Abstract
Aperiodic photonic crystals can open up novel routes for more efficient photon management due to increased degrees of freedom in their design along with the unique properties brought about by the long-range aperiodic order as compared to their periodic counterparts. In this work we first describe the fundamental notions underlying the idea of thermal emission/absorption control on the basis of the systematic use of aperiodic multilayer designs in photonic quasicrystals. Then, we illustrate the potential applications of this approach in order to enhance the performance of daytime radiative coolers and solar thermoelectric energy generators.
Highlights
During the last few years, the search for materials exhibiting quite specific thermal emission properties has been spurred on by the necessity of attaining high-performance devices for light harvesting and thermal energy control
Though earlier designs were based in periodic layer sequences, more recent works have analyzed in detail the richness of quasiperiodic geometries, demonstrating that a nano-grating grown according to the Fibonacci sequence used as back-reflector in a thin film solar cell guarantees higher absorption enhancement with respect to the periodic counterpart over the whole incidence angle range, providing a slightly better performance of about 5% for angles less than 20° and for angles greater than 45° [31]
Whereas most experimental substrates considered up to now rely on specific materials, rather than engineered photonic crystals [33], the results reviewed in the previous sections clearly suggest that one may expect significant improvement in the spectral response of absorbing films based on aperiodic designs
Summary
During the last few years, the search for materials exhibiting quite specific thermal emission properties has been spurred on by the necessity of attaining high-performance devices for light harvesting and thermal energy control. A very convenient way to address this task consists in coating a suitable bulk material with a properly designed multilayered thin film, in order to exploit the beneficial optical properties contributed by each component in a synergetic way Within this approach the coat can act either as a passive filter (when the refractive indices of the layers material are all real valued) or as an active emitter (when at least one of the layers material in the film has a complex valued refraction index). Due to their characteristic highly fragmented frequency spectrum, aperiodic multilayers provide more full transmission peaks (alternatively, absorption bands) than periodic ones in a given frequency range for a given system length This feature stems from the richer structural complexity of aperiodic sequences (related to the presence of quasiperiodic and/or self-similar order related fingerprints), naturally leading to the presence of more resonant frequencies stemming from multiple interference effects throughout the structure. Arrangements, one can design optical devices offering a broader and more flexible design capability than their periodic counterparts for certain specific applications [3,4,5,6,7]
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