Organic-inorganic hybrid perovskite thin film, preparation method and terahertz functional device

Abstract

The application relates to an organic-inorganic hybrid perovskite film, a preparation method and a terahertz functional device, which are characterized in that a (PEA)2PbI4 precursor solution is prepared, a film is prepared by adopting a spin coating rotating speed of 500-2500 rpm, terahertz characteristics of the film are tested in a 0.1-2.2 THz frequency band by combining a terahertz time-domain spectroscopy system, and crystallization quality is analyzed by means of X-ray diffraction and a scanning electron microscope. The film performance has a highly ordered (00h) crystal face orientation, has a significant absorption peak at 1.5 THz, has a dielectric loss as low as 1.72, has a refractive index of 2.85, and has a transmission rate of > 90% in a < 1 THz frequency band, and the 1.5 / 1.8 THz double-peak absorption is caused by the synergistic effect of Pb-I skeleton vibration and layer coupling. The application clearly defines the structure-effect relationship between the spin coating process and the terahertz characteristics of the film, and provides key parameters and theoretical basis for the design of a terahertz modulator, a detector and a filter.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of organic-inorganic hybrid perovskite materials, in particular to the preparation process optimization of perovskite thin films and the study of terahertz spectral characteristics, and is especially suitable for the design and preparation of terahertz functional devices such as terahertz modulators, detectors and filters. BACKGROUND

[0002] Organic-inorganic hybrid perovskite materials have shown great application potential in the fields of solar cells, photodetectors and light-emitting diodes due to their excellent optoelectronic properties such as high light absorption coefficient, long carrier diffusion length and adjustable band gap. In recent years, with the rapid development of terahertz technology, its application demand in the fields of communication, imaging and biomedical medicine is increasingly urgent, but the lack of high-performance terahertz materials has become a key bottleneck restricting its development.

[0003] Organic-inorganic hybrid perovskite thin films have high dielectric constant and low loss in the terahertz waveband, providing a new idea for the development of new terahertz devices such as modulators, detectors and filters. In existing research, the Fang Ruiqian team confirmed the carrier dynamics of hybrid perovskite and its response in the terahertz waveband; the Ren Jie team studied the optoelectronic properties of two-dimensional perovskite (PEA) 2(MA) 2Pb3I 10 thin films through terahertz time-domain spectroscopy, and found that it has high refractive index and photoconductivity; the Shi Hunqi team constructed a super-wideband tunable terahertz absorber using perovskite thin films, realizing high-efficiency absorption in the 3.1-6.9THz frequency band.

[0004] However, the influence of the preparation process of perovskite thin films (especially the spin coating speed) on their terahertz spectral characteristics has not been systematically studied, and the structure-activity relationship between the crystalline quality of the thin film and the terahertz response is not clear, which limits the design and optimization of high-performance perovskite-based terahertz devices. Therefore, it is urgent to study the regulation mechanism of spin coating process parameters on the terahertz characteristics of perovskite thin films to provide theoretical and experimental basis for the development of terahertz devices. SUMMARY

[0005] The present application aims to solve the problem that the existing technology lacks systematic research on the influence of spin coating process parameters (such as speed) on the terahertz spectral characteristics of organic-inorganic hybrid perovskite thin films, and the structure-activity relationship between the crystalline quality of the thin film and the terahertz response is not clear, and provides an organic-inorganic hybrid perovskite thin film, a preparation method and a terahertz functional device.

[0006] The present application studies the spectral characteristics of (PEA)2PbI4 thin films prepared at different spin-coating speeds (500-2500 rpm) in the 0.1-2.2 THz frequency band by a terahertz time-domain spectroscopy (THz-TDS) system, and analyzes the crystalline quality of the organic-inorganic hybrid perovskite thin films by X-ray diffraction (RD) and scanning electron microscopy (SEM), to reveal the structure-activity relationship between the crystalline quality (crystal orientation, defect density, etc.) of the thin film and the terahertz response, and determine that 1500 rpm is the optimal spin-coating speed and the corresponding terahertz characteristic parameters (such as high absorption at 1.5 THz, low dielectric loss, high transmittance, etc.).

