Ligand functionalized germanium quantum dots, and preparation method and application thereof

Abstract

The application discloses ligand-functionalized germanium quantum dots and a preparation method and application thereof, and relates to the field of photoelectric thin films. The surface of the germanium quantum dots is bonded with ligands through chemical bonds, and the ligands are AX compounds. The AX type compound is used as the surface ligand of the germanium quantum dots, which solves the core contradictions that have long restricted the application of the germanium quantum dots from the nature of material chemistry, namely, the contradiction between surface stabilization and charge transport, and the contradiction between intrinsic characteristics of the material and solution processability.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic thin film technology, and in particular to a ligand-functionalized germanium quantum dot, its preparation method, and its application. Background Technology

[0002] Germanium (Ge), as the first semiconductor material to achieve large-scale commercialization, was once a crucial cornerstone of modern semiconductor technology. Its bulk form, with its high carrier mobility and narrow bandgap, was widely used in early transistors and infrared optoelectronic devices, laying the foundation for microelectronics. However, the inherently high intrinsic carrier concentration of germanium bulk materials leads to significant device leakage current, and it is difficult to form a high-quality, stable intrinsic oxide layer similar to silicon. Interface defects and reliability issues are prominent, and these shortcomings have led to its gradual replacement by more stable silicon-based technologies in mainstream microelectronics.

[0003] In recent years, with the rapid development of nanotechnology and bandgap engineering, research on germanium-based materials has ushered in a new revival. Germanium quantum dots, as a novel nanoscale germanium-based material, exhibit a series of unique physicochemical properties, re-attracting the attention of the scientific research and industrial communities. Germanium quantum dots possess a high light absorption coefficient, enabling more efficient capture of photon energy; their high hole mobility provides favorable conditions for charge transport; and their tunable surface chemical properties endow them with diverse functional modification potential. Their good biocompatibility makes their application in the biomedical field possible. These advantages make germanium quantum dots show broad application prospects in multiple fields such as solar cells, photodetectors, field-effect transistors, and bioimaging. In photovoltaic applications, germanium quantum dots can serve as a highly efficient light-absorbing layer material, broadening the spectral response range of solar cells and improving the utilization rate of infrared photons. In the fields of transistors and photodetectors, their high carrier mobility and solution processability provide new avenues for manufacturing high-performance, low-cost flexible electronic devices, and are expected to drive the development of next-generation optoelectronic devices.

[0004] Despite the numerous superior properties and application potential of germanium quantum dots, improving their actual device performance still faces several technical bottlenecks. Existing germanium quantum dots generally suffer from numerous surface defects. Insufficiently passivated surfaces lead to accelerated carrier recombination rates, significantly reducing carrier mobility and consequently affecting the device's photoelectric conversion efficiency and response speed. Furthermore, traditional germanium quantum dot fabrication methods often rely on surface modification with long-chain organic ligands. While these long-chain ligands can stabilize the quantum dot structure to some extent, their insulating properties create potential barriers between quantum dots, hindering charge transport and causing a significant decrease in charge mobility within the quantum dot film, thus limiting further performance improvements. In addition, unoptimized surface ligands also result in poor stability of germanium quantum dots. Under the influence of external environments such as oxygen and moisture, quantum dots are prone to oxidation or aggregation, making it difficult to guarantee long-term device reliability. This has become a key obstacle restricting the transition of germanium quantum dots from the laboratory to practical applications.

[0005] Therefore, developing a ligand functionalization technology that can effectively passivate surface defects of germanium quantum dots while promoting charge transport has become an urgent need to break through existing bottlenecks and promote the industrial application of germanium quantum dots. Summary of the Invention

[0006] A ligand-functionalized germanium quantum dot, wherein the surface of the germanium quantum dot is chemically bonded with a ligand, wherein the ligand is an AX compound;

[0007] Wherein, A is a cation, and A is selected from at least one of organic amine cations, alkali metal cations, alkaline earth metal cations, sulfide-containing organic cations, transition metal cations, and rare earth metal cations.

[0008] X is an anion, and X is selected from at least one of the following: halide anions, thiocyanate anions, azide anions, cyanate anions, thiosulfate anions, and oxyanions.

