NaBiS 2 Polycrystalline thin film material, TiO 2 / NaBiS 2 heterojunction thin film and its optoelectronic detection application

Abstract

The present invention discloses a NaBiS2 polycrystalline thin film material, a TiO2 / NaBiS2 heterojunction thin film and their optoelectronic detection applications, belonging to the technical fields of new electronic materials and new devices. The present invention uses a secondary solution reaction method of a ternary solvent system of ethylenediamine, β-mercaptoethanol and 1,2-ethanedithiol to dissolve sodium hydroxide, bismuth oxide and sublimed sulfur as a precursor solution for forming NaBiS2, and adopts a solution spin-coating method to grow a pure-phase cubic NaBiS2 thin film with a band gap of 1.35 eV, and the surface morphology is flat, uniform and crack-free. The preparation process of the thin film is simple, the cost is low, and the product is a pure phase. At the same time, the present invention proposes an optoelectronic detection application of its heterojunction TiO2. The optoelectronic detector is successively composed of an FTO substrate, a TiO2 porous layer, a NaBiS2 light-absorbing layer and a cheap carbon electrode. A heterojunction is formed by combining the NaBiS2 light-absorbing layer with the TiO2 porous layer, making it have good self-powered characteristics, and providing an example of a new semiconductor thin film material, a preparation method and an optoelectronic detection application in the field of electronic materials and devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of new electronic materials and new devices, and specifically relates to a NaBiS 2 Polycrystalline thin film materials, TiO 2 / NaBiS 2 Heterojunction thin films and their photoelectric detection applications. Background Art

[0002] Semiconductor materials have a very broad application prospect in the field of electronic materials and devices. They have semiconductor properties and can be used to make semiconductor functional devices such as photodetectors, photodiodes, and solar cells. Among them, photodetectors have the ability to convert optical signals into electrical signals. This device has become a hot research topic in recent years and has important applications in communications, national defense, biomedicine, environmental monitoring, ocean detection, flame detection and other fields. Self-powered photodetectors can operate at zero volt bias, which has unique advantages in miniaturization, portability and sustainable operation of equipment without the need for additional external power supply.

[0003] In recent years, many semiconductor materials have been used in the light absorption layer of photodetectors, such as ZnO, MoS 2 , halide perovskites, etc., but there are still arduous challenges in terms of materials, processes, overall performance, etc. For example, the production efficiency of two-dimensional crystal structure materials obtained by mechanical exfoliation or transfer is low and often limited to laboratory research, and the integration compatibility is poor; the emerging halide perovskite materials are limited by the high toxicity of elements, poor air stability, and difficulty in large-area integration. Therefore, there is an urgent need to develop alternative new semiconductor materials. Recently, alkali bismuth ternary sulfide (ABiS 2 ) (A = Li, Na and K) have attracted great interest in photodetectors due to their non-toxicity, tunable band gap and low cost. 2 As ABiS 2 A member of the family, it has a narrow band gap of 1.35 eV, excellent photostability, and high chemical stability, and has the properties of mixed ions and covalent bonds, similar to halide perovskites, and is a promising photodetector material. However, due to the preparation of NaBiS 2 The raw materials are complex and difficult to dissolve, and the product is easy to form a single Bi with impurities. This has led to the development of pure phase cubic crystal structure NaBiS 2 Polycrystalline thin films are extremely difficult to produce, especially to obtain ideal high-quality thin film morphology, which seriously hinders the development of NaBiS 2 Application prospects of polycrystalline materials.

[0004] The existing technology discloses "a three-dimensional sodium bismuth sulfur flower-like microsphere structure and its preparation method and its application in wide-spectrum photodetectors" (publication number: CN114758896A). The method is a hydrothermal method, which uses sodium hydroxide, thiourea, and bismuth oxide to mix and place in a reactor to heat to form NaBiS 2 Flower-like microsphere powder, and then NaBiS 2 The flower-like microspheres were dispersed in deionized water or ethanol and then spin-coated into films. The polysulfide solution was then mixed with NaBiS 2 However, from the SEM image in the invention, it can be seen that the pores of the film are relatively large because the invention is synthesized by hydrothermal method NaBiS 2 Flower-shaped microsphere powder is dispersed in deionized water or ethanol for spin coating, instead of forming a precursor solution, which results in relatively large holes in the spin-coated film, which has a significant adverse effect on the photoelectric performance of the device. Another technical disclosure of "Application of Sodium Bismuth Disulfide Nanoparticles" (Publication No.: CN103553129B) is also a hydrothermal method, which uses a mixture of sodium hydroxide, carbon disulfide, and bismuth nitrate, and puts it into a reactor and heats it to form NaBiS 2 Nanoparticles, however, did not obtain NaBiS 2 Polycrystalline thin films. Generally, thin films have advantages over powders in terms of performance, stability, and application areas. However, it is relatively difficult to prepare high-quality thin films, especially for the development of NaBiS 2 Polycrystalline thin film. In the existing literature, Chi Yang et al. (ACS Appl. Energy Mater. 2019, 2, 182-186) successfully prepared NaBiS2 nanocrystals, but still spin-coated them in the form of a dispersion; Khadijeh Pournemat et al. (Journal of Colloid and Interface Science, 2023, 641: 1000-1013) used a hydrothermal method to synthesize TiO 2 、Bi 2 O 3 、NaBiS 2 Mixed powders are used in the field of photocatalysis; Huanchun Wang et al. (Catalysts, 2020, 10(4): 413) used a hydrothermal method to synthesize NaBiS 2 Powder and used in the field of photocatalysis. 2 There are few reports on the synthesis and optical detection of polycrystalline thin films, especially the use of NaBiS 2 The precursor solution forms a smooth, uniform, high-quality NaBiS 2 Therefore, the development of a NaBiS 2The solution synthesis method of polycrystalline thin films, improving their morphology, studying their optoelectronic properties and optoelectronic applications have far-reaching reference significance for the development of the next generation of optoelectronic technology. Summary of the invention

