A two-dimensional Se film / Spiro-MeOTAD heterojunction and its preparation method and application

Abstract

The present invention provides a two-dimensional Se film / Spiro-MeOTAD heterojunction and its preparation method and application, belonging to the technical field of semiconductor nanomaterials. In the present invention, Na2SeSO3 is used as a precursor, and a Se thin film is prepared by a solution method, transferred to a flexible substrate by a tape sticking method, and a Ga2O3 layer is prepared by a sputtering method as the i layer. Then, a Spiro-MeOTAD mixed solution is spin-coated uniformly on the Ga2O3 layer to form a p-i-p structure. This structure can reduce the dark current and increase the photocurrent. The device has a high photocurrent and a fast response time under a 0V bias voltage, realizing self-driven performance.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor nanomaterials, and in particular relates to a two-dimensional Se film / Spiro-MeOTAD heterojunction and a preparation method and application thereof. Background Art

[0002] Photodetectors can convert optical signals into electrical signals, and they play a very important role in optical communications, medical imaging, night vision, gas sensing, and security detection. As the application fields continue to expand and the diversity continues to grow, the demand for high-performance photodetectors, especially wide-spectrum detectors that can cover multiple band responses at the same time, is increasing. There are now semiconductor detectors suitable for different wavelengths, but they are often limited by the energy band characteristics of the materials themselves, and need to be selected and switched according to different occasions and environments, which is inconvenient in specific applications. Therefore, the demand for the development of optical detectors with wide-band responses is becoming increasingly strong. In addition, the development of optical detectors is also facing the problems of breakthroughs in performance such as response speed and detection rate, and improving integration while controlling costs. Due to its excellent physical properties, two-dimensional materials are another new generation of semiconductor materials with broad application prospects after silicon and compound semiconductors, providing ideas for breakthroughs in traditional optical detectors. First, the rich energy bands of two-dimensional materials provide the possibility for wide-band photoelectric detection; second, the thickness of the atomic layer of two-dimensional materials and quantum confinement lead to a strong exciton binding effect, which improves the light absorption efficiency; in addition, the surface of two-dimensional materials is naturally passivated and has no dangling bonds, so they can be well integrated with other materials and are not restricted by lattice matching. Various van der Waals heterojunctions created by stacking two materials can realize the functions of multiple materials at the same time; finally, two-dimensional layered semiconductors can adjust the band gap of materials by changing the number of layers, thereby modulating the optical absorption edge. Graphene is the most typical representative of two-dimensional materials, but its photogenerated carriers have a short lifetime and cannot be effectively separated in time, resulting in a small photocurrent; in addition, the light absorption rate of single-layer graphene is only 2.3%. Compared with graphene, Se has a higher photocurrent and higher light absorption rate, and the current preparation methods of Se mainly include electrodeposition, physical vapor deposition, chemical vapor deposition and spray pyrolysis. Considering economy, practicality and large-scale production, the flexibility of producing Se films is relatively large. Se films have different properties depending on the crystal phase. In particular, hexagonal selenium has the highest density, best stability, best ductility and highest toughness among all shapes of Se.

