WO2025079072A1

WO2025079072A1 - Photovoltaic paint including nanoparticles, that are applied at low temperatures, and elements coated by the photovoltaic paint

Info

Publication number: WO2025079072A1
Application number: PCT/IL2024/050989
Authority: WO
Inventors: Gary ZAIATS; Shlomit ZAMIR; Eyal Aharon
Original assignee: Solor Gs Ltd
Current assignee: Solor Gs Ltd
Priority date: 2023-10-09
Filing date: 2024-10-09
Publication date: 2025-04-17
Anticipated expiration: 2026-04-09

Abstract

Photovoltaic paints for forming photovoltaic coatings during production of structural elements and corresponding methods are provided. An anion solution including Se powder dissolved in e.g., oleylamine and hexanethiol is mixed with a cation solution including Cu, In and optionally Ga precursors dissolved in oleylamine and are heated to 160°C - a temperature that allows for standard industrial coating processes of various structural elements. After cooling of the mixture, CIGS/CIS nanoparticles (CuwInxGai-xSeyS2-y, with 0.1<w<l, 0<x<l and 0<y<2) precipitate on the substrate, and multiple layers may be used to form a specified coating thickness. The light absorbing coating may be combined with buffer layer(s) and contacts to form a photovoltaic device directly onto the structural elements - enabling application of photovoltaic paint on many types of surfaces (e.g., vehicles, buildings, constructions, etc.) and thereby enhancing significantly the ability to harvest and use solar power.

Description

PHOTOVOLTAIC PAINT INCLUDING NANOPARTICLES, THAT ARE APPLIED AT LOW TEMPERATURES, AND ELEMENTS COATED BY THE PHOTOVOLTAIC PAINT

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from U.S. Provisional Application No. 63/588,803, filed on October 9, 2023, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. TECHNICAL FIELD

[0002] The present invention relates to the field of photovoltaic devices, and more particularly, to photovoltaic paints that are based on Cu-In/Ga-Se/S nanoparticles and are applied at low temperatures, and production methods thereof.

2. DISCUSSION OF RELATED ART

[0003] Typical fabrication processes of Cu-In/Ga-Se/S (CIGS) thin film solar cells involve two main steps: (i) Deposition of the cationic precursors, and (ii) Selenization\sulfurization of the surface. Typically, the cationic precursors are deposited by employing ultra-high vacuum deposition techniques, such as evaporation or sputtering. Alternative non-vacuum deposition methods include use of (i) hydrazine solutions (which are hazardous, poisonous and explosive materials) of the corresponding metal salts or (ii) colloidal nanoparticles-based solution in organic solvents. Regardless of the chosen precursors deposition method, typically the film is annealed under Se\S vapors or H2Se\H2S gases at temperature of 500°C. The last step calcinates carbonaceous residuals, introduces anions and induces crystallization of CIGSeS photovoltaic phase. The high processing temperature and ultrahigh vacuum require high investment in fabrication facilities (CAPEX), highly qualified personnel and have high operational costs (OPEX). [0004] Other methods for fabrication of CIGS nanoparticles involve use of oleylamine and trioctylphosphine or diphenylphosphine as capping ligands. These phosphine compounds are generally known as being air sensitive, highly hazardous and some of them are highly pyrophoric materials. Moreover, although the high boiling temperatures of these compounds is advantageous during the synthesis step, they prescribe high annealing temperature during the subsequent annealing process. In some works that avoid use of phosphine compounds, GaCh is employed as a source for Ga ions. GaCh is highly sensitive to humidity and reacts violently upon exposure to vapors of water.

[0005] U.S. Patent Publication No. 20110056564, which is incorporated herein by reference in its entirety, discloses nanoparticle compositions comprising a copper indium gallium selenide, a copper indium sulfide, or a combination thereof; a layer comprising the nanoparticle composition; a photovoltaic device comprising the nanoparticle composition and/or the absorbing layer; and methods for producing the nanoparticle compositions, absorbing layers, and photovoltaic devices. [0006] U.S. Patent No. 11,222,989, which is incorporated herein by reference in its entirety, discloses methods of making a semiconductor layer from nanocrystals - using a film of nanocrystals capped with a ligand that is deposited onto a substrate. The nanocrystals are irradiated with pulsed light to remove the ligands from the nanocrystals and leave the nanocrystals in a semiconductor layer.

SUMMARY OF THE INVENTION

[0007] The following is a simplified summary providing an initial understanding of the invention. The summary does not necessarily identify key elements nor limit the scope of the invention, but merely serves as an introduction to the following description.

