A perovskite polycrystalline thin film, a preparation method thereof, and an application thereof

Abstract

The present invention relates to the technical field of perovskite thin films, and specifically discloses a perovskite polycrystalline thin film, a preparation method thereof and an application. The preparation method includes the following steps: dissolving PbI<subgt;2< / subgt> powder, PbBr<subgt;2< / subgt> powder, FAI powder, MAI powder and CsI powder in a solvent to obtain a perovskite precursor solution; spin-coating the perovskite precursor solution and annealing to obtain a perovskite polycrystalline thin film. When preparing the perovskite polycrystalline thin film, the present invention optimizes the material bandgap by adjusting the ratio of iodine (I) to bromine (Br) in the perovskite halogen site, so that when used for underwater optical communication, the responsivity of the detector in the blue-green light band can be improved. Compared with commercial silicon-based detectors, the detector prepared by using the perovskite polycrystalline thin film of the present invention has better weak light response, thus having higher linearity and signal-to-noise ratio, and can have a farther transmission distance under the same illumination conditions, effectively overcoming the defect of insufficient responsivity of traditional detectors in the blue-green light band.

Description

Technical Field

[0001] The present invention relates to the technical field of perovskite thin films, and particularly relates to a perovskite polycrystalline thin film, a preparation method thereof, and an application thereof. Background Art

[0002] Underwater communication technologies mainly include three categories: underwater acoustic communication, radio frequency electromagnetic communication, and optical communication. Underwater acoustic communication has become the mainstream due to the long-distance (tens of kilometers) transmission ability of sound waves. However, its bandwidth is limited (kHz level), the rate is only at the kbps level, and there are problems such as second-level delay and high energy consumption. Radio frequency electromagnetic communication performs well in resisting turbulence in turbid waters and can achieve a rate of 100 Mbps. However, high-frequency signals attenuate severely, the effective distance is usually less than 80 meters, and a relatively high operating power is required. In contrast, underwater optical communication has a fast data transmission rate (Gbps level), low transceiver cost, small size, strong anti-interference ability, and high security, and is a key research technology in the future underwater communication field.

[0003] However, due to the rapid attenuation of underwater light intensity, the detectors in the communication system need to have high sensitivity, and in order to exert the advantage of the transmission rate of optical communication, they need to have a fast response time at the same time. Among current detectors, detectors with high responsivity, such as photomultiplier tubes, avalanche detectors, etc., require stable external power supply, and the working voltage reaches dozens or even thousands of volts, which brings a burden to the stability and maintenance of the system. For common self-powered detectors, such as self-powered detectors based on silicon or gallium nitride, generally, the responsivity in the blue-green light band applicable to underwater optical communication is not high, and the response speed is also relatively limited. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide a perovskite polycrystalline thin film, a preparation method thereof, and an application thereof. When preparing, by adjusting the ratio of iodine to bromine in the perovskite halogen position, the band gap of the material is optimized, so that the responsivity of the detector in the blue-green light band can be improved when used for underwater optical communication.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] The present invention first provides a preparation method of a perovskite polycrystalline thin film, which includes the following steps: dissolving PbI2 powder, PbBr2 powder, FAI (formamidinium hydroiodide) powder, MAI (methylammonium iodide) powder, and CsI powder in a solvent to obtain a perovskite precursor solution; spin-coating the perovskite precursor solution and annealing to obtain a perovskite polycrystalline thin film.

[0007] By adjusting the ratio of iodine (I) to bromine (Br) in the perovskite halogen site, the present invention optimizes the material bandgap, so that when used for underwater optical communication, the responsivity of the detector in the blue-green light band can be improved; compared with commercial silicon-based detectors, due to the higher responsivity of perovskite in the blue-green light band, the detector prepared with the perovskite polycrystalline thin film of the present invention has better weak light response, thus having higher linearity and signal-to-noise ratio, and can have a longer transmission distance under the same illumination conditions, effectively overcoming the defect of insufficient responsivity of traditional detectors in the blue-green light band. The perovskite polycrystalline thin film of the present invention is prepared by a chemical solution method, and the preparation process is simple, which can reduce the preparation cost of the detector.

