Infrared optical device based on non-toxic noble metal chalcogenide quantum dot nanocrystals and manufacturing method therefor

Abstract

The present invention relates to an infrared optical device and a manufacturing method therefor, the infrared optical device comprising: a substrate; an electron transport layer; a first silver telluride quantum dot nanocrystalline layer having halogen atom ligands bonded thereto; a second silver telluride quantum dot nanocrystalline layer having thiol-based organic ligands bonded thereto; a hole transport layer; and a metal electrode, wherein these elements are sequentially stacked.

Description

Non-toxic noble metal chalcogenide quantum dot nanocrystal-based infrared optical device and method for manufacturing the same

[0001] The present invention relates to an infrared optical device based on non-toxic noble metal chalcogenide quantum dot nanocrystals that is sensitive to an infrared light source in the near infrared region to the extended short infrared region, and a method for manufacturing the same.

[0002] Silver chalcogenides have attracted significant interest in various applications, such as memory, due to their excellent electrical properties, low thermal conductivity, and crystal structures that are sensitive to environmental conditions. These unique characteristics are interestingly reflected in nanocrystals. For example, silver telluride nanocrystals change their crystal structure under temperature and pressure, ultimately undergoing a phase transition from a semiconductor to a superionic conductor.

[0003] Although many studies have been conducted on silver telluride nanocrystals, their fundamental properties, including the bulk bandgap energy, an important parameter, have not been clearly determined. Silver telluride nanocrystals with a monoclinic α-Ag2Te structure have been reported, which have a distinct exciton peak in the near-infrared (NIR) region (approximately 1.2 μm). In addition, silver telluride nanocrystals have been reported to absorb in the NIR region, and they are monoclinic β phases (energy gap of ~0.67 eV) only below 145 °C, at which point they transform into a face-centered cubic structure (α-Ag2Te structure).

[0004] Meanwhile, silver telluride quantum dot nanocrystals exhibiting quantum dot confinement effects have been reported, and it has also been reported that silver telluride quantum dot nanocrystals were synthesized from CdTe colloidal quantum dot nanocrystals exhibiting photoluminescence (PL) in the NIR region (approximately 1.1 μm) through a cation exchange method. In addition, silver telluride quantum dot nanocrystals exhibiting optical characteristics in the NIR region have been reported.

[0005] However, the wavelength of silver telluride quantum dot nanocrystals is limited to the near-infrared (NIR) region and does not extend into the extended infrared. To realize deep-tissue imaging, long-distance communication in unmanned vehicles, and telecommunications through atmospheric windows, the wavelength needs to be extended into the extended infrared.

[0006] In the extended infrared region, various quantum dot nanocrystals, such as HgSe, HgS, HgTe, PbSe, and PbS, have been intensively studied over the past decade due to their outstanding optical and electrical properties. However, these nanocrystals have limitations, such as high toxicity and low stability when exposed to the atmosphere.

[0007] The present invention provides an infrared optical device, which is sensitive to an infrared light source in the near infrared region to the extended short infrared region, and includes a substrate; an electron transport layer; a first silver telluride quantum dot nanocrystal layer to which a halogen atom ligand is bonded; a second silver telluride quantum dot nanocrystal layer to which a thiol-based organic ligand is bonded; a hole transport layer; and a metal electrode, which are sequentially laminated.

[0008] However, the technical problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0009] The present invention provides an infrared optical device comprising a substrate; an electron transport layer; a first silver telluride quantum dot nanocrystal layer bonded with a halogen atom ligand; a second silver telluride quantum dot nanocrystal layer bonded with a thiol-based organic ligand; a hole transport layer; and a metal electrode, which are sequentially stacked.

[0010] The substrate may include an ITO layer formed on glass or sapphire.

[0011] The electron transport layer may include zinc oxide (ZnO) or tin oxide (SnO2).

[0012] In the first tellurium silver quantum dot nanocrystal layer, the halogen atom ligand may include at least one selected from the group consisting of chloride (Cl), bromide (Br), and iodide (I).

[0013] In the second tellurium silver quantum dot nanocrystal layer, the thiol-based organic ligand may include at least one selected from the group consisting of ethanethiol, 1,2-ethanedithiol, 1-hexanethiol, 1,6-hexanedithiol, and 3-mercaptopropionic acid.

[0014] The above hole transport layer is molybdenum oxide (MoO x ) may be included.

[0015] The above metal electrode may include at least one selected from the group consisting of silver (Ag), aluminum (Al), and gold (Au).

[0016] The above infrared optical device can be sensitive to an infrared light source in the near infrared region or the extended short infrared region.

[0017] The near-infrared region or extended short-infrared region may be in the range of 1.2 μm to 3.0 μm.

[0018] In one embodiment of the present invention, a method for manufacturing an infrared optical device is provided, comprising: (a) depositing an electron transport layer on a substrate; (b) coating a first silver telluride quantum dot nanocrystal ink having a halogen atom ligand bonded thereto on the electron transport layer to manufacture a first silver telluride quantum dot nanocrystal layer; (c) coating a second silver telluride quantum dot nanocrystal ink having a thiol-based organic ligand bonded thereto on the first silver telluride quantum dot nanocrystal layer to manufacture a second silver telluride quantum dot nanocrystal layer; and (d) sequentially depositing a hole transport layer and a metal electrode on the second silver telluride quantum dot nanocrystal layer.

[0019] Before the above step (c), a step of pre-treating a solution containing a thiol compound may be included.

