CEMENTITIOUS PRODUCT SUITABLE IN PARTICULAR AS SUBSTRATE FOR A THIN FILM PHOTOVOLTAIC MODULE, AND METHOD OF PRODUCTION THEREOF

Abstract

The present invention relates to a substrate for a thin film photovoltaic module, characterized in that it is a cementitious product with average surface roughness Ra not higher than 500 nm. The invention also relates to the cementitious product as such, the thin film photovoltaic module comprising it, and a method of moulding both of them.

Claims

1-9. (canceled)

10. A cementitious product with an average surface roughness Ra not higher than 500 nm.

11. A method of manufacturing a cementitious product according to claim 10, characterized in that it comprises a step of forming said cementitious product inside a mould fed with a mixture of components of said cementitious product in a plastic state.

12. A method according to claim 11, characterized in that said forming occurs by compression.

13. A method according to claim 11, characterized in that said mould is at least partially coated with a material chosen from polyethylene terephthalate, polycarbonate, polyamide, polymethylmethacrylate, or other similar material capable of imparting an average surface roughness Ra not higher than 500 nm to the cementitious product during the step of moulding.

14. A method according to claim 11, characterized in that it comprises a step of mixing said components of said cementitious product in plastic state by means of calendering prior to said mould-forming.

15. A method of manufacturing a thin film photovoltaic module, characterized in that a thin film with photovoltaic properties is deposited on a substrate according to claim 1.

16. The use of a cementitious product with an average surface roughness Ra not higher than 500 nm as a film substrate in a thin film photovoltaic module.

Description

DESCRIPTION OF THE DRAWINGS

[0032] For the purpose of better understanding of the characteristics and advantages of the invention, a non-limiting example of practical implementation of a method for moulding a cementitious product of the invention is presented below, referring to the appended drawings.

[0033] Referring to FIG. 1, the phases of a preferred embodiment of the process for production of products made of cementitious material according to the invention are illustrated schematically as a flow chart.

[0034] A mixer of the intensive type (1) is charged with: [0035] a cementitious-base solid mixture comprising one or more components selected from cement, sand, aggregates, fillers of mineral or pozzolanic origin, rheology modifiers, super-plasticizers, pigments, [0036] water, stored in a liquids feeder, [0037] optionally additives, in liquid form.

[0038] The solid-phase components are mixed in mixer (1) for a time preferably between 30 seconds and 15 minutes, depending on the characteristics of the mixer and the ambient temperature, until a homogeneous mixture is obtained. Then the liquid components, including water, are added and mixing continues for a time between 30 seconds and 10 minutes, once again depending on the characteristics of the mixer and the ambient temperature. At the end of the mixing phase, the mixture can be in various semisolid forms, from moist powder with small granular agglomerates, to a cohesive, homogeneous paste.

[0039] The mixture thus obtained is sent to a mixing machine or homogenizer (2), which is preferably a high-shear calender mixer, which gives a plastic, cohesive laminar material of thin and uniform thickness.

[0040] This is then supplied to the moulding phase (3), in moulds having a micrometric surface roughness, preferably metal moulds of the type used for cementitious applications coated at least partially with materials such as polyethylene terephthalate such as Mylar and the like, polycarbonate, polyamide, polymethylmethacrylate such as Plexiglas and the like, able to impart to the cementitious product, during the moulding phase, the surface and roughness characteristics according to the invention.

[0041] The moulding phase is carried out in controlled temperature conditions, between 25 and 150 C., preferably between 50 and 120 C., more preferably between 70 and 100 C. The moulding pressure applied is between 1 bar and 200 bar, preferably between 40 bar and 150 bar, more preferably between 60 bar and 120 bar. The moulding time depends on the conditions of temperature and pressure and on the cementitious composition, and is between 1 and 60 minutes.

[0042] Cementitious products are thus produced with thickness between 1 and 10 mm, preferably 2-7 mm and more preferably 3-6 mm.

