A tin(ii)-based perovskite hybrid heterojunction thin film, a preparation method and a photodetector

Abstract

The application relates to a divalent tin (II) based perovskite mixed heterojunction thin film, a preparation method and a photodetector, and belongs to the technical fields of non-toxic inorganic perovskite materials, photodetector materials and devices. The mixed heterojunction thin film is composed of FA 1‑x Cs x SnBr3 tin-based perovskite material and PVK, the value range of x is 0.05-0.2, the molar ratio of FA 1‑x Cs x SnBr3 and PVK is 200:1-600:1. The tin-based perovskite material FA 1‑x Cs x SnBr3 is mixed with PVK, and the molar ratio of doping is optimized, and finally a bulk heterojunction thin film which is beneficial to the generation and transmission of photo-generated carriers is obtained. The introduction of PVK can not only effectively passivate the defects on the surface of the FA 1‑x Cs x SnBr3 thin film, but also further prevent the erosion of water and oxygen to the tin (II) based perovskite FA 1‑x Cs x SnBr3. The photodetector prepared by taking the mixed heterojunction thin film as an active layer of a tin-based perovskite photodetector has excellent performance.

Description

TECHNICAL FIELD

[0001] The application relates to a tin (II) -based perovskite mixed heterojunction thin film, a preparation method and a photodetector, and belongs to the technical field of non-toxic inorganic perovskite materials, photodetector materials and devices. BACKGROUND

[0002] Photodetectors have numerous potential applications in image sensing, optical communication, automated manufacturing, chemical / biological measurement and military measurement. In recent years, due to the long carrier diffusion distance, high carrier mobility and simple preparation process of organic-inorganic hybrid halide perovskite materials, the materials have become one of the most promising semiconductor materials in photodetectors, solar cells and light-emitting diodes. Although photodetectors based on perovskite materials have made great progress in recent years, most high-performance photodetectors are based on devices prepared from lead-containing perovskite materials. As known, lead not only causes serious pollution to the natural environment, but also causes chronic lead poisoning in the human body due to long-term accumulation of lead in the body. The above factors are considered to be the biggest obstacle for further commercial application of lead-based perovskite photodetectors. Therefore, it is necessary to replace lead in perovskite materials with other non-lead elements.

[0003] The general chemical formula of the perovskite material is ABX3, wherein A is a monovalent cation such as Cs + , MA + or FA + ; B is a divalent cation such as Pb 2+ , Sn 2+ or Ge 2+ ; and X is a halide anion such as Cl - , Br - or I - . In the perovskite crystal structure, a single B-site divalent cation is coordinated with six X-site monovalent anions to form a [BX6] 4- octahedral structure, and each octahedron is connected by sharing vertices and surrounds the A-site cation, and finally expands to form a network structure in three dimensions. For perovskite materials, the Goldschmidt tolerance factor t is a key empirical index for judging the stability of the perovskite structure, and its expression is:

[0004]

[0005]

[0006] And the octahedral factor μ is a key factor for the formation of the aforementioned [BX6] 4- octahedral structure, and its expression is: ​

[0007]

[0008] Where R A R B and R X These represent the ionic radii of the three elements in the perovskite general formula ABX3. The perovskite crystal structure is stably maintained when t is between 0.813 and 1.107. Furthermore, when t is between 0.9 and 1.0, the perovskite crystal exhibits a perfect cubic structure. The optimal value of μ is between 0.44 and 0.90.

[0009] Among many non-lead elements, tin not only has a similar ionic radius to lead, but also belongs to Group IVA of the same periodic table. Therefore, tin is considered the best choice to replace lead in perovskite materials. However, because the electrons in the 5s orbital of divalent tin(II) do not exhibit the "inert pair effect" as the electrons in the 6s orbital of divalent lead(II), the two 5s electrons of divalent tin(II) are more easily lost and oxidized to tetravalent tin(IV). When divalent tin(II) is oxidized to tetravalent tin(IV), the high density of tetravalent tin(IV) vacancy defects gradually extends from the crystal surface into the interior of the material under the action of ion diffusion, ultimately causing a severe decline in the photoelectric properties of tin-based perovskite materials. Summary of the Invention

[0010] In view of this, the purpose of this invention is to provide a divalent tin(II)-based perovskite hybrid heterojunction thin film, its preparation method, and a photodetector. The stability of the divalent tin(II)-based perovskite material is improved through A-site cation engineering and surface passivation engineering, and the resulting high-performance divalent tin(II)-based perovskite material is then used to fabricate a photodetector. Firstly, by using a certain concentration of Cs... + Incorporating Cs into the FASnBr3 lattice not only makes the crystal structure of divalent tin-based perovskite materials approach a perfect state, but also... + The introduction of [the substance] further reduces the rate of oxidation of divalent tin(II). Furthermore, mixing poly(N-vinylcarbazole) (PVK) with the aforementioned perovskite precursor solution not only improves the film-forming properties of the active layer material, but also, when used as an active layer tin-based perovskite photodetector, significantly enhances the separation efficiency of photogenerated carriers. The application of this strategy allows the full advantages of tin-based perovskite materials to be realized, and this strategy can be fully utilized in the fabrication of high-performance tin-based perovskite photodetectors.

