Active light-emitting layer of light-emitting diode, preparation method therefor and light-emitting diode

Abstract

Disclosed in the present invention are an active light-emitting layer of a light-emitting diode, a preparation method therefor and a light-emitting diode. The preparation method comprises: by means of taking SnI2 and CsI as precursors, adding one or more of N-phenylthiourea, thiourea, N,N'-diphenylthiourea, aminothiourea, β-naphthylthiourea, urea, phenylurea, N,N'-diphenylurea, β-naphthylurea, amino acid and N,N'-methylenebisacrylamide, and adding SnF2 or SnCl2; and using a spin-coating method to prepare an active light-emitting layer CsSnI3. A CsSnI3-based long-wavelength near-infrared light-emitting diode provided in the present invention applies intrinsic p-type doping characteristics of tin-based halide perovskite while reducing the carrier defect density, thus obtaining near-infrared light-emitting devices having high radiant intensity and improved operating stability.

Description

Active light-emitting layer of light-emitting diode, preparation method thereof, and light-emitting diode Technical Field

[0001] The present invention relates to a perovskite light-emitting diode, in particular to a bright and stable near-infrared non-lead perovskite light-emitting diode, in particular to an active light-emitting layer thereof, and belongs to the field of diodes. Background Art

[0002] Near-infrared light-emitting diodes (NIR LEDs) have broad application prospects in night vision, biomedical imaging, sensing, and optical communications. Currently, NIR luminescent materials mainly rely on traditional III-V group (III-V) epitaxially grown inorganic semiconductor materials, such as gallium arsenide and aluminum indium gallium arsenide. However, the high-temperature processing process increases the cost of material preparation and limits their integration into multifunctional photonic platform systems. Therefore, it is necessary to develop new, solution-processable NIR luminescent materials.

[0003] In recent years, significant progress has been made in the research of short-wavelength near-infrared light-emitting diodes (NIRLEDs) with emission peaks below 900 nm. However, long-wavelength NIRLEDs (>900 nm) based on organic semiconductors and colloidal quantum dots (QDs) still face challenges such as low radiation intensity and poor operational stability (see Table 1 in the Detailed Description section), which limit their practical application. Therefore, further research and development of novel, solution-processable, long-wavelength NIR luminescent materials is needed to improve their radiation intensity and operational stability, laying the foundation for practical applications.

[0004] Metal halide perovskites have shown great application potential in the field of light-emitting diodes due to their excellent optical and electrical properties. In particular, tin-based halide perovskites (THP), especially all-inorganic black orthorhombic (γ)CsSnI3, have great potential in the development of near-infrared light-emitting diodes due to their small band gap (~1.3eV), high hole mobility and excellent inherent all-inorganic structural stability. However, the Sn in tin-based halide perovskites is 2+ Easily oxidized to Sn 4+ , resulting in the material having a very high background hole doping concentration (heavily p-type doping) and defect density, which in turn triggers strong non-radiative recombination and significantly reduces the luminescence performance of the material.

[0005] Summary of the Invention

[0006] In order to solve the problems of heavy p-type doping and high defect density in tin-based halide perovskites in the prior art, the present invention provides a bright and stable near-infrared non-lead perovskite light-emitting diode.

[0007] The technical solutions of the present invention are as follows:

[0008] A method for preparing an active light-emitting layer of a light-emitting diode is characterized in that SnI2 and CsI are used as precursors, one or more of N-phenylthiourea, thiourea, N,N'-diphenylthiourea, thiosemicarbazide, β-naphthylthiourea, urea, phenylurea, N,N'-diphenylurea, β-naphthylurea, amino acid, N,N'-methylenebisacrylamide, and SnF2 or SnCl2 are added, and the active light-emitting layer CsSnI3 is prepared by a spin coating method.

[0009] Preferably, SnI2 and CsI are used as precursors, and N-phenylthiourea and SnF2 are added.

[0010] Preferably, the method specifically includes the following steps:

[0011] (1) Prepare N-phenylthiourea solution by dissolving N-phenylthiourea in dimethyl sulfoxide.

[0012] (2) Dissolve SnI2, CsI and SnF2 in dimethyl sulfoxide to prepare a precursor solution containing SnF2.

[0013] (3) Adding N-phenylthiourea solution to the precursor solution containing SnF2 to obtain the desired composition,

[0014] (4) Stir the solution evenly and filter it.

[0015] (5) Using a two-step method from low speed to high speed, CsSnI3 light-emitting layers of different compositions are spin-coated on the substrate.