[0043] The moulded product, after extraction from the mould 3, undergoes curing and seasoning, shown respectively by 4 and 5 in FIG. 1, with the product being held in a climate chamber, inside a perforated box, to avoid direct contact with water or other materials that might impair the final surface characteristics. The optimum curing conditions preferably envisage a temperature of 25 C. and relative humidity (RH) of 95%, for 24 hours.

[0044] Next, the product is seasoned in a chamber conditioned at 20 C. and relative humidity of 50%.

[0045] In the products according to the present invention, the average surface roughness Ra is measured by means of a contactless optical profilometer, such as 3D Talysurf CCI Lite (Taylor-Hobson), equipped with an automatic stage and with autofocus. The system uses scanning green light interferometry to obtain images and measurements of the parts analysed, supplying quantitative information about surface structure without physical contact with it. The light beam, after passing through the optical path of the microscope, is split in two inside the interferometry objective. One part is reflected from the sample while the other part is reflected from a high-quality reference surface inside the objective.

[0046] The two beams are recombined and the resultant light is directed onto a solid-state camera. The interference between the two wavefronts generates an image formed from light and dark bands, called interference fringes, which are indicative of the surface structure of the part analysed. Since the interference fringes are only produced when the surface being analysed is at the focus, a vertical scan must be performed to be able to acquire interferograms that characterize the level of each pixel making up the matrix of the CCD camera. Scanning is performed by means of a piezoelectric transducer placed at the base of the optical head of the microscope. The system is equipped with various types of objectives (50x, 20x, 10x, 5x, 2.5x), use of which depends on the surface characteristics of the sample to be examined.

[0047] While the objective performs the scan, the camera records images of the intensity of the interference fringes. Analysis of the range of frequencies permits localization of the level for each pixel unambiguously and extremely accurately. The measurements obtained are both three-dimensional and two-dimensional: the vertical measurement (perpendicular to the surface being examined) is obtained by interferometry, while the lateral measurements (in the plane of the sample) are obtained from the calibration of the magnification generated by the objective.

[0048] The 3D data characterizing the surface, obtainable using the technique described, are as follows: [0049] height parameters: Sq, SSk, Sku, Sp, Sv, Sz, Sa, defined according to standard ISO 25178; [0050] planarity parameters: FLTt, FLTp, FLTv, FLTq defined according to standard ISO 12781;

[0051] The 2D data characterizing the surface, obtainable using the technique described, are as follows: [0052] height parametersroughness profile: Rp, Rv, Rz, Rc, Rt, Ra, Rq, Rsk, Rku, defined according to standard ISO 4287; [0053] spacing parametersroughness profile: RSm, Rdq, defined according to standard ISO 4287; [0054] peak parametersroughness profile: RPc, defined according to standard ISO 4287.

[0055] For proceeding to deposition of the photovoltaic film, a sheet of substrate formed according to the present invention is preferably strength-tested in the vacuum conditions required by the film deposition process. In particular the sheet is submitted, in a vacuum chamber, to gradual variation of pressure up to 3.210-5 mbar. The variation in surface roughness recorded shows the compatibility of the cementitious substrate with the simulated conditions of the process for deposition of the layer of photovoltaic film based on CIGS. Furthermore, a test with the sample held at 500 C. for one hour must not lead to changes in the roughness profile that are significant for the purposes of application of a thin film of the CIGS type.

[0056] The following examples of preparation of a cementitious product according to the invention illustrate the invention without limiting its scope in any way.

EXAMPLE 1

[0057] The solid components shown in Table 1 were mixed in an intensive mixer of the Eirich type for 3 minutes.

TABLE-US-00001 TABLE 1 COMPONENTS wt. % Cement: Alipre Italcementi 48.0 Cugini filler (<250 m) 36.0 Culminal C4051 1.0 Cimfluid Adagio P1 0.3 Water 14.7 with water/cement ratio = 0.30

[0058] On completion of this phase, water was added and mixing was continued for a further 3 minutes.

[0059] On completion, the mixture was in the form of moist granules. The solid mass was mixed in a calender kneader for 5 minutes.