[0011] To achieve the above object, the technical scheme of the present application is as follows:

[0012] A tin(II)-based perovskite hybrid heterojunction thin film, the hybrid heterojunction thin film is made of FA 1-x Cs x SnBr3 tin-based perovskite material and polyvinyl carbazole (Poly(N-vinylcarbazole), PVK) are mixed, the value range of x is 0.05-0.2, FA 1-x Cs x The molar ratio of SnBr3 and PVK is 200:1-600:1.

[0013] Preferably, the value range of x is 0.1-0.15.

[0014] Preferably, FA 1-x Cs x The molar ratio of SnBr3 and PVK is 300:1-400:1.

[0015] A preparation method of the tin(II)-based perovskite hybrid heterojunction thin film, the steps of the method are as follows:

[0016] First, prepare FA 1-x Cs x SnBr3 tin-based perovskite material is dissolved in a solvent to obtain a perovskite precursor solution, and a stable FA 1-x Cs x SnBr3 tin-based perovskite precursor solution, then mix the PVK solution with the above perovskite precursor solution and fully dissolve, then use a filter head to filter to obtain a mixed precursor solution, finally use a one-step spin coating method to spin coat the above mixed precursor solution on a substrate, and anneal at 70-100℃ for 0.5-1h to obtain a tin(II)-based perovskite hybrid heterojunction thin film.

[0017] Preferably, the concentration of the tin(II)-based perovskite precursor solution is 0.4-1M, and the concentration of the PVK solution is less than or equal to 5mM.

[0018] Preferably, the solvent is N,N-dimethylformamide (DMF) or dimethyl sulfoxide (DMSO).

[0019] Preferably, the solvent of the PVK solution is N,N-dimethylformamide (DMF).

[0020] A laminated tin-based perovskite photodetector, the photodetector comprising a metal top electrode, a hole transport layer (HTL), a bulk heterojunction active layer, an electron transport layer (ETL) and a transparent conductive bottom electrode arranged in order from top to bottom; wherein the mixed bulk heterojunction active layer is a tin (II) based perovskite mixed bulk heterojunction film with greatly improved stability.

[0021] Preferably, the thickness of the metal top electrode is 100-150 nm; the thickness of the hole transport layer (HTL) is 50-100 nm; the thickness of the bulk heterojunction active layer is 100-800 nm; the thickness of the electron transport layer (ETL) is 50-250 nm; and the thickness of the transparent conductive bottom electrode is 50-120 nm.

[0022] Preferably, the metal top electrode is Ag, Al or Au; the hole transport layer is MoO3 or NiO; and the electron transport layer is a ZnO or TiO2 film. The metal top electrode and the hole transport layer are both prepared by a thermal evaporation method; the ZnO film is prepared by a sol-gel method; and the transparent conductive bottom electrode is indium tin oxide (ITO).

[0023] Preferably, the laminated tin-based perovskite photodetector is prepared by the following method, the method steps comprising:

[0024] (1) preparing an electron transport layer on a transparent conductive bottom electrode substrate by a sol-gel method;

[0025] (2) spin-coating the mixed precursor solution on the electron transport layer by a one-step spin-coating method to obtain a mixed bulk heterojunction active layer;

[0026] (3) preparing a hole transport layer on the bulk heterojunction active layer by a thermal evaporation method;

[0027] (4) preparing a metal top electrode on the hole transport layer by a thermal evaporation method using a mask plate to obtain a laminated tin-based perovskite photodetector.

[0028] Preferably, in step (1), the spin-coating speed is 1500-2500 rpm and the spin-coating time is 20-60 s.

[0029] Preferably, in step (2), the spin-coating speed is 800-2000 rpm and the spin-coating time is 20-60 s.

[0030] Advantages

[0031] The present application firstly introduces different molar concentrations of Cs ions into FASnBr3, and since the ionic radius of the Cs ion is much smaller than that of the FA cation, the introduction of an appropriate concentration of Cs ions will improve the FA 1-x Cs x The film-forming property of the tin-based perovskite material of FASnBr3 is improved. Meanwhile, the FA 1-x Cs x The crystal structure of the tin-based perovskite material of FASnBr3 is also regulated to a certain extent due to the change of the t factor, so that the above-mentioned tin-based perovskite material FA 1-x Cs x The stability of FASnBr3 is greatly improved. In addition, by mixing the FA 1-x Cs x The precursor solution of FASnBr3 is mixed with PVK to obtain a mixed heterojunction material, and the separation efficiency of the photo-generated carriers produced under light conditions is further improved.

[0032] The present application introduces the tin(II)-based perovskite material FA 1-x Cs x SnBr3 is mixed with PVK, and by optimizing the doping molar ratio, a bulk heterojunction thin film that is conducive to the generation and transport of photo-generated carriers is finally obtained. The introduction of PVK not only effectively passivates the defects on the surface of the FA 1-x Cs x SnBr3 thin film, but also further prevents the erosion of water and oxygen on the tin(II)-based perovskite FA 1-x Cs x SnBr3. It is worth noting that the introduction of PVK in an appropriate concentration ratio in the tin-based perovskite material FA 1-x Cs x SnBr3 does not affect the crystal structure of FA 0.9 Cs 0.1 SnBr3. Therefore, the high-quality FA 1- x Cs x The obtained mixed heterojunction thin film of FASnBr3:PVK will play a crucial role in the preparation of high-performance tin-based perovskite photodetectors based on the above-mentioned material.

