Perovskite polycrystalline film and preparation method and application thereof

Abstract

The invention relates to the technical field of perovskite thin films, and particularly discloses a perovskite polycrystalline thin film and a preparation method and application thereof, and the preparation method 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; and spin-coating the perovskite precursor solution, and annealing to obtain the perovskite polycrystalline thin film. When the perovskite polycrystalline thin film is prepared, the ratio of iodine (I) to bromine (Br) in perovskite halogen sites is adjusted, and the band gap of the material is optimized, so that the responsivity of a detector in blue-green light bands can be improved when the perovskite polycrystalline thin film is used for underwater optical communication, and compared with a commercial silicon-based detector, the photoelectric conversion efficiency is improved. A detector prepared by using the perovskite polycrystalline thin film has better weak light response, so that the detector has higher linearity and signal-to-noise ratio, can have a farther transmission distance under the same illumination condition, and effectively overcomes the defect of insufficient responsivity of a traditional detector in blue-green light wave bands.

Description

Technical Field

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

[0002] Underwater communication technologies mainly include underwater acoustic communication, radio frequency electromagnetic communication and optical communication. Underwater acoustic communication has become mainstream due to its ability to transmit sound waves over long distances (tens of kilometers), but its bandwidth is limited (kHz level), the rate is only kbps level, and there are problems of second-level delay and high energy consumption. Radio frequency electromagnetic communication has good anti-turbulence performance in turbid waters and can achieve a rate of 100Mbps, but high-frequency signals are severely attenuated, the effective distance is usually less than 80 meters, and higher 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. It is a key research technology in the field of underwater communications in the future.

[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 take advantage of the transmission rate of optical communication, they also need to have a fast response time. Among the current detectors, detectors with high responsiveness, such as photomultiplier tubes and avalanche detectors, require a stable external power supply, and the operating voltage reaches tens or even thousands of volts, which brings a burden to the stability and maintenance of the system. Common self-powered detectors, such as silicon-based or gallium nitride self-powered detectors, generally have low responsiveness in the blue-green light band suitable for underwater optical communications, 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 film and its preparation method and application. During the preparation, the ratio of iodine to bromine in the halogen position of the perovskite is adjusted to optimize the material band gap, so that when used for underwater optical communication, the detector's responsiveness in the blue-green light band can be improved.

[0005] To achieve the above object, the present invention adopts the following technical solutions: The present invention first provides a method for preparing a perovskite polycrystalline thin film, which comprises the following steps: 2 Powder, PbBr 2 powder, FAI (formamidine hydroiodide) powder, MAI (methylamine iodide) powder and CsI powder are dissolved in a solvent to obtain a perovskite precursor solution; the perovskite precursor solution is spin-coated and annealed to obtain a perovskite polycrystalline film.

[0006] The present invention optimizes the band gap of the material by adjusting the ratio of iodine (I) to bromine (Br) in the halogen position of the perovskite, so that the detector can achieve an improvement in the responsiveness in the blue-green light band when used for underwater optical communication; compared with commercial silicon-based detectors, since the responsiveness of perovskite in the blue-green light band is higher, the detector prepared by using the perovskite polycrystalline 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 lighting conditions, effectively overcoming the defect of insufficient responsiveness of traditional detectors in the blue-green light band. The perovskite polycrystalline 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.

[0007] As a further improvement of the above solution of the present invention, the structural formula of the perovskite polycrystalline film is FA 0.8 MA 0.15 Cs 0.05 PbI x Br 3-x , where 1.5≤x≤3.

[0008] As a further improvement of the above scheme of the present invention, the solvent is obtained by mixing N,N-dimethylformamide and dimethyl sulfoxide in a volume ratio of 3-4:1.

[0009] As a further improvement of the above solution of the present invention, the concentration of the perovskite precursor solution is 0.8-1.5M.

[0010] As a further improvement of the above solution of the present invention, the annealing is performed at 100-120° C. for 15-20 min.

[0011] The present invention also provides a perovskite polycrystalline thin film, which is prepared by the preparation method as described above.

[0012] The present invention also provides an application of the above-mentioned perovskite polycrystalline film in underwater optical communication.

[0013] The present invention also provides a photodetector, which comprises a cathode layer, an electron transport layer, a light absorption layer, a hole transport layer, and an anode layer which are arranged in sequence, wherein the light absorption layer adopts the perovskite polycrystalline film as described above.

