Alkali metal quaternary nanomaterials

Abstract

The present disclosure relates to alkali metal quaternary crystalline nanomaterials having the general formula A: I2-II-IV-VI4, where I is sodium (Na) or lithium (Li), II and IV are Zn or Sn, and VI is a chalcogen selected from the group consisting of sulfur (S), selenium (Se), and tellurium (Te). The crystalline phase of the alkali metal quaternary crystalline nanomaterials may be a simple mixed Cu-Au-like structure (PMCA), and has the space group: The nanomaterial may have a structure similar to that of the nanomaterial described above.

Description

[Technical Field]

[0001] The present disclosure relates to the production of alkali metal quaternary crystalline nanomaterials. [Background technology]

[0002] In the African and developing country context, providing a constant and reliable electricity supply in rural and informal settlements not connected to the formal electricity grid remains a challenge, especially when it comes to providing lighting.

[0003] The lack of proper infrastructure often requires the use of candles or kerosene lamps, which pose safety and health risks. Innovative and cost-effective solutions are needed to remedy this problem.

[0004] Solar power generation has been widely investigated to improve access to electricity and to provide a stable power supply. Of particular importance are the relatively small size of solar panels, which can be manufactured effectively and cheaply, easily transported to remote areas, and provide reliable power. In recent years, thin-film solar cells have been investigated as an efficient solar cell.

[0005] Quaternary materials, such as zinc pyrite (or kesterite)-based structures with the general formula I2-II-IV-VI4, are particularly promising. Thin-film solar cells based on zinc pyrite have a maximum efficiency of 12.6%, but this figure remains low.

[0006] The main technical challenge of existing zinc pyrite-based thin-film solar cells is the open-circuit voltage (V oc ) is insufficient. ocThe shortcoming is the presence of many defects and disorders within the crystal structure, which affect the electronic band structure of the absorber and consequently limit the photovoltaic conversion efficiency. Although other quaternary materials have been synthesized, maintaining the zinc pyrite-based structure has been shown to be advantageous and superior to other structures, such as pyrite-based structures.

[0007] Generally, attention has focused on the transition metals in zinc pyrite, with copper-containing zinc pyrites such as Cu2ZnSnSe4 (CZTSe) being representative. Because transition metal chemistry is highly specialized, and to avoid changing the structure of the zinc pyrite system to a different crystalline form, prior art variations of zinc pyrite have only involved minimal doping with other metals to improve the noted limiting inefficiencies. However, excessive doping risks causing a space group change that adversely affects efficiency. Zinc pyrite possesses a unique packing arrangement in the space group: TIFF0007805006000001.tif911. Prior art has shown that certain crystal phases provide efficiency of use, which is a disincentive to altering the zinc pyrite crystal phase.

[0008] Furthermore, known methods for synthesizing quaternary materials use harsh synthesis conditions, are difficult to reproduce, and once synthesized, cannot be compacted to suit the manufacturing methods for quaternary solar cells, which require solution-based synthesis techniques.

[0009] New and innovative nanomaterials are needed for use in solar cells and a sustainable energy economy, as well as less harsh, more cost-effective and less time-consuming synthesis methods. Summary of the Invention

[0010] According to a first aspect of the present disclosure, a compound of general formula A: I2‐II‐IV‐VI4 An alkali metal quaternary crystalline nanomaterial is provided, having wherein I can be sodium (Na) or lithium (Li); II and IV may be transition metals; VI may be a chalcogen containing sulfur (S), selenium (Se), or tellurium (Te); And the crystalline phase of the crystalline nanomaterial must not be zinc pyrostanium and / or pyrostanium (or stannite).

[0011] The crystalline phase of the alkali metal quaternary crystalline nanomaterials is a primitive mixed Cu-Au-like structure (PMCA) (space group: TIFF0007805006000002.tif818).

[0012] In Formula A, I can be Li, II can be Zn, IV can be Sn, and VI can be Se, such that the alkali metal quaternary crystalline nanomaterial can be Li2ZnSnSe4 (LZTSe), and the crystalline phase of the nanomaterial can be a simple mixed Cu-Au-like structure (PMCA), and the nanomaterial can be in the space group: TIFF0007805006000003.tif818 may be included.

[0013] In Formula A, I can be Na, II can be Zn, IV can be Sn, and VI can be Se, such that the alkali metal quaternary crystalline nanomaterial can be Na2ZnSnSe4 (NZTSe), and the crystalline phase of the nanomaterial can be a simple mixed Cu-Au-like structure (PMCA), and the nanomaterial can be in the space group: TIFF0007805006000004.tif818 may be included.

[0014] In Formula A, I can be Li, II can be Zn, IV can be S, and VI can be S, such that the alkali metal quaternary crystalline nanomaterial can be Li2ZnSnS4 (LZTS), and the crystalline phase of the nanomaterial can be a simple mixed Cu-Au-like structure (PMCA), and the nanomaterial can be in the space group: TIFF0007805006000005.tif818 may be included.

[0015] In Formula A, I can be Na, II can be Zn, IV can be Sn, and VI can be S, such that the alkali metal quaternary crystalline nanomaterial can be Na2ZnSnS4 (NZTS), and the crystalline phase of the nanomaterial can be a simple mixed Cu-Au-like structure (PMCA), and the nanomaterial can be in the space group: TIFF0007805006000006.tif818 may be included.

[0016] The alkali metal quaternary crystalline nanomaterial may be Li2ZnSnSe4 (LZTSe), and the crystalline phase may be zinc pyrite and / or pyrite-free, and may be a simple mixed Cu-Au-like structure (PMCA) (space group: TIFF0007805006000007.tif818).

[0017] The alkali metal quaternary crystalline nanomaterial may be Na2ZnSnSe4 (NZTSe), and the crystalline phase may be zinc pyrite and / or pyrite-free, and may be a simple mixed Cu-Au-like structure (PMCA) (space group: TIFF0007805006000008.tif818).

[0018] The alkali metal quaternary crystalline nanomaterial may be Li2ZnSnS4 (LZTS), and the crystalline phase may be zinc pyrite and / or pyrite, but not be a simple mixed Cu-Au-like structure (PMCA) (space group: TIFF0007805006000009.tif818).

[0019] The alkali metal quaternary crystalline nanomaterial may be Na2ZnSnS4 (NZTS), and the crystalline phase may be zinc pyrite and / or pyrite, but not be a simple mixed Cu-Au-like structure (PMCA) (space group: TIFF0007805006000010.tif818).

[0020] Alkali metal quaternary crystalline nanomaterials according to the present disclosure may be provided as nanoparticles.

[0021] The alkali metal quaternary crystalline nanomaterials may be adapted to provide photovoltaic cells.

