ELECTRO-CONDUCTIVE BACK-SHEET COMPRISING AN ALUMINIUM AND A METAL LAYER

Abstract

The present invention relates to an electro-conductive back-sheet for back-contact photovoltaic cell technologies comprising an aluminum layer, a cold sprayed metal layer on top of the aluminum layer and a polymeric back-sheet having an (OTR) of at least 20 cm3/m2.Math.atm per day. The metal used for the metal layer is chosen from the group consisting of copper, tin, silver or nickel, or mixtures of two or more thereof or alloys of two or more thereof. Preferably the metal is copper. The metal layer preferably has a thickness in the range of 50 nm-10 m. The present invention further relates to process for the manufacturing of the electro-conductive back-sheet. The present invention also relates to a photovoltaic module comprising the electro-conductive back-sheet.

Claims

1. Electro-conductive polymeric back-sheet for back-contact photovoltaic cells comprising an aluminum layer, a cold sprayed metal layer on top of the aluminum layer characterized in that the polymeric back-sheet has an oxygen transmission rate (OTR) of at least 20 cm3/m2.Math.atm per day.

2. Electro-conductive polymeric back-sheet according to claim 1 wherein the metal is chosen from the group consisting of copper, tin or nickel, or mixtures of two or more thereof or alloys of two or more thereof.

3. Electro-conductive polymeric back-sheet according to claim 1 wherein the metal used for the metal layer is copper.

4. Electro-conductive polymeric back-sheet according to claim 1 wherein the polymeric back-sheet has an (OTR) of at least 40 cm3/m2.Math.atm per day.

5. Electro-conductive polymeric back-sheet according to claim 1 wherein the cold sprayed metal layer has a thickness in the range of 1 m-50 m

6. Electro-conductive polymeric back-sheet according to claim 5 wherein the cold sprayed metal layer is applied in form of lines or is applied over the whole surface of the aluminum layer.

7. Electro-conductive polymeric back-sheet according to claim 1 wherein the polymeric back-sheet is a mono- or multilayer back-sheet.

8. Electro-conductive polymeric back-sheet according to claim 1 wherein the polymeric back-sheet comprises more than one thermoplastic polymer layer chosen from the group selected of polyolefins, polyamides, polyesters or fluorinated polymers

9. Electro-conductive polymeric back-sheet according to claim 1 wherein the polymeric back-sheet is a multilayer back-sheet comprising at least a polyamide layer and a polypropylene layer.

10. Electro-conductive polymeric back-sheet according to claim 9 wherein the polymeric back-sheet further comprises a polyethylene layer.

11. Process for the manufacturing of an electro-conductive back-sheet according to claim 1 comprising the steps of: (a) providing an aluminum layer and a metal that is cold sprayed on the aluminum layer to provide an aluminum coated metal layer (b) providing a polymeric back-sheet comprising one or more polymeric layer(s) (c) lamination of the aluminum coated metal layer and the polymeric back-sheet

12. Process for the manufacturing of an electro-conductive back-sheet according to claim 1 comprising the steps of: (a) providing the aluminum layer on the polymeric back sheet via extrusion/lamination (b) cold spraying the metal layer on the aluminum containing polymeric back sheet.

13. Process for the manufacturing of an electro-conductive back-sheet according to claim 11 wherein the more polymeric layers in the back-sheet are co-extruded and/or laminated.

14. Process for the manufacturing of an electroconductive back-sheet according to claim 11 wherein the metal is cold sprayed locally.

15. Process for the manufacturing of an electro-conductive back-sheet according to claim 11 further comprising the step of patterning the electro-conductive back-sheet.

16. Photovoltaic module comprising the electro-conductive back-sheet according to claim 11.

Description

FIGURES

[0057] FIG. 1 shows the relative change of strain at break in % of back-sheets with different OTR values under UV exposure over time.

[0058] FIG. 2 shows the relative change of max in % of back-sheets with different OTR values under UV exposure over time.

[0059] FIG. 3 shows the relative change of strain at break in % of back-sheets with different OTR values at Damp heat 85 C./85% RH over time.

[0060] FIG. 4 shows electrochemical analysis of the oxidation sensitivity of neat metal foils established in a 3-electrode set up via a stepwise dissolution measurement (Procedure in described in Metrohm Autolab application note COR08). A high cumulative charge corresponds to an increased overall oxidation rate.

[0061] FIG. 5 refers to a backsheet with high OTR and shows good mechanical performance after 2000 hrs hydrolytic ageing.

[0062] FIG. 6 refers to a backsheet with low OTR and shows bad mechanical performance after 2000 hrs hydrolytic ageing.

