FR2982256A1 - SUBSTRATE FOR PHOTOVOLTAIC CELL - Google Patents

Abstract

The subject of the invention is a substrate comprising at least one glass sheet provided on one side with at least one electrode, characterized in that said glass has a chemical composition comprising the following constituents, in a weight content varying within the limits - After defined: SiO 60-75% AlO 0 - 7% CaO 5-15% MgO 0-10% Na O 8-15% KO 0 - 5% SnO 0, 8-5%.

Description

The invention relates to the field of substrates for photovoltaic cells. It relates more specifically substrates for photovoltaic cells comprising at least one float glass sheet provided on one side with at least one electrode. The use of a thin-film photovoltaic material makes it possible to replace expensive substrates made of silicon with substrates comprising glass sheets. The material with photovoltaic properties, and generally the electrode, are deposited in a thin layer by deposition processes such as evaporation, sputtering, chemical vapor deposition (CVD) or sublimation (CSS) on the glass sheet. The latter must generally be heated at high temperature, either during the deposition or after the deposition (annealing treatment, selenization, etc.), and thus undergoes temperatures of the order of 500 ° C. or more. These treatments make it possible, for example, to improve the crystallinity of the layers and therefore their electronic conduction or photovoltaic properties. High temperatures, however, have the disadvantage of causing deformation of the glass sheet when it is standard soda-lime glass. Glasses of higher thermal resistance have been proposed, but have a high production cost, especially because of the use of expensive raw materials (carriers of barium or strontium, for example), or particularly high melting temperatures. In addition, some of these glasses are not suitable for forming glass float. The object of the invention is to obviate these drawbacks, by proposing a glass composition having improved thermal resistance making it compatible with the processes used in the manufacture of cells based on photovoltaic materials in a thin layer, which also makes it possible to produce a glass, especially by floating, under very favorable economic conditions.

For this purpose, an object of the invention is a substrate comprising at least one glass sheet provided on one side with at least one electrode, characterized in that said glass has a chemical composition comprising the following constituents, in a weight content varying within the limits defined below: SiO 2 60-75% Al 2 O 3 0-7% CaO 5-15% MgO 0-10% Na 2 O 8-15% K 2 O 0-5% SnO 2 0.8-5%. While being of the silico-soda-lime type, such as standard glass, these compositions surprisingly make it possible to impart high thermal resistances to glass substrates, characterized in particular by lower annealing temperatures of at least 30 ° C. higher than those of standard glass. The sum of the weight contents of SiO 2, Al 2 O 3, CaO, MgO, Na 2 O, K 2 O and SnO 2 is preferably at least 95%, especially 98%. The content of SrO, BaO and / or ZrO2 is advantageously zero so as not to penalize the cost of the glass sheet. The other constituents of the composition may be impurities originating from the raw materials (in particular iron oxide) or due to the degradation of the refractories of the melting furnace or refining agents (in particular SO 3). Silica (SiO2) is the main formative element of glass. In too low levels, the hydrolytic resistance of the glass, especially in basic medium, would be reduced too much. On the other hand, contents above 75% lead to an increase in the viscosity of the highly detrimental glass. The silica content is preferably greater than or equal to 62%, especially 63% and even 64%, and / or less than or equal to 74%, especially 73% or 72%.

Alumina (Al 2 O 3) makes it possible to increase the hydrolytic resistance of the glass and to reduce its refractive index, the latter advantage being particularly significant when the substrate is intended to constitute the front-face substrate of the photovoltaic cell.

The addition of lime (Ca0) has the advantage of reducing the high temperature viscosity of the glass, and thus of facilitating its melting and refining, while increasing the lower annealing temperature, and therefore the thermal stability. The increase in the liquidus temperature and the refractive index attributable to this oxide, however, lead to limiting its content. The CaO content is preferably greater than or equal to 8%, especially 9% and / or less than or equal to 14%, especially 13%, and even 12%.

Magnesia (Mg0) is useful for improving the chemical durability of glass and decreasing its viscosity. High levels, however, lead to increased risks of devitrification.

