Thin-film photovoltaic module having silver sulfide coating and method for manufacturing the same

Abstract

The thin film photovoltaic module with silver sulfide coating includes a glass substrate, on which a back contact layer, an absorption layer and a front electrode layer are sequentially stacked, and a metal grid conforming to the front electrode layer is coated on the upper surface of the front electrode layer, the metal grid is made of a paste containing silver, and the surface of the metal grid is covered with a black silver sulfide coating. The black silver sulfide coating formed on the surface of the metal grid reduces the optical reflection of the metal grid, lowering its reflectance, thereby reducing the brightness and improving the appearance of the photovoltaic circuit and module with the metal grid.

Description

Technical Field

[0001] The present invention belongs to the technical field of solar cells, and particularly relates to a thin-film photovoltaic module having a silver sulfide coating and a method for manufacturing the same.

Background Art

[0002] In order to improve the performance of CIGS (copper indium gallium diselenide) photovoltaic modules, in recent years, a technology has been developed by Avancis to improve conductivity by applying grid lines to a photovoltaic circuit. The grid lines are used to supplement the medium conductivity of the uppermost layer of the circuit absorber stack, which consists of zinc oxide doped with aluminum oxide (AZO) or other transparent conductive oxides (TCO) and has a specific ratio of metal conductivity. Due to its high metal conductivity, the grid becomes like a large number of busbars, providing a less obstructive path for charge carriers, allowing the charge carriers to flow along the side of the circuit facing the light. In this case, the series resistance of the solar power generation module is reduced.

[0003] Since the metal field is opaque, the conductive promotion effect by the grid is offset, so the area covered by the metal field becomes photovoltaically inactive, and the total dead area on the circuit increases. The grid consists of a highly reflective silver paint and is applied in the form of nanoparticles using a printing process. Therefore, most of the light irradiated on the grid is reflected without being absorbed. For an observer of a PV circuit or PV module equipped with a silver grid, the grid circuit or grid module appears brighter (higher L value) compared to a CIGS-PV circuit or module without a grid.

[0004] The SKALA type photovoltaic module from Avancis GmbH, commonly used in building-integrated photovoltaics (BIPV), utilizes the high absorption (low L* value) of the CIGS circuit, which acts as a deep black background for the front glass, giving it a very specific visible reflection spectrum achieved by magnetron sputtering. The combination of the circuit background and the colored front glass results in a photovoltaic module with distinct colors, each having specific color values ​​L*, a*, b*, or L, C, h. Some of the colors of the PV modules thus produced, particularly those with relatively low L* values, cannot be produced using the grid circuit because its reflectivity is too high. This applies largely to black and anthracite, which cannot be produced at all with the grid circuit, and to some extent to colors such as dark gray, gray, and bronze, and these colors exhibit measurable and / or visible brightness variations. [Overview of the project] [Problems that the invention aims to solve]

[0005] This invention provides a CIGS thin-film photovoltaic module having a silver sulfide coating and a method for manufacturing the same, addressing the shortcomings of the prior art. A specific technical proposal is as follows. [Means for solving the problem]

[0006] A thin-film photovoltaic module having a silver sulfide coating includes a glass substrate, on which a back contact layer, an absorption layer, and a front electrode layer are sequentially laminated. The upper surface of the front electrode layer is coated with a metal grid that conforms to the front electrode layer, the metal grid is made of a silver-containing paste, and the surface of the metal grid is covered with a black silver sulfide coating.

[0007] Furthermore, the metal grid consists of at least 10% or 40% silver.

[0008] Furthermore, one of the following methods for applying the metal grid is adopted: screen printing, inkjet printing, or parallel extrusion spraying.

[0009] A method for manufacturing a CIGS thin-film photovoltaic module having a silver sulfide coating includes the following steps:

[0010] Step S1: Fabricate a planar thin-film photovoltaic circuit.

[0011] Step S2: Form a metal grid by coating.

[0012] Step S3: The metal grid is cured or sintered.

[0013] Step S4: A metal grid is brought into contact with or exposed to a sulfide capable of forming sulfur ions, and a black silver sulfide coating is formed on its surface by reaction.

[0014] Step S5: Remove sulfide residue from the outside of the silver sulfide coating connected to the top layer of the metal grid, then perform a washing and drying process.

