Detector with positive and negative photoresponse and preparation method thereof

Abstract

The invention provides a detector with positive and negative photoresponse and a preparation method thereof, and relates to the technical field of photoelectric detection. The detector comprises a substrate layer, and a perovskite thin film layer, an upper conversion layer and an electrode layer which are sequentially stacked on the substrate layer, the up-conversion layer comprises NaYGdF4: Yb < 3 + >, Er < 3 + > and NaYF4 up-conversion particles with a core-shell structure. The photoelectric detector can detect visible light and near-infrared light on a single pixel at the same time and generate positive and negative bidirectional photoelectric response, so that diversified coding of optical signals in the same pixel is realized, and new possibility is provided for optical information processing.

Description

Technical Field

[0001] The present invention relates to the field of photoelectric detection technology, and in particular to a detector with positive and negative light responses and a preparation method thereof. Background Art

[0002] As a key bridge for the conversion of optical and electrical signals, photoelectric detection technology has become a research hotspot in optical information communication terminals due to its potential ability to extract multi-degree-of-freedom information from optical signals. With the rapid development of the Internet of Things era, traditional photoelectric detectors have encountered severe challenges in improving comprehensive performance such as lightweight size, low power consumption, and system integration. In this context, inspired by the retinal perception mechanism, dual-band photodetectors have emerged in recent years. This type of detector can simultaneously identify optical signals of two independent frequencies, opening up a new path for improving system integration by significantly reducing the number of effective pixels.

[0003] At present, photodetectors based on perovskite and organic heterostructures have achieved visible light-near infrared dual-band detection by regulating the direction of the electric field. However, their initial bias setting limits their ability to respond quickly in complex environments. 2.4 I 0.6 Although the FAPbI3 / FAPbI3 heterojunction photodetector can achieve 532nm and 650nm dual-mode spectral selection without bias setting, the identified wavelength is highly dependent on the direction of the incident photons regulated by the digital micromirror device, and a free-space optical waveguide system needs to be built at the front end of the device, which increases the complexity of the system; in addition, the wavelength recognition method based on the conversion current difference relies on bandpass filters or concentrators to maintain the consistency of light intensity at each wavelength, which to a certain extent restricts the further improvement of detection accuracy and integration.

[0004] Therefore, developing a new wavelength resolution method that does not require additional optical components and complex operations has become a key issue that needs to be urgently addressed in this field. Summary of the invention

[0005] In view of this, the present invention proposes a detector with positive and negative light response and a preparation method thereof. Through the synergistic effect of methylammonium lead iodide (MAPbI3) and upconversion nanoparticles (UCNPs), bipolar light response of green light and infrared light is achieved, providing a novel, simple and effective technical strategy for the development of high-performance photodetectors in complex optical communication scenarios.

[0006] In a first aspect, the present invention provides a detector with positive and negative light response, comprising: a substrate layer, and a perovskite thin film layer, an upconversion layer and an electrode layer sequentially stacked on the substrate layer;

[0007] The up-conversion layer includes a core-shell structure of NaYGdF4:Yb 3+, Er 3+ @NaYF4 upconversion particles.

[0008] In one or some possible embodiments, the thickness of the upconversion layer is 400 - 500 nm.

[0009] In a second aspect, the present invention relates to a method for preparing the above-mentioned detector with positive and negative light responses, comprising the following steps:

[0010] S1. Prepare a perovskite thin film layer on the substrate layer by using a two-step spin coating method;

[0011] S2. Coat the NaYGdF4:Yb 3+ , Er 3+ @NaYF4 upconversion particles with a core-shell structure onto the perovskite thin film layer to prepare an upconversion layer;

[0012] S3. Evaporate an electrode layer on the upconversion layer to obtain a photodetector.

[0013] In one or some possible embodiments, in step S1, the preparation of the perovskite thin film layer specifically includes:

[0014] Prepare a MAPbI3 perovskite precursor solution. Under the protection of an inert gas, spin coat the MAPbI3 perovskite precursor solution on the substrate layer. The spin coating conditions are as follows: in the first step, spin coat at a rotation speed of 800 - 1000 rpm for 10 - 15 s, and in the second step, spin coat at a rotation speed of 3000 - 3500 rpm for 40 - 45 s. At 15 - 20 s before the end of the second spin coating, dropwise add chlorobenzene onto the rotating MAPbI3 substrate. After spin coating is completed, anneal at 100 - 120 °C for 5 - 10 min to form a perovskite thin film layer on the substrate layer.

[0015] Furthermore, the volume of the MAPbI3 perovskite precursor solution is 200 - 250 μL.

[0016] Furthermore, to regulate the crystallization kinetics of the perovskite precursor solution and optimize the microstructure and surface uniformity of the thin film, it is necessary to introduce chlorobenzene as a highly volatile antisolvent. The dropping method of the chlorobenzene is: vertical dropping.

[0017] By adopting the above technical solution, chlorobenzene can accelerate the volatilization of the solvent in the precursor solution, induce uniform nucleation by changing the solution supersaturation and inhibit abnormal grain growth, and finally form a perovskite crystalline thin film with high density, thereby obtaining better optoelectronic properties.

[0018] In one or some possible embodiments, the method for preparing the MAPbI3 perovskite precursor solution is as follows: Methylammonium iodide and lead iodide are mixed and dissolved in an organic solvent at a molar ratio of 1:1 to 1.2, and stirred at 60-80 °C for more than 24 h to obtain the MAPbI3 perovskite precursor solution.

[0019] Furthermore, the molar ratio of methylammonium iodide to lead iodide is 1:(1.0-1.2); the organic solvent is selected from one of N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or γ-butyrolactone (GBL).

[0020] Furthermore, the thickness of the perovskite thin film layer is 200-400 nm.

[0021] In one or some possible embodiments, in step S2, the preparation of the upconversion layer specifically includes:

[0022] Spin-coating a core-shell structured NaYGdF4:Yb 3+ ,Er 3+ @NaYF4 upconversion particle dispersion on the perovskite thin film layer at a rotation speed of 2000-3000 rpm, and annealing at 100-130 °C for 5-10 min to obtain the upconversion layer.

[0023] Furthermore, the mass concentration of the core-shell structured NaYGdF4:Yb 3+ ,Er 3+ @NaYF4 upconversion particle dispersion is 0.1 mmol / mL.

[0024] In one or some possible embodiments, the preparation of the core-shell structured NaYGdF4:Yb 3+ ,Er 3+ @NaYF4 upconversion particle dispersion includes the following steps:

[0025] S21. After preparing a precursor solution containing a yttrium source, a gadolinium source, a ytterbium source, and an erbium source, add a methanol solution of ammonium fluoride and a methanol solution of sodium hydroxide, stir and dissolve, heat under an inert gas, add ethanol to precipitate the product, centrifuge and separate, and wash the precipitate, and dissolve it in cyclohexane to obtain a NaYGdF4:Yb 3+ ,Er 3+ core layer solution;

[0026] S22. Add the precursor solution containing the yttrium source, the methanol solution of ammonium fluoride, and the methanol solution of sodium hydroxide to the NaYGdF4:Yb 3+ ,Er 3+In the core layer solution, after heating under an inert gas, the particulate precipitate is centrifuged and collected, washed, and then dispersed in cyclohexane to obtain NaYGdF4:Yb 3+ ,Er 3+ @NaYF4 upconversion particle dispersion liquid.

