KR20100119871A - Photovoltaic cell and substrate for photovoltaic cell - Google Patents

Abstract

The present invention relates to a photovoltaic cell (1) comprising an absorptive photovoltaic material, in particular a cadmium-based photovoltaic material, the photovoltaic cell comprising a front substrate 10, in particular a transparent glass substrate, the substrate being on a major surface, in particular a silver substrate A transparent electrode coating 100 comprising a thin stack comprising at least one metallic functional layer 40 and at least two antireflective coatings 20, 60, wherein the antireflective coating comprises at least one antireflective layer 24, 26; 66, 68, respectively, wherein the functional layer 40 is disposed between the two antireflective coatings 20, 60, and is disposed on the metallic functional layer 40 on the opposite side from the substrate. 60 includes two or more antireflective layers 66, 68, wherein the antireflective layer 68 furthest from the metallic functional layer 40 is more resistant than the antireflective layer 66 closest to the metallic functional layer 40. It is characterized by.

Description

Photovoltaic and photovoltaic substrates {PHOTOVOLTAIC CELL AND SUBSTRATE FOR PHOTOVOLTAIC CELL}

The present invention relates to photovoltaic front substrates, in particular transparent glass substrates and photovoltaic cells comprising such substrates.

In photovoltaic cells, a photovoltaic system having a photovoltaic material that generates electrical energy through the effect of incident radiation is disposed between the backplate substrate and the front substrate, which is the first substrate to pass before the incident radiation reaches the photovoltaic material. .

In photovoltaic cells, the front substrate generally has a transparent electrode coating below the major surface that is turned towards the photoelectric material, which is in electrical contact with the photoelectric material disposed below if the main direction of arrival of the incident radiation is assumed to pass via the top surface. Have

Thus, the front electrode coating generally constitutes the negative terminal of the photovoltaic cell.

Of course, the photovoltaic cell also has an electrode coating that constitutes the positive terminal of the photovoltaic cell in the direction of the backplate substrate, but generally the electrode coating of the backplate substrate is not transparent.

In the context of the present invention, the term "photovoltaic cell" should be understood to mean any assembly of components that generate a current between their electrodes by solar radiation conversion, and the dimensions of this assembly, the strength of the generated current and It does not matter whether the voltage, in particular the assembly of these components, has one or more internal electrical connections (serial and / or parallel). Therefore, the concept of "photocell" in the context of the present invention is equivalent to the concept of "photovoltaic module" or "photovoltaic panel".

Materials commonly used for transparent electrode coating of front substrates are generally transparent conductive oxide (TCO) based materials, such as indium tin oxide (ITO) based, or aluminum doped zinc oxide (ZnO: Al). Or boron doped zinc oxide (ZnO: B) based, or fluorine doped tin oxide (SnO ₂ : F) based materials.

The materials may be chemically, for example by CVD (chemical vapor deposition), optionally by PECVD (plasma enhanced CVD), or physically, for example by cathode sputtering, optionally by magnetron sputtering (ie, magnetically enhanced sputtering). Deposited by vacuum deposition.

However, in order to obtain the desired electrical conductivity or the desired low resistance, electrode coatings made of TCO-based materials must be deposited at relatively thick physical thicknesses of approximately 500 to 1000 nm and sometimes even higher, given the cost of these materials. Deposition of the material into a layer having such a thickness would be costly.

If the deposition process requires a heat source, the manufacturing cost is further increased.

Another major drawback of electrode coatings made from TCO-based materials is the fact that, for selected materials, the physical thickness is determined so that there is always a compromise between the final resulting electrical conductivity and the final resulting transparency. The larger the higher the conductivity but the lower the transparency, conversely the smaller the physical thickness, the higher the transparency but the lower the conductivity.

Therefore, electrode coatings made of TCO-based materials cannot independently optimize the conductivity and its transparency of the electrode coating.

The prior art international patent application WO 01/43204 teaches a method of making a photovoltaic cell, in which the transparent electrode coating is not made of a TCO-based material, but rather a thin film stack deposited on the main surface of the front substrate. Wherein the coating comprises in particular at least one metallic functional layer of silver substrate and at least two antireflective coatings, each of the antireflective coatings comprising at least one antireflective layer, the functional layer being between the two antireflective coatings Is placed.

The method is meaningful in that one or more high refractive layers made of oxides or nitrides can be deposited below the metallic functional layer and above the photovoltaic material, given the direction of incident light entering the cell from above.

In the exemplary embodiment provided in the above international patent application publication, two antireflective coatings disposed on both sides of the metallic functional layer, ie an antireflective coating disposed below the metallic functional layer in the direction of the substrate and the metallic functional layer on the opposite side from the substrate The antireflective coating disposed thereon comprises at least one layer each made of a highly refractive material, in this case zinc oxide (ZnO) or silicon nitride (Si ₃ N ₄ ).

However, this solution can be further improved.

The prior art also discloses US Patent US 6 169 246, which relates to a photovoltaic cell having a cadmium-based absorbing photovoltaic material, said cell having a transparent glass front substrate having a transparent electrode coating composed of a transparent conductive oxide (TCO) on a major surface thereof. It includes.

According to this patent, the buffer layer does not form part of the TCO electrode coating or photovoltaic material since a buffer layer made of zinc stannate is interposed on and under the photoelectric material.

An important object of the present invention is to improve the efficiency of the cell by making charge transfer easily between the electrode coating and the photovoltaic material, in particular cadmium-based material.

Another important object is also to produce transparent thin film based electrode coatings which are simple to manufacture and which are as inexpensive to produce on an industrial scale.