[0016] (6) Annealing to form an active light-emitting layer.

[0017] Further preferably, the doping content of N-phenylthiourea is 40% of the amount of Sn, and the amount ratio of SnI2, CsI, N-phenylthiourea and SnF2 is: SnI2:CsI:N-phenylthiourea:SnF2 chemical substance amount stoichiometric ratio is 1:1:0.05-1:0.02-2.

[0018] The most preferred molar ratio of SnI2:CsI:N-phenylthiourea:SnF2 is 1:1:0.4:0.1.

[0019] Further preferably, in step (5), the CsSnI3 light-emitting layer is spin-coated on the substrate in a two-step method in a glove box filled with nitrogen, first rotating at 500-1000 rpm for 5-20 s with an acceleration speed of 100-200 rpm / s, and then rotating at 3000-6000 rpm for 30-60 s with an acceleration speed of 500-1000 rpm / s.

[0020] Further preferably, the concentrations of H2O and O2 in the nitrogen-filled glove box are less than 0.1 ppm.

[0021] More preferably, in step (6), annealing is performed at 50-150° C. for 2-30 minutes to form an active light-emitting layer. An active light-emitting layer of a light-emitting diode prepared by the above method.

[0022] A near-infrared non-lead perovskite light-emitting diode, characterized in that its structure comprises an indium tin oxide glass substrate anode, a poly (3,4-ethylenedioxythiophene):polystyrene-sulfonate) hole injection layer, an active light-emitting layer (CsSnI3), a 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene electron transport layer, and a LiF / Al cathode, wherein the active light-emitting layer (CsSnI3) is selected from the active light-emitting layer of the aforementioned light-emitting diode.

[0023] The technical effects of the present invention are as follows:

[0024] The present invention provides a long-wavelength near-infrared light-emitting diode based on CsSnI3. By simultaneously utilizing the intrinsic p-doping properties of tin-based halide perovskites and reducing the carrier defect density, a near-infrared light-emitting device with high radiation intensity and long-term operating stability is achieved. This invention pioneers the control of the crystallization growth process of the CsSnI3 precursor under tin-rich conditions, enabling better control of the intrinsic p-type hole doping concentration and reducing the defect density, thereby improving radiation intensity and stability. Using SnI2 and CsI as precursors, N-phenylthiourea and SnF2 (or SnCl2) are added, and the active light-emitting layer CsSnI3 is prepared by spin coating. During this process, SnF2 provides a tin-rich environment to reduce the intrinsic hole doping density, while N-phenylthiourea (NPTU) helps slow the crystallization growth process, further regulating the intrinsic p-type hole doping concentration and reducing the carrier defect density.

[0025] The structural characteristic of N-phenylthiourea is that it has a C=S double bond, which is the main chemical functional group; therefore, other substances containing C=S double bonds will also have similar effects: such as thiourea, N,N'-diphenylthiourea, thiosemicarbazide and β-naphthalenethiourea.

[0026] In addition, since the chemical properties of the C=S double bond are similar to those of the C=O double bond, substances containing C=O double bonds will also have similar effects: urea, phenylurea, N,N'-diphenylurea, β-naphthylurea, amino acids and N,N'-methylenebisacrylamide, etc.

[0027] By taking advantage of these advantages, high-performance near-infrared light-emitting diodes were successfully prepared. The peak emission wavelength of the obtained near-infrared light-emitting diodes was 948nm and the radiation intensity was 226W sr -1 m -2, at 100mA cm -2 At a high constant current density, the device's operating half-life is 39.5 hours (under nitrogen flow to cool the device, the stability measurement is 125 hours). These performance indicators significantly surpass previously reported near-infrared light-emitting diodes with emission peaks exceeding 900nm. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG1 is a device energy level diagram of a light emitting diode of an embodiment;

[0029] FIG2 is a cross-sectional SEM image of a light emitting diode device according to an embodiment;

[0030] FIG3 is a normalized electroluminescence spectrum of the light emitting diode devices of the embodiment and the comparative example;

[0031] FIG4 is an electroluminescence spectrum of light-emitting diode devices of the embodiment and the comparative example at different operating voltages;

[0032] FIG5 is a current density-voltage-radiation intensity characteristic curve of an embodiment;

[0033] Figure 6 shows (a) the external quantum efficiency-current density characteristic curve and (b) the current density at 300 mA cm -2 The steady-state output radiation intensity and external quantum efficiency of NS-CsSnI3 light-emitting diode devices working at high current density;

