Inverse opal structure lead-free double-perovskite near-infrared photoelectric detector for pulse monitoring, and preparation method and application of inverse opal structure lead-free double-perovskite near-infrared photoelectric detector

Abstract

The invention discloses a lead-free double-perovskite near-infrared photoelectric detector with an inverse opal structure for pulse monitoring and a preparation method and application thereof, and belongs to the technical field of design and preparation of photoelectric detectors. The photoelectric detector is mainly composed of a conductive glass substrate, an electron transport layer, a perovskite layer of an inverse opal structure, a hole transport layer and a silver electrode layer. According to the inverse opal structure lead-free double-perovskite near-infrared photoelectric detector combined with the organic conjugated polymer, the light field regulation and control characteristic of the photonic crystal is utilized, the near-infrared light absorption efficiency is improved, meanwhile, the perovskite film quality is optimized, defects are reduced, and the photoelectric conversion performance is improved. The pulse monitoring device prepared by the method can realize high-precision and real-time pulse signal acquisition, and a more environment-friendly and efficient technical scheme is provided for health monitoring and wearable equipment.

Description

Technical Field

[0001] The present invention belongs to the field of design and preparation of photodetectors, and particularly relates to a lead-free double perovskite near-infrared photodetector with an inverse opal structure for pulse monitoring, a preparation method thereof, and an application thereof. Background Art

[0002] Pulse monitoring technology has wide applications in the fields of medical health, sports monitoring, intelligent wearable devices, etc. Traditional pulse monitoring methods mainly rely on photoplethysmography (PPG), in which a near-infrared light source and a photodetector are the core components. Near-infrared light (NIR) can effectively detect blood flow changes due to its excellent biological tissue penetration, thereby realizing accurate acquisition of pulse signals. Existing near-infrared photodetectors mostly use lead-based perovskite materials or silicon-based detectors. The former has environmental pollution and stability problems, and the latter has limited absorption ability in the near-infrared band, affecting detection sensitivity and signal quality. Lead-free double perovskite (such as Cs2AgBiBr6) is more environmentally friendly because it does not contain heavy metal lead, but due to its large bandgap, it naturally lacks the ability to absorb near-infrared light. In the prior art, doping Sn 2+ can reduce the bandgap of Cs2AgBiBr6, and a photodetector prepared by combining it with an organic conjugated polymer with near-infrared response to form a heterojunction can achieve full-spectrum response from ultraviolet to near-infrared, but doping Sn 2+ is prone to cause irregular holes in the perovskite thin film, resulting in a large number of film defects, which is not conducive to the performance of the photodetector. In addition, the light absorption efficiency of planar perovskite is limited and it is difficult to meet the high-performance requirements. Photonic crystals, especially inverse opal structures, are nano-microstructured materials with a spatially periodic arrangement, which can modulate electromagnetic waves through periodic dielectric constant changes to form a photonic bandgap. At specific frequencies near the photonic bandgap, the group velocity of photons will be significantly reduced, thereby enhancing the local light field and improving the light absorption ability. Introducing photonic crystals into photodetectors can not only improve the light absorption efficiency, but also optimize the growth quality of perovskite thin films, reduce film defects, and thus improve the overall performance of photodetectors.

[0003] Based on this, the present invention proposes a lead-free double perovskite near-infrared photodetector with an inverse opal structure for pulse monitoring, a preparation method thereof, and an application thereof. By utilizing the light field regulation characteristics of photonic crystals, the near-infrared light absorption efficiency is improved, while the quality of perovskite thin films is optimized, defects are reduced, and the photoelectric conversion performance is improved, providing an innovative solution for high-sensitivity and environmentally friendly pulse monitoring. Summary of the Invention

[0004] Aiming at the pollution problems caused by lead-based perovskites to the human body and the environment during the preparation process in the prior art, as well as the defect of poor stability of tin-based perovskites, the present invention provides an anti-opal structured lead-free double perovskite near-infrared photodetector for pulse monitoring, its preparation method and application. The present invention designs an IO-Cs2AgBiBr6:Sn / PDPP3T photodetector, in which the anti-opal structure can effectively enhance the light absorption ability, and PDPP3T, as the near-infrared light absorption layer and hole transport layer, can expand the response range of the lead-free double perovskite detector. Under the irradiation of an 808 nm near-infrared laser, the light-to-dark current ratio is 1×10 6 , and the detectivity is 4.0×10 12 Jones, and the performance remains 88% after being placed in air for 2 months. Based on its excellent near-infrared photodetection performance, the present invention can be applied to non-invasive pulse monitoring, and high-precision and real-time pulse signal acquisition can be achieved under both resting and exercise conditions, providing a more environmentally friendly and efficient technical solution for health monitoring and wearable devices.