[0007] To achieve the above application purposes, in the first aspect, the present application adopts the following technical solutions: a preparation method of an organic-inorganic hybrid perovskite thin film, comprising the following steps:

[0008] Preparation of (PEA)2PbI4 precursor solution, spin-coating process is used to coat the precursor solution on the substrate, and the spin-coating speed is 500-2500 rpm;

[0009] Characterization of the spin-coated thin film, including testing its terahertz spectral characteristics in the 0.1-2.2 THz frequency band by a terahertz time-domain spectroscopy system, and analyzing its crystalline quality by X-ray diffraction and scanning electron microscopy;

[0010] The terahertz spectral characteristics include an absorption peak at 1.5 THz, a dielectric loss ≤1.72, a refractive index ≥2.85, and a transmittance >90% in the <1 THz frequency band.

[0011] Further, the optimal spin-coating speed is 1500 rpm.

[0012] Further, the preparation of (PEA)2PbI4 precursor solution comprises:

[0013] Dissolve PEAI and PbI2 in dimethylformamide at a molar ratio of 2:1, and stir at room temperature for at least 6 hours.

[0014] Further, the stirring rate is 800 rpm, and the stirring temperature is 25±2℃.

[0015] Further, the spin-coated thin film is annealed, and the annealing temperature is 80℃.

[0016] Further, the absorption coefficient at 1.5 THz is 37-39 cm -1 .

[0017] Further, the XRD spectrum of the thin film contains periodic diffraction peaks corresponding to the (00h) crystal plane (h=4, 6, 8…), and has a highly ordered crystal orientation.

[0018] In a second aspect, the application provides an organic-inorganic hybrid perovskite film prepared by the above method, the film being a (PEA)2PbI4 film, and having terahertz spectral characteristics in a 0.1-2.2 THz frequency band.

[0019] 1. An absorption peak exists at 1.5 THz, the dielectric loss is ≤1.72, the refractive index is ≥2.85, and the transmittance in a <1 THz frequency band is >90%.

[0020] Further, the film also has a secondary absorption peak at 1.8 THz, and the 1.5 THz absorption peak and the 1.8 THz secondary absorption peak form a double-peak structure, which is derived from the synergistic effect of Pb-I skeleton vibration and interlayer coupling.

[0021] In a third aspect, the application provides a terahertz functional device comprising the above organic-inorganic hybrid perovskite film, and the device is a terahertz modulator, a terahertz detector or a terahertz filter.

[0022] Compared with the prior art, the application has the following beneficial effects:

[0023] 1. The structure-activity relationship between spin coating process parameters and terahertz characteristics of (PEA)2PbI4 films is clarified, and the mechanism by which the rotation speed affects key parameters such as terahertz absorption, dielectric properties and transmittance by regulating the crystalline quality (crystal plane orientation, defect density) of the film is revealed.

[0024] 2. It is determined that 1500 rpm is the optimal spin coating rotation speed, and the film prepared at this parameter has a highly ordered (00h) crystal plane orientation and the lowest defect density, and presents a significant absorption peak (absorption coefficient 38 cm -1 ), low dielectric loss (1.72), high refractive index (2.85) and high transmittance (>90%) in a <1 THz frequency band, and the performance is better than that of samples prepared at other rotation speeds;

[0025] 3. The physical mechanism of the 1.5 / 1.8 THz double-peak absorption structure of the (PEA)2PbI4 film (derived from the synergistic effect of Pb-I skeleton vibration and interlayer coupling) is revealed, providing a theoretical basis for the design of terahertz devices.

[0026] 4. The application fills the gap in the systematic study of the effect of spin coating process parameters on the terahertz characteristics of perovskite films, and provides key parameters and experimental support for the design of perovskite-based terahertz modulators, detectors and filters, promoting the development of high-performance terahertz functional devices.

