A solar blind ultraviolet photodetector and a preparation method thereof

Abstract

This invention discloses a solar-blind ultraviolet photodetector and its fabrication process, belonging to the field of photoelectric detection technology. The detector comprises a substrate, a bottom electrode, an electron transport layer, a lead-free low-dimensional metal halide active layer, a hole transport layer, and a top electrode arranged sequentially. The lead-free low-dimensional metal halide active layer is a Cs-Cu-I system with a zero-dimensional unit or one-dimensional chain-like crystal structure. The lead-free low-dimensional metal halide active layer is prepared by vacuum deposition of CsI and CuI. The detector of this invention exhibits high detectivity, fast response speed, low dark current, and high spectral selectivity. It achieves controllable fabrication of a high-phase-purity low-dimensional active layer, avoiding solvent residue and phase purity fluctuations problems associated with solution methods. Furthermore, its fabrication process is compatible with flexible substrates, showing significant application prospects in fields such as space communication, environmental monitoring, safety early warning, and wearable devices.

Description

Technical Field

[0001] This invention relates to the field of photoelectric detection technology, specifically to a solar-blind ultraviolet photodetector and its fabrication method. Background Technology

[0002] Solar-blind UV detection holds irreplaceable strategic significance in fields such as missile warning, space communication, high-voltage solar corona monitoring, and precise measurement of environmental ultraviolet radiation. The "solar-blind" band refers to the vacuum ultraviolet region with response wavelengths strictly within the 200-280 nm range. Because the ozone layer in the Earth's atmosphere almost completely absorbs light in this band, the background noise is extremely low, allowing for near-zero background interference and high signal-to-noise ratio monitoring. Currently, mainstream solar-blind detectors primarily rely on wide-bandgap semiconductor materials, such as gallium oxide (Ga2O3) or aluminum gallium nitride (AlGaN). However, Ga2O3 suffers from severe persistent photoconductivity (PPC), resulting in long device response recovery times, and its thin-film growth typically requires high-vacuum or high-temperature epitaxial equipment, making it difficult to adapt to large-area and flexible electronic devices. While lead-based halide perovskites have high photoelectric conversion efficiency, their narrow intrinsic bandgap and strong absorption of visible light necessitate expensive filtering systems to achieve solar-blind functionality. Furthermore, the biotoxicity and environmental sensitivity of lead severely restrict its commercialization process.

[0003] In contrast, non-lead metal halides, represented by cesium-copper-iodine, exhibit superior exciton confinement effects due to their naturally ultrawide bandgap (>3.5 eV) and unique low-dimensional (0D / 1D) electronic structure, enabling microsecond-level responses and picoampere-level dark currents. However, existing methods mostly rely on solution spin-coating / antisolvent-induced crystallization, and the purity, compactness, and batch-to-batch consistency of the thin film phase are significantly affected by the process window and environment, making them difficult to integrate with micro / nano patterned array fabrication. Therefore, a controllable process based on full vacuum deposition is urgently needed to achieve precise construction of low-dimensional phases and build efficient charge-selective heterojunctions, thereby obtaining zero-bias self-powered solar-blind ultraviolet detection. Summary of the Invention

[0004] To address the problems existing in the prior art, the present invention aims to provide a solar-blind ultraviolet photodetector and its fabrication method. The present invention achieves a high-phase-purity, dense and uniform low-dimensional Cs-Cu-I lead-free low-dimensional metal halide active layer by precisely controlling the evaporation flux ratio, deposition rate and film thickness of CsI and CuI. Furthermore, it utilizes the band selectivity formed by ZnO and HT50 and the built-in electric field to achieve high detectivity, high spectral selectivity and zero-bias self-powered operation.

[0005] This invention provides the following technical solution: The present invention provides a solar-blind ultraviolet photodetector, which includes a substrate, a bottom electrode, an electron transport layer (ETL), a lead-free low-dimensional metal halide active layer, a hole transport layer (HTL), and a top electrode arranged sequentially.