[0015] Furthermore, the form of the sulfide may be any one of the following: a soluble sulfide, gaseous hydrogen sulfide, or an organic sulfide.

[0016] Furthermore, the soluble sulfide is a hygroscopic alkali metal sulfide.

[0017] Furthermore, the hygroscopic alkali metal sulfide is powdered sodium sulfide.

[0018] Furthermore, the method of applying the powdered sodium sulfide to the metal grid involves forming a concentrated aqueous sodium sulfide solution within at least one hour due to the moisture absorption behavior of the sodium sulfide and the moisture in the air, and then reacting this aqueous solution with the silver on the surface of the metal grid to form a silver sulfide coating.

[0019] Furthermore, another form of applying the powdered sodium sulfide to the metal grid is to prepare an aqueous sodium sulfide solution in advance and contact and react it with the metal grid by any one of the methods of spraying, dipping, scraping, and impregnation to form a silver sulfide coating.

[0020] Furthermore, the aqueous sodium sulfide solution can also be applied to the surface of the metal grid by heating, vacuum evaporation, or vacuum deposition.

[0021] Furthermore, in all cases where hygroscopic alkali metal sulfides are used, after the sulfidation process, one or more washing steps should be carried out, and several drying steps should be carried out to remove the coating agent and some contained water to remove trace moisture in the processed metal grid circuit.

[0022] Furthermore, when using the gaseous hydrogen sulfide, place the metal grid in an airtight chamber filled with gaseous hydrogen sulfide, and the filling concentration and duration of the gaseous hydrogen sulfide are determined by the reaction rate of silver sulfide on the metal grid surface and the thickness or color of the desired silver sulfide coating.

[0023] Furthermore, the reaction between the silver on the metal grid surface and the organic sulfide varies depending on the aggregation state, that is, the organic sulfide reacts with the silver on the metal grid surface by gas-phase release or liquid-phase wetting to form a silver sulfide coating.

[0024] The beneficial effects of the present invention are as follows.

[0025] By forming a black silver sulfide coating on the surface of the metal grid, the optical reflection of the metal grid is reduced, and by reducing its reflectivity, the brightness of the photovoltaic circuit and module having the metal grid is reduced, and the appearance is improved.

Brief Description of the Drawings

[0026] [Figure 1]FIG. 1A is a schematic diagram of a general standard structure of a conventional solar cell, and FIG. 1B is a schematic diagram of the structure of the solar cell of the present invention. [Figure 2] It is a demonstration diagram of a concentrated Na2S solution prepared from hygroscopic Na2S powder on the surface of a circuit having grid lines (horizontal) and element structures (vertical) in the present invention under the influence of atmospheric humidity. [Figure 3] It is a demonstration diagram of current measurement on the surface of a circuit treated with Na2S for about 15 hours in the present invention. [Figure 4] It is a demonstration diagram of current measurement on the surface of a circuit not treated with Na2S in the present invention. [Figure 5] It is a demonstration diagram (in a wet state) of a circuit using silver grid lines treated with Na2S in the present invention. [Figure 6] It is a demonstration diagram (in a dry state) of a circuit using silver grid lines treated with Na2S in the present invention. [Figure 7] It is a demonstration diagram of comparison between an untreated (left) circuit and a circuit treated with Na2S (right) of the present invention.

Embodiments for Carrying out the Invention

[0027] In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be described in more detail below in connection with embodiments. It should be understood that the specific embodiments described here are only used for interpreting the present invention and are not used for limiting the present invention.

[0028] In the technical solution of the embodiment of the present application, in order to solve the technical problem of the high reflectivity of the metal grid in the thin-film photovoltaic module, the overall idea is as follows.

[0029] Currently, dissipating charge from the irradiated side of a ClGS thin-film photovoltaic cell by adding an additional grid on top of the front electrode layer made of TCO within a ClGS thin-film photovoltaic module has long been considered ineffective, especially since the usual printing technique for crystalline silicon PV is screen printing. In comparison, GIGS thin-film PV requires a very large printing screen, thus requiring a large amount of silvery printing paste. The silvery printing paste is exposed to the environment during printing, leading to premature degradation. Due to the need for a small printing width, the silvery paste gradually reaches its limit as it passes through the printing screen. Therefore, all publications on the topic of metal grids and CIGS photovoltaic cells published to date have focused on this point.