[0005] In order to achieve the above invention purpose, the present invention provides the following technical solutions: A lead-free double perovskite near-infrared photodetector with an anti-opal structure for pulse monitoring, the detector mainly consists of a substrate, a conductive anode, an electron transport layer, an anti-opal structured lead-free double perovskite light absorption layer, a hole transport layer and a metal cathode arranged in sequence; the anti-opal perovskite light absorption layer is Sn 2+ -doped Cs2AgBiBr6, and the hole transport layer is PDPP3T, which also serves as the near-infrared light absorption layer in this device.

[0006] Furthermore, the anti-opal structured lead-free double perovskite light absorption layer is obtained by using polystyrene spheres as a soft template, filling the gaps between the polystyrene spheres with a perovskite precursor solution, and then removing the soft template. The thickness of the anti-opal structured lead-free double perovskite light absorption layer is 150~600 nm.

[0007] Furthermore, the substrate is glass or a transparent flexible material, the flexible material is one or more of polyimide, polydimethylsiloxane and polyethylene terephthalate, the conductive anode is ITO or FTO, the electron transport layer is TiO2 or SnO2, and the thickness is 50~200 nm; the thickness of the hole transport layer is 100~300 nm; the metal cathode is Ag or Au, and the thickness is 100~200 nm.

[0008] A preparation method of a lead-free double perovskite near-infrared photodetector with an anti-opal structure for pulse monitoring, the process is as follows: (1) Prepare a TiO2 or SnO2 electron transport layer on a cleaned and pretreated ITO or FTO substrate; (2) Drop the PS sphere solution onto the surface of deionized water. Wait for an ordered monolayer PS film to form at the air-water interface. Then drop the sodium dodecyl sulfate solution to promote the dense arrangement of PS spheres. Tilt the substrate and pick up the PS monolayer film on the electron transport layer. Dry it at 55 - 65 °C for 5 - 30 min to form a PS thin film. (3) Spin-coat the Cs2AgBiBr6-Sn precursor solution on the PS thin film. Anneal it at 250 - 270 °C for 1 - 2 min. Then soak the sample in chlorobenzene for 5 - 15 min to remove the PS template. Anneal it again at 250 - 270 °C for 5 - 15 min to obtain FTO / TiO2 / IO-CABB-Sn. (4) Spin-coat the PDPP3T solution on FTO / TiO2 / IO-CABB-Sn and perform annealing treatment to form a PDPP3T hole transport layer. Use the vacuum thermal evaporation method to evaporate the electrode on the hole transport layer to complete the device preparation.

[0009] Further, in step (1), the ITO or FTO substrate is ultrasonically cleaned successively with absolute ethanol, conductive glass cleaner, and deionized water, dried with nitrogen, and then treated with ultraviolet-ozone for 10 - 20 minutes.

[0010] Further, in step (1), the electron transport layer is TiO2, which consists of a dense TiO2 layer and a mesoporous TiO2 layer. The preparation process of the dense TiO2 layer precursor solution is as follows: Mix absolute ethanol, tetrabutyl titanate, concentrated nitric acid, and ultrapure water in a volume ratio of (4 - 6):1:(0.1 - 0.3):(0.1 - 0.3). The mesoporous TiO2 layer precursor solution is obtained by mixing deionized water and TiO2 slurry in a mass ratio of (6 - 8):1. First, spin-coat the dense TiO2 layer precursor solution on the substrate and anneal it at 490 - 510 °C for 20 - 40 minutes. Then spin-coat the mesoporous TiO2 layer precursor solution on the dense TiO2 layer. First, anneal it at 90 - 110 °C for 5 - 15 minutes, and then anneal it at 490 - 510 °C for 20 - 40 minutes to obtain the TiO2 electron transport layer.

[0011] Specifically, the preparation process of the dense TiO2 layer precursor solution in step (1) is as follows: Mix absolute ethanol, tetrabutyl titanate, concentrated nitric acid, and ultrapure water in a ratio of 5:1:0.2:0.1. After spin-coating the dense TiO2 layer precursor solution, anneal it at 500 °C for 30 min. The mesoporous TiO2 layer precursor solution is obtained by stirring and mixing absolute ethanol and TiO2 slurry in a mass ratio of 7:1. After spin-coating the mesoporous TiO2 layer precursor solution, first anneal it at 100 °C for 10 minutes and then at 500 °C for 30 minutes.

[0012] Further, in step (2), the concentration of the PS sphere solution is 1-2 wt%, and the diameter of the PS spheres is 300-1500 nm; the preparation process of the sodium dodecyl sulfate solution is as follows: dissolve sodium dodecyl sulfate in a solvent of ethanol and deionized water with a volume ratio of (1-2):(1-2), and the concentration of sodium dodecyl sulfate is 1-3 g / L.

[0013] Specifically, in step (2), the PS sphere precursor solution is prepared by diluting the original PS sphere solution with different diameters at a concentration of 5% to 1.5% with a water / ethanol mixed solution (volume ratio 1:1). The concentration of the sodium dodecyl sulfate (SDS) aqueous solution is 2 g / L. The annealing treatment means annealing at 60 °C on a hot plate for 10 minutes.

