Université de Fribourg

Thin-film structural coloration from simple fused scales in moths

Kilchoer, Cédric ; Steiner, Ullrich ; Wilts, Bodo D.

In: Interface Focus, 2019, vol. 9, no. 1, p. 20180044

The metallic colouration of insects often originates from diverse nanostructures ranging from simple thin films to complex three-dimensional photonic crystals. In Lepidoptera, structural colouration is widely present and seems to be abundant in extant species. However, even some basal moths exhibit metallic colouration. Here, we have investigated the origin of the vivid metallic colours of...

Université de Fribourg

When black and white make green: the surprising interplay of structure and pigments

Sai, Tianqi ; Wilts, Bodo D. ; Sicher, Alba ; Steiner, Ullrich ; Scheffold, Frank ; Dufresne, Eric R.

In: CHIMIA International Journal for Chemistry, 2019, vol. 73, no. 1, p. 47–50

The natural world is teeming with color, which originates either from the wavelength- dependent absorp- tion of light by pigments or from scattering from nanoscale structures, or both. While the latter ' structural color ' has been a topic of intense study in recent years, the most vibrant colors in nature involve contributions from both structure and pigment. The study of structure–pigment...

Université de Fribourg

Towards polymers with molecular auxeticity

Alizadeh, Mahshid ; Tennie, Iris K. ; Steiner, Ullrich ; Kilbinger, Andreas F. M.

In: CHIMIA International Journal for Chemistry, 2019, vol. 73, no. 1, p. 25–28

For many decades, it has been challenging to synthesize auxetic materials at the molecular level. Auxetic materials exhibit counterintuitive behavior; they expand perpendicularly to the direction in which they are stretched. An aromatic macrocycle containing a sequence of N-substituted and N-unsubstituted amides was designed to resemble the re-entrant structure found in macromolecular auxetic...

Université de Fribourg

Efficient and stable inorganic perovskite solar cells manufactured by pulsed flash infrared annealing

Sanchez, Sandy ; Christoph, Neururer ; Grobety, Bernard ; Phung, Nga ; Steiner, Ullrich ; Saliba, Michael ; Abate, Antonio

In: Advanced Energy Materials, 2018, vol. 8, no. 30, p. 1802060

Organic–inorganic perovskite solar cells have achieved impressive power conversion efficiency over the past years, yet operational stability remains the key concern. One strategy to improve long‐term stability is to replace the thermally unstable organic with inorganic cations comprising the perovskite lattice. Here, for the first time, pulsed infrared light is used to drive the...

Université de Fribourg

A Ga-doped SnO2 mesoporous contact for UV stable highly efficient perovskite solar cells

Roose, Bart ; Johansen, Christian M. ; Dupraz, Kevin ; Jaouen, Thomas ; Aebi, Philipp ; Steiner, Ullrich ; Abate, Antonio

In: Journal of Materials Chemistry A, 2018, vol. 6, no. 4, p. 1850–1857

Increasing the stability of perovskite solar cells is a major challenge for commercialization. The highest efficiencies so far have been achieved in perovskite solar cells employing mesoporous TiO2 (m-TiO2). One of the major causes of performance loss in these m-TiO2-based perovskite solar cells is induced by UV- radiation. This UV instability can be solved by replacing TiO2 with SnO2; thus ...

Université de Fribourg

Nanoparticle shapes of LiMnPO4, Li+ diffusion orientation and diffusion coefficients for high volumetric energy Li+ ion cathodes

Kwon, Nam Hee ; Yin, , Hui ; Vavrova, Tatiana ; Lim, Jonathan H-W. ; Steiner, Ullrich ; Grobéty, Bernard ; Fromm, Katharina M.

In: Journal of Power Sources, 2017, vol. 342, p. 231–240

Nanoparticles of LiMnPO₄ were fabricated in rod, elongated as well as cubic shapes. The 1D Li⁺ preferred diffusion direction for each shape was determined via electron diffraction spot patterns. The shape of nano-LiMnPO₄ varied the diffusion coefficient of Li⁺ because the Li⁺ diffusion direction and the path length were different. The particles with the shortest dimension along the...