Preparation method of substrate-free bismuth sulfide-based heterojunction thin film and application thereof in flexible self-driven photodetector
By fabricating Bi2S3/ZnO heterojunction thin films and designing asymmetric electrodes, the substrate dependence and photogenerated carrier recombination problems of flexible photodetectors were solved, achieving efficient and stable self-driven photodetector performance.
Patent Information
- Application Number
- CN202610315575.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-03-16
- Publication Date
- 2026-06-26
AI Technical Summary
Existing flexible photodetectors are highly dependent on the substrate, have complex fabrication processes, are prone to failure, and exhibit rapid recombination of photogenerated electron-hole pairs in Bi2S3 thin films, resulting in low detection performance and difficulty in self-driving.
Bi2S3/ZnO heterojunction films were prepared by solution method, and nanofibers were interwoven to form an interconnect network structure. Combined with asymmetric electrode design, a substrate-free flexible self-driven photodetector was constructed.
It achieves high sensitivity and fast response self-driven photoelectric detection, suitable for large-scale industrial production, with excellent flexibility and stability, and applicable to detection of multiple spectra.
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Figure CN122294633A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the technical field of semiconductor optoelectronic devices and their fabrication, specifically relating to a method for preparing a substrate-free bismuth sulfide-based heterojunction thin film and its application in a flexible self-driven photodetector. Background Technology
[0002] With the development of technology and the advent of the intelligent era, photodetectors, with their advantages of flexibility, have attracted widespread attention in the field of flexible electronics due to their ability to overcome the mechanical constraints of traditional rigid devices and their bendability. However, most reported flexible devices currently rely on spin coating or secondary transfer processes to "transplant" semiconductor materials onto flexible substrates for fabrication. The fabrication process for these devices is not only complex, but also prone to failure risks such as interface delamination and material fracture during repeated bending and use.
[0003] More importantly, these devices are highly dependent on specific flexible substrates such as polymers, carbon thin films, or cellulose paper, which to some extent limits the diversity of application scenarios and operating environments for flexible detectors. In contrast, substrate-free flexible detectors based on semiconductor thin film materials that possess excellent flexibility without substrate constraints offer broad prospects for expanding the application fields of flexible devices. Furthermore, flexible self-powered detectors, which can effectively detect incident light without relying on external energy, have advantages such as simple structure, fast response speed, high sensitivity, and low energy consumption, enabling them to operate unattended for extended periods. Therefore, the research and development of substrate-free flexible self-powered detectors has become a highly anticipated and popular research area.
[0004] As a key component of substrate-free flexible photodetectors, the development of substrate-independent flexible semiconductor thin film materials is crucial. Bismuth sulfide (Bi2S3) is an emerging narrow bandgap semiconductor material (1.2-1.7 eV) with high carrier mobility (~200 cm⁻¹). 2 ·V -1 ·s -1 Bi₂S₃ possesses advantages such as high light absorption coefficient. More importantly, its inherent chain structure and significant anisotropy enable its growth into ultralong nanowires. The numerous interwoven nanowires can form highly flexible, self-supporting Bi₂S₃ films that can exist independently of the substrate. However, single Bi₂S₃ films suffer from rapid recombination of photogenerated electron-hole pairs, which can affect the detection performance of flexible detectors based on them. Therefore, coupling Bi₂S₃ films with other semiconductor materials to construct heterojunctions is an effective strategy to improve the separation efficiency of photogenerated carriers.
