Preparation method of organic halogen ammonium salt surface-modified lead sulfide colloidal quantum dots

Abstract

The present invention discloses a method for preparing organic halogen ammonium salt-surface-modified lead sulfide colloidal quantum dots. The method comprises the following steps: dissolving PbS CQDs in n-octane; dissolving the organic halogen ammonium salt in dimethyl sulfide (DMF) to obtain a ligand solution; adding the prepared ligand solution to the prepared PbS CQD n-octane solution; stirring to transfer the PbS CQDs from the n-octane phase to the DMF solution phase; and, after phase separation, separating the PbS CQDs from the DMF solution phase and drying to obtain organic halogen ammonium salt-coordinated PbS CQD powder. The present invention utilizes mixed organic halogen ammonium salts to replace mixed metal halides for quantum dot surface modification, thereby reducing the use of lead compounds. While ensuring surface passivation of the quantum dots, the method provides a green, safe, and environmentally friendly method for quantum dot surface modification.

Description

Technical Field

[0001] The invention relates to the field of quantum dot materials, and in particular to a method for preparing organic halogen ammonium salt surface-modified lead sulfide colloidal quantum dots. Background Art

[0002] Quantum dots are a type of zero-dimensional material that has size-dependent bandgap tunability due to the quantum confinement effect. They can be synthesized by solution method and are compatible with CMOS. They have broad application prospects in solar cells, photodetectors and other fields.

[0003] The surface of quantum dots synthesized by the solution method is wrapped by insulating long-chain organic ligands, which limits the transmission of electrons between quantum dots and is not suitable for devices. Therefore, the quantum dots need to be surface modified. The ligand exchange method is usually used to replace the old ligands with new ligands to modify the surface of quantum dots. As the size of lead sulfide quantum dots increases, the quantum dots change from regular octahedrons to regular tetrahedrons, and the non-polar (100) faces increase, which increases the difficulty of surface modification. In current research, metal halides such as lead iodide and lead bromide are mostly used to modify the surface of quantum dots. However, surface modification of lead sulfide quantum dots in this way usually involves the generation of a large amount of waste liquid containing lead metal halides, which will cause serious harm if not properly handled.

[0004] Based on the above problems, there is an urgent need to find a green and safe method that can effectively passivate lead sulfide quantum dots. Summary of the Invention

[0005] In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a method for lead-free surface modification of lead sulfide quantum dots, which can be used for infrared detection.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] The first aspect of the present invention provides a method for preparing organic halogen ammonium salt surface-modified lead sulfide colloidal quantum dots, comprising the following steps:

[0008] (1) PbS CQDs were dissolved in n-octane; an organic halogen ammonium salt was dissolved in DMF to obtain a ligand solution;

[0009] (2) adding the prepared ligand solution to the prepared PbS CQDs n-octane solution; stirring to transfer the PbS CQDs from the n-octane phase to the DMF solution phase; after phase separation, washing the DMF solution phase with the n-octane solution, separating the PbS CQDs from the DMF solution phase and drying to obtain organic halogen ammonium salt coordinated PbS CQDs powder;

[0010] The organic halogen ammonium salt is at least one of methylamine hydroiodide (MAI), ethylamine hydroiodide (EAI), butylamine hydroiodide (BAI), formamidine hydroiodide (FAI), 2-phenylethylamine hydroiodide (PEAI), methylamine hydrobromide (MABr), ethylamine hydrobromide (EABr), butylamine hydrobromide (BABr), formamidine hydrobromide (FABr), and 2-phenylethylamine hydrobromide (PEABr).

[0011] The present invention is not limited to the specific source of lead sulfide quantum dots (PbS CQDs), which can be commercially available or homemade using existing technology.

[0012] Preferably, the organic halogen ammonium salt is at least one of 2-phenylethylamine hydroiodide (PEAI) and 2-phenylethylamine hydrobromide (PEABr); further preferably, the organic halogen ammonium salt is 2-phenylethylamine hydroiodide (PEAI) and 2-phenylethylamine hydrobromide (PEABr).