[0014] Further, in step (3), the concentration of the Cs2AgBiBr6-Sn precursor solution is 0.2-0.4 mol / L, and the molar doping concentration of Sn is 35-55%.

[0015] Further, the preparation process of the Cs2AgBiBr6-Sn precursor solution in step (3) is as follows: dissolve CsBr, BiBr3, AgBr, and SnBr2 in DMSO according to a molar ratio of 2:1:1:(0.35-0.55), and stir at 65-75 °C for 2-4 h to obtain a 0.2-0.4 mol / L Cs2AgBiBr6-Sn precursor solution.

[0016] Specifically, the preparation process of the Cs2AgBiBr6-Sn precursor solution in step (3) is as follows: dissolve CsBr, BiBr3, and AgBr in DMSO according to a molar ratio of 2:1:1:0.45, and stir magnetically at 70 °C for 3 h to obtain a 0.3 mol / L Cs2AgBiBr6-Sn precursor solution. The annealing treatment means annealing at 250 °C on a hot plate.

[0017] Further, in step (4), dissolve PDPP3T in a mixed solvent of chloroform and ortho-dichlorobenzene with a volume ratio of 1:(3-5), and stir in the dark at 65-75 °C for 5-7 hours to prepare a PDPP3T solution with a concentration of 4-6 mg / mL; the annealing treatment means annealing at 95-105 °C for 5-15 min.

[0018] Specifically, the concentration of the PDPP3T solution in step (4) is 5 mg / mL. The annealing treatment means annealing at 100 °C on a hot plate.

[0019] The above preparation method yields a lead-free double perovskite photodetector with an inverse opal structure. The schematic diagram of its preparation steps is as Figure 1 shown.

[0020] Application of the above-mentioned lead-free double perovskite near-infrared photodetector with an inverse opal structure for pulse monitoring in human pulse monitoring. It includes a dark box, a near-infrared light source, a Keithley 2400 source meter. Two electrodes of the Keithley 2400 source meter are connected to the lead-free double perovskite near-infrared photodetector with an inverse opal structure. The near-infrared light source and the lead-free double perovskite near-infrared photodetector with an inverse opal structure are located inside the dark box, and the wavelength of the near-infrared light source is 808 nm.

[0021] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are as follows: 1. For the first time, PS spheres are used as a soft template to construct a lead-free double perovskite photodetector with an inverse opal structure. By adjusting the diameter of the PS spheres and optimizing the quality of the perovskite thin film, non-radiative recombination and dark current are effectively reduced, and the device stability is improved. PDPP3T fills the holes in the perovskite thin film, increases the contact area of the heterojunction, and improves the transport efficiency of photo-generated carriers, thus significantly improving the performance of the photodetector. The slow photon effect of the inverse opal structure enhances the light absorption ability. Its photon bandgap coincides with the absorption range of PDPP3T, realizing more efficient photoelectric conversion and improving the near-infrared response sensitivity.

[0022] 2. The invented IO-CABB-Sn photodetector exhibits excellent performance under 808 nm light illumination. The specific experimental results are shown in Table 1. The light-to-dark current ratio reaches 1×10 6 , the detectivity is 4.0×10 12 Jones, and the linear dynamic range (LDR) is 152.1 dB. It has good long-term stability: the performance remains 88% after being placed in an air environment for 2 months. This device reaches the leading level in the field of near-infrared lead-free double perovskite photodetectors, and at the same time overcomes the environmental instability of tin-lead-based perovskites and the potential hazards of lead to the human body and the ecosystem.

[0023] 3. The optimized FTO / TiO2 / IO-CABB-Sn / PDPP3T / Ag photodetector exhibits excellent near-infrared detection ability and is used for high-sensitivity photodetection applications. Based on this detector, the present invention further develops a precise non-invasive pulse monitoring device, which can be used for human health monitoring and realizes efficient and non-invasive physiological signal detection. Brief Description of the Drawings

[0024] Figure 1 It is a schematic diagram of the preparation process of the FTO / TiO2 / IO-CABB-Sn / PDPP3T thin film; Figure 2SEM photos of PS soft template layers (FTO / TiO2 / PS) with diameters of 300, 500, and 1000 nm and FTO / TiO2 / IO-CABB-Sn; Figure 3 Among them: a is the cross-sectional view of FTO / TiO2 / PS1000, and the inset is the optical photo of 1000 nm PS spheres on the substrate. b is the cross-sectional view of FTO / TiO2 / IO1000-CABB-Sn; Figure 4 Among them: a is the absorption spectrum of the FTO / TiO2 / PS thin film, and b is the absorption spectrum of FTO / TiO2 / IO-CABB-Sn; Figure 5 is the curve of the change of the photodetector current with time tested under an 808 nm laser with an illumination intensity of 35 mW / cm 2 Table 1 shows the detailed performance parameters; Figure 6 is the optical response speed of Comparative Example 1 and Example 3; Figure 7 is the performance test of Example 3 after being placed in an air environment for 2 months; Figure 8 is the schematic diagram of the device for near-infrared photodetector pulse monitoring; Figure 9 is the pulse signal obtained by using the near-infrared photodetector to monitor the human body at rest and the pulse signal measured by the smart watch; Figure 10 is the pulse signal obtained by using the near-infrared photodetector to monitor the human body after 3 minutes of exercise and the pulse signal measured by the smart watch; Figure 11 is the information diagram of the cardiac cycle obtained by amplifying the pulse signal after 3 minutes of exercise for analysis; Detailed implementation manners

