Preparation method of high-quality ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystal with adjustable band gap

Abstract

The invention relates to the technical field of semiconductor materials, and discloses a preparation method of band-gap-adjustable high-quality ZnInGa / CuInS / ZnS / ZnS colloidal quantum well nanocrystals, which comprises the following steps: synthesizing ZIGS quantum dots, mixing a zinc precursor, an indium precursor, a gallium precursor, a sulfur precursor, organic acid, organic amine and 1-octadecene, degassing, and heating to synthesize ZIGS nanocrystals; mixing the ZIGS nanocrystal, organic amine and 1-octadecene, degassing, heating, and injecting a copper, indium and sulfur precursor solution to obtain a ZIGS / CIS nanocrystal; mixing the ZIGS / CIS nanocrystal, organic amine and 1-octadecene, degassing, heating, adding a zinc oleate aqueous solution and the sulfur precursor solution a, reacting, and purifying to obtain the ZIGS / CIS / ZnS colloidal quantum well nanocrystal. And repeating the preparation steps of the ZIGS / CIS / ZnS colloidal quantum well nanocrystal to obtain the ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystal. According to the cadmium-free ZnInGa / CuInS / ZnS / ZnS colloidal quantum well nanocrystal prepared by the method, the optimal quantum yield is greater than 99%, and the luminescence peak position is tunable in the range of 533-742 nm.

Description

Technical Field

[0001] The present invention belongs to the technical field of luminescent semiconductor synthesis, and specifically relates to a method for preparing high-quality ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystals with adjustable band gaps. Background Art

[0002] Traditional semiconductor materials face significant challenges in near-infrared (NIR) optoelectronic devices, mainly due to their inherent physical defects and lack of effective carrier confinement, which often lead to non-radiative recombination. Classical quantum dot structures, such as CdSe / ZnS core-shell quantum dots, attempt to improve optical properties by growing wide-bandgap shells. However, these systems still face problems such as lattice mismatch, interface defects, and uneven shell growth. For example, the accumulation of lattice strain between the core and shell causes shell cracking or core-shell separation, thereby weakening carrier confinement. In addition, the passivation efficiency of surface ligands in traditional core-shell quantum dots is limited, making it difficult to completely suppress surface defects. These problems are particularly prominent under long-term irradiation or high temperatures, and photooxidation significantly reduces stability. Lead sulfides (such as PbS, PbSe) have become promising materials for infrared detectors and solar cells due to their broad absorption spectra and high carrier mobilities. However, the toxicity of lead limits the commercial application of these materials under global environmental regulations. In addition, lead-based materials are prone to forming surface dangling bonds and deep trap states during synthesis, which exacerbates non-radiative recombination, thereby reducing the efficiency and lifespan of devices. These challenges highlight the urgent need to develop efficient and environmentally friendly alternative materials.

[0003] Colloidal quantum well (CQW) structures, as a promising solution, exhibit excellent optical and device performance. Current research on CQWs mainly focuses on cadmium-based materials (such as CdS / CdSe / CdS or CdS / CdSe / CdS / ZnS), which have become a research hotspot due to their excellent quantum confinement effect and tunable optical properties. However, the high toxicity of cadmium and strict environmental regulations severely limit its commercial prospects. Copper indium sulfide (CIS) quantum dots, as a cadmium-free alternative material, are attracting attention due to their narrow bandgap (1.5 - 2.1 eV), NIR emission ability, and low toxicity. However, traditional CIS core-shell structures (such as CIS / ZnS) face multiple challenges: (1) The lattice mismatch between CIS and ZnS forms dense interfacial defects, leading to significant non-radiative recombination; (2) Copper vacancies and sulfur dangling bonds on the surface of CIS form deep trap states, hindering the further improvement of photoluminescence quantum yield (PLQY); (3) The cation exchange process between the core and shell is complex, resulting in poor synthesis reproducibility and stability. Although alloying (such as Cu-In-Zn-S) or graded shell design can solve some problems, these strategies usually involve complex synthesis processes and lack good structural controllability, limiting their application in high-performance devices.

[0004] Therefore, a novel ZIGS / CIS / ZnS / ZnS colloidal quantum well (CQW) structure is needed to solve the above problems and simultaneously achieve the preparation of efficient, environmentally friendly, stable, and tunable NIR optoelectronic device materials. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing high-quality ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystals with tunable bandgaps in view of the above-mentioned deficiencies of the prior art. The present invention provides a cadmium-free, high-PLQY, structurally stable, and bandgap-tunable colloidal quantum well material, which solves the problems of interfacial defects, lattice strain, and toxicity through precise bandgap engineering and synthesis strategies, and realizes the commercial application of high-performance NIR optoelectronic devices.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is: A method for preparing high-quality ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystals with tunable bandgaps, the preparation method comprising the following steps:

[0007] S1. Synthesis of ZIGS quantum dots

[0008] Preliminary preparation of precursors: After mixing a zinc precursor, an indium precursor, a gallium precursor, a sulfur precursor, an organic acid, an organic amine, and 1-octadecene, degassing treatment is performed to obtain precursors;

[0009] Generation of ZIGS nanocrystals: Heat and hold the precursor under nitrogen protection, then raise the temperature for reaction and keep warm. After the reaction ends, naturally cool the obtained reaction solution to room temperature;

[0010] Purification of ZIGS nanocrystals: Add an anti-solvent to the cooled reaction solution to precipitate the primary product of ZIGS nanocrystals, and then purify by centrifugation to obtain ZIGS nanocrystals with a transition shell layer;

[0011] Synthesis of S2, ZIGS / CIS quantum dots

[0012] Shell preparation: Mix the ZIGS nanocrystals with a transition shell layer obtained in S1 with an organic amine and 1-octadecene, and then perform degassing treatment to obtain reaction solution a;

[0013] Growth of CIS shell: Heat the reaction solution a, and then inject a copper precursor solution, an indium precursor solution, and a sulfur precursor solution to obtain reaction solution b;

[0014] Purification of ZIGS / CIS nanocrystals: Add an anti-solvent a to the reaction solution b to precipitate the primary product of ZIGS / CIS nanocrystals, and then purify by centrifugation to obtain ZIGS / CIS nanocrystals with a transition shell layer;

[0015] S3, Synthesis of ZIGS / CIS / ZnS colloidal quantum well nanocrystals

[0016] ZnS shell preparation: Mix the ZIGS / CIS nanocrystals with a transition shell layer obtained in S2 with an organic amine and 1-octadecene, and then perform degassing treatment to obtain reaction solution c;

[0017] ZnS shell growth: Heat the reaction solution c, and add an aqueous solution of zinc oleate and a sulfur precursor solution a for epitaxial growth of the ZnS shell to obtain reaction solution d;

[0018] Purification of ZIGS / CIS / ZnS colloidal quantum well nanocrystals: After the reaction solution d is cooled to room temperature, add an anti-solvent b to the cooled reaction solution d to precipitate the primary product of ZIGS / CIS / ZnS colloidal quantum well nanocrystals, and repeatedly wash the ZIGS / CIS / ZnS colloidal quantum well nanocrystals primary product to obtain purified ZIGS / CIS / ZnS colloidal quantum well nanocrystals;

[0019] S4, Synthesis of ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystals

[0020] ZnS shell preparation: The purified ZIGS / CIS / ZnS colloidal quantum well nanocrystals obtained in S3 are mixed with an organic amine and 1-octadecene, and then degassed to obtain a reaction solution e.

[0021] ZnS shell growth: The reaction solution e is heated, and an aqueous solution of zinc oleate and a sulfur precursor solution b are added for epitaxial growth of the ZnS shell to obtain a reaction solution f.

[0022] Purification of ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystals: After the reaction solution f is cooled to room temperature, an anti-solvent c is added to precipitate a primary product of ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystals. The primary product of ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystals is washed repeatedly to obtain purified ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystals.

[0023] Preferably, the zinc precursor in S1 is one or more of diethylzinc, zinc acetate, zinc oleate, and zinc halide; the indium precursor is indium acetate, indium chloride, or indium acetylacetonate; the gallium precursor is gallium acetylacetonate or gallium chloride; the sulfur precursor is sulfur powder; the organic acid is octadecenoic acid; the organic amine is a linear primary amine, and the linear primary amine is octadecylamine or oleylamine; the molar volume ratio of the zinc precursor, indium precursor, gallium precursor, sulfur precursor, organic acid, organic amine, and 1-octadecene is 0.2 mmol: 0.2 mmol: 0.2 mmol: 0.8 mmol: 1 mL: 5 mL: 5 mL; the precursor is heated to 120 °C under nitrogen protection and held for 60 min, then the temperature is raised to 200 °C for reaction and kept warm for 60 min; the anti-solvent is ethanol, and the volume ratio of the reaction solution to the anti-solvent is 1:4.

[0024] Preferably, the molar volume ratio of the ZIGS nanocrystals with a transition shell layer, organic amine, and 1-octadecene in S2 is 0.05 mmol: 5 mL: 5 mL; the organic amine is a linear primary amine, and the linear primary amine is octadecylamine or oleylamine; the copper precursor solution is one or more of an aqueous copper chloride solution, an aqueous copper acetate solution, and an aqueous copper acetylacetonate solution, the indium precursor solution is one or more of an aqueous indium acetate solution and an aqueous indium chloride solution, and the sulfur precursor solution is one or more of an aqueous sulfur powder solution and dodecyl mercaptan; the copper precursor solution, the indium precursor solution, and the sulfur precursor solution form a total precursor solution, the volume ratio of the reaction solution a to the total precursor solution is 10:3, the concentration of the copper precursor solution is 0.1 mmol / mL, the concentration of the indium precursor solution is 0.1 mmol / mL, the concentration of the sulfur precursor solution is 0.2 mmol / mL, the antisolvent a is ethanol, and the volume ratio of the reaction solution b to the antisolvent a is 1:5.

