Maskless patterned plasma fabrication of interdigitated back contact silicon heterojunction solar cells: Characterization and optimization

We demonstrate a novel method to fabricate passivated interdigitated back contact (IBC) crystalline silicon solar cells incorporating a maskless, patterned plasma etching step. After deposition in a plasma-enhanced chemical vapor deposition (PECVD) chamber, the intrinsic and doped hydrogenated amorphous silicon and microcrystalline silicon layers (necessary for the passivated interdigitated contacts in such heterojunction technology (HJT) devices) are patterned via a single, maskless etching step, also performed in a PECVD chamber. The patterning step relies on selectively lighting an etching plasma within slits in the patterned powered electrode when it is placed very close to the substrate. The process flow is characterized and optimized at each step using spectroscopic ellipsometry, photoluminescence, and surface photovoltage mapping. It is shown that a critical step is the removal of a damaged layer formed on the surface after the patterned etching. Without this step, the IBC-HJT solar cells systematically exhibit S-shaped curves in their current-voltage (I–V) characteristics (giving fill factors below 25%). Once this critical step is included, the solar cells display I–V curves with fill factors above 65%, demonstrating the advantage of the maskless plasma patterning process.