[0006] The lead-free low-dimensional metal halide active layer is a Cs-Cu-I system with a zero-dimensional unit or a one-dimensional chain crystal structure. The lead-free low-dimensional metal halide active layer is prepared by vacuum deposition of CsI and CuI, and the molar ratio of Cs to Cu in the lead-free low-dimensional metal halide active layer matches the stoichiometric ratio of the target low-dimensional phase.

[0007] In this invention, a "zero-dimensional unit" refers to a crystal structure unit formed by completely separating isolated anion clusters with cations, such as [Cu₂I₅]. 3- Bitetrahedral clusters were Cs + A zero-dimensional structure formed by the complete encapsulation of cations. A "one-dimensional chain framework" refers to a one-dimensional chain structure formed by anions connected through shared corners or edges, such as [CuI3]. 2- Chain by Cs + One-dimensional structures formed by cation separation. Both of these low-dimensional structures belong to the category of crystal structure dimensions, which is different from the morphological dimensions of one-dimensional nanowires obtained through methods such as catalytic growth.

[0008] Furthermore, the lead-free low-dimensional metal halide active layer is formed by CsI and CuI through dual-source co-evaporation deposition or sequential evaporation combined with solid-phase reaction.

[0009] The dual-source co-evaporation method specifically involves placing CsI and CuI in two independent evaporation sources and simultaneously heating and evaporating them under vacuum conditions. The two vapor streams mix, react, nucleate, and grow on the substrate surface to form a Cs-Cu-I thin film. During the evaporation process, the evaporation rates of the two sources can be monitored in real time using a quartz crystal film thickness gauge, and a feedback control system maintains a stable rate. By adjusting the heating temperature or power of the two sources, the deposition rate ratio of CsI to CuI can be controlled, thereby controlling the stoichiometry of the thin film.

[0010] The sequential evaporation combined with solid-state reaction method specifically involves: first, depositing a CsI thin film on a substrate, followed by a CuI thin film to form a CsI / CuI stack structure; then, through annealing, causing a solid-state reaction between the two films to generate a Cs-Cu-I compound. The ratio of Cs to Cu can be controlled by adjusting the thickness of each layer. Preferably, multiple CsI / CuI stacks can be deposited using a multi-cycle deposition method, followed by uniform annealing.

[0011] Furthermore, the molar ratio of Cs to Cu in the lead-free low-dimensional metal halide active layer is 3:2, and the lead-free low-dimensional metal halide active layer has a zero-dimensional Cs3Cu2I5 crystal structure.

[0012] Furthermore, the molar ratio of Cs to Cu in the lead-free low-dimensional metal halide active layer is 1:2, and the lead-free low-dimensional metal halide active layer has a one-dimensional CsCu2I3 crystal structure.

[0013] Furthermore, the electron transport layer is ZnO, SnO2, or TiO2, with a thickness of 20-50 nm.

[0014] The electron transport layer selectively extracts photogenerated electrons while blocking hole injection, thereby reducing dark current and interface recombination. Preferably, the electron transport layer in this invention is prepared by vacuum deposition.

[0015] Furthermore, the hole transport layer is made of an organic semiconductor material. Preferably, the hole transport layer is made of HT50 or NiO. x The hole transport layer selectively extracts photogenerated holes while blocking electron injection. Preferably, the hole transport layer is prepared by vacuum deposition and has a thickness of 10-80 nm.

[0016] Preferably, to further optimize hole extraction efficiency, an interface conditioning layer can be disposed between the hole transport layer and the top electrode. The function of the interface conditioning layer is to adjust the contact barrier between the hole transport layer and the metal electrode, thereby reducing the contact resistance. Preferably, the interface conditioning layer is made of MoO3 and has a thickness of 1-15 nm.

[0017] Furthermore, the substrate is either a rigid substrate or a flexible substrate. The rigid substrate is selected from quartz glass and silicon wafer; the flexible substrate is selected from polyimide (PI), polyethylene terephthalate (PET), and polyethylene naphthalate (PEN).

[0018] Furthermore, the materials selected for the bottom and top electrodes should take into account work function matching and conductivity. At least one of the bottom and top electrodes is a transparent electrode, made of fluorine-doped tin oxide (FTO), indium-doped tin oxide (ITO), or a metal nanowire mesh. Preferably, the bottom electrode is a transparent electrode so that light enters from the substrate side; the top electrode is made of a material selected from Au, Ag, and Al, and its thickness is preferably 50-200 nm.