[0020] An infrared optical device according to the present invention is characterized in that it is sensitive to an infrared light source in the near infrared region to the extended short infrared region (range of 1.2 μm to 3.0 μm) by sequentially stacking a substrate; an electron transport layer; a first silver telluride quantum dot nanocrystal layer to which a halogen atom ligand is bonded; a second silver telluride quantum dot nanocrystal layer to which a thiol-based organic ligand is bonded; a hole transport layer; and a metal electrode.

[0021] Accordingly, the infrared optical device according to the present invention not only has excellent external quantum efficiency but also has the advantage of low manufacturing cost, and is expected to be utilized in various scientific, military, and industrial fields.

[0022] Figure 1 is a schematic diagram showing the preparation of Halide-Ag2Te ink or MPA-Ag2Te ink in dimethylformamide (DMF) through ligand exchange and phase transition from OLA-Ag2Te CQDs in hexane (hex).

[0023] Figures 2(a) to (c) show the absorption spectrum, FTIR spectrum, and XPS spectrum of OLA-Ag2Te CQD, Halide-Ag2Te ink, or MPA-Ag2Te ink, respectively, and Figures 2(d) to (f) show the N 1s, I 3d, and S 2p in the high-resolution XPS spectrum of OLA-Ag2Te CQD, Halide-Ag2Te ink, or MPA-Ag2Te ink, respectively.

[0024] Figure 3(a) shows the results of measuring the space charge limited current (SCLC) of a device having various ratios of halide ligands, and Figure 3(b) shows the electron mobility and trap density obtained from the SCLC measurement of a device having various ratios of halide ligands.

[0025] Figures 4(a) and (b) show the ultraviolet photoelectron spectroscopy (UPS) spectra of CBI- and MPA-Ag2Te inks, respectively, Figure 4(c) shows the energy level alignment of the Ag2Te photodetector, and Figure 4(d) schematically shows the structure of the Ag2Te photodetector. Figure 4(e) shows a cross-sectional scanning electron microscope (SEM) image (scale bar: 500 nm) of the CI-Ag2Te photodetector, Figure 4(f) shows the current density (JV) curves of the Ag2Te photodetector with various ratios of halide ligands under dark conditions, and Figure 4(g) shows the JV curves of the CI-Ag2Te photodetector under dark (solid line) and illuminated (dotted line) conditions. Fig. 4(h) shows the external quantum efficiency (EQE) spectra of the CI-Ag2Te photodetector at bias voltages of 0, 0.2, and 0.3 V, and Fig. 4(i) shows the bias voltage-dependent photoresponse of the CI-Ag2Te photodetector.

[0026] Next-generation optoelectronic devices are desirable for combining wavelength-tunable, non-toxic infrared sensitivity and bipolar spectroscopy. Infrared colloidal quantum dots (CQDs) made of unbounded atomic species offer a solution for tunable bandgaps through quantum confinement effects and for designing doping properties at the atomic level. Ag2Te CQDs have been shown to possess a tunable bandgap across the extended shortwave infrared (eSWIR). However, conventional synthesis methods employ alkylthiol ligands, which hinder the ligand engineering and doping strategies required to create highly conductive Ag2Te CQD solids with controlled doping. In this invention, we report a novel synthesis process that utilizes alkylamine ligands to realize intrinsic and p-type Ag2Te CQD inks through facile ligand engineering. The resulting optical devices operated at a wavelength of approximately 1.7 μm, achieving an external quantum efficiency (EQE) of 16%. These performances demonstrate the potential of low-toxicity Ag2Te CQDs for infrared optoelectronics and sensing applications.

[0027]

[0028] In other words, the inventors of the present invention, while striving to expand the wavelength range that is non-toxic and has absorption and photoluminescence properties, first used an amine compound that is easily substituted as a ligand of a silver precursor, and then further treated the second silver precursor with a halide and a thiol compound, respectively, to cause ligand exchange and layer exchange, thereby producing silver telluride quantum dot inks in which halogen atom ligands and thiol organic ligands are each bonded, and applied these as the intrinsic / n-type layer and the p-type layer of an infrared optical device, respectively, thereby completing the present invention.

[0029]

[0030] In this specification, the term "near-infrared to extended near-infrared region" can be viewed as a concept of light that includes all of the near-infrared, short-infrared, or mid-infrared. In particular, "having photoluminescence properties in the near-infrared to extended near-infrared region" broadly means exhibiting photoluminescence (PL) within a range of 1.2 μm to 3.0 μm.

[0031]

[0032] Hereinafter, the present invention will be described in detail.

[0033]

[0034] Infrared optical device and method for manufacturing the same

[0035]

[0036] The present invention provides an infrared optical device comprising a substrate; an electron transport layer; a first silver telluride quantum dot nanocrystal layer bonded with a halogen atom ligand; a second silver telluride quantum dot nanocrystal layer bonded with a thiol-based organic ligand; a hole transport layer; and a metal electrode, which are sequentially stacked.

[0037] In addition, the present invention provides a method for manufacturing an infrared optical device, characterized by comprising the steps of: (a) stacking an electron transport layer on a substrate; (b) coating a first silver telluride quantum dot nanocrystal ink having a halogen atom ligand bonded thereto on the electron transport layer to manufacture a first silver telluride quantum dot nanocrystal layer; (c) coating a second silver telluride quantum dot nanocrystal ink having a thiol-based organic ligand bonded thereto on the first silver telluride quantum dot nanocrystal layer to manufacture a second silver telluride quantum dot nanocrystal layer; and (d) sequentially stacking a hole transport layer and a metal electrode on the second silver telluride quantum dot nanocrystal layer.