EXAMPLES

Example 1

[0063] Oxygen permeation measurements of thermoplastics polymeric layers in formulated back-sheets are performed according to ASTM D 3985 with a MOCON OX-Tran 2/21 at 38 C., 0% RH, area of the back-sheet samples 50 cm2. These measurements are done in duplo. Results are given in table 1.

[0064] Water permeation measurements of thermoplastics polymeric layers in formulated back-sheets. are performed according to ASTM F 1249 with a MOCON Permatran-W700 at 38 C., 90% RH-0% RH. These measurements are done in duplo.

[0065] Results are given in table 2.

TABLE-US-00001 TABLE 1 Oxygen Permeation Data OTR Permeation Material Thickness cm3/(m2 - cm3 - mm/m2 .Math. Back-sheet (m) day) .Math. atm day .Math. atm PA12-PP-PE 386.2 384.9 148.6 PA12-PP-PE 389.4 384.1 149.6 PA12-PP 369.7 353.0 130.5 PA12-PP 371.9 355.0 132.0 PET 1142 2.74 3.13 PVF-PET-PVF 350.0 9.12 3.19 FPP*-PA6-PE 342.8 46.3 15.9 PE-PA6-PP 348.0 44.9 15.6 *FPP = Flexible PP

TABLE-US-00002 TABLE 2 Water vapor Permeation Data Vapour Coefficient of Transmission permeability Average Material rate Thickness [g-mm]/ [g-mm]/ Back-sheet g/[m.sup.2-day] mm [m.sup.2-day] [m.sup.2-day] PA12-PP-PE 0.815 0.3795 0.309 0.310 PA12-PP-PE 0.817 0.3808 0.311 PA12-PP 0.736 0.3781 0.278 0.281 PA12-PP 0.774 0.3658 0.283 0.281 PVF-PET-PVF 2.132 0.3556 0.758 0.758

Example 2

[0066] Power output performance is measured on 22 mini-modules at 500 hrs damp heat ageing (85% RH; 85 C.), comprising the below indicated electro-conductive back-sheets.

[0067] Current (I) and Voltage (V) characteristics of the solar cells prior to module manufacturing are measured using SUNSIM flash-tester and the IV characteristics of the modules are measured using a Pasan III A flash-tester under standard testing conditions [1000 W/m.sup.2, AM1.5 spectrum].

[0068] FF [%] is a parameter which, in conjunction with V.sub.oc and I.sub.sc, determines the maximum power from a solar cell. The FF is defined as the ratio of the maximum power from the solar cell to the product of V.sub.oc and I.sub.sc.

[0069] In table 3 results are shown for electro-conductive backsheets based on pure metallic copper (Cu) with high and low OTR and based on physical vapor deposited (PVD) copper on aluminum (Al/Cu PVD) with high OTR.

TABLE-US-00003 TABLE 3 OTR cm3/m2.atm Pm [W] per day/ Max Cell Conductive back-sheet back-sheet power Isc [A] Voc [V] FF [%] eff [%] PA12-PP-PE-Cu 384 0.3% 0.6% 0.1% 0.9% 0.4% PA12-PP-PE-Cu 0.8% 0.6% 0.1% 1.2% 0.8% PA12-PP-PE-Cu 1.0% 0.8% 0.1% 1.6% 0.9% PA12-PP-PE-Cu 0.7% 0.8% 0.1% 1.4% 0.7% PVF-PET-PVF-Cu. 9 0.8% 0.5% 0.2% 0.5% 0.9% PVF-PET-PVF-Cu 0.7% 0.6% 0.2% 0.3% 0.7% PVF-PET-PVF-Cu 0.8% 0.7% 0.2% 0.3% 0.7% PVF-PET-PVF-Cu 0.8% 0.7% 0.1% 0.2% 0.8% PA12-PP-PE-Al/Cu PVD 384 13% 0.1% 0.0% 13% 13% PA12-PP-PE-Al/Cu PVD 15% 0.2% 0.1% 15% 15% PA12-PP-PE-Al/Cu PVD 18% 0.0% 0.1% 18% 18% PA12-PP-PE Al/Cu PVD 19% 0.1% 0.1% 19% 19%

[0070] The results in Table 3 show that replacing pure metallic copper in electro-conductive backsheets with high OTR by Al/Cu PVD results in very and too high-power decay (>5%) already after 500 hrs dampheat ageing.

Example 3

[0071] Power output performance was measured of 22 mini-modules after 1000 hrs damp heat ageing (85% RH; 85 C.) comprising the below indicated electro-conductive back-sheets. The copper layer is applied either via PVD (Al/Cu PVD) or via cold spray (Cs) (Al/Cu Cs).

[0072] IV-characteristics (current-voltage) are measured. Results are given in table 4.