[0019] Secondly, the present invention also provides a method for preparing the above-mentioned solar-blind ultraviolet photodetector, comprising the following steps: S1. Fabricate the bottom electrode on the substrate; S2. An electron transport layer is deposited on the surface of the bottom electrode by vacuum deposition; S3. Under high vacuum conditions, CsI and CuI are deposited as evaporation sources by adopting a dual-source co-evaporation method or a sequential evaporation combined with solid-phase reaction. By controlling the deposition amount of CsI and CuI, the ratio of the two is matched with the target stoichiometry, and a non-lead low-dimensional metal halide active layer of Cs-Cu-I system is formed on the surface of the electron transport layer. S4. A hole transport layer and a top electrode are sequentially deposited on the Cs-Cu-I lead-free low-dimensional metal halide active layer by vacuum deposition.

[0020] Furthermore, in step S1, a bottom electrode is prepared on the substrate by sputtering or thermal evaporation.

[0021] Preferably, step S1 further includes treating the bottom electrode with ultraviolet ozone or plasma to remove surface contaminants and regulate the work function.

[0022] Furthermore, in step S2, an electron transport layer is formed on the bottom electrode by magnetron sputtering, atomic layer deposition, or evaporation deposition.

[0023] Furthermore, in step S3, an annealing process is included after the deposition. The annealing process is carried out at a temperature of 60-200°C for 10-60 minutes. The annealing is performed under vacuum or inert gas conditions.

[0024] Further, in step S4, a hole transport layer and a top electrode are sequentially deposited on the non-lead low-dimensional metal halide active layer of the Cs-Cu-I system by thermal evaporation deposition.

[0025] Preferably, in step S4, after depositing the hole transport layer, an interface conditioning layer is deposited on the hole transport layer by thermal evaporation deposition; and then a top electrode is deposited on the interface conditioning layer.

[0026] Furthermore, after step S4, there is also a step of encapsulation using epoxy resin, UV-curable adhesive, or silicone.

[0027] The present invention has the following technical effects: This invention employs a lead-free, low-dimensional metal halide, Cs-Cu-I, as the active layer. Its zero-dimensional or one-dimensional crystal structure possesses an ultra-wide bandgap and strong exciton confinement effect, endowing the device with intrinsic solar-blind spectral selectivity while significantly suppressing dark current. This solves the problems of high toxicity, the need for filters, and high dark current associated with lead-based materials. The active layer is prepared using a vacuum deposition process. By precisely controlling the deposition amounts of CsI and CuI to match the target stoichiometry, this process avoids phase purity fluctuations and solvent residue interface contamination caused by solvents such as DMF / DMSO and antisolvents in solution methods. This achieves a thin active layer. The film exhibits high density, uniformity, and batch consistency. The device stack, consisting of a substrate, bottom electrode, electron transport layer, active layer, hole transport layer, and top electrode, utilizes gradient energy level matching between the electron transport layer and the active layer, and between the active layer and the hole transport layer, to create a built-in electric field at the interface. This enables efficient separation and collection of photogenerated carriers under zero bias, achieving self-powered solar-blind ultraviolet detection and solving the energy consumption problem of traditional devices requiring external bias power. Furthermore, the vacuum deposition process is highly compatible with mask patterning technology, facilitating selective deposition and large-area array fabrication of the active layer, providing a feasible solution for integrated device manufacturing. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the device structure of the solar-blind ultraviolet photodetector provided in Embodiment 1 of the present invention; Figure 2 The XRD values ​​of the thin film prepared in Example 1 are compared with the theoretical values ​​of Cs3Cu2I5.

[0030] Figure 3 The spectral response curves of the solar-blind ultraviolet photodetector prepared in Example 1 under different bias voltages.

[0031] Figure 4 The thin film absorption spectra are those of Examples 1 and 2.

[0032] Figure 5 The dark current of the devices in Example 1 and Example 2 is compared.

