Core-shell perovskite heterojunction and preparation method and application thereof

Abstract

The invention discloses a core-shell perovskite heterojunction and a preparation method and application thereof. The core-shell perovskite heterojunction has a three-dimensional continuous interface, the core-shell perovskite heterojunction comprises a first perovskite phase as a core and a second perovskite phase as a shell, the chemical formula of the first perovskite phase is APbX3, and the chemical formula of the second perovskite phase is APbY3; wherein A is a monovalent cation and comprises any one of Cs < + >, HC (NH2) 2 < + > and CH3NH3 < + > or a combination of at least two of Cs < + >, HC (NH2) 2 < + > and CH3NH3 < + >; x and Y are respectively selected from Cl <-> or I <->, and X is not equal to Y. The core-shell perovskite heterojunction provided by the invention has a three-dimensional continuous interface, the contact area of heterogeneous components can be fully increased, the preparation process is simplified, the production cost is reduced, and the defects in the prior art are overcome, so that the batch controllable production of the core-shell perovskite heterojunction is realized, and the development and application of the perovskite heterojunction in the field of photoelectric devices are promoted.

Description

Technical Field

[0001] The present invention relates to a perovskite heterojunction, in particular to a core-shell perovskite heterojunction and a preparation method and application thereof, belonging to the technical field of perovskite synthesis. Background Art

[0002] Halide perovskite materials, with their excellent properties such as high light absorption coefficient, long carrier diffusion length, high fluorescence quantum yield, and narrow emission spectrum half-width, have shown great application potential in a wide range of optoelectronic devices, including light-emitting diodes, solar cells, photodetectors, and lasers. In recent years, halide perovskite materials have become a research hotspot in the scientific research field.

[0003] Perovskite heterojunction structures play a crucial role in optoelectronic device applications. By constructing a heterojunction, effective carrier control is achieved, promoting the separation and transport of photogenerated carriers, thereby improving device performance. For example, in solar cells, heterojunctions can reduce carrier recombination and increase photoelectric conversion efficiency. In light-emitting diodes, they can improve carrier injection and recombination efficiency, enhancing luminescence performance.

[0004] Among the many perovskite heterojunctions, APbCl3 and APbI3 (A is a monovalent cation, such as Cs + , FA + or MA + Heterojunctions composed of APbCl₃@APbI₃ (e.g., APbCl₃) have unique advantages. APbCl₃ has a relatively wide bandgap and a short photoluminescence wavelength, while APbI₃ has a narrower bandgap and a longer photoluminescence wavelength. This combination of different bandgaps enables the APbCl₃@APbI₃ perovskite heterojunction to achieve a wider range of light absorption and emission, promising applications in broadband photodetectors and multicolor light-emitting diodes.

[0005] However, current research on APbCl3@APbI3 perovskite heterojunctions still faces numerous challenges. For example, conventional heterojunction preparation methods can be complex, costly, and difficult to precisely control the heterojunction structure, leading to unstable heterojunction quality and performance. CN118064975A ​​discloses a perovskite CsPbCl3 / CsPbI3 periodic heterojunction nanowire and its preparation method. The resulting heterojunction is grown on a pre-treated M-plane sapphire substrate. A magnetron source mobile chemical vapor deposition device is used to achieve the replacement of the drug source in a high-temperature environment. The device is controlled stably by a stepper motor, making it easy to adjust the replacement rate. This results in the successful preparation of a large-scale periodic heterojunction nanowire array. CN114293248A discloses a perovskite CsPbCl3 / CsPbI3 heterojunction nanowire and a preparation method thereof. This technical solution uses a controllable dual-temperature zone tubular furnace and a large-tube-in-small-tube growth mode. The type of deposited material is changed by changing the material of the evaporation source, and the pressure, growth temperature, airflow size, and isolation time are precisely controlled to grow CsPbCl3 / CsPbI3 heterojunction nanowires with steep interfaces. The CsPbCl3 nanowires are single-crystal nanowires with a photoluminescence wavelength of 420nm; the CsPbI3 nanowires are single-crystal nanowires with a photoluminescence wavelength of 700nm. The heating temperature during the preparation process is 580-610°C. The high-temperature operation requires higher requirements for instruments and equipment, making it unsuitable for mass production, which limits its further application in optoelectronic devices. Moreover, the CsPbCl3 / CsPbI3 heterojunction nanowires obtained above are lateral heterojunctions, the interface is a steep two-dimensional plane, the contact area is small and the component mutation is obvious, which can only achieve discrete luminescence of CsPbCl3 and CsPbI3, and cannot meet the demand for multi-color luminescence at the same site brought by the continuous interface.