[0034] FIG7 shows (a) the current density-voltage-radiation intensity characteristic curve and (b) the external quantum efficiency-current density characteristic curve of the C-CsSnI3 light-emitting diode device;

[0035] FIG8 is (a) the current density-voltage-radiation intensity characteristic curve and (b) the external quantum efficiency-current density characteristic curve of the S-CsSnI3 light-emitting diode device;

[0036] FIG9 is a statistical histogram of the maximum radiation intensity of the NS-CsSnI3 light-emitting diode device;

[0037] FIG10 is a peak external quantum efficiency distribution diagram of the NS-CsSnI3 light-emitting diode device;

[0038] Figure 11 shows the near-infrared light-emitting diodes prepared under different conditions at 100 mA cm -2 Working stability at constant current density, stability comparison of NS-CsSnI3 light-emitting diode with (dark red line) and without (orange line) nitrogen flow;

[0039] Figure 12 shows photographs of CsSnI3 thin films prepared under different conditions before and after annealing, where 0, 3, and 10 minutes represent the films before annealing;

[0040] FIG13 is a schematic diagram of the preparation of the light-emitting layer CsSnI3 of a light-emitting diode device;

[0041] Figure 14 shows SEM images of S-CsSnI3 (b1), N(5%)-S-(b2), N(40%)-S-(b3), and N(100%)-S-CsSnI3 films (b4);

[0042] Figure 15 SEM images of C-CsSnI3 thin films spin-coated on PEDOT:PSS without additives, scale bar 1 μm;

[0043] FIG16 is an X-ray diffraction pattern of CsSnI3 thin films prepared under different conditions;

[0044] Figure 17 shows the concentrations of NPTU, NPTU+CsI, NPTU+SnI2 and NPTU+CsI+SnI2 in DMSO-d6 solution. 13 C NMR spectroscopy;

[0045] Figure 18 is the H NMR spectra of NPTU, NPTU+CsI, NPTU+SnI2 and NPTU+CsI+SnI2 in DMSO-d6 solvent solution;

[0046] Figure 19 is a hydrogen nuclear magnetic resonance spectrum of NPTU, NPTU+CsI, NPTU+SnI2 and NPTU+CsI+SnI2 in DMSO-d6 solvent solution (partial magnification, 3.2-3.5 ppm);

[0047] Figure 20 shows the Fourier transform attenuated total reflection infrared spectra of NPTU, NPTU+CsI and NPTU+SnI2;

[0048] FIG21 is a Fourier transform attenuated total reflection infrared spectrum of CsSnI3 thin films prepared with and without NPTU;

[0049] Figure 22 shows the high-resolution S2p X-ray photoelectron spectra of NPTU and NS-CsSnI3 films;

[0050] Figure 23 shows the high-resolution Cs~3d (a) and I~3d (b) X-ray photoelectron spectra of CsSnI3 films prepared under different conditions;

[0051] Figure 24 shows the high-resolution Sn 3d X-ray photoelectron spectra of C-CsSnI3 film (a), S-CsSnI3 film (b), and NS-CsSnI3 film (c);

[0052] Figure 25 shows the Sn content in CsSnI3 films prepared under different conditions.4+ proportion;

[0053] Figure 26 shows the high-resolution Sn 3d X-ray photoelectron spectra of C-CsSnI3 film (a), S-CsSnI3 film (b), and NS-CsSnI3 film (c). DETAILED DESCRIPTION

[0054] In order to better understand the present invention, the present invention will be further explained below in conjunction with specific embodiments.

[0055] Example

[0056] In this example, a CsSnI3-based near-infrared light-emitting diode (NIRLED) was fabricated. The device structure consists of an indium tin oxide glass substrate anode, a poly(3,4-ethylenedioxythiophene:polystyrene sulfonate) (PEDOT:PSS) hole injection layer (HIL), an active light-emitting layer (CsSnI3), a 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBI) electron transport layer (ETL), and a LiF / Al cathode (see Figure 1). Using SnI2 and CsI as precursors, CsSnI3 thin films were prepared by spin coating with the addition of N-phenylthiourea (NPTU) and SnF2 (films prepared with NPTU and SnF2 additives are designated NS-CsSnI3). During this process, SnF2 provides a tin-rich environment to reduce the intrinsic hole doping concentration, while NPTU helps slow the crystal growth process, further regulating the intrinsic p-type hole doping concentration and reducing the carrier defect density.

