Fully Solution‐Processed Photonic Structures from Inorganic/Organic Molecular Hybrid Materials and Commodity Polymers

Abstract

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.

Femtosecond Laser‐Induced Refractive Index Patterning in Inorganic/Organic Hybrid Films

“…In order to scrutinize 3D laser machining as a methodology toward complex photonic structures, we selected titanium oxide hydrates/PVAl hybrids as model material system for RI patterning because it has been shown that this hybrid material's RI can be readily tuned via its composition and heat exposure. Indeed, an increase of the RI of up to 1.83 at 550 nm, induced upon a thermal treatment (multistep annealing on hot plate at 150 °C), has been reported, [ 19 ] achieved for a material of 60 vol% inorganic content. For such a hybrid material, e.g., made from TiCl 4 , the change in refractive index was attributed to the thermal activation of further hydrolysis and condensation reactions of OH and Cl groups present in the pristine hybrid material.…”

“…Accordingly, the presence of the inorganic species still leads to an increase in RI while keeping the light transmission high (no light scattering occurs as no nanoparticles or aggregates form) and the chromatic dispersion low. [18,19] Such hybrids offer many opportunities for optical device engineering, and they may pave the way for the straightforward design and fabrication of high-performance 3D photonic circuits, provided a suitable index patterning procedure is identified. The reason is that the overall light management in photonic devices requires precise patterning of the refractive index, ideally in two or three dimensions.…”

“…[ 34 ] Here, we demonstrate the relatively high‐resolution local enhancement of the refractive index by ultrashort pulse direct laser processing in solution‐processable inorganic/organic hybrid materials, thus approaching the requirements for use in high‐efficiency photonic devices and possible integration with standard light generation or sensor applications (e.g., LEDs, CCD/CMOS). [ 4 ] As model system, we selected an organic/inorganic hybrid material formed from poly(vinyl alcohol) (PVAl) cross‐linked with different contents of titanium oxide hydrates [ 19 ] to cover a broad RI range, prepared with a water‐based sol–gel method and deposited by spin coating starting from an aqueous solution. Through femtosecond laser micromachining, a large increase of the local RI (Δ n ≈ 10 −1 , up to n = 1.86 at 550 nm) with a transmittance >90% over the entire visible wavelength regime is obtained in the irradiated regions.…”

Converting an Organic Light-Emitting Diode from Blue to White with Bragg Modes

“…The Bragg modes do not require precise layer thicknesses which means low-quality, low-cost DBRs such as all-plastic ones can be used. 37,38 Importantly, the color temperature depends on the DBR while the internal quantum efficiency depends on the preconversion OLED. Naturally, changing the emitter to something other than TDAF can also affect the color temperature.…”

“…Our device architecture does not depend on the substrate and incorporates metallic contacts instead of indium tin oxide films which are difficult to control and contain the scarce material indium. The Bragg modes do not require precise layer thicknesses which means low-quality, low-cost DBRs such as all-plastic ones can be used. , Importantly, the color temperature depends on the DBR while the internal quantum efficiency depends on the preconversion OLED. Naturally, changing the emitter to something other than TDAF can also affect the color temperature.…”