[0006] To overcome these limitations, researchers have begun exploring more advantageous core-shell perovskite heterojunctions in recent years. This structure significantly increases the contact area and interaction strength between heterogeneous components by encapsulating another perovskite material outside the core material. For example, CN107474823A discloses a perovskite nanocrystal material with a core-shell structure and a preparation method thereof. The crystal is an APbX3 / BPbX3 composite lattice structure in the form of clustered quantum dots. Using a solution method, a layer of BPbX3 perovskite material with a similar band gap is encapsulated outside the APbX3 perovskite single core. This effectively passivates the surface of the perovskite nanocrystal composite material, reduces luminescence from defect states on the crystal surface, and enhances the intrinsic emission properties of the material. Despite many successful attempts, core-shell heterojunctions with perovskite phases with large band gap differences (such as APbCl3 and APbI3) still face significant challenges. The design of such core-shell heterojunctions requires precise control of the composition gradient to avoid internal stress accumulation, while also ensuring high quality at the core-shell interface and a good crystal growth pattern. This places higher demands on the preparation process, and currently no prior art has reported on this. Summary of the Invention

[0007] The main purpose of the present invention is to provide a core-shell perovskite heterojunction and a preparation method thereof to overcome the deficiencies in the prior art.

[0008] Another object of the present invention is to provide applications of the core-shell perovskite heterojunction.

[0009] To achieve the aforementioned object of the invention, the technical solutions adopted by the present invention include:

[0010] An embodiment of the present invention provides a core-shell perovskite heterojunction having a three-dimensional continuous interface. The core-shell perovskite heterojunction includes a first perovskite phase as a core and a second perovskite phase as a shell. The chemical formula of the first perovskite phase is APbX3, and the chemical formula of the second perovskite phase is APbY3.

[0011] Where A is a monovalent cation, including Cs + 、HC(NH2)2 + 、CH3NH3 + Any one or a combination of at least two of: X, Y are selected from Cl - or I - , and X≠Y.

[0012] An embodiment of the present invention also provides a method for preparing a core-shell perovskite heterojunction, which includes: in a closed container, allowing the first perovskite phase APbX3 to undergo a gas-solid anion exchange reaction with a Y source to form a core composed of the first perovskite phase APbX3 and a shell composed of the second perovskite phase APbY3, thereby preparing a core-shell perovskite heterojunction.

[0013] The embodiment of the present invention also provides the application of the core-shell perovskite heterojunction in the field of optoelectronic devices.

[0014] Compared with the prior art, the beneficial effects of the present invention include at least:

[0015] 1) The present invention utilizes Cl - with I - The significant difference in ionic radius (Δr = 21.5%) triggers thermodynamic immiscibility. When different lattice sites are substituted, local lattice distortion at the diffusion front leads to stress accumulation, ultimately triggering a phase separation mechanism to form a core-shell intermediate. The self-assembly of core-shell heterojunctions is achieved through controlled gas-solid anion exchange. The heterogeneous combination of perovskites with different band gaps enables a wider range of light absorption and emission, and expands the scope of applications.

[0016] 2) Compared with lateral heterojunctions with steep interfaces, the resulting core-shell perovskite heterojunction has a three-dimensional continuous interface, which can maximize the contact area of ​​the heterogeneous components and achieve multi-color luminescence at the same site; and the preparation method is controllable and easy to implement, applicable to perovskite systems of different dimensions, universal, and suitable for mass production, promoting the development and application of perovskite heterojunctions in the field of optoelectronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 This is a photoluminescence spectrum of the core-shell perovskite heterojunction obtained in Example 1 of the present invention;

[0019] Figure 2a and Figure 2b They are the element distribution diagrams of Cs, Pb, I, and Cl in the core-shell perovskite heterojunction obtained in Example 1 of the present invention and the element distribution spectrum of I and Cl across the core-shell perovskite heterojunction nanowire;

[0020] Figure 3 This is a graph showing the thermal stability test results of the core-shell perovskite heterojunction obtained in Example 1 of the present invention;

[0021] Figure 4 X-ray diffraction spectra of the CsPbCl3 perovskite single crystal, core-shell perovskite heterojunction, and heat-treated at 210°C for 2h obtained in Example 2 of the present invention;