[0033] The mixed heterojunction thin film described in the present application is used as the active layer of the tin-based perovskite photodetector, and the active layer is placed between the electron transport layer ZnO thin film and the hole transport layer MoO3 thin film. On the one hand, the above-mentioned measures reduce the water and oxygen as much as possible and FA 1-x Cs xThe contact of SnBr3 active layer material can reduce the probability of oxidation of divalent tin (II) in tin-based perovskite as much as possible; on the other hand, the introduction of the electron transport layer ZnO thin film and the hole transport layer MoO3 thin film can reduce the rate of injection of carriers from the electrode when the photodetector works under negative bias to a certain extent, that is, the dark current of the entire device is effectively inhibited. At the same time, their introduction can also act as an extraction layer of photo-generated carriers to promote the separation and transmission efficiency of photo-generated carriers in the entire device, so that the performance of the prepared tin (II)-based perovskite photodetector is greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is the FA described in Example 1 of the present application 1-x Cs x Scanning electron microscope (SEM) photos of SnBr3; (a) is the SEM photo of FA SnBr3; (b) is the SEM photo of FA 0.9 Cs 0.1 SEM photos of SnBr3; (c) is the SEM photo of FA 0.8 Cs 0.2 SEM photos of SnBr3; (d) is the SEM photo of FA 0.7 Cs 0.3 SEM photos of SnBr3.

[0035] Figure 2 is the FA described in Example 1 of the present application 1-x Cs x X-ray diffraction (XRD) patterns of SnBr3 tin (II)-based perovskite material; (a) is the XRD pattern of FA SnBr3, FA 0.95 Cs 0.05 SnBr3, FA 0.9 Cs 0.1 SnBr3, FA 0.8 Cs 0.2 SnBr3 and FA 0.7 Cs 0.3 X-ray diffraction (XRD) patterns of SnBr3; (b) is the XRD pattern of FA SnBr3 and FA 0.9 Cs 0.1 X-ray diffraction (XRD) patterns of SnBr3; (c), (d) and (e) are the XRD patterns of FA SnBr3, FA 0.95 Cs 0.05 SnBr3, FA 0.9 Cs 0.1 SnBr3, FA 0.8 Cs 0.2 SnBr3 and FA 0.7 Cs 0.3 Partial X-ray diffraction (XRD) patterns of SnBr3.

[0036] Figure 3 FASnBr3and FA 0.9 Cs 0.1 XPS spectra of Sn element in SnBr3tin (II) -based perovskite material. (a) is the XPS spectrum of Sn element in FASnBr3perovskite material; (b) is the XPS spectrum of Sn element in FA 0.9 Cs 0.1 XPS spectrum of Sn element in SnBr3perovskite material.

[0037] Figure 4 FA 0.9 Cs 0.1 XPS spectra of C, Cs, N and Br elements in SnBr3.

[0038] Figure 5 (a) is FASnBr3, FA 0.9 Cs 0.1 SnBr3and FA 0.9 Cs 0.1 UV-Vis absorption spectrum of SnBr3: PVK bulk heterojunction sample; Figure 5 (b) is FA 0.9 Cs 0.1 (Ahν) ~ hν curve corresponding to the SnBr3: PVK bulk heterojunction film. 2

[0039] Figure 6 FA 0.9 Cs 0.1 Scanning electron microscope (SEM) photos of SnBr3: PVK bulk heterojunction film under different molar ratios (K = M Perovskite : M PVK ); (a) K = 1:0; (b) K = 600:1; (c) K = 300:1; (d) K = 200:1; (e) K = 120:1.

[0040] Figure 7 FA 0.9 Cs 0.1 High resolution scanning electron microscope (HRSEM) photos of SnBr3: PVK bulk heterojunction film under different molar ratios (K = M Perovskite : M PVK ); (a) molar ratio K = 1:0; (b) molar ratio K = 300:1.

[0041] Figure 8 ​is the FA described in embodiment 2 of the present application 0.9 Cs 0.1 X-ray diffraction (XRD) patterns of SnBr3:PVK bulk heterojunction films with different PVK doping concentrations (0-5.0 mM).

[0042] Figure 9 is a device structure schematic diagram of a high-performance tin (II) based perovskite photodetector described in embodiment 3 of the present application; the substrate of ITO is a 1.1 mm thick glass substrate.

[0043] Figure 10 is the FA described in embodiment 3 of the present application 0.9 Cs 0.1 UPS spectra of SnBr3:PVK mixed bulk heterojunction films. (a) is the FA 0.9 Cs 0.1 The secondary cut-off edge of SnBr3:PVK; (b) is the FA 0.9 Cs 0.1 The valence band edge of SnBr3:PVK.

[0044] Figure 11 is a band structure schematic diagram of a high-performance tin (II) based perovskite photodetector described in embodiment 3 of the present application.

[0045] Figure 12 is a photodetector ITO / ZnO / FA 0.9 Cs 0.1 I-V curves of SnBr3:PVK / MoO3 / Ag under different incident light power densities. The light intensities are 0, 6.9 μW / cm 2 , 15.3 μW / cm 2 , 25.3 μW / cm 2 , 45.7 μW / cm 2 and 85.0 μW / cm 2 , respectively.