[0005] In view of the problems existing in the above disclosed technologies, the present invention proposes a cubic crystal structure NaBiS 2 Polycrystalline thin film materials, TiO 2 / NaBiS 2 Heterojunction thin film and its photoelectric detection application. The present invention discloses a pure phase cubic crystal structure of NaBiS 2 A method for preparing a polycrystalline thin film by a three-solvent secondary solution reaction method to prepare NaBiS 2 The precursor solution was spin-coated to obtain a uniform, dense, crack-free NaBiS 2 Polycrystalline thin film. At the same time, the present invention provides TiO 2 / NaBiS 2 Heterojunction photodetection applications, NaBiS 2 Polycrystalline thin film as light absorbing layer and TiO 2 The porous layers are combined to form a heterojunction, and combined with a cheap carbon electrode to form a photodetector, which exhibits low dark current and self-powered characteristics, thereby realizing a photodetector with excellent self-powered characteristics. Specifically, the present invention adopts the following technical solutions:

[0006] First, the present invention provides a NaBiS 2 The synthesis method of polycrystalline thin film is as follows: ethylenediamine and β-mercaptoethanol are used to initially dissolve sodium hydroxide, bismuth oxide, and sublimed sulfur, and the mixture is reacted at 50-70 °C for 6 h, and then allowed to stand and part of the supernatant is removed to form a primary solution. 1,2-ethanedithiol is then added to the primary solution and reacted at 50-70 °C for 3 h to form a secondary solution, namely NaBiS 2 Precursor solution, and then pure phase cubic NaBiS is grown on the substrate by solution spin coating. 2 Thin film materials.

[0007] Among them, preferably, the mass ratio of sodium hydroxide, bismuth oxide and sublimated sulfur is 0.05-0.06:0.2-0.25:0.15-0.18.

[0008] Preferably, the volume ratio of ethylenediamine to β-mercaptoethanol is 3.8-4.2:0.8-1.2.

[0009] Preferably, the volume ratio of the primary solution to 1,2-ethanedithiol is 1.8-2.2:0.8-1.2.

[0010] Second, the present invention also provides a TiO 2 / NaBiS 2 Heterojunction film, which is based on NaBiS 2 Thin film and TiO 2 The porous layer forms a heterojunction. 2 / NaBiS 2 Preparation method of heterojunction thin film:

[0011] Preferably, TiO 2 We use 30 NR-D TiO2 produced by Greatcell Solar in Australia. 2 The slurry was mixed with ethanol at a mass ratio of 1:5 and stirred at room temperature for 1 day to obtain TiO 2 The solution was then spin-coated on the substrate and then placed in a muffle furnace for annealing at 125 °C for 5 min; 325 °C for 5 min; 375 °C for 5 min; and 450 °C for 30 min to obtain TiO 2 Porous layer.

[0012] Preferably, TiO 2 / NaBiS 2 The heterojunction film is made of NaBiS 2 The precursor solution was spin-coated on a TiO 2 The porous layer was deposited on the substrate by using a coating machine at an acceleration of 500 rad / s to 2000 rpm, rotating for 20 s, annealing on a hot stage at 400 °C for 10 min, cooling for 5 min, and repeating for 3 times to obtain TiO 2 / NaBiS 2 Heterojunction thin films.

[0013] Third, the TiO 2 / NaBiS 2 The heterojunction film can be used in semiconductor optoelectronic devices, such as photodetectors, solar cells, photoelectric storage devices or photodiodes. 2 / NaBiS 2 The heterojunction film is more suitable for application in photodetectors. The photodetector obtained by the present invention exhibits low dark current and good self-powered performance. 2 The material can be used as a photosensitive thin film light absorbing layer of a photodetector. The application can be carried out using a method comprising the following steps:

[0014] 1) Clean the conductive glass substrate and spin coat TiO on it 2 porous layer;

[0015] 2) Solution-grown NaBiS on the porous layer 2 film;

[0016] 3) In NaBiS 2 The film is covered with a cheap carbon electrode.

[0017] A self-powered photodetection device can be obtained by the above method.

[0018] Furthermore, the TiO 2 / NaBiS 2 Heterojunction thin films are used in photodetector applications, which can be achieved using the following method steps:

[0019] Step 1: Configure TiO 2 Solution

[0020] The 30 NR-D TiO2 produced by Greatcell Solar in Australia was purchased. 2 The slurry was mixed with ethanol and stirred at room temperature for 1 day to obtain TiO 2 Solution.