[0030] By minimizing the light shielding and light absorption losses of the metal grid on the front electrode layer, while simultaneously optimizing the TCO and the current flowing through the grid, CIGS batteries with a grid can provide better overall performance than CIGS batteries without a grid, i.e., achieve higher efficiency. One of the key features of such a grid is the high aspect ratio of the grid lines and the reduced TCO layer thickness, which optimizes light transmission efficiency.

[0031] In contrast, in crystalline silicon photovoltaic cells, front metal contacts are gradually replaced by back contacts. To realize an "all-black module" with a "typical battery structure" in crystalline silicon photovoltaic cells, in addition to the actual structure and coating of the solar cell, busbars with a black coating on the outside are used to absorb light to the maximum extent. Due to their relatively high aspect ratio, their visibility is low, so it is not necessary to blacken the narrower grid lines.

[0032] In CIGS photovoltaics, the requirements for visual uniformity and low reflectivity of the circuit have been relatively easy to meet. Therefore, ClGS circuits manufactured using the methods commonly used until now (without a grid) are well-suited for constructing color solar modules, as the color carrier (such as an interference color layer on the front glass) needs to make the background as dark and uniform as possible and minimize color shift. Although it increases efficiency, the combination of CIGS-PV and a metal grid somewhat negates the good applicability of CIGS circuits to color solar modules. This is because the brightness of the carrier circuit supporting the grid is too high (too high L* value), making it difficult to produce dark module colors, the grid pattern becomes visible through the color glass, changing the visual appearance, and the overall module color becomes a brighter hue. Due to the novelty of the problem, there is still no mature, commercially available solution to this issue. One necessary way to reduce the silvery sheen of the grid lines is to reduce the visible area of ​​the highly reflectivity metal by increasing the aspect ratio. However, the solution described here not only reduces the grid line width but also usually darkens the grid lines.

[0033] The method described herein relates to a device that generates electrical energy from light using the internal photovoltaic effect, in which a semiconductor, such as copper-indium-gallium-di(sulfide) (CIGS or CIGSSe) or doped silicon, functions as an absorbing layer that converts light energy into electrical energy, and the movement of charge on the light-facing side does not occur solely through the entire surface layer of a thin transparent conductive layer (e.g., in the case of a CIGS solar cell, transparent conductive oxide (TCO)), but rather the conduction of charge carriers is supported by metallic conductive paths ("grids") applied to the TCO.

[0034] To better understand the above technical proposal, the following will provide a detailed explanation of the technical proposal by combining the drawings in the specification with specific embodiments.

[0035] As shown in Figure 1, the thin-film photovoltaic module having a silver sulfide coating includes a glass substrate, on which a back contact layer 3, an absorption layer 1, and a front electrode layer 2 are sequentially laminated. The upper surface of the front electrode layer 2 is coated with a metal grid 4 that fits the front electrode layer 2. The metal grid 4 is made of a silver-containing paste, and the surface of the metal grid 4 is covered with a black silver sulfide coating 5.

[0036] By adopting the above-described technology, this thin-film photovoltaic module reduces the optical reflection of the metal grid and lowers its reflectivity by forming a black silver sulfide coating on the surface of the metal grid, thereby reducing the brightness of the photovoltaic circuit and module having a metal grid and improving its appearance.

[0037] Preferably, the metal grid 4 consists of at least 10% or 40% silver.

[0038] By adopting the above-described technology, in the case of a silicon solar cell in which the front electrode layer faces light, the conduction of charge carriers occurs via a metal conductor track ("grid") applied to the front electrode layer and preferably consisting of at least 10% to 40% silver.

[0039] Preferably, one of the following methods for applying the metal grid 4 is used: screen printing, inkjet printing, or parallel extrusion spraying.

[0040] By adopting the above technical proposal, printing technologies other than screen printing, such as inkjet printing (Avancis) or "parallel (extrusion) spraying," can be used. In addition, there are ways to minimize the area covered by the coating grid and maximize conductivity with the highest possible aspect ratio.

[0041] A method for manufacturing a thin-film photovoltaic module having a silver sulfide coating includes the following steps:

[0042] Step S1: Fabricate a planar thin-film photovoltaic circuit.

