|
Metallic nanostructures revealing plasmonic effects are a promising approach for improved photon management in thin solar cells. Irregular structures, as found in literature, suffer from parasitic absorption as a result of the varying dimensions of the particles. The parasitic absorption can be minimized by realising regularly ordered particles. Our fabrication process, suitable to meet these requirements, is based on interference lithography (IL), UV nanoimprint lithography (UV-NIL) and lift-off. As a process capable of large area structure origination, we use IL for the realization of master structures. Combining IL with NIL as a replication technique, the process chain is very versatile concerning nanoparticle shapes, sizes and arrangements. In the UV-NIL process, a flexible silicone stamp, which was replicated from the master structure, is pressed into a resist, which is cross-linked by UV light. A plasma etching step is applied to remove the residual resist layer. Afterwards, the substrate is coated with a thin metal layer and finally a lift-off is carried out. This results in metallic nanoparticles arranged in a regular pattern on the substrate. We show simulations and experimental results of round and elliptical disks and half spheres arranged in crossed and hexagonal gratings on glass and silicon. The elliptical particles show polarization dependent resonance effects. In a model assisted parameter study, we demonstrate the influence of various structure parameters on the absorption enhancement in silicon. Finally, optical measurements of ordered silver nanoparticles on the rear side of a silicon wafer are shown.
|
