An Inorganic/Organic Molecular Hybrid Material for Fully Solution-Processed Photonic Structures

Photonic crystals are nanostructures that efficiently control light with negligible losses by creating a photonic band gap, a range of wavelengths that are reflected rather than transmitted. This effect arises from the periodic variation in refractive indices within the structure. With sufficient contrast, light can be reflected, guided, or confined, a mechanism which can be applied to nanoscale technologies in optics and photonics. Here, we show that films of a titanium oxide hydrate (TiOH) / poly(vinyl alcohol) (PVA) hybrid material can be fully processed from solution under ambient conditions, and can be precisely designed to reach target properties for applications in a variety of photonic structures. The refractive index n of hybrid thin films can be tuned between 1.4 and 1.8 by adjusting the material’s composition and through post-deposition techniques like photonic curing. Higher inorganic (TiOH) content and photonic curing in the presence of ultraviolet light was shown to correlate with a higher hybrid refractive index. Meanwhile, thickness of the films could be increased with increased inorganic content, but was shown to decrease after photonic curing. These properties could be leveraged to generate multilayer photonic structures with high reflectance, low optical losses, and a precise photonic band gap. Distributed Bragg reflectors (DBRs) could be reliably produced by layering the high-n inorganic/organic hybrid with a low-n polymer, with solution-processed structures of up to 21 layers yielding efficient performance. Solution-processed optical microcavities with up to 12 layers on either side of the cavity were also shown to exhibit strong light-matter coupling with low optical losses, with performance on par with structures fabricated from more resource-intensive processes. Placing an active material at the center of a microcavity was also shown using photoluminescence measurements to generate coherent condensates of light-matter quasiparticles known as exciton-polaritons. This research will be a major step in unlocking the countless applications of photonic crystals in nanotechnology, including optical communication, sensing, diodes, photovoltaics, and quantum information systems.