Therefore, as claimed in claim 1, one subject of the present invention is generically a photovoltaic cell having an absorbent photovoltaic material, in particular a cadmium-based material. The cell comprises a front substrate, in particular a transparent glass substrate, having a transparent electrode coating on a major surface, in particular a thin electrode stack comprising at least one metallic functional layer of a silver substrate and at least two antireflective coatings; Each comprises one or more antireflective layers, the functional layer being disposed between the two antireflective coatings, wherein the antireflective coating disposed on the metallic functional layer on the opposite side from the substrate comprises two or more antireflective layers, the most from the metallic functional layer The far antireflective layer is characterized by being more resistant than the antireflective layer closest to the metallic functional layer.

The resistivity ρ corresponds to the product of the resistance R _□ per layer □ of the layer and its actual thickness.

In a preferred variant of the invention, the antireflective layer furthest from the metallic functional layer is at least 5 times, or even at least 10, or even at least 50, or even at least 100 times the resistivity of the antireflective layer closest to the metallic functional layer, Even at least 200 times, or at least 500 times, or even at least 1000 times.

The farthest and more resistive antireflective layer from the metallic functional layer is from 5 × 10 ⁻³ Ω.cm to 10 Ω.cm, or from 10 ⁻² Ω.cm to 5 Ω.cm, or even from 5 × 10 ⁻² Ω.cm to It is preferable to have a specific resistance p of 1 Ωcm.

The more conductive antireflective layer closest to the metallic functional layer is 10 ⁻⁵ Ω.cm or more but less than 5 × 10 ⁻³ Ω.cm, or 5 × 10 ^-4 Ω.cm to 2 × 10 ^-3 Ω.cm, or even It is preferable to have a resistivity p between 10 ^-4 Ω.cm and 10 ^-3 Ω.cm.

Further, the antireflective layer furthest from the metallic functional layer preferably has an optical thickness of 2-50% of the total optical thickness of the antireflective coating furthest from the substrate, and in particular 2 to 2 of the total optical thickness of the antireflective coating furthest from the substrate. Have an optical thickness of 25%, or even 5-20%.

The antireflective layer furthest from the metallic functional layer preferably has an actual thickness of 2 to 100 nm, preferably 5 to 50 nm, or even 10 to 30 nm.

Antireflection layer

Optionally doped zinc oxide (ZnO), for example ZnO: Al, ZnO: B, or ZnO: Ga;

Optionally doped tin oxide (SnO ₂ ), for example SnO ₂ : F;

Optionally doped titanium oxide (TiO ₂ ), for example TiO ₂ : Nb;

Optionally doped gallium oxide (Ga ₂ O ₃ );

Optionally doped indium oxide (In ₂ O ₃ );

Optionally doped silicon oxide (SiO ₂ ) substrate, or

Indium tin mixed oxide (ITO),

Gallium zinc mixed oxide (GZO),

Indium zinc hybrid oxide (IZO),

Zinc tin hybrid oxide (Zn ₂ SnO ₄ ), or

It is preferably based on an indium gallium zinc mixed oxide (IGZO), which oxide is optionally nonstoichiometric.

The antireflective layer closest to the metallic functional layer is generally a transparent conductive oxide (TCO) substrate obtained from at least one element of Al, Ga, Sn, Zn, Sb, In, Cd, Ti, Zr, Ta, W and Mo, in particular the It is preferred that it is an oxide substrate based on the other of said elements doped with at least one of the elements, said oxide being optionally substoichiometric in oxygen.

The term "dope" is understood herein to mean the presence of one or more other metal elements in an atomic ratio of metal (or oxygen element) in the range of 0.5 to 10%.

Hybrid oxides are oxides of metallic elements herein, and each metallic element is present in an atomic ratio of up to 10% of the metal (excluding oxygen elements).

In one particular embodiment, the antireflective layer closest to the metallic functional layer and the antireflective layer furthest from the metallic functional layer are the same oxide substrate, in particular

Zinc oxide (ZnO);

Tin oxide (SnO ₂ );

Titanium oxide (TiO ₂ );

Gallium oxide (Ga ₂ O ₃ );

Indium oxide (In ₂ O ₃ );

Silicon oxide (SiO ₂ ) substrate or

Indium tin mixed oxide (ITO),

Gallium zinc mixed oxide (GZO),

Indium zinc hybrid oxide (IZO),

Zinc tin hybrid oxide (Zn ₂ SnO ₄ ), or

It is based on indium gallium zinc mixed oxide (IGZO), which oxide is optionally nonstoichiometric.

The antireflective layer, which is closest to the metallic functional layer and less resistant, preferably constitutes the first layer of the top antireflective coating disposed on the metallic functional layer on the opposite side from the substrate.

The antireflective layer furthest from the metallic functional layer and more resistive preferably constitutes the last layer of the upper antireflective coating disposed on the metallic functional layer on the opposite side from the substrate. Thus, the antireflective layer furthest from the metallic functional layer constitutes the last layer of the electrode coating, and thus is in direct contact with the photoelectric material.

On the one hand, it is particularly preferred that the interface between the electrode coating according to the invention comprising the last layer more resistive in optical definition, and on the other hand as smooth as possible the boundary between the photoelectric material, in particular the cadmium-based material.

Thus, the antireflective layer furthest from the metallic functional layer preferably has a surface roughness of 5 to 250 angstroms, in particular 15 to 100 angstroms, or 10 to 50 angstroms.

Observing that the absorbance of conventional photovoltaic materials differs from material to material, the inventors have attempted to define the necessary optical properties needed to form thin film stacks of the types shown above in order to form front electrode coatings for solar cells.

The antireflective coating disposed on the metallic functional layer on the opposite side from the substrate preferably has an optical thickness of approximately ½ of the maximum absorption wavelength λ _m of the photoelectric material.

The antireflective coating disposed below the metallic functional layer in the direction of the substrate preferably has an optical thickness of approximately ⅛ of the maximum absorption wavelength λ _m of the photoelectric material.

However, in a preferred variant, the maximum absorption wavelength λ _m of the photovoltaic material is weighted by the solar spectrum. In this embodiment, the antireflective coating disposed on the metallic functional layer on the opposite side of the substrate has an optical thickness of approximately ½ of the maximum wavelength λ _M of the product of the absorption spectrum and the solar spectrum of the photovoltaic material.