[0033] Explanation of reference numerals in the attached figures: 100-substrate, 201-bottom electrode, 301-electron transport layer, 401-lead-free low-dimensional metal halide active layer, 501-hole transport layer, 601-top electrode. Detailed Implementation

[0034] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] It should be understood that, when used in this specification and the appended claims, the terms “comprising” and “including” indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0036] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0037] Example 1 A solar-blind ultraviolet photodetector, such as Figure 1 As shown, it includes a substrate 100, a bottom electrode 201, an electron transport layer 301, a lead-free low-dimensional metal halide active layer 401, a hole transport layer 501, and a top electrode 601 arranged sequentially.

[0038] The substrate 100 is made of quartz glass.

[0039] The bottom electrode 201 is made of ITO.

[0040] The electron transport layer 301 is made of ZnO.

[0041] The lead-free low-dimensional metal halide active layer 401 is a Cs-Cu-I system with a zero-dimensional unit or a one-dimensional chain crystal structure; in this embodiment, the lead-free low-dimensional metal halide active layer 401 is 0D Cs3Cu2I5.

[0042] The lead-free low-dimensional metal halide active layer 401 is prepared by vacuum deposition of CsI and CuI.

[0043] The hole transport layer 501 uses HT50.

[0044] The material for the top electrode 601 is Ag.

[0045] The above-mentioned method for fabricating a solar-blind ultraviolet photodetector includes the following steps: S1, Substrate 100 pretreatment: Quartz glass was selected as the substrate and ultrasonically cleaned sequentially with pure water, acetone, and isopropanol for 15 minutes each, followed by drying with a nitrogen gun. The cleaned substrate was then subjected to ultraviolet-ozone treatment for 20 minutes to remove surface organic contaminants and adjust the work function.

[0046] S2, Preparation of bottom electrode 201: An ITO bottom electrode with a thickness of 150 nm was deposited on the substrate by magnetron sputtering. Sputtering conditions: base vacuum 5 × 10⁻⁶. - 4 The working pressure was 0.5 Pa, the sputtering power was 100 W, the Ar gas flow rate was 20 sccm, and the deposition time was 15 minutes. The deposited ITO electrode was then subjected to oxygen plasma treatment for 2 minutes with the following parameters: oxygen flow rate 0.5 L / min and power 100 W.

[0047] S3, Electron transport layer 301 deposition: A ZnO electron transport layer was deposited on an ITO electrode using magnetron sputtering. Sputtering conditions: background vacuum 5 × 10⁻⁶. -4 Pa, working gas pressure 0.5 Pa, sputtering power 100 W, Ar:O2 flow ratio 20:1, deposition time 10 minutes, film thickness 30 nm.

[0048] S4, Non-lead low-dimensional metal halide active layer 401 dual-source co-evaporation: The ZnO-deposited substrate was transferred to a vacuum evaporation chamber with a base vacuum better than 5 × 10⁻⁶. -4 Pa. CsI and CuI were deposited using a dual-source co-evaporation method: CsI ​​source: heating temperature 550℃, preheat and stabilize for 10 minutes before deposition; CuI source: heating temperature 450℃, preheat and stabilize for 10 minutes before deposition; The deposition rates of both sources were monitored in real time using a quartz crystal film thickness gauge. Heating power was controlled via PID feedback, and rate corrections were made based on the density and molecular weight differences between CsI and CuI to maintain a CsI to CuI molar ratio of 3:2. The corresponding measured rates were: CsI rate at 1.0 Å / s, CuI rate at 0.67 Å / s, a CsI:CuI rate ratio of 3:2, a total deposition thickness of 200 nm, and a deposition time of 120 seconds.

[0049] Substrate temperature: room temperature.

[0050] The deposited sample was subjected to vacuum conditions (<10) -3 The sample was annealed at 120℃ for 20 minutes. During the annealing process, the sample was heated naturally, held at that temperature for 20 minutes, and then cooled naturally to room temperature.

[0051] S5, Hole transport layer 501 deposition: HT50 hole transport layer was deposited on the active layer using thermal evaporation. Evaporation conditions: background vacuum 5 × 10⁻⁶. -4 Pa, evaporation rate 0.5 Å / s, deposition thickness 40 nm.