[0025] Preferably, in S2, the reaction solution a is heated to 180 °C, and the copper precursor solution, indium precursor solution, and sulfur precursor solution are respectively injected at a rate of 2.0 mL / h through an injection pump, and the volume ratio of the copper precursor solution, indium precursor solution, and sulfur precursor solution in the total precursor solution is 1:1:1.

[0026] Preferably, the molar volume ratio of the ZIGS / CIS nanocrystals with a transition shell layer, organic amine, and 1-octadecene in S3 is 0.1 mmol: 5 mL: 5 mL; the organic amine is a linear primary amine, and the linear primary amine is octadecylamine or oleylamine; the sulfur precursor solution a first uses the sulfur precursor solution of octadecene and then uses dodecyl mercaptan; the volume ratio of the reaction solution c, zinc oleate aqueous solution, sulfur precursor solution of octadecene, and dodecyl mercaptan is 10:10:5:2.

[0027] Preferably, in S3, the reaction solution c is heated to 230 °C, and the zinc oleate aqueous solution and the sulfur precursor solution a are respectively injected at a rate of 5.0 mL / h through an injection pump, and the concentration of the zinc oleate aqueous solution is 0.1 mmol / mL.

[0028] Preferably, the antisolvent b in S3 is acetone or ethanol, the volume ratio of the reaction solution d to the antisolvent b is 1:4, and the ZIGS / CIS / ZnS colloidal quantum well nanocrystal primary product is repeatedly washed with ethanol.

[0029] Preferably, the molar volume ratio of the purified ZIGS / CIS / ZnS colloidal quantum well nanocrystals, organic amine, and 1-octadecene in S4 is 0.1 mmol: 5 mL: 5 mL; the organic amine is a linear primary amine, and the linear primary amine is octadecylamine or oleylamine; the reaction solution e is heated to a temperature of 230 °C; the sulfur precursor solution b first uses the sulfur precursor solution of octadecene and then uses dodecyl mercaptan; the volume ratio of the reaction solution e, zinc oleate aqueous solution, sulfur precursor solution of octadecene, and dodecyl mercaptan is 10:10:5:2.

[0030] Preferably, in S4, the zinc oleate aqueous solution and the sulfur precursor solution b are respectively injected at a rate of 5.0 mL / h by an injection pump, and the concentration of the zinc oleate aqueous solution is 0.1 mmol / mL; the volume ratio of the reaction solution f and the antisolvent c is 1:4, and the antisolvent c is acetone or ethanol; the ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystal crude product is repeatedly washed with ethanol.

[0031] Preferably, the degassing treatment step in S1 is: after mixing the zinc precursor, indium precursor, gallium precursor, sulfur precursor, organic acid, organic amine, and 1-octadecene, under nitrogen protection, evacuate and replace the gas, and under the condition of a temperature of 100-120 °C, evacuate for 30 min; the degassing treatment step in S2 is: after mixing the ZIGS nanocrystals with a transition shell layer with organic amine and 1-octadecene, under nitrogen protection, evacuate and replace the gas, and under the condition of a temperature of 100-120 °C, evacuate for 30 min; the degassing treatment step in S3 is: after mixing the ZIGS / CIS nanocrystals with a transition shell layer with organic amine and 1-octadecene, under nitrogen protection, evacuate and replace the gas, and under the condition of a temperature of 100-120 °C, evacuate for 30 min; the degassing treatment step in S4 is: after mixing the purified ZIGS / CIS / ZnS colloidal quantum well nanocrystals with organic amine and 1-octadecene, under nitrogen protection, evacuate and replace the gas, and under the condition of a temperature of 100-120 °C, evacuate for 30 min.

[0032] The present invention provides a preparation method of high-quality ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystals with adjustable bandgap, having the following beneficial effects:

[0033] The present invention proposes a novel ZIGS / CIS / ZnS / ZnS colloidal quantum well (CQW) structure, which overcomes the above limitations through precise bandgap engineering and advanced synthesis strategies. This structure has a wide-bandgap ZIGS (ZnInGaS, 3.6 eV) seed core, a CIS (1.9 eV) quantum well layer, and a ZnS (3.7 eV) shell. This design achieves strong spatial confinement of electron-hole wave functions through type-I band alignment. By simultaneously controlling the kinetic competition between bidirectional cation exchange and shell epitaxial growth, the controllable preparation of monodisperse CQWs (size: 4.9 nm, relative standard deviation: 4.0%) is realized. Spectral analysis shows that its photoluminescence peak is between 533 nm and 742 nm, and the PLQY exceeds 99% in the visible region and over 80% in the NIR region, setting a record high for the CIS system. This result is attributed to effective defect passivation through bidirectional interface gradient alloying and epitaxial growth of the shell. The present invention not only provides a new strategy for the design of cadmium-free quantum well materials but also opens up important application prospects for high-resolution displays, in vivo imaging, and night vision technologies. The ZIGS / CIS / ZnS / ZnS colloidal quantum well type nanocrystals of the present invention are applicable to optoelectronic devices in different wavelength ranges, especially infrared optoelectronic applications.