In this variation, the antireflective coating disposed below the metallic functional layer in the direction of the substrate also has an optical thickness of approximately 의 of the maximum wavelength λ _M of the product of the absorption spectrum and the solar spectrum of the photovoltaic material.

In a preferred embodiment, the antireflective coating disposed on the metallic functional layer has an optical thickness of 0.45 to 0.55 times the maximum absorption wavelength λ _m of the photovoltaic material, and preferably, the antireflective coating disposed on the metallic functional layer is photoelectric It has an optical thickness of 0.45 to 0.55 times the maximum wavelength λ _M of the product of the absorption spectrum and the solar spectrum of the material.

Further, in a preferred embodiment, the antireflective coating disposed below the metallic functional layer has an optical thickness of 0.075 to 0.175 times the maximum absorption wavelength λ _m of the photoelectric material, and preferably, the antireflective disposed under the metallic functional layer The coating has an optical thickness of 0.075 to 0.175 times the maximum wavelength λ _M of the product of the absorption spectrum of the photovoltaic material and the solar spectrum.

Thus, according to the invention, in order to obtain the highest efficiency of the photovoltaic cell, the optimum optical path is a function of the maximum absorption wavelength λ _m of the photovoltaic material, or preferably the maximum wavelength λ of the product of the absorption spectrum and the solar spectrum of the photovoltaic material. _It is defined as a function of _M.

The solar spectrum referred to herein is the AM 1.5 solar spectrum defined by the ASTM standard.

In the context of the present invention, the term "coating" should be understood to mean that there may be several layers of different materials in the coating.

In the context of the present invention, the term "antireflective layer" should be understood in terms of its nature to mean that the material is nonmetallic, ie not metal. In the context of the present invention, the term refers to the resistivity of a conductor (typically ρ <10 ⁻³ Ω · cm), the resistivity of an insulator (typically ρ> 10 ⁹ Ω · cm), or the resistivity of a semiconductor (usually the It should not be understood to introduce any restrictions on the resistivity of a material, which can be between two values).

Completely surprisingly independent of any other properties, a thin film stack with a functional monolayer having an antireflective coating disposed over a metallic functional layer having an optical thickness of approximately four times the optical thickness of the antireflective coating disposed under the metallic functional layer. The optical path of the electrode coating having a can improve the efficiency of the solar cell, and can also improve the resistance to stress generated during operation of the cell.

The purpose of the coatings disposed on the side of the metallic functional layer is to impart "antireflective" to the metallic functional layer. This is why they are called "antireflective coatings".

In fact, even with a small physical thickness (approximately 10 nm) by the functional layer alone, the desired conductivity of the electrode coating can be obtained, but the layer will be highly resistant to the passage of light and electromagnetic radiation.

In the absence of such an antireflection system, the light transmittance would be too low and the light reflectivity would be too high (in the visible and near-infrared region as it is a matter of the manufacture of photocells).

As used herein, the term "optical path" has a specific meaning and is used to refer to the sum of the various optical thicknesses of the various antireflective coatings on the bottom or top of the (each) metallic functional layer of the produced interference filter. The optical thickness of the coating is equal to the product of the physical thickness of the layer and the refractive index of the material if only a single layer is present in the coating, or the sum of the product of the physical thickness of each layer and the refractive index of the material of each layer, if multiple layers are present It is recalled that

The optical path according to the invention is, absolutely, a function of the physical thickness of the metallic functional layer, but is actually within the range of the physical thickness of the metallic functional layer which makes it possible to obtain the desired conductance, that is to say it does not appear to change. Thus, the solution according to the invention is suitable when the functional layer (s) is a silver substrate and has a (total) physical thickness of 5 nm to 20 nm.

The type of thin film stack according to the invention is for the manufacture of glazing with improved thermal insulation of the "low-e, low-emissivity" and / or "solar control" type and is used in the field of construction or automotive glazing. Known.

Accordingly, the inventors have found that it is particularly desirable to reinforce, in particular, heat-treat, a particular stack of the type used for low emissivity glazing, in particular a substrate having a stack, i. It has been appreciated that the stack used when desired can be used to make electrode coatings for photovoltaic cells.

Therefore, another subject of the present invention is a thin film stack for building glazing in order to produce a photovoltaic front substrate, in particular a stack of the type of "reinforceable" or "reinforced" having the features according to the invention, in particular the low according to the invention. Emissivity stacks, specifically low emissivity stacks to be "enhanced" or "enhanced".

The term "reinforceable" stack or substrate within the context of the present invention is to be understood to mean that the essential optical and thermal properties (expressed as sugar resistance, directly related to emissivity) are preserved during the heat treatment.

Thus, for example, glazing panels incorporating reinforced and unreinforced substrates coated in the same stack, on one and the same surface of a building, are distinguished from one another simply by visually observing color and / or light reflectance / transmittance upon reflection. In this impossible state, they can be placed close together.

For example, a stack or substrate coated with a stack having the following changes before and after heat treatment will be considered reinforceable since these changes will not be noticed visually:

Light transmittance change ΔT _L less than 3%, or even less than 2% (in the visible region); And / or

Small light reflectivity change ΔR _L less than 3%, or even less than 2% (in the visible region); And / or

(Lab 시스템에서). -Less color change of less than 3, or even less than 2

(In a lab system).

A stack or substrate to be "strengthened" in the context of the present invention is understood to mean that the optical and thermal properties of the coated substrate are acceptable after heat treatment, while not previously acceptable or in some cases not at all acceptable. shall.