[0043] Step S2: Form a metal grid by coating.

[0044] Step S3: The metal grid 4 is cured or sintered.

[0045] Step S4: The metal grid 4 is brought into contact with or exposed to a sulfide capable of forming sulfur ions, and a black silver sulfide coating 5 is formed on its surface by reaction.

[0046] Step S5: Remove any sulfide residue from the outside of the silver sulfide coating 5 connected to the top layer of the metal grid 4, and then perform a washing and drying process.

[0047] By employing the above-described technical proposal, the thin-film photovoltaic module is darkened by the method described in the present invention, resulting in the entire thin-film photovoltaic module becoming optically very dark and obtaining a more uniform solar cell or photovoltaic circuit surface. In a broader sense, the present invention relates to any type of solar cell having a silver-based metal grid, i.e., a crystalline silicon solar cell having a metal grid on the upper part of the light incident side, i.e., on top of the emitter layer of a crystalline silicon solar cell. The reflectivity is reduced by selectively covering the highly reflective metallic silver surface of the grid with a dark layer without significantly affecting the optical or electrical properties of other components of the solar cell.

[0048] The method of the present invention is based on the fact that black silver sulfide is always formed when silver metal comes into contact with sulfide ions or other forms of reactive sulfur compounds that can at least intermediately form sulfide ions. Since such silver sulfide formation also occurs within the metal grid in the layers near the surface when in contact with a suitable form of reactive sulfur compound, a black silver sulfide coating is formed on the metal grid.

[0049] The active sulfur that reacts with elements to produce silver(II) sulfide follows the following chemical equation.

[0050] Ag+S → AgS Furthermore, the following chemical equation applies to the reaction between elemental silver and sulfide ions.

[0051] Ag+S 2- →AgS+2e- Preferably, the form of the sulfide may be any one of soluble sulfides, gaseous hydrogen sulfide, or organic sulfides.

[0052] Sulfur may exist in the form of elemental sulfur ("sulfur powder"), or it may be supplied to the reaction mainly in the form of soluble sulfides, such as alkali metal sulfides like sodium sulfide, gaseous or dissolved hydrogen sulfide, or sulfur-containing organic substances ("organosulfides") that can release sulfur as sulfides into the grid metal. By employing the above technical proposal, sulfur can be transported into the metal grid in various dosage forms and used in the reaction.

[0053] When elemental sulfur is used to carry out the reaction, vapor deposition of sulfur from the gas phase is preferable to achieve the most uniform coating on the circuit surface. While it is also possible to precipitate elemental sulfur from a carbon disulfide solution, this is not recommended for occupational safety and environmental protection reasons. By setting a predetermined storage period in the presence of the sulfur-containing reagent, the reaction process can be controlled, and the color intensity and depth of the silver sulfidation process within the grid can be controlled. Depending on the type of sulfur-containing reagent, heat treatment may be necessary after application to the circuit, and this temperature control can also be used to control the reaction process.

[0054] After the sulfur-containing reagent is removed, the stability of the formed silver sulfide means that no further reactions or side reactions are expected. This is because the CIGS structure is already saturated with chalcogenide sulfides and selenides on the one hand, and on the other hand, the layered package is well protected by the AZO outer layer and possible other migration-suppressing layers when exposed to sulfur-containing foreign matter, so that sulfide ions selectively react with the surface of the silver grid. The grid applied to the circuit as a suspension of nanoparticles is annealed after application for sintering, and the porosity of the gate silver is almost eliminated, so there is no risk of sulfur erosion at the depth of the grid lines.

[0055] The silver grid line sulfidation process described herein may be used to darken grid lines on a crystalline silicon solar cell, provided that the materials used and produced do not damage the crystalline silicon cell.

[0056] Preferably, the soluble sulfide is a hygroscopic alkali metal sulfide, and the hygroscopic alkali metal sulfide is powdered sodium sulfide.

[0057] Preferably, the method of applying the powdered sodium sulfide to the metal grid 4 involves forming a concentrated aqueous sodium sulfide solution within at least one hour due to the moisture absorption behavior of the sodium sulfide and the moisture in the air, and then reacting this aqueous solution with the silver on the surface of the metal grid 4 to form a silver sulfide coating 5.

