Final Report Summary - PHOTOSI (Silicon nanocrystals coated by photoactive molecules: a new class of organic-inorganic hybrid materials for solar energy conversion)
Luminescent silicon nanocrystals are the protagonists of the PhotoSi project. They occupy a niche in the realm of quantum dots, offering several advantages: silicon is abundant, essentially non-toxic and can form robust chemical bonds with ligands at the nanocrystal surface. From the optical point of view, SiNCs are strong light emitters, but weak absorbers. The idea of the PhotoSi project was to circumvent this drawback by surface functionalization of SiNCs with chromophores that are strong light absorbers and are able to efficiently transfer the excitation energy to the silicon core. We thus obtained light-harvesting antennae, where excitation energy absorbed by the chromophores is funneled to the silicon core that emits light. We investigated two main applications of these systems: (i) bioimaging and optical sensors: long-lived and oxygen-insensitive luminescence is a rare combination of properties, useful to obtain high contrast in images from scattering biological tissues; (ii) luminescent solar concentrators: SiNCs, embedded in a transparent polymeric slab, absorb UV light and emit in the red and near-infrared spectral region; the emitted light is conveyed to the edges by wave-guide effects and converted into electricity by conventional silicon photovoltaic cells.