[0038]

[0039] In other words, the infrared optical device (or photodetector) according to the present invention comprises a substrate; an electron transport layer; a first silver telluride quantum dot nanocrystal layer to which a halogen atom ligand is bonded; a second silver telluride quantum dot nanocrystal layer to which a thiol-based organic ligand is bonded; a hole transport layer; and a metal electrode, which are sequentially laminated. This means that each layer is formed in contact with each other, and is not limited to not including a different configuration between each layer.

[0040]

[0041] First, the infrared optical device according to the present invention includes a substrate, and an electron transport layer for transporting electrons can be laminated on the substrate [step (a)].

[0042] The substrate may be an ITO layer formed on glass or sapphire. At this time, the thickness of the substrate (particularly, the ITO layer) may be 30 nm to 150 nm.

[0043] In addition, the electron transport layer may include zinc oxide (ZnO) or tin oxide (SnO2), and in particular, it is preferable to include zinc oxide (ZnO), but is not limited thereto. At this time, the thickness of the electron transport layer may be 30 nm to 300 nm.

[0044]

[0045] Next, a first silver telluride quantum dot nanocrystal layer having a halogen atom ligand bonded thereto, as a layer having intrinsic or n-type characteristics, can be deposited on the electron transport layer [step (b)].

[0046] In the first silver telluride quantum dot nanocrystal layer, the halogen atom ligand may include at least one selected from the group consisting of chloride (Cl), bromide (Br), and iodide (I), and although chloride (Cl) and iodide (I) are preferably included in view of further improving the external quantum efficiency of the finally manufactured infrared optical device, the present invention is not limited thereto. In some cases, an amine compound ligand may be partially bound. In this case, the thickness of the first silver telluride quantum dot nanocrystal layer may be 50 nm to 400 nm.

[0047]

[0048] The first silver telluride quantum dot nanocrystal layer can be manufactured by coating a first silver telluride quantum dot nanocrystal ink to which a halogen atom ligand is bound. In the first silver telluride quantum dot nanocrystal ink to which the halogen atom ligand is bound, the concentration of the first silver telluride quantum dot nanocrystal to which the halogen atom ligand is bound is preferably maintained at a relatively high concentration of 150 mg / mL to 400 mg / mL (preferably, 250 mg / mL to 350 mg / mL), but is not limited thereto.

[0049]

[0050] More specifically, the first silver telluride quantum dot nanocrystal ink having a halogen atom ligand bonded thereto can be manufactured by the steps of (b-1) preparing a first solution including Ag2Te quantum dot nanocrystals by injecting a tellurium precursor into a solution including a first silver precursor and an amine compound; and (b-2) further treating the prepared first solution with a second solution including a second silver precursor and a halide to cause ligand exchange and layer exchange. That is, as a method utilizing solution-phase ligand exchange and layer exchange, it has the advantage of being simple and easy compared to the layer-by-layer method.

[0051]

[0052] In the above step (b-1),

[0053] The first silver precursor is silver acetate, silver hexafluorophosphate, silver neodecanoate, silver nitrate, silver trifluoromethanesulfonate, silver carbonate, silver chloride, silver perchlorate, silver tetrafluoroborate, silver trifluoroacetate, silver 2-ethylhexanoate, silver fluoride, silver perchlorate hydrate, silver lactate, silver It is preferable that at least one selected from the group consisting of silver acetylacetonate, silver methanesulfonate, silver heptafluorobutyrate, silver chlorate, silver pentafluoropropionate, and silver hydrogenfluoride, but is not limited thereto. In a specific embodiment of the present invention, silver acetate was used as the first silver precursor.

[0054] The above amine-based compound is a ligand of the first silver precursor and is intended to temporarily bind to the Ag2Te quantum dot nanocrystals. At this time, the amine-based compound is characterized in that, compared to the thiol-based compound that has been conventionally used as a ligand of the silver precursor, the bonding force with the first silver precursor is not strong and substitution is easy. Specifically, the amine-based compound may include at least one selected from the group consisting of oleylamine, octylamine, aniline, 4,4'-bipyridine, p-phenylenediamine, ethylenediamine, and tris(2-aminoethyl)amine, and is preferably oleylamine, but is not limited thereto.

[0055] That is, since the amine-based compound corresponds to a ligand that is easily substitutable, it can facilitate further processing of the second silver precursor and the halide or thiol-based compound while bound to the Ag2Te quantum dot nanocrystal. Accordingly, the amine-based compound bound to the final non-stoichiometric silver telluride quantum dot nanocrystal is reduced through ligand exchange and layer exchange. If the additional processing amount of the second silver precursor is significant, the final non-stoichiometric silver telluride quantum dot nanocrystal may not be bound to the amine-based compound at all.

[0056] In addition, the molar ratio of the first precursor and the amine compound may be 1:20 to 1:60, and the molar ratio of the first precursor and the amine compound is preferably 1:30 to 1:40, but is not limited thereto.

[0057] The above tellurium precursor may be hydrophobic ligand-tellurium, and at this time, the hydrophobic ligand is preferably at least one selected from the group consisting of trioctylphosphine, oleylamine, dodecanethiol, trioctylphosphine oxide, tetraoctylammonium bromide, triphenylphosphine, and oleic acid, but is not limited thereto. In a specific embodiment of the present invention, trioctylphosphine-tellurium was used as the tellurium precursor.

[0058] The injection amount of the tellurium precursor needs to be adjusted so that the molar ratio of Ag ions and Te ions is 2:1. In addition, the injection of the tellurium precursor can be performed at 70°C to 120°C.

[0059] Accordingly, the Ag2Te quantum dot nanocrystals can be viewed as stoichiometric silver telluride quantum dots because the molar ratio of Ag ions and Te ions is 2:1.