Soda (Na2O) is useful for reducing viscosity at high temperature and liquidus temperature. Too high levels, however, lead to degrade the hydrolytic strength of the glass and its thermal stability, while increasing the cost. The Na 2 O content is preferably in a range from 10% to 13%. Potash (K2O) has the same advantages and disadvantages, but seems to degrade thermal stability even more. Its content is therefore preferably at most 2%, especially 1%, and even 0.5% or 0.1%. Tin oxide increases the thermomechanical strength of glass. Its content is preferably at least 0.9%, especially 1%, and even 1.1% and / or less or equal to 4%, especially 3.5%, even 3% and even 2.5%. or 2%. Levels within a range of 1% to 4%, especially 1% to 3% and even 1% to 2% are particularly advantageous. The glass is preferably colorless. For this purpose, it is preferably free of coloring agents, with the exception of iron oxide which is an unavoidable impurity. Thus, the contents of cobalt oxide, copper oxide, rare earth oxide or selenium are preferably zero. Colorless glass means a glass such that its colorimetric coordinates a * and b * are each in a range from -2 to +2, especially from -1 to +1 for a thickness of 3 mm, taking into consideration the illuminant D65 as defined by the ISO / IEC 10526 standard and the CIE colorimetric reference observer 1931 as defined by ISO / IEC 10527. The glass preferably has a chemical composition comprising the following constituents, in a weight content varying within the limits defined below: SiO 2 68-75% Al 2 O 3 0-3% CaO + MgO 11-16.2% Mg0 0-6.5% Na2O 12-12% K20 0-1.5% SnO2 1-2%.

According to a first preferred embodiment, the weight content of MgO is at most 1%, especially 0.5% and even 0.1%. The CaO content is advantageously at least 11.5% or even 12%. The Na 2 O content is preferably at least 10% or even 11%. It is advantageously at most 12%. Particularly preferred compositions comprise the following constituents, in a weight content varying within the limits defined below: SiO 2 71-74.2% Al 2 O 3 0-3% CaO 11.5-13% MgO 0-1% Na 2 O 12 , 4%, especially 11-12%, K20 0-1.5% SnO2 0.8-5%.

According to a second preferred embodiment, the weight content of MgO is at least 4%, even 4.5% or 5% and / or at most 6%. The CaO content is preferably between 9 and 10.5%. The Na 2 O content is advantageously at least 9.5%, even 10% and / or at most 11%. Particularly preferred compositions comprise the following constituents, in a weight content varying within the limits defined below: SiO 2 70-74% Al 2 O 3 0-2% CaO 9-10.5% MgO 4-6.5%, especially 4- 6% Na2O 10-11% K20 0-1% SnO2 0.8-5%. The melting of the glass may be carried out in continuous furnaces, heated with electrodes and / or using burners, aerated and / or immersed and / or arranged in the vault of the oven so that the flame impact the raw materials or the glass bath. The raw materials are generally pulverulent and include natural materials (sand, feldspars, limestone, dolomite, nepheline syenite ...) or artificial materials (sodium or potassium carbonate, sodium sulphate. "). can be brought, for example, by cassiterite or malayaite, the latter being a silicate of calcium and tin.The raw materials are charged and then undergo fusion reactions in the physical sense of the term 25 and various chemical reactions The molten glass is then conveyed to a forming step during which the glass sheet will take shape.The forming is carried out in a known manner, for example by floating, that is, by pouring the molten glass (at a viscosity of the order of 3000 poles) onto a bath of molten tin, or by rolling between rolls, the resulting glass ribbon is then annealed carefully. ent to eliminate any thermal stresses within it, before being cut to the desired dimensions. The thickness of the glass sheet is typically between 2 and 6 mm, especially between 2.5 and 4 mm. The electrode is preferably in the form of a thin layer deposited on the substrate (generally on the entire face of the substrate), directly in contact with the substrate or in contact with at least one underlayer. It may be a transparent and electroconductive thin layer, for example based on tin oxide (doped with fluorine or antimony), zinc oxide (doped with aluminum or gallium) or based on tin oxide and indium (ITO) It may still be a thin metal layer, for example molybdenum. The transparent layers are generally used when the substrate is intended to form the front face substrate of the photovoltaic cell, as explained in more detail later in the text. The term "front face" is understood to mean the face traversed first by solar radiation. The metal electrode may also be a silver layer, capable of reflecting light radiation, useful for example in an application as a mirror, especially a mirror for concentrating solar energy. The electrode may also consist of a stack of thin layers of which at least one is electroconductive. The electrode in the form of a thin layer may be deposited on the substrate by various deposition methods, such as chemical vapor deposition (CVD) or sputtering deposition, in particular assisted by a magnetic field (magnetron process). In the CVD process, halide or organometallic precursors are vaporized and transported by a carrier gas to the surface of the hot glass, where they decompose under the effect of heat to form the thin layer. The advantage of the CVD process is that it can be implemented in the process of forming the glass sheet by floating. It is thus possible to deposit the layer when the glass sheet is on the tin bath, at the exit of the tin bath, or in the lehr, that is to say when the glass sheet is annealed to eliminate mechanical stress. The CVD process is particularly suitable for depositing fluorine or antimony doped tin oxide layers. The sputtering process will be preferentially used for the deposition of molybdenum layers, doped zinc oxide or ITO.