[0022] Applicants have surprisingly provided alkali metal quaternary crystalline nanomaterials of general formula A, in which the crystalline phase is not zinc pyrite or pyrite. The unique solid-state properties of the alkali metal quaternary crystalline nanomaterials of the present disclosure provide enhanced physicochemical properties. Without being limited by theory, the enhanced physicochemical properties may be due to quantum confinement effects facilitated by the unique crystalline structure, and / or size and / or morphology, of the alkali metal quaternary crystalline nanomaterials described herein.

[0023] According to a second aspect of the present disclosure, there is provided a method for chemically synthesizing an alkali metal quaternary crystalline nanomaterial having general formula A according to the first aspect of the present disclosure, the method comprising: dissolving a VI selected from the group consisting of sulfur (S), selenium (Se), and tellurium (Te) in an amphiphilic capping agent under inert conditions to form a first solution; heating the solvent under reflux to about 75°C to about 120°C, preferably about 100°C, to form a second solution; mixing the first and second solutions and heating to about 120°C to about 220°C, preferably about 200°C, to form a third solution; dissolving at least one of the group consisting of CuCl, LiCl, Li(acac), LiS, and NaCl in the amphiphilic capping agent to form a fourth solution; adding the fourth solution to the third solution to form a fifth solution; adding at least one of zinc chloride or tin chloride to the fifth solution to form a sixth solution; and heating the sixth solution at about 120°C to about 220°C, preferably about 200°C, for 30 minutes to 2 hours, preferably 1 hour; Includes:

[0024] The method may further comprise the step of adding a flocculating agent, preferably an alcohol.

[0025] The method may further comprise the step of washing away excess capping agent.

[0026] The method may further comprise a step of centrifuging to provide for recovery of the alkali metal quaternary crystalline nanomaterial.

[0027] The capping agent may be one of the group consisting of hexadecylamine, oleic acid, trioctylphosphine oxide, and oleylamine.

[0028] The solvent may be one of the group consisting of hexadecylamine, oleic acid, trioctylphosphine oxide, and oleylamine. It should be understood that the capping agent may include at least four roles in use: capping the nanoparticles; controlling the growth of crystalline nanomaterials; providing a high boiling point solvent; and providing a reducing agent.

[0029] According to a third aspect of the present disclosure, there is provided a solar cell comprising a substrate to which the alkali metal quaternary crystalline nanomaterial of the first aspect is applied.

[0030] The substrate may be molybdenum coated glass.

[0031] The alkali metal quaternary crystalline nanomaterials may be applied to the substrate by means of coating, preferably spin coating.

[0032] The solar cell may further include a CdS coating.

[0033] The solar cell may further include a ZnO coating.

[0034] The solar cell may further include Al.

[0035] Typically, solar cells are provided in a layered arrangement, preferably arranged in layers such as a sandwich.

[0036] According to a fourth aspect of the present disclosure, there is provided a method for manufacturing a solar cell according to the third aspect, the method comprising: (i) providing a solution of the alkali metal quaternary crystalline nanomaterial of the first aspect in a solvent, preferably toluene; (ii) coating, preferably spin-coating, the solution of alkali metal quaternary crystalline nanomaterial onto the molybdenum-coated glass substrate to form an alkali metal quaternary crystalline nanomaterial-coated substrate; (iii) drying the alkali metal quaternary crystalline nanomaterial-coated substrate at about 60°C to 80°C; (iv) providing a solution of CdS in a solvent, preferably toluene; (v) coating, preferably spin-coating, the dried alkali metal quaternary crystalline nanomaterial coated substrate with the CdS solution to provide a CdS coated substrate; and (vi) Coating, preferably spin-coating, ZnO onto the CdS-coated substrate. Includes:

[0037] In a preferred embodiment, the manufacturing process is carried out in the aforementioned order to provide a sandwich layered arrangement.

[0038] The method may further comprise depositing (or splattering) aluminum onto the CdS coated substrate, preferably under thermal evaporation in high vacuum. There is further provided anything substantially as described, illustrated and / or exemplified herein with reference to any one of the Examples and / or Figures herein. [Brief explanation of the drawings]

[0039] [Figure 1] 1A-1C show the crystal structures of prior art CZTSe, (a) zinc pyrithione, and (b) pyrithione. [Figure 2] FIG. 1 shows XRD patterns of CZTSe, LZTSe, and NZTSe according to the present disclosure. [Figure 3] FIG. 1 shows Raman spectra of (a) CZTSe, (b) LZTSe, and (c) NZTSe. [Figure 4] TEM images of (a) CZTSe, (b) LZTSe, and (c) NZTSe. [Figure 5] 1A-1B show solar cell designs according to the present disclosure (a) shown diagrammatically and (b) as photographs of fabricated exemplary embodiments. [Figure 6] FIG. 1 shows J-V curves for devices derived from (a) CZTSe, (b) LZTSe, and (c) NZTSe. [Figure 7] FIG. 1 shows a synthesis procedure for LZTS. [Figure 8] 1 shows PMCA structures of (a) zinc pyrite, (b) pyrite, and (c) LZTS. [Figure 9ab] X-ray diffraction patterns of LZTS nanoparticles synthesized using a lithium source, LiCl, at precursor ratios of (a) 1:1:1:1 and (b) 2:1:0.25:2 are shown. [Figure 9cd] X-ray diffraction patterns of LZTS nanoparticles synthesized using a lithium source Li(acac) at precursor ratios of (c) 1:1:1:1 and (d) 2:1:0.25:2 are shown. [Figure 9ef]X-ray diffraction patterns of LZTS nanoparticles synthesized using a lithium source, Li2S, with precursor ratios of (e) 1:1:1:1 and (f) 2:1:0.25:2 Li2S. [Figure 10] TEM micrographs of LZTS nanoparticles synthesized using different lithium sources (LiCl, Li(acac), and LiS) at different precursor ratios (1:1:1:1 and 2:1:0.25:2): (a) using LiCl as a lithium source at a precursor ratio of 1:1:1:1; (b) using LiCl as a lithium source at a precursor ratio of 2:1:0.25:2; (c) using Li(acac) as a lithium source at a precursor ratio of 1:1:1:1; (d) using Li(acac) as a lithium source at a precursor ratio of 2:1:0.25:2; (e) using LiS as a lithium source at a precursor ratio of 1:1:1:1; and (f) using LiS as a lithium source at a precursor ratio of 2:1:0.25:2. [Figure 11] FIG. 1 shows the 7Li-MAS-NMR spectra of LiCl, Li(acac), and Li2S, and the corresponding LZTS spectra. [Figure 12] Figure 1 shows Tauc plots obtained from UV-visible absorption spectra of LZTS nanoparticles synthesized using different lithium sources ((a) LiCl, (b) Li(acac), (c) LiS) at different precursor ratios (1:1:1:1, 2:1:0.25:2). [Figure 13] FIG. 1 shows the Raman spectrum of LZTS nanoparticles synthesized using a lithium source, Li2S, in a precursor ratio of 2:1:0.25:2. [Figure 14] (a) Cyclic voltammetry of Pt and LZTS at a scan rate of 50 mV / s, (b) Nyquist plot of EIS for a symmetric cell with LZTS on GC, and (c) electrochemical equivalent circuit. [Figure 15ab] (a) and (b) EIS Nyquist plots of symmetric cells using Pt and LZTS on ITO substrates. [Figure 15cd] (c) and (d) Tafel plots of Pt and LZTS electrodes on FTO substrates. [Figure 15e] (e) Electrochemical equivalent circuit. [Figure 16ab] Figure 1 shows (a) DSSC mechanism and (b) band diagrams of DSSCs of LZTS on ITO and FTO substrates. [Figure 16cd] J-V curves of LZTS DSSCs on (c) ITO substrate and (d) FTO substrate. DETAILED DESCRIPTION OF THE INVENTION