[0046] Figure 13 is a photodetector ITO / ZnO / FA 0.9 Cs 0.1 Responsivity and specific detectivity of SnBr3:PVK / MoO3 / Ag under 405 nm light irradiation with different incident light power densities.

[0047] Figure 14 is a photodetector ITO / ZnO / FA 0.9 Cs 0.1 Responsivity and specific detectivity of SnBr3:PVK / MoO3 / Ag under 405 nm light irradiation with different incident light power densities. 2I-t response curve of the SnBr3: PVK / MoO3 / Ag device under 405 nm light irradiation.

[0048] Figure 15 is the I-V curve of the tin-based perovskite photodetector ITO / ZnO / FA 0.9 Cs 0.1 SnBr3: PVK / MoO3 / Ag under 405 nm light irradiation with incident light power density of 6.9 μW / cm 2 The enlarged view of the I-t response curve of the SnBr3: PVK / MoO3 / Ag device under 405 nm light irradiation. From the graph, the rise time and fall time of the above device can be known.

[0049] Figure 16 is the I-V curve of the tin-based perovskite photodetector ITO / ZnO / FA 0.9 Cs 0.1 SnBr3: PVK with molar ratio K = 1:0; (b) the active layer FA 0.9 Cs 0.1 SnBr3: PVK with molar ratio K = 300:1.

[0050] Figure 17 is the I-V curve of the tin-based perovskite photodetector ITO / ZnO / FA 0.9 Cs 0.1 SnBr3: PVK / MoO3 / Ag under different incident light power densities; (a) without light irradiation; (b) under 405 nm light irradiation with incident light power density of 25.3 μW / cm 2 DETAILED DESCRIPTION

[0051] The application will be further described in detail below with specific examples.

[0052] In the following examples or comparative examples:

[0053] ​The absorption spectra of nanomaterials were analyzed using a UV-visible-near infrared spectrophotometer (Shimadzu, UV-3600). The photoelectric properties of the devices were measured using a semiconductor parameter analysis system (Keithley 4200-SCS) under dark and irradiation of 405 nm laser wavelength. Field emission scanning electron microscope (SEM) images and high-resolution scanning electron microscope (HRSEM) images of sample materials were taken using a JSM-7500F. X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) were recorded by PHI QUANTERA-II SXM. X-ray diffraction (XRD) patterns were recorded by a Rigaku Ultima IV X-ray diffractometer. All characterizations were performed in air at room temperature environment.

[0054] Example 1

[0055] A FA with excellent quality and stable performance 1-x Cs x A method for preparing a SnBr3 film, which is prepared by a one-step spin coating method 1-x Cs x A method for preparing a SnBr3 (x = 0, 0.1, 0.2 and 0.3) active layer film, which is as follows:

[0056] FABr (0.6 (1-x) M), SnBr2 (0.6 M), CsBr (0.6x M) and SnF2 (0.06 M) were first dissolved in N, N-dimethylformamide and stirred on a magnetic stirrer at 50°C for 12 hours to completely dissolve, and then the obtained precursor solution was filtered with a 0.45 μm nylon filter head to obtain a perovskite precursor solution, which was spin-coated on a glass substrate at a rotation speed of 1000 rpm, the spin-coating time was 30 s, and finally it was placed on a hot stage at 70°C for annealing treatment for 1 hour to obtain a FA 1- x Cs x SnBr3 film.

[0057] The FA 1-x Cs x The SEM image of the SnBr3 film is as shown in Figure 1 , Figure 1 (a)-(d) reveal that different concentrations of Cs ions are doped into FASnBr3 to obtain a FA 1-x Cs x The SEM image of the SnBr3 film. It can be seen that the FA 0.9 Cs 0.1 The quality of the SnBr3 film is the highest. (a) SEM photo of FASnBr3; (b) FA 0.9 Cs0.1 SEM image of SnBr3; (c)FA 0.8 Cs 0.2 SEM image of SnBr3; (d)FA 0.7 Cs 0.3 SEM image of SnBr3.

[0058] The FA 1-x Cs x The XRD pattern of the SnBr3 thin film is shown below. Figure 2 As shown, this figure illustrates FA 1-x Cs x The crystallization of SnBr3 was investigated. Furthermore, with increasing Cs ion doping concentration in the FASnBr3 lattice, the 2θ corresponding to its main diffraction peak shifted towards a larger value, indicating that the incorporation of Cs ions improved the crystallization of FASnBr3. 1-x Cs x The lattice constant of SnBr3 is decreasing.

[0059] The FASnBr3 and FA 0.9 Cs 0.1 XPS spectra of SnBr3 thin films are as follows: Figure 3 As shown in the figure, this diagram illustrates that the oxidation rate of tin(II) is indeed suppressed to some extent by incorporating Cs ions into the FASnBr3 lattice. 0.9 Cs 0.1 XPS spectra of other elements in SnBr3 thin films are as follows: Figure 4 As shown.