Another object of the invention is a semiconductor device comprising at least one substrate according to the invention and at least one thin layer of a material with photovoltaic properties deposited on said at least one substrate.

The material with photovoltaic properties is preferably chosen from compounds of CdTe type and sulphides and / or selenides of copper, in particular of Cu (In, Ga) (S, Se) 2 and Cu2 (Zn, Sn) (S, Se) 4. By (In, Ga) we mean that the material can comprise In and / or Ga, according to any combination of possible contents: x can take any value from 0 to 1. In particular, x can be zero (CIS type material). When x and y are non-zero, the material is of CIGS type. The expressions (Zn, Sn) and (S, Se) must be understood in the same way. A material of the Cu2ZnSn (S, Se) 4 type is called CZTS. The material with photovoltaic properties may also be in amorphous or polycrystalline silicon.

The photovoltaic material is deposited on the semiconductor device, above the electrode, and generally in contact therewith. Different deposition techniques are possible, examples of which include evaporation, sputtering, chemical vapor deposition (CVD), electrolytic deposition or sublimation (CSS). By way of example, in the case of CI (G) S type layers, there may be mentioned sputtering or electroplating processes (followed by a selenization step) or coevaporation. An additional electrode may be deposited on (and in particular in contact with) the layer of photovoltaic material. It may be a transparent and electroconductive thin layer, for example based on tin oxide (doped with fluorine or antimony), zinc oxide (doped with aluminum or gallium ), or based on tin oxide and indium (ITO). It may still be a metal layer, for example gold or nickel alloy and aluminum. The transparent layers are generally used when the substrate is intended to form the rear-face substrate of the photovoltaic cell, as explained in more detail later in the text. Buffer layers may also be interposed between the photovoltaic material layer and the additional electrode. In the case of materials of type CI (G) S, it may for example be an n-doped layer of CdS, In.Sy or ZnMgO. Finally, passivating layers, typically intrinsic ZnO or intrinsic ZnMgO may be interposed between the buffer layer (or the photovoltaic material layer) and the additional electrode.

Another object of the invention is a photovoltaic cell comprising a semiconductor device according to the invention. An object of the invention is finally a photovoltaic module comprising a plurality of photovoltaic cells according to the invention. Depending on the technology used, the substrate according to the invention may be the front or rear face substrate of the photovoltaic cell. For example, in the case of photovoltaic materials based on IC (G) S or CZTS, the photovoltaic material layer is generally deposited on the rear face substrate (provided with its electrode, typically molybdenum). It is therefore the backside substrate which then has a glass sheet having the advantageous chemical composition described above. In the case of CdTe technology on the other hand, the photovoltaic material is often deposited on the front-face substrate, so that the aforementioned chemical composition is used for the glass sheet of the front-face substrate.