[0021] Step 2: Spin coating TiO 2 layer

[0022] Place the cleaned FTO in an ozone cleaning machine for 15 min. 2 The solution was spin-coated on FTO and annealed to form FTO / TiO 2 structure.

[0023] Step 3: Preparation of NaBiS 2 polycrystalline film

[0024] FTO / TiO 2 Place in ozone cleaning machine for 15 min, then place in nitrogen filled glove chamber, and place FTO / TiO 2 Place it on the glue machine and mix the prepared NaBiS 2 Solution spin coating on FTO / TiO 2 Then anneal and cool for 3 times to obtain FTO / TiO 2 / NaBiS 2 Composite laminated film structure.

[0025] Step 4: Build the carbon electrode

[0026] In FTO / TiO 2 / NaBiS 2 A layer of cheap conductive carbon paste is brushed on the upper surface of the composite laminated film as a top electrode, and then placed in a vacuum drying oven for drying to obtain a complete photodetector.

[0027] Preferably, in step 1, TiO 2 The mass ratio of slurry to ethanol is 1:5.

[0028] Preferably, in step 2, the coating machine is accelerated to 2000 rpm at an acceleration of 2000 rad / s, rotated for 20 s, and placed in a muffle furnace for annealing at 125°C for 5 min; 325°C for 5 min; 375°C for 5 min; and 450°C for 30 min.

[0029] Preferably, in step 3, the coating machine is accelerated to 2000 rpm at an acceleration of 500 rad / s, rotated for 20 s, annealed on a hot stage at 400° C. for 10 min, cooled for 5 min, and repeated 3 times.

[0030] Preferably, in step 4, the temperature of the vacuum drying oven is 120° C. and the time is 15 min.

[0031] The beneficial effects of the present invention are embodied in:

[0032] 1) Compared with the prior art, the NaBiS prepared by the present invention 2 The film spin-coated from the precursor solution has pure cubic NaBiS 2 The film has a simple preparation process, low preparation cost and a purer product.

[0033] 2) NaBiS obtained by spin coating 2 The film has no impurity peaks, and the measured band gap is 1.35 eV. The film morphology is relatively flat, dense, and crack-free, which is similar to TiO 2 The formation of heterojunctions by porous structure films is expected to show broad application prospects in the field of electronic materials and devices.

[0034] 3) Prepared FTO / TiO 2 / NaBiS 2 The photodetector with C composite stack has a low dark current: 3.8×10 -6 A / cm 2 Its It curve measured under 0V bias shows good self-powered characteristics. It has obvious optical switching response under the excitation light of 530 nm, 625 nm, 730 nm and 810 nm. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The FTO / TiO 2 / NaBiS 2 Schematic diagram of the structure of the self-powered photodetector of / C.

[0036] Figure 2 The NaBiS prepared by the present invention 2 X-ray diffraction pattern of polycrystalline thin film.

[0037] Figure 3 The NaBiS prepared by the present invention 2 UV / visible / near-infrared diffuse reflectance-converted absorption spectra of polycrystalline thin films.

[0038] Figure 4 The NaBiS prepared by the present invention 2 Scanning electron micrograph of polycrystalline thin film.

[0039] Figure 5 The NaBiS-based 2 The volt-ampere characteristic curve of the photodetector under dark conditions.

[0040] Figure 6 The NaBiS-based 2 The volt-ampere characteristic curve of the photodetector under light of different wavelengths.

[0041] Figure 7 The NaBiS-based 2 It characteristic curves of the photodetector under light of different wavelengths.

[0042] Figure 8 The six pieces of NaBiS prepared in Example 3 of the present invention are 2 X-ray diffraction pattern of polycrystalline thin film. (a) 0.0264 g sodium hydroxide, 0.1538 g bismuth oxide, 4 mL ethylenediamine, 1 mL β-mercaptoethanol, (b) 0.0528 g sodium hydroxide, 0.3076 g bismuth oxide, 4 mL ethylenediamine, 1 mL β-mercaptoethanol, (c) 0.0528 g sodium hydroxide, 0.2307 g bismuth oxide, 0.16 g sublimed sulfur, 4 mL ethylenediamine, 1 mL β-mercaptoethanol, (d) 0.0528 g sodium hydroxide, 0.1538 g bismuth oxide, 0.16 g sublimed sulfur, 4 mL ethylenediamine, 1 mL β-mercaptoethanol, (e) 0.0528 g sodium hydroxide, 0.2307 g bismuth oxide, 0.16 g sublimed sulfur, 3 mL primary solution, 1.5 mL 1,2-ethanedithiol, (f) 0.0528 g Sodium hydroxide, 0.2307 g bismuth oxide, 0.16 g sublimed sulfur, 2 mL primary solution, 1 mL 1,2-ethanedithiol.