[0013] Preferably, the concentration of the ligand solution is 300-400 mg / ml.

[0014] Preferably, in step (2), the concentration of the prepared PbS CQDs n-octane solution is 90-120 mg / ml.

[0015] Preferably, in step (2), the volume ratio of the ligand solution to the prepared PbS CQDs n-octane solution is 1:(2.5-3.5).

[0016] Preferably, in step (2), the stirring is magnetic stirring, and the stirring time is 5-10 minutes.

[0017] The second aspect of the present invention provides organic halogen ammonium salt surface-modified lead sulfide colloidal quantum dots, which are prepared by the preparation method of organic halogen ammonium salt surface-modified lead sulfide colloidal quantum dots.

[0018] A third aspect of the present invention provides a method for preparing a lead sulfide quantum dot film surface-modified with a mixed organic halogen ammonium salt, comprising the following steps:

[0019] (1) mixing and dissolving lead iodide, DMF, and DFP to obtain a mixed solution;

[0020] (2) dispersing the organic halogen ammonium salt surface-modified lead sulfide colloidal quantum dots in the mixed solution of step (1) to prepare a mixed ink;

[0021] (3) The mixed ink is spin-coated into a film by a uniform coating method; and the residual solvent is removed by annealing to obtain the mixed organic halogen ammonium salt surface-modified lead sulfide quantum dot film.

[0022] Preferably, the concentration of the lead iodide in the mixed solution is 50-70 mg / ml.

[0023] Preferably, the volume ratio of DMF to DFP is (3-5):1.

[0024] Preferably, the concentration of the organic halogen ammonium salt surface-modified lead sulfide colloidal quantum dots in the mixed ink is 250-350 mg / ml.

[0025] Preferably, the rotation speed of the spin coating method is 2000-3000 rpm, and the spin coating time is 20-40s.

[0026] Preferably, the annealing temperature is 90-110° C., and the annealing time is 8-12 minutes.

[0027] A fourth aspect of the present invention provides a mixed organic halogen ammonium salt surface-modified lead sulfide quantum dot film, which is prepared by the preparation method of the mixed organic halogen ammonium salt surface-modified lead sulfide quantum dot film.

[0028] A fifth aspect of the present invention provides a method for preparing a mixed organic halogen ammonium salt surface-modified lead sulfide quantum dot photodiode, comprising the following steps:

[0029] (1) mixing and dissolving lead iodide, DMF, and DFP to obtain a mixed solution;

[0030] (2) dispersing the organic halogen ammonium salt surface-modified lead sulfide colloidal quantum dots in the mixed solution of step (1) to prepare a mixed ink;

[0031] (3) Preparing a zinc oxide layer on the cleaned FTO glass by magnetron sputtering;

[0032] (4) spin coating the mixed ink on the zinc oxide layer to obtain a PbS CQDs thin film;

[0033] (5) preparing another lead sulfide quantum dot n-octane solution having a concentration of 35-45 mg / ml of lead sulfide quantum dots; spin-coating the lead sulfide quantum dot n-octane solution on the film obtained in step (4) to obtain a lead sulfide quantum dot film, which is then modified using an EDT-ethyl acetate solution; repeating the spin-coating lead sulfide quantum dot n-octane solution and the EDT-ethyl acetate solution modification steps to obtain a hole extraction layer;

[0034] (6) A gold electrode is evaporated on the hole extraction layer.

[0035] Preferably, in step (3), the FTO glass cleaning step is: scrubbing the FTO with detergent, and then cleaning the FTO in deionized water, acetone, and ethanol using an ultrasonic bath in sequence.

[0036] Preferably, in step (3), the parameters of the magnetron sputtering zinc oxide film are: at room temperature, the sputtering power is 90-110 W, the sputtering time is 15-25 min, and the sputtering gas is oxygen and / or argon.