[0027] 5.The application is not dependent on the "spin coating process" or the innovation of "perovskite material" itself, but the first application of (PEA)2PbI4 thin film in the terahertz wave band, through the optimization of the special process, the unique performance parameter mining and the original mechanism, the problem of lack of high-performance materials in the terahertz technology field is solved. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a flow chart of the preparation method of the organic-inorganic hybrid perovskite thin film of the embodiment of the application.

[0029] Figure 2 is a SEM image of the drop coating method of the embodiment of the application;

[0030] Figure 3 is a SEM image of the spin coating method of the embodiment of the application;

[0031] Figure 4 is a thin film absorption spectrum of the embodiment of the application;

[0032] Figure 5 is a thin film PL spectrum of the embodiment of the application;

[0033] Figure 6 is a thin film XRD spectrum of the embodiment of the application;

[0034] Figure 7 is a thin film output characteristic curve (negative pressure) of the embodiment of the application;

[0035] Figure 8 is a thin film output characteristic curve (positive pressure) of the embodiment of the application;

[0036] Figure 9 is a carrier transport mechanism schematic diagram of the embodiment of the application;

[0037] Figure 10 is a thin film schematic diagram of the embodiment of the application;

[0038] Figure 11 is a thin film absorbance schematic diagram of the embodiment of the application measured by a transmission THz-TDS system;

[0039] Figure 12 is a thin film absorption coefficient schematic diagram of the embodiment of the application measured by a transmission THz-TDS system;

[0040] Figure 13 is a thin film dielectric loss spectrum of the embodiment of the application measured by a transmission THz-TDS system;

[0041] Figure 14 is a thin film extinction coefficient schematic diagram of the embodiment of the application measured by a transmission THz-TDS system;

[0042] Figure 15 is a schematic diagram of the dielectric constant of the thin film measured by the transmission THz-TDS system of the embodiment of the present application;

[0043] Figure 16 is a schematic diagram of the refractive index of the thin film measured by the transmission THz-TDS system of the embodiment of the present application;

[0044] Figure 17 is a logarithmic coordinate diagram of the transmittance of the thin film measured by the transmission THz-TDS system of the embodiment of the present application;

[0045] Figure 18 is a linear transmittance diagram of the transmittance of the thin film measured by the transmission THz-TDS system of the embodiment of the present application. DETAILED DESCRIPTION

[0046] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art belong to the scope of protection of the present application.

[0047] Those skilled in the art should understand that in the disclosure of the present application, the terms "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate the orientation or positional relationship shown in the drawings, which are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the above terms cannot be understood as a limitation of the present application.

[0048] Embodiment 1

[0049] As shown in the following steps, the preparation method of the organic-inorganic hybrid perovskite thin film: Figure 1

[0050] Step one, prepare (PEA)2PbI4 precursor solution, use spin coating process to coat the precursor solution on the substrate, the rotation speed of the spin coating process is 500-2500 rpm;

[0051] In this embodiment, in the fume hood, 1.2 mmol of PEAI and 0.6 mmol of PbI2 powder are dissolved in 1 mL of dimethylformamide, and the (PEA)2PbI4 precursor solution is obtained by stirring at room temperature (25±2) ℃ for 6 h.

[0052] ​Preferably, the influence of stirring time on the uniformity of the solution is also systematically investigated during the preparation of the precursor solution. It is found that when the stirring time is prolonged from 3 hours to 6 hours, the transmittance of the solution is increased from 82% to 95%, and the amount of PbI2precipitate is reduced by about 60%. The optimized stirring parameters are as follows:

[0053] The magnetic stirring rate is 800 rpm, and the stirring is continued for 6 hours at room temperature (25±2) °C.

[0054] Temperature: The SEM of the sample at 50 °C shows that the grain size is about 80 nm, and there are obvious grain boundary pores. The XRD half-width is 0.38°. The grain size of the sample at 80 °C is increased to 120 nm, the porosity is reduced to less than 5%, the XRD half-width is reduced to 0.21°, and the diffraction intensity of the (00l) crystal plane is increased by about 40%.