[0040] Herein, the general provisions of the Summary of the Invention are repeated by reference thereto, and are not necessarily repeated in full to avoid repetition. The following detailed description and examples herein include specific embodiments of the present disclosure and should not be considered limiting in any respect. Several alternatives may be envisioned by those skilled in the art that do not depart from the scope of the present disclosure.

[0041] According to a first aspect of the present disclosure, there is provided an alkali metal quaternary crystalline nanomaterial having the general formula A(I2-II-IV-VI4), where I is sodium (Na) or lithium (Li), II and IV are Zn or Sn, and VI is a chalcogen selected from the group consisting of sulfur (S), selenium (Se), or tellurium (Te).

[0042] The crystalline phase of the alkali metal quaternary crystalline nanomaterial according to the present disclosure is not zinc pyrite and / or pyrite. The crystalline phase of the alkali metal quaternary crystalline nanomaterial is a simple mixed Cu-Au-like structure (PMCA) (space group: TIFF0007805006000011.tif818).

[0043] Preferably, the alkali metal quaternary crystalline nanomaterial is Li2ZnSnSe4 (LZTSe), and the crystalline phase is a simple mixed Cu-Au-like structure (PMCA) (space group: TIFF0007805006000012.tif818) or The alkali metal quaternary crystalline nanomaterial is Na2ZnSnSe4 (NZTSe), and the crystalline phase is a simple mixed Cu-Au-like structure (PMCA) (space group: TIFF0007805006000013.tif818).

[0044] In a further embodiment, the alkali metal quaternary crystalline nanomaterial is Li2ZnSnS4 (LZTS) and the crystalline phase is a simple mixed Cu-Au-like structure (PMCA) (space group: TIFF0007805006000014.tif818) or The alkali metal quaternary crystalline nanomaterial is Na2ZnSnS4 (NZTS), and the crystalline phase is a simple mixed Cu-Au-like structure (PMCA) (space group: TIFF0007805006000015.tif818).

[0045] It is understood that the alkali metal quaternary crystalline nanomaterials may be adapted to provide photovoltaic cells, the method of manufacture of which is provided below by way of example.

[0046] According to a second aspect of the present disclosure, there is provided a method for chemically synthesizing an alkali metal quaternary crystalline nanomaterial having general formula A according to the first aspect of the present disclosure, the method comprising: (i) dissolving VI4 selected from the group consisting of sulfur (S), selenium (Se), and tellurium (Te) in an amphiphilic capping agent under inert conditions to form a first solution; (ii) heating the solvent under reflux to about 75°C to about 120°C, preferably about 100°C, to form a second solution; (iii) mixing the first and second solutions and heating to between about 120°C and about 220°C, preferably about 200°C, to form a third solution; (iv) dissolving at least one of the group consisting of CuCl, LiCl, Li(acac), LiS, and NaCl in the amphiphilic capping agent to form a fourth solution; (v) adding the fourth solution to the third solution to form a fifth solution; (vi) adding at least one of zinc chloride or tin chloride to the fifth solution to form a sixth solution; and (vii) heating the sixth solution at about 120°C to about 220°C, preferably about 200°C, for 30 minutes to 2 hours, preferably 1 hour; Includes:

[0047] The method typically further comprises the step of adding a coalescing agent, preferably an alcohol.The method typically further comprises the step of washing away excess capping agent.

[0048] The method further comprises a step of centrifuging to provide for recovery of the alkali metal quaternary crystalline nanomaterial.

[0049] A preferred method of preparation is provided in the Examples herein below.

[0050] According to a third aspect of the present disclosure, there is provided a solar cell including a substrate to which the alkali metal quaternary crystalline nanomaterial of the first aspect is applied.

[0051] The substrate may be a molybdenum-coated glass, to which layers of alkali metal quaternary crystalline nanomaterials, CdS, ZnO, and finally Al sputtering are added. The layered structure is preferably in the form of a sandwich.

[0052] According to a fourth aspect of the present disclosure, there is provided a method for manufacturing a solar cell according to the third aspect, the method comprising: (i) providing a solution of the alkali metal quaternary crystalline nanomaterial of the first aspect in a solvent, preferably toluene; (ii) coating, preferably spin-coating, the solution of alkali metal quaternary crystalline nanomaterial onto the molybdenum-coated glass substrate to form an alkali metal quaternary crystalline nanomaterial-coated substrate; (iii) drying the alkali metal quaternary crystalline nanomaterial-coated substrate at about 60°C to 80°C; (iv) providing a solution of CdS in a solvent, preferably toluene; (v) coating, preferably spin-coating, the dried alkali metal quaternary crystalline nanomaterial coated substrate with the CdS solution to provide a CdS coated substrate; and (vi) Coating, preferably spin-coating, ZnO onto the CdS-coated substrate. Includes:

[0053] In a preferred embodiment, the fabrication method is carried out in the aforementioned order to provide a sandwich layered arrangement. The method may further comprise the step of depositing (or splattering) aluminum onto the CdS-coated substrate, preferably under thermal evaporation in high vacuum. A preferred fabrication method is provided in the Examples herein below.

[0054] Non-limiting examples are provided herein below to describe and illustrate preferred embodiments of the present disclosure. [Example]

[0055] Example 1 : Li2ZnSnSe4 (LZTSe) and Na2ZnSnSe4 (NZTSe) chemicals Copper chloride (CuCl), lithium chloride (LiCl), sodium chloride (NaCl), zinc chloride (ZnCl2), stannic chloride (SnCl4·5H2O), elemental selenium, oleylamine (OLA), ethanol, and toluene were purchased from Sigma-Aldrich and used without further purification.

