Honeycomb texturing of silicon via nanoimprint lithography for solar cell applications
A novel texturing method to realize a honeycomb texture on multicrystalline silicon solar cells is presented in this paper. The demonstrated process chain is based on nanoimprint lithography (NIL), where an ultra-violet (UV)-curable polymer layer is structured by mechanical embossing in a high-throughput process. This patterned polymer layer can then be used as an etching mask for plasma or wet chemical etching processes to transfer the defined pattern into the silicon substrates. Within this study, the whole process chain of this novel texturing scheme, using interference lithography, cast moulding, NIL, and plasma etching, is described with a focus on the NIL process. The textured substrates are characterized by reflection measurements, which are compared with standard solar cell textures. Besides optical measurements, first results of honeycomb textured solar cells are presented. Short-circuit current densities above 40 mA/cm2 were achieved on high-quality float zone material. To increase the feasibility of an industrial realization of this process chain, we are developing a roller-NIL tool to structure an etching mask in a continuous in-line process. First results of this novel tool are also shown in this study.