[0043] Fig. 9 The four sheets of NaBiS prepared in Example 4 of the present invention are 2 Scanning electron micrograph of a thin film made of NaBiS 2The films were annealed in two steps, and the annealing temperature was adjusted: (a) 100 ℃ / 350 ℃ annealing, (b) 100 ℃ / 400 ℃ annealing, (c) 100 ℃ / 450 ℃ annealing, and (d) 100 ℃ / 500 ℃ annealing.

[0044] Fig.10 The four sheets of NaBiS prepared in Example 4 of the present invention are 2 It characteristic curves of the film photodetector under different wavelengths of light and 0 V bias. (a) 100 ℃ / 350 ℃ annealing, (b) 100 ℃ / 400 ℃ annealing, (c) 100 ℃ / 450 ℃ annealing, (d) 100 ℃ / 500 ℃ annealing.

[0045] Fig.11 The four sheets of NaBiS prepared in Example 5 of the present invention are 2 Scanning electron micrograph of a thin film made of NaBiS 2 The film was annealed in a single step and the spin-coated NaBiS 2 Number of layers and annealing temperature: (a) one layer / 450 ℃ annealing, (b) three layers / 450 ℃ annealing, (c) one layer / 500 ℃ annealing, (d) three layers / 500 ℃ annealing.

[0046] Fig.12 The four sheets of NaBiS prepared in Example 5 of the present invention are 2 It characteristic curves of the thin film photodetector under different wavelengths of light and 0V bias. (a) One layer / 450 ℃ annealing, (b) Three layers / 450 ℃ annealing, (c) One layer / 500 ℃ annealing, (d) Three layers / 500 ℃ annealing. DETAILED DESCRIPTION

[0047] The following embodiments are further descriptions of the content of the present invention as an explanation of the technical content of the present invention, but the essential content of the present invention is not limited to the following embodiments. Ordinary technicians in this field can and should know that any simple changes or replacements based on the essential spirit of the present invention should fall within the scope of protection required by the present invention. Example 1

[0048] In this example, NaBiS was prepared according to the following steps. 2 Polycrystalline film:

[0049] Step 1. Configure NaBiS 2 Solution

[0050] Weigh 0.0528 g of sodium hydroxide, 0.2307 g of bismuth oxide, and 0.16 g of sublimed sulfur in a beaker, add 4 mL of ethylenediamine and 1 mL of β-mercaptoethanol. Place the mixture in silicone oil and stir for 6 hours at 60 °C. Then let it stand for 3 hours, and obvious stratification can be seen. After that, use a syringe to remove 3 mL of the supernatant to form a primary solution, and then add 1 mL of 1,2-ethanedithiol to the primary solution, continue to oil bath at 60 °C for 30 minutes, and obtain a reddish-brown secondary solution, which is NaBiS 2 Precursor solution.

[0051] Step 2: Preparation of NaBiS 2 polycrystalline film

[0052] Place the cleaned FTO in an ozone cleaner for 15 min, and then place it in a glove chamber filled with nitrogen. Place the FTO on a gelator and use a pipette to spread the prepared NaBiS 2 The solution was spin-coated on FTO, accelerated to 2000 rpm at 500 rad / s, spun for 20 s, annealed on a hot stage at 400 °C for 10 min, cooled for 5 min, and repeated 3 times to obtain NaBiS 2 Polycrystalline film. Example 2

[0053] In this example, FTO / TiO was prepared according to the following steps. 2 / NaBiS 2 / C composite stack photodetector:

[0054] Step 1: Configure TiO 2 Precursor solution

[0055] The 30NR-D TiO produced by Greatcell Solar in Australia was purchased. 2 The slurry was mixed with ethanol in a mass ratio of 1:5 and stirred at room temperature for 1 day to obtain TiO 2 Precursor solution.

[0056] Step 2: Spin coating TiO 2 layer

[0057] Place the cleaned FTO in an ozone cleaner for 15 min, then place the FTO on a gelling machine and use a pipette to spread the prepared TiO 2 The solution was spin-coated on FTO, accelerated to 2000 rpm at an acceleration of 2000 rad / s, rotated for 20 s, and placed in a muffle furnace for annealing at 125 °C for 5 min; 325 °C for 5 min; 375 °C for 5 min; and 450 °C for 30 min.

[0058] Step 3: Preparation of NaBiS 2 Polycrystalline FTO / TiO thin films 2 / NaBiS 2 Composite laminated film

[0059] FTO / TiO 2 Place in ozone cleaning machine for 15 min, then place in nitrogen filled glove chamber, and place FTO / TiO 2 Place it on the gelator and use a pipette to mix the prepared NaBiS 2 Solution spin coating on FTO / TiO 2 The sample was accelerated to 2000 rpm at 500 rad / s, rotated for 20 s, annealed on a hot stage at 400 °C for 10 min, cooled for 5 min, and repeated three times to obtain a NaBiS 2 Polycrystalline FTO / TiO thin films 2 / NaBiS 2 Composite laminated film.

[0060] Step 4: Build the carbon electrode

[0061] In FTO / TiO 2 / NaBiS 2 A layer of conductive carbon paste is brushed on the upper surface of the composite laminated film as the top electrode, and then placed in a vacuum drying oven at 120°C for 15 min to obtain a complete photodetector.