[0022] Figure 5 The photoluminescence spectrum of the CsPbI3 perovskite nanosheets reacting with BACl at different reaction times in Example 3 of the present invention is shown;

[0023] Figure 6 Schematic diagram of the change of microstructure along with the thickness of the shell during the reaction process in a typical embodiment of the present invention;

[0024] Figure 7 The CsPbBr3 perovskite and the obtained CsPb(Br x I 1-x )3 Fluorescence image of perovskite;

[0025] Figure 8 The CsPbBr3 perovskite and the obtained CsPb(Br x I 1-x )3 Photoluminescence spectrum of perovskite;

[0026] Figure 9 The CsPbBr3 perovskite and the obtained CsPb(Br x Cl 1-x )3 Fluorescence image of perovskite;

[0027] Figure 10 The CsPbBr3 perovskite and the obtained CsPb(Br x Cl 1-x )3 Photoluminescence change spectrum of perovskite. DETAILED DESCRIPTION

[0028] In response to the defects of the existing technology, the present invention proposes a core-shell perovskite heterojunction and a preparation method thereof. By utilizing the immiscibility of C1- and I-, perovskites with different band gaps are combined to achieve a wider range of light absorption and emission. The obtained core-shell perovskite heterojunction has a continuous interface, which can fully increase the contact area of ​​the heterogeneous components.

[0029] The following further explains the technical solution, its implementation process, and principles. However, it should be understood that within the scope of the present invention, the above-mentioned technical features of the present invention and the technical features specifically described below (in the embodiments) can be combined with each other to form new or preferred technical solutions. Due to space limitations, they will not be described here one by one.

[0030] As one aspect of the technical solution of the present invention, a core-shell perovskite heterojunction has a three-dimensional continuous interface. The core-shell perovskite heterojunction includes a first perovskite phase as a core and a second perovskite phase as a shell. The chemical formula of the first perovskite phase is APbX3, and the chemical formula of the second perovskite phase is APbY3.

[0031] Where A is a monovalent cation, including Cs + 、HC(NH2)2 + (FA + ), CH3NH3 + (MA + ) in any one or a combination of at least two; X, Y are selected from Cl - or I - , and X≠Y.

[0032] In some specific embodiments, the core-shell perovskite heterojunction includes a core composed of a first perovskite phase CsPbCl3 and a shell composed of a second perovskite phase CsPbI3.

[0033] In some specific embodiments, the core-shell perovskite heterojunction includes a core composed of a first perovskite phase CsPbI3 and a shell composed of a second perovskite phase CsPbCl3.

[0034] In some specific embodiments, the core-shell perovskite heterojunction includes an inner core composed of a first perovskite phase HC(NH2)2PbCl3 and an outer shell composed of a second perovskite phase HC(NH2)2PbI3.

[0035] In some specific embodiments, the core-shell perovskite heterojunction includes an inner core composed of a first perovskite phase CH3NH3PbCl3 and an outer shell composed of a second perovskite phase CH3NH3PbI3.

[0036] However, the structure of the core-shell perovskite heterojunction of the present invention is not limited to the above-mentioned cases, and other cases not listed in the application scope are also applicable.

[0037] In some specific embodiments, the core-shell perovskite heterojunction includes any one or more combinations of nanowires, nanosheets, thin films, or bulks, but is not limited thereto.

[0038] In some specific embodiments, the core-shell perovskite heterojunction can achieve dual-band emission, including a first photoluminescence band and a second photoluminescence band.

[0039] Furthermore, the first photoluminescence wavelength range is 400-450 nm.

[0040] Furthermore, the second photoluminescence wavelength range is 650-850 nm.

[0041] In some specific embodiments, the thickness of the first perovskite phase is 1 to 3000 nm.

[0042] In some specific embodiments, the thickness of the second perovskite phase is 1 to 3000 nm.

[0043] Furthermore, the content ratio of the first perovskite phase to the second perovskite phase is m:n, and both m and n are greater than 0 and less than or equal to 1.

[0044] The present invention utilizes Cl - with I - The significant difference in ionic radius (Δr = 21.5%) triggers thermodynamic immiscibility. When different lattice sites are substituted, local lattice distortion generated at the diffusion front leads to stress accumulation, ultimately triggering a phase separation mechanism to form a core-shell intermediate. Combining perovskites with different band gaps enables a wider range of light absorption and emission, and expands their application range.

