Proceedings Article | 2 May 2012
Benedikt Bläsi, Hubert Hauser, Christian Walk, Bernhard Michl, Aron Guttowski, Alexander Mellor, Jan Benick, Marius Peters, Sabrina Jüchter, Christine Wellens, Volker Kübler, Martin Hermle, Andreas Wolf
Proc. SPIE. 8438, Photonics for Solar Energy Systems IV
KEYWORDS: Lithography, Etching, Particles, Solar cells, Silicon, Photoresist materials, Photomasks, Nanoimprint lithography, Semiconducting wafers, Absorption
Since micro- and nanostructures for photon management are of increasing importance in novel high-efficiency solar cell
concepts, structuring techniques with up-scaling potential play a key role in their realization. Interference lithography
and nanoimprint processes are presented as technologies for origination and replication of fine-tailored photonic
structures on large areas.
At first, these structure origination and replication technologies are presented in detail: With the interference pattern of
two or more coherent waves, a wide variety of structures with feature sizes ranging from 100 nm to 100 μm can be
generated in photoresist by interference lithography. Examples are linear gratings, crossed gratings, hexagonal structures,
three dimensional photonic crystals or surface-relief diffusers. The strength of this technology is that homogeneous
structures can be originated on areas of up to 1.2 x 1.2 m<sup>2</sup>.
The structures in photoresist, the so-called master structures, can serve as an etching mask for a pattern transfer, as a
template for infiltration with different materials or they can be replicated via electroplating and subsequent replication
processes. Especially in combination with replication steps, the industrially feasible production of elaborate structures is
possible. As a particularly interesting process, nanoimprint lithography (NIL) is described in detail. As a way towards
industrial production, a roller NIL tool is presented.
After the description of the basic technologies, three application examples for solar cells are presented with details about
the design of the structures, the structuring processes, sample characterization and evaluation: (1) honeycomb structures
for the front side texturization of multicrystalline silicon wafer solar cells, (2) diffractive rear side gratings for absorption
enhancement in the spectral region near the band gap of silicon, and (3) plasmonic metal nanoparticle arrays
manufactured by combined imprint and lift off processes.