[0005] ZnO is a typical optoelectronic material with high exciton binding energy. More importantly, its band structure matches well with Bi₂S₃, and their coupling can form a type II band structure, effectively suppressing recombination of photogenerated carriers. Furthermore, the one-dimensional structure of ZnO is readily fabricated using simple and mild synthesis methods that do not damage the structure of the flexible Bi₂S₃ film. Therefore, ZnO nanorods can be densely grown on the surface of the ultralong nanofibers constituting the Bi₂S₃ film. The resulting layered structure facilitates multiple reflections of incident light, thereby enhancing the film's light utilization efficiency. Therefore, developing a substrate-free method for preparing Bi₂S₃ / ZnO heterojunction films and further applying it to the field of flexible self-driven photodetectors is of significant importance and research value. Summary of the Invention
[0006] The purpose of this invention is to overcome the problems of high substrate dependence of existing flexible photodetectors, low efficiency and difficulty in self-driving operation of photodetectors based on Bi2S3 materials, and to provide a method for preparing a self-supporting bismuth sulfide-based heterojunction thin film and its application in flexible self-driving photodetectors.
[0007] This invention employs a simple solution method to prepare a substrate-free Bi₂S₃ / ZnO heterojunction thin film, which is composed of a large number of ultra-long, brush-like Bi₂S₃ / ZnO nanofibers. The tightly interwoven nanofibers create an overall interconnected network structure. Based on this Bi₂S₃ / ZnO heterojunction thin film, an asymmetric electrode structure and material strategy are introduced to design a substrate-free flexible photodetector with self-driving characteristics. The method employed in this invention offers advantages such as simple operation, environmental friendliness, and low cost, making it suitable for large-scale industrial production and possessing high application prospects in the optoelectronic field.
[0008] The objective of this invention is to be achieved through the following technical solutions:
[0009] A method for preparing the above-mentioned self-supporting Bi2S3 / ZnO heterojunction thin film, the method comprising the following steps:
[0010] Step 1: Weigh 1-3 g of sodium hydroxide and disperse it evenly in 10-40 ml of deionized water; then add 1-2 g of thiourea to the sodium hydroxide solution; after stirring continuously for 2-5 minutes, slowly add 0.08-0.5 g of bismuth oxide and stir evenly.
[0011] Step 2: Transfer the mixed solution obtained in Step 1 to a high-pressure reactor, seal it, and place it in a constant temperature heating and drying oven. React at 200 °C for 20-48 hours. After the reaction is completed, allow it to cool naturally to room temperature, remove the Bi2S3 film, wash it, and finally dry it naturally in the air to obtain a self-supporting flexible Bi2S3 film.
[0012] Step 3: Prepare the ZnO seed layer. Cut the Bi2S3 film prepared in Step 2 into 1 cm × 1 cm pieces and fix them on the sample holder. After magnetron sputtering for 2-10 minutes, anneal in air for 30-90 minutes to obtain the ZnO seed layer on the Bi2S3 film.
[0013] Step 4: Dissolve zinc nitrate hexahydrate and hexamethylenetetramine in deionized water and stir until homogeneous. Transfer the solution to a polytetrafluoroethylene (PTFE) liner in a reactor. Then, vertically suspend the Bi₂S₃ film with a ZnO seed layer in the middle of the solution. Seal the reactor and react at 60-95 °C for 2-7 hours to obtain a substrate-free Bi₂S₃ / ZnO heterojunction flexible film.
[0014] Furthermore, the annealing temperature of the ZnO seed layer is 100-200 ℃.
[0015] Furthermore, the ZnO seed layer can also be prepared by the Czochralski method, which involves immersing the Bi2S3 film in zinc acetate solution and deionized water for 1 minute in sequence, and then drying it at 60 °C. This process is repeated 2-10 times to obtain the ZnO seed layer on the Bi2S3 film.
[0016] Furthermore, the ZnO seed layer can also be prepared by immersion method, that is, 40 mL of ethanol solution containing 0.02-0.08 g NaOH and 100 mL of ethanol solution containing 0.1-0.5 g zinc acetate are mixed, heated and stirred in a water bath at 70 °C for 2 hours, and then stored in the dark for 24 hours to obtain ZnO seed solution; the Bi2S3 film is immersed in ZnO seed solution for 30-50 min, and then dried at 60 °C for 60 min to obtain ZnO seed layer on Bi2S3 film.