[0062] Figure 1 The FTO / TiO 2 / NaBiS 2 Schematic diagram of the structure of the self-powered photodetector based on NaBiS / C. 2 As a light absorbing layer, TiO 2 The porous layer forms a heterojunction, with FTO as the bottom electrode and carbon paste as the top electrode.

[0063] Figure 2 The NaBiS prepared by the present invention 2 X-ray diffraction spectrum of polycrystalline film. It can be seen that the diffraction peaks at 26.834°, 31.802°, 44.532°, 52.758°, and 55.3° are similar to those of NaBiS 2 The diffraction peaks in PDF#97-061-6841 correspond to each other and no other impurity diffraction peaks are seen, indicating that the NaBiS synthesized in the present invention 2 The polycrystalline film is pure cubic NaBiS 2 .

[0064] Figure 3 The NaBiS prepared by the present invention2 The absorption spectrum of the polycrystalline film after UV / visible / near infrared diffuse reflection test and conversion. By converting the Kubelka-Munk formula and making a tangent to the absorption cutoff edge, we can get NaBiS 2 The band gap of polycrystalline thin films is 1.35 eV.

[0065] Figure 4 The NaBiS prepared by the present invention 2 Scanning electron microscope image of polycrystalline thin film. It can be seen that the NaBiS synthesized by the present invention 2 The polycrystalline film has no obvious holes, and the film is relatively flat, dense and crack-free.

[0066] Figure 5 The NaBiS-based 2 The volt-ampere characteristic curve of the photodetector under dark conditions. The dark current density at 0V bias is 3.8×10 -6 A / cm 2 .

[0067] Figure 6 The NaBiS-based 2 The volt-ampere characteristic curve of the photodetector under different wavelengths of light and 0V bias. Within the voltage range of ±2V, the device is illuminated with excitation light of 530 nm, 625 nm, 730 nm, and 810 nm wavelengths, and it can be seen that the device has a higher photocurrent when the excitation light of 625 nm wavelength is used.

[0068] Figure 7 The NaBiS-based 2 It characteristic curves of the photodetector under different wavelengths of light and 0V bias. The device has obvious optical switching response under 530 nm, 625 nm, 730 nm, and 810 nm excitation light, and is relatively better under 625 nm excitation light; the response under 0V bias indicates that the device has self-powered properties. Example 3

[0069] Compared with Example 1, the solution concentration and solvent system were changed to obtain NaBiS with partial impurity phase. 2 Polycrystalline film.

[0070] Step 1. Configure NaBiS 2 Solution

[0071] Different amounts of sodium hydroxide, bismuth oxide, and sublimed sulfur were weighed into 6 sample bottles: (a) 0.0264 g sodium hydroxide, 0.1538 g bismuth oxide; (b) 0.0528 g sodium hydroxide, 0.3076 g bismuth oxide; (c) 0.0528 g sodium hydroxide, 0.2307 g bismuth oxide, 0.16 g sublimed sulfur; (d) 0.0528 g sodium hydroxide, 0.1538 g bismuth oxide, 0.16 g sublimed sulfur; (e) 0.0528 g sodium hydroxide, 0.2307 g bismuth oxide, 0.16 g sublimed sulfur; (f) 0.0528 g sodium hydroxide, 0.2307 g bismuth oxide, 0.16 g sublimed sulfur. 4 mL ethylenediamine and 1 mL β-mercaptoethanol were added to the 6 sample bottles. The mixed solution in the bottle was placed in silicone oil and stirred for 6 hours at 60 °C oil bath. (e) and (f) were left to stand for 6 hours, and the solution was observed to be clearly separated, with black precipitate produced at the bottom. 2 mL of the supernatant in (e) was removed with a syringe to obtain a primary solution, 1.5 mL of 1,2-ethanedithiol was added to the primary solution, and the oil bath was continued at 60 °C for 30 minutes to obtain a red solution (e); 3 mL of the supernatant in (f) was removed with a syringe to obtain a primary solution, 1 mL of 1,2-ethanedithiol was added to the primary solution, and the oil bath was continued at 60 °C for 30 minutes to obtain a red solution (f).

[0072] Step 2: Preparation of NaBiS 2 polycrystalline film

[0073] Place the cleaned FTO in an ozone cleaner for 15 min, and then place it in a glove chamber filled with nitrogen. Place the FTO on a gelator and use a pipette to mix the 6 bottles of different NaBiS 2 The solutions were spin-coated on FTO, accelerated to 2000 rpm at 500 rad / s, spun for 20 s, annealed on a hot stage at 400 °C for 5 min, cooled for 3 min, and repeated 3 times to obtain 6 sheets of NaBiS 2 Polycrystalline film.