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Description of the Drawings

[0035] Figure 1 Schematic diagram of the band alignment of the ZnInGaS / CuInS / ZnS colloidal quantum well nanocrystal structure of the present invention.

[0036] Figure 2 XRD patterns of ZIGS nanocrystals, ZIGS / CIS nanocrystals, ZIGS / CIS / ZnS colloidal quantum well nanocrystals, and ZIGS / CIS / ZnS / ZnS colloidal quantum well nanocrystals.

[0037] Figure 3 Absorption spectra and PL spectra of ZIGS nanocrystals, ZIGS / CIS nanocrystals, ZIGS / CIS / ZnS colloidal quantum well nanocrystals, and ZIGS / CIS / ZnS / ZnS colloidal quantum well nanocrystals.

[0038] Figure 4 (a) TEM image of ZIGS nanocrystals; (b) TEM image of ZIGS / CIS nanocrystals; (c) TEM image of ZIGS / CIS / ZnS colloidal quantum well nanocrystals; (d) TEM image of ZIGS / CIS / ZnS / ZnS colloidal quantum well nanocrystals (the inset is a histogram of the size distribution).

[0039] Figure 5Absorption spectra and PL spectra of ZIGS / CIS / ZnS / ZnS colloidal quantum well nanocrystals with different emission peak positions.

[0040] Figure 6 Band gaps and PL emission positions of ZIGS / CIS / ZnS / ZnS colloidal quantum well nanocrystals with different emission peak positions.

[0041] Figure 7 PLQY of ZIGS / CIS / ZnS / ZnS colloidal quantum well nanocrystals with different emission peak positions. Detailed implementation manners

[0042] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0043] Chemicals used in the following embodiments: copper acetate (Cu(C2H3O2)2, 99.99%, Sigma-Aldrich), indium acetate (In(C2H3O2)3, 99.99%, Sigma-Aldrich), zinc acetate (Zn(C2H3O2)3, 99.99%, Sigma-Aldrich), zinc oxide (ZnO, 99%, Sigma-Aldrich), gallium acetate (Ga(C2H3O2)3, 99.99%, Sigma-Aldrich), sulfur (S, 99%, Sigma-Aldrich), 1-dodecanethiol (1-DDT, C 12 H 26 S, 98%, Sigma-Aldrich), oleic acid (OA, C 18 H 34 O2, 90%, Sigma-Aldrich), oleylamine (OLA, C 18 H 37 N, about 80 - 90% C18 content, AlfaAesar), 1-octadecene (ODE, C 18 H 36 , 90%, Sigma-Aldrich), n-hexane (C6H 14 , 97%, GHTECH), absolute ethanol (C2H6O, 99.7%, GHTECH). All chemicals were not further purified.

[0044] The following is an introduction in combination with specific embodiments:

[0045] The preparation method of high-quality ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystals with adjustable bandgap in this embodiment includes the following steps:

[0046] S1. Synthesis of ZIGS quantum dots

[0047] Precursor preparation: Add 0.2 mmol of zinc acetate, 0.2 mmol of indium acetate, 0.2 mmol of gallium acetylacetonate, 0.8 mmol of sulfur powder, 1 mL of octadecenoic acid, 5 mL of oleylamine, and 5 mL of 1-octadecene into a three-necked flask. Under nitrogen protection, evacuate and replace the gas, heat to 110 °C, evacuate for 30 min, and perform degassing treatment to obtain the precursor;

[0048] Generation of ZIGS nanocrystals: Keep the precursor at 120 °C for 60 min under nitrogen protection, then raise the temperature to 200 °C for reaction and keep warm for 60 min to generate ZIGS nanocrystals; after the reaction ends, the obtained reaction solution is naturally cooled to room temperature (25 °C);

[0049] Purification of ZIGS nanocrystals: Add 20 mL of ethanol to 5 mL of the cooled reaction solution to precipitate the primary product of ZIGS nanocrystals, and then purify by centrifugation to obtain ZIGS nanocrystals with a transition shell layer (abbreviated as ZIGS NCs);

[0050] S2. Synthesis of ZIGS / CIS quantum dots

[0051] Shell preparation: Add the ZIGS nanocrystals with a transition shell layer obtained in S1 (0.05 mmol) and 5 mL of octadecylamine and 5 mL of 1-octadecene into a three-necked flask. Under nitrogen protection, evacuate and replace the gas, heat to 110 °C, evacuate for 30 min, and perform degassing treatment to obtain reaction solution a;

