Hot-carrier generation and strong coupling in metal nanoparticles

Licentiate thesis, 2023

Metal nanoparticles are an emerging platform for energy applications such as photovoltaics, solar-to-fuel conversion and photocatalysis. Nanoparticles confine the oscillating electromagnetic field of visible light to very small volumes, which allows for efficient absorption and scattering of light in the solar spectral range.

The first part of this thesis concerns the formation of so-called hot carriers, which are highly energetic charge carriers that can be generated via the absorption of light and can drive processes relevant for energy applications. The exact mechanisms leading to the formation and transfer of hot carriers are, however, not fully understood, which hinders rational design of nanoparticles for these applications. Here, I have modeled the generation of hot carriers across nanoparticle-molecule junctions by time-dependent density functional theory calculations. I show the importance of energetic alignment between the frontier orbitals, the states in the nanoparticle, and the photon energy for the hot-carrier distribution, leading to a non-monotonic distance dependence.

The second part of this thesis focuses on modeling hybrid light-matter states. Hybrid light-matter states can form due the resonant interaction between light and electronic excitations, in a regime of light-matter interaction known as strong coupling. Common approaches for modeling strong coupling are usually limited to highly simplified descriptions of matter. Here, I derive a computationally efficient model based on dipolar coupling. A detailed description of the matter is retained by obtaining polarizabilities of components from time-dependent density functional theory. Finally, I show that the model accurately captures strong coupling behavior in nanoparticle-molecules assemblies.