TABLE-US-00004 TABLE 4 OTR cm3/m2.atm per day/ Conductive back-sheet back-sheet Pm [W] Isc [A] Voc [V] FF [%] Cell eff [%] PVF-PET-PVF-Al/Cu 9 1.9% +1.0% +0.2% 3.0% 1.9% PVD PVF-PET-PVF-Al/Cu 4.4% +1.2% +0.2% 5.7% 4.4% PVD PVF-PET-PVF-Al/Cu 1.4% +1.2% +0.2% 2.8% 1.4% PVD PVF-PET-PVF-Al/Cu 4.6% +1.0% +0.2% 5.6% 4.6% PVD PVF-PET-PVF-Al/Cu 9 0.5% +1.0% +0.2% 1.6% 0.5% Cs PVF-PET-PVF-Al/Cu 1.3% +0.5% +0.2% 1.9% 1.3% Cs PVF-PET-PVF-Al/Cu 0.0% +1.1% +0.3% 1.3% 0.0% Cs PA12-PP-Al/Cu PVD 353 7.6% +0.8% +0.2% 8.6% 7.7% PA12-PP-Al/Cu PVD 6.8% +0.8% +0.1% 7.7% 6.8% PA12-PP-Al/Cu PVD 8.0% +0.6% +0.1% 8.6% 8.0% PA12-PP-Al/Cu Cs 353 +0.4% +0.6% +0.2% 0.4% +0.4% PA12-PP-Al/Cu Cs 0.1% +0.8% +0.2% 1.0% 0.1% PA12-PP-Al/Cu Cs 0.2% +0.7% +0.1% 1.0% 0.2%

[0073] Table 4 indicates that electro-conducive backsheets with low OTR based on cold spray deposited copper on aluminum outperform PVD copper deposited aluminum. The results in Table 4 confirm the result of example 3, i.e. electro-conductive backsheets with high OTR based on PVD deposited copper on aluminum result in too high-power decay (>5%). However, it also shown that electro-conductive backsheets with high OTR based on cold spray deposited copper on aluminum show excellent performance in dampheat ageing.

Example 4

[0074] Power output performance was measured of 22 mini-modules after 3000 hrs damp heat ageing (85% RH; 85 C.) comprising the below indicated electro-conductive back-sheets. The copper layer is applied via cold spray (Cs).

[0075] IV-characteristics (current-voltage) are measured. Results are given in table 5.

TABLE-US-00005 TABLE 5 OTR cm3/m2.atm per day/ Conductive back-sheet back-sheet Pm [W] Isc [A] Voc [V] FF [%] Cell eff [%] PA12-PP-Al/Cu Cs 353 1.3% +0.7% +0.1% 2.1% 1.3% PA12-PP-Al/Cu Cs 1.7% +0.2% 0.1% 1.8% 1.7% PA12-PP-Al/Cu Cs 0.5% +0.8% 0.0% 1.4% 0.5%

[0076] Table 5 shows that that electro-conductive backsheets with high OTR based on cold spray deposited copper on aluminum show excellent performance even after 3000 hrs dampheat ageing (<<5% power decay).

Example 5

[0077] Power output performance was measured of 22 mini-modules from 0 to 2500 hrs hydrolytic ageing (95% RH; 85 C.) comprising the below indicated electro-conductive back-sheets. The copper layer is applied via cold spray (Cs). The average power decay of 4 modules of the same built is indicated as function of hydrolytic ageing time in table 6. Moreover, table 6 also refers to the FIGS. 5 and 6 of the modules of each built after 2000 hrs hydrolytic ageing.

TABLE-US-00006 TABLE 6 OTR cm3/ m2.atm Power Power Power Power Power per day/ [%] [%] [%] [%] [%] Conductive back- t = t = t = t = t = back-sheet sheet 500 1000 1500 2000 2500 PA12-PP-Al/ 353 +1.0% +1.3% +0.6% +0.3% 0.8% Cu Cs PET-Al/Cu Cs 3 +1.3% +0.8% +0.0% 1.4% 3.8% Conductive OTR cm3/ FIGS. 5 and 6 show one of the modules back-sheet m2.atm after 2000 hrs hydrolytic ageing per day/ Back-sheet PA12-PP-Al/ 353 Backsheet shows good mechanical Cu Cs performance after 2000 hrs (FIG. 5) PET-Al/Cu Cs 3 Backsheet loses its mechanical integrity after 2000 hrs (FIG. 6)

[0078] Table 6 shows that electro-conductive backsheets with high OTR based on cold spray deposited copper on aluminum outperform electro-conductive backsheets with low OTR based on cold spray deposited copper on aluminum. Table 6 clearly indicates that this is caused by the much better mechanical performance of electro-conductive backsheets with high OTR in hydrolytic ageing (as also shown in FIG. 6), i.e. the low OTR backsheet based on PET completely loses its mechanical integrity after 2000 hrs resulting in a strong increase in power decay.