[0060] Meanwhile, the first solution may include various known non-polar solvents, and in a specific embodiment of the present invention, hexane was used.

[0061]

[0062] In the above step (b-2),

[0063] The second silver precursor is silver nitrate, silver acetate, silver hexafluorophosphate, silver neodecanoate, silver trifluoromethanesulfonate, silver carbonate, silver chloride, silver perchlorate, silver tetrafluoroborate, silver trifluoroacetate, silver 2-ethylhexanoate, silver fluoride, silver perchlorate hydrate, silver lactate, silver It is preferable that at least one selected from the group consisting of silver acetylacetonate, silver methanesulfonate, silver heptafluorobutyrate, silver chlorate, silver pentafluoropropionate, and silver hydrogenfluoride, but is not limited thereto. In a specific embodiment of the present invention, silver acetate was used as the second silver precursor, similar to the first silver precursor.

[0064] The above halide is treated together with a second silver precursor to act as a halogen atom ligand, wherein the halogen atom ligand can bind to subsequently produced non-stoichiometric silver telluride quantum dot nanocrystals through ligand exchange and layer exchange. Specifically, the halide can include at least one selected from the group consisting of tetrabutylammonium chloride (TBAC1), tetrabutylammonium bromide (TBAC1), and tetrabutylammonium iodide (TBAI).

[0065] In addition, the molar ratio of the second silver precursor and the halide or thiol-based compound may be 1:1 to 1:60, and the molar ratio of the second silver precursor and the halide is preferably 1:1 to 1:10, and the molar ratio of the second silver precursor and the thiol-based compound is preferably 1:40 to 1:50, but is not limited thereto.

[0066] At this time, when the halide is further processed, an ink having intrinsic or n-type characteristics can be manufactured by acting as a halogen atom ligand on the subsequently manufactured non-stoichiometric silver telluride quantum dot nanocrystals through ligand exchange and layer exchange.

[0067] The second silver precursor has a smaller molar number than the first silver precursor, and the molar ratio of the first silver precursor and the second silver precursor may be 5:1 to 30:1, and is preferably 10:1 to 20:1, but is not limited thereto.

[0068] Following this additional processing, the diameter of the subsequently produced non-stoichiometric silver telluride quantum dot nanocrystals becomes larger, and the emission frequency can be further red-shifted as the molar ratio of Ag and Te increases non-stoichiometrically. In addition, as the molar ratio of Ag and Te increases non-stoichiometrically, the excess Ag acts as a sacrificial atom to prevent oxidation of the nanocrystals, resulting in excellent air stability. However, if the molar ratio of Ag and Te becomes too large, there is a limit as the amount of Te is not sufficient for further growth.

[0069] Meanwhile, the second solution may include various known polar solvents, and in a specific embodiment of the present invention, dimethylformamide was used.

[0070] The above ligand exchange refers to a state in which the amine-based compound bound to the subsequently manufactured non-stoichiometric silver telluride quantum dot nanocrystal is reduced, or a state in which no amine-based compound is bound to the subsequently manufactured non-stoichiometric silver telluride quantum dot nanocrystal.

[0071] The above layer exchange means that the subsequently manufactured non-stoichiometric silver telluride quantum dot nanocrystals move from the first solution to the second solution according to the above ligand exchange.

[0072] According to the method described above, in the subsequently manufactured first silver telluride quantum dot nanocrystal ink, the molar ratio of Ag and Te in the subsequently manufactured first silver telluride quantum dot nanocrystal may be greater than 2 and less than or equal to 5. At this time, by controlling the molar ratio of Ag and Te, the absorption and photoluminescence characteristics in the near-infrared region to the extended short-infrared region may be controlled. The near-infrared region to the extended short-infrared region may be in the range of 1.2 μm to 3.0 μm.

[0073]

[0074] Next, a second silver telluride quantum dot nanocrystal layer having p-type characteristics and having a thiol-based organic ligand bonded thereto can be laminated on the first silver telluride quantum dot nanocrystal layer [step (c)].

[0075] In the second silver telluride quantum dot nanocrystal layer, the thiol-based organic ligand may include at least one selected from the group consisting of ethanethiol, 1,2-ethanedithiol, 1-hexanethiol, 1,6-hexanedithiol, and 3-mercaptopropionic acid, and preferably includes 3-mercaptopropionic acid, but is not limited thereto. In some cases, an amine-based compound ligand may be partially bound. In this case, the thickness of the second silver telluride quantum dot nanocrystal layer may be 5 nm to 50 nm.

[0076]

[0077] The second silver telluride quantum dot nanocrystal layer can be manufactured by coating a second silver telluride quantum dot nanocrystal ink to which a thiol-based organic ligand is bound. In the second silver telluride quantum dot nanocrystal ink to which the thiol-based organic ligand is bound, the concentration of the second silver telluride quantum dot nanocrystal to which the thiol-based organic ligand is bound is preferably maintained at a relatively low concentration of 5 mg / mL to 50 mg / mL, but is not limited thereto.

[0078]

[0079] More specifically, the second silver telluride quantum dot nanocrystal ink having a thiol-based organic ligand bonded thereto can be manufactured by the steps of (c-1) preparing a first solution including Ag2Te quantum dot nanocrystals by injecting a tellurium precursor into a solution including a first silver precursor and an amine-based compound; and (c-2) further treating the prepared first solution with a second solution including a second silver precursor and a thiol-based compound to cause ligand exchange and layer exchange. That is, as a method utilizing solution-phase ligand exchange and layer exchange, it has the advantage of being simple and easy compared to the layer-by-layer method.