For example, a stack or substrate coated with a stack having the following properties after heat treatment but not meeting one or more of the following properties before heat treatment is considered to be "hardened" in the context of the present invention:

High light transmission T _L (in the visible range) of at least 65%, or even 70%, or even 75%; And / or

Low absorbance of 10% or less, or even 8% or less, or even 5% or less (in the visible range, defined as 1-T _L -R _L ); And / or

- at least as long as conventional high resistance per □ □ the conductive oxide is used per resistance R _□, particularly 20 Ω / □ or less, or even 15 Ω / □ or less, or even 10 Ω / □ or less.

Thus, the electrode coating must be transparent. Therefore, the electrode coating should have a minimum average light transmittance of 65%, or even 75%, more preferably 85%, even especially 90% or more in the 300 to 1200 nm wavelength range when deposited on the substrate.

If the front substrate is subjected to a heat treatment, in particular a tempered heat treatment after deposition of the thin layer and prior to mounting the front substrate into the photovoltaic cell, the substrate coated with the stack serving as the electrode coating may have a low transparency before such a heat treatment. For example, the substrate may have a light transmittance of less than 65%, or even less than 50% in the visible region before the heat treatment.

The important point is that the electrode coating must be transparent before the heat treatment, and after the heat treatment, at least 65%, or even at least 75%, more preferably at least 85%, even in the 300 to 1200 nm wavelength range (in the visible region) In particular, it should be enough to have an average light transmittance of 90% or more.

Moreover, in the context of the present invention, the stack does not have the absolute highest possible light transmittance, but in the context of the photovoltaic cell according to the present invention.

In addition, the antireflective coating disposed below the metallic functional layer acts as a barrier to diffusion, in particular as a barrier to the diffusion of sodium from the substrate, thereby causing the electrode coating, more specifically the metallic functional layer, in particular during any heat treatment. In particular, it may also have a chemical barrier function to protect during the reinforcement heat treatment.

In another particular embodiment, the substrate comprises a base antireflective layer having a low refractive index near the refractive index of the substrate under the electrode coating, wherein the base antireflective layer is preferably a silicon oxide substrate or an aluminum oxide substrate or a mixture of both. .

In addition, this dielectric layer constitutes a barrier to diffusion of chemical diffusion barrier layers, in particular sodium derived from the substrate, so that the electrode coating and more specifically the metallic functional layer, in particular during heat treatment, in particular during the heat treatment heat treatment or of the photovoltaic material Can protect for treatment.

In the context of the present invention, a dielectric layer refers to a layer that does not participate in charge transfer (current) or a layer in which the effect of participation in charge transfer can be considered zero compared to the effects of other layers of the electrode coating.

Furthermore, the base antireflection layer preferably has a physical thickness of 10 to 300 nm, or 35 to 200 nm, more preferably 50 to 120 nm.

This metallic functional layer may be a silver, copper or gold substrate and may be selectively doped with at least one of these elements.

The expression "based on" is generally understood to mean a layer containing mainly the substance, that is, a layer containing 50% or more of the substance in molar mass. Therefore, the expression "based on" includes doping.

The metallic functional layer is preferably deposited on the thin dielectric layer in crystallized form, and the dielectric layer is also preferably crystallized (hence the dielectric layer is termed a "wet layer" as it promotes proper crystallographic orientation of the metal layer deposited on top. ).

The thin film stack producing the electrode coating is preferably a functional monolayer coating, ie a single functional layer. However, it may be a functional multilayer, in particular a functional bilayer.

Thus, the functional layer is preferably an oxide, in particular a zinc oxide substrate, and is deposited on top of or even directly over the wet layer, optionally doped with aluminum.

The physical (or actual) thickness of the wet layer is preferably 2 to 30 nm, more preferably 3 to 20 nm.

The wet layer is dielectric and preferably has a resistivity ρ of 0.5 Ω.cm <ρ <200 Ω.cm or 50 Ω.cm <ρ <200 Ω.cm (defined as the product of the resistance per □ of layer and its thickness). It is a substance having.

The stack is generally obtained by a series of depositions performed using vacuum techniques such as sputtering, optionally magnetron sputtering. In addition, one or even two very thin coatings, termed "blocker coatings" and do not form part of an antireflective coating and are disposed on, on or on each side of a metallic functional layer, in particular a metal layer of a silver substrate Wherein the coating is present on the lower surface of the functional layer in the direction of the substrate and acts as a bond, nucleation and / or protective coating during possible heat treatments performed after deposition, the coating being on the upper surface of the functional layer and That the metallic functional layer is damaged by the attack and / or migration of oxygen, particularly during any heat treatment, or even by the movement of oxygen when the upper layer is deposited by sputtering in the presence of oxygen. It acts as a protective coating or "sacrifice" coating to prevent.

In the context of the present invention, when it is specified that a layer or coating (including one or more layers) is deposited directly under or just above another deposited layer or coating, another layer is interposed between these two deposited layers or coatings. Can't be.

Preferably, the at least one blocker coating is a Ni or Ti substrate or a Ni-based alloy, in particular a NiCr alloy substrate.

Preferably, the coating disposed below the metallic functional layer in the direction of the substrate comprises a layer of a mixed oxide substrate, in particular a layer of a zinc tin mixed oxide or an indium tin mixed oxide (ITO) substrate.

In addition, the coating disposed below the metallic functional layer in the direction of the substrate and / or the coating disposed over the metallic functional layer may be of a silicon nitride substrate selectively doped with a layer having a high refractive index, in particular at least two refractive indexes, for example aluminum or zirconium. It may comprise a layer.

In addition, the coating disposed below the metallic functional layer in the direction of the substrate and / or the coating disposed over the metallic functional layer may comprise a layer having a very high refractive index, in particular a refractive index of at least 2.35, for example a layer of a titanium oxide substrate. .

The substrate may comprise a coating of a photovoltaic material, in particular a cadmium-based material substrate, on top of the electrode coating on the opposite side from the front substrate.

Thus, the preferred structure of the front substrate according to the invention is a type of substrate / (optional base antireflective layer) / electrode coating / photoelectric material, or other type of substrate / (selective base antireflective layer) / electrode coating / photoelectric material Structure of electrode coating.