[0058] One way to apply soluble sulfides by adopting the above technical proposal is to use them in the form of an aqueous solution. The simplest method may be to use powdered sodium sulfide (as an inexpensive, water-soluble, and hygroscopic sulfide) to form a silver grid and distribute it finely across the circuit. Due to the moisture in the air and the hygroscopic behavior of sodium sulfide, a concentrated solution will form within a few hours. The aqueous solution of sodium sulfide will react with the silver surface of the metal grid, affecting its reflectivity.

[0059] Preferably, another form of applying the powdered sodium sulfide to the metal grid 4 is to prepare an aqueous sodium sulfide solution in advance and bring it into contact with and react with the metal grid 4 by one of the following methods: spraying, dipping, scraping, or impregnation, to form a silver sulfide coating 5.

[0060] By adopting the above technical proposal, soluble sulfides may be applied by another method of pre-preparing an aqueous sodium sulfide solution. This solution allows the aqueous sodium sulfide solution to come into contact with the circuit and act on the silver surface of the grid wires within a specific time period, for example, by methods such as spraying, immersion, scraping, or impregnation.

[0061] Preferably, the aqueous sodium sulfide solution can also be applied to the surface of the metal grid by heating, vacuum evaporation, or vacuum deposition.

[0062] By adopting the above-described technical proposal, these methods are superior to the aforementioned methods that utilize aqueous components, due to the known sensitivity of circuit materials to water and moisture. Thanks to this process, the circuit does not come into contact with large amounts of water or aqueous solutions.

[0063] Preferably, in all cases where a hygroscopic alkali metal sulfide is used, one or more washing steps should be performed after the sulfidation process, and trace amounts of moisture in the treated metal grid 4 circuits should be removed by several drying steps to remove the coating agent and any contained water.

[0064] By adopting the above-described technical proposal, in all cases where the metal grid circuit comes into contact with alkali metal-containing materials, it is desirable that the absorber stack on the CIGS be equipped with a low-porosity sodium diffusion barrier layer (AZO, SiNxOy) to prevent uncontrolled diffusion of alkali ions into the absorber. In all cases where alkali metal sulfides are used, after sulfidation, one or more washing steps are required to remove excess reagent, and multiple drying steps are required to remove water and trace moisture from the treated circuit.

[0065] Furthermore, non-aqueous solvents, sulfides soluble in aqueous solutions, or other sulfur-containing chemicals may be used to treat the metal grid on the circuit. Using anhydrous solvents can avoid the effects of water on the potential degradation of the circuit material.

[0066] Preferably, when using gaseous hydrogen sulfide, the metal grid 4 is placed in an airtight chamber filled with gaseous hydrogen sulfide, and the filling concentration and duration of the gaseous hydrogen sulfide are determined by the reaction rate of silver sulfide on the surface of the metal grid 4 and the desired thickness or color of the silver sulfide coating 5.

[0067] By adopting the above technical proposal, the reaction can be carried out under boundary conditions, such as the presence of other gases (e.g., oxygen) that may be present during the reaction and potentially inhibit it, and the acidic reaction product may inhibit the formation of a dark silver sulfide layer. The optimal temperature and humidity of the gas mixture can be determined by a specific series of tests.

[0068] Preferably, the reaction between the silver on the surface of the metal grid 4 and the organic sulfide differs depending on the aggregation state, that is, the organic sulfide reacts with the silver on the surface of the metal grid 4 by gas-phase release or liquid-phase wetting to form a silver sulfide coating 5.

[0069] By adopting the above technical proposal, the application of gaseous or volatile organic sulfur compounds via the gas phase is similar to the treatment of the grid surface with gaseous hydrogen sulfide, and the liquid phase treatment of the metal grid surface with dissolved gaseous or volatile organic sulfur compounds is similar to wetting with a solution of soluble solid or liquid sulfides, such as sodium sulfide.

[0070] The experimental evidence for the process function in this invention is as follows:

[0071] As shown in Figure 3, when the current on the circuit treated with Na2S for approximately 15 hours was measured, the measured current value was 2.47 mA, and the peak value during the measurement was 2.6 mA. As shown in Figure 4, when the current on the circuit not treated with Na2S (the adjacent part of the circuit board used in Figure 2) was measured under almost the same light irradiation conditions, the measured instantaneous current value was 2.08 mA, and the peak value during the measurement was 2.5 mA.