[0017] A method for fabricating a substrate-free flexible self-driven photodetector based on a Bi₂S₃ / ZnO heterojunction thin film, the method comprising the following steps:
[0018] By fixing a Bi2S3 / ZnO heterojunction thin film on a vapor deposition substrate, and then depositing the same metal electrodes of different sizes at both ends of the Bi2S3 / ZnO heterojunction thin film using electron beam evaporation, thermal evaporation or magnetron sputtering techniques, a substrate-free Bi2S3 / ZnO flexible photodetector with self-driving characteristics is obtained.
[0019] Furthermore, the metal electrode is made of metals such as Cu, Ag, Cr, Al or Ni, and the electrode thickness is 20-150 nm.
[0020] Furthermore, different metals of the same size can be deposited at both ends of the Bi2S3 / ZnO heterojunction film, with the metal electrodes at both ends being Ag and Cu electrodes, Au and Ag electrodes, or Au and Ni electrodes, etc.
[0021] A method for fabricating a photoelectrochemical flexible self-driven photodetector based on a Bi₂S₃ / ZnO heterojunction thin film, the method comprising the following steps:
[0022] A Bi2S3 / ZnO thin film is directly bonded to the conductive surface of a flexible substrate. Then, a solid electrolyte is uniformly coated on the surface of the Bi2S3 / ZnO thin film. Finally, another flexible substrate is placed on the electrolyte with the conductive surface facing down. After drying, a Bi2S3 / ZnO flexible photodetector with self-driving characteristics is obtained.
[0023] Furthermore, the flexible substrate is made of conductive PET, PEN, and PI, etc.
[0024] Furthermore, the solid electrolyte is a quasi-solid polysulfide gel electrolyte or a quasi-solid iodine gel electrolyte, etc.
[0025] Beneficial effects
[0026] The advantages of this invention compared to existing technologies are as follows: This invention successfully fabricates a substrate-free Bi₂S₃ / ZnO heterojunction thin film, in which one-dimensional ZnO nanorods are grown on ultra-long Bi₂S₃ nanofibers. These brush-like Bi₂S₃ / ZnO composite nanowires interweave to form a large-area Bi₂S₃ / ZnO flexible thin film. The method of this invention is simple, reproducible, low-cost, and environmentally friendly, making it suitable for large-scale industrial production. Based on the Bi₂S₃ / ZnO heterojunction flexible thin film, a simple and substrate-free flexible self-driven photodetector was designed. The fabricated flexible detector exhibits excellent self-driven detection capabilities for ultraviolet to infrared light under conditions without external bias and under bending conditions, including high sensitivity, fast response speed, and good cycle stability. This is of great significance for the further development of flexible optoelectronic devices. Attached Figure Description
[0027] Figure 1 An optical photograph of the Bi2S3 / ZnO heterojunction flexible thin film prepared in Example 1 of this invention;
[0028] Figure 2 This is a SEM image of the Bi2S3 / ZnO heterojunction flexible thin film prepared in Example 1 of the present invention;
[0029] Figure 3 The image shows the XRD pattern of the Bi2S3 / ZnO heterojunction flexible thin film prepared in Example 1 of this invention.
[0030] Figure 4 Time-resolved current curves of the Bi2S3 / ZnO substrate-free flexible self-driven photodetector prepared in Example 2 under ultraviolet light irradiation when it is in a flat state;
[0031] Figure 5 Time-resolved current curves of the Bi2S3 / ZnO substrate-free flexible self-driven photodetector prepared in Example 2 under ultraviolet light irradiation when it is in a bent state;
[0032] Figure 6 Time-resolved current curves of the Bi2S3 / ZnO substrate-free flexible self-driven photodetector prepared in Example 3 under infrared light irradiation when it is in a flat state;
[0033] Figure 7 The time-resolved current curve of the Bi2S3 / ZnO substrate-free flexible self-driven photodetector prepared in Example 3 under infrared light irradiation when it is in a bent state. Detailed Implementation
[0034] The technical solution of the present invention will be further described below with reference to the embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.