[0037] Preferably, the EDT-ethyl acetate solution modification treatment includes the following steps: dripping the EDT-ethyl acetate solution onto the lead sulfide quantum dot film, immersing it for 20-40 seconds, spinning it dry, and washing the film with ethyl acetate; the EDT-ethyl acetate solution is an ethyl acetate solution with an EDT concentration of 0.015-0.025wt%.

[0038] A sixth aspect of the present invention provides a photodiode, which is prepared by the preparation method of the mixed organic halogen ammonium salt surface-modified lead sulfide quantum dot photodiode.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] This invention provides a method for preparing lead sulfide quantum dots surface-modified with mixed organic halogen ammonium salts. By replacing mixed metal halides with mixed organic halogen ammonium salts for quantum dot surface modification, the use of lead compounds is reduced. While ensuring surface passivation of the quantum dots, this method provides a green, safe, and environmentally friendly quantum dot surface modification method.

[0041] Compared to metal halide surface-modified lead sulfide colloidal quantum dots, organohalogen ammonium salt-modified lead sulfide quantum dots significantly reduce the use of lead-containing compounds while maintaining passivation effectiveness. Lead sulfide quantum dot films surface-modified with mixed organohalogen ammonium salt ligands exhibit excellent responsiveness to near-infrared light. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 Absorption spectra of lead sulfide quantum dots surface-modified with different organic halogen ammonium salts obtained in Example 1 and Comparative Examples 1-4;

[0043] Figure 2 The absorption spectra of the lead sulfide quantum dots surface-modified with organic halogen ammonium salts obtained in Example 2 and Example 1 are shown;

[0044] Figure 3 This is a scanning electron micrograph of a film of large-sized lead sulfide quantum dots surface-modified with mixed organic halogen ammonium salts prepared in Example 4;

[0045] Figure 4 This is the current-voltage curve of the film of large-sized lead sulfide quantum dots surface-modified with mixed organic halogen ammonium salt prepared in Example 4. DETAILED DESCRIPTION

[0046] The following is a further description of specific embodiments of the present invention. It should be noted that the description of these embodiments is intended to facilitate understanding of the present invention and does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0047] The experimental methods in the following examples are conventional methods unless otherwise specified, and the experimental materials used in the following examples are commercially available unless otherwise specified.

[0048] Example 1

[0049] This embodiment provides a method for preparing lead sulfide quantum dots surface-modified with an organic halogen ammonium salt, comprising the following steps:

[0050] (1) PbS quantum dots with a first exciton absorption peak at 980 nm were synthesized and dispersed in n-octane at a concentration of 100 mg / ml.

[0051] The synthesis method for lead sulfide quantum dots is as follows: using an anhydrous and oxygen-free Schreck apparatus. Synthesis is performed by hot injection. In a 250ml round-bottomed flask equipped with a magnet, 1.35g of lead oxide, 6ml of oleic acid, and 30ml of octadecene are added. A vacuum pump and an argon bottle are connected. The solution is evacuated for 3 minutes, then purged with argon for 3 minutes, repeated three times. Finally, the solution is heated to 120°C under vacuum and held for 1 hour. 600μl of hexamethyldisilathioane is dissolved in 5ml of octadecene to prepare the S solution, which is then stirred to dissolve evenly. The temperature of the solution in the round-bottomed flask is lowered to 100°C, and the S solution is rapidly injected. The reaction is allowed to proceed for 5 minutes, yielding lead sulfide quantum dots with a first exciton absorption peak at 980nm.

[0052] (2) Prepare an organic halogen ammonium salt ligand solution.

[0053] Specifically, 300 mg of 2-phenylethylamine hydroiodide (PEAI) was dissolved in 1 ml of N,N-dimethylformamide (DMF).

[0054] (3) Injecting the organic halogen salt ligand DMF solution prepared in step (2) into the lead sulfide quantum dot n-octane solution in step (1) at a volume ratio of 1:3.

[0055] (4) The mixed solution in step (3) was shaken for 5 minutes and allowed to stand to allow the mixed solution to separate.