[0072] As shown in Figure 5, the circuit using silver grid lines showed reduced brightness of the grid lines in the region treated with sulfide (the large dark spot on the left) after being treated with Na2S. The circuit shown here is in a wet state, and as a result, the overall brightness of the circuit and the grid lines are similar to the appearance in a stacked state.

[0073] As shown in Figure 6, the circuit using silver grid wires treated with Na2S is shown under a microscope (magnification approximately 5x) in a dry state. The center of the treated area shown here is on the left side of the image (darkened horizontal grid lines appearing gray), while the circuit lines without the silver sulfide layer (bright horizontal grid lines) are located on the right side of the image, in the upper and lower regions.

[0074] As shown in Figure 7, comparing the untreated circuit (left) with the circuit treated with Na2S (right), the grid of the treated circuit on the right (the area in the upper right corner) is almost invisible from the surrounding absorbers due to the optical masking of silver sulfide.

[0075] As can be seen from the experimental results in Figures 3 to 7, the silver sulfide coating formed by the surface reaction of the metal grid after treatment with Na2S reduces the reflectivity of the thin-film photovoltaic module, thereby increasing the photoelectric conversion efficiency of the thin-film photovoltaic module. It also reduces the brightness of the photovoltaic circuit and module with the metal grid, improving its appearance.

[0076] The foregoing describes only preferred embodiments of the present invention and is not intended to limit it. Any modifications, substitutions with equivalents, improvements, etc., made within the scope of the spirit and principles of this application should all be included within the scope of protection of the present invention. [Explanation of Symbols]

[0077] 1. Absorption layer 2 Front electrode layer 3. Backside contact layer 4 Metal grid 5. Silver sulfide coating

Claims

1. Step S1 involves sequentially laminating a back contact layer, an absorption layer, and a front electrode layer onto a glass substrate to fabricate a planar thin-film photovoltaic circuit. Step S2 involves forming a metal grid consisting of 10% or 40% silver by coating, Step S3 involves hardening or sintering the metal grid, Step S4 involves contacting or exposing a metal grid to a soluble sulfide capable of forming sulfur ions, thereby forming a black silver sulfide coating on its surface by reaction. Step S5 involves removing sulfide residue from the outside of the silver sulfide coating connected to the uppermost layer of the metal grid, and performing a washing and drying process. A method for manufacturing a thin-film photovoltaic module having a silver sulfide coating, characterized by including the following:

2. The soluble sulfide is a hygroscopic alkali metal sulfide. A method for manufacturing a thin-film photovoltaic module having a silver sulfide coating as described in feature 1.

3. The hygroscopic alkali metal sulfide is powdered sodium sulfide. A method for manufacturing a thin-film photovoltaic module having a silver sulfide coating as described in feature 2.

4. The method of applying the powdered sodium sulfide to the metal grid involves forming a concentrated sodium sulfide aqueous solution within at least one hour due to the hygroscopic behavior of the sodium sulfide and moisture in the air, and then reacting this aqueous solution with the silver on the surface of the metal grid to form a silver sulfide coating. A method for manufacturing a thin-film photovoltaic module having a silver sulfide coating as described in feature 3.

5. Another method of applying the powdered sodium sulfide to a metal grid involves preparing an aqueous sodium sulfide solution in advance and contacting and reacting it with the metal grid by one of the following methods: spraying, dipping, scraping, or impregnation, to form a silver sulfide coating. A method for manufacturing a thin-film photovoltaic module having a silver sulfide coating as described in feature 3.

6. The aqueous sodium sulfide solution is applied to the surface of the metal grid by heating, vacuum evaporation, and vacuum deposition. A method for manufacturing a thin-film photovoltaic module having a silver sulfide coating as described in feature 5.

7. In all cases where a hygroscopic alkali metal sulfide is used, in step S5, one or more washing steps are performed, and several drying steps are performed to remove the coating agent and any contained water, thereby removing any trace moisture from the treated metal grid circuit. A method for manufacturing a thin-film photovoltaic module having a silver sulfide coating according to any one of claims 2 to 6.

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