In one specific variant, the electrode coating is a stack for building glazing, in particular a "reinforceable" stack for building glazing or a stack for building glazing to be "hardened", in particular a low emissivity stack, in particular a "reinforceable" low emissivity stack or "reinforced" Low emissivity stack, which is a feature of the present invention.

The invention furthermore relates to a photovoltaic substrate according to the invention, in particular an architectural glazing substrate coated with a thin film stack having the features of the invention, in particular an "reinforceable" substrate or "reinforcement" for an architectural glazing with the features of the invention. Substrates for architectural glazing, in particular low emissivity substrates, in particular "reinforceable" low emissivity substrates or features to be "reinforced" low emissivity substrates having the features of the invention.

All layers of the electrode coating are preferably deposited by vacuum deposition techniques, but the first layer or first layers of the stack are optionally vacuumed by other techniques, for example by pyrolysis type pyrolysis techniques or CVD. It is not intended to exclude that it may optionally be deposited under plasma enhancement.

Advantageously, electrode coatings according to the invention with thin film stacks are much more mechanically resistant than TCO electrode coatings. Thus, the life of the photovoltaic cell can be increased.

Also advantageously, due to its small physical thickness when compared to electrodes made of TCO-based materials, electrodes consisting of one or more metallic functional layers according to the invention are much more difficult to etch, especially by laser etching (low energy and short time). It is easy and there is no need to perform a longitudinal separation step (called a “modular” step) over the entire thickness of the electrode, and this etching step also requires less material than for an electrode made of TCO-based material for the same etch width. Is removed, thereby reducing the risk that the removed material will contaminate the cell.

Also advantageously, the electrode coating according to the invention can also be used as a back electrode coating, especially where at least a small part of the incident radiation is desired to pass completely through the photovoltaic cell.

Hereinafter, the details and advantageous features of the present invention will be described through the non-limiting examples shown in the accompanying drawings.

1 shows a prior art photovoltaic front substrate having a base antireflective layer coated with an electrode coating made of transparent conductive oxide.

2 shows a photovoltaic front substrate according to the invention coated with an electrode coating consisting of a functional monolayer thin film stack and having a base antireflective layer.

3 shows quantum efficiency curves for three types of photovoltaic materials.

4 shows the actual yield curve corresponding to the product of absorption spectra and solar spectra of the three photovoltaic materials.

5 is a view for explaining the principle of the durability test for photovoltaic cells.

6 is a cross-sectional view of a photovoltaic cell.

In Figures 1, 2, 5 and 6, the ratios of the thicknesses of the various coatings, layers and materials have not been strictly observed to make them easier to review.

1 shows a prior art photovoltaic front substrate 10 ′ with an absorbing photoelectric material 200, which substrate 10 ′ is a transparent electrode consisting of a TCO layer 66 conducting current on the major surface. Has a coating 100 '.

The front substrate 10 ′ is disposed in the photovoltaic cell such that the front substrate 10 ′ is the first substrate to pass before the incident radiation R reaches the photovoltaic material 200.

In addition, the substrate 10 'includes a base antireflective layer 22 having a low refractive index n ₂₂ close to the refractive index of the substrate under the electrode coating 100', ie directly above the substrate 10 '.

Substrate 10 ′ further includes a buffer layer (not shown) on electrode coating 100 ′ and below photovoltaic material 200.

2 shows a photovoltaic front substrate 10 according to the present invention.

The front substrate 10 also has a transparent electrode coating 100 on the major surface, where the electrode coating 100 comprises at least one metallic functional layer 40 of a silver substrate and at least two antireflective coatings 20, 60. A thin film stack comprising a thin film stack, wherein the coating comprises at least one thin antireflective layer (24, 26; 66, 68), wherein the functional layer (40) is disposed between the two antireflective coatings, Of these, what is called the bottom anti-reflective coating 20 is disposed below the functional layer in the direction of the substrate, and the other, which is called the top anti-reflective coating 60 is disposed on the functional layer in the opposite direction of the substrate.

The thin film stack constituting the transparent electrode coating 100 of FIG. 2 has a stack structure of a low emissivity substrate stack structure type that can be selectively reinforced or reinforced with a functional monolayer, which is for example architectural glazing used in buildings. It can be found in the commercially available field.

Two examples of Example 1 and Example 2 were prepared based on a stack structure with the following functional monolayers:

For example 1 is based on the structure shown in FIG. 1;

The case of Example 2 is based on the structure shown in FIG. 2 except that the stack does not comprise an overblocker coating.

In addition, in all the examples below, the layer is deposited on substrates 10 ', 10 made of transparent soda lime glass having a thickness of 4 mm.

The indices given below were measured at a typical 550 nm wavelength.

The electrode coating 100 ′ of Example 1 is a conductive aluminum doped zinc oxide substrate.

The stack constituting the electrode coating 100 of Example 2 consists of a thin film stack comprising the following in order:

An antireflection layer 24, which is a dielectric layer based on titanium oxide, having a refractive index n = 2.4;

An antireflection layer 26 which is a dielectric oxide based wet layer, in particular an antireflection layer having an index of refraction n = 2, which is optionally a doped zinc oxide substrate;

Optionally, a lower surface blocker coating (not shown), such as a Ti substrate or a NiCr alloy substrate coating, which may be disposed directly below the functional layer 40 but is not provided herein; This coating is generally needed in the absence of the wet layer 26, but is not necessarily necessary;

A single functional layer 40 made of silver and disposed herein directly above the wet coating 26;

A top blocker coating 50, which is a Ti substrate or a NiCr alloy substrate and which may be disposed directly above the functional layer 40, but which is not provided in the embodiment;

A conductive antireflective layer having a zinc oxide substrate doped with aluminum, having a refractive index of n = 2, and having a specific resistance of 0.35 × 10 ⁻³ Ω.cm to 2.5 × 10 ⁻³ Ω.cm, in particular approximately 10 ⁻³ Ω.cm (66) wherein the layer is deposited directly above the functional layer 40 under an argon atmosphere from a ceramic target (comprising about 2% aluminum, 49% zinc and 49% oxygen);

A dielectric termination layer 68, which is antireflective, based on tin zinc oxide Sn _x Zn _y O _z , has a refractive index of n = 2.1, and has a resistivity of approximately 1 Ω.cm, wherein the layer is 25% oxygen ( 0 ₂ ) and deposited from a metal target (comprising about 50% tin, 50% zinc) under an atmosphere consisting of 75% argon).

