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Periodic nanostructures imprinted on high-temperature stable sol-gel films by ultraviolet-based nanoimprint lithography for photovoltaic and photonic applications

: Back, Franziska; Bockmeyer, Matthias J.; Rudigier-Voigt, Eveline; Löbmann, Peer


Thin solid films 562 (2014), pp.274 - 281
ISSN: 0040-6090
Journal Article
Fraunhofer ISC ()
Nanostruktur; sol-gel; Film; Beschichtung; Lithographie; Photovoltaik; Photonik; Werkstoff

Nanostructured sol–gel films with high-temperature stability are used in the area of electronics, photonics or biomimetic materials as light-trapping architectures in solar cells, displays, waveguides or as superhydrophobic surfaces with a lotus effect. In this work, high-temperature stable 2-μm nanostructured surfaces were prepared by ultraviolet-based nanoimprint lithography using an alkoxysilane binder incorporating modified silica nanoparticles. Material densification during thermal curing and microstructural evolution which are destined for a high structural fidelity of nanostructured films were investigated in relation to precursor chemistry, particle morphology and particle content of the imprint resist. The mechanism for densification and shrinkage of the films was clarified and correlated with the structural fidelity to explain the influence of the geometrical design on the optical properties. A high internal coherence of the microstructure of the nanostructured films results in a critical film thickness of > 5 μm. The structured glassy layers with high inorganic content show thermal stability up to 800 °C and have a high structural fidelity > 90% with an axial shrinkage of 16% and a horizontal shrinkage of 1%.
This material allows the realization of highly effective light-trapping architectures for polycrystalline silicon thin-film solar cells on glass but also for the preparation of 2D photonic crystals for telecommunication wavelengths.