[0060] Next, the material was compressed in a square mould, made of steel coated with Mylar, with dimensions 2525 cm and thickness 3 mm, at a pressure of 80 bar and at a temperature of 80 C., for 10 minutes. Curing of the moulded product took place in a climate chamber inside a perforated box, to avoid direct contact with water or other agents that might compromise the final surface characteristics of the product. The curing conditions were 25 C., 95% relative humidity, for 24 hours. After that, the product was stored in a chamber conditioned at 20 C. and 50% relative humidity.

[0061] The breaking stress, measured according to standard UNI EN ISO 10545-4 on test bars of thickness 3 mm, length 100 mm and width 20 mm, was found to be 25 MPa.

[0062] Measurement of the surface roughness Ra according to standard ISO 4287 showed a value of 16 nm.

[0063] With the composition of example 1, a sheet was produced for application of CIGS thin film photovoltaic modules.

[0064] To be able to proceed to deposition of the photovoltaic film, the sheet formed as described above was strength-tested in the vacuum conditions required by the deposition process. In the test, the sheet was submitted, in a vacuum chamber, to gradual variation of pressure up to 3.210-5 mbar. At the end of this test, the samples of sheet did not show significant changes in their surface roughness for the purposes of the performance required for application of the CIGS; in fact the value of Ra measured after the test was 20 nm.

[0065] The test with holding of the sample at 500 C. for one hour did not lead to changes in the roughness profile that were significant for the purposes of application of CIGS technology.

EXAMPLE 2

[0066] Essentially as described in example 1, but using the components shown in Table 2, a louver element was obtained.

TABLE-US-00002 TABLE 2 COMPONENTS wt. % Cement: Alipre Italcementi 48.0 Cugini filler (<250 m) 36.0 Culminal C4051 1.0 Melflux 1641 F 0.3 Water 14.7 water/cement = 0.30

[0067] The moulding process differed from example 1 in that the phase of moulding of the mixture was carried out at 100 bar and 90 C., for 8 minutes. The thickness of the moulded panel was equal to 4 mm.

[0068] The breaking stress, measured according to standard UNI EN ISO 10545-4 on test bars of thickness 4 mm, length 100 mm and width 20 mm, was equal to 26 MPa. The measured value of surface roughness, expressed as Ra according to standard ISO 4287, was 22 nm.

EXAMPLE 3

[0069] Essentially as described in example 1 but using the components according to Table 3, a roofing-tile for application of flexible solar cells was obtained.

TABLE-US-00003 TABLE 3 COMPONENTS wt. % Cement: Ultracem 52,5R Italcementi 46.9 Cugini filler (<250 m) 35.2 Culminal C4051 1.0 Cimfluid Adagio P1 0.3 Pigment: Rosso (red) 1020 Siof 2.3 Water 14.3 water/cement = 0.30

[0070] The moulding process differed from that in example 1 in that the moulding phase was carried out at 120 bar and 90 C., for 25 minutes.

[0071] The thickness of the roofing-tile was 5 mm.

[0072] The breaking stress, measured according to standard UNI EN ISO 10545-4 on test bars of thickness 4.5 mm, length 100 mm and width 20 mm, was found to be 24 MPa.

[0073] The measured value of surface roughness, expressed as Ra according to standard ISO 4287, was 18 nm.

EXAMPLE 4

[0074] Essentially as described in example 1, but using the components shown in Table 4, a roofing sheet was produced.

TABLE-US-00004 TABLE 4 COMPONENTS wt. % Cement: Alipre Italcementi 50.3 Cugini filler (<250 m) 16.5 Cugini aggregate (0.8-1.4 mm) 21.1 Melflux 1641 F 0.7 Cimfluid Adagio P1 0.4 Water 11.0 water/cement = 0.22

[0075] The moulding process differed from that in example 1 by the presence of coarse aggregate (0.8-1.4 mm).

[0076] The thickness of the resultant sheet was 6 mm.

[0077] The surface roughness, expressed as Ra according to standard ISO 4287, was found to be 500 nm.