[0052] S6, Top electrode 601 deposition: An Ag top electrode was deposited on the HT50 hole transport layer using thermal evaporation. Evaporation conditions: background vacuum 5 × 10⁻⁶. -4 Pa, evaporation rate 1 Å / s, deposition thickness 100 nm. The effective device area is defined as 0.1 cm² using a mask. 2 .

[0053] Example 2 A solar-blind ultraviolet photodetector, this embodiment is basically the same as embodiment 1, the only difference is that: the non-lead low-dimensional metal halide active layer 401 is a one-dimensional CsCu2I3 crystal structure, and the dual-source co-evaporation conditions of the non-lead low-dimensional metal halide active layer 401 in step S4 are different.

[0054] Specifically, step S4 of this embodiment is as follows: S4, Non-lead low-dimensional metal halide active layer 401 dual-source co-evaporation: The CsI source rate stabilized at 0.33 Å / s; The CuI source rate stabilized at 0.67 Å / s; The two-source rate ratio CsI:CuI = 1:2 (corresponding to a molar ratio of 1:2); The total deposition thickness was still controlled at 200 nm.

[0055] Example 3 This embodiment is basically the same as embodiment 1, except that an interface conditioning layer is provided between the hole transport layer 501 and the top electrode 601, and an interface conditioning layer deposition step is added between the deposition of the hole transport layer 501 and the deposition of the top electrode 601. S5. Deposition of hole transport layer 501 (same as in Example 1) S5-1, Deposition of Interface Conditioning Layer A MoO3 interface conditioning layer was deposited on an HT50 hole transport layer using thermal evaporation. Evaporation conditions: background vacuum 5 × 10⁻⁶. -4 Pa, evaporation rate 0.2 Å / s, deposition thickness 5 nm.

[0056] S6, Top electrode 601 deposition An Ag top electrode was deposited on the MoO3 interface conditioning layer under the same conditions as in Example 1.

[0057] The remaining steps are exactly the same as in Example 1.

[0058] Example 4 This embodiment is basically the same as Embodiment 1, except that a flexible polyimide (PI) film is used instead of quartz glass as the substrate, and the preparation process is also not exactly the same: The fabrication method of the solar-blind ultraviolet photodetector in this embodiment includes the following steps: S1, Substrate 100 pretreatment: A 125μm thick polyimide (PI) film was selected as the substrate and ultrasonically cleaned with pure water, acetone, and isopropanol for 10 minutes each, and then dried with a nitrogen gun.

[0059] S2, Preparation of bottom electrode 201: The ITO bottom electrode was deposited by room temperature magnetron sputtering under the same conditions as in Example 1.

[0060] S3, Electron transport layer 301 deposition: The ZnO electron transport layer was deposited by room temperature magnetron sputtering under the same conditions as in Example 1.

[0061] S4, Non-lead low-dimensional metal halide active layer 401 dual-source co-evaporation: Same as Example 1.

[0062] S5, Hole transport layer 501 deposition: The HT50 hole transport layer was deposited using room temperature thermal evaporation under the same conditions as in Example 1.

[0063] S6, Top electrode 601 deposition: The Ag top electrode was deposited using room temperature thermal evaporation, under the same conditions as in Example 1.

[0064] S7, Package: To further improve the environmental stability of the device, UV-curable adhesive was used for encapsulation. The UV-curable adhesive was dropped onto the device surface, covering the edges of the active area, and then cured under a UV lamp for 5 minutes.

[0065] Comparative Example 1 The only difference between this comparative example and Example 1 is that the active layer is prepared using a solution method instead of a vacuum deposition process.

[0066] Specifically, step S4 is as follows: S4. Preparation of non-lead low-dimensional metal halide active layer 401 by solution method: CsI ​​and CuI were dissolved in a mixed solvent of DMF:DMSO = 1:1 in a molar ratio of 3:2 to prepare a 0.5 mol / L precursor solution; Next, spin-coat the precursor solution onto the substrate with deposited ZnO at 3000 rpm for 30 seconds. During spin coating, 100 μL of toluene antisolvent was added dropwise at the 15th second. After spin coating, anneal on a hot plate at 100°C for 20 minutes.