[0045] Compared with lateral heterojunctions with steep interfaces, the resulting core-shell perovskite heterojunction has a continuous interface, which can maximize the contact area of ​​the heterogeneous components and achieve multi-color luminescence at the same site.

[0046] As another aspect of the technical solution of the present invention, a method for preparing a core-shell perovskite heterojunction involves:

[0047] In a sealed container, the first perovskite phase APbX3 and a Y source undergo a gas-solid anion exchange reaction to form a core composed of the first perovskite phase APbX3 and a shell composed of the second perovskite phase APbY3, thereby preparing the core-shell perovskite heterojunction.

[0048] In some specific embodiments, the temperature of the gas-solid anion exchange reaction is 140-280° C., preferably 145-220° C. The present invention realizes the self-assembly construction of the core-shell heterojunction through controllable gas-solid anion exchange. The appropriate temperature helps to generate sufficient Y source vapor, thereby driving Y to effectively diffuse into the lattice of the first perovskite phase APbX3, and through halogen ion exchange, the second perovskite phase APbY3, Cl - with I - The significant difference in ionic radius causes lattice distortion, resulting in interfacial stress triggering phase separation, and then forming a core composed of the first perovskite phase APbX3 and a shell composed of the second perovskite phase APbY3. The composition of the core-shell perovskite heterojunction can be precisely adjusted by controlling the reaction process. - and I- Low miscibility. Too low a temperature will result in a slow ion diffusion rate, while too high a temperature may cause crystal structure degradation or excessive ion exchange, affecting the stability and performance of the resulting core-shell perovskite heterojunction.

[0049] In some specific embodiments, the gas-solid anion exchange reaction lasts for 1 to 240 minutes, preferably 5 to 180 minutes. If the reaction time is too short, insufficient gas-solid anion exchange may result in insufficient or incomplete shell thickness of the resulting core-shell structure, affecting its photoelectric performance and stability. If the reaction time is too long, excessive anion exchange may result, potentially leading to complete conversion to a single-phase second perovskite phase, APbY3, and failure to form a core-shell structure.

[0050] like Figure 6 As shown in Figure 1, the microstructure changes with the shell thickness during the i→ii reaction process, where blue represents the first perovskite phase and purple represents the second perovskite phase. Figure 6 As shown in Figure 1, at the initial stage of the reaction, the Cl content is high. Due to the lattice mismatch, the CsPbI3 in the interface region is in a compressed state as a whole. In particular, a very thin micro-strain layer is formed near the CsPbCl3, which contains both compressive and tensile stresses. As the reaction proceeds, when the shell gradually thickens (see Figure 2), the CsPbI3 in the interface region is in a compressed state as a whole. Figure 6 In step ii), the interfacial stress on the portion of CsPbI3 away from CsPbCl3 gradually decreases, and the region begins to recover its original interplanar spacing, a phenomenon known as lattice relaxation. This entire process primarily describes the path from initial lattice compression to eventual lattice relaxation.

[0051] In some specific embodiments, when Y is 1 - When, the Y source can include any one or a combination of at least two of formamidine hydroiodide (FAI), ethylamine hydroiodide (EAI), butylamine hydroiodide (BAI), methylammonium iodide (MAI), HI or I2, but is not limited thereto.

[0052] In other specific embodiments, when Y is Cl - When, the Y source can include any one or a combination of at least two of methylammonium chloride (MACl), formamidine hydrochloride (FACl), ethylamine hydrochloride (EACl), butylammonium chloride (BACl) or HCl, but is not limited thereto.

[0053] In some specific embodiments, the added amount of the Y source is 0.1 to 200 mg / mL.

[0054] In some specific embodiments, the synthesis method of the first perovskite phase APbX3 includes: preparing the first perovskite phase APbX3 by at least one of a solution method, a direct synthesis method, and an anion exchange method.

[0055] In some more specific embodiments, the solution method includes: placing a substrate containing PbI2 or PbO in an AX solution, and obtaining the first perovskite phase APbX3 after heating, standing and washing.

[0056] Furthermore, the concentration of the AX solution is 5 to 30 mg / mL.

[0057] Furthermore, the AX solution includes AX and a solvent, and the solvent may include any one or a combination of at least two of methanol, ethanol, n-propanol, isopropanol, etc., but is not limited thereto.

[0058] Furthermore, the heating temperature is 60-90° C. and the heating time is 8-16 hours.