Layers of tin zinc mixed oxide substrate over their entire thickness, depending on the targets used to deposit these layers, may vary the variable Sn / Zn ratio over their entire thickness, especially when several targets of different compositions are used to deposit the layers or It should be appreciated that it may have a variable dopant concentration.

For example, the photovoltaic material 200 is based on cadmium telluride.

The quantum efficiency QE of this material is shown in FIG. 3 along with the quantum efficiency of microcrystalline silicon (grain size is approximately 100 nm) and the quantum efficiency of amorphous (ie amorphous) silicon, and other photoelectric materials are also within the context of the present invention. Is suitable in

Recall that in this specification, as is well known, the quantum efficiency QE is a representation of the probability (between 0 and 1) of the incident photons having a given wavelength on the x-axis being converted to electron-hole pairs.

As can be seen from FIG. 3, the maximum absorption wavelength λ _m , that is, the wavelength at which the quantum efficiency is maximum (ie, the wavelength when the quantum efficiency is maximum) is as follows:

The maximum absorption wavelength of amorphous silicon a-Si, ie λ _m (a-Si), is 520 nm;

The maximum absorption wavelength of the microcrystalline silicon μc-Si, ie λ _m (μc-Si), is 720 nm;

The maximum absorption wavelength of cadmium telluride CdTe, ie λ _m (CdTe), is 600 nm.

In the first order approximation of the optical path of the stack, the maximum absorption wavelength λ _m is sufficient.

Therefore, the antireflective coating 20 disposed below the metallic functional layer 40 in the direction of the substrate has an optical thickness of approximately 의 of the maximum absorption wavelength λ _m of the photoelectric material, and the metallic functional layer 40 on the opposite side from the substrate. The antireflective coating 60 disposed thereon has an optical thickness of approximately ½ of the maximum absorption wavelength λ _m of the photovoltaic material.

Table 1 below summarizes the preferred range of optical thicknesses for each of the coatings 20 and 60 and the three materials in nm.

TABLE 1

However, it has been found that the optical formation of the stack can be improved by correlating this probability with the wavelength distribution of sunlight at the Earth's surface, taking into account quantum efficiency to obtain improved real yields. Here, normalized solar spectrum AM1.5 was used.

In this case, the antireflective coating 20 disposed below the metallic functional layer 40 in the direction of the substrate has an optical thickness of approximately 의 of the maximum wavelength λ _M of the product of the absorption spectrum and the solar spectrum of the photoelectric material. The antireflective coating 60 disposed on the metallic functional layer 40 on the opposite side from has an optical thickness of approximately ½ of the maximum wavelength λ _M of the product of the absorption spectrum of the photovoltaic material and the solar spectrum.

As can be seen from FIG. 4, the maximum wavelength λ _M of the product of the absorption spectrum and the solar spectrum of the photovoltaic material, ie the wavelength when the yield is maximum (ie the wavelength when the maximum value) is as follows:

The maximum wavelength of amorphous silicon a-Si, ie λ _M (a-Si), is 530 nm;

The maximum wavelength of the microcrystalline silicon μc-Si, ie λ _M (μc-Si), is 670 nm;

The maximum wavelength of cadmium telluride CdTe, ie λ _M (CdTe), is 610 nm.

Table 2 below summarizes the preferred range of optical thicknesses for each coating 20 and 60 and the three materials in nm.

TABLE 2

In all embodiments, the base antireflective layer 22 of the silicon oxide substrate was deposited directly on the substrate. Since the refractive index n ₁₅ of the layer is low and similar to that of the substrate, the optical thickness of the layer was not taken into account when defining the optical path of the stack according to the invention.

The conditions for depositing the layers are known to those skilled in the art because the layers are stacked in a manner similar to that used for low emissivity or solar control applications.

In this regard, those skilled in the art can refer to patent applications EP 718 250, EP 847 965, EP 1 366 001, EP 1 412 300 or EP 722 913.

Table 3 below summarizes the physical thicknesses measured in nanometers and material of each of the layers in Examples 1 and 2, respectively, and Table 4 below presents the main features of Examples 1 and 2.

The performance characteristic P is calculated by the so-called "TSQE" method, where the product of the integral value of the spectrum over the corresponding entire radiation range and the quantum efficiency QE of the cell is used.

The light reflection property R _L is measured under light emitter D ₆₅ .

Examples 1 and 2 were each tested to determine the resistance of the electrode coating to stresses generated during operation (especially in the presence of an electrostatic field) of a cell prepared as shown in FIG. 5.

For this test, a portion of the substrate 10, 10 ′, for example a 5 cm × 5 cm dimension, each coated with the electrode coating 100, 100 ′ but without the photovoltaic material 200 at about 200 ° C. It was deposited on the metal plate 5 disposed on the heat source 6.

The test applies an electric field for 20 minutes to the substrate 10, 10 ′ coated with the electrode coating 100, 100 ′, creates an electrical connection 102 on the surface of the coating, the connection 102 and the The metal plate 5 was connected to the terminal of the power supply 7 which carries DC current under about 200V.

At the end of the test, the sample was once cooled and the percentage of coating remaining relative to the entire surface of the sample was measured.

The percentage of coating remaining after the resistance test was expressed as% CR.