[0008] One aspect of the present invention provides a method comprising: (i) mixing an anion solution with a cation solution, wherein the anion solution comprises a powder of Se dissolved in a mixture of at least one linear amine having a boiling point above 200°C (e.g., oleylamine and/or dodecylamine) and hexanethiol, and the cation solution comprises Cu-acetate, InCh and Ga- acetylacetonate dissolved in oleylamine and heated to temperature of e.g., 100°C under vacuum, (ii) heating the mixture to a temperature of 160°C or less, e.g., maintaining the reaction for 2-8 hours under inert conditions, and precipitating nanoparticles from the heated mixture after cooling thereof, wherein the nanoparticles have the formula Cu_wIn_xGai-_xSe_yS2-y, wherein 0.1<w<l, 0<x<l and 0<y<2.

[0009] One aspect of the present invention provides a photovoltaic paint comprising nanoparticles having the formula Cu_wIn_xGai-_xSe_yS2-y, wherein 0.1<w<l, 0<x<l and 0<y<2, wherein the photovoltaic paint is applicable on a substrate at a temperature below 160°C to form a photovoltaic device. [0010] One aspect of the present invention provides a photovoltaic device comprising a structural element having a photovoltaic coating comprising the photovoltaic paint, applied as part of the photovoltaic coating onto the structural element as the substrate.

[0011] These, additional, and/or other aspects and/or advantages of the present invention are set forth in the detailed description which follows, possibly inferable from the detailed description, and/or learnable by practice of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] For a better understanding of embodiments of the invention and to show how the same may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings in which like numerals designate corresponding elements or sections throughout. In the accompanying drawings:

[0013] Figure 1 is a high-level flowchart illustrating a method, according to some embodiments of the invention.

[0014] Figure 2 is a high-level schematic illustration of photovoltaic coatings forming photovoltaic devices, according to some embodiments of the invention.

[0015] Figure 3 provides a Raman characterization of the nanoparticles, according to some embodiments of the invention.

[0016] Figure 4 provides an XPS (X-ray photoelectron spectroscopy) analysis of the nanoparticles, according to some embodiments of the invention.

[0017] Figure 5 provides a light absorbance curve of the nanoparticles, according to some embodiments of the invention.

[0018] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

DETAILED DESCRIPTION OF THE INVENTION

[0019] In the following description, various aspects of the present invention are described. For purposes of explanation, specific configurations and details are set forth in order to provide a thorough understanding of the present invention. However, it will also be apparent to one skilled in the art that the present invention may be practiced without the specific details presented herein. Furthermore, well known features may have been omitted or simplified in order not to obscure the present invention. With specific reference to the drawings, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

[0020] Before at least one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is applicable to other embodiments that may be practiced or carried out in various ways as well as to combinations of the disclosed embodiments. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.

[0021] Some embodiments of the present invention provide efficient and economical methods and mechanisms for preparing photovoltaic paint that includes CIGS/CIS nanoparticles and is appliable at low temperatures, and thereby provide improvements to the technological field of photovoltaic devices.

[0022] Photovoltaic paints for forming photovoltaic coatings during production of structural elements and corresponding methods are provided. Anion solutions including Se powder dissolved in high boiling amine(s) and hexanethiol (which provides sulfur) are mixed with cation solutions including Cu, In and optionally Ga dissolved in e.g., oleylamine and are heated to 160°C to form the CuInGaSe/CuInSe thin multi-layered film. Advantageously, this temperature range is suitable for standard industrial coating processes of various structural elements. After cooling of the mixture, CIGS/CIS nanoparticles (Cu_wIn_xGai-_xSe_yS2-y, with 0.1<w<l, 0<x<l and 0<y<2) precipitate on the substrate, and multiple layers may be used to form a specified coating thickness. The light absorbing coating may be part of a photovoltaic device that further includes buffer layer(s) and contacts, and may be formed directly onto the structural elements - enabling application of photovoltaic paint on many types of surfaces (e.g., vehicles, buildings, constructions, etc.) and thereby enhancing significantly the ability to harvest and use solar power.