[0067] The remaining steps are exactly the same as in Example 1.

[0068] Comparative Example 2 This comparative example is basically the same as Example 1, except that the hole transport layer is prepared using a high-temperature annealing process to prepare NiO. x .

[0069] Specifically, step S5 is as follows: S5, Hole transport layer deposition: Ni(CH3COO)2·4H2O was dissolved in ethanol to prepare a 20 mg / mL solution, and an equimolar amount of ethanolamine was added as a stabilizer. Ni(CH3COO)2 solution was spin-coated onto the active layer at 3000 rpm for 30 seconds. The spin-coated sample was placed in a muffle furnace and annealed at 400°C for 1 hour to form NiO. x Hole transport layer.

[0070] The remaining steps are exactly the same as in Example 1.

[0071] Comparative Example 3 This comparative example is basically the same as Example 1, except that the active layer is prepared by single-source evaporation without rate ratio control.

[0072] Specifically, step S4 is as follows: S4, Single-source evaporation of non-lead low-dimensional metal halide active layer 401: CsI ​​and CuI were mixed at a molar ratio of 3:2 and ground until homogeneous. The mixed powders are placed in the same evaporation source and heated to evaporate; No rate ratio control was performed; only the total deposition thickness was controlled to be 200 nm.

[0073] The remaining steps are exactly the same as in Example 1.

[0074] Comparative Example 4 This comparative example is basically the same as Example 1, except that the evaporation rate ratio of CsI to CuI deviates from the target stoichiometric ratio during the preparation of the active layer.

[0075] S4, Non-lead low-dimensional metal halide active layer 401 dual-source co-evaporation: The CsI source rate stabilized at 0.25 Å / s; The CuI source rate stabilized at 0.75 Å / s; The two-source rate ratio CsI:CuI = 1:3 (corresponding to a molar ratio of 1:3); The total deposition thickness was controlled at 200 nm. The remaining conditions are the same as in Example 1.

[0076] Comparative Example 5 This comparative example is basically the same as Example 1, except that the annealing temperature of the active layer is increased to 300°C.

[0077] To verify the technical effect of the present invention, the solar-blind ultraviolet photodetectors of Examples 1-4 and Comparative Examples 1-5 were subjected to the following performance tests.

[0078] (1) Active layer quality test The active layer quality test included X-ray diffraction (XRD) analysis of the film's phase composition and crystallinity, scanning electron microscopy (SEM) observation of the surface morphology, and atomic force microscopy (AFM) testing of the surface roughness. The test results are shown in Table 1 below. The XRD values ​​of the film prepared in Example 1 are compared with the theoretical values ​​of Cs3Cu2I5. Figure 2 As shown.

[0079] Table 1 Results of Active Layer Quality Test As shown in Table 1, Examples 1-4 of this invention all yielded low-dimensional Cs-Cu-I films with high phase purity, dense and uniform surfaces, and low roughness. The film prepared by the solution method in Comparative Example 1 contained impurities and exhibited significant surface defects; Comparative Examples 3 and 4 suffered from multiphase coexistence or severe impurities due to improper processes; and Comparative Example 5 resulted in film decomposition due to high-temperature annealing.

[0080] (2) Optical performance testing Optical performance testing included measuring the absorption spectrum of the thin film using a UV-Vis spectrophotometer and calculating the optical band gap; measuring exciton emission using photoluminescence (PL) spectroscopy and calculating the exciton binding energy using variable-temperature PL. The results are shown in Table 2. The solar blindness / visible light suppression ratio was defined as the ratio A of the absorbance at 280 nm to that at 400 nm. 280 / A 400 The spectral response curves of the solar-blind ultraviolet photodetector prepared in Example 1 under bias voltages of -0.5 V to 1 V are shown below. Figure 3 As shown. The absorption spectra of the thin films prepared in Examples 1 and 2 are as follows. Figure 4 As shown; the comparison results of dark current of devices fabricated under different CsI to CuI evaporation rate ratios are as follows. Figure 5 As shown. It should be noted that, Figure 4 , Figure 5The "1:2" and "3:2" in the figure correspond to the CsI to CuI evaporation rate ratios in Example 2 and Example 1, respectively, and are used as legend symbols for the performance test results of the solar-blind ultraviolet photodetectors prepared in Example 2 and Example 1.