[0035] Example 1:
[0036] This embodiment provides a method for preparing a substrate-free Bi2S3 / ZnO heterojunction flexible thin film, and the specific implementation steps are as follows:
[0037] 2 g of sodium hydroxide was uniformly dispersed in 20 mL of deionized water. Then, 0.76 g of thiourea was added to the sodium hydroxide solution, followed by the slow addition of approximately 0.093 g of bismuth oxide. The mixture was stirred thoroughly to obtain a precursor solution. This solution was transferred to a high-pressure reactor, sealed, and placed in a constant-temperature drying oven for hydrothermal growth at 200 °C for 24 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The film was then removed, washed, and air-dried. The obtained Bi₂S₃ film was fixed onto a sample holder, and a ZnO seed layer was prepared using magnetron sputtering. Finally, the ZnO seed layer was obtained by annealing in air at 150 °C for 30 minutes. Zinc nitrate hexahydrate and hexamethylenetetramine were dissolved in 30 mL of deionized water and stirred until homogeneous. This solution was then transferred to a polytetrafluoroethylene (PTFE) reactor liner, and the Bi₂S₃ film with the ZnO seed layer was immersed in it. The reaction vessel was sealed and the reaction was carried out at 95 °C for 3 h. After the reaction was completed, a Bi2S3 / ZnO heterojunction film was obtained.
[0038] Figure 1 The optical image shows the Bi₂S₃ / ZnO heterojunction film, revealing its excellent flexibility, indicating the successful fabrication of a substrate-free Bi₂S₃ / ZnO film. To further observe the microstructure of the Bi₂S₃ / ZnO heterojunction film, it was characterized using scanning electron microscopy, with the results shown below. Figure 2 As shown, the Bi2S3 / ZnO heterojunction film is composed of interwoven nanofibers, with uniformly long ZnO nanorods densely growing on ultra-long Bi2S3 nanowires, giving the Bi2S3 / ZnO film a brush-like layered structure, which is beneficial for improving light utilization. Figure 3 The XRD patterns of the prepared Bi2S3 / ZnO heterojunction films are presented. Characteristic peaks belonging to the (020), (120), (220), (130), (230), (141) and (421) crystal planes of Bi2S3 can be observed. In addition, the (100), (002), (101) and (103) crystal planes corresponding to ZnO are also observed, which confirms the successful preparation of the substrate-free Bi2S3 / ZnO heterojunction film.
[0039] Example 2:
[0040] This embodiment provides a method for fabricating a substrate-free flexible self-driven photodetector based on a Bi2S3 / ZnO heterojunction thin film. The specific implementation steps are as follows:
[0041] The substrate-free Bi2S3 / ZnO heterojunction film prepared in Example 1 was fixed on a sample holder, a mask was placed on its surface, and one side of the Bi2S3 / ZnO flexible film was blocked. The metal electrode Ag was deposited on the unblocked Bi2S3 / ZnO film side by electron beam evaporation. Then, the film on the side with the deposited electrode Ag was blocked, and the other side was exposed. The metal electrode Au was deposited on the other side of the Bi2S3 / ZnO film by electron beam evaporation, thus obtaining a self-supporting flexible Bi2S3 / ZnO photodetector with self-driving characteristics.
[0042] Using ultraviolet light as the incident light source, the photodetector capability of a substrate-free flexible photodetector of Bi₂S₃ / ZnO was evaluated under conditions without applied bias voltage. The results are as follows: Figure 4 As shown, when the device is exposed to incident light, a photocurrent is immediately generated, with a maximum value of approximately 0.013 μA. Upon removal of the incident light, the current rapidly decreases and returns to its initial value under dark conditions. Furthermore, the Bi₂S₃ / ZnO flexible photodetector maintains essentially consistent photoresponse characteristics across five cycles, indicating excellent stability of the constructed flexible device.