[0003] Conventional broadband detectors require external power to effectively detect optical signals, which limits their practical applications and makes them uneconomical. In a low-carbon society, energy conservation and efficiency have become a top priority in association with sustainable development, "green economy" and reducing carbon emissions. Therefore, future photodetectors are expected to have low energy consumption and excellent photosensitivity. Self-biased optical devices have attracted much attention, using the built-in electric field of heterojunctions (including Schottky junctions and pn junctions) to separate photogenerated carriers. However, many attempts are needed to control the interface between metals and semiconductors to adjust the Schottky barrier height and stability. Complex transfer techniques and the inability to mass-produce on an assembly line have greatly limited the large-scale practical application of two-dimensional materials. Many of the oxides commonly used in heterojunctions require extremely complex doping processes to obtain p-type materials (such as β-Ga2O3). In addition, high-temperature synthesis, complex manufacturing processes and low toughness have all limited their further application to a certain extent. Organic semiconductors have become a powerful substitute for inorganic semiconductors, among which p-type conductive polymers (polyaniline PANI, polypyrrole PPy and polythiophene PEDOT / P3HT) are favored by researchers, mainly relying on their advantages of light weight, flexibility, easy synthesis, large-area low-cost preparation, and unique electronic and optical properties similar to metals or semiconductors. However, PANI, PPy and PEDOT / P3HT are all acidic solutions and are corrosive. In comparison, Spiro-MeOTAD is more suitable as a hole transport material due to its advantages such as neutrality and non-corrosiveness, good toughness, non-toxicity and environmental protection, good light transmittance, and simple and scalable production. There are related studies on the combination of Spiro-MeOTAD and semiconductor materials such as TiO2, ZnO, and WO3, but no one has studied the combination of Spiro-MeOTAD and Se in depth. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a two-dimensional Se film / Spiro-MeOTAD heterojunction and its preparation method and application. For the pn junction, the depletion region width is relatively narrow, resulting in most photons being absorbed by the area outside the depletion region, thereby affecting the separation of photogenerated electron-hole pairs. The present invention adopts a pip structure to increase the built-in potential and accelerate the separation of electron-hole pairs, effectively increasing the photocurrent.

[0005] A method for preparing a two-dimensional Se film comprises the following steps:

[0006] (1) spin coating a hydrophilic solution on the surface of a flexible substrate;

[0007] (2) adding selenium to a Na2SO3 solution to react at 70°C-120°C to obtain a Na2SeSO3 solution, and adding tannic acid and ascorbic acid to obtain a mixed solution;

[0008] (3) Immersing the flexible substrate obtained in step (1) into the mixed solution 2 obtained in step (2), and growing the two-dimensional Se film at 0° C.-8° C. for 0.5 h-3 h.

[0009] In one embodiment of the present invention, in step (1), the flexible substrate is made of PET, PEN or PI, or the flexible substrate is a mica sheet.

[0010] In one embodiment of the present invention, in step (1), the hydrophilic solution is a methanol solution, a SnCl2 solution or a carboxylic acid solution.

[0011] In one embodiment of the present invention, in step (2), the molar concentration ratio of tannic acid to ascorbic acid is 0.5-6:1.

[0012] The invention also provides a two-dimensional Se film.

[0013] A method for preparing a two-dimensional Se film / Spiro-MeOTAD heterojunction, when the two-dimensional Se film / Spiro-MeOTAD heterojunction is a pp structure, comprises the following steps: spraying a Spiro-MeOTAD solution onto the surface of the two-dimensional Se film, standing and drying to form the two-dimensional Se film / Spiro-MeOTAD heterojunction.

[0014] A method for preparing a two-dimensional Se film / Spiro-MeOTAD heterojunction, when the two-dimensional Se film / Spiro-MeOTAD heterojunction is a pip structure, comprises the following steps: placing the two-dimensional Se film on the surface of a Ga2O3 layer, coating a Spiro-MeOTAD solution on the other side of the Ga2O3 layer to obtain the two-dimensional Se film / Spiro-MeOTAD heterojunction.

[0015] In one embodiment of the present invention, the replacement layer for the Ga2O3 layer is a MgO layer, a ZnS layer, a MgGaO layer or a MgZnO layer.

[0016] The present invention also provides a two-dimensional Se film / Spiro-MeOTAD heterojunction.

[0017] The present invention also provides application of the two-dimensional Se film / Spiro-MeOTAD heterojunction in a photoelectric detector.