[0056] (5) The mixed solution was washed three times with n-octane, and the supernatant was discarded to obtain a lead sulfide quantum dot solution.

[0057] (6) adding a mixed solution of ethyl acetate and ethanol to the lead sulfide quantum dot solution in step (5), centrifuging at a speed of 5000 rpm for 5 minutes to obtain lead sulfide quantum dot sedimentation and vacuum drying.

[0058] Comparative Example 1

[0059] 300 mg of methylamine hydroiodide (MAI) was used instead of 300 mg of 2-phenylethylamine hydroiodide in Example 1, and the remaining technical means were consistent with Example 1 to obtain methylamine hydroiodide-coordinated lead sulfide quantum dots.

[0060] Comparative Example 2

[0061] 300 mg of ethylamine hydroiodide (EAI) was used instead of 300 mg of 2-phenylethylamine hydroiodide in Example 1, and the remaining technical means were consistent with Example 1 to obtain lead sulfide quantum dots coordinated by ethylamine hydroiodide.

[0062] Comparative Example 3

[0063] 300 mg of butylamine hydroiodide (BAI) was used instead of 300 mg of 2-phenylethylamine hydroiodide in Example 1, and the remaining technical means were consistent with Example 1 to obtain butylamine hydroiodide-coordinated lead sulfide quantum dots.

[0064] Comparative Example 4

[0065] 300 mg of formamidine hydroiodide (FAI) was used instead of 300 mg of 2-phenylethylamine hydroiodide in Example 1, and the remaining technical means were consistent with Example 1 to obtain formamidine hydroiodide coordinated lead sulfide quantum dots.

[0066] Characterization of the first exciton absorption peak of the lead sulfide quantum dots surface modified with organic halogen ammonium salt obtained in Example 1 and Comparative Examples 1-4. Figure 1 .

[0067] Depend on Figure 1 It can be seen that the lead sulfide quantum dots modified with 2-phenylethylamine hydroiodide exhibit a narrower absorption peak, indicating that compared with other organic halogen salt ligands, 2-phenylethylamine hydroiodide exhibits a better effect of passivating the surface of quantum dots, such as Figure 1 MAI, EAI, BAI, FAI, and PEAI are methylamine hydroiodide, ethylamine hydroiodide, butylamine hydroiodide, formamidine hydroiodide, and 2-phenylethylamine hydroiodide, respectively.

[0068] Example 2

[0069] 300 mg of 2-phenylethylamine hydroiodide and 50 mg of 2-phenylethylamine hydrobromide were used instead of 300 mg of 2-phenylethylamine hydroiodide in Example 1. The remaining technical means were consistent with those in Example 1 to obtain lead sulfide quantum dots coordinated by mixed organic halogen salts.

[0070] Comparative Example 5

[0071] 300 mg of methylamine hydroiodide and 50 mg of methylamine hydrobromide were used instead of 300 mg of 2-phenylethylamine hydroiodide in Example 1. The remaining technical means were the same as those in Example 1 to obtain lead sulfide quantum dots coordinated by mixed organic halogen salts.

[0072] Comparative Example 6

[0073] 300 mg of ethylamine hydroiodide and 50 mg of ethylamine hydrobromide were used instead of 300 mg of 2-phenylethylamine hydroiodide in Example 1. The remaining technical means were the same as those in Example 1 to obtain lead sulfide quantum dots coordinated by mixed organic halogen salts.

[0074] Comparative Example 7

[0075] 300 mg of butylamine hydroiodide and 50 mg of butylamine hydrobromide were used instead of 300 mg of 2-phenylethylamine hydroiodide in Example 1. The remaining technical means were the same as those in Example 1 to obtain lead sulfide quantum dots coordinated by mixed organic halogen salts.

[0076] Comparative Example 8

[0077] 300 mg of formamidine hydroiodide and 50 mg of formamidine hydrobromide were used instead of 300 mg of 2-phenylethylamine hydroiodide in Example 1. The remaining technical means were the same as those in Example 1 to obtain lead sulfide quantum dots coordinated by mixed organic halogen salts.