In addition, independently of the preceding test, in Example 2, the strengthening operation was simulated by performing a heat treatment (HT) consisting of annealing at a temperature of about 620 ° C. for 6 minutes and suddenly cooling the atmosphere (20 ° C.). The data measured after this heat treatment are given in the last column of Table 4 below. Thus, the applied heat treatment is more stressful than conventional heat treatment applied to the electrode coating within the context of the process for depositing the cadmium-based photoelectric coating.

TABLE 3

Table 4

In Example 2, the optical thickness of the coating 60 over the metallic functional layer was 291 nm (= 135 × 2 + 10 × 2.1), and the optical thickness of the coating 20 under the metallic functional layer was 78.8 nm (= 27). X 2.4 + 7 x 2).

This example has a better resistivity R _□ (−2.6 ohms / □) and better performance P (+ 0.2%) than the TCO electrode coating (Example 1) coated with the same material and made of a thin film stack. It is shown that it is possible to obtain an electrode coating coated with cadmium telluride having. Optical thicknesses of the coatings 20 and 60 of Example 2 fall within the recommended range for the CdTe photoelectric material 200 in accordance with Tables 1 and 2.

The use of cadmium-based photovoltaic materials, in particular photovoltaic materials in combination with CdTe and CdS, requires electrode coating because the processing of this photovoltaic material requires a step which is generally carried out in a controlled non-oxidizing atmosphere at temperatures between 300 ° C and 700 ° C. It needs to withstand heat treatment.

Surprisingly, it has been found that this step is very similar to the reinforcing step known to those skilled in the art of glass substrates for vehicles or buildings, even though the atmosphere of intensification is generally not controlled.

Thus, it is particularly advantageous to select thin film stacks known for vehicle or building applications that withstand hardening heat treatments, referred to as "reinforceable" stacks or "to strengthen" stacks when the photovoltaic material is cadmium based.

For example, Example 2 shows that the variation of data during the applied heat treatment is minor. Therefore, the selected stack may be considered "enhanced."

In addition, within the context of the present invention, the thin film stack forming the electrode coating has a light reflectance at the absence of photoelectric material, which is lower than the light reflectivity of the TCO electrode coating without photoelectric material, both before and after heat treatment. It is worth mentioning the point.

FIG. 6 shows a photovoltaic cell 1 with a front substrate 10 and a backplate substrate 20 according to the invention through which incident radiation R penetrates when viewed in cross section.

For example, a photovoltaic material 200 made of amorphous silicon or crystalline or microcrystalline silicon or cadmium telluride or copper indium diselenide (CuInSe ₂ or CIS) or copper indium gallium selenium is disposed between these two substrates. This will consist of a layer 220 of n-doped semiconductor material and a layer 240 of p-doped semiconductor material to generate a current. Respectively, between the front substrate 10 and the layer 220 of n-doped semiconductor material on the one hand, and the layer 240 and backplate substrate 20 of the p-doped semiconductor material on the other hand. Electrode coatings 100 and 300 complete the electrical structure.

The electrode coating 300 may be silver or aluminum based, or may consist of a thin film stack according to the invention with one or more metallic functional layers.

In the above, this invention was demonstrated based on the Example. Of course, those skilled in the art will be able to practice various modifications of the invention without departing from the scope of the invention as defined by the appended claims.

Claims (24)

