Solution processed inorganic semiconductors: high performing hybrid materials for photonics

Photonic crystals (PhCs) are defined as composites made of media bearing different dielectric constant or refractive index ordered in a mono, bi or tridimensional periodic structure, and whose lattice constant is comparable to the wavelength of visible or near-infrared light. PhCs are nowadays exploited in functional architecture, enhancement of photon absorption for photovoltaic cells, emission control, lasing, and sensing. Recently, fabrication of polymer planar photonic crystals from polymer solutions has been receiving particular attention thanks to the ease of tuning of their properties and of scaling their fabrications on large areas. Although major improvements of their performances were made through sophisticated engineering of their structure and properties, solution processed structures still cannot compete with vacuum-deposited inorganic systems which are capable of reaching higher dielectric contrasts, strongly sought-after for their applicability. On the other hand, these fabrications are hardly scalable and extremely costly. We will demonstrate an alternative way to prepare highly inorganic transparent hybrid thin films of titania (TiO2) and silica (SiO2) in presence of a polymer stabilizer via spin-coating including comparison with similar structures from literature. Fabrication of films is achieved by exploiting sol-gel like in situ reactions between inorganic matrices from alkoxide precursors and polymer additive. The new titania based hybrid shows the highest refractive index reported in the literature for solution processed films leading to the largest value of dielectric contrast for solution processable planar PhCs. Moreover, the design of the hybrids allows for mutual processability with colloidal semiconductor nanocrystals in the fabrication of optical microcavities for emission control and lasing applications. Some examples will be reported and discussed.