[0060] Example 2

[0061] A highly stable FA 0.9 Cs 0.1 A method for preparing SnBr3:PVK precursor solution, using a one-step spin-coating method to prepare high-quality FA. 0.9 Cs 0.1 The method for using the SnBr3:PVK active layer thin film is as follows:

[0062] First, FABr (0.54M), SnBr2 (0.6M), CsBr (0.06M), and SnF2 (0.06M) were dissolved in N,N-dimethylformamide with PVK at different molar ratios (K = 1:0, 600:1, 300:1, 200:1, and 120:1), and stirred on a magnetic stirrer at 50°C for 12 hours to ensure complete dissolution. Then, the above FABr was filtered through a 0.45μm nylon filter. 0.9 Cs 0.1 The SnBr3:PVK mixed precursor solution was filtered. Then the filtered FA... 0.9 Cs 0.1The SnBr3:PVK precursor solution was spin-coated onto a glass substrate at 1000 rpm for 30 seconds, and then annealed on a hot plate at 70°C for 1 hour.

[0063] The FASnBr3, FA 0.9 Cs 0.1 SnBr3 and FA 0.9 Cs 0.1 The UV-Vis absorption spectrum of SnBr3:PVK material is as follows: Figure 5 As shown in (a). Meanwhile, by Figure 5 (b) It can be seen that FA 0.9 Cs 0.1 The band gap of SnBr3:PVK is approximately 2.24 eV.

[0064] The FA 0.9 Cs 0.1 SEM images of SnBr3:PVK films are shown below. Figure 6 As shown, Figure 6 (a)-6(e) revealed the incorporation of PVK in different molar ratios into FA. 0.9 Cs 0.1 FA in SnBr3 0.9 Cs 0.1 SEM images of SnBr3:PVK films; (a) K = 1:0; (b) K = 600:1; (c) K = 300:1; (d) K = 200:1; (e) K = 120:1. From Figure 6 It can be seen that when FA 0.9 Cs 0.1 When the molar ratio K of SnBr3 to PVK is less than 300:1, the above FA 0.9 Cs 0.1 SnBr3:PVK films have high quality, and when FA 0.9 Cs 0.1 The film quality is highest when the molar ratio of SnBr3 to PVK is 300:1; however, when FA... 0.9 Cs 0.1 When the molar ratio of SnBr3 to PVK is 120:1, FA 0.9 Cs 0.1 The quality of SnBr3:PVK films began to decline, FA 0.9 Cs 0.1 Obvious cracks appeared in the SnBr3:PVK film.

[0065] Depend on Figure 7 FA 0.9 Cs 0.1High-resolution scanning electron microscopy (HRSEM) images of SnBr3:PVK bulk heterojunctions under different PVK doping concentrations show that PVK incorporation has a significant impact on FA. 0.9 Cs 0.1 The improvement in film-forming properties of SnBr3 films is particularly significant. Figure 7 This demonstrates that the incorporation of a certain concentration of PVK significantly improves FA. 0.9 Cs 0.1 The film-forming properties of SnBr3 thin films. The quality of the active layer thin film plays a crucial role in the performance of photodetectors. The presence of pores and cracks on its surface will cause a large number of defects. These defects not only lead to higher dark current, but also become recombination centers for photogenerated carriers, resulting in lower photocurrent. The appropriate concentration of PVK doping will improve the performance of the photodetector. 0.9 Cs 0.1 The SnBr3 active layer exhibits a certain passivation effect, meaning that the film-forming properties of the active layer film are greatly improved; simultaneously, PVK and FA... 0.9 Cs 0.1 The bulk heterojunction formed by SnBr3 can further improve the carrier separation efficiency and ultimately realize the fabrication of high-performance tin-based perovskite photodetectors.

[0066] At different PVK doping concentrations (0–5.0 mM), the FA 0.9 Cs 0.1 The XRD pattern of the SnBr3:PVK bulk heterojunction film is shown below. Figure 8 As shown in the figure. This figure demonstrates that the incorporation of low concentrations of PVK does not affect FA. 0.9 Cs 0.1 The crystallization of SnBr3 has an impact; once FA 0.9 Cs 0.1 When the molar ratio of SnBr3 to PVK is below 300:1, its crystallinity decreases sharply; moreover, when the above molar ratio is below 120:1, FA is almost impossible to observe. 0.9 Cs 0.1 The diffraction peak of SnBr3, i.e., FA 0.9 Cs 0.1 The diffraction peaks of SnBr3 were completely obscured by the diffraction peaks of PVK.

[0067] Example 3

[0068] A method for fabricating a high-performance tin-based perovskite photodetector, wherein a high-quality FA is prepared by a one-step spin-coating method. 0.9 Cs 0.1 SnBr3:PVK is used as the active layer of the device, and the method is as follows:

[0069] Firstly, FABr (0.54 M), SnBr2 (0.6 M), CsBr (0.06 M), SnF2 (0.06 M) and PVK with a concentration of 2.0 mM were dissolved in N, N-dimethylformamide and stirred on a magnetic stirrer at 50°C for 12 hours to make them completely dissolved. Before use, the FA 0.9 Cs 0.1 SnBr3:PVK precursor solution was filtered using a 0.45 μm nylon filter head.

[0070] A method for preparing a high-performance tin (II) -based perovskite photodetector, the preparation steps of the method are as follows:

[0071] (1) The 110 nm ITO patterned glass substrate was ultrasonically cleaned with deionized water, isopropanol, acetone and ethanol respectively for 15 minutes, and then dried with nitrogen and placed in a UV ozone cabinet for 10 minutes before the next experiment.