[0080] The above steps (c-1) and (c-2) can be performed in the same manner as the above steps (b-1) and (b-2) described above, except that the halide is replaced with a thiol compound.

[0081] The above thiol-based compound and optionally the halide are treated with a second silver precursor to function as a thiol-based organic ligand, wherein the thiol-based organic ligand can bind to the finally manufactured non-stoichiometric silver telluride quantum dot nanocrystals through ligand exchange and layer exchange. Specifically, the thiol-based compound may include at least one selected from the group consisting of ethanethiol, 1,2-ethanedithiol, 1-hexanethiol, 1,6-hexanedithiol, and 3-mercaptopropionic acid, and preferably includes 3-mercaptopropionic acid, but is not limited thereto.

[0082]

[0083] Meanwhile, before the step (c), a step of pre-treating a solution containing a thiol-based compound may be included. By pre-treating the solution containing such a thiol-based compound, an intrinsic / n-type layer and a p-type layer can be laminated separately. At this time, in the solution containing the thiol-based compound, the concentration of the thiol-based compound may be 0.1 (v / v)% to 20 (v / v)%, and is preferably 1 (v / v)% to 10 (v / v)%, but is not limited thereto.

[0084]

[0085] Next, a hole transport layer and a metal electrode can be sequentially stacked on the second silver telluride quantum dot nanocrystal layer [step (d)].

[0086] The above hole transport layer is molybdenum oxide (MoO x ) may be included. At this time, the thickness of the hole transport layer may be 5 nm to 20 nm.

[0087] Additionally, the metal electrode may include at least one selected from the group consisting of silver (Ag), aluminum (Al), and gold (Au). At this time, the thickness of the metal electrode may be 30 nm to 200 nm.

[0088]

[0089] As reviewed above, the infrared optical device according to the present invention is characterized in that it is sensitive to an infrared light source in the near infrared region to the extended short infrared region (range of 1.2 μm to 3.0 μm) by sequentially stacking a substrate; an electron transport layer; a first silver telluride quantum dot nanocrystal layer bonded with a halogen atom ligand; a second silver telluride quantum dot nanocrystal layer bonded with a thiol-based organic ligand; a hole transport layer; and a metal electrode.

[0090] Accordingly, the infrared optical device according to the present invention not only has excellent external quantum efficiency but also has the advantage of low manufacturing cost, and is expected to be utilized in various scientific, military, and industrial fields.

[0091]

[0092] Hereinafter, preferred examples are presented to aid in understanding the present invention. However, the following examples are provided solely to facilitate a better understanding of the present invention, and the scope of the present invention is not limited by the following examples.

[0093]

[0094] [Example]

[0095] Example 1: Preparation of non-toxic noble metal chalcogenide quantum dot ink (Halide-Ag2Te ink)

[0096] (1) Synthesis of OLA-Ag2Te CQDs

[0097] Under a nitrogen flow, 4 mmol of silver acetate (AgAc) was dissolved in 40 mL of a 121.6 mmol solution of pre-degassed oleylamine (OLA) in a three-necked round-bottom flask. When the solution temperature reached the desired temperature (70–130 °C), 2 mL of 1 M trioctylphosphine-Te (TOP-Te) was rapidly injected into the flask. After the reaction time, the solution was quenched with a water bath. The Ag2Te CQD solution was precipitated with isopropyl and methanol to remove the residue, and the product was redispersed in hexane and stored.

[0098] (2) Preparation of Halide-Ag2Te ink

[0099] A ligand-exchange stock solution was prepared by dissolving 0.25 mmol of AgAc, 0.25 mmol of tetrabutylammonium chloride (TBACl), 0.25 mmol of tetrabutylammonium bromide (TBABr), and 0.25 mmol of tetrabutylammonium iodide (TBAI) in 10 mL of DMF, respectively. 3 mL of the ligand-exchange stock solution was mixed with 4 mL of the Ag2Te CQD solution (6.25 mg / mL) in a falcon tube and vortexed. After ligand exchange and phase transition, the hexane layer was removed. The halide-Ag2Te solution was washed with hexane three times by vortexing and precipitated with toluene. The product was redispersed in a mixture of DMF and ACN (300 mg / mL).

[0100]

[0101] Example 2: Preparation of non-toxic noble metal chalcogenide quantum dot ink (MPA-Ag2Te ink)

[0102] The same procedure as in Example 1 was followed, except that a ligand exchange stock solution was prepared by dissolving a mixture of 0.25 mmol of AgAc, 11.5 mmol of 3-mercaptopropionic acid (MPA), and 0.1 mmol of tetrabutylammonium iodide (TBAI) in 10 mL of DMF.

[0103]

[0104] Example 3: Fabrication of a photodetector

[0105] A 120 nm thick ZnO layer was deposited on a 70 nm thick ITO substrate using a conventional sol-gel method. Then, a 150 nm thick intrinsic layer was deposited on the ZnO / ITO substrate by spin-coating the halide-Ag2Te ink (300 mg / mL) prepared in Example 1 at 2000 rpm for 30 s. Then, the substrate was pretreated with an IPA solution containing 5 (v / v)% MPA for 15 s and washed three times with IPA. Then, a 20 nm thick p-type layer was deposited by spin-coating the MPA-Ag2Te ink (30 mg / mL) prepared in Example 2 at 2000 rpm for 30 s. Then, a 10 nm thick MoO was deposited using a thermal evaporator. x Layers and 100 nm thick aluminum electrodes were sequentially laminated.

