SOLAR CELLS

Abstract

The invention relates to solar cells or solar cell modules comprising a layer on or in the front radiation-receiving side of the solar cell comprising effect pigments consisting of a transparent or semi-transparent flake-form substrate coated with one or more layers of transparent or semi-transparent materials and optionally with a post coating, and a process for their preparation.

Claims

1-24. (canceled)

25. A digital printing method that achieves a solar cell by printing at least a portion of said solar cell, wherein the solar cell comprises at least one layer on or in the front radiation-receiving side of the solar cell or solar cell module comprising at least one effect pigment consisting of a transparent or semi-transparent flake-form substrate coated with one or more layers of transparent or semi-transparent materials and with a post coating.

26. An energy system that contains a solar cell or a module of a solar cell, and which contains energy storage means, wherein the solar cell or solar cell module comprises at least one layer on or in the front radiation-receiving side of the solar cell or solar cell module comprising at least one effect pigment consisting of a transparent or semi-transparent flake-form substrate coated with one or more layers of transparent or semi-transparent materials and with a post coating.

27. A solar cell or solar cell module comprising at least one dry layer on or in a front radiation-receiving side of the solar cell or solar cell module comprising at least one effect pigment consisting of a transparent or semi-transparent flake-form substrate selected from synthetic mica flakes, natural mica flakes, glass flakes, SiO.sub.2 flakes, Al.sub.2O.sub.3 flakes, TiO.sub.2 flakes, BiOCl flakes and mixtures of said flakes, said substrate being coated with one or more layers of transparent or semi-transparent materials and optionally with a post coating, and wherein said at least one effect pigment reflects a part of the visible light of the solar spectrum, and the at least one dry layer of said at least one effect pigment homogeneously colors the solar cell or solar cell module, and the concentration of the at least one effect pigment in said at least one dry layer is from 0.1 to 30 g/m.sup.2, and the solar cell or solar cell module has a more homogeneous appearance compared to an otherwise identical solar cell or solar cell module that does not contain the at least one dry layer containing said at least one effect pigment, and optionally where a metal based conducting part of the solar cell or solar cell module are colored black or dark blue and a black or dark blue back sheet is located on a rear side of the solar cell or solar cell module, and optionally where on top of the at least one layer on or in the front radiation-receiving side black or dark blue pattern is placed covering a space between single cells and bus bars, conducting path and soldering points or where metal based conducting parts of the solar cell or solar cell module are black or dark blue or where a black or dark blue back sheet is located on a rear side of the solar cells or solar cell modules.

28. The solar cell or solar cell module according to claim 27, where the at least one effect pigment and/or an effect pigment layer selectively reflects 1-100% of the visible light of the solar spectrum; the at least one effect pigment and/or an effect pigment layer has a transparency for radiation in the range of 260 to 1200 nm, of at least 30%; the at least one effect pigment and/or an effect pigment layer has a reflection level of 1 to 40% for radiation in the range of 260 to 1200 nm; the at least one effect pigment and/or an effect pigment layer has a reflection level of <20%, for radiation in the range of 260 to 1200 nm; the at least one effect pigment is selected from pearlescent pigments, interference pigments and multi-layer pigments; the amount of at least one effect pigment in an application medium is in the range of 1-40%, by weight based on solid parts of the application medium; the thickness of an effect pigment comprising layer is in the range of 1 to 200 m; the internal quantum efficiency of said solar cell or solar cell module is 0.7 at 260 to 1200 nm wavelength; the at least one effect pigment and/or an effect pigment layer creates a current loss [A/m.sup.2] of less than 40; the at least one effect pigment and/or an effect pigment layer creates an efficiency reduction [W/m.sup.2] of less than 40%; the external quantum efficiency of said solar cell or solar cell module is 0.6 at 260 to 1200 nm wavelength; the at least one effect pigment is based on a flake-form glass substrate or a flake-form SiO.sub.2 substrate or a flake-form Al.sub.2O.sub.3 substrate; the flake-form substrate is coated with one or more layers of metal oxides and/or metal oxide hydrates of Ti, Sn, Si, Al, Zr or Zn; the at least one effect pigment is comprised in a layer on the exterior of the solar cell, on or in a lamination material, directly on a photoactive material of the solar cell or on a protective substrate covering a solar cell module; or the at least one effect pigment is comprised in a sol-gel based, polymer-based layer or a layer based on glass frits on an interior or exterior facing glass layer.