[0027] In one or some possible embodiments, in step S21, the molar ratio of the yttrium source, gadolinium source, ytterbium source, and erbium source is 78:5:20:2; the molar ratio of ammonium fluoride to sodium hydroxide is 8:3 to 3.5.

[0028] Furthermore, the yttrium source is selected from yttrium acetate (Y(CH3COO)3) or yttrium chloride (YCl3); the gadolinium source is selected from gadolinium acetate hexahydrate (Gd(CH3COO)3·6H2O) or gadolinium chloride (GdCl3); the ytterbium source is selected from ytterbium acetate tetrahydrate (Yb(CH3COO)3·4H2O) or ytterbium chloride (YbCl3); the erbium source is selected from erbium acetate (Er(CH3COO)3) or erbium chloride (ErCl3).

[0029] Furthermore, the preparation method of the precursor solution containing the yttrium source, gadolinium source, ytterbium source, and erbium source is: dissolving Y(CH3COO)3, Gd(CH3COO)3·6H2O, Yb(CH3COO)3·4H2O, and Er(CH3COO)3 in 1-octadecene (ODE) and oleic acid (OA) according to the above molar ratio to obtain a precursor solution containing the yttrium source, gadolinium source, ytterbium source, and erbium source.

[0030] Furthermore, the volume of the ODE is 15 - 20 mL, and the volume of the OA is 6 - 10 mL.

[0031] In one or some possible embodiments, in step S22, the molar ratio of ammonium fluoride to sodium hydroxide is 8:5 to 5.5.

[0032] Furthermore, after the precursor solution containing the yttrium source is heated to form a transparent solution, it is cooled to about 80°C and added to the core layer solution in step S21.

[0033] In one or some possible embodiments, in step S3, the thickness of the electrode layer is 80 - 100 nm, and the distance between adjacent two electrode layers is 150 - 180 nm.

[0034] The detector with positive and negative light responses provided by the present invention and its preparation method have the following beneficial effects compared with the prior art:

[0035] (1) The photodetector prepared by the present invention has a photocurrent of 0.8 mW / cm at a wavelength of 500 nm 2Under the excitation of green light, when a bias voltage of 10 V is applied, the responsivity is 41.22 mA / W, and the normalized specific detectivity is 3.31×10 8 Jones, and the external quantum efficiency is 10.22%. Under the excitation of near-infrared light with a wavelength of 980 nm and an intensity of 50 mW / cm 2 When a bias voltage of 10 V is applied, it is found that the photocurrent is lower than the dark current. The calculated responsivity is 100.24 μA / W, and the normalized specific detectivity is 7.91×10 5 Jones, and the external quantum efficiency is 1.273×10 -2 %.

[0036] (2) The photodetector prepared by the present invention can simultaneously detect visible light and near-infrared light on a single pixel and generate positive and negative bidirectional photoelectric responses. By utilizing the cross-relaxation effect generated by the excitation of upconversion nanoparticles with 980-nm near-infrared light, which causes the photocurrent to decrease, and the mechanism that the perovskite material promotes the current to rise through the forward photoconductivity effect under visible light illumination, unique symbolic encoding of light with different wavelengths is achieved within the same device. By analyzing these photoelectric response characteristics and light intensity information, the photodetector of the present invention can achieve the discrimination of multi-dimensional optical signals, demonstrating its application potential in the field of intelligent photoelectric detection. Description of the Drawings

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0038] Figure 1 is a schematic structural diagram of the photodetector provided by the present invention; in the figure, 1 is the base layer, 2 is the perovskite thin film layer, 3 is the upconversion layer, and 4 is the electrode layer;

[0039] Figure 2 is a scanning electron microscope image of the perovskite thin film layer provided by the present invention by way of example;

[0040] Figure 3 is a scanning electron microscope image of the upconversion particles provided by the present invention by way of example;

[0041] Figure 4 is a scanning electron microscope image of the upconversion layer provided by the present invention by way of example;

[0042] Figure 5 is a voltage-current performance test diagram of the photodetector provided by the present invention under different conditions. Detailed Embodiments

[0043] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of 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.

[0044] As Figure 1 shown, the present invention provides a detector with positive and negative light responses, including: a base layer 1, and a perovskite thin film layer 2, an upconversion layer 3, and an electrode layer 4 that are sequentially stacked on the base layer 1.

[0045] In an embodiment of the present invention, the perovskite thin film layer 2 serves as a light absorption layer and has a thickness of 200-400 nm; the upconversion layer 3 has a thickness of 400-500 nm; the electrode layer 4 has a thickness of 80-100 nm, and the distance between adjacent electrode layers 4 is 150-180 nm.

[0046] Specifically, the thickness of the perovskite thin film layer 2 can be any value among 200 nm, 300 nm, 400 nm or the range value between any two of the above; the thickness of the upconversion layer 3 can be any value among 400 nm, 450 nm, 500 nm or the range value between any two of the above; the thickness of the electrode layer 4 can be any value among 80 nm, 90 nm, 100 nm or the range value between any two of the above, and the distance between adjacent electrode layers 4 can be any value among 150 nm, 160 nm, 170 nm, 180 nm or the range value between any two of the above.

[0047] In an embodiment of the present invention, the base layer is a glass substrate; the perovskite thin film layer 2 is a MAPbI3 perovskite thin film; the upconversion layer 3 includes core-shell structured NaYGdF4:Yb 3+ ,Er 3+ @NaYF4 upconversion particles; the material of the electrode layer includes but is not limited to a gold (Au) electrode.

[0048] In an embodiment of the present invention, the preparation method of the MAPbI3 perovskite precursor solution includes:

[0049] Mix methylammonium iodide (MAI) and lead iodide (PbI2) at a molar ratio of 1:(1.0-1.2), dissolve them in an organic solvent, heat to 60-80 °C and stir for more than 24 h to obtain the MAPbI3 perovskite precursor solution.

[0050] Specifically, the molar ratio of MAI to PbI2 can be set to any value among 1:1, 1:1.1 or 1:1.2, or a range value between any two of the above; the heating temperature can be set to any value among 60°C, 70°C, 80°C, or a range value between any two of the above.

[0051] In an embodiment of the present invention, the preparation of the perovskite thin film layer 2 includes the following steps:

[0052] Take 200 - 250 μL of the MAPbI3 perovskite precursor solution, and spin-coat it on the substrate layer 1 under nitrogen protection. The spin-coating conditions are as follows: in the first step, spin-coat at a speed of 800 - 1000 rpm for 10 - 15 s; in the second step, spin-coat at a speed of 3000 - 3500 rpm for 40 - 45 s. At 15 - 20 s before the end of the second spin-coating, vertically drop 100 - 150 μL of chlorobenzene onto the rotating MAPbI3 substrate. After spin-coating is completed, anneal at 100 - 120°C for 5 - 10 min to form the perovskite thin film layer 2 on the substrate layer 1.