[0106]

[0107] Experimental Example: Characterization of Non-Toxic Precious Metal Chalcogenide Quantum Dot Inks

[0108] (1) UV-Vis absorption measurement

[0109] UV-vis absorption data were collected at 5 nm resolution from 600–2000 nm using a LAMBDA 1050+ spectrometer.

[0110] (2) FTIR measurement

[0111] Thermofisher iS50, 8000-450 cm -1 , resolution 0.4 cm -1 , FTIR measurements were performed in attenuated total reflection (ATR) mode.

[0112] (3) XPS measurement

[0113] XPS measurements were performed using a K-alpha model with a monochromatic Al X-ray source (Al Kα line: 1486.6 eV). The XPS results were calibrated to a C 1s value of 284.8 eV.

[0114] (4) UPS measurement

[0115] Nexsa with He(I) at energy 21.22 eV TM UPS spectra were measured using an X-ray photoelectron spectrometer.

[0116] (5) JV curve and EQE measurement

[0117] A Keithley 2400 source meter was used for current-voltage measurements via a voltage sweep mode from -1 V to +1 V in 0.02 V steps without any gap delay time. The EQE of the devices was measured using an EnlinTech QE-R quantum efficiency analyzer, 350–1750 nm, 10 nm resolution, and mechanically truncated monochromatic light at 210 Hz.

[0118] (6) Speed ​​measurement

[0119] The time response of the device was measured using an oscilloscope (DSO8104A Infinium, Agilent). A 1310 nm diode laser (Thorlabs ML725B8F) modulated at 10 kHz by a function generator (Agilent 33220A) was used as the light source. 10 3 VA -1 The Femto DHPCA-100 preamplifier of the setup was used to amplify the photodetector signal.

[0120]

[0121] Ink-phase CQDs are often prepared by a two-phase in-solution exchange method, in which two immiscible solvents are vigorously mixed with the ligand of interest dissolved in the opposite phase of the CQDs. Conventionally, Ag2Te CQDs synthesized with alkylthiols cannot efficiently cross the layer boundary because the thiols are tightly bound to the CQD surface. Conventional metal halides, such as tetrabutylammonium hydroxide (TBAX), assist in the ligand exchange process, and shorter alkylthiol ligand exchange methods are less effective in generating ink-phase CQDs synthesized with alkylthiols. Therefore, we modified the conventional synthesis method to produce Ag2Te CQDs passivated with oleylamine (OLA) to facilitate the ligand exchange process. Alkylamines, such as OLA, are L-type ligands that bind to the surface metal atoms of the nanocrystals. They act as reducing and capping agents that control the growth of the nanoparticles. Alkylamines have been widely used as stable ligands to synthesize Ag nanoparticles. Due to the weak bonding with alkylamines, Ag2Te CQDs prepared by a modified synthesis demonstrated effective ligand exchange and ink dispersibility. Briefly, the modified synthesis involved mixing pre-degassed OLA with silver acetate in a three-necked flask under a nitrogen flow. Because the silver precursor dissolved in OLA rapidly generates silver nanoparticles at room temperature and even more rapidly at elevated temperatures, it was essential to rapidly increase the temperature of the OLA-Ag precursor solution to the desired temperature. A trioctylphosphine-tellurium (TOP-Te) solution was injected into the OLA-Ag precursor, and crystal growth was effectively terminated by rapid temperature quenching. To improve the monodispersity of the CQDs, a size-selective washing process with isopropyl alcohol was performed to remove byproducts and large-sized CQDs, and the solution was finally dispersed in hexane.

[0122] To replace the original ligands with new ligands for efficient charge transport and to generate intrinsic and p-type Ag2Te QD inks, the inventors used an in-solution exchange process using halide and MPA ligands, respectively (Fig. 1). The synthesized Ag2Te CQDs (OLA-Ag2Te) dispersed in a nonpolar solvent were mixed with a polar ligand-exchanged storage solution to obtain a nonpolar (ε r =1.88, hexane) and polar solvents (ε r =36.71, DMF) promoted ligand exchange across the layer boundaries between the phases. Halide ligand exchange reservoir solutions were prepared by mixing silver acetate with TBAX (X=Cl, Br, I) and dissolved in dimethylformamide (DMF) without noticeable precipitation. In these solutions, TBAX reacted with the silver precursor to form silver halide complexes that were highly soluble in DMF. MPA ligand exchange reservoir solutions were prepared by mixing silver acetate, MPA, and TBAI in DMF. Both halide and MPA ligand exchange required silver complexes in the reservoir solutions to promote the processes. It is worth noting that ligand exchange for alkylthiol-capped Ag2Te CQDs was not effective even with increased concentration reservoir solutions (Figure 1). The final ink product was thoroughly washed to remove any residues from the solution. The MPA-passivated Ag2Te QD ink was found to have a relatively higher band edge level than the halide ink due to the surface dipoles, as demonstrated in various systems. Both the halide and MPA ligand-exchanged inks exhibited excellent colloidal stability in pure DMF solvent for over 40 days without any evidence of precipitation.

[0123] Figure 2(a) shows the absorption spectra of Ag2Te CQDs before and after the ligand exchange process. Each Ag2Te CQD sample for the intrinsic and p-type ink bases was carefully selected to form a successful junction in the nip architecture. To prepare the halide-Ag2Te ink for infrared photodetectors, OLA-Ag2Te CQDs exhibiting a bandgap energy at 1450 nm were synthesized. For the p-type Ag2Te CQDs, we used a relatively small particle size (d = ~4 nm) to have a bandgap at 1050 nm, which enabled efficient blocking of photogenerated electrons while transferring holes to the collection electrode. Interestingly, a significant redshift in the bandgap wavelength was observed after the ligand exchange process, suggesting particle size growth promoted by the silver precursor in the exchange solution, which was also confirmed by the linewidth broadening of the XRD pattern.