[0014] The present invention also provides a method for preparing a photoelectric detector, which comprises the following steps: Providing a glass substrate, cleaning and drying it, and obtaining an anode layer; preparing a hole transport layer on the anode layer; A perovskite polycrystalline thin film is prepared on the hole transport layer by the preparation method as described above to obtain a light absorption layer; preparing an electron transport layer on the light absorbing layer; Silver is deposited on the electron transport layer to form a cathode layer.

[0015] The present invention also provides an underwater optical communication system, comprising: A photodetector as described above; A laser light source, used for emitting laser light to the photodetector; a signal generator, which is used to modulate the laser light emitted by the laser light source; and An oscilloscope is connected to the photodetector signal.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. In the preparation of the perovskite polycrystalline film, the ratio of iodine (I) to bromine (Br) in the perovskite halogen position is adjusted. - The ionic radius (196 pm) is smaller than that of I - (220 pm), increasing the Br content will cause the perovskite lattice to shrink and increase the band gap of the material. This band gap widening reduces the thermal loss of high-energy photons, enables carriers to relax to the band edge faster, and achieves efficient charge separation under the built-in electric field of 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 improve the carrier collection efficiency, so that when used for underwater optical communication, the detector can achieve an improvement in the responsivity of the blue-green light band; compared with commercial silicon-based detectors, since the responsivity of perovskite in the blue-green light band is higher, the detector prepared using the perovskite polycrystalline 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 lighting conditions, effectively overcoming the defect of insufficient responsivity of traditional detectors in the blue-green light band. The perovskite polycrystalline 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.

[0017] 2. The photodetector made of the perovskite polycrystalline thin film prepared by the present invention has an external quantum efficiency (EQE) of 95.84% near the 510nm band, and the responsivity is improved to 0.402 A / W, which is suitable for high-sensitivity detection in underwater weak light environments. Compared with the same type of silicon-based photodetectors, it is more suitable for use 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 communications.

[0018] 3. The photodetector made of the perovskite polycrystalline thin film prepared by the present invention adopts a vertical heterojunction structure, and achieves the purpose of normal operation without an external voltage by effectively utilizing incident light. The self-powered function of the entire detector can be realized, and the light response current can be output without an external power supply, which significantly reduces the system power consumption and safety hazards, and improves the long-term operation stability of the underwater communication system. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic diagram of the structure of a photoelectric detector proposed by the present invention; Figure 2 EQE curves of the photodetectors prepared in Examples 1-6 and commercial silicon-based devices; Figure 3 is the average EQE graph of the photodetectors prepared in Examples 1-6; Figure 4 The responsivity of the photodetector prepared in Example 1 and the commercial silicon-based device; Figure 5 is a linear dynamic range diagram of the photodetector prepared in Example 1; Figure 6 It is a structural schematic diagram of the underwater optical communication system in Test Example 3; Figure 7 This is the transmission rate-bit error rate diagram of the underwater optical communication system in test example 3.

[0020] Figure 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

[0021] For ease of understanding of the present invention, the present invention will be described more fully 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, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. 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.

[0023] Example 1 This embodiment proposes a photoelectric detector, combined with Figure 1, which comprises 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, and the preparation method thereof comprises the following steps: (1) Forming the anode layer 5: The ITO (indium tin oxide) glass was ultrasonically cleaned with acetone, isopropanol, and ethanol for 15 min respectively, dried with nitrogen, and treated with ultraviolet ozone for 20 min; (2) Formation of hole transport layer 4: Spin coating of 50 μL NiO x The solution was spin-coated onto the surface of the anode layer 5, and after spin coating, it was annealed at 120°C for 20 min. After cooling to room temperature, 80 μL of a mixed solution of (2-(9H-carbazole-9-yl)ethyl)phosphonic acid (2PACz) and 4-(3,6-dimethyl-9H-carbazole-9-yl)butyl]phosphonic acid (Me-4PACz) (2PACz and Me-4PACz were mixed in a volume ratio of 1:1) was applied to the NiO at 4000 rpm for 30 s. x surface, and then annealed at 100°C for 10 min to obtain a hole transport layer 4; (3) Formation of perovskite polycrystalline thin film FA 0.8 MA 0.15 Cs 0.05 PbI 2.25 Br 0.75 :Weigh lead iodide PbI according to the target stoichiometric ratio 2 Powder, Lead Bromide PbBr 2 powder, formamidine hydroiodide FAI powder, methylamine iodide MAI powder and cesium iodide CsI powder are dissolved in a solvent (N,N-dimethylformamide DMF and dimethyl sulfoxide DMSO are mixed in a volume ratio of 4:1) to prepare a 1M perovskite precursor solution; 50 μL of the perovskite precursor solution is spin-coated onto the hole transport layer under spin-coating conditions of 1000 rpm for 10 s and 5000 rpm for 40 s, and 150 μL of chlorobenzene is added as an anti-solvent 7 s before the end of spin-coating; after spin-coating, the film is annealed at 100° C. for 20 min to obtain a perovskite polycrystalline film as a light absorption layer 3; (4) Forming electron transport layer 2: thermally evaporating 20 nm of C60 and 7 nm of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) on the perovskite polycrystalline film in sequence to form electron transport layer 2; (5) Forming cathode layer 1: 100 nm of Ag was evaporated on the electron transport layer to form cathode layer 1, thereby obtaining a perovskite photodetector.