[0053] Specifically, the volume of the MAPbI3 perovskite precursor solution can be any value among 200 μL, 210 μL, 220 μL, 230 μL, 240 μL, 250 μL, or a range value between any two of the above; the speed of the first spin-coating can be any value among 800 rpm, 900 rpm, 1000 rpm, or a range value between any two of the above, and the time can be any value among 10 s, 11 s, 12 s, 13 s, 14 s, 15 s, or a range value between any two of the above; the speed of the second spin-coating can be any value among 3000 rpm, 3100 rpm, 3200 rpm, 3300 rpm, 3400 rpm, 3500 rpm, or a range value between any two of the above, and the time can be any value among 40 s, 41 s, 42 s, 43 s, 44 s, 45 s, or a range value between any two of the above; the annealing temperature can be any value among 100°C, 110°C, 120°C, or a range value between any two of the above, and the time is any value among 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, or a range value between any two of the above.

[0054] Example 1

[0055] This example provides a method for preparing a MAPbI3 perovskite thin film layer 1, including the following steps:

[0056] 0.158 g of methylammonium iodide (MAI) and 0.461 g of lead iodide (PbI2) were added to 1 ml of N,N-dimethylformamide (DMF), and stirred continuously at 60 °C for more than 24 h to form a precursor solution. 200 μL of the perovskite precursor solution was aspirated and spin-coated on a glass substrate. In the first step, it was spin-coated at a speed of 800 rpm for 15 s, and in the second step, it was spin-coated at a speed of 3000 rpm for 40 s. And 20 s before the end of the second spin-coating, 100 μL of chlorobenzene was vertically dropped onto the rotating MAPbI3 substrate. Finally, annealed at 100 °C for 5 min to obtain a MAPbI3 perovskite thin film layer 1 with a thickness of 300 nm, as Figure 2 shown.

[0057] It can be seen from Figure 2 that the MAPbI3 perovskite thin film prepared by the present invention has good crystallinity.

[0058] Example 2

[0059] This example provides a method for preparing a MAPbI3 perovskite thin film layer 1, including the following steps:

[0060] 0.158 g of methylammonium iodide (MAI) and 0.461 g of lead iodide (PbI2) were added to 1 ml of dimethyl sulfoxide (DMSO), and stirred continuously at 70 °C for more than 24 h to form a precursor solution. 220 μL of the perovskite precursor solution was aspirated and spin-coated on a glass substrate. In the first step, it was spin-coated at a speed of 900 rpm for 12 s, and in the second step, it was spin-coated at a speed of 3100 rpm for 42 s. And 15 s before the end of the second spin-coating, 100 μL of chlorobenzene was vertically dropped onto the rotating MAPbI3 substrate. Finally, annealed at 110 °C for 8 min to obtain a MAPbI3 perovskite thin film layer 1 with a thickness of 200 nm.

[0061] Example 3

[0062] This example provides a method for preparing a MAPbI3 perovskite thin film layer 1, including the following steps:

[0063] 0.158 g of methylammonium iodide (MAI) and 0.469 g of lead iodide (PbI2) were added to 1 ml of γ-butyrolactone (GBL), and stirred continuously at 80 °C for more than 24 h to form a precursor solution. 240 μL of the perovskite precursor solution was aspirated and spin-coated on a glass substrate. In the first step, it was spin-coated at a speed of 1000 rpm for 10 s, and in the second step, it was spin-coated at a speed of 3400 rpm for 40 s. And 18 s before the end of the second spin-coating, 100 μL of chlorobenzene was vertically dropped onto the rotating MAPbI3 substrate. Finally, annealed at 120 °C for 10 min to obtain a MAPbI3 perovskite thin film layer 1 with a thickness of 400 nm.

[0064] Example 4

[0065] This example provides a method for preparing the MAPbI3 perovskite thin film layer 1, including the following steps:

[0066] Add 0.158 g of methylammonium iodide (MAI) and 0.461 g of lead iodide (PbI2) into 1 ml of N,N-dimethylformamide (DMF), and continuously stir at 60 °C for more than 24 h to form a precursor solution. Pipette 250 μL of the perovskite precursor solution onto a glass substrate for spin coating. In the first step, spin coat at a speed of 800 rpm for 14 s, and in the second step, spin coat at a speed of 3500 rpm for 45 s. And 20 s before the end of the second spin coating, vertically drop 100 μL of chlorobenzene onto the rotating MAPbI3 substrate. Finally, anneal at 100 °C for 5 min to obtain the MAPbI3 perovskite thin film layer 1 with a thickness of 360 nm.

[0067] In the embodiment of the present invention, the preparation of the NaYGdF4:Yb 3+ ,Er 3+ @NaYF4 upconversion particle dispersion includes the following steps:

[0068] S21. Dissolve yttrium source, gadolinium source, ytterbium source and erbium source in a molar ratio of 78:5:20:2 in 15 - 20 mL of 1-octadecene and 6 - 10 mL of oleic acid. Heat the mixture at a temperature of 100 - 130 °C for 10 - 20 min, then under a nitrogen atmosphere, stir and heat to 150 °C - 180 °C, and then cool to room temperature to obtain a precursor solution containing yttrium source, gadolinium source, ytterbium source and erbium source. Dissolve ammonium fluoride and sodium hydroxide in a molar ratio of 8:(5 - 5.5) in 10 - 20 mL of methanol solution respectively, heat to 50 °C under stirring conditions and keep for 30 - 45 min, then heat to 100 - 120 °C under vacuum conditions and keep for 30 - 45 min, then heat to 300 - 320 °C and keep for 1 - 1.5 h, and finally cool to room temperature, add ethanol to precipitate the product, centrifuge at a speed of 7000 - 8000 rpm for 20 - 30 min, separate and wash the precipitate, and disperse the precipitate in 10 - 15 mL of cyclohexane to obtain the NaYGdF4:Yb 3+ ,Er 3+ core layer solution;

[0069] S22. Dissolve the yttrium source in 6 - 10 ml of oleic acid and 15 - 20 ml of 1-octadecene, stir and heat to 150 - 180 °C to form a transparent solution. When the temperature drops to 80 °C, add NaYGdF4:Yb 3+ ,Er 3+In the core layer solution, after dissolution and cooling to room temperature, ammonium fluoride and sodium hydroxide are dissolved in 10 - 20 mL of methanol solution respectively at a molar ratio of 8:(5 - 5.5), then added to the mixed solution. Under vacuum conditions, it is heated at 100 - 130 °C for 20 - 30 min, then heated to 300 - 320 °C and maintained for 1 - 1.5 h. Finally, it is centrifuged at a speed of 7000 - 8000 r / min for 20 - 30 min to obtain granular precipitates. After washing, the granular precipitates are dispersed in 10 - 15 mL of cyclohexane to obtain a core - shell structured NaYGdF4:Yb 3+ ,Er 3+ @NaYF4 up - conversion particle dispersion liquid.