[0056] Nanocrystal synthesis A three-neck round-bottom flask was charged with 15 mL of capping agent (OLA) and inertized by purging with nitrogen gas. Under reflux and vigorous magnetic stirring, the solvent was heated to 100 °C. Then, 4 mmol of selenium dissolved in the capping agent was added. The temperature was further increased to 200 °C, at which point 2 mmol of CuCl / LiCl / NaCl, also dissolved in the capping agent, was added, followed by 1 mmol of zinc chloride and tin chloride. The reaction was carried out at 200 °C for 1 hour. Ethanol was added to agglomerate the particles and wash away excess capping agent. The nanocrystals were then collected by centrifugation and dried at room temperature before characterization.

[0057] Characterization Technology Powder XRD patterns of the as-synthesized materials were measured using a Bruker D2 phaser (D2-205530) diffractometer using secondary graphite monochromated Cu-Kα radiation (λ = 1.5418 Å) at 30 kV and 10 mA. Measurements were performed using a glancing incident detector angle of 2°, 2θ values ​​ranging from 5 to 90° with a 0.036° step, a step time of 0.5 s, and a temperature of 25°C.

[0058] Raman analysis was performed using a "T64000 series II triple spectrometer system" from HORIBA Scientific, Jobin Yvon Technology Co., Ltd. Raman spectra were obtained using an Olympus microscope with a 50x objective and a laser power of 1.5 mW using a 514.5 nm argon laser.

[0059] Transmission electron microscopy (TEM) was performed using an FEI Technai T12 TEM microscope in TEM mode with an accelerating voltage of 120 kV and a beam spot diameter of 3 inches. Samples were first suspended in toluene, and the nanomaterial suspension was dropped onto a lacey carbon copper grid. The grid was allowed to dry at room temperature before analysis. A Varian Cary Eclipse (Cary 50) UV-vis spectrophotometer was used to measure the absorption of the nanocrystals. Absorption spectra were acquired in toluene and placed in a quartz cell (or cuvette) with a 1 cm path length.

[0060] Fabrication of solar cells Device assemblies were fabricated by spin-coating 50 μL of a toluene solution of different nanoparticles (CZTSe, LZTSe, or NZTSe) onto a molybdenum-coated glass substrate at 300 rpm. The resulting film was dried and baked at 70 °C. A toluene solution containing CdS was also spin-coated at 5000 rpm to form a very thin window layer. A ZnO layer was then spin-coated at 3000 rpm. Aluminum top contacts were sputtered through a shadow mask to create a patterned electrode array. The aluminum was deposited by thermal evaporation in high vacuum. The final device area was 0.08 cm. 2 This is defined by the overlap of the Mo electrode and the Al electrode. Photovoltaic characteristics such as current (I) and voltage (V) were measured using a digital source meter (Keithley Instruments, Model 2400) in the dark and at AM1.5, 100 mW cm -2 The measurements were taken under illumination from a "Newport ABA" solar simulator operating at standard conditions.

[0061] Results and Discussion The bulk crystal structures of prior art CZTSe and LZTSe have been reported in the literature. CZTSe crystallizes into two major crystalline structures, known as zinc pyrite and stannite, which are tetragonal. These two structures are very similar, with cations located at tetrahedral sites in both, but differ in the stacking arrangement of Cu and Zn atoms along the c-axis. Figure 1 shows the crystal structures and atomic arrangements of zinc pyrite and stannite. In the zinc pyrite structure, the cation layers along the c-axis are arranged in the order Cu-Sn, Cu-Zn, Cu-Sn, and Cu-Zn. In the stannite structure, Zn-Sn cation layers sandwiched between Cu-Cu layers are periodically repeated, with Cu atoms located at 4d and Zn atoms located at 2a. The Madelung potentials are −15.30 V and −21.62 V, respectively. The Sn atoms are located at 2b in both structures. Theoretical studies suggest that zinc pyrite is slightly lower in energy than the stannite phase and is therefore thermodynamically more stable, and therefore most particles are expected to crystallize in the zinc pyrite form.

[0062] LZTSe single crystals have been shown to crystallize in the wurtzite-zinc pyrostanate structure, which can be considered a superstructure of the rare hexagonal diamond, lonsdaleite. Applicants have demonstrated that LZTSe according to the present disclosure has a crystal structure in the space group: We were very surprised to find that PMCA has a tetragonal crystal structure with TIFF0007805006000016.tif818. This was surprising and unexpected. Without being limited by theory, it is possible that an unusual chemical synthesis method provided the unexpected crystal structure. It is often the combination of physical properties such as crystal structure and / or size and / or morphology that results in unique properties during use.

[0063] Figure 2 shows the XRD patterns of the synthesized CZTSe, LZTSe, and NZTSe nanocrystals. The XRD pattern of CZTSe exhibits all diffraction peaks consistent with a zinc pyrite phase (PDF 00-052-0868). While the XRD pattern from a single crystal of LZTSe is consistent with wurtzite-zinc pyrite, no other reports of LZTSe and NZTSe have shown this pattern to be distinct from the typical zinc pyrite and pyrite patterns associated with quaternary materials. Furthermore, the observed pattern is not consistent with common impurities such as ZnSe, SnSe, LiSe, or NaSe. While three peaks in the 20° to 30° region would be expected for a wurtzite-zinc pyrite phase, these peaks are absent in the observed diffraction patterns of LZTSe and NZTSe. The observed pattern indicates a phase similar to PMCA, which was surprising and unexpected.

[0064] To further investigate the structure, Raman spectroscopy was performed, and the results are shown in Figure 3. The Raman spectrum of CZTSe exhibits a peak at 177 cm -1 , 187cm -1 , 213cm -1 , 231cm -1 The Raman spectrum of LZTSe shows four expected peaks consistent with the zinc pyrithione phase. The Raman spectrum of LZTSe shows a peak at a lower wavenumber (127 cm) that is distinct from CZTSe. -1 ), which is also confirmed in the spectrum of NZTSe (121 cm -1 ) 235cm of LZTSe -1 is 231cm for CZTSe -1 It is similar to the peak at 247cm, but slightly shifted. -1 The peaks at 1000 nm may indicate structural differences between LZTSe and NZTSe. The Raman results support the XRD data that the crystal structure of LZTSe and NZTSe nanoparticles may be PMCA. PMCA resembles zinc pyrithione and pyrithione, but can be considered as a combination of two zinc pyrithione and pyrithione unit cells. This structure has never been observed experimentally in the prior art.

[0065] TEM images (Figure 4) show that all particles are spherical. The average particle sizes are 9.0 ± 1.07 nm, 6.06 ± 0.9 nm, and 8.3 ± 2.7 nm for CZTSe, LZTSe, and NZTSe, respectively. The standard deviation for the NZTSe particles is slightly larger than that for the CZTSe and LZTSe particles, suggesting a more polydisperse sample. However, all particles are below 10 nm, likely due to quantum confinement effects.