[0025] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0026] The preparation of a lead-free double perovskite near-infrared photodetector with an inverse opal structure involves the following raw materials: Solution A (dense layer TiO2 precursor solution): Prepared by mixing 2.5 mL of absolute ethanol, 0.5 mL of tetrabutyl titanate, 0.1 mL of nitric acid (commercially available concentrated nitric acid), and 50 μL of ultrapure water, and stirring at room temperature for 6 h.

[0027] Solution B (mesoporous layer TiO2 precursor solution): Prepared by mixing TiO2 slurry (model 30NR-D, purchased from Xi'an Baolai Optoelectronic Technology Co., Ltd.) and absolute ethanol in a weight ratio of 1:7, and stirring at room temperature for 6 hours.

[0028] Solution C (polystyrene sphere aqueous solution): Precursor solutions of PS spheres with different diameters were prepared by diluting a 5 wt% PS stock solution (purchased from Shanghai Huizhi Biotechnology Co., Ltd.) to 1.5 wt% with a water / ethanol mixed solution (volume ratio 1:1). Among them, PS sphere solutions with diameters of 300 nm (C1), 500 nm (C2), and 1000 nm (C3) were prepared respectively.

[0029] Solution D (sodium dodecyl sulfate (SDS) aqueous solution): 0.02 g of SDS was dissolved in a solvent mixture of 10 mL of ethanol and deionized water in a volume ratio of 1:1.

[0030] Solution E (perovskite precursor solution): CsBr (76.6 mg, 0.36 mmol), AgBr (33.8 mg, 0.18 mmol), BiBr3 (80.7 mg, 0.18 mmol), and SnBr2 (22.6 mg, 0.081 mmol) were dissolved in 600 μL of dimethyl sulfoxide (DMSO), and stirred at 70 °C for 3 h in a glove box to obtain a 0.3 mol / L Cs2AgBiBr6-Sn precursor solution (CABB-Sn).

[0031] Solution F (PDPP3T solution): 5 mg of poly(diketopyrrolopyrrole-terthiophene) (PDPP3T) (purchased from Beijing Shuolun Organic Optoelectronic Technology Co., Ltd.) was dissolved in 1 mL of a mixed solvent of chloroform and ortho-dichlorobenzene in a volume ratio of 1:4, and stirred at 70 °C in the dark for 6 hours.

[0032] According to the use of PS sphere precursor solutions with different diameters corresponding to Example 1, Example 2, and Example 3, the preparation process is as Figure 1 shown.

[0033] Example 1: (1)Prepare the FTO substrate: Ultrasonically clean the FTO surface with absolute ethanol, conductive glass cleaner, and deionized water for 20 minutes in sequence. After drying with nitrogen, treat it with UV-O3 for 15 minutes to remove residual organic substances and increase the hydrophilicity of the glass surface.

[0034] (2)Prepare the TiO2 electron transport layer: Spin-coat 30 μL of Solution A on the FTO glass at 4000 rpm for 30 seconds. Subsequently, anneal it in a muffle furnace at 500 °C for 30 min to obtain dense TiO2 (m-TiO2). Then spin-coat 35 μL of Solution B on the m-TiO2 at 3000 rpm for 30 s, place it on a heating plate at 100 °C and anneal for 10 min, and then anneal it in a muffle furnace at 500 °C for 30 min to obtain a TiO2 electron transport layer with a thickness of about 100 nm, namely FTO / TiO2.

[0035] (3)Prepare the opal soft template layer: As Figure 1 shown, use the dipping method to assemble a single-layer PS template on the FTO / TiO2 substrate. Slowly inject 60 μL of Solution C1 with a diameter of 300 nm onto the surface of deionized water. After an ordered single layer is formed at the air-water interface, add 6 μL of Solution D to the petri dish to form a dense and ordered single-layer PS film. Incline the substrate and place it in water to slowly pick up the PS single layer and dry it at 60 °C for 10 minutes to obtain the FTO / TiO2 / PS300 film. The scanning electron microscope (SEM) image is as Figure 2 shown, and the absorption spectrum is as Figure 4 shown in a.