[0070] In step S21, exemplarily: the volume of 1 - octadecene used can be any value among 15 mL, 16 mL, 18 mL, 20 mL or the range value between any two of the above; the volume of oleic acid used can be any value among 6 mL, 8 mL, 10 mL or the range value between any two of the above; the molar ratio of ammonium fluoride and sodium hydroxide can be any value among 8:5, 8:5.2, 8:5.5 or the range value between any two of the above. Similar explanations can be made for the remaining range values involved in the steps, which will not be elaborated here.

[0071] In step S22, exemplarily: the molar ratio of ammonium fluoride and sodium hydroxide can be any value among 8:5, 8:5.2, 8:5.4, 8:5.5 or the range value between any two of the above. Similar explanations can be made for the remaining range values involved in the steps, which will not be elaborated here.

[0072] Example 5

[0073] This example provides a preparation method of a core - shell structured NaYGdF4:Yb 3+ ,Er 3+ @NaYF4 up - conversion particle dispersion liquid, including the following steps:

[0074] Dissolve 0.78 mmol of yttrium acetate, 0.05 mmol of gadolinium acetate hexahydrate, 0.2 mmol of ytterbium acetate tetrahydrate, and 0.02 mmol of erbium acetate in 15 mL of 1-octadecene and 6 mL of oleic acid, and place the mixture in a 100 mL three-necked flask. Slowly flush nitrogen into the three-necked flask to expel as much air in the flask as possible. Then, heat the mixture at 110 °C for 15 min, continue to flush nitrogen to remove the possible moisture in the flask. Subsequently, under a nitrogen atmosphere, stir and heat the mixture to 160 °C, and then cool it to room temperature. After that, add 4 mmol of ammonium fluoride and 2.5 mmol of sodium hydroxide to 10 mL of methanol solution respectively. After dissolving them evenly under magnetic stirring, add the obtained solution to the previous mixture. After complete dissolution, stir and heat it to 50 °C under nitrogen conditions and keep it for 30 min, then heat it to 100 °C under vacuum conditions and keep it for 30 minutes to completely remove methanol. Subsequently, continue to heat it to 310 °C and keep it at this temperature for 1.2 h. Finally, after natural cooling to room temperature, add ethanol to obtain a precipitate, centrifuge it at 7500 r / min for 25 min, pour off the supernatant, collect the precipitate product, wash it twice with ethanol and cyclohexane in turn, and then disperse the precipitate product in 10 mL of cyclohexane to obtain the NaYGdF4:Yb 3+ ,Er 3+ core layer solution.

[0075] Dissolve 1 mmol of yttrium acetate in 6 ml of oleic acid and 15 ml of 1-octadecene, place it in a three-necked flask and continuously stir and heat it to 160 °C until a transparent solution is formed while removing residual water and residues. After the temperature drops to 80 °C, add the NaYGdF4:Yb 3+ ,Er 3+ core layer solution. After complete dissolution, cool the mixed solution to room temperature. Add 4 mmol of NH4F and 2.5 mmol of NaOH to 10 mL of methanol solution respectively. After dissolving them evenly under magnetic stirring, add the obtained solution to the mixed solution, and then heat it to 120 °C under vacuum conditions and keep it for 25 min to completely remove methanol. Subsequently, heat the mixed solution to 320 °C in a nitrogen environment and keep it for 1 h. Finally, centrifuge the obtained mixed solution at a speed of 7000 - 8000 r / min for 25 min, pour off the supernatant, collect the granular precipitate product, wash it twice with ethanol and cyclohexane in turn to obtain the core-shell structured NaYGdF4:Yb 3+ ,Er 3+ @NaYF4 upconversion particles, as Figure 3 shown;

[0076] The core-shell structured NaYGdF4:Yb 3+ ,Er 3+@NaYF4 upconversion particles were dispersed in 10mL cyclohexane to obtain the core-shell structure of NaYGdF4:Yb 3+ ,Er 3+ @NaYF4 upconversion particle dispersion.

[0077] Depend on Figure 3 It can be seen that the size of the upconversion particles prepared by the present invention is at the level of 30-40 nm, and the upconversion nanoparticles have a relatively stable hexagonal crystal phase, and the interplanar spacing thereof conforms to the (100) crystal plane of the hexagonal phase of the upconversion nanoparticles.

[0078] Example 6

[0079] This embodiment provides a core-shell structure of NaYGdF4:Yb 3+ ,Er 3+ The method for preparing the NaYF4 upconversion particle dispersion comprises the following steps:

[0080] Dissolve 0.78mmol of yttrium chloride, 0.05mmol of gadolinium chloride, 0.2mmol of ytterbium chloride and 0.02mmol of erbium chloride in 15mL of 1-octadecene and 6mL of oleic acid, and place the mixture in a 100mL three-necked flask. Slowly flush nitrogen into the three-necked flask to remove as much air as possible from the flask. Then, heat the mixture at 110℃ for 15min, continue to charge nitrogen to remove any moisture that may be present in the flask. Then, stir and heat the mixture to 160℃ under a nitrogen atmosphere, and then cool to room temperature. After that, add 4mmol of ammonium fluoride and 2.5mmol of sodium hydroxide to 10mL of methanol solution respectively, dissolve evenly under magnetic stirring, add the resulting solution to the previous mixture, and after fully dissolving, stir and heat to 50℃ under nitrogen and keep for 30min, and then heat to 100℃ under vacuum and keep for 30 minutes to completely remove methanol. Then continue to heat to 310 ° C and keep at this temperature for 1.2 hours. Finally, after cooling naturally to room temperature, add ethanol to obtain a precipitate, centrifuge at a speed of 7500r / min for 25 minutes, pour out the supernatant, collect the precipitate, wash it twice with ethanol and cyclohexane in turn, and then disperse the precipitate in 10mL cyclohexane to obtain NaYGdF4:Yb 3+ ,Er 3+ Nuclear layer solution.

[0081] Dissolve 1 mmol of yttrium chloride in 6 ml of oleic acid and 15 ml of 1-octadecene in a three-necked flask and heat to 160 °C with continuous stirring until a transparent solution is formed. Remove the residual water and residues at the same time. When the temperature drops to 80 °C, add NaYGdF4:Yb 3+ ,Er 3+In the core layer solution, after complete dissolution, the mixed solution was cooled to room temperature. 4 mmol of NH4F and 2.5 mmol of NaOH were respectively added to 10 mL of methanol solution. After dissolving uniformly under magnetic stirring, the obtained solution was added to the mixed solution, and then heated to 120 °C under vacuum conditions and maintained for 25 min to completely remove methanol. Subsequently, the mixed solution was heated to 320 °C in a nitrogen environment and maintained for 1 h. Finally, the obtained mixed solution was centrifuged at a speed of 7000 - 8000 r / min for 25 min, the supernatant was poured out, and the particulate precipitate product was collected. After washing twice with ethanol and cyclohexane in sequence, core-shell structured NaYGdF4:Yb 3+ ,Er 3+ @NaYF4 upconversion particles were obtained;

[0082] Core-shell structured NaYGdF4:Yb 3+ ,Er 3+ @NaYF4 upconversion particles were dispersed in 10 mL of cyclohexane to obtain a dispersion of core-shell structured NaYGdF4:Yb 3+ ,Er 3+ @NaYF4 upconversion particle dispersion.