[0124] The surface ligands of Ag2Te CQDs were characterized using Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) (Fig. 2(b)-(f)). The FTIR spectrum of OLA-Ag2Te CQDs showed a peak at ~2922 cm corresponding to the asymmetric and symmetric stretching vibrations of CH2 of OLA. -1 and ~2851 cm -1 showed distinct peaks at . The bending and stretching vibration modes of NH2 of OLA ligand were at ~1600 and 3300 cm, respectively. -1 In contrast, the Halide- and MPA-QD inks showed a significant decrease in the peak intensity of the vibrational mode of the OLA ligand. The FTIR spectrum of the Halide-Ag2Te QD ink showed a TBA in the exchanged CQD solution. + The presence of residues was indicated. MPA-Ag2Te CQDs (MPA-Ag2Te) ink showed a free carboxylic acid at 1710 cm -1exhibited C=O stretching, indicating the presence of MPA ligands that passivate the nanocrystal surface through thiol termini. For reference, the bound carboxylate had a peak at 1520 cm -1 It shows a peak of C=O bond, which was not observed in the present invention.

[0125] XPS spectra before and after ligand exchange showed striking changes in the carbon, nitrogen, and iodine binding energy spectra (Fig. 2(c)). A strong NH bond was observed in the N 1s scan at 399.3 eV, indicating the presence of OLA ligands in the synthesized Ag2Te CQDs, whereas the halide- and MPA-Ag2Te CQDs showed a significant decrease in the intensity of the NH peak (Fig. 2(d)). After ligand exchange, the halide and MPA ligands binding to the Ag2Te CQDs were examined by high-resolution XPS spectra. Depending on the halide ligand combination, the binding peaks of I, Cl, and Br ligands were indicated at 619.1, 200, and 68 eV, respectively (Fig. 2(e)). For the MPA-Ag2Te CQDs, the S 2p scan suggested a well-passivated surface with thiol ligands, which was consistent with our previous results (Fig. 2(f)). Based on the FTIR and XPS spectra, the inventors concluded that the original OLA ligands were effectively removed from the Ag2Te CQD surface and successfully replaced with the desired ligands.

[0126] We investigated the crystal structures of OLA-, halide-, and MPA-Ag2Te CQDs using X-ray diffraction (XRD). The XRD patterns did not show significant changes after the ligand exchange process. The spectra were consistent with monoclinic Ag2Te. The sharpening of the XRD patterns after ligand exchange indicated an increase in the size of the Ag2Te CQDs during the ligand exchange process, according to the Scherrer equation (where D, λ, K, β, and θ are the mean particle diameter (Å), the wavelength of X-ray radiation (Å), the crystal shape factor, the full width at half maximum of the XRD peak, and the Bragg angle, respectively). Using space charge limited current (SCLC) measurements, the trap density and carrier mobility for electrons in the halide-Ag2Te CQD films were determined for various combinations of halide ligands (Fig. 3(a), (b)). The structure of the ITO / ZnO / intrinsic Ag2Te / LiF / Al device was used to allow electrons to flow freely while holes were blocked. The current density (JV) curves exhibited a slope change from the ohmic regime to the trap-filling limit (TFL); subsequently, increasing the voltage showed another slope change when the space charge regime was reached. From the SCLC results, the carrier mobility (μ) was calculated by the following equation.

[0127] Equation (1)

[0128] Here J, ε0, ε r (Ag2Te= 25), V and L are current density, vacuum permittivity, relative permittivity, applied voltage, and thickness of Ag2Te film, respectively.

[0129] The obtained values ​​for CBI- and CI-Ag2Te films were 5.6×10 -2 and 8.0×10 -2 cm 2 v -1 s -1 , and has higher mobility than previously reported lead chalcogenide CQDs. - , Br - , I- (CBI) and Cl - , I - Voltage (V) reached in the trap-filling regime of (CI)-Ag2Te films TFL ) are 0.141 and 0.139 V, respectively, indicating a slightly lower trap state density for the CI-Ag2Te film. The trap density (ρ) of the CBI- and CI-Ag2Te films Tr ) is estimated as follows.

[0130] Equation (2)

[0131] Here, e is the elementary charge. As shown in Fig. 3(b), ρ of each film Tr Each is 1.3×10 16 and 6.2×10 15 cm -3 , CBI-Ag2Te and CI-Ag2Te. The calculated results show that Br ligands increase the trap density of the film.

[0132] To evaluate the band alignment of the Ag2Te photodetector device, ultraviolet photoelectron spectroscopy (UPS) was performed. Figure 4(a) shows the UPS spectrum of the halide-Ag2Te CQD. The valence band (VB) energy levels of the halide-Ag2Te QD ink were calculated from a linear fitting of the UPS spectrum, and the bandedge values ​​were determined by evaluating the absorption spectrum. The VB of the MPA-Ag2Te QD ink was obtained using the same method (Figure 4(b)). Figure 4(c) shows the energy level diagram vs. vacuum level of the Ag2Te photodetector device.

[0133] While MPA-Ag2Te CQDs exhibited p-type characteristics, halide-Ag2Te CQDs exhibited intrinsic characteristics. Therefore, MPA-Ag2Te CQDs were ideal for forming a p-type layer in nip Ag2Te devices to effectively block electrons. In IR photodetectors, zinc oxide (ZnO) NCs served as an electron transport layer (ETL) in a similar manner to conventional methods. In addition, molybdenum oxide (MoO x ) served as a hole transport layer (HTL) that efficiently blocks electron back-injection.

