Roll to roll fabrication of thin film silicon solar cells on nano-textured substrates.

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 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 with textured barrier layer yielded efficiencies of about 3.7%.