The photovoltaic cell is formed by joining the substrates of the front face and rear face, for example by means of a lamination interlayer of thermosetting plastic material, for example PVB, PU or EVA. According to a first embodiment, the photovoltaic cell according to the invention comprises, as a front-face substrate, the substrate according to the invention, the chemical composition of the glass sheet of said substrate further comprising iron oxide in a weight content. not more than 0,02%, in particular 0,015%. In this case, it is important that the optical transmission of the glass is as high as possible. The glass sheet preferably comprises no agent absorbing visible or infrared radiation (especially at a wavelength between 380 and 1000 nm) other than iron oxide (whose presence is unavoidable). In particular, the composition of the glass preferably does not contain agents chosen from the following agents, or any of the following agents: transition element oxides such as CoO, CuO, Cr 2 O 3, MnO 2, rare earth oxides such as CeO 2, La 2 O 3, Nd 2 O 3, or elemental coloring agents such as Se, Ag, Cu, Au. These agents often have a very powerful undesirable coloring effect, occurring at very low levels, sometimes of the order of a few ppm or less (1 ppm = 0.0001%). Still in order to maximize the optical transmission of glass, redox (defined as the ratio between the ferrous iron content expressed as FeO and the total iron content expressed as Fe2O3) is preferably at most 0.2 , especially 0.1. The glass sheet is preferably such that its energy transmission (TE) calculated according to the ISO 9050: 2003 standard is greater than or equal to 90%, in particular 90.5%, or even 91% and even 91.5%, for a thickness 3.2 mm. The front face substrate may be provided, on the face opposite to that carrying the electrode, with an antireflection coating, for example porous silica or comprising a stack of thin layers alternating high and low refractive index layers.

In the context of this embodiment, a substrate according to the invention is typically used provided with an ITO electrode and / or doped SnO2 (for example fluorine or antimony), then a photovoltaic material in CdTe, then an additional electrode made of gold or nickel-aluminum alloy, in order from the substrate. The backside substrate is preferably of standard silico-soda-lime glass.

According to a second embodiment, the photovoltaic cell according to the invention comprises, as rear-face substrate, the substrate according to the invention, the chemical composition of the glass sheet of said substrate further comprising iron oxide in a weight content. at least 0.05%, in particular ranging from 0.08 to 2%, especially from 0.08 to 0.2%. In the context of this embodiment, a substrate according to the invention is typically used, provided with a molybdenum electrode, on which a photovoltaic material is deposited in CI (G) S or in CZTS, followed by an additional electrode made of doped ZnO. , and optionally a CdS n doped buffer layer between these two last layers. A passivating layer, for example intrinsic ZnO or intrinsic ZnMgO may be interposed between the buffer layer and the additional electrode. High levels of iron oxide (from 0.5% to 2%) can in this case correct the aesthetic appearance due to the presence of molybdenum. The front face substrate is preferably made of extra-clear glass of standard soda-lime-calcium composition. The present invention will be better understood on reading the detailed description below of nonlimiting exemplary embodiments. The following tables illustrate certain compositions according to the invention (examples 1 to 16) as well as a standard composition (comparative example C1). In addition to the chemical weight composition, the tables indicate the following physical properties: called S and the lower annealing temperature, expressed in ° C, the temperature at which the glass has a viscosity of 100 Poises, called T2 and expressed in ° C, the temperature at which the glass has a viscosity of 3162 Poises, called T3.5 and expressed in ° C, the forming margin, called AT and expressed in ° C, corresponding to the difference between the temperature T3.5 and the temperature to the liquidus. Cl 1 2 3 4 5 SiO 2 71.8 71.6 68.7 70.7 70.7 70.9 A1202 0.6 1.74 1.76 0.59 1.33 1.68 CaO 9.5 12, 3 10.3 10.4 10.2 12.7 MgO 4.0 1.2 6.5 5.8 5.3 0.1 Na2O 13.7 11.8 11.2 11.1 10.9 12, 0 K2O 0 0.08 0.07 0.01 0.07 1.28 SO2 0.28 0.26 0.24 0.24 0.24 0.28 SnO2 0 1.1 1.2 1.2 1, 2 1.1 S (° C) 510 546 553 549 551 543 T2 (° C) 1421 1482 1466 1490 1474 1447 T3.5 (° C) 1093 1157 1149 1172 1155 1123 AT (° C) 78 27 -21 42 15 Table 1 6 7 8 9 10 11 SiO 2 69.2 68.3 69.9 69.6 72.4 72.0 A1203 0.7 0.6 1.8 1.8 1.8 1.8 CaO 9, 7 9.8 9.8 9.8 11.7 11.7 MgO 3.95 4.2 6.1 6.0 0.9 0.9 Na2O 14.6 14.8 10.7 10.6 11 4 11.4 K2O 0.01 0.01 0.01 0.01 0.01 0.01 SO3 0.27 0.27 0.3 0.3 0.3 0.3 SnO2 1.6 2.1 1 , 2.0 2.0 2.0 S (° C) 526 525 548 556 556 560 T2 (° C) 1396 1413 1467 1468 1445 1457 T3.5 (° C) 1087 1094 1146 1147 1147 1148 AT (° C) ) 57 34 16 17 -23 -22 Table 2 12 13 14 15 16 Si02 67.9 66.6 64.1 66.3 69.1 A1203 3.0 4.0 5.0 3.95 1.8 Ca0 10 , 4 10.0 10.0 10.5 10.4 Mg0 4.0 5.0 5.0 3.0 5.5 Na20 12.4 12.1 12.6 12.4 10.9 K20 0.0 1 0.01 0.01 1.4 0.04 S03 0.3 0.3 0.3 0.27 0.25 Sn02 1.9 2.0 3.1 2.0 1.9 S (° C) 544 546 560 538 552 T2 (° C) 1433 1429 1422 T3.5 (° C) 1126 1123 1124 AT (° C) 36 23 -16 Table 3 The compositions make it possible to obtain glasses having lower annealing temperatures. about 30 ° C to 50 ° C higher than that of standard glass due to the addition of tin oxide. This results in better mechanical behavior, and glass sheets less able to deform during the manufacturing steps of the solar cells. Most of these glass compositions are floatable under good conditions, as evidenced by the positive forming margins.