[0074] Figure 8 The six pieces of NaBiS prepared in Example 3 of the present invention are 2 X-ray diffraction patterns of polycrystalline thin films. (a), (b), (c), and (d) are the results of the single-step reaction of NaBiS prepared using a two-solvent system of ethylenediamine and β-mercaptoethanol. 2Films, where no sublimed sulfur was added to (a) and (b), and sublimed sulfur was added to (c) and (d), and the concentration of (a) was lower than that of (b), and the concentration of (c) was higher than that of (d). Comparing (a) and (b) and (c) and (d), it can be seen that the content of impurity Bi can be significantly reduced by reducing the concentration, but the generation of impurity Bi cannot be fundamentally avoided; comparing (a) and (c) and (b) and (d), it can be seen that by adding solute sublimed sulfur, part of the impurity Bi can be consumed, but some remains. (e) and (f) are the preparation of NaBiS by the secondary solution reaction method of the three-solvent system of ethylenediamine, β-mercaptoethanol, and 1,2-ethanedithiol. 2 By comparing (e) and (f), we can see that the concentration of (e) is lower than that of (f). From the XRD in (e), we can see that the reaction produces NaBiS 2 , Bi, but there are still some unknown peaks, while (f) produces pure cubic NaBiS 2 , and there are no other impurity peaks. Therefore, the optimized result is: using the secondary solution reaction method of the three-solvent system, adding sublimated sulfur and adjusting the concentration of the precursor solution, pure phase cubic NaBiS 2 film. Example 4

[0075] Compared with Example 2, the annealing process was changed and the NaBiS-based 2 Thin film photodetectors.

[0076] Step 1: Configure TiO 2 Precursor solution

[0077] The 30NR-D TiO produced by Greatcell Solar in Australia was purchased. 2 The slurry was mixed with ethanol in a mass ratio of 1:5 and stirred at room temperature for 1 day to obtain TiO 2 Precursor solution.

[0078] Step 2: Spin coating TiO 2 layer

[0079] Prepare 4 cleaned FTO conductive glasses, put the cleaned FTO into the ozone cleaning machine for 15 min, and then put the FTO on the glue machine, use a pipette to spread the prepared TiO 2 The solution was spin-coated on FTO, accelerated to 2000 rpm at an acceleration of 2000 rad / s, rotated for 20 s, and placed in a muffle furnace for annealing at 125 °C for 5 min; 325 °C for 5 min; 375 °C for 5 min; and 450 °C for 30 min.

[0080] Step 3. Configure NaBiS2 Precursor solution

[0081] Weigh 0.0528 g of sodium hydroxide, 0.2307 g of bismuth oxide, and 0.16 g of sublimed sulfur in a beaker, add 4 mL of ethylenediamine and 1 mL of β-mercaptoethanol. Place the mixture in silicone oil and stir for 6 hours at 60 °C. Then let it stand for 3 hours, and obvious stratification can be seen. After that, use a syringe to remove 3 mL of the supernatant to form a primary solution, and then add 1 mL of 1,2-ethanedithiol to the primary solution, continue to oil bath at 60 °C for 30 minutes, and obtain a reddish-brown secondary solution, which is NaBiS 2 Precursor solution.

[0082] Step 4: Preparation of NaBiS-based 2 Thin-film photodetectors

[0083] The 4 spin-coated TiO 2 Place the FTO / TiO 2 Place it on the gelator and use a pipette to mix the prepared NaBiS 2 The solution was spin-coated on FTO, accelerated to 2000 rpm at 500 rad / s, and rotated for 20 s. Then, it was annealed on a hot stage at 100 °C for 1 hour, and then transferred to the preheated hot stages at 350 °C, 400 °C, 450 °C, and 500 °C for secondary annealing for 20 minutes. Thus, four TiO sheets with different secondary annealing processes were obtained. 2 / NaBiS 2 Polycrystalline film.

[0084] Step 5: Build the electrodes

[0085] Four FTO / TiO 2 / NaBiS 2 A layer of conductive carbon paste is brushed on the upper surface of the composite laminated film as the top electrode, and then placed in a vacuum drying oven at 120°C for 15 min to obtain a complete photodetector.

[0086] Fig. 9 The four sheets of NaBiS prepared in Example 4 of the present invention are 2Scanning electron microscope images of the film. (a) is annealed at 100 ℃ / 350 ℃, (b) is annealed at 100 ℃ / 400 ℃, (c) is annealed at 100 ℃ / 450 ℃, and (d) is annealed at 100 ℃ / 500 ℃. Comparing (a), (b), (c), and (d), it can be seen that when the secondary annealing temperature is 450 ℃, the film has the most cracks, followed by 350 ℃, and the least at 400 ℃, but there are still cracks. It can be seen that the film formed by the secondary annealing method is relatively dense, but too high a temperature or a high thickness may cause the film to crack. Therefore, compared with Example 1, when spin-coating NaBiS 2 Secondary annealing of the precursor solution did not achieve excellent film morphology.

[0087] Fig.10 The four sheets of NaBiS prepared in Example 4 of the present invention are 2 It characteristic curves of the photodetector of the film under different wavelengths of light and 0V bias. Among them, (a) is annealed at 100 ℃ / 350 ℃, (b) is annealed at 100 ℃ / 400 ℃, (c) is annealed at 100 ℃ / 450 ℃, and (d) is annealed at 100 ℃ / 500 ℃. It can be seen that the four photodetectors all show obvious photoelectric effect under the irradiation of excitation light of 530 nm, 625 nm, 730 nm, and 810 nm, and all show the strongest photoelectric performance under the irradiation of excitation light of 625 nm, but all have obvious pyroelectric effect. Compared with the film under 350 ℃ and 450 ℃ process, the current is larger at 400 ℃ and 500 ℃ because the film has fewer cracks. Compared with Example 2, the response speed of the It characteristic curve in this example is slower and the switching ratio is lower. Example 5

[0088] Compared with Example 2, the annealing process and NaBiS 2 The number of layers of thin film spin coating, NaBiS based on single-step annealing method 2 Thin film photodetectors.

