Boosting Hot Electron Generation of Plasmonic Nanoparticles in TiO2/TiN Nanocavities for Solar Energy Conversion

Abstract

The efficient generation and harvesting of hot electrons (HEs) remains a key challenge in advanced nanophotonic applications. Here, we propose a novel strategy to boost HE generation by incorporating plasmonic nanoparticles (NPs)─including Au, Ag, Pt, and TiN─into TiO₂/TiN nanocavities. While our previous study on TiO₂/TiN nanotube arrays achieved excellent optical absorption across 200–1300 nm, it showed weak absorption in the 350–600 nm visible range. To overcome this limitation, we decorate the nanostructure with plasmonic NPs. Comprehensive analytical, finite-difference time-domain (FDTD), and finite element method (FEM) simulations reveal strong coupling between nanocavity modes and plasmonic Mie resonances, leading to significantly enhanced absorption in the visible range. Among the examined materials, the optimized 70 nm TiN NPs placed at the bottom of the nanocavity demonstrate the best performance, outperforming noble metals in both optical and cost efficiency. Quantum mechanical analysis of HE generation shows that the TiN NPs within TiO₂/TiN nanocavities achieve a hot carrier generation rate of ∼10¹⁴ s^–1 at a wavelength of 600 nm, with a red-shifted spectral response compared to noble metals. The observed HE enhancement is attributed to localized electric fields (hot spots) induced by Mie resonances. These findings pave the way for advanced hot electron device engineering with potential applications in photodetectors, photocatalysis, and solar energy conversion in the visible spectrum.