[0059] Furthermore, the standing temperature is 15 to 35° C., and the standing time is 8 to 16 hours.

[0060] In some more specific embodiments, the direct synthesis method includes: mixing and reacting the AX solution and PbX2 in a molar ratio of 0.8 to 1.2:1, and obtaining the first perovskite phase APbX3 after annealing.

[0061] In some more specific embodiments, the anion exchange method comprises: making APbBr3 or APb(Br x X 1-x )3 perovskite undergoes a halogen ion exchange reaction to obtain the first perovskite phase APbX3, where the value range of x is greater than 0 and less than 1.

[0062] In some specific embodiments, the method for preparing the core-shell perovskite heterojunction specifically includes:

[0063] The first perovskite phase APbX3 and a Y source are placed in a sealed container, and a gas-solid anion exchange reaction is carried out at 140 to 280° C. for 1 to 240 minutes to obtain the core-shell perovskite heterojunction.

[0064] The preparation method of the present invention realizes the self-assembly construction of core-shell heterojunctions through controllable gas-solid anion exchange, and the heterogeneous combination of perovskites with different band gaps enables it to achieve a wider range of light absorption and emission, thereby increasing the scope of application; moreover, the preparation method is controllable and easy to implement, applicable to perovskite systems of different dimensions, and has universal applicability, so as to realize the controllable batch production of core-shell perovskite heterojunctions.

[0065] As another aspect of the technical solution of the present invention, it also relates to the application of the core-shell perovskite heterojunction in the field of optoelectronic devices.

[0066] Furthermore, the optoelectronic device includes at least any one of a light emitting diode, a solar cell, a photodetector, and the like.

[0067] The technical solution of the present invention is further described in detail below in conjunction with several preferred embodiments and the accompanying drawings. Obviously, the embodiments described are only a part of the embodiments of the present invention, rather than all of the embodiments. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on it. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0068] Example 1

[0069] CsPbCl3 perovskite nanowires and 20 mg of BAI were placed in a 20 mL sealed sample bottle, and a gas-solid anion exchange reaction was carried out at 170°C for 10 minutes to obtain the core-shell perovskite heterojunction, including a first perovskite phase CsPbCl3 as a core and a second perovskite phase CsPbI3 as a shell, wherein the content ratio of the first perovskite phase to the second perovskite phase was 0.6:0.36;

[0070] The CsPbCl3 perovskite nanowires are prepared using a solution method, including placing a glass sheet with deposited PbI2 in a 10 mg / mL CsCl methanol solution, reacting at 80°C for 12 hours, and standing at 25°C for 12 hours. After washing, the CsPbCl3 perovskite nanowires are obtained.

[0071] Example 2

[0072] A CsPbCl3 perovskite single crystal and 35 mg of FAI were placed in a 30 mL sealed sample bottle, and a gas-solid anion exchange reaction was performed at 175° C. for 60 minutes to obtain the core-shell perovskite heterojunction, comprising a first perovskite phase CsPbCl3 as a core and a second perovskite phase CsPbI3 as a shell, wherein the content ratio of the first perovskite phase to the second perovskite phase was 0.25:0.71;

[0073] The CsPbCl3 single crystal is obtained by a direct synthesis method, which includes mixing equal volumes of 0.025M CsCl solution (DMSO to DMF volume ratio of 3:1) and 0.025M PbCl2 solution (DMSO to DMF volume ratio of 3:1), drop-coating the mixture on a glass substrate, and annealing at 140°C to obtain the CsPbCl3 perovskite single crystal.

[0074] Example 3

[0075] CsPbI3 perovskite nanosheets and 30 mg of BACl were placed in a 25 mL sealed sample bottle, and a gas-solid anion exchange reaction was carried out at 180°C for different times (0-60 min) to obtain the core-shell perovskite heterojunction, including a first perovskite phase CsPbI3 as a core and a second perovskite phase CsPbCl3 as a shell, wherein when the reaction time was 20 min, the content ratio of the first perovskite phase to the second perovskite phase was 0.76:0.23; when the reaction time was 40 min, the content ratio of the first perovskite phase to the second perovskite phase was 0.51:0.43; when the reaction time was 60 min, the content ratio of the first perovskite phase to the second perovskite phase was 0.21:0.78.

[0076] The CsPbI3 perovskite nanosheets are obtained by using CsPbBr3 through an anion exchange method.

[0077] Example 4

[0078] This embodiment is basically the same as embodiment 1, except that the Y source in the gas-solid anion exchange reaction is I2.

