Flat-Optics Photon Harvesting in Large-Scale 2D Semiconductor Layers for Photoconversion Applications

The development of clean light harvesting platforms and technologies is crucial in view of a new generation of photonic devices with impact in renewable energy conversion and environmental applications. For this purpose, nanophotonic methodologies hold great promise. Specifically, both plasmonics and flat optics approaches offer exciting opportunities to enhance light-matter interactions at the nanoscale, making them highly appealing for applications in photoconversion and sensing.<br/>In this context, we present innovative solutions for large-scale light trapping to maximize photon harvesting in ultra-thin semiconductor layers. Within them an emerging class of materials is represented by the Two-dimensional (2D) Transition Metal Dichalcogenides semiconductor (TMDs) layers that are characterized by exceptional optoelectronic properties tunable in the Visible and Near-Infrared spectrum [1]. Among them few-layer MoS₂ is notable for an electronic bandgap in the Visible range and a high optical absorption coefficient. Such intriguing optical response combined with high chemical reactivity qualifies this 2D semiconductor layer as a promising candidate in photoconversion and energy storage applications [2].<br/>The first solution presented is based on large area plasmonic metasurfaces obtained by ion beam assisted self-organized process. Nanostructured templates that can be used to laterally confine arrays of plasmonic nanoantennas with tunable optical response [3].<br/>The second solution is based on large area periodic nanograting templates, fabricated by Laser Interference Lithography, to reshape large-scale (cm²) two-dimensional MoS₂ semiconductor layers as an active optical element featuring a flat optics configuration that enhances the light coupling by arising of photonic anomalies [4,5].<br/>Light harvesting performances of the proposed solutions were tested by photocatalytic and photoelectrochemical experiments. The plasmonic system is used in an Oxygen Evolution Reaction (OER) reaction with both the function of a transparent electrode and a co-catalyst coupled to an ultra-thin film of TiO₂. On the other hand the subwavelength reshaping of ultra-thin semiconductor layers results in enhanced methylene blue photobleaching [6].<br/>These light harvesting platforms are thus promising in view of various large-scale applications such as waste water treatment, dye molecules sensing and energy storage.<br/><br/>[1] M. Barelli et al., ACS Appl. Nano Mater. 5, 3470 3479 (2022)<br/>[2] F. Mak et al., Nat. Photonics, 10, 216–226 (2016)<br/>[3] Z. Li et al., Photochem. Photobiol. C Photochem. Rev. 35, 39–55 (2018)<br/>[4]M. Bhatnagar et al., Nanoscale, 12, 24385 (2020)<br/>[5] M. Bhatnagar et al., ACS Appl. Mater. Interfaces 13, 13508–13516 (2021)<br/>[6] G. Ferrando et al., Nanoscale 15, 1953–1961 (2023)