[0052] Growth of CIS shell: Heat 10 mL of the reaction solution a to 180 °C, and then inject 1.0 mL of an aqueous copper chloride solution with a concentration of 0.1 mmol / mL, 1.0 mL of an aqueous indium acetate solution with a concentration of 0.1 mmol / mL, and 1.0 mL of an aqueous sulfur powder solution with a concentration of 0.2 mmol / mL into it at a rate of 2.0 mL / h through an injection pump to epitaxially grow a CIS transition shell, obtaining reaction solution b;

[0053] Purification of ZIGS / CIS nanocrystals: Add 25 mL of ethanol to 5 mL of the reaction solution b to precipitate the primary product of ZIGS / CIS nanocrystals, and then purify by centrifugation to obtain ZIGS / CIS nanocrystals with a transition shell layer (abbreviated as ZIGS / CIS NCs);

[0054] S3. Synthesis of ZIGS / CIS / ZnS Colloidal Quantum Well Nanocrystals

[0055] ZnS shell preparation: Add the ZIGS / CIS nanocrystals with a transition shell obtained in 0.1 mmol S2, 5 mL of octadecylamine, and 5 mL of 1-octadecene into a three-necked flask. Under nitrogen protection, evacuate and replace the gas, heat to 110 °C, evacuate for 30 min for degassing treatment to obtain reaction solution c;

[0056] ZnS shell growth: Heat 10 mL of the reaction solution c to 230 °C, and inject 10 mL of an aqueous zinc oleate solution with a concentration of 0.1 mmol / mL, 5 mL of a sulfur precursor solution of 1-octadecene with a concentration of 0.1 mmol / mL, and 2 mL of dodecyl mercaptan through an injection pump at a rate of 5.0 mL / h for epitaxial growth of the ZnS shell to obtain reaction solution d;

[0057] Purification of ZIGS / CIS / ZnS colloidal quantum well nanocrystals: After the reaction solution d is cooled to room temperature (25 °C), add 20 mL of ethanol (or acetone) to 5 mL of the reaction solution d to precipitate the primary product of ZIGS / CIS / ZnS colloidal quantum well nanocrystals. Wash the primary product of ZIGS / CIS / ZnS colloidal quantum well nanocrystals repeatedly with ethanol to obtain purified ZIGS / CIS / ZnS colloidal quantum well nanocrystals (abbreviated as ZIGS / CIS / ZnS CQWs);

[0058] S4. Synthesis of ZnInGaS / CuInS / ZnS / ZnS Colloidal Quantum Well Nanocrystals

[0059] ZnS shell preparation: Add the purified ZIGS / CIS / ZnS colloidal quantum well nanocrystals obtained in 0.1 mmol S3, 5 mL of organic amine, and 5 mL of 1-octadecene into a three-necked flask. Under nitrogen protection, evacuate and replace the gas, heat to 110 °C, evacuate for 30 min for degassing treatment to obtain reaction solution e;

[0060] ZnS shell growth: Heat 10 mL of the reaction solution e to 230 °C, and inject 10 mL of an aqueous zinc oleate solution with a concentration of 0.1 mmol / mL and 5 mL of a sulfur precursor solution of 1-octadecene with a concentration of 0.1 mmol / mL and 2 mL of dodecyl mercaptan through an injection pump at a rate of 5.0 mL / h for epitaxial growth of the ZnS shell to obtain reaction solution f;

[0061] Purification of ZnInGaS / CuInS / ZnS / ZnS Colloidal Quantum Well Nanocrystals: After cooling the reaction solution f to room temperature (25 °C), 20 mL of acetone (or ethanol) was added to 5 mL of the cooled reaction solution f to precipitate the primary product of ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystals. The primary product of ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystals was washed repeatedly with ethanol to obtain purified ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystals (abbreviated as ZIGS / CIS / ZnS / ZnS colloidal quantum well nanocrystals); the outermost layer of the ZIGS / CIS / ZnS / ZnS colloidal quantum well nanocrystals is thicker than that of the ZIGS / CIS / ZnS colloidal quantum well nanocrystals.

[0062] In this Example S1, the zinc precursor can also be one or more of diethylzinc, zinc oleate, and zinc halide; the indium precursor can also be indium chloride or indium acetylacetonate; the gallium precursor can also be gallium chloride; the organic amine can also be octadecylamine; in S2, the copper precursor solution can also be one or more of aqueous copper acetate solution and aqueous copper acetylacetonate solution; the indium precursor solution can also be an aqueous indium chloride solution or a mixed solution of aqueous indium acetate solution and aqueous indium chloride solution; the sulfur precursor solution can also be dodecyl mercaptan or a mixed solution of aqueous sulfur powder solution and dodecyl mercaptan; the organic amine can also be octadecylamine; in S3, the organic amine can also be octadecylamine; in S4, the organic amine can also be octadecylamine; the degassing treatments in S1, S2, S3, and S4 can also be at temperatures of 100 °C, 102 °C, 104 °C, 105 °C, 108 °C, 109 °C, 111 °C, 115 °C, 119 °C, or 120 °C