Claims (13)

REVENDICATIONS1. Substrate comprising at least one glass sheet provided on one side with at least one electrode, characterized in that said glass has a chemical composition comprising the following constituents, in a weight content varying within the limits hereinafter defined: SiO 2 75% A1203 0-7% Ca0 5-15% Mg0 0-10% Na2O 8-15% K20 0-5% 5nO2 0.8-5%. 2. Substrate according to the preceding claim, such that the sum of the weight contents of SiO 2, Al 2 O 3, CaO, MgO, Na 2 O, K 2 O and SnO 2 is at least 95%, especially 98%. 3. Substrate according to one of the preceding claims, such that the weight content of MgO is at most 1%, especially 0.5%. 4. Substrate according to claim 1 or 2, such that the weight content of MgO is at least 4%. 5. Substrate according to one of the preceding claims, such that the content of SnO 2 is in a range from 1 to 4%, especially from 1 to 3%. 6. Substrate according to one of the preceding claims, such that the glass has a chemical composition comprising the following constituents, in aweighing weight range within the limits defined below: SiO 2 68-75% A1203 0-3% Ca0 + Mg0 11 -16.2% Mg0 0-6.5% Na2O 12-12% K20 0-1.5% SnO2 1-2%. 7. Substrate according to one of the preceding claims, such that the electrode is a transparent and electroconductive thin layer based on tin oxide doped with fluorine or antimony, zinc oxide doped with aluminum. or gallium, based on tin oxide and indium or a thin layer of molybdenum. 8. Semiconductor device comprising at least one substrate according to one of the preceding claims and at least one thin layer of a material with photovoltaic properties deposited on said at least one substrate. 9. Semiconductor device according to the preceding claim, such that the material with photovoltaic properties is chosen from CdTe type compounds and sulphides and / or selenides of copper, in particular of Cu (In, Ga) (S, Se) type. 2 and Cu2 (Zn, Sn) (S, Se) 4. Photovoltaic cell comprising a semiconductor device according to one of the preceding device claims. 11. Photovoltaic cell according to the preceding claim, comprising as a front face substrate a substrate according to one of claims 1 to 7, the chemical composition of the glass sheet of said substrate further comprising iron oxide in a weight content not more than 0,02%, in particular 0,015%. 12. Photovoltaic cell according to claim 10, comprising as a rear face substrate a substrate according to one of claims 1 to 7, the chemical composition of the glass sheet of said substrate further comprising iron oxide in a weight content at least 0.05%, in particular ranging from 0.08 to 2%. Photovoltaic module comprising a plurality of photovoltaic cells according to one of the preceding cell claims.