[0057] For the convenience of comparison, CsSnI3 films without additives (denoted as C-CsSnI3) and CsSnI3 films with only SnF2 additives (denoted as S-CsSnI3) were prepared for comparison.

[0058] The specific preparation process is as follows:

[0059] Materials: Tin (II) iodide (SnI2, 99.999%), Tin (II) fluoride (SnF2, 99%), Cesium iodide (CsI, 99.999%), and N-phenylthiourea (>98%) were purchased from Sigma-Aldrich. PEDOT:PSS (AI 4083) was purchased from Ossila.

[0060] Preparation of perovskite solution and film: First, 112 mg of SnI2 and 73 mg of CsI were dissolved in 1 mL of DMSO (0.3 M concentration measured as elemental Sn) to prepare a control precursor solution without additives, recorded as C-CsSnI3. Next, 112 mg of SnI2, 73 mg of CsI and 4.7 mg of SnF2 were dissolved in 1 mL of DMSO (0.3 M, containing 10% SnF2 after dissolution) to prepare a precursor solution containing SnF2, recorded as S-CsSnI3. To prepare the NPTU solution, 152 mg of NPTU was dissolved in 1 mL of DMSO (1 M). For the precursor solution containing NPTU, a certain amount of NPTU (1 M) was added to the S-CsSnI3 precursor solution to obtain the desired composition, recorded as NS-CsSnI3. Before spin coating, the solution needed to be stirred evenly and filtered. In a nitrogen-filled glove box (H2O and O2 concentrations <0.1ppm), CsSnI3 light-emitting layers of different compositions were spin-coated on the substrate using a two-step method commonly used for thin film preparation. First, the film was spun at 1000rpm for 10s (acceleration rate of 200rpm / s), followed by spun at 5000rpm for 60s (acceleration rate of 800rpm / s). Finally, it was annealed at 100°C for 10min to form the active light-emitting layer. It should be noted that the optimized doping content of NPTU is 40% (molar fraction compared to Sn). In order to perform photoluminescence, low-temperature-dependent photoluminescence, time-resolved photospectroscopy, UV-visible absorption spectroscopy, femtosecond transient absorption spectroscopy, and X-ray diffraction spectroscopy measurements, 80mg / ml PMMA / chlorobenzene solution was spin-coated on top of the perovskite layer at 6000rpm for 50s.

[0061] In addition, when one or more of thiourea, N,N'-diphenylthiourea, thiosemicarbazide, β-naphthylthiourea, urea, phenylurea, N,N'-diphenylurea, β-naphthylurea, amino acid, and N,N'-methylenebisacrylamide having similar chemical property groups are added, or when SnCl2 is used in combination, all preparation processes and the obtained products are consistent with those of this embodiment.

[0062] Cross-sectional scanning electron microscopy of the device (Figure 2) reveals that the active light-emitting layer CsSnI3 forms discrete submicron-structured perovskite crystals, with a perovskite film thickness of approximately 40-50nm. Notably, the emission peak of the electroluminescence (EL) spectrum of the NS-CsSnI3 LED is centered at approximately 948nm, a red-shift compared to the other two control samples, C-CsSnI3 (emission peak at 920nm) and S-CsSnI3 (emission peak at 942nm) (Figure 3). Furthermore, the full width at half maximum (FWHM) of the luminescence spectrum of the NS-CsSnI3 LED is reduced to 71nm, much smaller than the 135 and 81nm of the C-CsSnI3 and S-CsSnI3 LEDs, respectively. Furthermore, it was observed that the peak position of the EL spectrum remained consistent at different operating voltages, showing no shift, demonstrating the device's excellent EL spectrum stability (Figure 4). It can be seen that this example successfully prepared a near-infrared light-emitting diode based on CsSnI3. By adding N-phenylthiourea and SnF2, the film preparation process was optimized and the performance of the device was improved. This study provides new ideas and methods for the development of efficient and stable near-infrared light-emitting diodes. In addition, Figures 5 and 6 show that the NS-CsSnI3 light-emitting diode can produce a power of more than 2800mA cm -2 It operates under high current density conditions and exhibits a very large 226W sr -1 m -2 This value is much greater than the 14 and 103W sr of C-CsSnI3 and S-CsSnI3 light-emitting diodes. -1 m -2 The radiation intensity of the NS-CsSnI3 LED is also much higher than that of other long-wavelength near-infrared LEDs with emission peaks exceeding 900 nm, including organic materials based on the noble metal Pt(II), lead sulfide quantum dots, silver sulfide quantum dots, and hybrid Pb-Sn halide perovskite LEDs.