29. A process for the preparation of solar cells or solar cell modules according to claim 27, where a coating composition comprising at least one effect pigment comprising a transparent or semi-transparent flake-form substrate coated with one or more layers of transparent or semi-transparent materials and optionally a post coating, one or multiple organic or inorganic binders, is applied to the solar cells or solar cell modules.

30. A process according to claim 29, where the coating composition is applied by screen printing, flexo printing, gravure printing, offset printing, inkjet printing, digital printing, slot die coating, spray coating, dip coating, doctor blade/knife coating, curtain coating, film transfer coating or aerosol jetting; on top of the coating composition comprising at least one effect pigment applied to the solar cells or solar cell modules a black or dark blue pattern is placed covering a space between single cells and bus bars, conducting path and soldering points; metal based conducting parts of the solar cells are black or dark blue; a black or dark blue back sheet is applied on a rear side of the solar cells or solar cell modules.

31. The solar cell or solar cell module according to claim 27, where the at least one effect pigment and/or an effect pigment layer selectively reflects 5-40% of the visible light of the solar spectrum; the transparency for radiation for the solar cell or solar cell module is >80%; the at least one effect pigment and/or an effect pigment layer has a reflection level of 1 to 30% for radiation in the range of 260 to 1200 nm; the at least one effect pigment and/or an effect pigment layer has a reflection level of <10% for radiation in the range of 260 to 1200 nm; the amount of the at least one effect pigment in the application medium is in the range of 1-15% by weight based on solid parts of the application medium; said lamination material is EVA (ethyl vinyl acetate film), TPU (thermoplastic polyurethane) or silicone; the layer containing the at least one effect pigment is located within visible parts of the solar cell or solar cell module; the concentration of the at least one effect pigment in said at least one layer is from 0.4 to 30 g/m.sup.2; the flake-form substrate is selected from coated or uncoated flakes of synthetic or natural mica, glass flakes, SiO.sub.2 flakes, Al.sub.2O.sub.3 flakes, or mixtures of the said flakes; metal based conducting part of the solar cell or solar cell module are colored black or dark blue and are not visible on the front radiation-receiving side of the solar cell or solar cell module; the concentration of the at least one effect pigment in said at least one dry layer is from 1 to 16 g/m.sup.2; or the concentration of the at least one effect pigment in said at least one dry layer is from 0.1 to 3.1 g/m.sup.2.

Description

EXAMPLES

Example 1

[0092] c-Si solar cells (CZ) are coated with different layers comprising different effect pigments, different effect pigment concentrations and/or effect pigment mixtures. The layers comprising effect pigments render the surface appearance of sheets of encapsulated materials to different colors, as e. g. green or violet.

[0093] For example, an ink containing Pyrisma Green (3%) in Proell Aqua Jet FGL M 093 varnish (95.5%) and Proell Defoamer L36459 (1.5%) is printed on a standard c-Si panels using manual flat-bed screen printer. Mesh PET1500 54/137-64W from Sefar is used (parameters of the mesh: 137 l/inch, 115 m mesh opening and 64 m thread diameter). Squeegee used for printing is a manual squeegee with hardness of 75 shore. The layer is dried at room temperature in ambient conditions.

[0094] Further effect pigments and effect pigment concentrations are listed in Table 1.

TABLE-US-00001 TABLE 1 Example Pigment Pigment (Cell) Pigment Concentration g/m.sup.2 1 Colorstream Viola Fantasy 12% 3.1 2 Pyrisma Green 12% 3.1 3 Colorstream Tropic Sunrise 12% 3.1 4 Miraval (formerly 3% 2.3 Colorstream) Pacific Twinkle 5 Pyrisma Green 6% 3.1 6 Miraval 5402 Pacific Twinkle 6% 3.1 7 Miraval 5426 Magic Green 3% 3.1 8 Miraval 5426 Magic Green 6% 0.8 9 Iriodin 231 Rutile Fine Green 3% 1.6 10 Iriodin 231 Rutile Fine Green 6% 1.6 11 Iriodin 231 Rutile Fine Green 9% 0.8 12 Iriodin 299 Flash Green 3% 1.6 13 Iriodin 299 Flash Green 6% 0.8 14 Iriodin 299 Flash Green 9% 1.6 15 Xirallic T60-24 Stellar Green 6% 2.3 16 Xirallic T60-24 Stellar Green 9% 3.1 17 Xirallic T60-24 Stellar Green 12% 0.8 18 Pyrisma T30-24 Green 3% 1.6 19 Colorstream T10-01 Viola 3% 2.3 Fantasy 20 Colorstream T10-01 Viola 6% 1.6 Fantasy 21 Colorstream T10-01 Viola 9% 2.3 Fantasy 22 H.sup.2O-Lack Prll FGL M093 no pigment no pigment 23 UV-Lack Schmid Rhyner no pigment no Wessco 34.238.30 pigment 24 Pyrisma Green Mirror 6% 1.6 (HM 43-16)

[0095] Impacts of pigment layers onto c-Si solar cells are assessed by reflection measurements.