[0043] Detection capability under bending conditions is crucial for evaluating the flexibility advantages of photodetectors. Therefore, the detection performance of a Bi₂S₃ / ZnO flexible photodetector was tested under the same illumination conditions with the device bent at 60 degrees. Figure 5 As shown, the device exhibits a rapid response to ultraviolet light, with a maximum current of approximately 0.0128 μA. In the absence of light, the Bi₂S₃ / ZnO flexible photodetector also quickly returns to its initial state. Compared to the flat state, the maximum current decreases by only about 1.5%, indicating that the flexible device maintains good detection capabilities even under bending conditions and demonstrates excellent cycling stability. These results demonstrate that the fabricated substrate-free Bi₂S₃ / ZnO flexible photodetector has significant application potential in future wearable detection applications.
[0044] Example 3:
[0045] This embodiment provides a method for fabricating a substrate-free flexible self-driven photodetector based on a Bi2S3 / ZnO heterojunction thin film. The specific implementation steps are as follows:
[0046] The substrate-free Bi2S3 / ZnO heterojunction thin film prepared in Example 1 was fixed on a sample holder. A mask with a rectangular window shape of 2 mm long and 1 mm wide was used to cover the surface of the thin film, and an Au electrode was deposited by electron beam evaporation. Subsequently, the mask was replaced with a mask with a rectangular window shape of 1 mm long and 0.5 mm wide, and an Au electrode was deposited again by electron beam evaporation on the corresponding thin film area on the other side, thus obtaining a self-supporting flexible Bi2S3 / ZnO photodetector with self-driving characteristics.
[0047] Figure 6 and Figure 7 The figures show the time-resolved current curves of the Bi₂S₃ / ZnO flexible detector under infrared illumination in its flat and bent states, respectively. As can be seen from the figures, the device exhibits a rapid response to infrared light both before and after bending, with maximum currents of approximately 0.027 μA and 0.024 μA, respectively. The current retention rate of the Bi₂S₃ / ZnO flexible detector in the bent state exceeds 88%. Furthermore, the Bi₂S₃ / ZnO flexible detector demonstrates essentially consistent photoresponse behavior across five on / off optical cycles, and the maximum photocurrent remains essentially unchanged, showcasing the device's excellent cycle stability. All of the above detection performance was tested under zero bias conditions, indicating that the fabricated substrate-free Bi₂S₃ / ZnO detector possesses excellent self-driven infrared light detection capability.
[0048] The above description of the present invention is only a preferred embodiment of the present invention and is not intended to limit the implementation of the present invention. Those skilled in the art can easily make corresponding modifications or alterations based on the main concept and spirit of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of protection claimed in the claims.
Claims
1. A substrate-free Bi₂S₃ / ZnO heterojunction thin film, characterized in that, The Bi2S3 / ZnO heterojunction is composed of ultra-long Bi2S3 nanofibers and ZnO short nanorods, forming an overall brush-like structure. The ZnO nanorods are grown on the surface of the Bi2S3 nanofibers. The film is composed of a large number of brush-like Bi2S3 / ZnO ultra-long fibers, which are tightly interwoven to make the substrate-free film present an overall cross-linked network structure.
2. The brush-like Bi₂S₃ / ZnO heterojunction according to claim 1, characterized in that, The Bi2S3 is a one-dimensional fiber structure with a length of 100 µm-5 mm and a diameter of 30-300 nm; the ZnO nanorods have a length of 50-2000 nm and a diameter of 10-100 nm.
