DSM Patents High Performance Silver-Free PV Back Layer

Michelle

DSM Patents High Performance Silver-Free PV Back Layer

DSM, HQ Neerlen, Netherlands has a patent family relating to production of an electro-conductive back-sheet comprising either pure copper or a copper-aluminium metal layer for a photovoltaic (solar) cell. The cell is reported in the patent to have a high oxygen transmission rate (OTR). The patent family which has a priority date of 6th October 2017, has been filed in the USA, Spain, Europe, China, Hong Kong, and India. The latest patent publication number is WO2019068934A11.

Photovoltaic (PV) modules are at the heart of solar power systems and consist of a core layer encapsulated in laminate designed to protect against mechanical and weathering-related influences. The encapsulation consists of a glass front layer with an ethylene-vinyl acetate (EVA) copolymer and a glass or polymeric back layer which shields against UV light, moisture, and oxygen. Typical back sheets are made from fluoropolymer and polyesters (e.g., polyethylene terephthalate (PET).

PV modules comprising EWT (emitter-wrap-through) or MWT (metal-wrap-through) or IBC (interdigitated back-contact) solar cells contain an electrically conductive patterned back sheet for which connect to electrical contacts on the solar cell back surface. such a back sheet comprises a polymer layer and a patterned conductive layer made of copper (or copper alloy). There has been a desire to decrease or replace the copper due to its increasing cost. Aluminium is an alternative however it has poor solderability and high contact resistance, and so a thin layer of copper is thermally sprayed onto the aluminium e.g., from Hanita Coatings. The downside of this approach is thermal degradation, high resistance due to increased oxygen transfer rate (OTR) and corrosion issues especially in more humid settings. This results in lower power output. The polymers can be adjusted to achieve an OTR of less than 20 cm3/m2.atm per day but these have decreased hydrolytic resistance and UV stability which adversely affects the durability and lifetime of the module.

Figure 1: Results on the Damp Heat Resistance with High OTR PA/PP/PE vs. PET and Stepwise Dissolution Measurement for Cold Sprayed Cu/Al conductive sheet vs other metal formulations1

To overcome this issue, the inventors developed a cold-spray deposition method for the copper which allows for layers to be built up quickly, under atmospheric conditions and at low cost. In addition, using polyamide (PA)/polypropylene (PP)/polyethylene (PE) polymers with high OTR’s (384 are used as the back sheet polymer and these are compatible with the Cu/Al of the invention.

Results on power decay were superior to several other formulations including Al/Cu prepared by standard vapour deposition, pure copper, pure aluminium, or Al-Cu-Ag. Good mechanical performance was achieved after 2,000 hrs of ageing. Even though UV resistance was similar, damp heat resistance was far better with the PA/PP/PE layer compared with PET. The results are shown in Figure 1. above.

  1. Van Duijnhoven, F, Henricus, G and Janssen, R. IN407312A1. Electro-Conductive Back-Sheet Comprising An Aluminium And A Metal Layer. Sept 30, 2022.
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  3. NorthStar. Northstar Corporate Presentation. Northstar. [Online] Q4 2022a. https://docsend.com/view/e8c53v3mdyupcxg5.