[0009] According to embodiments of the present invention, one of the technical solutions has at least one of the following advantages or beneficial effects:

[0010] This invention innovatively uses AX-type compounds as surface ligands for germanium quantum dots. This design fundamentally solves two core contradictions that have long restricted the application of germanium quantum dots from the perspective of materials chemistry.

[0011] The first challenge is the contradiction between surface stabilization and charge transport. While traditional long-chain organic ligands (such as oleylamine) can provide steric hindrance to stabilize quantum dots, their long hydrocarbon chains form an effective insulating barrier, severely hindering the overlap of electronic wave functions and charge tunneling between quantum dots, resulting in poor film conductivity. The AX ligand used in this invention has its anion X bonded to surface Ge atoms via direct covalent bonds (Ge-X) or strong coordination bonds. This bonding method provides chemical stability far exceeding that of physical adsorption, efficiently and persistently saturating surface dangling bonds and passivating defect states originating from uncoordinated electrons or weak Ge-O bonds. Simultaneously, the AX ligand's ionic properties result in an extremely thin passivation layer on the quantum dot surface, allowing for close packing of quantum dots during film formation. This significantly reduces the barrier to charge tunneling between particles, thereby improving carrier mobility.

[0012] The second issue is the contradiction between the intrinsic properties of the material and its solution processability. Bare germanium quantum dots have high surface energy, making them prone to aggregation and difficult to disperse; while traditional ligand-modified quantum dots are often only soluble in nonpolar solvents, incompatible with the polar processing solvents commonly used in high-performance optoelectronic devices. AX ligands endow quantum dot surfaces with unique ionic or strongly polar characteristics. This surface property allows them to be dispersed in strongly polar solvents.

[0013] According to one embodiment of the present invention, A is selected from at least one of methylamine cation, formamidinium cation, guanidine cation, cesium ion, rubidium ion, potassium ion, sodium ion, lithium ion, antimony ion, bismuth ion, cobalt ion, manganese ion, copper ion, cerium ion, europium ion, tetramethylguanidine cation, and tetraethylamine cation. The selected cations have suitable size and electronic properties. Through electrostatic interactions with anions and their own steric effects, they stabilize the surface structure and may modulate the energy level positions on the quantum dot surface. This is beneficial for reducing charge traps and promoting the injection and transport of specific charge carriers (holes or electrons), thereby adapting to the energy level alignment requirements of different optoelectronic devices.

[0014] According to one embodiment of the present invention, X is selected from at least one of iodide ions, bromide ions, chloride ions, thiocyanate ions, and cyanate ions. Halogen ions (iodide ions, bromide ions, chloride ions) and pseudohalogen ions (thiocyanate ions and cyanate ions) have moderate electronegativity and size, and can form chemical bonds with Ge of suitable strength, which is the key to achieving efficient and stable surface passivation.

[0015] According to one embodiment of the present invention, the sulfide-containing organic cation is selected from one of thiomethylamine cation, selenoethylamine cation, and thioguanidine cation.

[0016] According to one embodiment of the present invention, the oxyacid anion is selected from one of acetate, oxalate, sulfate, phosphate, and nitrate.

[0017] According to one embodiment of the present invention, the ligand-functionalized germanium quantum dots have a particle size of 1-100 nm, preferably 2-80 nm. In terms of photoelectric performance modulation, the 1-100 nm size precisely covers the entire span from the strong quantum confinement effect region to the weak quantum confinement effect region. When the particle size is smaller than the exciton Bohr radius of germanium (approximately 24 nm), the quantum confinement effect becomes significant, and the energy of the conduction band and valence band edge states increases sharply with decreasing size. This allows the optical bandgap of the material to be continuously and predictably tuned in the near-infrared to visible light range, providing a basis for designing optoelectronic devices with specific spectral responses (such as solar cells with tuned absorption edges and detectors at specific wavelengths). In terms of surface chemical modification, quantum dots in this size range have extremely high specific surface area and a large proportion of surface atoms, making surface ligand reactions highly efficient and necessary. Sufficient surface reaction sites ensure that AX ligands can be fully grafted, achieving effective coverage of most surface defects. If the particle size is too large (>100 nm), the specific surface area decreases sharply, the surface effect on the overall properties weakens, and the surface modification advantages of this invention will no longer be prominent; if the particle size is too small (<1 nm), the cluster structure is unstable, the surface energy is extremely high, and it is difficult to apply in practice.