[0072] (2) 0.5 M zinc acetate hydrate was added to a mixed solution containing 96% (volume fraction) ethylene glycol methyl ether and 4% (volume fraction) ethanolamine, and stirred until it was completely dissolved. Then 100 μL of the precursor solution was spin-coated at a speed of 2000 rpm for 30 seconds, and then placed on a hot stage at 300°C for annealing for 5 minutes. Finally, the residue was cleaned with deionized water, acetone and ethanol respectively, and then placed on a hot stage at 100°C for drying for 5 minutes to obtain a ZnO electron transport layer.

[0073] (3) The prepared FA 0.9 Cs 0.1 SnBr3:PVK precursor solution was spin-coated on the ZnO film at a speed of 1000 rpm for 30 seconds, and finally annealed on a hot stage at 70°C for 1 hour.

[0074] (4) The MoO3 hole transport layer material was prepared on the above prepared FA 0.9 Cs 0.1 SnBr3:PVK film surface by thermal evaporation method, with a thickness of about 70 nm.

[0075] (5) A 120 nm gold top electrode was thermally evaporated onto the hole transport layer MoO3 through a mask plate, and finally a high-performance tin-based perovskite photodetector was obtained, and its structure is shown in Figure 9 .

[0076] The UPS spectrum of the FA 0.9 Cs 0.1 SnBr3:PVK film is shown in Figure 10As shown, the conduction band and valence band of the sample are calculated to be-3.38 eV and-5.62 eV, respectively. Figure 11 The energy band diagram of the photodetector is shown in the following.

[0077] The FA-based 0.9 Cs 0.1 The I-V curve of the photodetector prepared by SnBr3: PVK under 405 nm light irradiation is shown in the following. Figure 12 As shown, the photocurrent of the photodetector gradually increases with the increase of light intensity.

[0078] In order to evaluate the performance of the self-driven photodetector, the key performance indicators, such as the photosensitivity (K), the photoresponse rate (R) and the specific detectivity (D * ), are described as follows.

[0079] Under the irradiation of incident light, the ratio of the photocurrent generated by the photodetector to the dark current generated by the device in the absence of light is called the "on / off" current ratio, which can also be called the "light / dark" current ratio, and the calculation formula is as follows:

[0080]

[0081] where I ill is the current generated by the device under light, I dark is the dark current through the device in the absence of light, and the difference between the two is the photocurrent I ph . Generally speaking, the larger the "on / off" current ratio, the better the performance of the photodetector. To increase the "on / off" current ratio of the device, two aspects can be considered: one is to increase the photocurrent. Common methods include selecting a carrier transport layer material with a more matched energy band to improve the extraction efficiency of photo-generated carriers; in addition, the purpose of increasing the photocurrent of the device can also be achieved by reducing the defects in the active layer material to reduce the recombination rate of photo-generated carriers. The other is to reduce the dark current. For divalent tin (II) based perovskite, the oxidation of divalent tin will introduce a large number of tin vacancy defects, which will lead to a high dark current of the tin-based perovskite photodetector. Therefore, surface passivation of the active layer is also a means to reduce the dark current of the device.

[0082] Under the irradiation of 405 nm laser with an intensity of 25.3 μW / cm 2 , the K value of the divalent tin (II) based perovskite photodetector of the present embodiment is 298.49, and the K value will increase with the increase of the intensity of the incident light.

[0083] The ratio of the photocurrent generated by the photodetector under illumination to the product of the incident light power and the effective area of the device is defined as the responsivity (R), which can directly reflect the photoelectric conversion capability of the photodetector, and is an important measure of the spectral and frequency characteristics of photoelectric conversion. The calculation formula is:

[0084]

[0085] The signal-to-noise ratio obtained by the photodetector under unit power radiation is called "specific detectivity" (Specific detectivity, D * ), which can also be called "normalized detectivity". It is an important performance parameter of the photodetector, and is an important means to measure its sensitivity and detection capability. The calculation formula is:

[0086]

[0087] Where I p is the photocurrent of the device, I d is the dark current of the device, P opt is the incident light power per unit area (i.e. illumination intensity), A is the effective area of the light incident on the device, and e is the basic charge of an electron.

[0088] Under the illumination of 25.3 μW / cm 2 of 405 nm laser, the tin (II) based perovskite photodetector described in the embodiment obtained a responsivity of 4.09 × 10 2 A / W at -0.2 V, and the corresponding specific detectivity (D * ) was 1.23 × 10 14 Jones. As shown in Figure 13 , the responsivity and specific detectivity both decrease with the increase of the incident light power intensity.

[0089] The I-T curve of the photodetector prepared based on the FA 0.9 Cs 0.1 SnBr3:PVK mixed heterojunction under the illumination of 405 nm light is shown in Figure 14 . Figure 15 is a magnified image of the local I-T curve in Figure 14 . From the figure, it can be seen that the rise time and fall time of the above photodetector are 54.89 ms and 54.85 ms, respectively.