[0036] (4)Prepare the perovskite light-absorbing layer with an inverse opal structure: Spin-coat 55 μL of Solution E on the FTO / TiO2 / PS300 film in a glove box at 3000 rpm for 60 s, then anneal it on a heating plate at 260 °C for 1 min. Immerse the sample in chlorobenzene for 10 min to remove the PS template, and then anneal it on a heating plate at 260 °C for 10 min to obtain a perovskite light-absorbing layer with an inverse opal structure (IO300-CABB-Sn) with a thickness of about 500 nm. The absorption spectrum is as Figure 4 shown in b of

[0037] (5)Prepare the PDPP3T hole transport layer and the electrode: Drop 45 μL of Solution F on the FTO / TiO2 / IO300-CABB-Sn, spin-coat it at 3000 rpm for 30 s, and then anneal it on a heating plate at 100 °C for 10 min to obtain a PDPP3T hole transport layer with a thickness of about 180 nm. Evaporate an Ag electrode with a thickness of about 150 nm on the hole transport layer by vacuum thermal evaporation. Finally, obtain an effective photosensitive area of 0.04 cm 2 .

[0038] Example 2: (1) Prepare the FTO substrate: Ultrasonically clean the FTO surface with absolute ethanol, conductive glass cleaner, and deionized water for 20 minutes in sequence. After drying with nitrogen, treat it with UV-O3 for 15 minutes to remove residual organic matter and increase the hydrophilicity of the glass surface.

[0039] (2) Prepare the TiO2 electron transport layer: Spin-coat 30 μL of Solution A on the FTO glass at 4000 rpm for 30 seconds. Subsequently, place it in a muffle furnace and anneal at 500 °C for 30 min to obtain dense TiO2 (m-TiO2). Then spin-coat 35 μL of Solution B on m-TiO2 at 3000 rpm for 30 s, place it on a heating table at 100 °C and anneal for 10 min, and then anneal in a muffle furnace at 500 °C for 30 min to obtain a TiO2 electron transport layer with a thickness of about 100 nm, namely FTO / TiO2.

[0040] (3) Prepare the opal soft template layer: Adopt the dipping method to assemble a single-layer PS template on the FTO / TiO2 substrate. Slowly inject 60 μL of Solution C2 with a diameter of 500 nm onto the surface of deionized water. After an ordered single layer is formed at the air-water interface, add 6 μL of Solution D to the petri dish to form a dense and ordered single-layer PS film. Tilt the substrate and slowly pick up the PS single layer in water and dry it at 60 °C for 10 minutes to obtain the FTO / TiO2 / PS500 film. The electron scanning microscope (SEM) photograph is as Figure 2 shown, and the absorption spectrum is as Figure 4 shown in a of

[0041] (4) Prepare the perovskite light-absorbing layer with an inverse opal structure: Spin-coat 55 μL of Solution E on the FTO / TiO2 / PS500 film at 3000 rpm in a glove box for 60 s, then anneal on a hot plate at 260 °C for 1 min. Immerse the sample in chlorobenzene for 10 min to remove the PS template, and then anneal on a hot plate at 260 °C for 10 min to obtain a perovskite light-absorbing layer with an inverse opal structure (IO500-CABB-Sn) with a thickness of about 500 nm. The absorption spectrum is as Figure 4 shown in b of

[0042] (5) Preparation of the PDPP3T hole transport layer and the electrode: 45 μL of solution F was dropped onto FTO / TiO2 / IO300-CABB-Sn, spin-coated at 3000 rpm for 30 s, and then annealed on a hot plate at 100 °C for 10 min to obtain a PDPP3T hole transport layer with a thickness of approximately 180 nm. An Ag electrode with a thickness of approximately 150 nm was deposited on the hole transport layer by vacuum thermal evaporation. Finally, an effective photosensitive area of 0.04 cm 2 .

[0043] Example 3: (1) Preparation of the FTO substrate: The surface of the FTO was ultrasonically cleaned with absolute ethanol, conductive glass cleaner, and deionized water for 20 minutes in sequence. After drying with nitrogen, it was treated with UV-O3 for 15 minutes to remove residual organic substances and increase the hydrophilicity of the glass surface.

[0044] (2) Preparation of the TiO2 electron transport layer: 30 μL of solution A was spin-coated on the FTO glass at 4000 rpm for 30 s. Subsequently, it was placed in a muffle furnace and annealed at 500 °C for 30 min to obtain dense TiO2 (m-TiO2). Then, 35 μL of solution B was spin-coated on m-TiO2 at 3000 rpm for 30 s, placed on a hot plate at 100 °C and annealed for 10 min, and then annealed in a muffle furnace at 500 °C for 30 min to obtain a TiO2 electron transport layer with a thickness of approximately 100 nm, namely FTO / TiO2.