[0078] During the implementation process, the mixed organic halogen ammonium salt coordinated lead sulfide colloidal quantum dots obtained in Comparative Examples 5, 7, and 8 have poor dispersibility in DMF, butylamine, and 2,6-difluoropyridine (DFP), which limits their further spin coating and application in diode devices.

[0079] Characterization of the first exciton absorption peak of the lead sulfide quantum dots surface modified with organic halogen ammonium salt obtained in Example 1 and Example 2. The characterization results are shown in Figure 2 .

[0080] Depend on Figure 2 It can be seen that the lead sulfide quantum dots after surface modification with mixed organic halogen ammonium salts exhibit a narrower absorption peak, indicating that compared with organic iodine salts, the addition of organic bromide salts can further improve the effect of organic halogen salt surface modification of lead sulfide quantum dots.

[0081] Example 3

[0082] This embodiment provides a method for preparing lead sulfide quantum dots surface-modified with a mixed organic halogen salt, comprising the following steps:

[0083] (1) PbS quantum dots with a first exciton absorption peak at 1640 nm were synthesized and dispersed in an n-octane solution at a concentration of 100 mg / ml.

[0084] The synthesis method of lead sulfide quantum dots is as follows: Lead sulfide quantum dots are synthesized by continuous hot injection using an anhydrous and oxygen-free Schreck apparatus. 1.35g of lead oxide, 11.5ml of oleic acid, and 150ml of octadecene are added to a 250ml round-bottomed flask equipped with a magnet. A vacuum pump and an argon bottle are connected. The solution is evacuated for 3 minutes and then purged with argon for 3 minutes, repeated three times. Finally, the solution is heated to 110°C under vacuum and kept warm for 1 hour. Solution S1 is prepared by dissolving 210μl of hexamethyldisilathioane in 6ml of octadecene. Solution S2 is prepared by dissolving 600μl of hexamethyldisilathioane in 10ml of octadecene. Solution S1 is rapidly injected into the flask. After a 7-minute reaction, solution S2 is injected into the flask at a rate of 0.5ml per minute. After 13 injections, the flask is immersed in an ice-water bath to quench growth, thereby obtaining a large-sized lead sulfide quantum dot solution. Purification of lead sulfide quantum dots: The obtained lead sulfide quantum dot solution was added to a mixed solvent of ethyl acetate and acetonitrile, and the mixture was centrifuged at 6000 rpm for 5 minutes. After removing the supernatant, the centrifugation was repeated three times to obtain a lead sulfide quantum dot precipitate, which was then vacuum dried for 12 hours to obtain a dry lead sulfide quantum dot powder.

[0085] (2) Prepare a mixed organic halide ammonium salt ligand solution.

[0086] 300 mg of 2-phenylethylamine hydroiodide and 50 mg of 2-phenylethylamine hydrobromide were dissolved in 1 ml of N,N-dimethylformamide (DMF).

[0087] (3) The mixed organic halogen ammonium salt ligand DMF solution prepared in step (2) is injected into the lead sulfide quantum dot n-octane solution in step S11 at a volume ratio of 1:3.

[0088] (4) The mixed solution in step (3) was stirred for 12 hours to allow the mixed solution to phase separate.

[0089] (5) The mixed solution was washed three times with n-octane, and the supernatant was discarded to obtain a lead sulfide quantum dot solution.

[0090] (6) Adding a mixed solution of ethyl acetate and ethanol to the lead sulfide quantum dot solution in step (5), centrifuging at a speed of 5000 rpm for five minutes to obtain lead sulfide quantum dot sedimentation and vacuum drying.

[0091] Example 4

[0092] This embodiment provides a method for preparing a large-sized lead sulfide quantum dot film surface-modified by a mixed organic halogen ammonium salt, comprising the following steps:

[0093] (1) Prepare lead sulfide quantum dots surface-modified with mixed organic halogen ammonium salts according to Example 3.