[0055] Therefore, a high-quality 2D (PEA)2PbI4thin film with high crystallinity can be obtained at a low annealing temperature (80 °C) without special treatment by using the spin coating method.

[0056] In this embodiment, the spin coating time optimization experiment shows that:

[0057] When the spin coating time is 30 seconds, a thin film with a thickness of about 200 nm is formed, and the SEM shows that the surface uniformity is good, and the width of the edge "coffee ring" is less than 50 μm;

[0058] When the spin coating time is 45 seconds, the thickness of the thin film is reduced to 150 nm, but pinhole defects appear in some areas;

[0059] When the spin coating time is 60 seconds, the thickness is further reduced to 120 nm, but the crystalline orientation degree is reduced by about 20%.

[0060] Mechanism: When the spin coating time is 30 seconds, the solvent evaporation rate (about 0.2 μL / s) and the centrifugal force generated by the rotation speed of 1500 rpm are in the best balance, which can ensure sufficient solvent evaporation time and avoid component segregation caused by excessive centrifugation. The thin film prepared under this parameter has the best crystalline orientation and surface morphology.

[0061] From Figure 2 and Figure 3 it can be clearly seen that, Figure 2 the SEM image of the surface of the (PEA)2PbI4thin film in the state of drop coating is presented, Figure 3The surface SEM images of (PEA)2PbI4 thin films in spin-coating state show a dense but disordered nanoparticles accumulation condition with very prominent pores between the particles, which means that non-uniform crystallization phenomenon caused by slow evaporation, while spin-coating generates a more uniform mixed morphology. The density of spin-coating thin film is obviously better than that of drop-coating sample, and such difference will directly affect the carrier mobility and interface scattering behavior in the terahertz band.

[0062] From Figure 4 and Figure 5 It can be seen that the spin-coating speed has a greater impact on the optical properties of (PEA)2PbI4 thin films:

[0063] 2000 rad / min may be the best process parameter, which can ensure high crystalline quality and strong exciton luminescence. Although 3000 rad / min can reduce the size of the crystal grains, it may cause an increase in defects, resulting in a decrease in PL efficiency. The crystalline quality of the drop-coating method is between 1500 and 2000 rad / min, but its PL intensity is relatively low, and its film uniformity may not be as good as that of spin-coating.

[0064] In general, 2000 rad / min spin-coating method performs best in balancing crystalline quality and optical properties, and is suitable for the preparation of high-performance optoelectronic devices.

[0065] Step two, the spin-coated thin film is characterized, including testing its terahertz spectral characteristics in the 0.1-2.2 THz frequency band using a terahertz time-domain spectroscopy system, and analyzing its crystalline quality by combining X-ray diffraction and scanning electron microscopy; the terahertz spectral characteristics include an absorption peak at 1.5 THz, a dielectric loss ≤1.72, a refractive index ≥2.85, and a transmittance >90% in the <1 THz frequency band.

[0066] In this embodiment, Menlo Systems TeraK15 terahertz time-domain spectroscopy system is used for testing, the sample thickness is 50±5 μm, and the test environment humidity is controlled at ≤20%. The parallel plate electrode configuration (spacing 0.5 mm) is used for dielectric constant testing, and the data is processed by Kramers-Kronig transformation. Three sets of repeated experiments show that the absorption coefficient at 1.5 THz is 37.8, 39.2, and 38.5 cm -1 (RSD=1.8%), which confirms the reliability of the data.

[0067] The present application adopts a transmission terahertz time-domain spectroscopy (THz-TDS) system for testing, which mainly consists of a femtosecond laser, a terahertz pulse generation and detection light path, and a data acquisition and processing module. During the experiment, the femtosecond laser is divided into pump light and probe light after being split, wherein the pump light excites the InAs emitter to generate terahertz pulses through the photo rectification effect, and the terahertz pulses are focused by a parabolic mirror and transmitted through the sample; the probe light is collinearly incident to the ZnTe detection crystal together with the terahertz pulses modulated by the sample, the terahertz electric field information is converted into the polarization state change of the probe light through the electro-optic sampling technology, then after being split by the Wollaston prism and differentially detected, the time domain signal is extracted by using the lock-in amplification technology, and finally the frequency domain spectral characteristics of the sample are obtained by Fourier transform. The entire optical path system is filled with nitrogen and the humidity is controlled below 1% to eliminate the strong absorption interference of water vapor on the terahertz wave.

