POLYMER SHEET

Abstract

The invention is directed to a polymer sheet and its use as part of a solar panel and glass element. The sheet comprises multiple coextruded polymer layers, wherein at least two or more layers of the polymer sheet comprise a luminescence downshifting compound for at least partially absorbing radiation having a certain wavelength and re-emitting radiation at a longer wavelength than the wavelength of the absorbed radiation, and wherein a luminescence downshifting compound in a first polymer layer can absorb more radiation at a lower wavelength than the luminescence downshifting compound present in a next layer.

Claims

1.-45 (canceled)

46. A polymer sheet composition comprising at least two coextruded polymer layers, wherein at least one of the coextruded polymer layers comprises a luminescence downshifting compound for at least partially absorbing radiation having a certain wavelength and re-emitting radiation at a longer wavelength than the wavelength of the absorbed radiation, and wherein at least one of the coextruded polymer layers comprises (i) a polymethylmethacrylate or an alkylmethacrylate, and/or (ii) an alkylacrylate copolymer, functionalized polyolefins, ionomers; or mixtures thereof

47. The polymer sheet of claim 46, wherein a luminescence downshifting compound is present in a first polymer layer, and wherein the luminescence downshifting compound can absorb more radiation at a lower wavelength than the luminescence downshifting compound present in a second polymer layer.

48. The polymer sheet of claim 46, wherein the radiation comprises UV radiation.

49. The polymer sheet of claim 46, wherein the sheet comprises two outer polymer layers and at least one inner polymer layer and wherein an outer polymer layer or both outer polymer layers has a melting point T1 which at least 10 C. below the melting point T2 of at least one inner polymer layer.

50. The polymer sheet of claim 49, wherein at least one of the outer polymer layers comprises a silane coupling agent.

51. A method for making a polymer sheet, comprising the steps of: (i) providing one or more master batch polymer materials for each polymer layer, and (ii) co-extruding the master batch polymer materials to layers forming the polymer sheet; wherein at least one of the layers comprises a luminescence downshifting compound for at least partially absorbing radiation having a certain wavelength and re-emitting radiation at a longer wavelength than the wavelength of the absorbed radiation, and wherein at least one of the polymer layers comprises (i) a polymethylmethacrylate or an alkylmethacrylate, and/or (ii) an alkylacrylate copolymer, functionalized polyolefins, or mixtures thereof.

52. The method of claim 51, wherein the polymer materials are extruded at an extrusion temperature for each sub-layer so chosen that the largest difference in melt flow index of the polymers of the sublayers at the extrusion temperature as applied for each sub-layer is lower than 3 MFI points.

53. An element comprising: (i) two layers of glass, and (ii) a transparent polymer layer comprising a polymer sheet of claim 46, wherein the transparent polymer layer is present between the two layers of glass.

54. The element of claim 53, wherein the glass of the glass layer is a borosilicate glass or a soda lime glass.

55. The element of claim 53, wherein the total thickness of the glass element is less than 5 mm, and/or wherein at least one of the glass layers has a thickness of between 0.1 and 2 mm.

56. A method for changing the properties of sun light in the process of growing plants, the method comprising: placing an element of claim 53 between the sun light and a plant, wherein the composition alters the sun light to which the plant is exposed.

57. The method of claim 56, wherein the element of claim 53 is present on the roof of a greenhouse.

58. A method for changing the properties of sun light in a process of generating electricity, the method comprising: exposing an element of claim 53 to sun light, wherein in the presence of sun light, the composition generates an electric current.

59. The method of claim 58, wherein the element of claim 53 further comprises a photovoltaic cell.

60. A photovoltaic module comprising: (i) a layer comprising a photovoltaic cells, and (ii) a cover layer comprising the element of claim 53, and optionally wherein the photovoltaic cell is a thin film cadmium telluride photovoltaic cell.

61. A photovoltaic solar cell comprising: (i) an element of claim 53, (ii) a transparent electrode layer, (iii) an n-type semiconductor layer, (iv) a cadmium telluride absorber layer, and (v) a back contact.

62. A method for enhancing the performance of a photovoltaic cell, the method comprising: placing a polymer sheet of claim 46 between sun light and a photovoltaic cell, wherein the polymer sheet causes luminescent downshifting of sunlight, thereby enhancing the performance of the photovoltaic cell.

63. A solar panel comprising (i) a polymer sheet of claim 46, and (ii) a photovoltaic cell.

64. The solar panel of claim 63, wherein the panel has a layer sequence of a glass layer, the polymer sheet, the photovoltaic cell, an encapsulant layer and a back sheet.

65. A method for manufacturing a solar panel, the method comprising: (i) providing a stack comprising the following layers: (a) a glass layer, (b) a polymer sheet of claim 46, (c) a layer comprising a photovoltaic cell, (d) a polymer encapsulant layer, and (e) a glass layer, and (ii) exposing the stack to an elevated lamination temperature, thereby manufacturing a solar panel.

66. The method of claim 65, wherein the lamination temperature is between 115 and 175 C. and wherein the environment of the stack has a pressure of less than 30 mBar.