[0066] Nanocrystals for solar cells can provide unique properties different from bulk materials, such as multiple exciton generation and hot carrier injection, both of which are desirable properties. The as-synthesized nanocrystals were then used to fabricate solar cells with the configuration shown in Figure 5. Each layer was solution-processed, and the Al electrode was sputter-coated. The device area, corresponding to the connection between the Mo electrode and the Al strip, was 0.08 cm. 2 By patterning the electrodes, an array of small devices can be created, minimizing defects and maximizing the solar cell's power output.

[0067] Figure 6 shows the current density-voltage curve (J-V curve) of a solar cell. The J-V curve can be used to evaluate the performance of a solar cell, and important parameters can be extracted using the following equation: TIFF0007805006000017.tif30100(in the formula, V oc is the open circuit voltage, Jsc is the short circuit current, and FF is the fill factor. can be used to calculate the efficiency. The solar cell is rated at AM1.5 and 100 mW cm -2 The evaluation was carried out under standard lighting conditions.

[0068] The extracted parameters are listed in Table 1. The bandgaps of the synthesized materials were determined using UV-visible (UV-visible) spectrophotometry. While the exact bandgaps of the materials are not provided for similar devices referenced herein, the bandgap of CZTSe is generally reported to be 1.03–1.5 eV. Here, the bandgaps of CZTSe, LZTSe, and NZTSe, respectively, were 1.03 eV, 1.91 eV, and 1.59 eV, respectively. These are firmly in the visible region of the solar spectrum. Reducing the size of LZTSe and NZTSe shifts the bandgap toward the desirable "Shockley Queisser Efficiency Limit," which occurs at 1.34 eV. The "Shockley Queisser Efficiency Limit" is the theoretical maximum efficiency for harvesting power from a solar cell using a single p-n junction.

[0069] TIFF0007805006000018.tif60152

[0070] The fabricated CZTSe solar cells have significantly improved Jsc, V compared to reported CZTSe devices. oc The results showed that the FF values ​​and efficiencies were low. However, under the same fabrication conditions, NZTSe and LZTSe in particular showed improved results compared to CZTSe. The inherent properties of the absorber layer, Jsc and V oc (LZTSe is 46.9mA / cm 2 and 486 mV, NZTSe is 19.5 mA / cm 2 and 405 mV), which is much higher than that of reported CZTSe devices. This indicates that the alkali metal quaternary crystalline nanomaterials according to the present disclosure are able to achieve the open circuit voltages (V oc ) shortage, which is a surprising and unexpected advance.

[0071] TIFF0007805006000019.tif52144

[0072] In this case, the FF can be improved by improving the quality and thickness of the active layer. In the device shown in Figure 5, defects in the coating were visible. This is a common phenomenon when using a low-viscosity solvent, such as toluene, as the spin-coating medium. The subsequent layers redissolved due to poor adhesion to the substrate. This resulted in pinholes in the device, shorting out the underlying layers and reducing the shunt resistance. Table 2 shows the effect of increasing the FF up to 60%, which, as seen in the literature, is achievable for zinc-yellow stannite solar cells. In particular, increasing the FF for LZTSe solar cells dramatically improved the efficiency by more than threefold, from 5.65% to 18.95%. This is far superior to previous reports of laboratory-scale zinc-yellow stannite nanocrystal solution-based solar cell devices.

[0073] Example 2 : Li2ZnSnS4 (LZTS) Experimental Section material Lithium chloride (LiCl, 99.98%), lithium acetylacetonate (Li(acac), 99.95%), lithium sulfide (LiS, 99.98%), zinc chloride (ZnCl2, 98%), stannic chloride (SnCl4·5H2O, 97.5%), elemental sulfur (S, ≥ 99%), oleylamine (OLA, 70%), methanol (96%), ethanol (96%), toluene (anhydrous, 95%), hexane (anhydrous, 95%), isopropanol (anhydrous, 99%), lithium perchlorate (≥ 95%), lithium iodide (99.9%), sodium iodide Materials used in the synthesis and analysis of quaternary chalcogenide nanoparticles include ammonium hydroxide (anhydrous, ≥99.9%), 4-tert-butylpyridine (98%), N-methyl-2-pyrrolidone (anhydrous NMP, 99.5%), white titania paste reflector (TiO, 20.0 wt%), Whatman® glass microfiber filter paper, indium-doped tin oxide-coated glass slides (surface resistivity ~8–12 Ω / square inch), fluorine-doped tin oxide-coated glass slides (surface resistivity ~7 Ω / square inch), and N-719 dye (95%). All chemicals were purchased from Sigma-Aldrich, except for stannic chloride, which was purchased from Saarchem. All chemicals were used without further purification.

[0074] Colloidal synthesis of LZTS nanoparticles The nanoparticles were synthesized using a hot-injection colloidal method. Oleylamine (OLA, 10 mL) was heated to 100 °C with stirring under nitrogen gas. This also served as a solvent / surfactant purging step. At 100 °C, the constituent precursors were added according to the set sequence shown in Figure 7. After the final precursor addition, the temperature was increased to 200 °C and held for 45 min. The precursor molar ratios were varied to obtain Li:Zn:Sn:S samples with 1:1:1:1 and 2:1:0.25:2 ratios in all three reactions. The resulting particles were then coagulated using ethanol, collected by centrifugation at 3000 rpm, and dried at room temperature.

[0075] Fabrication of dye-sensitized solar cells (DSSCs) DSSCs typically consist of a dye-modified nanocrystalline titanium dioxide (TiO2) electrode fabricated on a transparent conductive oxide (TCO), a platinum (Pt) counter electrode (CE), and an electrolyte solution with an iodide / triiodide redox couple dissolved between the electrodes. The best DSSCs have achieved efficiencies of just under 12%. This modest efficiency can be balanced by further reducing the cost of DSSCs, which can be achieved by replacing some of the components. Platinum is an excellent electrocatalyst, but it is notoriously expensive. Several studies have reported using CZTS and its derivatives as CEs in DSSCs. PVP-CZTS and CA-CZTS nanofibers have been synthesized and used as CEs in DSSCs, demonstrating power conversion efficiencies (PCEs) of 3.10% and 3.90%, respectively. The PCEs of these nanomaterials were found to be in the range of 7.4–7.8%.