[0083] Example 7

[0084] This example provides a method for preparing a dispersion of core-shell structured NaYGdF4:Yb 3+ ,Er 3+ @NaYF4 upconversion particle dispersion, which includes the following steps:

[0085] Dissolve 0.78 mmol of yttrium chloride, 0.05 mmol of gadolinium chloride, 0.2 mmol of ytterbium chloride and 0.02 mmol of erbium chloride in 15 mL of 1-octadecene and 6 mL of oleic acid, and place the mixture in a 100 mL three-necked flask. Slowly flush nitrogen into the three-necked flask to expel as much air in the flask as possible. Then, heat the mixture at 110 °C for 15 min, continue to flush nitrogen to remove the possible moisture in the flask. Subsequently, under a nitrogen atmosphere, stir and heat the mixture to 160 °C, and then cool it to room temperature immediately. After that, add 4 mmol of ammonium fluoride and 2.7 mmol of sodium hydroxide to 10 mL of methanol solution respectively. After dissolving them evenly under magnetic stirring, add the obtained solution to the previous mixture. After fully dissolving, stir and heat it to 50 °C under nitrogen conditions and keep it for 30 min, and then heat it to 100 °C under vacuum conditions and keep it for 30 minutes to completely remove methanol. Subsequently, continue to heat it to 310 °C and keep it at this temperature for 1.2 h. Finally, after naturally cooling to room temperature, add ethanol to obtain a precipitate, centrifuge it at 7500 r / min for 25 min, pour off the supernatant, collect the precipitate product, wash it with ethanol and cyclohexane twice in sequence, and then disperse the precipitate product in 10 mL of cyclohexane to obtain NaYGdF4:Yb 3+ ,Er 3+ core layer solution.

[0086] Dissolve 1 mmol of yttrium chloride in 6 ml of oleic acid and 15 ml of 1-octadecene, place it in a three-necked flask and continuously stir and heat it to 160 °C until a transparent solution is formed while removing residual water and residues. When the temperature drops to 80 °C, add NaYGdF4:Yb 3+ ,Er 3+ in the core layer solution. After fully dissolving, cool the mixed solution to room temperature. Add 4 mmol of NH4F and 2.7 mmol of NaOH to 10 mL of methanol solution respectively. After dissolving them evenly under magnetic stirring, add the obtained solution to the mixed solution, and then heat it to 120 °C under vacuum conditions and keep it for 25 min to completely remove methanol. Subsequently, heat the mixed solution to 320 °C in a nitrogen environment and keep it for 1 h. Finally, centrifuge the obtained mixed solution at a speed of 7000 - 8000 r / min for 25 min, pour off the supernatant, collect the particulate precipitate product, wash it with ethanol and cyclohexane twice in sequence to obtain core-shell structured NaYGdF4:Yb 3+ ,Er 3+ @NaYF4 upconversion particles;

[0087] The core-shell structured NaYGdF4:Yb 3+ ,Er 3+ @NaYF4 upconversion particles are dispersed in 10 mL of cyclohexane to obtain core-shell structured NaYGdF4:Yb3+ ,Er 3+ @NaYF4 upconversion particle dispersion.

[0088] Example 8

[0089] This embodiment provides a core-shell structure of NaYGdF4:Yb 3+ ,Er 3+ The method for preparing the NaYF4 upconversion particle dispersion comprises the following steps:

[0090] Dissolve 0.78mmol of yttrium acetate, 0.05mmol of gadolinium acetate hexahydrate, 0.2mmol of ytterbium acetate tetrahydrate and 0.02mmol of erbium acetate in 15mL of 1-octadecene and 6mL of oleic acid, and place the mixture in a 100mL three-necked flask. Slowly flush nitrogen into the three-necked flask to remove as much air as possible. Then, heat the mixture at 110℃ for 15min, continue to charge nitrogen to remove any water that may be present in the flask. Then, stir and heat the mixture to 160℃ under a nitrogen atmosphere, and then cool to room temperature. After that, add 4mmol of ammonium fluoride and 2.5mmol of sodium hydroxide to 10mL of methanol solution respectively, dissolve evenly under magnetic stirring, add the resulting solution to the previous mixture, and after fully dissolving, stir and heat to 50℃ under nitrogen and keep for 30min, and then heat to 100℃ under vacuum and keep for 30 minutes to completely remove methanol. Then continue to heat to 310 ° C and keep at this temperature for 1.2 hours. Finally, after cooling naturally to room temperature, add ethanol to obtain a precipitate, centrifuge at a speed of 7500r / min for 25 minutes, pour out the supernatant, collect the precipitate, wash it twice with ethanol and cyclohexane in turn, and then disperse the precipitate in 10mL cyclohexane to obtain NaYGdF4:Yb 3+ ,Er 3+ Nuclear layer solution.

[0091] Dissolve 1 mmol of yttrium acetate in 6 ml of oleic acid and 15 ml of 1-octadecene in a three-necked flask and heat to 160 °C with continuous stirring until a transparent solution is formed. Remove the residual water and residue at the same time. When the temperature drops to 80 °C, add NaYGdF4:Yb 3+ ,Er 3+In the nuclear layer solution, after complete dissolution, the mixed solution was cooled to room temperature. 4 mmol of NH4F and 2.5 mmol of NaOH were respectively added to 10 mL of methanol solution. After being dissolved evenly under magnetic stirring, the obtained solution was added to the mixed solution, and then heated to 120 °C under vacuum conditions and maintained for 25 min to completely remove methanol. Subsequently, the mixed solution was heated to 320 °C in a nitrogen environment and maintained for 1 h. Finally, the obtained mixed solution was centrifuged at a speed of 7000 - 8000 r / min for 25 min, the supernatant was poured out, and the granular precipitate product was collected. After washing twice with ethanol and cyclohexane in sequence, the core-shell structured NaYGdF4:Yb 3+ ,Er 3+ @NaYF4 upconversion particles were obtained;

[0092] The core-shell structured NaYGdF4:Yb 3+ ,Er 3+ @NaYF4 upconversion particles were dispersed in 10 mL of cyclohexane to obtain the core-shell structured NaYGdF4:Yb 3+ ,Er 3+ @NaYF4 upconversion particle dispersion.