[0081] Table 2 Optical performance test results As shown in Table 2, the Cs3Cu2I5 active layer in Example 1 of this invention has an ultrawide bandwidth of approximately 3.92 eV, with its absorption edge strictly below 310 nm, exhibiting excellent intrinsic solar blindness characteristics. Experimental data show that its solar blindness / visible light suppression ratio reaches 2.5 × 10⁻⁶. 3 The above is noteworthy. It is worth noting that the exciton binding energy of Example 1 is as high as 480 meV. This strong exciton confinement effect originates from its 0D anion cluster structure, making the photogenerated excitons less susceptible to thermal phonon scattering at room temperature, thus ensuring high photoelectric conversion efficiency. Comparative Example 2 uses NiO prepared by high-temperature annealing at 400℃. x In the hole transport layer, the active layer has undergone severe phase decomposition, damaging the film structure and making it impossible to effectively measure optical performance data. Comparative Example 3, a mixture of Cs3Cu2I5 and CsCu2I3, shows the absorption edge contributed by both phases, making it impossible to accurately fit a single bandgap value and exciton binding energy. Comparative Example 4, due to a deviation in the stoichiometry, introduces one-dimensional impurities, causing a redshift in the absorption edge, resulting in a loss of precise solar-blind selectivity, weak and unstable exciton emission signals, and an inability to effectively fit the exciton binding energy. Comparative Example 5, annealed at 300℃, completely decomposes the film, making it impossible to measure optical performance.

[0082] (3) Electrical performance testing The electrical performance of the prepared solar-blind ultraviolet photodetector was tested, and the results are shown in Table 3: Table 3 Electrical performance test results As can be seen from Table 3, the devices prepared in the embodiments of the present invention have excellent electrical performance.

[0083] Regarding extremely low noise suppression, the dark current of all embodiments is in the picoampere (pA) level under zero bias conditions. In particular, the dark current of Embodiment 1 under zero bias is only 0.82 pA, while the dark current of Comparative Embodiment 1, which uses a solution-based active layer, is as high as 85.6 pA. x Comparative Example 2, with its hole transport layer, achieves an even higher dark current suppression capability of 450 pA. The excellent dark current suppression capability of the device in this invention is attributed to the extremely low defect state density of the thin film prepared by the vacuum method, and the tight coupling of the heterojunction interface grown in situ under full vacuum, which effectively suppresses the injection of thermally generated charge carriers.

[0084] In terms of detectivity and responsivity, all embodiments exhibit excellent responsivity and detectivity. Among them, Embodiment 3, by introducing a MoO3 interface conditioning layer, optimizes the energy level matching between the active layer and the top electrode, maximizing hole extraction efficiency and achieving a specific detectivity D* as high as 2.2 × 10⁻⁶. 13 Jones. In contrast, Comparative Example 1 showed a significant decrease in responsivity and detectivity due to solvent residue and phase purity fluctuations introduced by the solution method; Comparative Example 2 suffered severe performance degradation due to active layer decomposition caused by the high-temperature process; and Comparative Examples 3 and 4 had lower responsivity and detectivity than the embodiments of the present invention due to low phase purity of the active layer or the presence of impurities.

[0085] In terms of response speed, compared to the millisecond (ms) delays commonly found in existing Ga2O3 detectors (as shown in Table 4), the response time of the device of this invention is shortened to the microsecond level. In particular, the rise / fall time of Example 3 is only 8 / 25 μs, which is due to the unique electronic structure of Cs3Cu2I5 and the high-quality heterojunction interface brought about by vacuum processing, which greatly reduces the trapping and recombination of charge carriers during transport.

[0086] Regarding self-powered characteristics, all embodiments exhibit significant photocurrent response at 0V bias, while the photocurrent of Comparative Examples 1-4 at zero bias is lower than that of the embodiments of the present invention, and some comparative examples require an external bias to obtain an effective response. This is because the energy level gradient formed between the ZnO electron transport layer and the HT50 hole transport layer creates a strong built-in electric field on both sides of the active layer, realizing the self-driven separation of photogenerated carriers.