[0008] As a further improvement of the above solution of the present invention, the structural formula of the perovskite polycrystalline thin film is FA 0.8 MA 0.15 Cs 0.05 PbI x Br 3-x , where 1.5 ≤ x ≤ 3.

[0009] As a further improvement of the above solution of the present invention, the solvent is obtained by mixing N,N-dimethylformamide and dimethyl sulfoxide in a volume ratio of 3-4:1.

[0010] As a further improvement of the above solution of the present invention, the concentration of the perovskite precursor solution is 0.8-1.5 M.

[0011] As a further improvement of the above solution of the present invention, the annealing is carried out at 100-120 °C for 15-20 min.

[0012] The present invention also provides a perovskite polycrystalline thin film prepared by the preparation method as described above.

[0013] The present invention also provides an application of the perovskite polycrystalline thin film as described above in underwater optical communication.

[0014] The present invention also provides a photodetector, which includes a cathode layer, an electron transport layer, a light absorption layer, a hole transport layer, and an anode layer arranged in sequence, and the light absorption layer uses the perovskite polycrystalline thin film as described above.

[0015] The present invention also provides a preparation method of a photodetector, which includes the following steps:

[0016] Provide a glass substrate, clean and dry it to obtain an anode layer;

[0017] Prepare a hole transport layer on the anode layer;

[0018] Use the preparation method as described above to prepare a perovskite polycrystalline thin film on the hole transport layer to obtain a light absorption layer;

[0019] Prepare an electron transport layer on the light absorption layer;

[0020] Deposit silver on the electron transport layer to form a cathode layer.

[0021] The present invention also provides an underwater optical communication system, which includes:

[0022] The photodetector as described above;

[0023] A laser light source, which is used to emit laser light to the photodetector;

[0024] A signal generator, which is used to modulate the laser light emitted by the laser light source; and

[0025] An oscilloscope, which is signal-connected to the photodetector.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. When preparing the perovskite polycrystalline thin film in the present invention, by adjusting the ratio of iodine (I) to bromine (Br) in the perovskite halogen site, since the ionic radius of Br - (196 pm) is smaller than that of I - (220 pm), increasing the Br content will cause the perovskite lattice to shrink, increasing the bandgap of the material. This bandgap broadening reduces the thermalization loss of high-energy photons, enables carriers to relax to the band edge faster, and achieves efficient charge separation under the driving of the built-in electric field in the heterojunction, thereby improving the responsivity. At the same time, Br doping can passivate halogen vacancy defects, inhibit non-radiative recombination, extend the carrier diffusion length, and also improve the carrier collection efficiency, so that when used in underwater optical communication, the responsivity of the detector in the blue-green light band can be improved; compared with commercial silicon-based detectors, since perovskite has a higher responsivity in the blue-green light band, the detector prepared with the perovskite polycrystalline thin film of the present invention has better weak light response, thus having higher linearity and signal-to-noise ratio, and can have a longer transmission distance under the same illumination conditions, effectively overcoming the defect of insufficient responsivity of traditional detectors in the blue-green light band. The perovskite polycrystalline thin film of the present invention is prepared by a chemical solution method, and the preparation process is simple, which can reduce the preparation cost of the detector.

[0028] 2. The photodetector prepared with the perovskite polycrystalline thin film prepared by the present invention has an external quantum efficiency (EQE) of 95.84% near the 510 nm band, and the responsivity is increased to 0.402 A / W, which is suitable for high-sensitivity detection in the underwater weak light environment. Compared with the same type of silicon-based photodetectors, it is more suitable as an underwater optical communication component, with low preparation cost, simple preparation process, high sensitivity, and fast response speed, and has significant advantages in the field of optical communication.

