Optical coatings and films based on photonic semiconductor nanostructure assemblies

Photonic semiconductor nanostructure assemblies offer unique possibilities for light manipulation as well as for tailoring light-matter interaction by appropriate choice of their geometrical and material properties. The material-structure combination offers a variety of options for wavelength specific applications, deriving from the electronic properties of semiconductors and optical properties of individual and assemblies of nanostructures (particles, disks, pillars/wires etc.). We present an overview of our research on optical coatings based on semiconductor nanostructure assemblies focusing on their optical properties, different fabrication technologies and selected application examples. Design and simulations of the optical coatings are performed by finite difference time domain calculations, and are used as a guideline for fabrication. We discuss different routes for fabrication of nanostructured optical films/coatings including directed assembly and patterning of nanoparticles from solution phase, solution synthesis, combination of dry etching and colloidal lithography, transfer printing, and generation of flexible polymer films with embedded nanostructures. The fabricated films are validated by optical measurements and some device specific properties such as omni-directional broad-band anti-reflection in solar cells and efficient light extraction in light emitting diodes are demonstrated.