[0096] Reflection data are used to estimate max. power absorption/max. photo current generation of treated cells: [0097] Spectral reflectance is recorded in wavelength interval between 280 nm to 1200 nm. [0098] Transmission of cells artificially set to zero (as this is also expected for real-life conditions of Si solar cells comprising an almost completely rear side coverage of sintered and alloyed aluminium paste which conventionally forms the rear side electrode of such devices). [0099] Regularly full absorption of short wavelength light by cell's bulk Calculation of absorption of light by whole system [0100] Absorption in pigment layers, SiNx and Al neglected (since unknown) [0101] Transposition of power absorption to max. achievable photo current based on AM1.5G spectrum (according to IEC 60904-3 Ed. 2 which is equivalent to ASTM G173-03). For this purpose, afore-mentioned reference spectrum is taken and irradiation intensity is re-calculated by interpolation of spectrum applying single nanometer resolution as stepwidth for the wavelength regime of 280 nm to 1200 nm. Integration of the interpolated spectrum yields a total irradiation intensity of 835.998 W/m.sup.2. Latter is very good agreement with integral for the same wavelength range of the original reference spectrum whose irradiation intensity amounts to 836.19 W/m.sup.2. The difference between the original spectrum and the interpolated one amounts to 0.2%. [0102] Reflectance standard (PTFE) [0103] Cary 5000 (UV/ViS/NIR); Agilent [0104] All cells (where applicable) are probed 4-time [0105] Cells are subjected to reflectivity measurement [0106] Measurement setup is checked by using reference sample [0107] Light incidence perpendicular to surface of cells [0108] Reflectivity is measured from front side of cells [0109] Front side: within this context, solar cell's surface covered by SiN.sub.x is per definition considered as the so-called front side; colored, opposite to full Al electrode [0110] Measurements are performed with three repetitions (4 measurements in total)

[0111] Irradiated surface is amounted to cover large area fractions up to 1 cm in diameter.

[0112] Thus, reflectance data are averaged integrals comprising metallized/non-metallized surface.

[0113] Measured data are averaged and averages are used for further considerations: [0114] Averaged mean reflectance of the cell [0115] Estimation of standard deviation & variance [0116] Estimation of T-error range according to probability of 99% (confidence interval) [0117] carried out using PTFE-standard as reference [0118] Sample beam not covered and sealed by light absorbing lid during measurement in order to not unintentionally damage of destroy fragile silicon solar cells.

[0119] Results are summarized in Table 2.

TABLE-US-00002 TABLE 2 max. Photo max. Power rel. Current rel. Absorbed Power Possible Current [W/m.sup.2] Loss [%] [A/m.sup.2] Loss [%] AM1.5G 836.0 0.00 464.4 0.00 Reference 769.9 0.00 427.7 0.00 Cell 01 (violet) 650.0 15.57 370.0 13.49 Cell 02 (green) 656.5 14.73 364.4 14.80 Cell 03 (green) 524.2 31.91 285.7 33.20 Cell 04 739.5 3.96 408.4 4.51 Cell 05 698.7 9.25 387.2 9.46 Cell 6 702.0 8.83 387.4 9.43 Cell 7 752.0 2.33 416.1 2.71 Cell 8 738.3 4.11 408.7 4.44 Cell 9 724.2 5.93 401.1 6.22 Cell 10 684.7 11.07 379.8 11.19 Cell 11 651.6 15.37 361.7 15.42 Cell 12 743.2 3.47 411.5 3.80 Cell 13 715.9 7.01 397.2 7.13 Cell 14 693.0 9.99 384.9 10.01 Cell 15 706.9 8.18 392.9 8.14 Cell 16 681.3 11.51 379.1 11.35 Cell 17 654.5 15.00 364.5 14.77 Cell 18 733.4 4.75 406.0 5.08 Cell 19 727.8 5.47 407.2 4.80 Cell 20 691.3 10.21 390.0 8.82 Cell 21 661.2 14.12 375.6 12.18 Cell 22 774.4 0.59 428.2 0.11 Cell 23 777.7 1.02 429.8 0.49 Cell 24 702.5 8.76 389.6 8.91

Example 2

[0120] Solar mini modules are prepared in a way that layers containing effect pigments according to the invention in a water based resin are directly printed on commercially available Al-BSF solar cells. The modules are afterwards contacted by manual soldering and encapsulated between a glass plate and a tedlar backsheet using either thermoplastic polyurethane (TPU) or ethyl-vinyl acetate (EVA). The efficiency is measured in standardized setup under AM1.5.