[0045] (3) Preparation of the opal soft template layer: The monolayer PS template was assembled on the FTO / TiO2 substrate by the dipping method. 60 μL of solution C3 with a diameter of 1000 nm was slowly injected onto the surface of deionized water. After an ordered monolayer was formed at the air-water interface, 6 μL of solution D was added to the petri dish to form a dense and ordered monolayer PS film. The substrate was tilted and placed in water, and the PS monolayer was slowly picked up and dried at 60 °C for 10 minutes to obtain the FTO / TiO2 / PS1000 film. The electron scanning microscope (SEM) photograph is as Figure 2 shown, and the cross-sectional view is as Figure 3 shown in a of Figure 4 shown in a of

[0046] (4) Preparation of perovskite light-absorbing layer with inverse opal structure: In a glove box, 55 μL of Solution E was spin-coated onto the FTO / TiO2 / PS1000 film at 3000 rpm for 60 s, and then annealed on a hot plate at 260 °C for 1 min. The sample was immersed in chlorobenzene for 10 min to remove the PS template, and then annealed on a hot plate at 260 °C for 10 min to obtain a perovskite light-absorbing layer (IO1000-CABB-Sn) with an inverse opal structure and a thickness of about 500 nm. The scanning electron microscope (SEM) image is as shown in Figure 2 shown, and the cross-sectional view is as shown in Figure 3 b in Figure 4 . The absorption spectrum is as shown in

[0047] b in 2 .

[0048] Figure 2 are scanning electron microscope (SEM) images of PS soft template layers (FTO / TiO2 / PS) with diameters of 300, 500, and 1000 nm and FTO / TiO2 / IO-CABB-Sn; it can be seen that the PS spheres are periodically and uniformly arranged on the substrate. After removing the soft template, the IO-CABB-Sn film not only has good film quality but also retains a penetrable pore structure.

[0049] Figure 3 a in

[0050] Figure 4In it, a is the absorption spectrum of the FTO / TiO2 / PS thin film. PS spheres with different diameters lead to the spatial periodicity of the refractive index due to the periodic arrangement of close packing, forming a photonic band gap (PBG). The PBG can reduce the group velocity of photons at wavelengths near it, so that the light absorption in a specific band can be improved by adjusting the diameter of the PS spheres. The PS thin films of 300, 500, and 1000 nm respectively improve the light absorption at about 405, 639, and 861 nm, proving the successful preparation of the photonic crystal soft template. Figure 4 In it, b is the absorption spectrum of FTO / TiO2 / IO-CABB-Sn. Due to the presence of the soft template, the absorption of the perovskite is improved, and there is an additional absorption peak near 861 nm, representing the successful preparation of the inverse protein perovskite. In addition, the range of its enhanced light absorption coincides exactly with the absorption range of PDPP3T, which is beneficial to enhancing the near-infrared light absorption of PDPP3T.

[0051] Comparative Example 1 Prepare a planar structure FTO / TiO2 / CABB-Sn / PDPP3T / Ag photodetector.

[0052] (1) Prepare the FTO substrate: ultrasonically clean the FTO surface with absolute ethanol, conductive glass cleaner, and deionized water in sequence for 20 minutes. After drying with nitrogen, treat it with UV-O3 for 15 minutes to remove residual organic substances and increase the hydrophilicity of the glass surface.

[0053] (2) Prepare the TiO2 electron transport layer: Spin-coat 30 μL of Solution A on the FTO glass at 4000 rpm for 30 seconds. Subsequently, place it in a muffle furnace and anneal it at 500 °C for 30 min to obtain dense TiO2 (m-TiO2). Then spin-coat 35 μL of Solution B on m-TiO2 at 3000 rpm for 30 s, place it on a heating table at 100 °C and anneal it for 10 min, and then anneal it in a muffle furnace at 500 °C for 30 min to obtain a TiO2 electron transport layer with a thickness of about 100 nm, namely FTO / TiO2.

[0054] (3) Perovskite light-absorbing layer: Spin-coat 55 μL of Solution E on FTO / TiO2 at 3000 rpm in a glove box for 60 s, and anneal it on a hot plate at 260 °C for 10 min to obtain a perovskite light-absorbing layer with a thickness of about 500 nm (FTO / TiO2 / CABB-Sn).

[0055] (4) Preparation of the PDPP3T hole transport layer and the electrode: 45 μL of solution F was dropped onto FTO / TiO2 / CABB-Sn, spin-coated at 3000 rpm for 30 s, and then annealed on a hot plate at 100 °C for 10 min to obtain a PDPP3T hole transport layer with a thickness of approximately 180 nm. An Ag electrode with a thickness of 150 nm was deposited on the hole transport layer by vacuum thermal evaporation to obtain FTO / TiO2 / CABB-Sn / PDPP3T / Ag. The effective photosensitive area was 0.04 cm 2 .

[0056] The photodetectors prepared in Comparative Example 1 and Examples 1 - 3 were tested for the change curve of the photodetector current with time under an 808 nm laser with an illumination intensity of 35 mW / cm 2 , and the performance parameters are as Figure 5 shown in Table 1.

