prepare the precursor solution, weigh the lead source, organic spacer cation salt, and A-site cation salt according to the stoichiometric ratio of the target quantum well width n, dissolve them in a mixed solvent of DMF and DMSO, and add MACl; wherein the volume ratio of DMF to DMSO is (5:1) to (30:1), and pure DMF solution is used, and the amount of MACl added is 10% to 90% of the molar amount of the A-site cation salt;
[0013] Thin film deposition and resting at room temperature;
[0014] Heat annealing.
[0015] Preferably, the target quantum well width n is greater than or equal to 3.
[0016] Preferably, the relationship between the target quantum well width n, the DMF:DMSO volume ratio, and the amount of MACl added satisfies the following: when the target quantum well width n increases, the DMF:DMSO volume ratio increases, which means that the amount of DMSO added decreases, and the amount of MACl added increases.
[0017] Preferably, the target quantum well width n is 3, the DMF:DMSO volume ratio is (15:1) - (pure DMF), and the MACl addition amount is 30%-40%.
[0018] Preferably, the target quantum well width n is 4, the DMF:DMSO volume ratio is (20:1) - (pure DMF), and the MACl addition amount is 50%-90%.
[0019] Preferably, the target quantum well width n is 5, the DMF:DMSO volume ratio is (25:1)-(30:1), and the MACl addition amount is 70%-90%.
[0020] A two-dimensional perovskite phase pure thin film, prepared by the aforementioned method, has an X-ray diffraction pattern showing only one set of diffraction peaks corresponding to the width n value of a single target quantum well.
[0021] Compared with existing technologies, the present invention provides a method for preparing two-dimensional perovskite phase-pure thin films. Based on the universality of the specific combination of "low DMSO solvent ratio" and "precise amount of MACl additive" for guiding phase-pure thin films, this method reliably prepares phase-pure thin films with different n values by simply following the above parameter adjustment rules, without needing to develop complex processes for each n value. This method exhibits good repeatability, and the resulting thin films have high phase purity and good crystallinity. Attached Figure Description
[0022] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.
[0023] Figure 1 This is a schematic diagram of the preparation process of the present invention;
[0024] Figure 2 This is a phase diagram of solvent (DMF / DMSO ratio) and additive (MACl content) parameters for obtaining phase-pure thin films with different n values (n=3,4,5), determined through numerous experiments in this invention. The parameter regions for obtaining high phase purity are clearly marked in the figure.
[0025] Figure 3 The X-ray diffraction (XRD) patterns of the n=1 to n=5 phase pure thin films prepared by the method of the present invention are shown respectively, and they are perfectly matched with their respective single crystal simulation spectra, proving their high phase purity and crystallinity.
[0026] Figure 4 The UV-Vis absorption spectra of pure phase films corresponding to n=1 to n=5 show a single, sharp exciton absorption peak, further confirming the phase purity.
[0027] Figure 5 The images show a comparison of the surface morphology of the n=4 thin films in the comparative example (mixed phase) and the example (phase pure), respectively, which shows that the surface of the phase pure film is smoother and denser.
[0028] Figure 6For comparison of the transmission electron microscope (TEM) and electron diffraction patterns of the comparative example and the n=4 thin film, it is shown that the phase-pure thin film has single-crystal diffraction characteristics, while the mixed-phase thin film has polycrystalline ring diffraction.
[0029] Figure 7 The comparison diagram shows the photoluminescence wavelength mapping (PL mapping) of the comparative example and the n=4 thin film, which visually demonstrates that the emission wavelength of the phase-pure thin film is spatially uniform, while the mixed-phase thin film exhibits significant fluctuations.
[0030] Figure 8 The following are in-situ UV-Vis absorption spectral evolution diagrams of thin film crystallization processes with different n values, where... Figure 8 a and 8b clearly demonstrate the pathways through which the n=4 and n=5 films undergo mesophase transitions;
[0031] Figure 9 To obtain the UV-Vis absorption spectra of n=4 films prepared by adding equimolar amounts (50%, relative to MAI) of MAI or MACl to the solvent optimized (DMF:DMSO=20:1), the film using MAI as an additive showed a wider phase distribution, demonstrating the unique role of MACl in narrowing the phase distribution and achieving high phase purity, which cannot be replaced by MAI. Detailed Implementation
[0032] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.
[0033] As attached Figure 1 To be continued Figure 9 As shown:
[0034] A method for preparing two-dimensional perovskite phase pure thin films allows for precise control of n values from 1 to 5 (preferably n=3, 4, 5). Furthermore, the crystallization process of films with a target n value ≥ 4 follows a transformation path containing a detectable perovskite mesophase of n=3. The steps include:
[0035] To prepare the precursor solution, the lead source (such as PbI2), organic spacer cation salt (such as BAI), and A-site cation salt (such as MAI) were dissolved in a mixed solvent of DMF and DMSO according to the target quantum well width n value. Methylammonium chloride (MACl) was added, and the mixture was heated and stirred at 70°C for 2 hours.