[0090] Ideally, the tin-based perovskite photodetector with a passivated dense thin film on the surface can be summarized as follows: under the irradiation of incident light, there will be the generation of photo-generated carriers in the active layer, and the photo-generated carriers will be rapidly separated at the interface between the active layer and other semiconductor materials. The presence of the electron transport layer and the hole transport layer will make the separated photo-generated carriers flow in opposite directions to form a larger photocurrent. To further improve the performance of the photodetector, firstly, the recombination rate of the photo-generated carriers needs to be reduced; secondly, it is necessary to ensure that the photo-generated carriers have a high separation efficiency, and that the separated photo-generated carriers can quickly reach the electrode and be collected. The PVK is doped into the FA 0.9 Cs 0.1 SnBr3not only improves the quality of the active layer thin film, but also greatly inhibits the surface defects. In addition, the use of the mixed heterojunction also greatly improves the separation efficiency of the photo-generated carriers in the active layer. The use of the ZnO electron transport layer and the MoO3hole transport layer further improves the transport efficiency of the photo-generated carriers in the device.

[0091] Example 4

[0092] In this example, the FA 0.9 Cs 0.1 The concentration ratio of SnBr3and PVK is 600:1, and the rest is the same as in Example 3.

[0093] Under the irradiation of 25.3 μW / cm 2 of 405 nm laser, the tin(II)-based perovskite photodetector in this example obtained a responsivity of 3.11 x 10 2 A / W at -0.2 V, and the corresponding specific detectivity was 5.64 x 10 13 Jones.

[0094] Example 5

[0095] In this example, the FA 0.9 Cs 0.1 The concentration ratio of SnBr3and PVK is 200:1, and the rest is the same as in Example 3.

[0096] Under the irradiation of 25.3 μW / cm 2 of 405 nm laser, the tin(II)-based perovskite photodetector in this example obtained a responsivity of 2.16 x 10 2 A / W at -0.2 V, and the corresponding specific detectivity was 4.42 x 10 13 Jones.

[0097] Comparative Example 1 Comparative Example 1

[0098] In this comparative example, the FA in the active layer 0.9 Cs 0.1 The concentration ratio of SnBr3 to PVK was 1:0, and the rest was the same as in Example 3.

[0099] At 25.3 μW / cm 2 Under 405nm laser irradiation, the tin(II)-based perovskite photodetector described in this embodiment achieved a 1.66×10⁻⁶ Ω·cm laser output at -0.2V. 2 The responsivity of A / W corresponds to a specific detectivity of 7.33 × 10⁻⁶. 12 Jones.

[0100] Comparative Example 2

[0101] In this comparative example, the FA in the active layer 0.9 Cs 0.1 The concentration ratio of SnBr3 to PVK was 120:1, and the rest of the conditions were the same as in Example 3.

[0102] At 25.3 μW / cm 2 Under 405nm laser irradiation, the tin(II)-based perovskite photodetector described in this embodiment achieved a 1.81×10⁻⁶ Ω·cm laser output at -0.2V. 2 The responsivity of A / W corresponds to a specific detectivity of 2.21 × 10⁻⁶. 13 Jones.

[0103] After being doped with different concentrations of PVK, based on FA 0.9 Cs 0.1 Tin(II) based perovskite photodetector ITO / ZnO / FA was prepared by fabricating a bulk heterojunction thin film of SnBr3:PVK. 0.9 Cs 0.1 SnBr3:PVK / MoO3 / Ag.

[0104] The FA-based 0.9 Cs 0.1 SnBr3 and FA 0.9 Cs 0.1 The IV curve of the photodetector prepared by SnBr3:PVK (K=300:1) under no-light conditions is shown below. Figure 16 As shown. When PVK is incorporated into FA 0.9 Cs 0.1 After SnBr3, the current ratio of the above devices at +0.3V / -0.3V voltage increased from the original 18.3 to 337, and the performance was greatly improved.

[0105] After being doped with PVK at different concentrations, based on FA 0.9 Cs 0.1The photodetector fabricated from the SnBr3:PVK bulk heterojunction thin film performs well in the absence of light and at a power of 25.3 μW / cm². 2 The IV characteristic curve under 405nm laser irradiation is as follows Figure 17 As shown.