[0063] Testing and Characterization

[0064] The crystal structure was determined using a Rigaku Japan SmartLab SE X-ray diffractometer (XRD). The morphology and size of the nanoparticles were measured by JEOL JEM-2200FS transmission electron microscopy (TEM) and high-resolution TEM (HRTEM), with the nanoparticles dispersed on a copper grid with an ultrathin carbon film. The absorption spectrum at room temperature was measured using a UV / Vis / NIR spectrometer (UV 3600i Plus, Shimadzu). The solid-state photoluminescence (PL) spectra were obtained using a spectrofluorometer (RF-6000, Shimadzu) and an Ocean Optics Maya 2000pro spectrometer. The transient photoluminescence (TrPL) spectra were tested using a HORIBA QuantaMater 8000. The photoluminescence quantum yield (PLQY) was measured using an integrating sphere of the HORIBA QuantaMater 8000 with an excitation wavelength of 365 nm.

[0065] Summary of optimization points

[0066] Suppression of surface defects:

[0067] Through the two-way cation exchange treatment of ZIGS and ZnS and the multi-layer shell structure, the defects on the surface of the nanocrystals were effectively reduced, improving the photoluminescence quantum yield (PLQY) and luminescence stability.

[0068] Tunability of the bandgap:

[0069] By adjusting the injection time of the sulfur precursor solution of the CIS shell and the growth time of the CIS shell, fine tuning of the bandgap of the ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well was achieved, covering an ultra-wide emission range (533 - 742 nm). The change in the emission peak position depends on the injection time of the sulfur precursor of the CIS shell and the growth time of the CIS shell, with growth times of 10, 30, 60, 90, 120, 180 minutes; the photoluminescence peak position is tunable in the range of 533 - 742 nm.

[0070] Achievement of a high-quality core-shell structure:

[0071] The epitaxial growth of a high-quality shell (ZnS shell) ensured the high crystalline quality and excellent optical properties of the ZIGS / CIS / ZnS / ZnS colloidal quantum well nanocrystals.

[0072] Effect and verification of Example 1

[0073] The ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystals prepared through the above-mentioned Example 1 were characterized by ultraviolet-visible absorption spectroscopy (UV-Vis), photoluminescence spectroscopy (PL), transmission electron microscopy (TEM), and X-ray diffraction (XRD), etc., and the following effects were verified:

[0074] High PL quantum yield: As shown in Figure 3 , 6 and 7, for the ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystals, the PLQY exceeds 99% in the visible light region and exceeds 80% in the NIR region, showing excellent photoluminescence performance.

[0075] Wide emission range: As shown in Figure 5 , the emission wavelength can be widely tuned in the range of 533 nm to 742 nm, achieving ultra-wideband emission.

[0076] Excellent crystal quality: The TEM image ( Figure 4 shown) shows a uniform core-shell structure, and the XRD pattern ( Figure 2 shown) confirms the high crystallinity of the ZIGS, CIS, and ZnS phases.

[0077] Effective defect suppression: The two-way cation exchange of ZIGS and ZnS and the epitaxial growth of the CIS shell improve the luminescence stability and efficiency of the nanocrystals.

[0078] Application prospects: The high-quality ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystals with tunable bandgaps prepared by the present invention have broad application prospects due to their high PLQY, wide emission range, and excellent infrared emission performance, including but not limited to:

[0079] Photodetectors: High-efficiency visible-infrared light detection ability, suitable for environmental monitoring, medical diagnosis, and security fields.

[0080] Optical sensors: Used for high-sensitivity infrared light sensing applications.

[0081] Display technology: As a luminescent material in visible and infrared display devices, providing a high-brightness display effect.

[0082] Conclusion

[0083] The present invention proposes a novel ZIGS / CIS / ZnS / ZnS colloidal quantum well (CQW) structure, which has a wide-bandgap ZIGS seed core, a CIS quantum well layer, and a ZnS shell. This design achieves strong spatial confinement of electron-hole wave functions through type-I band alignment. By simultaneously controlling the competitive kinetics of bidirectional cation exchange of ZIGS and ZnS and epitaxial growth of the CIS shell layer, the controllable preparation of monodisperse CQWs is realized. Spectral analysis shows that its NIR photoluminescence peak is between 688 nm and 742 nm, and the PLQY exceeds 99% in the visible region and exceeds 80% in the NIR region, setting a record high for the CIS system. This result is attributed to effective defect passivation through bidirectional interfacial gradient alloying and epitaxial growth of the shell layer, solving the problems of limited improvement in optical performance and surface defects in the prior art. The present invention not only provides a new strategy for the design of cadmium-free quantum well materials, but also opens up important application prospects in the fields of high-resolution display, in vivo imaging, and night vision technology.