3. The method for preparing a substrate-free Bi₂S₃ / ZnO heterojunction thin film according to claim 1, characterized in that, The method includes the following steps: Step 1: Weigh 1-3 g of sodium hydroxide and disperse it evenly in 10-40 ml of deionized water; then add 1-2 g of thiourea to the sodium hydroxide solution. After stirring continuously for 2-5 minutes, slowly add 0.08-0.5 g of bismuth oxide and stir until homogeneous; Step 2: Transfer the mixed solution obtained in Step 1 to a high-pressure reactor, seal it, and place it in a constant temperature heating and drying oven. React at 200 °C for 20-48 hours. After the reaction is completed, allow it to cool naturally to room temperature, remove the Bi2S3 film, wash it, and finally dry it naturally in the air to obtain a substrate-free flexible Bi2S3 film. Step 3: Prepare the ZnO seed layer. Cut the Bi2S3 film prepared in Step 2 into 1 cm × 1 cm pieces and fix them on the sample holder. After magnetron sputtering for 2-10 minutes, anneal in air for 30-90 minutes to deposit the ZnO seed layer on the Bi2S3 film. Step 4: Dissolve zinc nitrate hexahydrate and hexamethylenetetramine in deionized water and stir until homogeneous. Transfer the solution into a polytetrafluoroethylene (PTFE) reactor liner. Then, vertically suspend the Bi2S3 film with the ZnO seed layer in the middle of the solution. Seal the reactor and react at 60-95 °C for 2-7 hours to obtain a substrate-free Bi2S3 / ZnO heterojunction flexible film.
4. The method for preparing Bi2S3 / ZnO heterojunction thin films according to claim 3, characterized in that: In step three, the annealing temperature is 100-200 ℃.
5. The method for preparing Bi₂S₃ / ZnO heterojunction thin films according to claim 3, characterized in that: In step three, the ZnO seed layer can also be prepared by the Czochralski method, in which the Bi2S3 film is soaked in zinc acetate solution and deionized water for 1 minute in sequence, and then dried at 60 °C. This process is repeated 2-10 times to obtain the ZnO seed layer on the surface of the ultra-long Bi2S3 nanofibers that constitute the Bi2S3 film.
6. The method for preparing Bi₂S₃ / ZnO heterojunction thin films according to claim 3, characterized in that: In step three, the ZnO seed layer can also be prepared by immersion. 40 mL of an ethanol solution containing 0.02-0.08 g NaOH and 100 mL of an ethanol solution containing 0.1-0.5 g zinc acetate are mixed and heated and stirred in a water bath at 70 °C for 2 hours. Then, the mixture is stored in the dark for 24 hours to obtain the ZnO seed solution. The Bi2S3 film is immersed in the ZnO seed solution for 30-50 min, then removed and dried at 60 °C for 60 min. This results in the growth of a ZnO seed layer on the surface of the ultralong Bi2S3 nanofibers that constitute the Bi2S3 film.
7. A substrate-free flexible self-driven Bi₂S₃ / ZnO heterojunction thin-film photodetector, characterized in that: The self-driven photodetector consists only of a substrate-free Bi2S3 / ZnO flexible thin film and two metal electrodes; the substrate-free flexible self-driven photodetector can be cut into any shape; the two metal electrodes are different from each other in at least one of the material composition and geometric structure.
8. A substrate-free flexible self-driven photodetector based on a Bi₂S₃ / ZnO heterojunction thin film according to claim 7, characterized in that: The metal electrode material is one or two of the metals such as Cu, Ag, Au, Cr, Al or Ni, and the electrode thickness is 20-150 nm.
9. A flexible self-driven photodetector based on a Bi₂S₃ / ZnO heterojunction thin film, comprising a Bi₂S₃ / ZnO heterojunction thin film, a solid electrolyte, and a flexible conductive substrate, characterized in that: A Bi2S3 / ZnO thin film is directly bonded to the conductive surface of a flexible substrate. Then, a solid electrolyte is uniformly coated on the surface of the Bi2S3 / ZnO thin film. Finally, another flexible substrate is placed on the electrolyte with the conductive surface facing down. After drying, a Bi2S3 / ZnO flexible photodetector with self-driving characteristics is obtained.
10. The method for fabricating a Bi₂S₃ / ZnO flexible self-driven photodetector according to claim 9, characterized in that... The flexible conductive substrate is conductive PET, PEN, or PI; the solid electrolyte is a quasi-solid polysulfide gel electrolyte or a quasi-solid iodine gel electrolyte.