Front substrate 10, in particular having a transparent electrode coating 100 on the major surface, in particular a thin film stack comprising at least one metallic functional layer 40 of a silver substrate and at least two antireflective coatings 20, 60 A photovoltaic cell 1 having an absorptive photoelectric material, in particular a cadmium-based material, comprising a transparent glass substrate, wherein the antireflective coating comprises at least one antireflective layer 24, 26; 66, 68, wherein the functional layer ( 40 is disposed between two antireflective coatings 20, 60, and the antireflective coating 60 disposed on the metallic functional layer 40 on the opposite side from the substrate comprises two or more antireflective layers 66, 68, The antireflective layer 68 farthest from the metallic functional layer 40 is more resistive than the antireflective layer 66 closest to the metallic functional layer 40. The antireflective layer 68 of claim 1 wherein the antireflective layer 68 furthest from the metallic functional layer 40 is at least 5 times, or even 10 times, or even more than the resistivity of the antireflective layer 66 closest to the metallic functional layer 40. A photovoltaic cell (1) characterized by having a resistivity of at least 100 times. The photovoltaic cell according to claim 1, wherein the antireflection layer 68 furthest from the metallic functional layer 40 has a resistivity ρ of 5 × 10 ⁻³ Ω.cm to 10 Ω.cm. ). The antireflection layer 66 closest to the metallic functional layer 40 has a resistivity p of at least 10 ⁻⁵ Ω · cm and less than 5 × 10 ⁻³ Ω.cm. Photocell 1, characterized in that. 5. The antireflective layer 66 closest to the metallic functional layer 40 and the antireflective layer 68 furthest from the metallic functional layer 40 are the same oxide substrate. Zinc oxide (ZnO) in particular; Tin oxide (SnO ₂ ); Titanium oxide (TiO ₂ ); Gallium oxide (Ga ₂ O ₃ ); Indium oxide (In ₂ O ₃ ); Based on silicon oxide (SiO ₂ ), or indium tin mixed oxide (ITO), gallium zinc mixed oxide (GZO), indium zinc mixed oxide (IZO), zinc tin mixed oxide (Zn ₂ SnO ₄ ), or indium gallium zinc mixed oxide A photovoltaic cell (1), wherein the oxide is (IGZO) based and the oxide is optionally nonstoichiometric. The optical thickness of any one of claims 1 to 5, wherein the antireflective layer 68 farthest from the metallic functional layer 40 is 2-50% of the optical thickness of the antireflective coating 60 farthest from the substrate. Photovoltaic cell (1), in particular having an optical thickness of 2 to 25% of the optical thickness of the antireflective coating (60) furthest from the substrate. 7. The antireflective layer 68 furthest from the metallic functional layer 40 has an actual thickness of 2 to 100 nm, preferably 5 to 50 nm. Photovoltaic cell (1). The antireflective coating 60 according to any one of the preceding claims, wherein the antireflective coating 60 disposed on the metallic functional layer 40 on the opposite side from the substrate has an optical thickness of approximately ½ of the maximum absorption wavelength λ _m of the photovoltaic material. Preferably, the antireflective coating 60 disposed on the metallic functional layer 40 on the opposite side of the substrate has an optical thickness of approximately ½ of the maximum wavelength λ _M of the product of the absorption spectrum and the solar spectrum of the photoelectric material. Photovoltaic cell (1). The antireflective coating 60 disposed on the metallic functional layer 40 has an optical thickness of 0.45 to 0.55 times the maximum absorption wavelength λ _m of the photovoltaic material, Photovoltaic cells, characterized in that the antireflective coating 60 preferably disposed on the metallic functional layer 40 has an optical thickness of 0.45 to 0.55 times the maximum wavelength λ _M of the product of the absorption spectrum and the solar spectrum of the photovoltaic material. (One). 10. The antireflective coating 20 according to any one of claims 1 to 9, arranged under the metallic functional layer 40 in the direction of the substrate, results in an optical thickness of approximately 의 of the maximum absorption wavelength λ _m of the photovoltaic material. Wherein the antireflective coating 20 disposed below the metallic functional layer 40 in the direction of the substrate has an optical thickness of approximately 의 of the maximum wavelength λ _M of the product of the absorption spectrum and the solar spectrum of the photoelectric material. Photocell 1 characterized by the above-mentioned. The antireflective coating (20) disposed under the metallic functional layer (40) has an optical thickness of 0.075 to 0.175 times the maximum absorption wavelength λ _m of the photovoltaic material. Preferably, the antireflective coating 20 disposed below the metallic functional layer 40 has an optical thickness of 0.075 to 0.175 times the maximum wavelength λ _M of the product of the absorption spectrum and the solar spectrum of the photoelectric material. Photovoltaic cell (1). 12. The electrode antireflection layer according to any one of the preceding claims, wherein the electrode coating 100 comprises a base antireflective layer 22 having a low refractive index n ₂₂ close to the refractive index of the substrate immediately above the substrate 10, The base antireflective layer (22) is preferably a silicon oxide substrate or an aluminum oxide substrate or a mixture of silicon oxide and aluminum oxide. 13. The photovoltaic cell (1) according to claim 12, wherein the base antireflective layer (22) has a physical thickness of 50 to 300 nm. Photovoltaic cell (1) according to one of the preceding claims, characterized in that the functional layer (40) is an oxide substrate, in particular a zinc oxide substrate, and is deposited on the optionally doped wet layer (26). . 15. The functional layer 40 according to any one of the preceding claims, wherein the functional layer 40 is disposed directly over the one or more bottom blocker coatings 30 and / or just below the one or more top blocker coatings 50. Photocell 1, characterized in that. The photovoltaic cell (1) according to one of the preceding claims, characterized in that the at least one blocker coating (30, 50) is a Ni or Ti substrate or a Ni-based alloy, in particular a NiCr alloy substrate. The method according to claim 1, wherein the coating 20 below the metallic functional layer in the direction of the substrate comprises a layer of a mixed oxide substrate, in particular a zinc tin mixed oxide or an indium tin mixed oxide (ITO) substrate. Photocell (1) characterized in that. 18. The layer according to claim 1, wherein the coating 20 under the metallic functional layer and / or the coating 60 over the metallic functional layer in the direction of the substrate has a very high refractive index, in particular a refractive index. A photovoltaic cell (1) comprising a layer of at least 2.35, for example a layer of titanium oxide. 19. Photovoltaic cell (1) according to any of the preceding claims, characterized in that it comprises a coating (200) of a photovoltaic material, in particular a cadmium-based material, on the electrode coating (100) on the opposite side from the substrate (10). ). 22. The method according to any of the preceding claims, wherein the electrode coating 100 is a stack for building glazing, in particular a "temperable" stack for building glazing or a stack for building glazing, in particular low A photovoltaic cell (1), characterized in that it consists of an emissivity stack, in particular a " enhanced " low emissivity stack or a " enhanced " low emissivity stack. A substrate 10 coated with the thin film stack for the photovoltaic cell 1 of claim 1, in particular a substrate for architectural glazing, in particular a substrate for "reinforceable" architectural glazing or for "hardening" architectural glazing. Substrate, in particular a low emissivity substrate, in particular a substrate which is a "reinforceable" low emissivity substrate or a low emissivity substrate to be "strengthened". Use of a substrate coated with a thin film stack for producing the photovoltaic cell 1, in particular the front substrate 10 of the photovoltaic cell 1 of claim 1, wherein the substrate is in particular one or more of silver substrates. A transparent electrode coating 100 consisting of a thin film stack comprising a metallic functional layer 40 and two or more antireflective coatings 20, 60, each of which has at least one antireflective layer 24, 26; 68, wherein the functional layer 40 is disposed between the two antireflective coatings 20, 60, and the antireflective coating 60 disposed on the metallic functional layer 40 on the opposite side from the substrate is at least two reflective. An antireflective layer (68) comprising an antireflective layer (66, 68) and furthest from the metallic functional layer (40) is more resistant than the antireflective layer (66) closest to the metallic functional layer (40). 23. The substrate 10 according to claim 22, wherein the substrate 10 with the electrode coating 100 is a substrate for building glazing, in particular a substrate for "strengthenable" or a substrate for building glazing to be "strengthened", in particular a "reinforceable" low. Emissivity substrate or low emissivity substrate to be "strengthened". Use according to claim 22 or 23, wherein the antireflective coating (60) disposed over the metallic functional layer (40) on the opposite side from the substrate has an optical thickness of approximately one half of the maximum absorption wavelength of the photovoltaic material.

Images