[0018] According to one embodiment of the present invention, the ligand is selected from at least one of methylamine iodide, formamidine iodide, cesium iodide, rubidium iodide, methylamine bromide, methylamine thiocyanate, methylamine cyanate, guanidine iodide, tetraethylamine iodide, tetramethylguanidine iodide, guanidine bromide, cesium chloride, bismuth iodide, antimony iodide, cobalt iodide, manganese iodide, copper iodide, cerium iodide, and europium iodide.

[0019] According to one embodiment of the present invention, the germanium quantum dots can be dispersed in a polar solvent to form a stable dispersion.

[0020] According to one embodiment of the present invention, the polar solvent is selected from at least one of N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, γ-butyrolactone, acetone, acetonitrile, methanol and ethanol.

[0021] A method for preparing the ligand-functionalized germanium quantum dots includes the following steps:

[0022] S1: Provides germanium quantum dots with hydrogen-terminated surfaces;

[0023] S2: React the hydrogen-terminated germanium quantum dots with a halogen in an organic solvent, and then react with the AX compound to obtain the ligand-functionalized germanium quantum dots.

[0024] According to embodiments of the present invention, one of the technical solutions has at least one of the following advantages or beneficial effects:

[0025] First, halogens react with hydrogen-capped Ge, followed by the addition of AX compounds. This step firmly grafts the target AX ligands onto the quantum dot surface, thereby achieving a precise conversion from a "clean surface" to a "specifically functionalized surface".

[0026] According to one embodiment of the present invention, step S2 is followed by step S3, which includes a purification operation of the ligand-functionalized germanium quantum dots.

[0027] According to one embodiment of the present invention, the halogen is selected from at least one of iodine, bromine, chlorine, and fluorine. The reactivity of different halogens can be used to control reaction conditions and final surface properties.

[0028] According to one embodiment of the present invention, the organic solvent is selected from at least one of toluene, benzene, chlorobenzene, o-dichlorobenzene, n-hexane, and cyclohexane. These nonpolar or weakly polar solvents facilitate the dissolution of halogen molecules and the homogeneous reaction, while not adversely affecting the hydrogen-terminated quantum dot surface.

[0029] According to one embodiment of the present invention, in step S2, the mass ratio of the halogen element to the germanium quantum dot whose surface is terminated by hydrogen is 200-500:20-100.

[0030] According to one embodiment of the present invention, in step S2, the mass ratio of the halogen element to the germanium quantum dot whose surface is terminated by hydrogen is 200-250:20-50.

[0031] According to one embodiment of the present invention, in step S2, the mass ratio of the halogen element to the germanium quantum dot whose surface is terminated by hydrogen is one of 250:50, 240:50, 230:50, 220:50, 210:50, and 200:50.

[0032] According to one embodiment of the present invention, the reaction temperature of step S2 is 10-100°C, preferably, the reaction temperature of step S2 is 10-100°C.

[0033] According to one embodiment of the present invention, in step S2, the reaction time of the germanium quantum dots with hydrogen-terminated surfaces and the halogen element in an organic solvent is 0.1-72 hours; preferably, the reaction time is 0.1-20 hours.

[0034] According to one embodiment of the present invention, the molar concentration of the AX compound in step S2 is 0.1-10 mol / L.

[0035] According to one embodiment of the present invention, preferably, the molar concentration of the AX compound in step S2 is one of 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, and 0.5 mol / L.

[0036] Another aspect of the present invention relates to a photoelectric functional thin film comprising the aforementioned ligand-functionalized germanium quantum dots. Because the thin film is composed of closely packed quantum dots with well-passivated surfaces, short ligands, and strong charge transport capabilities, it exhibits high carrier mobility, low defect state density, and good morphological uniformity.

[0037] In another aspect, the present invention provides an optoelectronic device comprising the aforementioned optoelectronic functional thin film.