[0029] 3. The photodetector prepared from the perovskite polycrystalline thin film prepared by the present invention adopts a vertical heterojunction structure, and realizes the purpose of normal operation without an external voltage by effectively utilizing incident light, can achieve the self-powered function of the entire detector, output a light response current without an external power supply, significantly reduce the system power consumption and safety hazards, and improve the long-term operation stability of the underwater communication system. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 FIG. is a schematic structural diagram of a photodetector proposed by the present invention;

[0031] Figure 2 FIG. is an EQE curve graph of the photodetectors prepared in Examples 1-6 and a commercial silicon-based device;

[0032] Figure 3 FIG. is an average EQE graph of the photodetectors prepared in Examples 1-6;

[0033] Figure 4 FIG. is the responsivity of the photodetector prepared in Example 1 and a commercial silicon-based device;

[0034] Figure 5 FIG. is a linear dynamic range graph of the photodetector prepared in Example 1;

[0035] Figure 6 FIG. is a schematic structural diagram of the underwater optical communication system in Test Example 3;

[0036] Figure 7 FIG. is a transmission rate-bit error rate graph of the underwater optical communication system in Test Example 3.

[0037] Reference numerals: 1, cathode layer; 2, electron transport layer; 3, light absorption layer; 4, hole transport layer; 5, anode layer; 6, signal generator; 7, laser light source; 8, glass water tank; 9, metal shell; 10, photodetector; 11, oscilloscope. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided so that the disclosure of the present invention can be understood more thoroughly and comprehensively.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0040] Example 1

[0041] This example presents a photodetector, which combines Figure 1 , including a cathode layer 1, an electron transport layer 2, a light absorption layer 3, a hole transport layer 4, and an anode layer 5 arranged in sequence. The preparation method includes the following steps:

[0042] (1) Forming the anode layer 5: The ITO (indium tin oxide) glass is ultrasonically cleaned with acetone, isopropanol, and ethanol for 15 minutes in sequence, dried with nitrogen, and treated with ultraviolet ozone for 20 minutes;

[0043] (2) Forming the hole transport layer 4: 50 μL of NiO x solution is spin-coated onto the surface of the anode layer 5 under the spin-coating conditions of 2000 rpm and 30 s. After spin-coating, it is annealed at 120 °C for 20 minutes; after cooling to room temperature, 80 μL of a mixed solution of (2-(9H-carbazol-9-yl)ethyl)phosphonic acid (2PACz) and 4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz) (2PACz and Me-4PACz are mixed in a volume ratio of 1:1) is coated onto the NiO x surface under the spin-coating conditions of 4000 rpm and 30 s, and then annealed at 100 °C for 10 minutes to obtain the hole transport layer 4;

[0044] (3) Forming the perovskite polycrystalline thin film FA 0.8 MA 0.15 Cs 0.05 PbI 2.25 Br 0.75 : Lead iodide PbI2 powder, lead bromide PbBr2 powder, formamidinium hydroiodide FAI powder, methylammonium iodide MAI powder, and cesium iodide CsI powder are weighed according to the target stoichiometric ratio and dissolved in a solvent (a mixture of N,N-dimethylformamide DMF and dimethyl sulfoxide DMSO in a volume ratio of 4:1) to prepare a 1 M perovskite precursor solution; 50 μL of the perovskite precursor solution is spin-coated onto the hole transport layer under the spin-coating conditions of 1000 rpm and 10 s and 5000 rpm and 40 s, and 150 μL of chlorobenzene is added dropwise as an antisolvent 7 s before the end of spin-coating; after spin-coating, it is annealed at 100 °C for 20 minutes to obtain the perovskite polycrystalline thin film, which serves as the light absorption layer 3;

[0045] (4) Forming the electron transport layer 2: 20 nm of C60 and 7 nm of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) are thermally evaporated onto the perovskite polycrystalline thin film in sequence to form the electron transport layer 2;

[0046] (5) Forming the cathode layer 1: Evaporating 100 nm of Ag on the electron transport layer to form the cathode layer 1, thereby obtaining the perovskite photodetector.

[0047] Example 2

[0048] This example uses the same implementation method as Example 1. The difference from Example 1 is that the structural formula of the perovskite polycrystalline thin film formed in this example is FA 0.8 MA 0.15 Cs 0.05 PbI 1.5 Br 1.5 .

[0049] Example 3

[0050] This example uses the same implementation method as Example 1. The difference from Example 1 is that the structural formula of the perovskite polycrystalline thin film formed in this example is FA 0.8 MA 0.15 Cs 0.05 PbI 1.75 Br 1.25 .

[0051] Example 4

[0052] This example uses the same implementation method as Example 1. The difference from Example 1 is that the structural formula of the perovskite polycrystalline thin film formed in this example is FA 0.8 MA [[ID=4I]] 0.15 Cs 0.05 PbI2Br.