[0068] Through this system, the terahertz spectral characteristics of the measured sample can be extracted, and the following are the parameters:

[0069] 1. Absorbance: the absorption intensity of the material to the terahertz wave, which is related to the sample thickness and absorption coefficient;

[0070] 2. Absorption Coefficient: the absorption ability of the material per unit thickness to the terahertz wave, with the unit of cm -1 ;

[0071] 3. Dielectric Loss: the imaginary part of the dielectric constant, reflecting the polarization relaxation or conductive loss in the material;

[0072] 4. Extinction Coefficient: describing the attenuation ability of the material to the terahertz wave, which is related to the absorption coefficient;

[0073] 5. Dielectric Constant: the real part represents the polarization ability, and the imaginary part represents the loss;

[0074] 6. Refractive Index: describing the change of the propagation speed of the terahertz wave in the material;

[0075] 7. Transmittance: the ratio of transmitted light intensity to incident light intensity, reflecting the transmission ability of the material to the terahertz wave.

[0076] In this embodiment, as Figure 6 shown in the X-ray diffraction spectrum of a typical (PEA)2PbI4 thin film, it contains a series of clearly periodically distributed diffraction peaks corresponding to the (00h) (h=4, 6, 8…) crystal surface, indicating that the thin film has high crystallinity.

[0077] In this embodiment, the comprehensive Figure 7 and Figure 8 The film output characteristics of the two figures are analyzed, and the device shows good controllability and stability in the positive and negative bias range. The smooth transition and regular change of the current-voltage curve show that the device has good interface characteristics and carrier transport performance. The symmetry change of the current in the negative bias region shows that the source and drain electrodes of the device have good symmetry, which is meaningful for bidirectional signal processing application. These characteristics lay a reliable electrical performance foundation for the practical application of the device.

[0078] Preferably, in order to show the film performance, the photoelectric characteristics of the film are also analyzed, and the charge carrier mobility is used to represent the ability of the carrier to move quickly in the channel. The mobility in the saturation region can be represented as:

[0079]

[0080] Where L is the channel length, i.e. the path length of the carrier transmission in the device; I D is the drain current, reflecting the number of carriers passing through the channel; W is the channel width, related to the cross-sectional area of the carrier transmission; C αx is the gate dielectric capacitance per unit area, reflecting the regulation ability of the gate to the channel; V G is the gate voltage, which is the source of the external electric field driving the carrier migration; V T is the threshold voltage, i.e. the minimum gate voltage required to enable effective transmission of carriers.

[0081] Preferably, the gate voltage (V G ) is set to 1V, the channel width (W) is 2mm, the channel length (L) is 260nm, and the gate dielectric capacitance per unit area C αx is 11.5nF / cm 2 . The hole mobility and electron mobility are estimated to be μH=2.55cm 2 V -1 s -1 and μE=2cm 2 V -1 s -1 , which provides a quantitative basis for evaluating the carrier transport efficiency of the film and the performance of the terahertz device.

[0082] Where the diffusion length is related to the mobility (μ) and the carrier lifetime (τ) as follows:

[0083]

[0084] Hole mobility μH=2.55cm2 V -1 s -1 , electron mobility μE=2cm 2 V -1 s -1 , thermal voltage ≈0.0259V (room temperature 300K), typical perovskite carrier lifetime τ≈1ns. Diffusion length is estimated to be 25.7nm.