[0038] According to one embodiment of the present invention, the optoelectronic device is a field-effect transistor, and the optoelectronic functional thin film constitutes the semiconductor channel layer of the field-effect transistor. Using the germanium quantum dot thin film of the present invention as the channel material of the FET, its high carrier mobility directly translates into high on-state current and transconductance of the device; its low defect state density helps to reduce the off-state current, thereby improving the on / off ratio and stability of the device.

[0039] According to one embodiment of the present invention, the optoelectronic device is a photodetector, and the optoelectronic functional thin film constitutes the light absorption layer or charge transport layer of the photodetector. When used as a light absorption layer, germanium quantum dots can effectively absorb photons over a wide spectral range and generate photogenerated carriers; when used as a charge transport layer, their high mobility can rapidly separate and transport photogenerated carriers. The two work together to improve the photoresponsivity, detectivity, and response speed of the detector.

[0040] According to one embodiment of the present invention, the optoelectronic device is a solar cell, and the optoelectronic functional thin film constitutes part of the hole transport layer, electron transport layer, interface modification layer, or photoactive layer of the solar cell. When used as a transport layer or interface layer, its good energy level tunability and high charge mobility are beneficial to the selective extraction and transport of charge carriers, reducing interface recombination; when used as a component of the photoactive layer, it can broaden the spectral response or enhance the built-in electric field, thereby improving the photoelectric conversion efficiency of the solar cell.

[0041] According to one embodiment of the present invention, the optoelectronic device is a light-emitting diode (LED), and the optoelectronic functional thin film constitutes the hole transport layer, electron transport layer, or interface modification layer of the LED. As a charge transport layer or interface layer, its efficient charge injection and balancing capabilities can effectively confine electrons and holes within the light-emitting layer for recombination, thereby improving the luminous efficiency, brightness, and stability of the LED.

[0042] In another aspect, the present invention provides a stable dispersion comprising the ligand-functionalized germanium quantum dots dispersed in a polar solvent, wherein the concentration of the ligand-functionalized germanium quantum dots in the polar solvent is 1-10 mg / mL.

[0043] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0044] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0045] Figure 1 The fluorescence spectrum of the ligand-functionalized germanium quantum dots prepared in Example 1.

[0046] Figure 2 This is a TEM image of the ligand-functionalized germanium quantum dots prepared in Example 1.

[0047] Figure 3 The transfer characteristic curve of the field-effect transistor based on MAI-GeQD thin film in Example 2 is shown.

[0048] Figure 4 This is the electroluminescence spectrum of the light-emitting diode in Example 3. Detailed Implementation

[0049] The terms "preferred," "more preferred," etc., used in this invention refer to embodiments of the invention that provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of this invention.

[0050] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0051] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of the present invention.

[0052] Unless otherwise specified, the reagents, methods and equipment used in this invention are all conventional reagents, methods and equipment in this technical field.

[0053] The AX compound described above in this invention requires that the size and electronegativity of its cation A and anion X be matched so that it can be stably bonded to the surface of germanium quantum dots by the method of this invention and achieve the technical effect.

[0054] In the examples, hydrogen-terminated germanium quantum dots were prepared according to the following literature: Lai, M., Wei, L., Huang, YH, Wang, XD, Yang, Z. (2024). Revisiting the Influence of Surface Alkoxylation on Colloidal Silicon Nanocrystals. ACS Photonics, 11(6), 2439-2449. After preparation, the hydrogen-terminated germanium quantum dots were dispersed in toluene for later use.

[0055] Example 1

[0056] A ligand-functionalized germanium quantum dot, wherein the surface of the germanium quantum dot is chemically bonded to a ligand, wherein the ligand is methylamine iodine.

[0057] A method for preparing the ligand-functionalized germanium quantum dots includes the following steps:

[0058] S1: Provides germanium quantum dots with hydrogen-terminated surfaces;

[0059] S2: Add 0.25 g (1.96 mmol) of elemental iodine and 10 mL of toluene to a 100 mL reaction flask protected by nitrogen, and stir magnetically until the elemental iodine is completely dissolved. Under a continuous nitrogen atmosphere, rapidly add approximately 50 mg of germanium quantum dots (GeQD) to the above clear iodine solution, and then place the reaction system in a dark environment at room temperature and stir for 13 hours to obtain a mixed solution. Measure 2 mL of a 0.1 mol / L methylamine iodide (MAI) solution (using dimethyl sulfoxide as solvent, named MAI / DMSO), add it to the above mixed solution, and immediately vortex for 10 minutes to obtain a solution containing the ligand-functionalized germanium quantum dots (MAI-GeQD).