Description

[0101] The following examples illustrate the invention:

Comparative Example 1

[0102] A mono layer EVA foil was produced as follows: A commercially available ethlyene vinyl acetate copolymer with a 33% vinylactetate content and an MFI of approximately 45 g/10 min was employed. A commercially available fluorescent perylene dye absorbing light at a wavelength of 578 nm, and emitting at a wavelength of 613 nm, was blended with the EVA material, in a concentration of 0.05% by weight, in a manner as for instance disclosed in U.S. Pat. No. 7,727,418.

[0103] The foil material further contained approximately 1% by weight of methacryloxypropyltrimethoxysilane as an adhesion promoter, and approximately 1 by weight of tert-Butylperoxy 2-ethylhexyl carbonate as peroxide cross-linking agent.

[0104] The material was blended homogeneously, and a thin plate of about 500 m thickness was pressed at a temperature of 110 C. of each blend.

[0105] The resulting plate was then laminated between two glasses using the following lamination protocol on a flat-bed vacuum laminator from Meier:

[0106] Temperature: 145 C.; Vacuum time: 300 seconds; Pressure ramp up: 30 seconds and Press time: 400 seconds.

[0107] The two samples were then placed into a UV weathering chamber, and subjected to an accelerated aging test, employing the test cycle disclosed as ISO 4892 part 2, Method A, Cycle 2, Entitled Plastics Methods of Exposure to Laboratory Light SourcesXenon Arc Lamps.

[0108] After 50 hours of exposure, the sample showed discoloration. A UV/VIS spectrometry was taken, showing that the sample no longer exhibit absorption typical for the perylene dye.

Example 1

[0109] A 3-layer co-extruded foil was produced with the following composition: Layer 1: EVA+1% methacryloxypropyltrimethoxysilane 1% by weight of tert-Butylperoxy 2-ethylhexyl at a thickness of 200 m, and further comprising a commercial light stabilization package containing a combination of HALS and anti-oxidants, to protect the EVA polymer matrix from degradation. Layer 2: PMMA+0.05% perylene dye, at a thickness of 50 m. Layer 3: EVA+1% methacryloxypropyltrimethoxysilane 1% by weight of tert-Butylperoxy 2-ethylhexyl, at a thickness of 200 m, further comprising the light stabilisation package of Layer 1.

[0110] The resulting sample showed a high stability of the perylene dye after 500 hours of UV weathering, while also typical encapsulation properties, such as adhesion, cross-linking, flow and encapsulation behaviour, which were provided by the EVA encapsulant layers on the outer layers of the sample.

Comparative Example 2

[0111] A zeolite containing nanoclusters of Silver (Ag) was mixed into an EVA matrix at a concentration level of 6%. Two samples were produced. One sample was stored in a dry environment, controlled by a desiccant, while the second sample was stored at ambient conditions.

[0112] After 2 days the ambiently stored sample showed a slight discoloration, whereas the first sample, stored in a moisture controlled environment, did not show this effect. After 20 days the ambiently stored sample showed severe discoloration to brown, and lost transparency. The remaining transparency was lower than 10% in a wavelength range of 250 to 800 nm. The sample under controlled humidity showed only a small discoloration.

Comparative Example 3

[0113] A further monolayer polymer sheet as in comparative example 2 was prepared, and laminated between two glasses using the same lamination cycle discussed in Example 1. The glass/glass sample was placed in a damp heat weathering chamber at 85 C. and 85% relative humidity. A discoloration was visible at the edges of the glass plates after just 50 hours of damp heat testing.

Comparative Example 4

[0114] Comparative Example 3 was repeated, however employing a glass/encapsulant/polymeric backsheet construction. The thus obtained element, and also placed in the weathering chamber. This sample turned quickly completely dark brown, illustrating the lower performance of the polymeric backsheet as moisture barrier as compared to the glass back plate of comparative example 4.

Example 3

[0115] In order to keep the typical EVA encapsulation properties, a multilayer film was prepared comprising of two 200 m thick EVA layers as outer layer and a thin middle layer consisting out of a polymer with better moisture barrier characteristics. The polymer that was chosen was a low density polyethylene. The melt index of the polyethylene was chosen is such a way that at the extrusion temperature of 110 C. the melt flow was similar to the melt flow of EVA polymer at the same temperature. The Ag/zeolite powder was mixed in the polyethylene layer. The resulting film showed the characteristic encapsulation properties of a standard EVA monolayer, but also provided protection of the Ag/zeolite in the middle layer since it was embedded in a polymer with better moisture characteristics.

[0116] A glass/encapsulant multilayer /PEF backsheet element was prepared, which showed no significant discoloration after 500 h in the damp heat test.

Example 4

[0117] A glass/multilayer/glass element was prepared, also applying an edge seal. This element showed no discoloration after 500 hours in the wet heat test. This construction keeps the largest portion of the moisture outside of the module, and it is expected that the multilayer polymer sheet will act as a second line of protection, and protect humidity ingress especially from moisture ingress via the junction box.