[0057] Table 1. Performance parameters of Comparative Example 1 and Examples 1 - 3 The photocurrents of the photodetectors in Examples 1 and 2 were both smaller than that of the planar CABB-Sn photodetector in Comparative Example 1. This was mainly because the smaller pore size of the perovskite inverse opal prevented the upper layer of PDPP3T from penetrating into the perovskite pores, hindering the transport of photo-generated carriers. However, the IO1000-CABB-Sn photodetector in Example 3 had better optoelectronic performance under an 808 nm laser, with a detectivity of 4.0×10 12 Jones. Its photocurrent was 7.7 times higher than that of the planar CABB-Sn, and the on / off current ratio reached 10 6 . This was mainly due to the larger pore size of the inverse opal, which allowed PDPP3T to penetrate into the perovskite pores, increasing the contact area between PDPP3T and CABB-Sn and providing more carrier separation areas for the CABB-Sn / PDPP3T heterojunction. In addition, the optical field enhancement range of the 1000 nm pore-size photonic crystal overlapped with the light absorption range of PDPP3T, further enhancing the optoelectronic performance of the device under an 808 nm laser.

[0058] Figure 6 are the optical response speeds of Comparative Example 1 and Example 3; the rise and fall times of the planar CABB-Sn in Comparative Example 1 were 5.16 / 6.34 ms, while the rise and fall times of the IO1000-CABB-Sn in Example 3 were only 1.31 / 0.25 ms, proving that the inverse opal structure provided a faster transport channel for carrier transport, thus improving the response speed of the photodetector.

[0059] Figure 7Performance test after 2 months in air environment for Example 3; its detectivity can still reach 2.26×10 12 Jones, and the responsivity remains 88% of the initial value, proving that the photodetector has good long-term stability.

[0060] Regarding the good optoelectronic performance of Example 3 under 808 nm laser, the present invention provides a pulse monitoring system. Its schematic diagram is shown in Figure 8 , including a dark box, a near-infrared light source, a Keithley 2400 source meter, and two electrodes of the Keithley 2400 source meter are connected to the photodetector. During the test, the finger is placed between the near-infrared light and the prepared photodetector under dark conditions, and the photodetector is connected to the Keithley 2400 source meter to display the current change in real time. The principle is that when the near-infrared light source passes through the finger, due to the different absorption of light by blood, the increase or decrease in blood volume will affect the degree of light absorption, resulting in the change of the photocurrent signal of the photodetector, thereby realizing the monitoring of the heartbeat. As Figure 9 and Figure 10 shown, the peaks and valleys correspond to the times when the arterial blood volume is the smallest and the largest during the cardiac cycle. By collecting the number of cardiac cycles within one minute, the heart rate (BPM) of the human body per minute can be obtained. It can be seen that the BPMs of the tests at rest and 3 minutes after exercise are 74 and 112 respectively, and the test results are highly consistent with the data measured by the smart watch. After magnifying this data as Figure 11 shown, the systolic and diastolic periods in the cardiac cycle are 0.19 seconds and 0.31 seconds respectively. By analyzing the cardiac cycle, it can also be used to evaluate arteriosclerosis, hemodynamic changes, and vascular health status.

[0061] Conclusion: The photocurrent values of Example 1 and Example 2 are both lower than those of the planar structure device in Comparative Example 1. This is mainly attributed to the fact that the inverse opal structure with a smaller pore size restricts the penetration of the organic conjugated polymer PDPP3T into the perovskite pores, resulting in insufficient contact area at the heterojunction interface and hindering the effective transport of photo-generated carriers. In contrast, Example 3 uses an inverse opal structure with a pore size of 1000 nm, and its photocurrent is significantly increased to 238 μA, and the dark current is as low as 2.26×10 -11 A, and the light-to-dark current ratio reaches 1×10 6 , and the detectivity (4.0×10 12 Jones) and the responsivity both reach the optimal level.

[0062] The PDPP3T used in the present invention is not only an infrared light-absorbing layer but also a good hole transport layer. PDPP3T can penetrate into the pores of the perovskite, increasing the contact area between PDPP3T and CABB-Sn, providing more carrier separation area for the CABB-Sn / PDPP3T heterojunction, and facilitating the rapid separation and transport of photo-generated carriers. In addition, the photonic crystal with a pore size of 1000 nm optimizes the film quality of Cs2AgBiBr6-Sn, reduces non-radiative recombination and film defects, and the unique light field regulation effect of the photonic crystal further improves the light absorption ability of the photodetector, synergistically improving the detection performance of the lead-free double perovskite Cs2AgBiBr6 at 808 nm through multiple effects.

[0063] The above are the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A lead-free double perovskite near-infrared photodetector with an inverse opal structure for pulse monitoring, characterized in that, The detector mainly consists of a substrate, a conductive anode, an electron transport layer, an inverse opal structured lead-free double perovskite light-absorbing layer, a hole transport layer, and a metal cathode, which are sequentially arranged; the inverse opal perovskite light-absorbing layer is Sn 2+ -doped Cs2AgBiBr6, and the hole transport layer is PDPP3T, which also serves as a near-infrared light-absorbing layer in this device.

2. The lead-free double perovskite near-infrared photodetector based on the inverse opal structure according to claim 1, wherein The described inverse opal structured lead-free double perovskite light-absorbing layer is obtained by using polystyrene spheres as a soft template, filling the gaps between the polystyrene spheres with a perovskite precursor solution, and then removing the soft template. The thickness of the inverse opal structured lead-free double perovskite light-absorbing layer is 150 - 600 nm.