[0060] S3: Centrifuge the solution containing the ligand-functionalized germanium quantum dots at 3000 rpm for 5 minutes to remove unreacted trace aggregates; then carefully transfer the supernatant to a 50 mL centrifuge tube, add 20 mL of methanol, centrifuge at 7800 rpm for 10 minutes, discard the colorless supernatant to obtain the precipitate of ligand-functionalized germanium quantum dots (MAI-GeQDs).

[0061] S4: Disperse MAI-GeQDs in 1 mL of N,N-dimethylformamide (DMF) to prepare a stable MAI-GeQDs DMF solution with a concentration of 50 mg / mL.

[0062] Example 2

[0063] A field-effect transistor based on ligand-functionalized germanium quantum dots prepared in Example 1 includes a silicon / silicon dioxide (Si / SiO2) substrate and a semiconductor layer, wherein the semiconductor layer is composed of ligand-functionalized germanium quantum dots prepared in Example 1.

[0064] The above-mentioned field-effect transistor is fabricated using the following steps:

[0065] A Si / SiO2 substrate is provided, which uses a heavily doped silicon wafer as the gate and has a 100 nm thick silicon dioxide layer thermally grown on its surface as the gate dielectric. The Si / SiO2 substrate is sequentially placed in detergent, deionized water, ethanol, acetone and isopropanol, and ultrasonically cleaned for 30 minutes each, then dried with nitrogen gas and subjected to ultraviolet ozone treatment at 80 W for 15 minutes.

[0066] In a nitrogen glove box, the DMF solution of MAI-GeQD prepared in Example 1 (concentration of 50 mg / mL) was spin-coated onto the treated Si / SiO2 substrate. The substrate was then placed on a hot plate in the glove box and annealed at 70°C for 15 minutes to obtain a substrate covered with a MAI-GeQD thin film. The spin-coating parameters were set as follows: spin speed of 2000 rpm and spin-coating time of 20 seconds.

[0067] The substrate covered with the MAI-GeQD thin film is transferred to a thermal evaporation system, where an 80 nm thick gold (Au) thin film is thermally evaporated and deposited on the semiconductor layer using a metal mask to form the source and drain electrodes. The channel length (L) and width (W) of the electrodes can be adjusted according to the mask design, with typical dimensions of L = 100 μm and W = 1400 μm.

[0068] Example 3

[0069] A light-emitting diode based on ligand-functionalized germanium quantum dots prepared in Example 1 includes an indium tin oxide (ITO) substrate, a hole transport layer, a quantum dot light-emitting layer, a zinc oxide (ZnO) electron transport layer, and a silver (Ag) electrode, wherein the hole transport layer is composed of ligand-functionalized germanium quantum dots prepared in Example 1.

[0070] The above-mentioned light-emitting diode is prepared by the following steps:

[0071] First, the DMF solution of MAI-GeQDs prepared in Example 1 was spin-coated at 3000 rpm onto an ITO substrate pre-coated with a poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) hole injection layer to form a hole transport layer.

[0072] Subsequently, a green quantum dot emitting layer and a ZnO electron transport layer were spin-coated onto the hole transport layer in sequence.

[0073] Finally, Ag electrodes are fabricated on the surface of the electron transport layer using a vapor deposition process, thus completing the fabrication of the entire device.

[0074] Performance testing:

[0075] Figure 1 The fluorescence spectrum of the ligand-functionalized germanium quantum dots (MAI-GeQD) prepared in Example 1 is shown. Figure 1 The horizontal axis should represent wavelength, and the vertical axis should represent fluorescence intensity. Figure 1 The fluorescence emission properties of germanium quantum dots (MAI-GeQDs) functionalized with methylamine iodide (MAI) ligands are shown. The significant and clear fluorescence emission peaks appearing in the figure directly demonstrate the material's high luminescence efficiency. This is attributed to the successful passivation of surface defects on the germanium quantum dots by the MAI ligands, which significantly reduces the density of nonradiative recombination centers (defect states), allowing photogenerated carriers to be effectively released as photons via radiative recombination, thus resulting in the observed strong fluorescence.