[0036] Thin film deposition and room temperature standing: The precursor solution is deposited onto the substrate to form a wet film, which is then left to stand at room temperature; the deposition process is spin coating, and the amount of the precursor solution used is 50 μL / cm³. 2The spin coating speed was 5000 rpm, the acceleration was 500 rpm / s, the spin coating time was 20 seconds, and 150 μL / cm³ of solvent was added 5 seconds before the end of the spin coating period. 2 The antisolvent promotes crystallization. Preferably, the antisolvent is toluene (TOL); the wet film is allowed to stand at a temperature of 20±5℃ for 10 minutes under a nitrogen atmosphere.
[0037] Thermal annealing is performed on the film after the static treatment to obtain a phase-pure two-dimensional perovskite film with a single n value. The annealing conditions are a temperature of 100°C and a time of 10 minutes.
[0038] The perovskite component has the general formula BA2MA. n-1 Pb n I 3n+1 The solvent is a mixture of DMF and DMSO; the additive is methyl ammonium chloride (MACl); Pb 2+ The concentration was 1.25 mol / L, the volume ratio of DMF to DMSO was (5:1) to (30:1), and pure DMF solution was used. The amount of MACl added was 10% to 90% of the molar amount of the A-site cation salt.
[0039] The target quantum well width n, DMF:DMSO volume ratio, and MACl addition amount are related as follows: when the target quantum well width n increases, the DMF:DMSO volume ratio increases, which means that the amount of DMSO added decreases, and the amount of MACl added increases.
[0040] In one embodiment, the target quantum well width n is 3, the DMF:DMSO volume ratio is (15:1) - (pure DMF), and the MACl addition amount is 30%-40%.
[0041] In one embodiment, the target quantum well width n is 4, the DMF:DMSO volume ratio is (20:1) - (pure DMF), and the MACl addition amount is 50%-90%.
[0042] In one embodiment, the target quantum well width n is 5, the DMF:DMSO volume ratio is (25:1)-(30:1), and the MACl addition amount is 70%-90%.
[0043] A two-dimensional perovskite phase pure thin film, prepared by the aforementioned method, has an X-ray diffraction pattern showing only one set of (0k0) diffraction peaks corresponding to the width n value of a single target quantum well.
[0044] An optoelectronic device having a functional layer comprising a two-dimensional perovskite phase pure thin film.
[0045] The following describes the embodiments of the present invention in detail by taking the representative preparation of films with n=4 and n=5 as examples. The film with n=3 can be obtained by adjusting the parameters in a similar manner (see Figure 2 (Phase diagram), the preparation of thin films with n=1, n=2 and higher n values can be adjusted with reference to this general rule.
[0046] Example 1:
[0047] Preparation of phase-pure n=4 two-dimensional perovskite thin films:
[0048] According to the chemical formula BA2MA3Pb4I 13 PbI₂, BAI, and MAI were weighed in stoichiometric proportions and dissolved in a mixed solvent of DMF and DMSO at a volume ratio of 20:1 to prepare a 1.25 M precursor solution. Methylammonium chloride (MACl) additive, equivalent to 50% of the molar amount of MAI, was added to this solution. The mixture was magnetically stirred at 70 °C for 2 hours to obtain a clear, homogeneous orange-yellow precursor ink.
[0049] The precursor solution was spin-coated onto a pre-cleaned glass substrate, and toluene was added dropwise as an antisolvent 5 seconds before the end of the spin-coating process. The wet film was then allowed to stand at room temperature (~25°C) under a nitrogen atmosphere for 10 minutes.
[0050] The film was transferred to a hot stage at 100°C and annealed for 10 minutes. After natural cooling, a pure perovskite film with n=4 phase was obtained.
[0051] Characterization and Effects:
[0052] Structural characterization: XRD patterns of the obtained thin films (as attached) Figure 3 The spectrum shown (as shown) displays only one set of sharp (0k0) diffraction peaks, perfectly consistent with the simulated spectrum of the n=4 single crystal, with no other impurity phase diffraction peaks, proving it to be a pure phase. Its UV-Vis absorption spectrum (as shown in the attached image) Figure 4 As shown, a single, sharp exciton absorption peak is observed at ~640 nm, without any other absorption shoulders, further confirming the high phase purity.