[0085] From Figure 9 the thin film carrier transport mechanism analysis, the top Au electrode as a hole injection end, the bottom Au electrode as a collection end, the middle SiO2insulating layer realizes electron blocking and hole transport through band offset. The purple marked electron traps in the Si substrate capture electrons through localized states to form a space charge region, and the yellow "Hole transport" area shows that the holes migrate along the valence band. This design separates the hole transport path and the electron trap space through band engineering, and the Au electrode work function and the Si valence band are matched to optimize the hole injection efficiency, while the SiO2layer suppresses the parasitic conduction of the Si substrate.

[0086] Embodiment 2

[0087] The embodiment provides an organic-inorganic hybrid perovskite thin film, which is prepared by the preparation method in embodiment 1, the thin film is a (PEA)2PbI4thin film, and the thin film has terahertz spectral characteristics in a 0.1-2.2THz frequency band:

[0088] 1.5THz exists an absorption peak, the dielectric loss is ≤1.72, the refractive index is ≥2.85, and the transmittance in the <1THz frequency band is >90%.

[0089] In this embodiment, as shown in Figure 10 , the (PEA)2PbI4thin films are respectively prepared by drop coating, 500r / min, 1000r / min, 1500r / min, 2000r / min and 2500r / min spin coating for 30s.

[0090] From Figure 11 it can be seen that the spin coating (1500 rpm) sample has an absorbance of 0.82 at 1.5 THz, which is better than the drop coating sample, indicating that spin coating can optimize the periodic arrangement of quantum wells. The wide absorption band in the low frequency region is related to the PEA + dipole relaxation, and the absorption intensity in the high frequency region drops sharply, which is attributed to the increase of interlayer stacking defects. The absorbance changes non-monotonously with the rotation speed:

[0091] The 500-1500 rpm range induced oriented crystallization and enhanced quantum confinement effect due to film thickness reduction, which improved the absorbance. However, the 2500 rpm sample showed a lower absorbance of 0.61 due to the phonon scattering caused by the grain boundary cracks. SEM confirmed that 1500 rpm was the optimal parameter, which could balance the film integrity and terahertz absorption performance.

[0092] The 1500 rpm sample showed an absorbance of 0.82 at 1.5 THz, corresponding to a modulation depth of about 35%, which was significantly better than the other samples. The 500 rpm sample showed a modulation depth of only 18% (absorbance of 0.42), and the 2500 rpm sample showed a lower absorbance of 0.61 due to the grain boundary cracks. At the same time, the carrier relaxation time of the 1500 rpm sample was 0.8 ps (corresponding to a modulation bandwidth of ≈1.25 THz), while the low-speed (500 rpm) sample was prolonged to 2.5 ps due to the defect state trapping, and the high-speed (2500 rpm) sample was accelerated by non-radiative recombination due to lattice stress (0.6 ps but the signal-to-noise ratio decreased).

[0093] From Figure 12 It can be seen that the (PEA)2PbI4 thin film has a characteristic absorption peak at 1.5 THz, which is shifted by <±0.03 THz and has a half-width of only 0.18 THz, which is directly related to the enhanced (00h) crystal plane orientation confirmed by XRD. The 500-1000 rpm samples showed a wide absorption platform at 1.0-1.2 THz, and all samples showed an absorption valley at 2.0 THz due to the phonon band gap.

[0094] The absorption intensity showed a non-monotonic change with the rotation speed: the quantum well structure was most ordered at 1500 rpm, while the absorption coefficient decreased to 25 cm -1 at 2500 rpm due to grain boundary cracks. The 1.8 THz sub-peak may be due to the [PbI6] 4- in-plane vibration and interlayer coupling. At the 1.5 THz peak: the intensity linearly increased as the temperature decreased (300 K→77 K), and the half-width narrowed from 0.18 THz to 0.09 THz; at the 1.8 THz peak: an inflection point appeared at 200 K, and the intensity first increased and then decreased, indicating that there was a critical temperature for interlayer coupling. At the same time, the activation energy of the 1.5 THz peak was ≈25 meV, which matched the out-of-plane vibration mode of the [PbI6] octahedron; the activation energy of the 1.8 THz peak was ≈12 meV, which corresponded to the torsional vibration energy level of the PEA + organic layer, confirming that the double peaks were due to the synergistic effect of Pb-I skeleton vibration (main peak) and organic-inorganic interface coupling (sub-peak). Therefore, the 1.5 THz absorption peak and the 1.8 THz sub-peak form a double-peak structure.

