volume is close to the surface, thereby reducing charge carrier recombination because the diffusion length from their excitation site to the catalyst-electrolyte interface is minimized. [7] Third, nanostructuring of photocatalysts increases the surface area compared to a planar film, enabling denser loading of active sites per geometric area. Whereas dissipation losses in metals limit the efficiencies of plasmonic resonances, high refractive index semiconductor photocatalyst nanoresonators are capable of also supporting Mieresonances in the form of electric and magnetic multipoles with negligible dissipation losses compared to metals. [8][9][10] Of particular interest are nonradiative excitations, such as the anapole, which lead to light confinement into the resonator and therefore high electromagnetic field strengths within the material. [11][12][13] In this type of excitation, far-field scattering is minimized and near-field energy inside the material reaches its maximum, making it particularly attractive, e.g., for photo catalytic applications. In a previous study, we demonstrated on the single particle level that resonant coupling of the anapole excitation wavelength to electronic transitions in substoichiometric TiO 2−x leads to enhanced electron-hole pair generation rates and catalytic yields under sub-bandgap excitation. [14] The upscaling from single particles to periodic arrays is accompanied by the emergence of lattice resonances, regardless of their metallic or dielectric character.

The exploitation of semiconductor nanocrystal (NC) films in novel electronic and optoelectronic applications requires a better understanding of charge transport in these systems. Here, we develop a model of charge transport in NC films, based on a generalization of the concept of transport energy level ET to nanocrystal assemblies, which considers both intra- and inter-NC charge transfer processes. We conclude that the role played by each of these processes can be probed from temperature-dependent measurements of charge carrier density n and mobility μ in the same films. The model also enables the determination of the position of the Fermi energy level EF with respect to ET, an important parameter of charge transport in semiconductor materials, from the temperature dependence of n. Moreover, we provide support to an essentially temperature-independent intra-NC charge carrier mobility, considered in the transport level concept, and consequently the frequently observed temperature dependence of the overall mobility μ in NC films results from a temperature variation of the inter-NC charge transport processes. Importantly, we also conclude that the temperature dependence of conductivity in NC films should result in general from a combination of temperature variations of both n and μ. By applying the model to solution-processed Si NC films, we conclude that transport within each NC is similar to that in amorphous Si (a-Si), with charges hopping along band tail states located below the conduction band edge. For Si NCs, we obtain values of ET - EF of ∼0.25 eV. The overall mobility μ in Si NC films is significantly further reduced with respect to that typically found in a-Si due to the additional transport constraints imposed by inter-NC transfer processes inherent to a nanoparticulate film. Our model accounting for inter- and intra-NC charge transport processes provides a simple and more general description of charge transport that can be broadly applied to films of semiconductor NCs.