Rapid and economic fabrication approach of dielectric reflectors for energy harvesting applications

Abstract

Dielectric reflectors are the passive components that have their potential demands for various purposes, such as back-end reflector in solar cells, the band pass filters in optical instruments, thermal reflector and so on. Though well-established techniques for manufacturing such reflectors are available, the demand for their low-cost production with a minimum number of coatings has attracted the attention of the scientific community. In this framework, this paper addresses the process optimization for the low-cost and rapid fabrication of dielectric TiO2/SiO2 reflectors with 100% reflectance. Numerous studies are carried out to explore the structural, morphological, and optical characteristics of reflectors. We summarize that the desired reflection band of a selective-wavelength range can be realized by varying the precursor and catalyst concentrations, annealing cycle, and the spin rate. With this, we noticed the shifting of reflection window from the visible (Vis) to near-infrared (NIR) wavelength region using reflectors of merely 2.5 stacks of TiO2/SiO2 films. We also performed the thermal response of the reflector by radiating an infrared light source and observed an exceptional performance indicating its thermal shielding application.

Mild Sol–Gel Conditions and High Dielectric Contrast: A Facile Processing toward Large-Scale Hybrid Photonic Crystals for Sensing and Photocatalysis

“…An alternative route to achieve solution-processed high dielectric contrast DBRs exploits sol–gel reactions of precursors of metal or metalloid oxides. , In these processes, the oxide precursors are hydrolyzed to form a sol which is then cast by spin- or dip-coating to from dry xerogel thin films, which in turn are densified by high-temperature reactive post-deposition annealing. , To this regard, several works have been reported on the fabrication of thin-film DBRs, − but the large reactivity of the precursors often leads to the formation of scattering centers. Moreover, the high temperatures needed for the stabilization of the thin films, up to and exceeding 500 °C, hinder their processability and their possible coupling with temperature-sensitive materials. − To solve this issue, polymers or small organic molecules can be used as stabilizers, also allowing the decrease of the temperature of post-deposition processes: poly­(imide)–TiO 2 hybrid thin films for transparent memory devices and mechanically performing acrylic resin–titania , are just a few examples of similar structures. In recent years, Stingelin and co-workers reported high optical quality thin films and DBRs based on high refractive hybrid titania obtained by hydrolyzation of TiCl 4 in cold water and subsequent mixing of the hydrated oxide product with a water solution of poly­(vinyl alcohol).…”

Sol-gel spin coating of dielectric reflector for energy harvesting and heat shielding applications

“…The proper tuning of the process parameters can identify the reflectors in the mentioned spectral region with the minimal number of layers. Venkatesh et al fabricated dielectric reflectors with TiO 2 and SiO 2 by varying the process parameters of sol-gel spin coating [10]. XRD, AFM and spectroscopic ellipsometry investigations on the fabricated thin films endorsed increase in precursor and catalyst concentration can increase the grain size and hence refractive index.…”

Extracting film thickness and optical constants from spectrophotometric data by evolutionary optimization

“…Film thickness influences micro-scale physics of electron mobility in thin-film transistors [ 7 ] to macro-scale physics of operating characteristics of solar cells [ 5 ]. Thickness variations by adjusting the catalyst concentration or by changing the heat-treatment process can be leveraged to shift the reflection band of a film from narrow to broad wavelength region, which benefits in fabricating dielectric reflectors for solar cells and bandpass filters for optical instruments [ 8 ]. Moreover, complex refractive index profiles and film thickness are crucial in designing appropriate polymers to produce effective lenses and ultraviolet (UV)-absorbing coatings [ 9 , 10 ].…”