[0094] (2) dissolving lead iodide in DMF and DFP solvents in a volume ratio of 4:1 to obtain a mixed solvent; specifically, the concentration of lead iodide is 60 mg / ml.

[0095] (3) dispersing the lead sulfide quantum dots surface-modified with the mixed organic halogen ammonium salt prepared in step (1) in the mixed solvent prepared in step (2) to prepare a lead sulfide quantum dot mixed ink; specifically, the concentration of the lead sulfide quantum dots in the mixed ink is 300 mg / ml.

[0096] (4) The lead sulfide quantum dot mixed ink in step (3) is spin-coated into a film by a uniform coating method; specifically, the spin coating parameters are: spin coating at a speed of 2500 rpm for 30 seconds.

[0097] (5) Annealing the film in step (4) to remove residual solvent; specifically, the annealing parameters are: annealing at 100° C. for 10 minutes.

[0098] Figure 3 This is a scanning electron microscope image of the lead sulfide quantum dot film modified with mixed organic halogen ammonium salt obtained in this example. The film is dense and relatively smooth as a whole, with almost no deep pinholes.

[0099] Figure 4 This is the current-voltage curve of the mixed organic halogen ammonium salt-modified lead sulfide quantum dot film obtained in this example. The gold electrode and the lead sulfide quantum dot film show good ohmic contact, and the quantum dot film has response and characteristics to 940nm near-infrared light.

[0100] Example 5

[0101] This embodiment provides a method for preparing a photodiode of lead sulfide quantum dots surface-modified with a mixed organic halogen ammonium salt, comprising the following steps:

[0102] (1) Cleaning the FTO glass sheet. Specifically, the cleaning steps are as follows: scrubbing the FTO with detergent, and then cleaning the FTO in deionized water, acetone, and ethanol using an ultrasonic bath.

[0103] (2) A zinc oxide thin film was deposited on the cleaned glass sheet by magnetron sputtering. Specifically, the sputtering process was as follows: at room temperature, the sputtering power was 100 W, the sputtering time was 20 min, and the sputtering gas was a mixture of oxygen and argon with a gas ratio of argon to oxygen = 1:99.

[0104] (3) A lead sulfide quantum dot film was spin-coated on the zinc oxide film according to Example 4.

[0105] (4) preparing lead sulfide quantum dots having a first exciton absorption peak at 950 nm by a hot injection method, and configuring the lead sulfide quantum dot n-octane solution with a concentration of 40 mg / ml; spin-coating the lead sulfide quantum dot n-octane solution on the film obtained in step (3) to obtain a lead sulfide quantum dot film, which is then modified using an EDT-ethyl acetate solution; repeating the spin-coating lead sulfide quantum dot n-octane solution and EDT-ethyl acetate solution modification steps to obtain a hole extraction layer. The EDT-ethyl acetate solution modification treatment includes the following steps: dripping the EDT-ethyl acetate solution onto the lead sulfide quantum dot film, immersing it for 30 seconds, spinning it dry, and washing the film three times with ethyl acetate; the EDT-ethyl acetate solution is an ethyl acetate solution with an EDT concentration of 0.02 wt%.

[0106] (5) A 100 nm thick patterned gold electrode was thermally evaporated on the film.

[0107] The embodiments of the present invention are described in detail above, but the present invention is not limited to the described embodiments. It is apparent to those skilled in the art that various changes, modifications, substitutions, and variations of these embodiments may be made without departing from the principles and spirit of the present invention, and the changes still fall within the scope of protection of the present invention.

Claims

1. A method for preparing organic halogen ammonium salt surface-modified lead sulfide colloidal quantum dots, characterized in that: The following steps are involved: (1) Dissolving lead sulfide quantum dots (PbS CQDs) in n-octane; dissolving an organic halogen ammonium salt in DMF to obtain a ligand solution; (2) adding the prepared ligand solution to the prepared PbS CQDs n-octane solution; stirring to transfer the PbS CQDs from the n-octane phase to the DMF solution phase; after phase separation, washing the DMF solution phase with the n-octane solution, separating the PbS CQDs from the DMF solution phase and drying to obtain organic halogen ammonium salt coordinated PbS CQDs powder; The organic halogen ammonium salt is a mixture of 2-phenylethylamine hydroiodide and 2-phenylethylamine hydrobromide.