[0134] The device structure of the Ag2Te photodetector is shown in Fig. 4(d) as glass / ITO / ZnO NC / CI-Ag2Te / MPA-Ag2Te / MoO x / Al was indicated. The intrinsic and p-type layers (halide and MPA) were deposited on the ZnO NCs via spin-coating. The thickness of the CQD film was determined to be ~150 nm as measured by cross-sectional scanning electron microscopy (SEM) images (Fig. 4(e)).

[0135] We observed significant differences in the dark current characteristics between the CI and CBI devices (Fig. 4(f)). The lower dark current and increased rectification ratio in reverse bias of the CI device are a result of the lower trap state density and corresponding energy dissipation pathways, which are consistent with the trends observed in the SCLC measurements. Under simulated sunlight illumination, we measured the short-circuit current (19.4 mA / cm) of the CI device. 2 ) was measured, which is the short-circuit current of the CBI element (17.5 mA / cm 2 ) was significantly higher than that of the CBI and CI elements, while the open circuit voltage did not increase significantly, as shown in Fig. 4(g). Although the thickness and fabrication method of the CBI and CI elements did not differ significantly, the trap density and I SC Because they are different from each other, the Ag2Te devices suggest that future optimization of the halide complex on the CQD surface may expand the possibility of achieving better performance.

[0136] The external quantum efficiency (EQE) spectra of the CI device were measured under various bias conditions (Fig. 4(h)). The CI device exhibited a significantly improved EQE compared to the CBI device, reaching a maximum of 16% at a bias voltage of 0.3 V at the exciton absorption peak at 1700 nm, whereas the EQE of the CBI device was limited to 2%. The EQE of the CI device was the highest among previous reports on Ag2Te CQD-based optical devices. The temporal photoresponse of the CI device under 1310 nm laser light is shown in Fig. 4(i) for biases of 0, 0.2, and 0.3 V. As the bias voltage increased, the fall time decreased to 2.7 μs.

[0137]

[0138] In conclusion, we demonstrated a Ag2Te CQD infrared optical device with an EQE of 16% at 1.7 μm at room temperature, and to realize it, we had to develop a process for producing bipolar Ag2Te QD inks. To this end, we developed a novel synthetic process in which the original ligand can be exchanged with a halide for native CQDs and with MPA for p-type CQDs. We demonstrated that the type of halide affects charge carrier transport and trap state density, where a mixture of chloride and iodide showed the best properties for the optical device. The optical device fabricated with this material exhibited an EQE of 19.4 mA / cm under sunlight illumination. 2 The photodetector exhibited a short-circuit current of 100 V, an EQE of 16% at 0.3 V, and a photoresponse time of 2.7 μs. These results highlight the potential of Ag2Te CQD-based photodetectors for extending photodetection capabilities to the eSWIR range through non-toxic materials and infrared optoelectronic applications.

[0139]

[0140] The foregoing description of the present invention is for illustrative purposes only. Those skilled in the art will readily appreciate that the present invention can be readily modified into other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. Substrate; electron transport layer; A first silver telluride quantum dot nanocrystal layer having a halogen atom ligand bonded thereto; A second silver telluride quantum dot nanocrystal layer bonded with a thiol-based organic ligand; hole transport layer; and An infrared optical device comprising sequentially stacked metal electrodes.

2. In paragraph 1, An infrared optical device, characterized in that the substrate comprises an ITO layer formed on glass or sapphire.

3. In paragraph 1, An infrared optical device, characterized in that the electron transport layer comprises zinc oxide (ZnO) or tin oxide (SnO2).

4. In paragraph 1, An infrared optical device in which, in the first tellurium silver quantum dot nanocrystal layer, the halogen atom ligand includes at least one selected from the group consisting of chloride (Cl), bromide (Br), and iodide (I).

5. In paragraph 1, An infrared optical device, wherein in the second tellurium silver quantum dot nanocrystal layer, the thiol-based organic ligand comprises at least one selected from the group consisting of ethanethiol, 1,2-ethanedithiol, 1-hexanethiol, 1,6-hexanedithiol, and 3-mercaptopropionic acid.

6. In paragraph 1, The above hole transport layer is molybdenum oxide (MoO x ) characterized by including an infrared optical device.

7. In paragraph 1, An infrared optical device, characterized in that the metal electrode comprises at least one selected from the group consisting of silver (Ag), aluminum (Al), and gold (Au).

8. In paragraph 1, An infrared optical device characterized in that the above infrared optical device is sensitive to an infrared light source in the near infrared region or the extended short infrared region.

9. In paragraph 8, An infrared optical device, characterized in that the near-infrared region or the extended short-infrared region is in the range of 1.2 ㎛ to 3.0 ㎛. 10.(a) A step of laminating an electron transport layer on a substrate; (b) a step of manufacturing a first silver telluride quantum dot nanocrystal layer by coating a first silver telluride quantum dot nanocrystal ink having a halogen atom ligand bonded thereto on the electron transport layer; (c) a step of manufacturing a second silver telluride quantum dot nanocrystal layer by coating a second silver telluride quantum dot nanocrystal ink having a thiol-based organic ligand bonded thereto on the first silver telluride quantum dot nanocrystal layer; and (d) A method for manufacturing an infrared optical device, characterized in that it comprises a step of sequentially stacking a hole transport layer and a metal electrode on the second tellurium silver quantum dot nanocrystal layer.

11. In paragraph 10, A method for manufacturing an infrared optical device, characterized in that it comprises a step of pre-treating a solution containing a thiol compound before the above step (c).

Images