[0076] Figure 2 The image shows a TEM image of the ligand-functionalized germanium quantum dots (MAI-GeQD) prepared in Example 1. The TEM image reveals that the quantum dot particles are well dispersed without significant agglomeration, confirming their good dispersibility in the solvent.

[0077] Figure 3 The figure shows the transfer characteristic curve of the field-effect transistor based on MAI-GeQD thin film in Example 2. The high current level and curve slope in the figure reflect that the MAI-GeQD thin film has good charge transport capability.

[0078] Figure 4 This is the electroluminescence spectrum of the light-emitting diode in Example 3. Figure 4The appearance of a sharp, single emission peak indicates that the device emits light with high color purity (e.g., green light). This result has dual significance: First, it demonstrates that MAI-GeQD material, acting as a hole transport layer, can effectively inject holes into the quantum dot emitting layer, where they recombine with electrons injected from the electron transport layer, resulting in luminescence. This indicates that its function as a charge transport material is effective. Second, the efficient luminescence also indirectly confirms the low level of nonradiative recombination at the MAI-GeQD / emitting layer interface, suggesting that the favorable surface properties of MAI-GeQD as an interface layer help reduce energy loss caused by interface defects.

[0079] The above are merely embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A ligand-functionalized germanium quantum dot, characterized in that: The surface of the germanium quantum dots is chemically bonded with ligands, which are AX compounds; Wherein, A is a cation, and A is selected from at least one of organic amine cations, alkali metal cations, alkaline earth metal cations, sulfide-containing organic cations, transition metal cations, and rare earth metal cations. X is an anion, and X is selected from at least one of the following: halide anions, thiocyanate anions, azide anions, cyanate anions, thiosulfate anions, and oxyanions.

2. The ligand-functionalized germanium quantum dot according to claim 1, characterized in that: The A is selected from at least one of methylamine cation, formamidinium cation, guanidine cation, cesium ion, rubidium ion, potassium ion, sodium ion, lithium ion, antimony ion, bismuth ion, cobalt ion, manganese ion, copper ion, cerium ion, europium ion, tetramethylguanidine cation, and tetraethylamine cation.

3. The ligand-functionalized germanium quantum dot according to claim 1, characterized in that: X is selected from at least one of iodide ion, bromide ion, chloride ion, thiocyanate ion and cyanate ion.

4. The ligand-functionalized germanium quantum dot according to claim 1, characterized in that: The ligand-functionalized germanium quantum dots have a particle size of 1-100 nm, preferably 2-80 nm.

5. The ligand-functionalized germanium quantum dot according to claim 1, characterized in that: The ligand is selected from at least one of methylamine iodide, formamidine iodide, cesium iodide, rubidium iodide, methylamine bromide, methylamine thiocyanate, methylamine cyanate, guanidine iodide, tetraethylamine iodide, tetramethylguanidine iodide, guanidine bromide, cesium chloride, bismuth iodide, antimony iodide, cobalt iodide, manganese iodide, copper iodide, cerium iodide, and europium iodide.

6. A method for preparing ligand-functionalized germanium quantum dots as described in any one of claims 1 to 5, characterized in that: Includes the following steps: S1: Provides germanium quantum dots with hydrogen-terminated surfaces; S2: The germanium quantum dots with hydrogen-terminated surfaces are reacted with a halogen in an organic solvent, followed by the addition of an AX compound to obtain the ligand-functionalized germanium quantum dots.

7. The method according to claim 6, characterized in that: The halogen element is selected from at least one of iodine, bromine, chlorine and fluorine.

8. The method according to claim 6, characterized in that: In step S2, the mass ratio of the halogen element to the germanium quantum dot with hydrogen-terminated surface is 200-500:20-100.

9. A photoelectric functional thin film, characterized in that: The optoelectronic functional thin film includes ligand-functionalized germanium quantum dots as described in any one of claims 1 to 5.

10. An optoelectronic device, characterized in that: Includes the photoelectric functional thin film as described in claim 9.

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