[0023] Figure 1 is a high-level flowchart illustrating a method 100, according to some embodiments of the invention. Method 100 may comprise preparing in separate containers an anion solution (e.g., Se powder in oleylamine and hexanethiol) and a cation solution (e.g., Cu-acetate, InCh and optionally Ga-acetylacetonate in oleylamine) (stage 105). Method 100 further comprises mixing the anion solution with the cation solution (stage 110), e.g., by injecting the anion solution into the cation solution, heating the mixture to a temperature of 160°C or less (stage 120), e.g., performing the reaction for 2-8 hours under inert conditions (e.g., in nitrogen and/or argon atmosphere), and precipitating nanoparticles from the heated mixture after cooling thereof (stage 130). The anion and cation solutions are configured to yield precipitated nanoparticles with the formula Cu_wIn_xGai-_xSe_yS2-y, wherein 0.1<w<l, 0<x<l and 0<y<2.

[0024] Advantageously, method 100 enables, and may comprise, direct application of the nanoparticles solution as a light-absorbing layer onto a substrate, to form a photovoltaic device that also includes top and bottom electric contacts and optionally buffer/electron conductive layers (stage 140). For example, method 100 may comprise applying top and bottom electric contact layers and buffer layer(s), as part of the photovoltaic coating that includes the light- absorbing layer (stage 140), with the layers being applied one by one according to a designed order (see nonlimiting examples in Figure 2).

[0025] The application of the heated mixture as the photovoltaic paint that forms the lightabsorbing layer (stage 140) may be carried out during a production process of various structural elements, as part of a photovoltaic coating applied thereto- due to the relatively low temperature of precipitation (160°C or less), contrasted with prior art reactions that require much higher temperatures (e.g., several hundred °C, e.g., 220-250°C in solution, and post-deposition heating to temperatures as high as 500°C or higher for other Cu-In-Se/S thin film fabrication methods). For example, method 100 may comprise applying photovoltaic paint including the CIGS/CIS nanoparticles in multiple layers, alternating with surface treatments, as part of the photovoltaic coating that includes the light-absorbing layer (stage 140).

[0026] The anion solution may comprise a powder of selenium (Se) (and optionally sulfur) dissolved in a mixture of at least one linear amine having a boiling point above 200°C (e.g., oleylamine and/or dodecylamine) and hexanethiol (providing S, or possibly other, e.g., shorter thiols having a boiling point below 160°C, but close to 160°C, to enable the reaction). Quantitatively, the anion solution comprises at least about 5wt% hexanethiol to ensure solubility of the powder, and may reach 20-35wt% hexanethiol. For example, the anion solution may comprise 7:1 oleylamine to hexanethiol, resulting in 14wt% of hexanethiol in the anion solution. In some embodiments, a powder of sulfur (S) may be used together with the Se powder, alternatively or complementarity, S is introduced from the thiol (e.g., hexanethiol).

[0027] The cation solution may comprise Cu-acetate, InCh and optionally Ga-acetylacetonate dissolved in oleylamine and heated to temperature of e.g., 100°C (possibly between 90-130°C) under vacuum. In some embodiments, the reaction may be maintained for 2-8 hours under inert conditions (e.g., in nitrogen and/or argon atmosphere).

[0028] In some embodiments, precipitating nanoparticles from the heated mixture may be carried out by mixing the heated mixture with a solvent (e.g., hexane, toluene, chloroform) and adding a corresponding anti-solvent (e.g., ethanol or methanol) into the mixture with the solvent (stage 132). [0029] Without being bound by theory, heating under vacuum degasses the solution, removing oxygen and moisture from the precursor solutions, and hence the solvent (oleylamine, or alternative solvents) is selected to have a high boiling point, e.g., above 200°C. Following the reaction and the deposition of the CIGS/CIS nanoparticles, the solvent(s) can be washed, but hexanethiol has to be evaporated, requiring the selected thiol(s) to have a lower boiling point, e.g., below 160°C. The selection of the at least one linear amine having a boiling point above 200°C may be carried out to optimize the removal process of this ligand(s). The use of hexanethiol is advantageous as it not pyrophoric, less hazardous to the environment and may be removed at much lower temperatures (e.g., <160°C) compared with prior art phosphines (e.g., >220°C).

[0030] Figure 2 is a high-level schematic illustration of photovoltaic coatings 200 forming photovoltaic devices 205, according to some embodiments of the invention. Disclosed photovoltaic coatings 200 may be applied to various substrates 90 using various embodiments of method 100. Devices 205 comprise substrate 90 (e.g., a structural element of any kind, which in use is exposed to the sun, or a polymer layer), onto which photovoltaic paint 210 is applied to form a lightabsorbing layer 220. Photovoltaic paint 210 and/or light-absorbing layer 220 may be formed by method 100 and comprise CIGS/CIS nanoparticles having the formula Cu_wIn_xGai-_xSe_yS2-y, wherein 0.1<w<l, 0<x<l and 0<y<2. Photovoltaic device 205 further comprises top and bottom electric contacts 95 comprising, e.g., metal nanowires connected to a top and a bottom of light-absorbing layer 220, and configured to collect the generated voltage (indicated schematically as AV) generated by the nanoparticles upon illumination thereof.