[0076] Preparation of the counter electrode The counter electrode ink was prepared by dispersing 40 mg of LZTS nanoparticles (LiS source in a ratio of 2:1:0.25:2) in a mixture of 1 mL of toluene and 0.1 mL of NMP. After vigorously stirring for 24 h, the homogeneous solution was sonicated for 10 min. Subsequently, the ink was applied to a pre-cleaned and pre-heated (80 °C) ITO / FTO substrate (ITO and FTO were ∼3.13 cm in area). 2 The solution was drop-cast onto a substrate. After the ink dried, each counter electrode was annealed at 80 °C for an additional 10 min. For comparative purposes, platinum was sputter-coated onto a pre-cleaned ITO / FTO substrate.

[0077] Fabrication of photoanode Titania (TiO2) paste was printed onto pre-cleaned ITO / FTO substrates by doctor blade method. The screen-printed substrates were then annealed at 350 °C for 30 min to remove residual organic compounds and ensure good contact between the TiO2 and N-719 dye. The N-719 dye was then dissolved in methanol (3.0 × 10 -4M) and used to sensitize TiO2. This dye mixture was dropped onto annealed TiO2 and allowed to dry overnight in the dark under ambient conditions.

[0078] Assembly of the device The photoanode electrode was positioned with the active layer facing up and the counter electrode facing down. The two electrodes were offset from each other, and a Whatman filter paper was sandwiched between them to define the active area and act as a sponge for the supporting redox electrolyte solution. The redox electrolyte solution consisted of 0.05 M iodine, 0.1 M lithium iodide, 0.1 M potassium iodide, 0.1 M sodium iodide, and 0.5 M 4-tert-butylpyridine, providing a negative electrochemical potential for the reduction process. The assembled device was held longitudinally with clasp clips on both sides to ensure uniform distribution.

[0079] Characterization The nanoparticles were characterized using the following techniques. UV-Vis absorption measurements were performed using a Varian Cary Eclipse (Cary 50) UV-Vis spectrophotometer. Powder samples were dispersed in toluene and placed in a 1-cm pathlength quartz cuvette for spectroscopic analysis. X-ray diffraction (XRD) measurements were performed using a Bruker D2 Phaser powder X-ray diffractometer, using Cu-Kα radiation (λ = 1.54060 Å) at 30 kV / 30 mA, a 2° angle, a 0.026° step for 2θ values ​​between 10 and 90°, a step time of 37 seconds, and a glancing angle detector at 25°C. A few milligrams of sample were placed on a zero-background holder and flattened on a glass slide. Morphology was obtained using an FEI Tecnai T12 transmission electron microscope (TEM) operated at 200 kV. The samples were dispersed in methanol and sonicated for 10 minutes. A drop of the suspended nanomaterials was then placed on a lacey carbon-coated copper grid and allowed to dry at room temperature before the sample was analyzed. Raman spectra were obtained using a Bruker Raman Senterra spectrophotometer with a 532 nm excitation laser and a very low laser power of 0.5 mV after placing the sample in a quartz holder. X-ray photoelectron spectroscopy (XPS) analysis was performed using a Physical Electronics PHI 5700 spectrometer with non-monochromatic Mg-Kα X-rays (300 W, 15 kV, 1253.6 eV) as the excitation source. 7 Li-MAS-NMR experiments were performed using a 7.05 T Bruker Avance III 300 MHz spectrometer ( 7 The measurements were performed at a rotation speed of 30 kHz using a Bruker 2.5 mm HFX MAS probe (m = 116.6 MHz for Li). Cyclic voltammetry (CV), electrochemical impedance (EIS), and Tafel polarization measurements were performed using a Biologic VMP 300. A triiodide (I) solution consisting of 0.1 M LiClO, 0.01 M LiI, and 0.001 M I dissolved in anhydrous acetonitrile was used. - / I 3- ) Redox electrolyte was used, scan rate 50 mV / s -1A glassy carbon electrode (GC, active area 0.07 cm) was used. 2 (below) and platinum (Pt, active area = 0.05 cm 2 ), ITO and FTO (active area 1.56 cm 2 After drop-casting the samples (see below), a three-electrode system was used to perform CV measurements using a Pt counter electrode, an Ag / AgCl reference electrode, and the synthesized CZTS / CZTSe working electrode. EIS measurements were performed in the dark using a symmetrical cell with two identical electrodes in the redox electrolyte used for DSSCs. The electrodes were analyzed between 100 kHz and 100 MHz, varying the open circuit potential of each sample. Tafel polarization analysis was performed over a potential window of -1.0 to 1.0 V, with a 100 mV s -1 The photocurrent-voltage (J-V) characteristic curves of DSCC were measured using an HP 4141B source measure unit (SMU) at a scan rate of 100 mW cm -2 Measurements were taken under ambient conditions under controlled lighting (AM1.5G).

[0080] Results and Discussion Synthesis and characterization of Li2ZnS4 (LZTS) In general, LZTS has a structure similar to CZTS and CZTSe, zinc pyrite (space group I4), pyrite (space group I42m), or simply mixed Cu-Au (PMCA; space group: TIFF0007805006000020.tif818) crystal structures, as shown in Figure 8.

[0081] The zinc pyrithione and pyrithione structures are It is a body-centered tetragonal crystal with a crystal structure of TIFF0007805006000021.tif818 (c≒2a), and can be thought of as two sulfur face-centered cubic (FCC) lattices stacked together, with Li, Zn, and Sn occupying half of the tetrahedral voids within the FCC lattices. The PMCA structure is as shown in Figure 8. TIFF0007805006000022.tif718 (c≒a) is a simple tetragonal crystal. The three distinct structures result from differences in the arrangement and stacking of the metal cations within the tetrahedral cavities. In the zinc pyrithione structure, two cation layers, Li and Zn or Li and Sn, alternate. In the pyrithione and PMCA structures, layers of Li alternate with layers of Zn and Sn. In the pyrithione structure, Zn and Sn atoms in the same layer swap positions every other layer. In PMCA, this swapping of Zn and Sn atoms does not occur every other layer, resulting in a simple tetragonal crystal, distinguishing it from the pyrithione structure. X-ray diffraction of these structures is very similar, with only minor differences apparent. The zinc pyrithione phase is more distorted than either pyrithione or PMCA, typically shifting by 0.2°. While pyrithione and PMCA are nearly indistinguishable, pyrithione is the more stable phase. However, the two can be distinguished by using experimental data from X-ray diffraction to calculate the lattice constants a, b, and c using equation (3) and matching them with the reference constants. Table 3 shows the lattice constants. TIFF0007805006000023.tif2083

[0082] TIFF0007805006000024.tif39150

[0083] Figures 9(a)-(f) show XRD patterns of LZTS synthesized according to the present disclosure using different lithium precursors and different precursor ratios, as well as a standard reference pattern for stannite. The LiCl and Li(acac) sources in both molar ratio configurations did not perfectly match the reference pattern, suggesting the presence of impurities. However, when changing to a LiS source, a 2:1:0.25:2 ratio perfectly matched the reference pattern, although not all planes were diffracted, suggesting preferred orientation. Since no reference pattern was available for PMCA, the lattice constants were calculated using equation (3).