[0093] Example 9

[0094] This example provides a method for preparing a core-shell structured NaYGdF4:Yb 3+ ,Er 3+ @NaYF4 upconversion particle dispersion, which includes the following steps:

[0095] Dissolve 0.78mmol of yttrium acetate, 0.05mmol of gadolinium acetate hexahydrate, 0.2mmol of ytterbium acetate tetrahydrate and 0.02mmol of erbium acetate in 15mL of 1-octadecene and 6mL of oleic acid, and place the mixture in a 100mL three-necked flask. Slowly flush nitrogen into the three-necked flask to remove as much air as possible. Then, heat the mixture at 110℃ for 15min, continue to charge nitrogen to remove any water that may be present in the flask. Then, stir and heat the mixture to 160℃ under a nitrogen atmosphere, and then cool to room temperature. After that, add 4mmol of ammonium fluoride and 2.5mmol of sodium hydroxide to 10mL of methanol solution respectively, dissolve evenly under magnetic stirring, add the resulting solution to the previous mixture, and after fully dissolving, stir and heat to 50℃ under nitrogen and keep for 30min, and then heat to 100℃ under vacuum and keep for 30 minutes to completely remove methanol. Then continue to heat to 310 ° C and keep at this temperature for 1.2 hours. Finally, after cooling naturally to room temperature, add ethanol to obtain a precipitate, centrifuge at a speed of 7500r / min for 25 minutes, pour out the supernatant, collect the precipitate, wash it twice with ethanol and cyclohexane in turn, and then disperse the precipitate in 10mL cyclohexane to obtain NaYGdF4:Yb 3+ ,Er 3+ Nuclear layer solution.

[0096] Dissolve 1 mmol of yttrium acetate in 6 ml of oleic acid and 15 ml of 1-octadecene in a three-necked flask and heat to 160 °C with continuous stirring until a transparent solution is formed. Remove the residual water and residue at the same time. When the temperature drops to 80 °C, add NaYGdF4:Yb 3+ ,Er 3+ In the core layer solution, after fully dissolving, the mixed solution was cooled to room temperature. 4mmol NH4F and 2.5mmol NaOH were added to 10mL of methanol solution respectively. After dissolving evenly under magnetic stirring, the resulting solution was added to the mixed solution, and then heated to 120℃ under vacuum conditions for 25min to completely remove methanol. The mixed solution was then heated to 320℃ in a nitrogen environment for 1h. Finally, the obtained mixed solution was centrifuged at a speed of 7000-8000r / min for 25min, the supernatant was poured off, the particle precipitation product was collected, and washed twice with ethanol and cyclohexane in turn to obtain NaYGdF4:Yb with a core-shell structure. 3+ ,Er 3+ @NaYF4 upconversion particles;

[0097] Core-shell structure of NaYGdF4:Yb 3+ ,Er 3+ @NaYF4 upconversion particles were dispersed in 10mL cyclohexane to obtain the core-shell structure of NaYGdF4:Yb3+ , Er 3+ @NaYF4 upconversion particle dispersion liquid.

[0098] In an embodiment of the present invention, the preparation of the upconversion layer 3 includes the following steps: spin-coating a core-shell structured NaYGdF4:Yb 3+ , Er 3+ @NaYF4 upconversion particle dispersion liquid on the perovskite thin film layer 2 at a rotation speed of 2000 - 3000 rpm, and then annealing at 100 - 130 °C for 5 - 10 min to obtain the upconversion layer 3.

[0099] Specifically, the spin-coating rotation speed can be any value among 2000 rpm, 2500 rpm, 3000 rpm or the range value between any two of the above; the annealing temperature is any value among 100 °C, 110 °C, 120 °C, 130 °C or the range value between any two of the above, and the time is any value among 5 min, 8 min, 10 min or the range value between any two of the above.

[0100] Based on the MAPbI3 perovskite thin film layer 2 prepared in Example 1 and the core-shell structured NaYGdF4:Yb 3+ , Er 3+ @NaYF4 upconversion particle dispersion liquid prepared in Example 5, the preparation of the upconversion layer 3 is provided in the following examples.

[0101] Example 11

[0102] The preparation method of the upconversion layer 3 in this example includes the following steps:

[0103] Spin-coat a 0.1 mmol / ml core-shell structured NaYGdF4:Yb 3+ , Er 3+ @NaYF4 upconversion particle dispersion liquid on the MAPbI3 perovskite thin film layer 2 at a rotation speed of 2000 rpm, and then anneal at 100 °C for 5 min to obtain an upconversion layer 3 with a thickness of 460 nm, as Figure 4 shown.

[0104] It can be Figure 4 seen that the upconversion nanoparticles prepared by the present invention have good dispersibility after being spin-coated on the surface of the perovskite layer.

[0105] Example 12

[0106] The preparation method of the upconversion layer 3 in this example includes the following steps:

[0107] Spin-coat a 0.1 mmol / ml core-shell structured NaYGdF4:Yb on the MAPbI3 perovskite thin film layer 2 at a rotation speed of 2400 rpm3+ , Er 3+ After the @NaYF4 upconversion particle dispersion liquid, it was annealed at 110 °C for 6 min to obtain the upconversion layer 3 with a thickness of 440 nm.

[0108] Example 13

[0109] The preparation method of the upconversion layer 3 in this example includes the following steps:

[0110] Spin-coat 0.1 mmol / ml core-shell structured NaYGdF4:Yb 3+ , Er 3+ @NaYF4 upconversion particle dispersion liquid on the MAPbI3 perovskite thin film layer 2, and then anneal it at 120 °C for 8 min to obtain the upconversion layer 3 with a thickness of 400 nm.

[0111] Example 14

[0112] The preparation method of the upconversion layer 3 in this example includes the following steps:

[0113] Spin-coat 0.1 mmol / ml core-shell structured NaYGdF4:Yb 3+ , Er 3+ @NaYF4 upconversion particle dispersion liquid on the MAPbI3 perovskite thin film layer 2, and then anneal it at 100 °C for 10 min to obtain the upconversion layer 3 with a thickness of 500 nm.

[0114] In the embodiment of the present invention, the preparation of the electrode layer 4 includes the following steps: deposit the electrode layer 4 with a thickness of 80 nm to 100 nm and a spacing of 150 to 180 μm on the upconversion layer 3 by thermal evaporation process to obtain the photodetector.

[0115] Furthermore, the process conditions of the thermal evaporation process include: use a mechanical pump and a molecular pump to make the vacuum degree in the sample chamber 3×10 -4 -5×10 -4 Pa, and start to pass current through the tungsten boat with solid gold particles to heat it up to about 2800 °C. After the gold atoms or molecules obtain sufficient kinetic energy, they break away from the solid / liquid surface to form a vapor phase, and thus deposit on the sample to form a gold electrode.

[0116] Specifically, the thickness of the electrode layer 4 can be any value among 80 nm, 90 nm, 100 nm or the range value between any two of the above, and the spacing is any value among 150 μm, 160 μm, 170 μm, 180 μm or the range value between any two of the above.

[0117] Based on the upconversion layer 3 prepared in Example 11, the preparation of the electrode layer 4 is carried out, and the following examples are provided.

[0118] Example 15

[0119] This example provides a preparation method of the electrode layer 4, including the following steps:

[0120] A gold electrode layer 4 with a thickness of 90 nm and a pitch of 150 μm is deposited on the upconversion layer 3 by a thermal evaporation process to obtain a photodetector.