[0031] It is noted that in any of the configurations, additional layers and/or surface treatments may be applied as part of photovoltaic coatings 200 to prepare operable photovoltaic devices 205. For example, photovoltaic coating 200 may comprise, in addition to top and bottom electric contacts 95A, 95B and light-absorbing layer 220, additional buffer layer(s) 96 and/or electron transport layer(s) 97 (conductive to electrons) to provide and/or improve the photovoltaic functionality. For example, buffer layer(s) 96 may comprise ZnMgO and/or ZnS layers or corresponding layers, and electron transport layer(s) 97 may comprise ZnO or corresponding layers. It is noted that in photovoltaic coating 200, light-absorbing layer 220 is the main light-absorbing and p-conducting layer, while buffer layer(s) 96 are the n-conducting layer(s). Buffer layer(s) 96 and/or electron transport layer(s) 97 may be positioned within photovoltaic coating 200 according to specific configurations related to the device functionality, e.g., in relation to the direction of incoming illumination.

[0032] For example, transparent substrates 90 may enable using a transparent top contact 95A (e.g., made of a transparent material that includes silver nanowires) to which light-absorbing layer 220 (photovoltaic paint layer(s) with CIGS/CIS nanoparticles) is adjacent. In some embodiments, substrate 90 and electrical contact 95B attached thereto may be transparent (e.g., made of a transparent material that includes silver nano wires), and photovoltaic paint 220 may be coated by top transparent electrical contact 95A - to form photovoltaic device 200 that may generate electricity from illumination through either or both sides of the device. For example, corresponding photovoltaic devices 205 may comprise windows onto which photovoltaic coating 200 is applied internally or externally, or any other transparent substrates 90 with corresponding transparent bottom contacts 95B. In another example, light may reach light-absorbing layer 220 through top contact 95A, e.g., comprising silver nanowires, applied on top of photovoltaic coating 200 and supported by buffer layer(s) 96, electron transport layer(s) 97 and bottom contact 90B. For example, various panels, vehicle particles, etc. may be coated by photovoltaic coating 200 during production, e.g., as a finishing coating layer, applied at relatively low temperatures which are easily applicable in current production methods for these structural elements. The coating process itself may comprise multiple steps, e.g., of applying each of the layers, and/or applying one or more layers in several steps (e.g., applying alternately multiple layers of photovoltaic paint 210 and surface treatments) until a requested layer thickness (e.g., between 200nm and 2000nm) is reached. [0033] In various embodiments, buffer (n-conducting) layer(s) 96 may be made, e.g., of films of any of: ZnS, ZMgS, MgO or Mg_xZni-_xO (0<x<l), AZO (aluminum-doped zinc oxide), GZO (gallium-doped zinc oxide) and/or IZO (indium-doped zinc oxide), as well as combinations thereof. In various embodiments, electron transport layer(s) 97 (conductive to electrons) comprises ZnO. [0034] Non limiting examples for ranges of layer thickness include: light-absorbing layer 220 may range between l-2pm, top contact 95A (e.g., including silver nanowires) may be about lOOnm (0.1pm), buffer layer(s) 96 may range between 30-50nm and electron transport layer(s) 97 may range between 50- lOOnm. It is further noted that light-absorbing layer 220 may be formed by applying multiple layers of photovoltaic paint 210 with the disclosed nanoparticles, as well as applying surface treatments to the layers to connect the CIGS/CIS particles chemically and electrically.

[0035] Non-limiting examples for structural elements as substrates 90 include at least a part of any one of: a construction, a building envelope, windows, a barrier, a panel, a polymer layer, a canopy, a cladding, a tile, a laminate, a vehicle, an aerial vehicle, etc. Specific examples may comprise any sun-exposed element in buildings (e.g., walls, roof, windows), vehicles (top and side surfaces of cars, buses, trains, ships, etc., wings in aerial vehicles), road and roadsides (separation walls or panels, including concrete walls, canopies, various laminates, various poles) or any type of panels in any sun-exposed location.

