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We show flat-optics photon harvesting in large-area polymeric/MoS2 nanogrooved templates. The strong optical confinement into the ultra-thin MoS2 boosts the photobleaching of polluting dyes, paving the way for realistic photoconversion applications.

Fostered by the recent advancements in photonic technologies, the need for all-optical dynamic control on complex photonic elements is emerging as more and more relevant, especially in integrated photonics and metasurface-based flat-optics. In this framework, optically-induced anisotropy has been proposed as powerful mean enabling tuning functionalities in several planar architectures. Here, we design and fabricate an anisotropic two-dimensional bull’s eye cavity inscribed within an optically-active polymeric film spun on a one-dimensional photonic crystal sustaining Bloch surface waves (BSW). Thanks to the cavity morphology, two surface resonant modes with substantially orthogonal polarizations can be coupled within the cavity from free-space illumination. We demonstrate that a dynamic control on the resonant mode energies can be easily operated by modulating the orientation of the optically-induced birefringence on the surface, via a polarized external laser beam. Overall, reversible blue- and red-shifts of the resonant BSWs are observed within a spectral range of about 2 nm, with a moderate laser power illumination. The polymeric structure is constituted by a novel blend of an azopolymer and a thermally-sensitive resist, which allows a precise patterning via thermal scanning probe lithography, while providing a significant structural integrity against photo-fluidization or mass-flow effects commonly occurring in irradiated azopolymers. The proposed approach based on tailored birefringence opens up new pathways to finely control the optical coupling of localized surface modes to/from free-space radiation, particularly in hybrid organic–inorganic devices.

Thin-film organic photovoltaic (OPV) devices represent an attractive alternative to conventional silicon solar cells due to their lightweight, flexibility, and low cost. However, the relatively low optical absorption of the OPV active layers still represents an open issue in view of efficient devices that cannot be addressed by adopting conventional light coupling strategies derived from thick PV absorbers. The light coupling to thin-film solar cells can be boosted by nanostructuring the device interfaces at the subwavelength scale. Here, we demonstrate broadband and omnidirectional photon harvesting in thin-film OPV devices enabled by highly ordered one-dimensional (1D) arrays of nanogrooves. Laser interference lithography, in combination with reactive ion etching (RIE), provides the controlled tailoring of the height and periodicity of the silica grooves, enabling effective tuning of the anti-reflection properties in the active organic layer (PTB7:PCBM). With this strategy, we demonstrate a strong enhancement of the optical absorption, as high as 19% with respect to a flat device, over a broadband visible and near-infrared spectrum. The OPV device supported on these optimized nanogrooved substrates yields a 14% increase in short-circuit current over the corresponding flat device, highlighting the potential of this large-scale light-harvesting strategy in the broader context of thin-film technologies.

Highly porous Germanium surfaces with uniformly distributed columnar nanovoid structures are fabricated over a large area (wafer scale) by large fluence Sn+ irradiation through a thin silicon nitride layer. The latter represents a one-step highly reproducible approach with no material loss to strongly increase photon harvesting into a semiconductor active layer by exploiting the moth-eye antireflection effect. The ion implantation through the nitride cap layer allows fabricating porous nanostructures with high aspect ratio, which can be tailored by varying ion fluence. By comparing the reflectivity of nanoporous Ge films with a flat reference we demonstrate a strong and omnidirectional reduction in the optical reflectivity by a factor of 96% in the selected spectral regions around 960 nm and by a factor of 67.1% averaged over the broad spectral range from 350 to 1800 nm. Such highly anti-reflective nanostructured Ge films prepared over large-areas with a self-organized maskless approach have the potential to impact real world applications aiming at energy harvesting.

Flat optics nanogratings supported on thin free-standing membranes offer the opportunity to combine narrowband waveguided modes and Rayleigh anomalies for sensitive and tunable biosensing. At the surface of high-refractive index Si3N4 membranes we engineered lithographic nanogratings based on plasmonic nanostripes, demonstrating the excitation of sharp waveguided modes and lattice resonances. We achieved fine tuning of these optical modes over a broadband Visible and Near-Infrared spectrum, in full agreement with numerical calculations. This possibility allowed us to select sharp waveguided modes supporting strong near-field amplification, extending for hundreds of nanometres out of the grating and enabling versatile biosensing applications. We demonstrate the potential of this flat-optics platform by devising a proof-of-concept nanofluidic refractive index sensor exploiting the long-range waveguided mode operating at the sub-picoliter scale. This free-standing device configuration, that could be further engineered at the nanoscale, highlights the strong potential of flat-optics nanoarrays in optofluidics and nanofluidic biosensing.

In this work the sensitivity of Bloch Surface Waves to laser-induced anisotropy of azo-polymeric thin layers is expe rimentally shown . The nanoscale reshaping of the films via thermal-Scanning Probe Lithography allows to couple light to circular photonic nanocavities, tailoring on-demand resonant BSW confined within the nanocavity.

The urgent environmental and energy challenges require novel solutions for efficient light harvesting and conversion in new-generation ultra-thin devices. Plasmonic nanoantennas and flat optics nanogratings can promote light matter interaction at the nanoscale being very attractive for ultra-thin photonics and sensing applications. In this work we developed two light trapping solutions based on large-scale nanomaterials. The first system is a large-scale (cm2) plasmonic metasurface based on self-organized gold nanostripes. The second is based on the periodic re-shaping of ultra-thin semiconducting MoS2 layers forming large-area flat-optics nanogratings. Under this condition Rayleigh Anomalies can be resonantly excited thus promoting in-plane light confinement and photon absorption into the few-layers material. To demonstrate the impact of these nanopatterned systems in photon harvesting we probed their efficiency into a prototypal photochemical reaction: the photo-bleaching of Methylene Blue (MB). We demonstrate the resonant enhancement of the photo-bleaching of these polluting dye molecules promoted either by the localized plasmon resonance in Au nanostripes or by the Rayleigh Anomaly in flat-optics MoS2 nanogratings. We investigate this effect through a quantitative analysis of the solution photodissociation induced by a monochromatic light. These results show the strong potential of flat-optics templates for light-harvesting and energy conversion in ultra-thin photonic devices.