ECN is developing a novel fabrication process for thin film silicon solar cells on steel foil. Key features in this process are: (1) application of an insulating barrier layer which enables monolithic interconnection and texturization of the rear contact with submicron structures for light trapping; (2) Si deposition with remote, linear PECVD; (3) series interconnection by laser scribing and printing after deposition of all layers, which reduces the total number of process steps. The barrier layer is essential for the monolithic series interconnection of cells, but we show that it also enables optimum light trapping in the solar cells. We can fabricate any arbitrary sub-micron surface profile by hot embossing the barrier layer. For deposition of doped and intrinsic silicon layers we use novel remote, linear plasma sources, which are excellently suited for continuous roll-to-roll processing. We have been able to fabricate device-quality amorphous and microcrystalline silicon layers with these sources. The first nip a-Si cells were made on steel substrates with flat barrier layer and had initial efficiencies of 6.3%, showing the potential of the concept.
Back-contact modules made using a conductive back-sheet foil have a number of advantages over conventional Hpattern modules including a higher power output, compatibility with very thin cells and efficient and high yield manufacturing. In this paper, we present the results of efficiency and material optimization for cost reduction when using metal-wrap-through (MWT) cells. This includes the use of an aluminum conductive back-sheet, a thinner encapsulant for reduced conductive adhesive consumption and an increased number of vias in the cell. Experimental and modelling results show that the cell and module performance can be improved at a reduced module costs (4% lower than current cost) whilst retaining reliability.
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