Roll to roll fabrication process of thin film silicon solar cells on steel foil

ECN is developing a novel fabrication process for thin film silicon solar cells on steel foil. Key features in this process chain are: 1) application of an insulating barrier layer which enables 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 the layers (reducing the total number of process steps). The barrier layer is primarily an enabler for monolithic series interconnection of cells, but we show that we can also fabricate any arbitrary sub-micron structure in this layer by hot embossing to achieve optimum light trapping in the solar cells. For deposition of doped and intrinsic silicon layers we use novel remote and 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. First pin a-Si solar cells have been made on FTO glass, yielding initial efficiencies up to 4.5%. First nip a-Si cells made on steel foil plus textured barrier layer yielded efficiencies of about 3.7%.