[0053] Example 5

[0054] This example uses the same implementation method as Example 1. The difference from Example 1 is that the structural formula of the perovskite polycrystalline thin film formed in this example is FA 0.8 [[ID=SZ]]MA 0.15 Cs 0.05 PbI 2.5 Br 0.5 .

[0055] Example 6

[0056] This example uses the same implementation method as Example 1. The difference from Example 1 is that the structural formula of the perovskite polycrystalline thin film formed in this example is FA 0.8 MA 0.15 Cs 0.05 PbI3.

[0057] Test Example 1

[0058] External quantum efficiency EQE of the photodetectors prepared in Test Examples 1-6 and the commercial silicon-based device FDS 100 in the blue and green light bands: Measured by the QE-R quantum efficiency measurement system of Shengyan Electronic Technology, and the system was calibrated before the test. The results are as Figure 2 shown. According to Figure 2 the EQE curve, Examples 1-6 show significantly higher optical responses than the commercial silicon-based device FDS 100 in the range of 490-510 nm. Especially for Example 1, the EQE peak at 490 nm is as high as 95.84%. It can be seen that the perovskite polycrystalline film in Example 1 has superiority.

[0059] Differentiating the EQE curves of each device, the band gaps of the photodetectors prepared in Examples 1-6 are 1.64 eV, 1.78 eV, 1.73 eV, 1.69 eV, 1.52 eV, and 1.49 eV respectively. According to the band gap data of Examples 1-6, it can be seen that as the I ratio increases, the band gap gradually decreases. The optimal band gap is 1.64 eV (x = 2.25), corresponding to the highest EQE, indicating that the material band gap and blue-green light absorption characteristics match best under this condition. As the Br ratio increases, the band gap gradually increases. Although the increase in the band gap may theoretically improve the EQE in this band, excessive Br will lead to an increase in the lattice contraction and ion migration problems, resulting in an increase in non-radiative recombination, and instead reducing the carrier collection efficiency, ultimately leading to a decrease in EQE. This indicates that the Br ratio needs to be controlled within a reasonable range to balance band gap optimization and defect suppression. Example 1 is the optimal value after comprehensive consideration.

[0060] To make the comparison results more obvious, the EQE values of the photodetectors prepared in Examples 1-6 near the blue-green window (490-510 nm) suitable for underwater optical communication are averaged respectively, and the results are as Figure 3 shown. Combining Figure 3 the average EQE comparison, when x = 2.25, the average response efficiency in the blue and green light bands reaches 95.59%, which is 10.69% higher than that when x = 3 (efficiency is 84.90%). This indicates that the content of I is the optimal choice within the range of x = 2.0-2.5, fully proving its suitability for high-sensitivity detection in underwater low-light environments.

[0061] Then, calculate the responsivity R of the photodetector prepared in Example 1 and the commercial silicon-based device FDS 100 by , and the results are as Figure 4 shown. From Figure 4 it can be seen that compared with the commercial silicon-based device FDS 100, the responsivity of the photodetector prepared in Example 1 is increased to 0.402 A / W at a wavelength of 490 nm, which is significantly higher than that of the commercial silicon-based detector in the blue and green light bands. This shows that the photodetector prepared by the present invention is more suitable for use as an underwater optical communication component than the same type of silicon-based photodetector.

[0062] Test Example 2

[0063] The photodetector prepared in Example 1 was measured for photocurrent density at different optical power densities on a probe station test system, and the linear dynamic range as shown in Figure 5 was obtained by linear fitting. As can be seen from Figure 5 it, the linear dynamic range of the photodetector prepared in Example 1 reached 165.62 dB. The responsivity at different optical power densities was calculated, and it was found that the responsivity fluctuated within a reasonable range. It can be seen that the photodetector of Example 1 has a similar responsivity at different optical power densities and has a good weak light response, and can work under a wide range of light intensities.