[0024] Example 2 This embodiment adopts the same implementation method as that of embodiment 1, and the difference from embodiment 1 is that the structure formula of the perovskite polycrystalline film formed in this embodiment is FA 0.8 MA 0.15 Cs 0.05 PbI 1.5 Br 1.5 .

[0025] Example 3 This embodiment adopts the same implementation method as that of embodiment 1, and the difference from embodiment 1 is that the structure formula of the perovskite polycrystalline film formed in this embodiment is FA 0.8 MA 0.15 Cs 0.05 PbI 1.75 Br 1.25 .

[0026] Example 4 This embodiment adopts the same implementation method as that of embodiment 1, and the difference from embodiment 1 is that the structure formula of the perovskite polycrystalline film formed in this embodiment is FA 0.8 MA 0.15 Cs 0.05 PbI 2 Br.

[0027] Example 5 This embodiment adopts the same implementation method as that of embodiment 1, and the difference from embodiment 1 is that the structure formula of the perovskite polycrystalline film formed in this embodiment is FA 0.8 MA 0.15 Cs 0.05 PbI 2.5 Br 0.5 .

[0028] Example 6 This embodiment adopts the same implementation method as that of embodiment 1, and the difference from embodiment 1 is that the structure formula of the perovskite polycrystalline film formed in this embodiment is FA 0.8 MA 0.15 Cs 0.05 PbI 3 .

[0029] Test Example 1 The external quantum efficiency EQE of the photodetectors prepared in test examples 1-6 and the commercial silicon-based device FDS 100 in the blue-green light band was measured by the QE-R quantum efficiency measurement system of Shengyan Electronic Technology. The system was calibrated before the test. The results are as follows: Figure 2 As shown. Figure 2From the EQE curves, Examples 1-6 show a significantly higher light response than the commercial silicon-based device FDS 100 in the range of 490-510nm, especially Example 1, where the EQE peak is as high as 95.84% at 490nm. It can be seen that the perovskite polycrystalline film in Example 1 has superiority.

[0030] The EQE curves of the devices were differentiated, and the band gaps of the photodetectors obtained in Examples 1-6 were 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, as the I ratio increases, the band gap gradually decreases, among which the optimal band gap is 1.64 eV (x=2.25), and the corresponding EQE is the highest, indicating that under this condition, the material band gap and the blue-green light absorption characteristics are best matched; 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 cause lattice contraction to aggravate the ion migration problem, induce an increase in non-radiative recombination, and reduce the carrier collection efficiency, which ultimately leads to a decrease in EQE, indicating that the Br ratio needs to be controlled in a reasonable range to balance band gap optimization and defect suppression, and Example 1 is the optimal value after comprehensive consideration.

[0031] In order to make the comparison result more obvious, the EQE values ​​of the photodetectors prepared in Examples 1-6 near the blue-green window (490-510 nm) applicable to underwater optical communication were averaged to obtain the following: Figure 3 As shown. Combined Figure 3 Compared with the average EQE of the samples, when x=2.25, the average response efficiency of the blue-green light band reaches 95.59%, which is 10.69% higher than that of x=3 (efficiency is 84.90%), indicating that the I content is optimal in the range of x=2.0-2.5, which fully proves its suitability for high-sensitivity detection in underwater weak light environments.

[0032] Then by The responsivity R of the photodetector prepared in Example 1 and the commercial silicon-based device FDS 100 were calculated. The results are as follows: Figure 4 As shown. Figure 4 It can be seen that compared with the commercial silicon-based device FDS 100, the photodetector prepared in Example 1 has a responsivity of 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-green light band. This shows that the photodetector prepared in the present invention is more suitable for use as an underwater optical communication component than the same type of silicon-based photodetector.