[0084] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation method of high-quality ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystals with adjustable bandgap, characterized in that, The preparation method includes the following steps: S1. Synthesis of ZIGS quantum dots Preliminary preparation of precursors: After mixing a zinc precursor, an indium precursor, a gallium precursor, a sulfur precursor, an organic acid, an organic amine, and 1-octadecene, degassing treatment is performed to obtain precursors. Formation of ZIGS nanocrystals: The precursors are heated and maintained under nitrogen protection, then the temperature is raised for reaction and heat preservation. After the reaction ends, the obtained reaction solution is naturally cooled to room temperature. Purification of ZIGS nanocrystals: An anti-solvent is added to the cooled reaction solution to precipitate a primary product of ZIGS nanocrystals, and then purification is carried out by centrifugation to obtain ZIGS nanocrystals with a transition shell layer. S2. Synthesis of ZIGS / CIS quantum dots Preparation of the shell layer: After mixing the ZIGS nanocrystals with a transition shell layer obtained in S1 with an organic amine and 1-octadecene, degassing treatment is performed to obtain reaction solution a. Growth of the CIS shell layer: The reaction solution a is heated, and then a copper precursor solution, an indium precursor solution, and a sulfur precursor solution are injected to obtain reaction solution b. Purification of ZIGS / CIS nanocrystals: An anti-solvent a is added to the reaction solution b to precipitate a primary product of ZIGS / CIS nanocrystals, and then purification is carried out by centrifugation to obtain ZIGS / CIS nanocrystals with a transition shell layer. S3. Synthesis of ZIGS / CIS / ZnS colloidal quantum well nanocrystals Preparation of the ZnS shell layer: After mixing the ZIGS / CIS nanocrystals with a transition shell layer obtained in S2 with an organic amine and 1-octadecene, degassing treatment is performed to obtain reaction solution c. Growth of the ZnS shell layer: The reaction solution c is heated, and an aqueous solution of zinc oleate and a sulfur precursor solution a are added for epitaxial growth of the ZnS shell layer to obtain reaction solution d. Purification of ZIGS / CIS / ZnS colloidal quantum well nanocrystals: After the reaction solution d is cooled to room temperature, an anti-solvent b is added to the cooled reaction solution d to precipitate a primary product of ZIGS / CIS / ZnS colloidal quantum well nanocrystals, and the primary product of ZIGS / CIS / ZnS colloidal quantum well nanocrystals is repeatedly washed to obtain purified ZIGS / CIS / ZnS colloidal quantum well nanocrystals. S4. Synthesis of ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystals Preparation of the ZnS shell layer: After mixing the purified ZIGS / CIS / ZnS colloidal quantum well nanocrystals obtained in S3 with an organic amine and 1-octadecene, degassing treatment is performed to obtain reaction solution e. Growth of the ZnS shell layer: The reaction solution e is heated, and an aqueous solution of zinc oleate and a sulfur precursor solution b are added for epitaxial growth of the ZnS shell layer to obtain reaction solution f. Purification of ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystals: After cooling the reaction solution f to room temperature, an anti-solvent c is added to precipitate a primary product of ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystals. The primary product of ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystals is washed repeatedly to obtain purified ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystals.

2. The preparation method of a high-quality ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystal with adjustable bandgap according to claim 1, characterized in that, The zinc precursor in S1 is one or more of diethylzinc, zinc acetate, zinc oleate, and zinc halide; the indium precursor is indium acetate, indium chloride, or indium acetylacetonate; the gallium precursor is gallium acetylacetonate or gallium chloride; the sulfur precursor is sulfur powder; the organic acid is oleic acid; the organic amine is a linear primary amine, and the linear primary amine is octadecylamine or oleylamine; the molar volume ratio of the zinc precursor, indium precursor, gallium precursor, sulfur precursor, organic acid, organic amine, and 1-octadecene is 0.2 mmol: 0.2 mmol: 0.2 mmol: 0.8 mmol: 1 mL: 5 mL: 5 mL; the precursor is heated to 120 °C under nitrogen protection and maintained for 60 min, then the temperature is raised to 200 °C for reaction and kept warm for 60 min; the anti-solvent is ethanol, and the volume ratio of the reaction solution to the anti-solvent is 1:

4.

3. The preparation method of a high-quality ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystal with adjustable bandgap according to claim 1, characterized in that, In S2, the molar volume ratio of the ZIGS nanocrystals with a transition shell layer, organic amine, and 1-octadecene is 0.05 mmol: 5 mL: 5 mL; the organic amine is a linear primary amine, and the linear primary amine is octadecylamine or oleylamine; the copper precursor solution is one or more of an aqueous solution of copper chloride, an aqueous solution of copper acetate, and an aqueous solution of copper acetylacetonate; the indium precursor solution is one or more of an aqueous solution of indium acetate and an aqueous solution of indium chloride; the sulfur precursor solution is one or more of an aqueous solution of sulfur powder and dodecyl mercaptan; the copper precursor solution, the indium precursor solution, and the sulfur precursor solution form a total precursor solution, the volume ratio of the reaction solution a to the total precursor solution is 10:3, the concentration of the copper precursor solution is 0.1 mmol / mL, the concentration of the indium precursor solution is 0.1 mmol / mL, the concentration of the sulfur precursor solution is 0.2 mmol / mL, the anti-solvent a is ethanol, and the volume ratio of the reaction solution b to the anti-solvent a is 1:

5.