[0087] In addition, both Comparative Example 2 and Comparative Example 5 failed due to the decomposition of the active layer. Specifically, Comparative Example 2 failed because the active layer was severely decomposed due to high-temperature annealing, and the effective response time could not be measured; Comparative Example 5 failed because the active layer was decomposed due to excessively high annealing temperature (300℃), and the device performance failed, so it is not included in the table.

[0088] In summary, this invention successfully constructed a high-purity, low-dimensional metal halide heterojunction by precisely controlling the all-vacuum deposition process. While achieving zero-bias self-powered operation, it also obtained extremely low noise levels and ultra-fast response speeds. All key performance indicators have reached or exceeded the levels of similar devices reported to date.

[0089] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and such modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A solar-blind ultraviolet photodetector, characterized in that, It includes a substrate, a bottom electrode, an electron transport layer, a lead-free low-dimensional metal halide active layer, a hole transport layer, and a top electrode arranged sequentially. The lead-free low-dimensional metal halide active layer is a Cs-Cu-I system with a zero-dimensional unit or a one-dimensional chain crystal structure. The lead-free low-dimensional metal halide active layer is prepared by vacuum deposition of CsI and CuI, and the molar ratio of Cs to Cu in the lead-free low-dimensional metal halide active layer matches the stoichiometric ratio of the target low-dimensional phase.

2. The solar-blind ultraviolet photodetector as described in claim 1, characterized in that, The lead-free low-dimensional metal halide active layer is formed by CsI and CuI through dual-source co-evaporation deposition or sequential evaporation combined with solid-phase reaction.

3. The solar-blind ultraviolet photodetector as described in claim 1, characterized in that, The molar ratio of Cs to Cu in the lead-free low-dimensional metal halide active layer is 3:2, and the lead-free low-dimensional metal halide active layer has a zero-dimensional Cs3Cu2I5 crystal structure.

4. The solar-blind ultraviolet photodetector as described in claim 1, characterized in that, The molar ratio of Cs to Cu in the lead-free low-dimensional metal halide active layer is 1:2, and the lead-free low-dimensional metal halide active layer has a one-dimensional CsCu2I3 crystal structure.

5. The solar-blind ultraviolet photodetector as described in claim 1, characterized in that, At least one of the bottom electrode and the top electrode is a transparent electrode, which is made of fluorine-doped tin oxide, indium-doped tin oxide, or a metal nanowire mesh.

6. The solar-blind ultraviolet photodetector as described in claim 1, characterized in that, The hole transport layer is made of organic semiconductor material.

7. The solar-blind ultraviolet photodetector as described in claim 1, characterized in that, An interface conditioning layer is also provided between the hole transport layer and the top electrode. The interface conditioning layer is made of MoO3 and has a thickness of 1-15 nm.

8. The solar-blind ultraviolet photodetector as described in claim 1, characterized in that, The substrate is a flexible substrate, which is selected from polyimide and polyethylene terephthalate.

9. A method for fabricating a solar-blind ultraviolet photodetector as described in any one of claims 1-8, characterized in that, Includes the following steps: S1. Fabricate the bottom electrode on the substrate; S2. An electron transport layer is deposited on the surface of the bottom electrode using a vacuum deposition process; S3. Under high vacuum conditions, CsI and CuI are deposited as evaporation sources by adopting a dual-source co-evaporation method or a sequential evaporation combined with solid-phase reaction. By controlling the deposition amount of CsI and CuI, the ratio of the two is matched with the target stoichiometry, and a non-lead low-dimensional metal halide active layer of Cs-Cu-I system is formed on the surface of the electron transport layer. S4. A hole transport layer and a top electrode are sequentially deposited on the Cs-Cu-I lead-free low-dimensional metal halide active layer using a vacuum deposition process.

10. The method for preparing a solar-blind ultraviolet photodetector as described in claim 9, characterized in that, In step S3, an annealing process is further included after the deposition. The annealing process is carried out at a temperature of 60-200°C for a time of 10-60 minutes.

Images