[0018] The above technical solution of the present invention has the following advantages compared with the prior art:

[0019] The present invention adopts a solution deposition method to grow a high-quality two-dimensional Se film with controllable thickness. The solution deposition method does not need to go through high temperature and more complicated production steps, and a layer of Se film can be deposited at room temperature and low temperature for a short time. Compared with vapor deposition, electrodeposition, spray pyrolysis and sputtering, the solution deposition method is more suitable for large-scale preparation of Se film. The two-dimensional Se film has very good toughness, which lays a certain physical condition for manufacturing bendable and foldable photodetectors; at the same time, the speed of Se's photoelectric response can also meet the detection of rapid changes in light under extreme conditions; Se's relatively narrow bandgap determines that it is suitable for wide-spectrum detection; at the same time, because of Se's higher light absorption rate, it can also have good responsiveness under conditions of lower light power density. The pip structure is adopted, and there are two built-in electric fields inside, which can minimize the recombination of photogenerated carriers in the depletion region to increase the photocurrent; and the built-in electric field generated by the Se / Ga2O3 / Spiro-MeOTAD band matching forms a self-driven mode, and no external bias voltage is required. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein

[0021] Figure 1 It is the It curve of the two-dimensional Se film / Ga2O3 / Spiro-MeOTAD obtained in Example 1 of the present invention.

[0022] Figure 2 It is the rise time and fall time of the two-dimensional Se film / Ga2O3 / Spiro-MeOTAD obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0023] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0024] Example 1: Preparation of a pip-structured two-dimensional Se film / Ga2O3 / Spiro-MeOTAD heterojunction flexible broadband detector

[0025] A layer of 1.5% methanol solution was spin-coated on a PET flexible substrate at 2000rpm / 30s. The precursor sodium selenosulfate solution was prepared as follows: elemental selenium powder was dispersed in a sodium sulfite solution and stirred at 90°C for 1h. 8mL of sodium selenosulfate solution (0.2M) was added to deionized water to make the total volume reach 200mL. Then 10mL of tannic acid and ascorbic acid were added to the total mixture, wherein the concentration ratio of tannic acid to ascorbic acid was 1:1.5. The treated flexible substrate was completely immersed in the total mixed solution, and then the temperature was reduced to 0°C±8°C and maintained for 1h to obtain a two-dimensional Se film of about 100nm thickness. The grown Se film was transferred to the Ga2O3 layer prepared by sputtering by tape. Generally, it is necessary to add a suitable proportion of substances to Spiro-MeOTAD to increase its hole transport capacity. Here, the present invention uses 73.2 mg of Spiro-MeOTAD powder dissolved in 1 mL of chlorobenzene; 18 μL of 4-tert-butylpyridine and a mixture of 520 mg / mL of lithium imide and acetonitrile are added. At a speed of 4000 rpm / 30 s, the Spiro-MeOTAD mixed solution is evenly spin-coated onto the other side of the Ga2O3 layer to form a pip structure. After testing, under irradiation with light of 404 nm wavelength from an LED light source, 0 V bias and 2.8 μW / cm 2 Under the condition of optical power density, the photocurrent reached 230pA (see Figure 1 ), the switch ratio reaches 470, the rise time is 50ms and the fall time is 80ms (see Figure 2 ).

[0026] Example 2: Preparation of pip-structured two-dimensional Se film / MgO / Spiro-MeOTAD heterojunction flexible broadband detector

[0027] A layer of 1.5% methanol solution was spin-coated on a PEN flexible substrate at 2000rpm / 30s. The precursor sodium selenosulfate solution was prepared as follows: elemental selenium powder was dispersed in a sodium sulfite solution and stirred at 90℃ for 1h. 8mL of sodium selenosulfate solution (0.2M) and 6mL of selenium sulfate solution (0.1M) were mixed, and deionized water was added to make the total volume reach 200mL. Then 10mL of tannic acid and ascorbic acid were added to the total mixture, where the concentration ratio of tannic acid to ascorbic acid was 1:1.5. The treated flexible substrate was completely immersed in the total mixed solution, and then the temperature was reduced to 0℃±8℃ and maintained for 1h to obtain a two-dimensional Se film of about 100nm thickness. The grown Se film was transferred to the MgO layer prepared by sputtering by tape. Generally, it is necessary to add a suitable proportion of substances to Spiro-MeOTAD to increase its hole transport capacity. Here, the present invention uses 73.2 mg of Spiro-MeOTAD powder dissolved in 1 mL of chlorobenzene; 18 μL of 4-tert-butylpyridine and a mixture of 520 mg / mL of lithium imide and acetonitrile are added. At a speed of 4000 rpm / 30 s, the Spiro-MeOTAD mixed solution is evenly spin-coated onto the other side of the Ga2O3 layer to form a pip structure. After testing, under irradiation with light of 404 nm wavelength from an LED light source, 0 V bias and 2.8 μW / cm 2 Under the conditions of optical power density, the photocurrent reached 152pA, the switching ratio reached 350, the rise time was 61ms, and the fall time was 146ms.