[0084] The obtained values ​​were closer to those of PMCA. A possible reason for the PMCA structure of LZTS is the difference in atomic radii between Cu (128 pm) and Li (152 pm). Furthermore, transition metals (Cu) are harder than alkali metals due to the larger number of unpaired electrons in their valence bands, which may promote distortion of the tetragonal structure of LZTS. In TEM images of LZTS synthesized using different lithium sources and different molar ratios, LiCl-based nanoparticles were quasi-spherical, polydisperse, and aggregated. An increase in size was observed with increasing concentration. Li(acac)-based nanoparticles were very small and formed an aggregated cloud-like morphology. No visible change was observed with changing the ratio. Li2S-derived particles were small, quasi-spherical, and very well dispersed. A slight increase in size was observed with changing the ratio.

[0085] X-ray photoelectron spectroscopy (XPS) is a useful technique for characterizing the surface chemistry and bonding of the resulting particles. XPS survey spectra were obtained for particles synthesized using various lithium sources and molar ratios. The spectra showed all components of LZTS except for lithium. Due to its low atomic number, XPS has very low sensitivity to lithium. The C 1s, N 1s, and O 1s observed in all spectra are attributed to the capping agent, OLA, and its oxidation.

[0086] Li 1s high-resolution spectra were measured for LZTS nanoparticles synthesized using different lithium sources (LiCl, Li(acac), Li2S) and different precursor ratios (1:1:1:1 and 2:1:0.25:2). Lithium was detected in all samples. The high-resolution spectra are more sensitive to low concentrations than the survey spectra. All samples showed metallic lithium (Li 0) and Li-S were detected. The intensity of the Li2S-derived particles (ratio 2:1:0.25:2) was much higher than that of the other particles, which may indicate the formation of LZTS. This is consistent with the observed XRD results. Zn 2p, Sn 3d, and S 2p high-resolution spectra were obtained for LZTS nanoparticles synthesized using different Li2S precursor ratios of 2:1:0.25:2. The Zn 2p spectrum for the LiCl source showed a doublet resolved into two peaks at 1045.4 eV and 1022.3 eV, with a peak spacing of 23.06 eV. 2+ Furthermore, the Sn 3d core level spectrum showed two peaks resolved into 3d3 / 2 (495.2 eV) and 3d5 / 2 (486.7 eV). The peak separation of 8.41 eV is due to Sn 4+ The high-resolution spectrum of S 2p shows two peaks, each of which can be deconvoluted to give two more peaks. The 2p3 / 2 and 2p1 / 2 doublets are both S 2- It was found that the Zn 2p spectrum of Li(acac) is also related to the Zn 2+ Broadly similar results were observed for the LZTS nanoparticles and Li2S, except that the S 2p spectrum of Li2S showed a doublet due to ions, indicating the presence of SOx species. To further confirm the formation of LZTS, the different lithium precursors used and the corresponding LZTS nanoparticles were analyzed. 7 The Li-MAS-NMR spectra are shown in Figure 11. A characteristic lithium peak at 2-3 ppm was observed for the commercially available precursors LiCl, Li(acac), and Li2S. This peak was also observed in the corresponding LZTS nanoparticles, albeit with a slight shift. This shift confirms the coordination of Li.

[0087] The optical properties of LZTS nanoparticles synthesized using different precursors and ratios are shown in Figures 12(a)-12(c). The band gaps of particles derived from LiCl, Li(acac), and LiS in a 1:1:1:1 ratio were 2.42 eV, 2.39 eV, and 3.09 eV, respectively. By varying the ratio, the band gaps were 3.13 eV, 3.23 eV, and 3.14 eV, respectively. The band gap of LiS-derived LZTS nanoparticles did not change with the ratio.

[0088] From the results of XRD, TEM, XPS, and NMR, it is clear that the LZTS nanoparticles synthesized from Li2S with a Li:Zn:Sn:S ratio of 2:1:0.25:2 is the best sample. Therefore, all subsequent characterizations and applications were based on this sample. Figure 13 shows the Raman spectrum of LZTS. -1 A prominent peak at 248 cm was observed, which is attributed to the A1 mode of the tetragonal PMCA structure. -1 and 330cm -1 ~363cm -1 The additional peaks were attributed to the B2 and A1 modes, respectively. This further confirmed the formation of LZTS. Furthermore, the Raman analysis did not show any indication of the presence of secondary phases.

[0089] Application of LZTS to the counter electrode of dye-sensitized solar cells LZTS nanoparticles synthesized from Li2S (2:1:0.25:2) were drop-cast onto a glassy carbon electrode to investigate their electrocatalytic activity for the reduction of triiodide ions. A three-electrode system was used to perform cyclic voltammetry measurements, and cyclic voltammograms (CVs) were obtained. The CVs, which have two pairs of redox peaks, correspond to the following equation: TIFF0007805006000025.tif2183

[0090] The catalytic activity depends on two parameters: the peak current |J_Red-1| and the peak-to-peak distance (Epp). The peak current values ​​for Pt and LZTS are 3.53 and 3.16 mA / cm, respectively. 2The Epp values ​​were 0.33 and 0.61 V (Table 4). The high peak current and low Epp suggest better catalytic performance and a faster reduction rate. The RedI shift observed near low potentials also indicates the low reversibility of the reaction.

[0091] TIFF0007805006000026.tif35146

[0092] To evaluate the charge transfer from the CE to the electrolyte, EIS was employed. - / I - The experiment was carried out in a symmetrical dummy cell with two identical electrodes sandwiching an electrolyte. Figures 14(a) to 14(c) show the Nyquist plots for Pt and LZTS, as well as the electrochemical equivalent circuits whose elements represent the four impedance characteristics. The abbreviation Rs stands for series resistance, and R ct denotes the charge transfer resistance at the CE / electrolyte interface. Furthermore, the abbreviation Cdl corresponds to the double layer capacitance, which is adopted when a perfect semicircle is obtained from the Nyquist plot, and describes the charge storage capability of the CE. Finally, Zw represents the Nernst diffusion element, which is often used in the low frequency region when the line is at 45° to the semicircle, and describes whether the interaction between the CE and the electrolyte is diffusion controlled. Two important parameters, Rs and R ct are summarized in Table 4. R ct A high value of indicates poor charge transfer.