[0089] Step 1: Configure TiO 2 Precursor solution

[0090] The 30NR-D TiO produced by Greatcell Solar in Australia was purchased. 2 The slurry was mixed with ethanol in a mass ratio of 1:5 and stirred at room temperature for 1 day to obtain TiO 2 Precursor solution.

[0091] Step 2: Spin coating TiO 2 layer

[0092] Prepare 4 cleaned FTO conductive glasses, put the cleaned FTO into the ozone cleaning machine for 15 min, and then put the FTO on the glue machine, use a pipette to mix the prepared TiO 2 The solution was spin-coated on FTO, accelerated to 2000 rpm at an acceleration of 2000 rad / s, rotated for 20 s, and placed in a muffle furnace for annealing at 125 °C for 5 min; 325 °C for 5 min; 375 °C for 5 min; and 450 °C for 30 min.

[0093] Step 3. Configure NaBiS 2 Precursor solution

[0094] Weigh 0.0528 g of sodium hydroxide, 0.2307 g of bismuth oxide, and 0.16 g of sublimed sulfur in a beaker, add 4 mL of ethylenediamine and 1 mL of β-mercaptoethanol. Place the mixture in silicone oil and stir for 6 hours at 60 °C. Then let it stand for 3 hours, and obvious stratification can be seen. After that, use a syringe to remove 3 mL of the supernatant to form a primary solution, and then add 1 mL of 1,2-ethanedithiol to the primary solution, continue to oil bath at 60 °C for 30 minutes, and obtain a reddish-brown secondary solution, which is NaBiS 2 Precursor solution.

[0095] Step 4: Preparation of NaBiS-based 2 Thin-film photodetectors

[0096] The 4 spin-coated TiO 2 Place the FTO / TiO 2 Place it on the gelator and use a pipette to mix the prepared NaBiS 2 The solution was spin-coated on FTO, accelerated to 2000 rpm at 500 rad / s, and spun for 20 s. Then, it was annealed on a hot plate at 450 °C for 20 min and one layer was spin-coated; (2) annealed on a hot plate at 450 °C for 20 min and three layers were spin-coated; (3) annealed on a hot plate at 500 °C for 20 min and one layer was spin-coated; (4) annealed on a hot plate at 500 °C for 20 min and three layers were spin-coated. Thus, four TiO sheets with different single-step annealing processes and different numbers of layers were obtained. 2 / NaBiS 2 Polycrystalline film.

[0097] Step 5: Build the electrodes

[0098] Four FTO / TiO 2 / NaBiS 2A layer of conductive carbon paste is brushed on the upper surface of the composite laminated film as the top electrode, and then placed in a vacuum drying oven at 120°C for 15 min to obtain a complete photodetector.

[0099] Fig.11 The four sheets of NaBiS prepared in Example 5 of the present invention are 2 Scanning electron micrograph of the film. NaBiS 2 The film was annealed in a single step and the spin-coated NaBiS 2 The number of layers and annealing temperature: (a) one layer / 450 ℃ annealing, (b) three layers / 450 ℃ annealing, (c) one layer / 500 ℃ annealing, (d) three layers / 500 ℃ annealing. It can be seen from the four figures that the films formed by the single-step annealing method are all spherical grains; by comparing (a) and (c) and (b) and (d), it can be seen that the higher the temperature, the larger the grains; by comparing (a) and (b) and (c) and (d), it can be seen that the more layers, the larger the holes, and there are more small grains attached to the surface.

[0100] Fig.12 The four sheets of NaBiS prepared in Example 5 of the present invention are 2 It characteristic curves of the film's photodetector under different wavelengths of light and 0V bias. Figure (a) shows one layer / 450 ℃ annealing, (b) three layers / 450 ℃ annealing, (c) one layer / 500 ℃ annealing, and (d) three layers / 500 ℃ annealing. It can be seen that the four photodetectors all exhibited obvious photoelectric performance under the irradiation of excitation light of 530 nm, 625 nm, 730 nm, and 810 nm, and all showed the strongest photoelectric performance under the irradiation of 625 nm excitation light, but all had obvious pyroelectric effect. By comparing (a) and (c), under the 500 ℃ annealing process, its current is larger because its grains are larger, there are fewer grain boundaries, and the current loss is low. By comparing (a) and (b) and (c) and (d), it can be seen that the number of layers is also an important factor affecting the performance. The single-layer film has a lower thickness, fewer grain boundaries, and lower loss of electrons when transmitting between grain boundaries, and the performance is better than that of the three-layer film. Compared with Example 2, the response speed of the It characteristic curve in this example is slower and the switching ratio is lower.