2. The method for preparing organic halogen ammonium salt surface-modified lead sulfide colloidal quantum dots according to claim 1, wherein: The concentration of the ligand solution is 300-400 mg / ml.

3. An organic halogen ammonium salt surface-modified lead sulfide colloidal quantum dots, characterized in that: The lead sulfide colloidal quantum dots are prepared by the preparation method of organic halogen ammonium salt surface-modified lead sulfide colloidal quantum dots according to claim 1 or 2.

4. A method for preparing a lead sulfide quantum dot film surface-modified with a mixed organic halogen ammonium salt, characterized in that: The following steps are involved: (1) Mixing and dissolving lead iodide, DMF, and 2,6-difluoropyridine (DFP) to obtain a mixed solution; (2) dispersing the organic halogen ammonium salt surface-modified lead sulfide colloidal quantum dots described in claim 3 in the mixed solution of step (1) to prepare a mixed ink; (3) Spin coating the mixed ink into a film by a coating method; annealing to remove the residual solvent to obtain the mixed organic halogen ammonium salt surface-modified lead sulfide quantum dot film.

5. The method for preparing a surface-modified lead sulfide quantum dot thin film of mixed organic halogen ammonium salt according to claim 4, wherein: The concentration of the lead iodide in the mixed solution is 50-70 mg / ml.

6. The method for preparing a mixed organic halogen ammonium salt surface-modified lead sulfide quantum dot film according to claim 4, wherein: The concentration of the organic halogen ammonium salt surface-modified lead sulfide colloidal quantum dots in the mixed ink is 250-350 mg / ml.

7. A mixed organic halogen ammonium salt surface-modified lead sulfide quantum dot film, characterized in that: The lead sulfide quantum dot film is prepared by the preparation method of the mixed organic halogen ammonium salt surface modified lead sulfide quantum dot film according to any one of claims 4 to 6.

8. A method for preparing a lead sulfide quantum dot photodiode surface-modified with a mixed organic halogen ammonium salt, characterized in that: The following steps are involved: (1) Mixing and dissolving lead iodide, DMF, and 2,6-difluoropyridine (DFP) to obtain a mixed solution; (2) dispersing the organic halogen ammonium salt surface-modified lead sulfide colloidal quantum dots described in claim 3 in the mixed solution of step (1) to prepare a mixed ink; (3) Preparing a zinc oxide layer on the cleaned FTO glass by magnetron sputtering; (4) spin coating the mixed ink on the zinc oxide layer to obtain a PbS CQDs thin film; (5) Prepare another lead sulfide quantum dot n-octane solution with a concentration of 35-45 mg / ml; spin-coat the lead sulfide quantum dot n-octane solution on the film obtained in step (4) to obtain a lead sulfide quantum dot film, and then modify it with an EDT-ethyl acetate solution; repeat the spin-coating lead sulfide quantum dot n-octane solution and EDT-ethyl acetate solution modification steps to obtain a hole extraction layer; (6) Vapor-depositing a gold electrode on the hole extraction layer.

9. The method for preparing a mixed organic halogen ammonium salt surface-modified lead sulfide quantum dot photodiode according to claim 8, wherein: The EDT-ethyl acetate solution modification treatment includes the following steps: dropping the EDT-ethyl acetate solution onto the lead sulfide quantum dot film, immersing it for 20-40 seconds, spinning it dry, and washing the film with ethyl acetate; the EDT-ethyl acetate solution is an ethyl acetate solution with an EDT concentration of 0.015-0.025 wt%.

10. A photodiode, characterized in that: The photodiode is prepared by the preparation method of the mixed organic halogen ammonium salt surface-modified lead sulfide quantum dot photodiode according to claim 8 or 9.

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