[0064] Test Example 3

[0065] The photodetector prepared in Example 1 was used as an underwater optical communication component for underwater transmission: The structure of the entire underwater optical communication system is as shown in Figure 6 where: A certain amount of water was filled in the glass water tank 8 to simulate the underwater environment; the underwater transmission distance was determined, and the metal shell 9 with a glass window (carrying the photodetector 10) was fixed at the corresponding position according to this distance; the metal shell 9 with a glass window could be pushed to move in the water tank to adjust the distance between the photodetector 10 and the laser light source 7, which was used to simulate an autonomous underwater vehicle; the 450-nm laser light source 7 was used to align with the photodetector 10 and emit modulated laser; the signal generator 6 was used to modulate the laser light source 7 to send signals; the oscilloscope 11 was directly connected to the photodetector 10 to obtain the received waveform information.

[0066] During underwater transmission, first turn on the laser light source 7, focus the laser light and align it with the glass incident surface of the photodetector 10; in a dark environment, change the settings of the signal generator 6 so that the laser light source 7 can send a modulated waveform; the photodetector 10 converts the received optical signal into an electrical signal, which is read by the oscilloscope 11 for subsequent observation and processing.

[0067] When the underwater transmission distance was 1 m, by changing the settings of the signal generator 6 and changing the signal transmission rate, the bit error rate at different transmission rates was measured, and the results are as shown in Figure 7 As can be seen from Figure 7 it, when the rate was less than 1.625 Mbps, the bit error rate BER was lower than 0.001, proving that the system had a high communication quality at the test rate.

[0068] An integrated underwater optical communication verification system applicable to self-powered detectors constructed in this test example (including a signal generator 6, a 450 nm laser source 7, a movable photodetector 10, etc.). The distance between the photodetector 10 and the laser source 7 can be adjusted, and each component can be replaced, so as to systematically verify the communication capabilities of self-powered detectors under different water qualities and different wavelength bands. This system can directly simulate the communication scenarios of autonomous underwater vehicles and provide a test platform for device optimization and application.

[0069] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0070] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent shall be subject to the appended claims.

Claims

1. Application of a perovskite polycrystalline thin film in a self-powered blue-green light photodetector, characterized in that: The self-powered blue-green light photodetector comprises a cathode layer, an electron transport layer, a light absorption layer, a hole transport layer, and an anode layer arranged in sequence, wherein the light absorption layer is made of a perovskite polycrystalline thin film; The preparation method of the perovskite polycrystalline film comprises the following steps: dissolving PbI2 powder, PbBr2 powder, FAI powder, MAI powder and CsI powder in a solvent to obtain a perovskite precursor solution; spin coating the perovskite precursor solution, annealing, and obtaining a perovskite polycrystalline film, wherein the structural formula of the perovskite polycrystalline film is FA 0.8 MA 0.15 Cs 0.05 PbI x Br 3-x , where x=2.

25.

2. Application of the perovskite polycrystalline thin film in a self-powered blue-green light photodetector according to claim 1, characterized in that: The solvent is obtained by mixing N,N-dimethylformamide and dimethyl sulfoxide in a volume ratio of 3-4:

1.

3. Application of the perovskite polycrystalline thin film in a self-powered blue-green light photodetector according to claim 1, characterized in that: The concentration of the perovskite precursor solution is 0.8-1.5M.

4. The use of the perovskite polycrystalline thin film in a self-powered blue-green light photodetector according to claim 1, characterized in that: The annealing is performed at 100-120° C. for 15-20 minutes.

5. The use of the perovskite polycrystalline thin film in a self-powered blue-green light photodetector according to claim 1, characterized in that: The preparation method of the self-powered blue-green light photodetector comprises the following steps: Providing a glass substrate, cleaning and drying it to obtain an anode layer; preparing a hole transport layer on the anode layer; preparing a perovskite polycrystalline thin film on the hole transport layer to obtain a light absorbing layer; preparing an electron transport layer on the light absorbing layer; Silver is deposited on the electron transport layer to form a cathode layer.

6. Application of the perovskite polycrystalline thin film in a self-powered blue-green light photodetector according to claim 1, characterized in that: The application is an application in an underwater optical communication system, and the underwater optical communication system includes: The self-powered blue-green photodetector; a laser light source, configured to emit laser light toward the photodetector; a signal generator, configured to modulate the laser light emitted by the laser light source; and An oscilloscope is connected to the photodetector signal.

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