[0101] The present invention provides a NaBiS 2 Preparation method of high-quality polycrystalline thin film of optoelectronic materials and TiO 2 / NaBiS 2 An example of heterojunction application in photoelectric detection. A three-solvent system of ethylenediamine, β-mercaptoethanol and 1,2-ethanedithiol was developed to dissolve sodium hydroxide, antimony oxide and sublimed sulfur as the synthesis of NaBiS 2A uniform, dense, crack-free pure-phase cubic NaBiS 2 The polycrystalline film has a band gap of 1.35 eV. By adjusting the NaBiS 2 The concentration of the precursor solution (Example 3) and the solvent system (Example 3) are used to form pure cubic NaBiS 2 Thin film; by adjusting NaBiS 2 The film forming temperature (Example 4), annealing times (Example 4) and spin coating times (Example 5) of NaBiS 2 Film morphology. According to Example 1, a dense and uniform film morphology was obtained, and the film preparation process was simple, and the raw materials and preparation costs were low. 2 Light absorbing layer and TiO 2 The heterojunction film and photodetector device of the porous layer showed excellent self-powered photodetection performance under an external bias of 0V, with a dark current of only 3.8×10 -6 A / cm 2 Therefore, in summary, NaBiS 2 As a ternary sulfide optoelectronic material, it provides technical reference and application examples for the preparation of thin films, construction of heterostructures and innovative applications of semiconductor functional devices.

[0102] It should be noted that the above-mentioned technical contents of the present invention are only for explanation and clarification to enable those skilled in the art to understand the technical essence of the present invention, so the technical contents are not used to limit the substantial protection scope of the present invention. The substantial protection scope of the present invention shall be subject to the claims. Those skilled in the art should know that any modification, equivalent substitution and improvement based on the substantial spirit of the present invention shall be within the substantial protection scope of the present invention.

Claims

1. A method for preparing a cubic crystal structure NaBiS2 polycrystalline thin film material, characterized in that: A secondary solution reaction method using a three-solvent system of ethylenediamine, β-mercaptoethanol and 1,2-ethanedithiol is used to dissolve sodium hydroxide, bismuth oxide and sublimed sulfur, and react at 50-70°C to form a NaBiS2 precursor solution, and a solution spin coating method is used and annealed at 400°C to grow a pure phase cubic structure NaBiS2 polycrystalline thin film material; the NaBiS2 precursor solution is prepared by the secondary solution reaction method of the three-solvent system, and specifically comprises the following steps: first, sodium hydroxide, bismuth oxide and sublimed sulfur are dissolved in a mixed solution of ethylenediamine and β-mercaptoethanol, reacted in an oil bath at 50-70°C for 6 hours, allowed to stand for 3 hours, and removed; Remove part of the supernatant to form a primary solution; then, add 1,2-ethanedithiol to the primary solution, continue to react in a 50-70°C oil bath for 30 minutes, and obtain a secondary solution of a three-solvent system, i.e., a NaBiS2 precursor solution; the mass ratio of the sodium hydroxide, bismuth oxide, and sublimed sulfur is 0.05-0.06: 0.2-0.25: 0.15-0.18; the volume ratio of ethylenediamine and β-mercaptoethanol is 3.8-4.2: 0.8-1.2; the removed supernatant is 55%-65% of the total solution, and the volume ratio of the added 1,2-ethanedithiol to the primary solution is 0.8-1.2: 1.8-2.

2.

2. A TiO2 / NaBiS2 heterojunction film, which is a heterojunction formed by the NaBiS2 precursor solution described in claim 1 and a TiO2 porous layer.

3. The method for preparing the TiO2 / NaBiS2 heterojunction film according to claim 2, which comprises spin coating a TiO2 porous layer on FTO using a solution spin coating method, and then spin coating a NaBiS2 precursor solution on the TiO2 porous layer, annealing on a hot plate at 400°C for 10 min, and cooling for 5 min to obtain a TiO2 / NaBiS2 heterojunction film.

4. Use of the TiO2 / NaBiS2 heterojunction film according to claim 2 or the TiO2 / NaBiS2 heterojunction film obtained by the preparation method according to claim 3 in a semiconductor optoelectronic device, wherein the semiconductor optoelectronic device is a photodetector, a photoelectric memory or a photodiode.

5. The use according to claim 4, characterized in that The TiO2 / NaBiS2 heterojunction film is applied in a photodetector, using the following method steps: Step 1: Spin coating of TiO2 porous layer: Spin-coat a TiO2 porous layer on FTO glass to form FTO / TiO2; Step 2: Spin coating NaBiS2 light absorbing layer: Prepare NaBiS2 precursor solution; spin-coat NaBiS2 precursor solution on FTO / TiO2 in a nitrogen environment, accelerate the coating machine from 500 rad / s to 2000 rpm, rotate for 20 s, anneal on a hot plate at 400 °C for 10 min, cool for 5 min, repeat 3 times, and obtain FTO / TiO2 / NaBiS2 composite laminated film; Step 3: Build the carbon electrode: A layer of conductive carbon paste was brushed on the upper surface of the FTO / TiO2 / NaBiS2 composite laminate film as the top electrode, and the film was placed in a vacuum drying oven at 120°C and dried for 15 min to obtain a complete photoelectric detection device.

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