Example

[0036] In a non-limiting example, the anion solution may comprise 8 mmol Se powder dissolved in a 7:3 by volume oleylamine:hexanethiol mixture and the cation solution may comprise 4 mmol Cu-acetate, 3 mmol InCE, 1 mmol Ga-acetylacetonate dissolved in oleylamine. Figures 3-5 provide experimental results for this non-limiting example, with the mixture heated under nitrogen and for 2-8 hours (or possibly longer). In various embodiments, the duration of the synthesis may be shortened to optimize the process yield and the purity of resulting light-absorbing layer 220. [0037] Figure 3 provides a Raman characterization of the nanoparticles, according to some embodiments of the invention. The methodology follows Witte et al. 2008 (Raman investigations of Cu(In, Ga)Se2 thin films with various copper contents. Thin Solid Films 517 (2), 867-869) and Zaretskaya el al. 2003 (Raman spectroscopy of CuInSe2, Thin films prepared by selenization. J. Phys. Chem. Solids 64 (9-10), 1989-1993). Figure 3 indicates a clear peak in the relative intensity of the Raman shift at about 175 cm'¹ which is characteristic for formation of a CuIn_xGai-_xSe_yS2-y phase and a broad peak at about 520 cm'¹ which is characteristic for Se-Se and Se-S bonds. Absence of spectroscopic features at 150 cm'¹ and 260 cm'¹ implies the absence of defects (like Cu(In,Ga)3Ses or Cu2(In,Ga)4Se?) and Cu2-_xSe phases respectively. It is noted that the duration of synthesis may be adjusted to fine-tune the compounds in the product (e.g., longer synthesis reduces the amounts of Cu2-_xSe phases).

[0038] Figure 4 provides an XPS (X-ray photoelectron spectroscopy) analysis of the nanoparticles, according to some embodiments of the invention. The elemental analysis by XPS of Figure 4 shows the presence of all elements in the photovoltaic paint, including the CIGS nanoparticles. The relative amount of each element is summarized in Table 1. This specific sample represents Ga-rich nanoparticles. However, the ratio between the cations may be modified by changing the ratio of the corresponding cations.

Table 1: Atomic composition of the nanoparticles.

[0039] It is noted that Table 1 provides a non-limiting example for the quantitative relations of the atoms within the formula Cu_wIn_xGai-_xSe_yS2-y, with 0.1<w<l, 0<x<l and 0<y<2. This example shows that all elements were indeed part of the disclosed nanoparticles as prepared by the disclsoed method, but is non-limiting in the sense that the percentage of the different atoms may be changed within these ranges during optimization and adaptation to commercial application. For example, in the final application gallium may be present in smaller amounts or even be absent, yielding CIS instead of CIGS nanoparticles, which may likewise be part of disclsoed photovoltaic paints.

[0040] Figure 5 provides a light absorbance curve of the nanoparticles, according to some embodiments of the invention. The light absorbance analysis of Figure 5 shows the characteristic light absorbance curve (light absorbance is unit-less, expressing the logarithm of the ratio of outgoing to incoming illumination) of nanoparticles with an energy bandgap of about 1.4 eV as a characteristic for samples with relatively high Ga content as evidenced in the XPS analysis (Figure 4). These results indicate that the bandgap is sufficient for the nanoparticles to be used in photovoltaic paint 210 for photovoltaic device 205.

[0041] Advantageously, compared to prior art methods, disclosed embodiments do not require ultra-high vacuum deposition techniques or use of hydrazine solutions, and do not require high temperature deposition and annealing temperatures. Moreover, the specific ligands that are used can be dissociated from the nanoparticles at much lower temperatures, reducing the hazards involved, and allowing simple deposition and application of the photovoltaic paint. Advantageously, disclosed embodiments avoid use of phosphines (used in the prior art to dissolve Se for producing CIGS), and enable using low synthesis temperatures (e.g., under 160°C, contrasted with prior art synthesis temperatures between 220-250°C in solution, and postdeposition heating to temperatures as high as 500°C or higher for other Cu-In-Se/S thin film fabrication methods) as well as low temperatures for removing the ligands.

[0042] It is noted that the term “about” used herein to modify values is understood to encompass ±10% of the respective value.