[0095] The THz absorption properties and room-temperature stability of the material make it have application potential in narrow-band filter and frequency marker devices, and the subsequent THz-TDS study of phonon thermal evolution can be used to optimize the energy band engineering.

[0096] From Figure 13 The dielectric loss spectrum analysis shows that the dielectric response of (PEA)2PbI4 thin film has a significant spin-coating process dependence. All the samples show common characteristics: high dielectric loss in the low-frequency region, followed by exponential decay and stabilization at >0.5 THz. Process optimization shows that the 1500 rpm sample performs best, with a loss value of only 1.72 at 0.3 THz, due to the improved order and reduced defect density of the thin film; the 500-1000 rpm samples show a plateau structure at 0.4-0.6 THz, suggesting a metastable arrangement of organic-inorganic interfaces; and the >1500 rpm samples show a loss rebound due to lattice stress defects. The responses of all samples converge in the high-frequency region, indicating reduced process sensitivity in this frequency range. This study provides a process control basis for low-loss design of THz functional devices.

[0097] From Figure 14 It can be seen that the extinction coefficient of (PEA)2PbI4 thin film is stable in the 0.5-2.0 THz frequency range, and the spin-coating speed has limited effect on the extinction coefficient, with the curves of samples at different speeds being staggered. This phenomenon is due to the two-dimensional layered nature of the material:

[0098] 1) Exciton absorption is mainly concentrated in the visible light region, and the response in the terahertz band is weak;

[0099] 2) Quantum confinement effect and organic-inorganic alternating structure lead to different terahertz absorption mechanisms from traditional semiconductors. It is worth noting that the extinction coefficient of the low-speed sample is slightly lower, while the 1500 rpm sample shows the best dielectric uniformity. This result reveals the application potential of two-dimensional perovskites in terahertz modulators and detectors.

[0100] Figure 15 The terahertz dielectric constant spectrum of (PEA)2PbI4 thin film reveals the close relationship between its polarization response and spin-coating process. The 1500 rpm sample performs best, with a dielectric constant of 9.8 at 0.2 THz, confirming that optimized spin-coating can enhance the polarization ability of the thin film. The dielectric constant changes regularly with the rotation speed: it stabilizes and rises in the 500-1500 rpm range, while the >1500 rpm sample shows a dielectric constant drop due to lattice distortion. The curves converge in the high-frequency region, where the dielectric response is dominated by [PbI6] 4- octahedral electron displacement polarization, and the 1500 rpm sample still maintains the best stability. This result provides a material basis for broadband terahertz device design and a new approach to optimizing dielectric properties through process control.

[0101] Figure 16 The refractive index spectrum in the figure reveals the significant dispersion characteristics of the (PEA)2PbI4 thin film: the refractive index in the low frequency region increases with the frequency, and tends to be stable after >0.5 THz. The sample with 1500 rpm has the best performance, and the refractive index at 1.0 THz reaches 2.85, which proves that process optimization can enhance the optical response. The gradient analysis of the curve shows that the samples with 500-1000 rpm have a gentle slope in the transition region of 0.3-0.7 THz; the samples with >1500 rpm have a reduced refractive index due to lattice defects. In the high frequency region, all samples converge in the interval of 2.5-2.9, and the sample with 1500 rpm maintains the best stability. The results provide key material parameters for the design of terahertz photon devices, and provide a new perspective for the structure-activity relationship study through the correlation between refractive index and rotation speed.