[0079] Example 5

[0080] This embodiment is basically the same as embodiment 1, except that the Y source in the gas-solid anion exchange reaction is EAI.

[0081] Example 6

[0082] This embodiment is basically the same as embodiment 3, except that the Y source in the gas-solid anion exchange reaction is EACl.

[0083] Example 7

[0084] A MAPbCl3 perovskite single crystal and 50 mg of MAI were placed in a 50 mL sealed sample bottle, and a gas-solid anion exchange reaction was carried out at 200°C for 45 minutes to obtain the core-shell perovskite heterojunction, including a first perovskite phase MAPbCl3 as the inner core and a second perovskite phase MAPbI3 as the outer shell, wherein the content ratio of the first perovskite phase to the second perovskite phase was 0.41:0.56.

[0085] The MAPbCl3 perovskite single crystal is obtained by a direct synthesis method, comprising: mixing equal volumes of 0.05M MACl solution (DMF) and 0.05M PbCl2 solution (DMF), drop-coating the mixture on a glass substrate, and annealing at 150°C to obtain the MAPbCl3 perovskite single crystal.

[0086] Example 8

[0087] A FAPbCl3 perovskite single crystal and 20 mg of FAI were placed in a 15 mL sealed sample bottle, and a gas-solid anion exchange reaction was carried out at 195°C for 30 minutes to obtain the core-shell perovskite heterojunction, including a first perovskite phase FAPbCl3 as a core and a second perovskite phase FAPbI3 as a shell, wherein the content ratio of the first perovskite phase to the second perovskite phase was 0.51:0.46.

[0088] The FAPbCl3 perovskite single crystal is obtained by a direct synthesis method, which includes mixing equal volumes of 0.1M FACl solution (DMSO to DMF volume ratio of 1:1) and 0.1M PbCl2 solution (DMSO to DMF volume ratio of 1:1), drop-coating the mixture on a glass substrate, and annealing at 160°C to obtain the FAPbCl3 perovskite single crystal.

[0089] Example 9

[0090] This embodiment is substantially the same as embodiment 1, except that the gas-solid anion exchange reaction is carried out at 140° C. for 240 min.

[0091] Example 10

[0092] This embodiment is substantially the same as embodiment 1, except that the gas-solid anion exchange reaction is carried out at 145° C. for 180 min.

[0093] Example 11

[0094] This embodiment is substantially the same as embodiment 1, except that the gas-solid anion exchange reaction is carried out at 220° C. for 5 minutes.

[0095] Example 12

[0096] This embodiment is basically the same as embodiment 1, except that the gas-solid anion exchange reaction is carried out at 280° C. for 1 minute.

[0097] The inventors of this case conducted performance tests using the core-shell perovskite heterojunction prepared in Examples 1-3 as an example, and the results are as follows:

[0098] FIG1 is a photoluminescence spectrum of the core-shell perovskite heterojunction obtained in Example 1, which consists of two emission peaks at 413 nm and 680 nm, corresponding to CsPbCl3 and CsPbI3, respectively.

[0099] Figure 2a Element distribution diagram of Cs, Pb, I, and Cl in the core-shell perovskite heterojunction obtained in Example 1. Figure 2bThis is the distribution spectrum of I and Cl elements across the core-shell perovskite heterojunction nanowire. It can be seen that the Cl element shows a trend of more in the middle and less on both sides, while the I element shows a trend of less in the middle and more on both sides, which proves that the Cl element is mainly distributed in the core of the core-shell perovskite heterojunction, and the I element is mainly distributed in the outer shell of the core-shell perovskite heterojunction.

[0100] Figure 3 In order to test the thermal stability of the core-shell perovskite heterojunction obtained in Example 1, the obtained core-shell perovskite heterojunction was heat-treated at 210°C in a nitrogen environment. It can be seen that as time goes by, the photoluminescence spectrum of the obtained core-shell perovskite heterojunction still maintains a double-peak emission and does not change much, indicating good stability.

[0101] Figure 4 The X-ray diffraction spectra of the CsPbCl3 perovskite single crystal, core-shell perovskite heterojunction and heat treatment at 210°C for 2h obtained in Example 2 show that the CsPbCl3 perovskite single crystal has good crystallinity and no obvious impurities; the obtained core-shell perovskite heterojunction exhibits diffraction peaks of CsPbCl3 and CsPbI3; and after heat treatment at 210°C for 2h, the position of the diffraction peak does not shift basically, indicating good stability.