[0106] For perovskite materials, large grain size, long carrier diffusion distance, high carrier mobility, and dense and uniform active layer films play a crucial role in the performance of perovskite photodetectors. However, the generally rapid crystallization rate of tin-based perovskite materials leads to problems such as poor film coverage and density. These problems not only accelerate the oxidation rate of divalent tin, but also introduce a large number of tin vacancy defects after the oxidation of divalent tin, resulting in persistently high dark current in tin(II)-based perovskite photodetectors. Incorporating a certain concentration of Cs ions into FASnBr3 can significantly improve the film formation properties of tin(II)-based perovskite films. Furthermore, incorporating a certain concentration of PVK into FASnBr3... 0.9 Cs 0.1 After SnBr3, the quality of the tin-based perovskite active layer film was significantly improved, and the dark current of the photodetector also increased from the original 10 -3 The A-level order dropped to 10. -6 The order of magnitude A is mainly due to the difference between PVK and FA. 0.9 Cs 0.1 Surface passivation of SnBr3 significantly reduces the defect density on its thin film surface. This reduction in defect density not only leads to a substantial decrease in the device's dark current but also allows the overall photocurrent to remain at a high level due to the reduction in surface recombination centers. However, with the continuous increase in PVK doping concentration, FA... 0.9 Cs 0.1 The SnBr3 grains appear to be split apart, and the corresponding dark current also shows a certain increase. The above test results indicate that when FA... 1-x When the concentrations of Cs ions and FA cations in CsxSnBr3 are 1:9, FA 1-x Cs x The film-forming properties of SnBr3 tin(II)-based perovskite films can be significantly improved, and the oxidation rate of divalent tin(II) in the perovskite material is also effectively suppressed. To further improve the performance of the above devices, different concentrations of PVK are doped into FA. 0.9 Cs 0.1 Preparation of ITO / ZnO / FA from SnBr3 precursor solution 0.9 Cs 0.1 SnBr3:PVK / MoO3 / Ag photodetector. Through the analysis of FA... 0.9 Cs 0.1The concentration of PVK in SnBr3 precursor solution was optimized, and it was found that the 2.0 mM PVK doped into 0.6 M FA 0.9 Cs 0.1 The photoelectric detector ITO / ZnO / FA prepared in SnBr3 precursor solution 0.9 Cs 0.1 The responsivity R and specific detectivity D of SnBr3:PVK / MoO3 / Ag * respectively reached 4.09×10 2 A / W and 1.23×10 14 Jones. Obviously, the performance of the above photoelectric detector can be greatly improved by surface passivation engineering and application of mixed heterojunction thin film.

[0107] The above is only a specific embodiment of the present application, but not limited thereto. Any simple change, equivalent replacement or modification made on the basis of the present application to solve basically the same technical problem or achieve basically the same technical effect shall fall within the protection scope of the present application.

Claims

1. A divalent tin (II) based perovskite hybrid heterojunction thin film, characterized by: The mixed heterojunction thin film is made of high-stability FA 1-x Cs x SnBr3 tin-based perovskite material and PVK are mixed, the value range of x is 0.05~0.2, FA 1- x Cs x The molar ratio of SnBr3 and PVK is 200:1~600:

1.

2. A divalent tin (II) based perovskite hybrid heterojunction thin film as claimed in claim 1, wherein: x is in the range of 0.1-0.

15.

3. A divalent tin (II) based perovskite hybrid heterojunction thin film as claimed in claim 1, wherein: Highly stable FA 1-x Cs x The molar ratio of SnBr3and PVK is 300: 1 to 400:

1.

4. A method for preparing a divalent tin (II) based perovskite hybrid heterojunction thin film as claimed in any one of claims 1 to 3, characterized in that: The method comprises the following steps: First, the FA 1-x Cs x Each precursor of a tin-based perovskite material SnBr3 is dissolved in a solvent to obtain a perovskite precursor solution, then the PVK solution is mixed and dissolved with the above perovskite precursor solution, and a mixed precursor solution is obtained by filtering with a filter head, finally the above mixed precursor solution is spin-coated on the substrate by one-step spin coating method, and annealed at 70-100℃ for 0.5-1h to obtain a tin(II)-based perovskite mixed heterojunction thin film.

5. The method for preparing a tin(II)-based perovskite hybrid heterojunction thin film as described in claim 4, characterized in that: The concentration of the perovskite precursor solution is 0.4-1M, and the concentration of the PVK solution is less than or equal to 5mM.

6. The method for preparing a tin(II)-based perovskite hybrid heterojunction thin film as described in claim 4, characterized in that: The solvent of the perovskite precursor solution is DMF or DMSO, and the solvent of the PVK solution is DMF.

7. A stacked tin (II) -based perovskite photodetector, characterized in that: The photodetector comprises a metal top electrode, a hole transport layer, a bulk heterojunction active layer, an electron transport layer and a transparent conductive bottom electrode arranged in sequence from top to bottom; wherein the bulk heterojunction active layer is a divalent tin (II) based perovskite hybrid heterojunction film according to any one of claims 1-3.

8. A layered tin (II) -based perovskite photodetector as claimed in claim 7, wherein: The thickness of the metal top electrode is 100-150nm; the thickness of the hole transport layer is 50-100nm; the thickness of the bulk heterojunction active layer is 100-800nm; the thickness of the electron transport layer is 50-250nm; and the thickness of the transparent conductive bottom electrode is 50-120nm. The metal top electrode is Ag, Al or Au; the hole transport layer is MoO3 or NiO; and the electron transport layer is a ZnO or TiO2 film.

9. A layered tin (II) -based perovskite photodetector as claimed in claim 7, wherein: The photodetector is prepared by the following method, and the method steps comprise: (1) an electron transport layer is prepared on a transparent conductive bottom electrode substrate by a sol-gel method; (2) a mixed precursor solution is spin-coated on the electron transport layer by a one-step spin coating method to obtain a mixed bulk heterojunction active layer; (3) a hole transport layer is prepared on the bulk heterojunction active layer by a thermal evaporation method; (4) a metal top electrode is prepared on the hole transport layer by a thermal evaporation method using a mask plate to obtain a stacked tin-based perovskite photodetector.

10. A layered tin (II) -based perovskite photodetector as claimed in claim 9, wherein: In step (1), the spin coating speed is 1500-2500rpm, and the spin coating time is 20-60s; in step (2), the spin coating speed is 800-2000rpm, and the spin coating time is 20-60s.

Images