Optical Properties of Anisotropic Gold Nanoparticles for Solar Light Harvesting and Photo-Thermoelectric Conversion

Abstract

Gold nanoparticles (Au NPs) are renowned for their optical properties, nonetheless, challenges persist for applications in broadband quantitative light harvesting from ultraviolet to the near infrared, for instance matching the emission spectrum of sunlight. The challenges are related to limited spectral coverage, low photothermal conversion efficiency, low photostability, low environmental, and economic sustainability of the NPs synthesis. Here, the optical properties of spherical Au NPs are compared with two anisotropic Au nanostructures, aggregated Au nanospheres and Au nanocorals, purposely designed to exhibit broadband absorption. The anisotropic Au NPs are obtained by a convenient, green, and scalable laser ablation in liquid procedure, with the nanocorals exhibiting flat plasmon absorption extending beyond 2500 nm. The optical and photothermal capabilities of these nanostructures are compared with experimental and numerical calculations. Besides, the Au NPs are tested against the direct transduction of light into electricity by photo-thermoelectric generators (photo-TEGs). In fact, the conversion efficiency of TEGs depends on the presence of a steep temperature gradient, achievable under broadband illumination of the anisotropic NPs. This investigation guides to the optimal anisotropic gold NPs for panchromatic light harvesting, which finds relevance across diverse sectors from sunlight energy conversion to photothermal effects in optoelectronics and biomedical applications.