[0102] Figure 5 The photoluminescence change spectra of the CsPbI3 perovskite nanosheets in Example 3 react with BACl at 180°C for different times. 0 min is the photoluminescence spectrum of the CsPbI3 nanosheets, which has a single emission peak at 705 nm. Subsequently, it reacts with BACl and generates CsPbCl3 over time, accompanied by the appearance of an emission peak around 415 nm, which is more obvious at 30-50 min.

[0103] Comparative Example 1

[0104] This comparative example is basically the same as Example 1, except that the temperature of the gas-solid anion exchange reaction is 120° C. Since the reaction temperature is too low, a core-shell structure cannot be produced, the ion migration rate is low, and the crystallinity of the shell product is poor.

[0105] Comparative Example 2

[0106] This comparative example is essentially the same as Example 1, except that the temperature of the gas-solid anion exchange reaction is 300° C. Due to the high reaction temperature, the gas-solid anion exchange is excessive, resulting in a single phase of CsPbI3 and severe damage to the morphology of the resulting perovskite.

[0107] Comparative Example 3

[0108] This comparative example is basically the same as Example 1, except that the gas-solid anion exchange reaction time is 0.5 min. Since the reaction time is too short, a core-shell structure cannot be produced.

[0109] Comparative Example 4

[0110] This comparative example is essentially the same as Example 1, except that the gas-solid anion exchange reaction lasted 300 minutes. Due to the excessively long reaction time, a core-shell heterojunction could not form, and the reaction was essentially converted to CsPbI3. Due to the loss of interfacial interactions, the stability of the core-shell perovskite heterojunction was somewhat inferior to that of the core-shell perovskite heterojunction.

[0111] Comparative Example 5

[0112] CsPbBr3 perovskite nanowires and 20 mg of BAI were placed in a 20 mL sealed sample bottle and subjected to gas-solid anion exchange reaction at 170 °C for 10 min to obtain CsPb(Br x I 1-x )3Perovskite;

[0113] The CsPbBr3 perovskite nanowires are prepared by a solution method, which includes placing a glass sheet with deposited PbI2 in a methanol solution of 8mg / mL CsBr, reacting at 85°C for 12 hours, and standing at 30°C for 12 hours. After washing, the CsPbBr3 perovskite nanowires are obtained. x I 1-x )3 Fluorescence photos of perovskite Figure 7 As shown, the photoluminescence spectrum changes as Figure 8 shown.

[0114] Comparative Example 6

[0115] The BAI in the gas-solid anion exchange reaction in Control Example 5 was replaced by BACl, and the other conditions were the same as those in Control Example 5 to obtain CsPb(Br x Cl 1-x )3 perovskite. CsPbBr3 perovskite and the obtained CsPb(Br x Cl 1-x )3 Fluorescence photos of perovskite Figure 9 As shown, the photoluminescence spectrum changes as Figure 10 shown.

[0116] In both Control Examples 5 and 6, CsPbBr3 was used as the first perovskite phase, and gas-solid anion exchange reactions were performed with BAI and BACl, respectively. Figure 7-10 It can be seen that the obtained mixed perovskite CsPb(Br x I 1-x )3 or CsPb(Br x Cl 1-x)3's luminescent color changes significantly, and its photoluminescence spectrum undergoes corresponding red shift / blue shift, and is a single peak, without forming a core-shell structure with dual emission. This is because Br - with I - and Cl - The size difference of Br is small, and the similar ionic radius makes Br - Can be more easily I - or Cl - Replace and enter the perovskite lattice without causing significant lattice distortion or structural stress; and are conducive to the formation of a uniform mixed halide perovskite phase (such as CsPb(Br x I 1-x )3 or CsPb(Br x Cl 1-x )3), rather than leading to phase separation or the formation of core-shell structures.

[0117] In summary, the present invention realizes the self-assembly construction of core-shell heterojunction through controllable gas-solid anion exchange, and the reaction process is easy to control. By controlling the reaction temperature and reaction time, the controllable preparation of core-shell perovskite heterojunction is achieved. The preparation method is simple, easy, universal, and suitable for mass production.

[0118] In addition, the inventors of this case also referred to the aforementioned embodiments and conducted experiments using other raw materials, process operations, and process conditions described in this specification, and obtained relatively ideal results.