[0121] Example 16

[0122] This example provides a preparation method of the electrode layer 4, including the following steps:

[0123] A gold electrode layer 4 with a thickness of 80 nm and a pitch of 160 μm is deposited on the upconversion layer 3 by a thermal evaporation process to obtain a photodetector.

[0124] Example 17

[0125] This example provides a preparation method of the electrode layer 4, including the following steps:

[0126] A gold electrode layer 4 with a thickness of 100 nm and a pitch of 170 μm is deposited on the upconversion layer 3 by a thermal evaporation process to obtain a photodetector.

[0127] Example 18

[0128] This example provides a preparation method of the electrode layer 4, including the following steps:

[0129] A gold electrode layer 4 with a thickness of 90 nm and a pitch of 180 μm is deposited on the upconversion layer 3 by a thermal evaporation process to obtain a photodetector.

[0130] The voltage-current test of the photodetector prepared in Example 15 is carried out using a Keithley 4200 digital source meter, and the voltage test range is -10 V to 10 V. The current diagrams under dark conditions, under green light illumination at 500 nm with an intensity of 0.8 mW / cm 2 and under near-infrared light excitation at 980 nm with an intensity of 50 mW / cm 2 are tested. The test results are as Figure 5 shown.

[0131] It can be Figure 5 seen that: under green light illumination, the photocurrent is higher than the dark current, showing a positive photoconductivity characteristic; under infrared light illumination, the photocurrent is lower than the dark current, showing a negative photoconductivity characteristic. This shows that the photodetector prepared by the present invention can exhibit bipolar response under different wavelength light excitations under a fixed bias condition, demonstrating excellent optoelectronic performance characteristics.

[0132] The fabricated photodetector was subjected to optoelectronic performance testing. Under a bias voltage of 10 V, the photocurrent and dark current of the device were measured. Generally, the performance of a photodetector is examined using the photoresponsivity, the normalized specific detectivity, and the external quantum efficiency. Their formulas are described as follows:

[0133]

[0134]

[0135] In the formulas, I photo and I dark are the photocurrent and dark current of the detection device respectively, P is the light power density of the light source, S is the effective response area, h is Planck's constant, e is the electric charge quantity, and c is the speed of light.

[0136] The test results were as follows: Under the excitation of green light with a wavelength of 500 nm and an intensity of 0.8 mW / cm 2 , when a bias voltage of 10 V was applied, the responsivity was 41.22 mA / W, the normalized specific detectivity was 3.31×10 8 Jones, and the external quantum efficiency was 10.22%. Under the excitation of near-infrared light with a wavelength of 980 nm and an intensity of 50 mW / cm 2 , when a bias voltage of 10 V was applied, it was found that the photocurrent was lower than the dark current. The calculated responsivity was 100.24 μA / W, the normalized specific detectivity was 7.91×10 5 Jones, and the external quantum efficiency was 1.273×10 -2 %.

[0137] Comparative Example 1

[0138] The difference from Example 15 was that when preparing the upconversion particles, gadolinium acetate hexahydrate was not added, and the steps were adjusted adaptively while the other conditions remained unchanged.

[0139] The above optoelectronic performance testing was carried out on the photodetector prepared in Comparative Example 1. The test results were as follows: Under the excitation of green light with a wavelength of 500 nm and an intensity of 0.8 mW / cm 2 , when a bias voltage of 10 V was applied, the responsivity was 28.45 mA / W, the normalized specific detectivity was 2.67×10 8 Jones, and the external quantum efficiency was 7.06%. Under the excitation of near-infrared light with a wavelength of 980 nm and an intensity of 50 mW / cm 2 , when a bias voltage of 10 V was applied, it was found that the photocurrent was lower than the dark current. The calculated responsivity was 46.41 μA / W, the normalized specific detectivity was 5.48×10 5Jones, the external quantum efficiency is 5.89×10 -3 %.

[0140] It can be found through comparison that the upconversion particles containing Gd element can improve the optoelectronic performance of the photodetector. This is because the doping of Gd 3+ ions into the NaYF4 matrix does not replace the Y 3+ ions in the matrix, and the effective radius of Gd 3+ ions is larger than that of Y 3+ ions. This replacement will cause the lattice expansion of the upconversion nanoparticles, and then increase the lattice plane spacing of NaYGdF4. This change not only helps the formation of the hexagonal phase of the upconversion nanoparticles, but also enhances the upconversion effect and thus improves the optoelectronic performance of the device.

[0141] Comparative Example 2

[0142] The difference from Example 15 is that: directly use 0.1 mmol / ml of NaYGdF4:Yb 3+ ,Er 3+ core layer solution to prepare the upconversion layer 3, and make adaptive adjustments to the steps, and keep the other conditions unchanged.

[0143] Perform the above optoelectronic performance tests on the photodetector prepared in Comparative Example 2. The test results are as follows: under the green light excitation with a wavelength of 500 nm and an intensity of 0.8 mW / cm 2 , when a bias voltage of 10 V is applied, the responsivity is 29.25 mA / W, and the normalized specific detectivity is 2.74×10 8 Jones, the external quantum efficiency is 7.25%. Under the near-infrared light excitation with a wavelength of 980 nm and an intensity of 50 mW / cm 2 , when a bias voltage of 10 V is applied, it is found that the photocurrent is lower than the dark current, and the calculated responsivity is 57.4 μA / W, and the normalized specific detectivity is 5.98×10 5 Jones, the external quantum efficiency is 7.29×10 -3 %.

[0144] It can be found through comparison that the core-shell structured upconversion particles can improve the optoelectronic performance of the device. This is because by epitaxial growth of an inert shell layer, surface defects can be suppressed and the hexagonal phase structure can be stabilized, and after encapsulation, the core particles can be isolated from the outside world, reducing the energy loss of the core nanoparticles, thereby enhancing the upconversion effect.

[0145] Comparative Example 3

[0146] The difference from Example 15 is that: when preparing the upconversion layer 3, use 0.05 mmol / L of the core-shell structured NaYGdF4:Yb3+ , Er 3+ Spin coating was carried out on the @NaYF4 upconversion particle dispersion, and the other conditions remained unchanged.

[0147] The above-mentioned optoelectronic performance tests were carried out on the photodetector prepared in Comparative Example 3. The test results were as follows: under the excitation of green light with a wavelength of 500 nm and an intensity of 0.8 mW / cm 2 , when a bias voltage of 10 V was applied, the responsivity was 225.66 mA / W, the normalized specific detectivity was 2.61×10 8 Jones, and the external quantum efficiency was 6.36%. Under the excitation of near-infrared light with a wavelength of 980 nm and an intensity of 50 mW / cm 2 , when a bias voltage of 10 V was applied, it was found that the photocurrent was lower than the dark current. The calculated responsivity was 36.91 μA / W, the normalized specific detectivity was 4.78×10 5 Jones, and the external quantum efficiency was 46.8×10 -3 %.

[0148] It can be found by comparison that upconversion nanoparticles with different concentrations will affect the upconversion effect. The detector prepared with the upconversion nanoparticle dispersion with a concentration of 0.1 mmol / L according to the present invention has a stronger upconversion effect, so the hindrance effect on carriers under 980 nm light illumination is stronger.