[0102] Figure 17 and Figure 18 The figure shows the correlation between the terahertz transmission characteristics of the (PEA)2PbI4 thin film and the spin coating speed. The logarithmic coordinate Figure 17 shows that the sample with 1500 rpm has the best transmission performance at 1.5 THz, and a characteristic low-loss window appears at 1.2 THz, while the sample with 2500 rpm sharply attenuates at 2.0 THz. The linear transmission Figure 18 shows that the sample with 1500 rpm maintains the highest transmittance throughout the process, reaching 38% at 1.8 THz. Comprehensive analysis shows that:

[0103] 1) The performance is gradually optimized in the interval of 500-1500 rpm, and the sample with 1500 rpm has both low loss and high transmission in the interval of 1.0-1.5 THz;

[0104] 2) The performance decreases after >1500 rpm, and the sample with 2500 rpm has the lowest transmittance at 2.0 THz. The results provide process optimization basis for the design of terahertz functional devices, and reveal the structure-activity relationship between microstructure evolution and macroscopic photoelectric performance.

[0105] Embodiment 3

[0106] The embodiment based on embodiment 1 or 2 provides a terahertz functional device, which comprises the organic-inorganic hybrid perovskite thin film of embodiment 2, and the device is a terahertz modulator, a terahertz detector or a terahertz filter.

[0107] The part of the present application not described in detail is the prior art, so the present application does not describe it in detail.

[0108] It can be understood that the term "one" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of one element can be one, and in another embodiment, the number of the element can be multiple, and the term "one" cannot be understood as a limitation on the number.

[0109] Although the professional terms are used more in this paper, but not to exclude the possibility of using other terms. Use of these terms is only more convenient to describe and explain the essence of the application; to interpret them as any kind of additional limitation is contrary to the spirit of the invention.

[0110] The application is not limited to the above best mode, anyone under the inspiration of the application can derive other various forms of products, but regardless of any change in its shape or structure, any technical solution with the same or similar to the application, falls within the scope of the application.

Claims

1. A method for preparing an organic-inorganic hybrid perovskite thin film, characterized by, The method comprises the following steps: Preparation of a (PEA)2PbI4 precursor solution, coating the precursor solution on a substrate by a spin coating process with a rotation speed of 1500 rpm; The thin film after spin coating is subjected to annealing treatment, and the annealing temperature is 80℃; The thin film after spin coating is characterized, which includes testing its terahertz spectral characteristics in the frequency range of 0.1-2.2 THz by using a terahertz time-domain spectroscopy system, and analyzing its crystalline quality by combining X-ray diffraction and scanning electron microscopy; The terahertz spectral characteristics include an absorption peak at 1.5 THz, a dielectric loss ≤1.72, a refractive index ≥2.85, and a transmittance >90% in the frequency range of <1 THz.

2. The production method according to claim 1, characterized by, The preparation of the (PEA)2PbI4 precursor solution comprises: Dissolving PEAI and PbI2 in a molar ratio of 2:1 in dimethylformamide, stirring at room temperature for at least 6 hours.

3. The preparation method according to claim 2, characterized in that, The stirring rate is 800 rpm, and the stirring temperature is 25±2℃.

4. The method of claim 1, wherein, The absorption coefficient at 1.5 THz is 37-39 cm -1 .

5. An organic-inorganic hybrid perovskite thin film, characterized in that, The thin film is prepared by the preparation method of any one of claims 1-4, and has terahertz spectral characteristics in the frequency range of 0.1-2.2 THz: There is an absorption peak at 1.5 THz, a dielectric loss ≤1.72, a refractive index ≥2.85, and a transmittance >90% in the frequency range of <1 THz.

6. The organic-inorganic hybrid perovskite thin film according to claim 5, characterized in that, The thin film also has a secondary absorption peak at 1.8 THz, and the 1.5 THz absorption peak and the 1.8 THz secondary absorption peak form a double-peak structure, which is derived from the synergistic effect of Pb-I skeleton vibration and interlayer coupling.

7. A terahertz functional device, characterized by, The device comprises the organic-inorganic hybrid perovskite thin film of claim 5 or 6, and the device is a terahertz modulator, a terahertz detector, or a terahertz filter.

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