3. The lead-free double perovskite near-infrared photodetector based on the inverse opal structure according to claim 1, characterized in that The substrate is glass or a transparent flexible material, and the flexible material is one or more of polyimide, polydimethylsiloxane, and polyethylene terephthalate. The conductive anode is ITO or FTO, and the electron transport layer is TiO2 or SnO2; the metal cathode is Ag or Au.

4. The preparation method of the lead-free double perovskite near-infrared photodetector with an inverse opal structure for pulse monitoring according to any one of claims 1 to 3, characterized in that The process is as follows: (1) Prepare a TiO2 or SnO2 electron transport layer on a cleaned and pretreated ITO or FTO substrate. (2) Drop the PS sphere solution onto the surface of deionized water. Wait for an ordered monolayer PS film to form at the air-water interface. Drop the sodium dodecyl sulfate solution to promote the close packing of the PS spheres. Tilt the substrate and pick up the PS monolayer film on the electron transport layer. Dry it at 55 - 65 °C for 5 - 30 min to form a PS film. (3) Spin-coat the Cs2AgBiBr6-Sn precursor solution on the PS film, anneal it at 250 - 270 °C for 1 - 2 min, then immerse the sample in chlorobenzene for 5 - 15 min to remove the PS template, and anneal it again at 250 - 270 °C for 5 - 15 min to obtain FTO / TiO2 / IO-CABB-Sn. (4) Spin-coat the PDPP3T solution on FTO / TiO2 / IO-CABB-Sn, perform annealing treatment to form a PDPP3T hole transport layer, and use vacuum thermal evaporation to deposit an electrode on the hole transport layer to complete the device preparation.

5. The preparation method of the lead-free double perovskite near-infrared photodetector with an inverse opal structure for pulse monitoring according to claim 4, characterized in that, In step (2), the concentration of the PS sphere solution is 1 - 2 wt%, and the diameter of the PS spheres is 300 - 1500 nm; the preparation process of the sodium dodecyl sulfate solution is as follows: dissolve sodium dodecyl sulfate in a solvent of ethanol and deionized water with a volume ratio of (1 - 2):(1 - 2), and the concentration of sodium dodecyl sulfate is 1 - 3 g / L.

6. The preparation method of the lead-free double perovskite near-infrared photodetector with an inverse opal structure for pulse monitoring according to claim 4, characterized in that, In step (3), the concentration of the Cs2AgBiBr6-Sn precursor solution is 0.2 - 0.4 mol / L, and the molar doping concentration of Sn is 35 - 55%.

7. The preparation method of the lead-free double perovskite near-infrared photodetector with an inverse opal structure for pulse monitoring according to claim 4, characterized in that, In step (4), dissolve PDPP3T in a mixed solvent of chloroform and ortho-dichlorobenzene with a volume ratio of 1:(3 - 5), stir it at 65 - 75 °C in the dark for 5 - 7 hours to obtain a PDPP3T solution with a concentration of 4 - 6 mg / mL; the annealing treatment means annealing at 95 - 105 °C for 5 - 15 min.

8. The preparation method of the lead-free double perovskite near-infrared photodetector with an inverse opal structure for pulse monitoring according to claim 4, characterized in that, In step (1), the electron transport layer is TiO2, which consists of a dense layer of TiO2 and a mesoporous layer of TiO2. The preparation process of the dense layer TiO2 precursor solution is as follows: absolute ethanol, tetrabutyl titanate, nitric acid and ultrapure water are mixed according to the volume ratio of (4 - 6):1:(0.1 - 0.3):(0.1 - 0.3). The mesoporous layer TiO2 precursor solution is obtained by mixing absolute ethanol and TiO2 slurry according to the mass ratio of (6 - 8):

1. First, the dense layer TiO2 precursor solution is spin-coated on the substrate, annealed at 490 - 510 °C for 20 - 40 minutes, then the mesoporous layer TiO2 precursor solution is spin-coated on the dense layer TiO2. First, it is annealed at 90 - 110 °C for 5 - 15 minutes, and then annealed at 490 - 510 °C for 20 - 40 minutes to obtain the TiO2 electron transport layer.

9. The method for preparing a lead-free double perovskite near-infrared photodetector with an inverse opal structure for pulse monitoring according to claim 4, characterized in that, The preparation process of the Cs2AgBiBr6-Sn precursor solution in step (4) is as follows: CsBr, BiBr3, AgBr and SnBr2 are respectively dissolved in DMSO according to the molar ratio of 2:1:1:(0.35 - 0.55), and stirred at 65 - 75 °C for 2 - 4 h to obtain a 0.2 - 0.4 mol / L Cs2AgBiBr6-Sn precursor solution.

10. Application of the lead-free double perovskite near-infrared photodetector with an inverse opal structure for pulse monitoring according to any one of claims 1 to 3 in human pulse monitoring.

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