Managing the interference effects from multiple thin-layer structures allows for the control of optical transmittance and reflectance properties -often with very high precision. Widely used and technologically significant examples of such structures are antireflection coatings (ARCs) and distributed Bragg reflectors (DBRs), which rely on the careful control of destructive and constructive interference, respectively, between incident and reflected/transmitted radiation. While these structures have been known for over a century and have been extremely well investigated for many decades, the growing emergence of printable, large area electronics based on soluble materials brings a new emphasis. Namely the availability and use of materials in multilayer environments that are capable of transferring well-established ideas to a solution-based production.Here, we demonstrate the solution-fabrication of ARCs and all dielectric mirrors based on a DBR design utilizing alternating layers of recently developed organic/inorganic hybrid materials comprised of poly(vinyl alcohol) (PVAl), cross-linked with titanium oxide hydrates, and commercially available bulk commodity plastics. Our dip-coated ARCs exhibit an 88 % reduction in reflectance across the visible compared to uncoated glass, and fully solution-coated DBRs provide a reflection of >99 % across a 100 nm spectral band in the visible region. Detailed comparisons with transfer-matrix methods (TMM) highlight the excellent optical quality of the structures. The investigation also demonstrates the extremely low optical losses and impressive interface qualities the constituent layers exhibit. Furthermore, when exposed to elevated temperatures, the hybrid material can display a notable, reproducible and irreversible change in both the refractive index and film-thickness while maintaining excellent optical performance. In addition to allowing a degree of post-deposition tuning of the photonic structures, this may lend itself to thermo-responsive applications, including security features and product-storage environment monitoring.

The relationship between charge transport and surface morphology is investigated by utilizing rubrene single crystals of varying thicknesses. In the case of pristine crystals, the surface conductivities decrease exponentially as the crystal thickness increases until ∼4 μm, beyond which the surface conductivity saturates. Investigation of the surface morphology using optical and atomic force microscopy reveals that thicker crystals have a higher number of molecular steps, increasing the overall surface roughness compared with thin crystals. The density of molecular steps as a surface trap is further quantified with the subthreshold slope of rubrene air-gap transistors. This thickness-dependent surface conductivity is rationalized by a shift from in-plane to out-of-plane transport governed by surface roughness. The surface transport is disrupted by roughening of the crystal surface and becomes limited by the slower vertical crystallographic axis on molecular step edges. Separately, we investigate surface-doping of rubrene crystals by using fluoroalkyltrichrolosilane and observe a different mechanism for charge transport which is independent of surface roughness. This work demonstrates that the correlation between crystal thickness, surface morphology, and charge transport must be taken into account when measuring organic single crystals. Considering the fact that these molecular steps are universally observed on organic/inorganic and single/polycrystals, we believe that our findings can be widely applied to improve charge transport understanding.

We demonstrate proof-of-concept refractive-index structures with large refractive-index-gradient profiles, using a micro-contact photothermal annealing (CPA) process to pattern organic/inorganic hybrid materials comprising titanium oxide hydrate within a poly(vinyl alcohol) binder....

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