4. The preparation method of a high-quality ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystal with adjustable bandgap according to claim 3, characterized in that In S2, the reaction solution a is heated to 180 °C, and the copper precursor solution, indium precursor solution, and sulfur precursor solution are respectively injected at a rate of 2.0 mL / h by an injection pump. The volume ratio of the copper precursor solution, indium precursor solution, and sulfur precursor solution in the total precursor solution is 1:1:

1.

5. The preparation method of a high-quality ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystal with adjustable bandgap according to claim 1, characterized in that, In S3, the molar volume ratio of the ZIGS / CIS nanocrystals with a transition shell layer, organic amine, and 1-octadecene is 0.1 mmol: 5 mL: 5 mL; the organic amine is a linear primary amine, and the linear primary amine is octadecylamine or oleylamine; the sulfur precursor solution a first uses the sulfur precursor solution of octadecene and then uses dodecyl mercaptan; the volume ratio of the reaction solution c, zinc oleate aqueous solution, sulfur precursor solution of octadecene, and dodecyl mercaptan is 10:10:5:

2.

6. The preparation method of a high-quality ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystal with adjustable bandgap according to claim 5, characterized in that, In S3, the reaction solution c is heated to 230 °C, and the zinc oleate aqueous solution and the sulfur precursor solution a are respectively injected at a rate of 5.0 mL / h through an injection pump, and the concentration of the zinc oleate aqueous solution is 0.1 mmol / mL.

7. The preparation method of a high-quality ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystal with adjustable bandgap according to claim 6, characterized in that, In S3, the anti-solvent b is acetone or ethanol, the volume ratio of the reaction solution d and the anti-solvent b is 1:4, and the ZIGS / CIS / ZnS colloidal quantum well nanocrystal crude product is repeatedly washed with ethanol.

8. A method for preparing a high-quality ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystal with adjustable bandgap, characterized in that, In S4, the molar volume ratio of the purified ZIGS / CIS / ZnS colloidal quantum well nanocrystals, organic amine, and 1-octadecene is 0.1 mmol: 5 mL: 5 mL; the organic amine is a linear primary amine, and the linear primary amine is octadecylamine or oleylamine; the reaction solution e is heated to a temperature of 230 °C; the sulfur precursor solution b first uses the sulfur precursor solution of octadecene and then uses dodecyl mercaptan; the volume ratio of the reaction solution e, zinc oleate aqueous solution, sulfur precursor solution of octadecene, and dodecyl mercaptan is 10:10:5:

2.

9. The preparation method of a high-quality ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystal with adjustable bandgap according to claim 8, characterized in that, In S4, the zinc oleate aqueous solution and the sulfur precursor solution b are respectively injected at a rate of 5.0 mL / h through an injection pump, and the concentration of the zinc oleate aqueous solution is 0.1 mmol / mL; the volume ratio of the reaction solution f and the anti-solvent c is 1:4, and the anti-solvent c is acetone or ethanol; the ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystal crude product is repeatedly washed with ethanol.

10. The preparation method of a high-quality ZnInGaS / CuInS / ZnS / ZnS colloidal quantum well nanocrystal with adjustable bandgap according to claim 1, characterized in that, The steps of the degassing treatment in S1 are as follows: After mixing the zinc precursor, indium precursor, gallium precursor, sulfur precursor, organic acid, organic amine, and 1-octadecene, under nitrogen protection, evacuate and replace the gas, and under the condition of a temperature of 100-120 °C, pump air for 30 min; the steps of the degassing treatment in S2 are as follows: After mixing the ZIGS nanocrystals with a transition shell layer with organic amine and 1-octadecene, under nitrogen protection, evacuate and replace the gas, and under the condition of a temperature of 100-120 °C, pump air for 30 min; the steps of the degassing treatment in S3 are as follows: After mixing the ZIGS / CIS nanocrystals with a transition shell layer with organic amine and 1-octadecene, under nitrogen protection, evacuate and replace the gas, and under the condition of a temperature of 100-120 °C, pump air for 30 min; the steps of the degassing treatment in S4 are as follows: After mixing the purified ZIGS / CIS / ZnS colloidal quantum well nanocrystals with organic amine and 1-octadecene, under nitrogen protection, evacuate and replace the gas, and under the condition of a temperature of 100-120 °C, pump air for 30 min.

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