[0149] Comparative Example 4

[0150] The difference from Example 15 is that the thickness of the upconversion layer is 520 nm, and the other conditions remain unchanged.

[0151] The above-mentioned optoelectronic performance tests were carried out on the photodetector prepared in Comparative Example 4. The test results were as follows: under the excitation of green light with a wavelength of 500 nm and an intensity of 0.8 mW / cm 2 , when a bias voltage of 10 V was applied, the responsivity was 20.26 mA / W, the normalized specific detectivity was 2.01×10 8 Jones, and the external quantum efficiency was 5.31%. Under the excitation of near-infrared light with a wavelength of 980 nm and an intensity of 50 mW / cm 2 , when a bias voltage of 10 V was applied, it was found that the photocurrent was lower than the dark current. The calculated responsivity was 30.82 μA / W, the normalized specific detectivity was 4.05×10 5 Jones, and the external quantum efficiency was 41.2×10 -3 %.

[0152] Comparative Example 5

[0153] The difference from Example 15 is that the thickness of the upconversion layer is 350 nm, and the other conditions remain unchanged.

[0154] The above-mentioned optoelectronic performance tests were carried out on the photodetector prepared in Comparative Example 5, and the test results were as follows: under the excitation of green light with a wavelength of 500 nm and an intensity of 0.8 mW / cm 2 , when a bias voltage of 10 V was applied, the responsivity was 34.62 mA / W, the normalized specific detectivity was 2.62×10 8 Jones, and the external quantum efficiency was 7.42%. Under the excitation of near-infrared light with a wavelength of 980 nm and an intensity of 50 mW / cm 2 , when a bias voltage of 10 V was applied, it was found that the photocurrent was lower than the dark current. The calculated responsivity was 45.02 μA / W, the normalized specific detectivity was 5.24×10 5 Jones, and the external quantum efficiency was 56.1×10 -3 %.

[0155] It can be found by comparison that the thickness of the upconversion particle film has an impact on the optoelectronic performance of the device. The higher the thickness, the stronger the hindrance of the upconversion layer to carriers, making it more difficult for carriers to cross the upconversion layer to reach the top electrode, thereby enhancing the negative response of the device; if the thickness is too low, it will result in less light absorption and a decrease in its negative response.

[0156] In summary, the photodetector prepared by the method of the present invention has excellent responsivity and external quantum efficiency, indicating its better optoelectronic performance.

[0157] The above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A detector with positive and negative light response, characterized in that: include: A substrate layer (1), and a perovskite thin film layer (2), an upconversion layer (3), and an electrode layer (4) sequentially stacked on the substrate layer (1); The up-conversion layer includes a core-shell structure of NaYGdF4:Yb 3+ ,Er 3+ @NaYF4 upconversion particles.

2. The detector with positive and negative photoresponse as claimed in claim 1, characterized in that: The thickness of the up-conversion layer (3) is 400-500 nm.

3. A method for preparing a detector having positive and negative photoresponse as claimed in claim 1 or 2, characterized in that: The following steps are involved: S1, preparing a perovskite thin film layer (2) on a substrate layer (1) by a two-step spin coating method; S2, using static spin coating method to prepare the core-shell structure of NaYGdF4:Yb 3+ ,Er 3+ @NaYF4 upconversion particles are coated onto the perovskite thin film layer (2) to prepare an upconversion layer (3); S3, vapor-depositing an electrode layer (4) on the up-conversion layer (3) to obtain a photodetector.

4. The method for preparing a detector having positive and negative light responses according to claim 3, characterized in that: In step S1, the preparation of the perovskite thin film layer (2) specifically includes: A MAPbI3 perovskite precursor solution is prepared, and under the protection of an inert gas, the MAPbI3 perovskite precursor solution is spin-coated on the substrate layer (1), and the spin-coating conditions are as follows: in the first step, the solution is spin-coated at a rotation speed of 800 to 1000 rpm for 10 to 15 seconds, and in the second step, the solution is spin-coated at a rotation speed of 3000 to 3500 rpm for 40 to 45 seconds. 15 to 20 seconds before the end of the second step of spin coating, chlorobenzene is dropped onto the rotating MAPbI3 substrate. After the spin coating is completed, the solution is annealed at 100 to 120° C. for 5 to 10 minutes to form a perovskite thin film layer (2) on the substrate layer (1).

5. The method for preparing a detector having positive and negative light responses according to claim 4, characterized in that: The preparation method of the MAPbI3 perovskite precursor solution is as follows: methylammonium iodide and lead iodide are mixed and dissolved in an organic solvent at a molar ratio of 1:1 to 1.2, and stirred at 60 to 80° C. for more than 24 hours to obtain the MAPbI3 perovskite precursor solution.

6. The method for preparing a detector having positive and negative photoresponse according to claim 3, characterized in that: In step S2, the preparation of the up-conversion layer (3) specifically comprises: The core-shell structure NaYGdF4:Yb is spin-coated on the perovskite film layer (2) at a rotation speed of 2000-3000 rpm. 3+ ,Er 3 + @NaYF4 upconversion particle dispersion is then annealed at 100-130°C for 5-10 minutes to obtain an upconversion layer (3).

7. The method for preparing a detector having positive and negative photoresponse according to claim 6, characterized in that: The core-shell structure of NaYGdF4:Yb 3+ ,Er 3+ The preparation of the NaYF4 upconversion particle dispersion includes the following steps: S21, after preparing a precursor solution containing yttrium source, gadolinium source, ytterbium source and erbium source, add methanol solution of ammonium fluoride and methanol solution of sodium hydroxide, stir and dissolve, heat under inert gas, add ethanol to precipitate the product, centrifuge and wash the precipitate, dissolve in cyclohexane to obtain NaYGdF4:Yb 3+ ,Er 3+ Nuclear layer solution; S22, adding the precursor solution containing yttrium source, methanol solution of ammonium fluoride and methanol solution of sodium hydroxide into the NaYGdF4:Yb 3+ ,Er 3+ The core layer solution was heated under inert gas, centrifuged and the precipitate was collected, washed and dispersed in cyclohexane to obtain the core-shell structure NaYGdF4:Yb 3+ ,Er 3+ @NaYF4 upconversion particle dispersion.

8. The method for preparing a detector having positive and negative light responses according to claim 7, characterized in that: In step S21, the molar ratio of the yttrium source, the gadolinium source, the ytterbium source and the erbium source is 78:5:20:2; and the molar ratio of the ammonium fluoride to the sodium hydroxide is 8:5-5.

5.

9. The method for preparing a detector having positive and negative light responses according to claim 7, characterized in that: In step S22, the molar ratio of the ammonium fluoride to the sodium hydroxide is 8:5-5.

5.

10. The method for preparing a detector having positive and negative photoresponse according to claim 3, characterized in that: In step S3, the thickness of the electrode layer is 80-100 nm, and the distance between two adjacent electrode layers is 150-180 nm.

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