[0053] Morphological characterization: SEM images (as attached) Figure 5 (As shown) The film surface is smooth and dense, with no obvious pores or second-phase particles. TEM (as shown in the attached image) Figure 6 As shown in the image, the pure-phase thin film exhibits single-crystal diffraction characteristics, displaying lattice fringes with uniform fringe spacing. PL mapping images (as attached) Figure 7 As shown, the entire observation area (50×50μm) is displayed. 2 The highly uniform distribution of emission wavelengths within the film confirms the homogeneity of phase composition on a macroscopic scale. (In-situ ultraviolet spectrum attached) Figure 8 This indicates that its crystallization process conforms to the phase transformation path described in this invention.
[0054] Example 2:
[0055] Preparation of phase-pure n=5 two-dimensional perovskite thin films:
[0056] According to the chemical formula BA2MA4Pb5I 16 Weigh the raw materials according to the stoichiometric ratio, dissolve them in a mixed solvent of DMF:DMSO = 25:1 (v / v), and prepare a 1.25M solution. Add MACl additive equivalent to 80% of the molar amount of MAI, and stir at 70°C for 2 hours.
[0057] Spin-coating to form a film and adding toluene as an anti-solvent, then letting it stand at room temperature for 10 minutes.
[0058] Annealing at 100℃ for 10 minutes yielded a pure thin film with n=5 phases.
[0059] Characterization: XRD patterns (attached) Figure 3 Matching the simulated spectrum with n=5 single crystal. In-situ ultraviolet spectrum (attached) Figure 8 The results show that its crystallization process conforms to the high n-value phase transformation path described in this invention.
[0060] Comparative Example 1:
[0061] Preparation of mixed-phase n=4 thin films (not following the parameter rules of this invention):
[0062] Except for changing the solvent to DMF:DMSO=4:1 (v / v) and not adding any MACl additives, the other steps are exactly the same as in Example 1.
[0063] Characterization: The UV-Vis absorption spectrum of the obtained thin film (attached) Figure 9 The image shows multiple exciton absorption shoulders corresponding to various impurity phases such as n=2, 3, ∞. (SEM image attached) Figure 5 The surface appears rough and porous, as indicated by TEM (with attached image). Figure 6 The mixed-phase film exhibits polycrystalline ring diffraction with lattice fringes of varying spacings. PL Mapping (attached) Figure 7 The results show that the emission wavelength fluctuates wildly in space.
[0064] Comparative Example 2:
[0065] Use MAI instead of MACl as an additive:
[0066] Except for replacing the additive MACl with an equimolar amount of MAI, the rest of the steps are exactly the same as in Example 1.
[0067] Characterization: The ultraviolet-visible absorption spectrum of the obtained thin film ( Figure 9The sample still showed a wide absorption edge and multiple exciton absorption shoulders, indicating that the phase purity was significantly lower than that of Example 1, proving that MACl is an irreplaceable additive for achieving high phase purity.
[0068] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.
Claims
1. A method for preparing a two-dimensional perovskite phase pure thin film, characterized in that the steps include... include: To prepare the precursor solution, weigh the lead source, organic spacer cation salt, and A-site cation salt according to the stoichiometric ratio of the target quantum well width n, dissolve them in a mixed solvent of DMF and DMSO, and add MACl; wherein the volume ratio of DMF to DMSO is (5:1) to (30:1), and pure DMF solution is used, and the amount of MACl added is 10% to 90% of the molar amount of the A-site cation salt; Thin film deposition and resting at room temperature; Heat annealing.
2. The method for preparing a two-dimensional perovskite phase pure thin film according to claim 1, characterized in that, The target quantum well width n is greater than or equal to 3.
3. The method for preparing a two-dimensional perovskite phase pure thin film according to claim 1, characterized in that, The target quantum well width n, DMF:DMSO volume ratio, and MACl addition amount are related as follows: when the target quantum well width n increases, the DMF:DMSO volume ratio increases, which means that the amount of DMSO added decreases, and the amount of MACl added increases.
4. The method for preparing a two-dimensional perovskite phase pure thin film according to claim 1, characterized in that, The target quantum well width n is 3, the DMF:DMSO volume ratio is (15:1) - (pure DMF), and the MACl addition amount is 30%-40%.
5. The method for preparing a two-dimensional perovskite phase pure thin film according to claim 1, characterized in that, The target quantum well has a width n of 4, a DMF:DMSO volume ratio of (20:1) - (pure DMF), and a MACl addition amount of 50%-90%.
6. The method for preparing a two-dimensional perovskite phase pure thin film according to claim 1, characterized in that, The target quantum well has a width n of 5, a DMF:DMSO volume ratio of (25:1) to (30:1), and a MACl addition of 70% to 90%.
7. A two-dimensional perovskite phase pure thin film, characterized in that, The method described in any one of claims 1-6 is used to prepare the X-ray diffraction pattern, which shows only one set of diffraction peaks corresponding to the width n value of a single target quantum well.