[0093] To evaluate the influence of the substrate on the electrocatalytic properties of LZTS, nanoparticles were drop-cast onto ITO and FTO substrates and used for EIS and Tafel plot measurements (see Figure 15). In the EIS measurements of the symmetric cell, the same equivalent circuit model as that of the GC was observed, as shown in Figure 15(e). The Rs and R of Pt and LZTS on both ITO and FTO were ctThe values ​​are reported in Table 5. When ITO was used as the substrate, Pt had the lowest Rs value compared to the FTO substrate. Similarly, LZTS had a lower Rs value when the substrate was ITO. The lower Rs value of Pt compared to LZTS for both substrates suggests that Pt has a higher conductivity. The charge transfer process, represented by the diameter of a semicircle in the high frequency region, is R ct This is reflected in the value of R ct If the value is low, the values ​​of Jsc and FF are high, so they are sorted. If the substrate is changed to FTO, the values ​​of Rs and R ct This indicates that solar cells using FTO may have inferior performance.

[0094] TIFF0007805006000027.tif55149

[0095] The Tafel polarization curves used to examine the interfacial charge transfer characteristics of the symmetric dummy counter electrode cell are shown in Figure 15. From the polarization curves, the exchange current density (J0) and the limiting diffusion current density (J lim Two important parameters were observed: ) Both parameters are affected by the anodic or cathodic contribution of each counter electrode, and are expressed by the following equations: TIFF0007805006000028.tif2057 (where R is the gas constant, T is the temperature (298 K), F is the Faraday constant, n (n = 2) is the number of electrons, R ct is the charge transfer resistance, D is the diffusion coefficient, and C is I3 - concentration, l is the spacer thickness.) From equation (6), J0 can be expressed as R ct Therefore, J0 is correlated with the electrocatalytic activity of CE, and a large J0 value means very good catalytic activity. lim A larger value of J0 leads to a larger diffusion coefficient D, which, according to equation (7), means higher catalytic activity. The J0 value of LZTS-ITO is comparable to that of state-of-the-art Pt, suggesting good electrocatalytic activity. However, the J0 value of LZTS with ITO substrate is limThe J and J values ​​of LZTS on an ITO substrate were smaller than those of Pt, indicating its low catalytic activity. lim was higher than the corresponding FTO, further suggesting that ITO should be the substrate of choice.

[0096] The LZTS nanoparticles were then used as the CE in DSSCs. Figure 16(a) shows the structure, band structure, and current density-voltage (J-V) curves of solar cells obtained from the two substrates. The performance of LZTS was compared to state-of-the-art Pt electrodes, but it should be noted that these devices require optimization. The results are also summarized in Table 6. It was observed that the type of substrate used affects the overall performance of the solar cells. The ITO substrate performed slightly better than the ITO substrate, but the degree of change was less than expected, consistent with the electrochemical data. This strongly suggests that optimization of the fabrication process is necessary. Also noteworthy from the data in Figure 16 and Table 6 is the low FF values ​​for all samples. This low FF value is due to the high Rs and low shunt resistance (Rsh) values ​​resulting from increased recombination at the DSSC interface.

[0097] TIFF0007805006000029.tif51130

[0098] LZTS nanoparticles were successfully synthesized for the first time by the hot injection method. By changing the lithium source from LiCl to Li(acac) and Li2S and varying the Li:Zn:Sn:S ratio from 1:1:1:1 to 2:1:0.25:2, LZTS nanoparticles with various properties were formed. Particles derived from LiCl and Li(acac) formed impurities, as observed from the XRD patterns, regardless of the ratio used. XPS, 7The presence of lithium and the formation of LZTS were confirmed by Li-MAS NMR and Raman spectroscopy. The Li2S source and a 2:1:0.25:2 ratio yielded the purest particles and were used for the first time as a CE in DSSCs. Two substrates, ITO and ITO, were used. LZTS was successfully used as an electrocatalyst in DSSCs. Different PCEs were obtained using different substrates. LZTS nanoparticles on ITO showed the best performance, with a PCE of 2.26%. It should be noted that this is a preliminary study and the device has not yet been optimized. Nevertheless, we have demonstrated that LZTS can be used as a CE in DSSCs.

[0099] Applicant has surprisingly found that the alkali metal quaternary crystalline nanomaterials described herein exhibit superior properties compared to prior art. Without being limited by theory, it is believed that the unique physicochemical properties imparted by the unique solid-state properties play a key role in this regard. Furthermore, the fabrication method is important for achieving the unique solid-state properties. Applicant anticipates conducting further experiments to clearly demonstrate the advantages over prior art solar cell devices. While the present disclosure has been described in detail with reference to specific embodiments and / or examples thereof, it will be understood that those skilled in the art will readily conceive of modifications, variations, and equivalents to these embodiments upon understanding the foregoing. Accordingly, the scope of the present disclosure should be assessed as that of the following claims and equivalents thereof, which claims are hereby incorporated by reference.

Claims

1. An alkali metal quaternary crystalline nanomaterial, comprising: General formula A: I ２ ‐II‐U‐UI ４ wherein I is sodium (Na) or lithium (Li); II and IV are Zn or Sn; VI is a chalcogen selected from the group consisting of sulfur (S), selenium (Se), and tellurium (Te). and The crystalline nanomaterial is (a) Li ２ ZnSnSe ４ (LZTSe), wherein in Formula A, I is Li, II is Zn, IV is Sn, and VI is Se; (b) Na ２ ZnSnSe ４ (NZTSe), wherein in Formula A I is Na, II is Zn, IV is Sn and VI is Se; (c) Li ２ ZnSnS ４ (LZTS), or (d) Na ２ ZnSnS ４ (NZTS), wherein in Formula A, I is Na, II is Zn, IV is Sn, and VI is S; the crystalline phase of the crystalline nanomaterial is a simple mixed Cu-Au-like structure (PMCA) rather than zinc pyrite and / or pyrite; The nanomaterial has the space group: An alkali metal quaternary crystalline nanomaterial having the formula:

2. A solar cell comprising a substrate to which the alkali metal quaternary crystalline nanomaterial according to claim 1 is applied.

3. The solar cell of claim 2 wherein the substrate is molybdenum coated glass.

4. The solar cell of claim 2 further comprising a CdS, ZnO or Al coating.

5. (i) providing a solution of the alkali metal quaternary crystalline nanomaterial of claim 1 in a solvent; (ii) coating the alkali metal quaternary crystalline nanomaterial solution onto a molybdenum-coated glass substrate to form an alkali metal quaternary crystalline nanomaterial-coated substrate; (iii) drying the alkali metal quaternary crystalline nanomaterial coated substrate at 60°C to 80°C; (iv) providing a solution of CdS in a solvent; (v) coating the dried alkali metal quaternary crystalline nanomaterial coated substrate with the CdS solution to provide a CdS coated substrate; and (vi) coating ZnO onto the CdS-coated substrate; The method for producing a solar cell according to claim 4 , comprising:

Images