[0043] In the above description, an embodiment is an example or implementation of the invention. The various appearances of "one embodiment”, "an embodiment", "certain embodiments" or "some embodiments" do not necessarily all refer to the same embodiments. Although various features of the invention may be described in the context of a single embodiment, the features may also be provided separately or in any suitable combination. Conversely, although the invention may be described herein in the context of separate embodiments for clarity, the invention may also be implemented in a single embodiment. Certain embodiments of the invention may include features from different embodiments disclosed above, and certain embodiments may incorporate elements from other embodiments disclosed above. The disclosure of elements of the invention in the context of a specific embodiment is not to be taken as limiting their use in the specific embodiment alone. Furthermore, it is to be understood that the invention can be carried out or practiced in various ways and that the invention can be implemented in certain embodiments other than the ones outlined in the description above.

[0044] The invention is not limited to those diagrams or to the corresponding descriptions. For example, flow need not move through each illustrated box or state, or in exactly the same order as illustrated and described. Meanings of technical and scientific terms used herein are to be commonly understood as by one of ordinary skill in the art to which the invention belongs, unless otherwise defined. While the invention has been described with respect to a limited number of embodiments, these should not be construed as limitations on the scope of the invention, but rather as exemplifications of some of the preferred embodiments. Other possible variations, modifications, and applications are also within the scope of the invention. Accordingly, the scope of the invention should not be limited by what has thus far been described, but by the appended claims and their legal equivalents.

Claims

CLAIMS What is claimed is:

1. A method comprising: mixing an anion solution with a cation solution, wherein: the anion solution comprises a powder of Se dissolved in a mixture of at least one linear amine having a boiling point above 200°C and hexanethiol, and the cation solution comprises Cu-acetate, InCh and Ga-acetylacetonate dissolved oleylamine and heated to temperature of 100°C under vacuum, heating the mixture to a temperature of 160°C or less under inert conditions, and precipitating nanoparticles from the heated mixture after cooling thereof, wherein the nanoparticles have the formula Cu_wIn_xGai-_xSe_yS2-y, wherein 0.1<w<l, 0<x<l and 0<y<2.

2. The method of claim 1, wherein the at least one linear amine having a boiling point above 200°C comprises oleylamine and/or dodecylamine.

3. The method of claim 1, wherein the anion solution comprises 8 mmol Se powder dissolved in a 7:3 by volume oleylamine:hexanethiol mixture.

4. The method of claim 1, wherein the cation solution comprises 4 mmol Cu-acetate, 3 mmol InCh, 1 mmol Ga-acetylacetonate dissolved in oleylamine.

5. The method of claim 1, wherein the mixing is carried out by injecting the anion solution into the cation solution.

6. The method of claim 1, wherein the heating is carried out under nitrogen and/or argon, and for at least two hours.

7. The method of claim 1, wherein the precipitating of the nanoparticles is carried out by mixing the heated mixture with a solvent and adding an anti-solvent into the mixture with the solvent.

8. The method of claim 7, wherein the solvent comprises at least one of hexane, toluene and chloroform and the anti-solvent comprises ethanol and/or methanol.

9. The method of claim 1 , further comprising applying the heated mixture as part of a photovoltaic coating onto a structural element during a production process of the structural element.

10. The method of claim 9, further comprising applying top and bottom electric contact layers as parts of the photovoltaic coating.

11. The method of claim 10, wherein the substrate is a polymer layer, and the top and/or bottom electric contacts comprise metal nanowires.

12. Photovoltaic paint comprising: nanoparticles having the formula Cu_wIn_xGai-_xSe_yS2-y, wherein 0.1<w<l, 0<x<l and <y<2, wherein the photovoltaic paint is applicable on a substrate at a temperature below 160°Co form a photovoltaic device.

13. A photovoltaic device comprising a structural element having a photovoltaic coating comprising the photovoltaic paint of claim 12, applied as part of the photovoltaic coating onto the structural element as the substrate.

14. The photovoltaic device of claim 13, wherein the photovoltaic coating is applied onto the structural element as part of a production process of the structural element.

15. The photovoltaic device of claim 13, wherein the photovoltaic coating further comprises at least top and bottom electric contact layers.

16. The photovoltaic device of claim 13, wherein the photovoltaic coating further comprises at least one buffer layer comprising ZnS/ZnMgS and/or ZnO.

17. The photovoltaic device of claim 13, wherein the structural element comprises at least a part of any one of: a construction, a building envelope, windows, a barrier, a panel, a polymer layer, a canopy, a cladding, a tile, a laminate, a vehicle and an aerial vehicle.

18. The photovoltaic device of claim 13, wherein the substrate and an electrical contact attached thereto are transparent, and the photovoltaic paint is coated onto the transparent electrical contact.