[0063] It is worth mentioning that the NS-CsSnI3 light-emitting diode exhibits the characteristics of low efficiency roll-off, reaching 142W sr -1 m -2 At high radiation intensity, the maximum external quantum efficiency is approximately 2.63% (see Figure 6). Figures 9 and 10 show the maximum radiation intensity and peak external quantum efficiency statistical histograms of the NS-CsSnI3 light-emitting diode, indicating that the device has good reproducibility, thus strongly demonstrating the effectiveness of the NPTU / SnF2 additive strategy for improving device performance.

[0064] Another important challenge facing tin-based halide perovskites in applications is their poor stability, which to some extent limits their practical applications. However, NS-CsSnI3 light-emitting diodes show significant advantages in operating stability.

[0065] Specifically, at 100 mA cm -2 When the device is working at a constant current density, the device stability half-life (T 50 ) reaches 39.5 hours, compared to 0.6 hours for the C-CsSnI3 light-emitting diode and 9.8 hours for the S-CsSnI3 light-emitting diode (Figure 11). In addition, by measuring in a constant nitrogen flow environment (to cool the device), the half-life of the NS-CsSnI3 light-emitting diode can even reach 125 hours. This data shows that the stability of the NS-CsSnI3 light-emitting diode has surpassed other long-wavelength near-infrared light-emitting diodes. Generally speaking, other near-infrared light-emitting diodes have a half-life of about 10mA cm -2 When working at a low current density, its half-life is usually only 3 minutes to 1 hour (as shown in Table 1).

[0066] Table 1 | Key performance parameters of the best-performing NIR LEDs (>900nm) based on different materials

[0067] The above proves that the near-infrared light-emitting diode based on CsSnI3 of this embodiment optimizes the preparation process of the thin film by adding N-phenylthiourea and SnF2, improves the performance of the device, and develops a high-efficiency and stable near-infrared light-emitting diode.

[0068] Controllable growth of CsSnI3 thin films:

[0069] To gain a deeper understanding of the fundamental reasons for the improved device performance after the introduction of NPTU / SnF2, a series of experiments were designed to investigate the film formation process. Figures 12 and 13 reveal that the crystallization growth process of the NS-CsSnI3 thin film is effectively regulated. Within just 10 minutes after spin coating (without annealing), the color of the C-CsSnI3 film rapidly changes from light yellow to dark brown, indicating that the crystallization process proceeds very rapidly and uncontrollably. In contrast, the crystallization process of S-CsSnI3 is slowed, while the crystallization process of NS-CsSnI3 is further delayed and regulated, with the film transitioning from colorless to a highly transparent yellow within 10 minutes after spin coating. These results demonstrate that SnF2 and NPTU effectively delay precursor nucleation and control the crystallization process, thereby promoting the formation of high-quality crystals. After annealing, the NS-CsSnI3 film exhibits a uniform dark brown color. Scanning electron microscopy images (Figures 14, 13, and 15) demonstrate that increasing the amount of NPTU in the precursor leads to a decrease in the distribution density of the crystals. Compared with traditional continuous films, NS-CsSnI3 films are discontinuous and present an isolated perovskite grain distribution morphology. This structure has been proven in FAPbI3-based light-emitting diodes to effectively improve the light extraction efficiency of the device.

[0070] X-ray diffraction (XRD) measurements show that all films are black-phase γCsSnI3 structures. Compared with C-CsSnI3 and S-CsSnI3 films, the characteristic peak intensities of NS-CsSnI3 films at 14.4° and 29.1° are significantly enhanced, indicating a higher degree of crystallinity (Figure 16). 1 H and 13 C nuclear magnetic resonance (NMR) spectroscopy further explored the interaction between NPTU and CsSnI3. The resonance signal of δ=181.42ppm generated by C=S in NPTU experienced chemical shifts of Δδ=0.24 to δ=181.18ppm and Δδ=0.29 to δ=181.13ppm after interacting with SnI2 and CsI+SnI2, respectively (Figure 17). This obvious chemical shift change indicates that there is a significant interaction between the C=S group and SnI2. However, when CsI is added, the chemical shift of the C=S group Δδ<0.12ppm. By comparison, it can be found that the interaction between NPTU and SnI2 is significantly stronger than the interaction between NPTU and CsI. This is mainly attributed to the interaction between SnI2 and CsI. 2+ The Lewis acid-base interaction between NPTU and NH group is relatively strong, while the hydrogen bond between NH group and I- is relatively weak. 1 H NMR and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy (Figures 18-21) also further confirmed the stronger interaction between NPTU and SnI2.