[0121] While the uncoated reference module shows an efficiency of up to 17.6% none of the tested solar mini modules shows a drop in efficiency exceeding 10% (rel.). Even a white appearing module shows an effective efficiency of 16% due to the selective reflection of light caused by effect pigments.

Example 3

[0122] Solar mini modules are prepared in a way that layers containing effect pigments according to the invention in a water based glass/frits mixtures are directly printed on commercially available low iron glass used for solar modules by screen printing and afterwards tempered at 600 C.-680 C. in an oven. In a second step a grid with colored ceramic color is printed on top of the layer in a design to be able to cover the bright areas like the space between single cells and the bus bars, conducting path and soldering points.

[0123] Modules are prepared with the following steps before it is fused. [0124] Glass plate covered with dark blue colored backsheet out of thermoplastic polyurethane (TPU) or ethyl-vinyl acetate (EVA). In this case a black multilayer backsheet from Dymat (Bk PYE SPV-L). [0125] Cells are placed and contacted by manual melding [0126] Second sheet out of thermoplastic polyurethane (TPU) or ethyl-vinyl acetate (EVA) is placed on top of the cells. [0127] On top the colored glass plate is placed in a manner that all remaining bright areas are covered by the dark grid. [0128] Module is heated at 100 C. in an vacuum oven to seal the module.

[0129] The efficiency is measured in standardized setup under AM1.5 conditions.

[0130] While the uncoated reference module shows an efficiency of up to 17.6% none of the tested solar mini modules shows a drop in efficiency exceeding 20% (rel.). Even a white appearing module shows an effective efficiency of 15.1% due to the selective reflection of light caused by effect pigments.

Example 4

[0131] A semi-transparent organic solar cell with an integrated blue LED (powered by the organic solar cell) is printed with an ink containing Pyrisma@ Green (3%) in Proell Aqua Jet FGL M 093 varnish (95.5%) and Proell Defoamer L36459 (1.5%) is printed using manual flat-bed screen printer. Mesh PET1500 54/137-64W from Sefar is used (parameters of the mesh: 137 l/inch, 115 m mesh opening and 64 m thread diameter). Squeegee used for printing is a manual squeegee with hardness of 75 shore. The layer is dried at room temperature in ambient conditions. The brightness of the LED integrated in the organic solar is based on its generated current and can thus be used to measure the efficiency. The LED shows the same brightness under illumination from the printed or non-printed side thus the effect pigment coating has a negligible impact on the current and efficiency of the organic solar cell.

Example 5

[0132] Spray coating of solar cells with effect pigment containing lacquer

[0133] Standard solar cells are by spray application with the regularly used devices.

[0134] The used pearlescent pigment, in this case green interference pigments, are stirred in a commercially available 2K refinish clearcoat from MIPA (MIPA CC4 2K Klarlack), the used concentration here is 1.13% on formulation. The coating is prepared as recommended by the supplier and adjusted to an application viscosity of 70-75 mPas at1000 1/s. Following effect pigments were used: [0135] Iriodin 9231 SW [0136] Iriodin 9235 SW [0137] Iriodin 97235 SW [0138] Miraval Green [0139] Xirallic Stellar Green SW

[0140] For the application of the so prepared coating on the solar cells an automated spraying device Oerter APL4.6 is used. In this case the coating is applied with a 1.4 mm nozzle in two cycles following each other immediately. Before stoving at 70 C. for 60 min the coating is allowed to dry at room temperature for 10 min. In the end a dry film thickness of about 40m is achieved.

[0141] The characteristic of green interference pigments is visible clearly on the solar cell panels, in certain angles the green color is visible, in others not. To characterize the panels and the effect of the used effect pigments on the efficiency of the panels further, measurement of reflectivity is done on the coated front side of the cells. Therefore, a Cary 5000 (UV/VIS/NIR) Agilent is used. As reference a not coated standard solar cell is used. With this setup it is determined that the rel. loss of achievable current is only between 4.5% (Xirallic Stellar Green SW) and 6.7% (Iriodin 9235 SW) depending on the used green interference pigment compared to a not coated solar cell.