[0028] Example 3: Preparation of pp-structured two-dimensional Se film / Spiro-MeOTAD heterojunction flexible broadband detector

[0029] A layer of 1.5% methanol solution was spin-coated on the PI flexible substrate by spin coating at 2000rpm / 30s. The preparation method of the precursor sodium selenosulfate solution is as follows: disperse the elemental selenium powder in the sodium sulfite solution and keep the temperature at 90℃ and stir for 1h. Mix 8mL of sodium selenosulfate solution (0.2M) and 6mL of selenium sulfate solution (0.1M), and then add deionized water to make the total volume reach 200mL. Then add 10mL of tannic acid and ascorbic acid to the total mixture, where the concentration ratio of tannic acid to ascorbic acid is 1:1.5. The treated substrate is completely immersed in the total mixed solution, and then the temperature is reduced to 0℃±8℃ and maintained for 1h to obtain a two-dimensional Se film with a thickness of about 100nm. Spin-coat a layer of Spiro-MeOTAD mixed solution on the two-dimensional Se film at a speed of 4000rpm / 30s, and let it stand for 1h at room temperature to naturally dry the residual liquid to form a pp structure heterojunction. After testing, the LED light source with a wavelength of 404nm, 0V bias and 2.8μW / cm2 Under the conditions of optical power density, the photocurrent reached 89pA, the switching ratio reached 280, the rise time was 72ms, and the fall time was 118ms.

[0030] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A method for preparing a two-dimensional Se film / Spiro-MeOTAD heterojunction, characterized in that: The following steps are involved: A two-dimensional Se film is placed on the surface of the Ga2O3 layer, and a Spiro-MeOTAD solution is coated on the other side of the Ga2O3 layer to obtain the two-dimensional Se film / Spiro-MeOTAD heterojunction.

2. The preparation method according to claim 1, characterized in that: The replacement layer of the Ga2O3 layer is a MgO layer, a ZnS layer, a MgGaO layer or a MgZnO layer.

3. The preparation method according to claim 1, characterized in that: The preparation of the two-dimensional Se film comprises the following steps: (1) Coating a hydrophilic solution on the surface of the flexible substrate; (2) adding tannic acid and ascorbic acid to a Na2SeSO3 solution to obtain a mixed solution; (3) Immersing the flexible substrate obtained in step (1) in the mixed solution obtained in step (2), and growing it at 0°C-8°C for 0.5h-3h to obtain the two-dimensional Se film.

4. The preparation method according to claim 3, characterized in that: In step (1), the flexible substrate is made of PET, PEN or PI, or the flexible substrate is a mica sheet.

5. The preparation method according to claim 3, characterized in that: In step (1), the hydrophilic solution is a methanol aqueous solution, a SnCl2 aqueous solution or a carboxylic acid aqueous solution.

6. The preparation method according to claim 3, characterized in that: In step (2), the molar concentration ratio of tannic acid to ascorbic acid is 0.5-6:

1.

7. The two-dimensional Se film / Spiro-MeOTAD heterojunction obtained by the preparation method according to any one of claims 1 to 6.

8. Application of the two-dimensional Se film / Spiro-MeOTAD heterojunction described in claim 7 in a photodetector.

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