[0071] X-ray photoelectron spectroscopy (XPS) further revealed the surface chemical composition of CsSnI3 and confirmed the strong chemical interaction between CsSnI3 and NPTU. Compared with pure NPTU, the S 2p XPS peak of NS-CsSnI3 film shifted slightly to a higher binding energy, which indicates that the electronegativity of S in NS-CsSnI3 was reduced (as shown in Figures 22-24). In addition, the Sn in C-CsSnI3 film 4+ The ratio is quite high, and its peak intensity is similar to that of Sn 2+ The peak intensities of Sn are comparable (as shown in Figures 25 and 26), which indicates that the perovskite surface and grain boundaries are severely oxidized. 2+ Easily oxidized to Sn 4+ is the main source of defect state formation in tin-based halide perovskites. However, compared with C-CsSnI3 and S-CsSnI3 films, the Sn 4+ These results indicate that NPTU can inhibit Sn 2+ The oxidation is mainly due to NC=S…Sn 2+ The strong Lewis acid-base interaction increases the Sn 2+ The electron density around Sn 2+ Oxidation provides protection.

[0072] It is noted that the above description is intended to help those skilled in the art understand the present invention, but is not intended to limit the scope of protection of the present invention. Any equivalent substitution, modification, improvement, and / or simplification of the above description that does not depart from the essence of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing an active light-emitting layer of a light-emitting diode, characterized in that Using SnI2 and CsI as precursors, adding one or several of N-phenylthiourea, thiourea, N,N'-diphenylthiourea, thiosemicarbazide, β-naphthylthiourea, urea, phenylurea, N,N'-diphenylurea, β-naphthylurea, amino acid, N,N'-methylenebisacrylamide, and SnF2 or SnCl2, a CsSnI3 active light-emitting layer is prepared by spin coating.

2. The method according to claim 1, characterized in that Using SnI2 and CsI as precursors, adding N-phenylthiourea and SnF2.

3. The method according to claim 1, characterized in that Specifically, it includes the following steps: (1) Prepare an N-phenylthiourea solution by dissolving N-phenylthiourea in dimethyl sulfoxide. (2) Dissolve SnI2, CsI, and SnF2 in dimethyl sulfoxide to prepare a precursor solution containing SnF2. (3) Add the N-phenylthiourea solution to the precursor solution containing SnF2 to obtain the desired composition. (4) Stir the solution evenly and filter it. (5) Spin coat the CsSnI3 light-emitting layer with different components on the substrate by a two-step method from low speed to high speed. (6) Anneal to form the active light-emitting layer.

4. The method according to claim 3, wherein The doping content of N-phenylthiourea is 40% of the molar amount of Sn, and the molar ratio of SnI2, CsI, N-phenylthiourea, and SnF2 is 1:1:0.05 - 1:0.02 - 2.

5. The method according to claim 4, characterized in that The molar ratio of SnI2:CsI:N-phenylthiourea:SnF2 is 1:1:0.4:0.

1.

6. The method according to claim 3, characterized in that In step (5), spin coat the CsSnI3 light-emitting layer on the substrate by a two-step method in a glove box filled with nitrogen. First, rotate at 500 - 1000 rpm for 5 - 20 s, with an acceleration rate of 100 - 200 rpm / s, and then rotate at 3000 - 6000 rpm for 30 - 60 s, with an acceleration rate of 500 - 1000 rpm / s.

7. The method according to claim 6, wherein The concentrations of H2O and O2 in the glove box filled with nitrogen are <0.1 ppm.

8. The method according to claim 3, wherein In step (6), anneal at 50 - 150 °C for 2 - 30 min to form the active light-emitting layer.

9. The active light-emitting layer of a light-emitting diode prepared by the method according to any one of claims 1 - 8.

10. A near-infrared non-lead perovskite light-emitting diode, characterized in that The structure is an indium tin oxide glass substrate anode, a poly(3,4-ethylenedioxythiophene):polystyrene sulfonate hole injection layer, an active light-emitting layer CsSnI3, a 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene electron transport layer, and a LiF / Al cathode, wherein the active light-emitting layer CsSnI3 is selected from the active light-emitting layer of a light-emitting diode according to claim 9.

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