[0033] Test Example 2 The photodetector prepared in Example 1 was tested on a probe station test system to obtain the photocurrent density at different light power densities, and the linear fitting result was as follows: Figure 5 The linear dynamic range is shown. Figure 5 It can be seen that the linear dynamic range of the photodetector prepared in Example 1 reaches 165.62 dB, and the responsivity under different light power densities is calculated, and it is found that the responsivity fluctuates within a reasonable range. It can be seen that the photodetector in Example 1 has similar responsivity under different light power densities, has good weak light response, and can operate in a wider light intensity range.

[0034] Test Example 3 The photoelectric detector prepared in Example 1 is used as an underwater optical communication component for underwater transmission: the structure of the entire underwater optical communication system is as follows: Figure 6 As shown, a glass water tank 8 is filled with a certain amount of water to simulate an underwater environment; the underwater transmission distance is determined, and a metal shell 9 with a glass window (carrying a photodetector 10) is fixed at a corresponding position according to the distance; the metal shell 9 with a glass window can be pushed to move in the water tank to adjust the distance between the photodetector 10 and the laser light source 7 to simulate an autonomous underwater vehicle; the 450nm laser light source 7 is used to align the photodetector 10 and emit a modulated laser; the signal generator 6 is used to modulate the laser light source 7 to send a signal; the oscilloscope 11 is directly connected to the photodetector 10 to obtain the received waveform information.

[0035] 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 setting 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, and reads it through the oscilloscope 11 for subsequent observation and processing.

[0036] When the underwater transmission distance is 1m, the signal transmission rate is changed by changing the setting of the signal generator 6, and the bit error rate under different transmission rates is measured. The results are as follows: Figure 7 As shown. Figure 7 It can be seen that when the rate is less than 1.625Mbps, the bit error rate BER is lower than 0.001, proving that the system has high communication quality at the test rate.

[0037] This test example constructs an integrated underwater optical communication verification system suitable for self-powered detectors (including a signal generator 6, a 450 nm laser light source 7, a movable photodetector 10, etc.). The distance between the photodetector 10 and the laser light source 7 can be adjusted, and each component can be replaced. The communication capability of the self-powered detector in different water qualities and different bands can be systematically verified. The system can directly simulate the communication scenario of an autonomous underwater vehicle and provide a test platform for device optimization and application.

[0038] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, 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, they should be considered to be within the scope of this specification.

[0039] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a perovskite polycrystalline thin film, characterized in that: It includes the following steps: PbI2 powder, PbBr2 powder, FAI powder, MAI powder and CsI powder are dissolved in a solvent to obtain a perovskite precursor solution; the perovskite precursor solution is spin-coated and annealed to obtain a perovskite polycrystalline film.

2. The method for preparing a perovskite polycrystalline thin film according to claim 1, characterized in that: The structural formula of the perovskite polycrystalline film is FA 0.8 MA 0.15 Cs 0.05 PbI x Br 3-x , where 1.5≤x≤3.

3. The method for preparing a perovskite polycrystalline thin film 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.

4. The method for preparing a perovskite polycrystalline thin film according to claim 1, characterized in that: The concentration of the perovskite precursor solution is 0.8-1.5M.

5. The method for preparing a perovskite polycrystalline thin film according to claim 1, characterized in that: The annealing is performed at 100-120° C. for 15-20 min.

6. A perovskite polycrystalline thin film, characterized in that: The invention is prepared by the preparation method described in any one of claims 1 to 5.

7. Application of the perovskite polycrystalline film as claimed in claim 6 in underwater optical communication.

8. A photoelectric detector, characterized in that: It comprises a cathode layer, an electron transport layer, a light absorption layer, a hole transport layer, and an anode layer which are arranged in sequence, and the light absorption layer adopts the perovskite polycrystalline film as claimed in claim 6.

9. A method for preparing a photoelectric detector, characterized in that: It includes the following steps: Providing a glass substrate, cleaning and drying it, and obtaining an anode layer; preparing a hole transport layer on the anode layer; A perovskite polycrystalline thin film is prepared on the hole transport layer by the preparation method according to any one of claims 1 to 5 to obtain a light absorption layer; preparing an electron transport layer on the light absorbing layer; Silver is deposited on the electron transport layer to form a cathode layer.

10. An underwater optical communication system, characterized in that: It includes: The photodetector according to claim 8; A laser light source, used for emitting laser light to the photodetector; a signal generator, which is used to modulate the laser light emitted by the laser light source; and An oscilloscope is connected to the photodetector signal.

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