[0119] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A core-shell perovskite heterojunction, characterized in that: The core-shell perovskite heterojunction has a three-dimensional continuous interface, and the core-shell perovskite heterojunction includes a first perovskite phase as a core and a second perovskite phase as a shell, the chemical formula of the first perovskite phase is APbX3, and the chemical formula of the second perovskite phase is APbY3; Where A is a monovalent cation, including Cs + 、HC(NH2)2 + 、CH3NH3 + Any one or a combination of at least two of: X, Y are selected from Cl - or I - , and X≠Y.

2. The core-shell perovskite heterojunction according to claim 1, characterized in that: The core-shell perovskite heterojunction comprises a core composed of a first perovskite phase CsPbCl3 and a shell composed of a second perovskite phase CsPbI3; And / or, the core-shell perovskite heterojunction comprises a core composed of a first perovskite phase CsPbI3 and a shell composed of a second perovskite phase CsPbCl3; And / or, the core-shell perovskite heterojunction comprises a core composed of a first perovskite phase HC(NH2)2PbCl3 and a shell composed of a second perovskite phase HC(NH2)2PbI3; And / or, the core-shell perovskite heterojunction includes a core composed of a first perovskite phase CH3NH3PbCl3 and a shell composed of a second perovskite phase CH3NH3PbI3.

3. The core-shell perovskite heterojunction according to claim 1, wherein: The core-shell perovskite heterojunction includes any one or more combinations of nanowires, nanosheets, thin films or bulks.

4. The core-shell perovskite heterojunction according to claim 1, wherein: The core-shell perovskite heterojunction can achieve dual-band emission, including a first photoluminescence band and a second photoluminescence band; Preferably, the first photoluminescence wavelength range is 400-450 nm; Preferably, the second photoluminescence wavelength range is 650-850 nm; and / or, the thickness of the first perovskite phase is 1 to 3000 nm; And / or, the thickness of the second perovskite phase is 1 to 3000 nm.

5. The method for preparing a core-shell perovskite heterojunction according to any one of claims 1 to 4, characterized in that: include: In a sealed container, the first perovskite phase APbX3 and a Y source undergo a gas-solid anion exchange reaction to form a core composed of the first perovskite phase APbX3 and a shell composed of the second perovskite phase APbY3, thereby preparing a core-shell perovskite heterojunction.

6. The preparation method according to claim 5, characterized in that: The temperature of the gas-solid anion exchange reaction is 140-280° C., preferably 145-220° C.; and / or the time of the gas-solid anion exchange reaction is 1-240 min, preferably 5-180 min.

7. The preparation method according to claim 5, characterized in that: When Y is I-, the source of Y includes any one of formamidine hydroiodide, ethylamine hydroiodide, butylamine hydroiodide, methylammonium iodide, HI or I2, or a combination of at least two thereof; and / or, when Y is Cl-, the source of Y includes any one of methylammonium chloride, formamidine hydrochloride, ethylamine hydrochloride, butylammonium chloride or HCl, or a combination of at least two thereof; And / or, the added amount of the Y source is 0.1 to 200 mg / mL.

8. The preparation method according to claim 5, characterized in that include: The first perovskite phase APbX3 is prepared by at least one of a solution method, a direct synthesis method, and an anion exchange method.

9. The preparation method according to claim 8, characterized in that The solution method comprises: placing a substrate containing PbI2 or PbO in an AX solution, and obtaining the first perovskite phase APbX3 after heating, standing and washing; Preferably, the concentration of the AX solution is 5 to 30 mg / mL; Preferably, the AX solution comprises AX and a solvent, and the solvent comprises any one of methanol, ethanol, n-propanol, and isopropanol, or a combination of at least two thereof; Preferably, the heating temperature is 60-90°C and the heating time is 8-16 hours; Preferably, the standing temperature is 15 to 35° C. and the standing time is 8 to 16 hours; And / or, the direct synthesis method comprises: mixing and reacting an AX solution and PbX2 in a molar ratio of 0.8 to 1.2:1, and obtaining the first perovskite phase APbX3 after annealing; And / or, the anion exchange method comprises: making APbBr3 or APb(Br x X 1-x )3 undergoes a halogen ion exchange reaction to obtain the first perovskite phase APbX3, where the value of x is greater than 0 and less than 1.

10. Use of the core-shell perovskite heterojunction according to any one of claims 1 to 4 in the field of optoelectronic devices, preferably, the optoelectronic device comprises at least any one of a light emitting diode, a solar cell, and a photodetector.

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