This talk will focus on engineering two types of nanoparticles with specific applications in solar energy conversion: colloidal quantum dots, for color-tuned solar cells, and plasmonic aluminum nanoparticles, for sustainable solar-powered photocatalysis. Inorganic colloidal nanoparticles are attractive materials for optical energy harvesting applications because they combine flexible, low-cost solution-phase synthesis and processing with the potential for novel functionality arising from their nanostructure. Colloidal quantum dots (CQDs) are semiconducting particles with band gaps that can be tuned via the quantum confinement effect for tailored spectral utilization. Specifically, CQD response can be tuned throughout the near and mid-infrared wavelengths, and they are therefore a promising materials system for photovoltaic devices that harvest non-visible solar radiation. Recent work on novel color-tuning strategies for building-integrated photovoltaics and infrared photodetectors will be discussed. Plasmonic nanoparticles are related metallic materials with localized surface plasmon resonances that can be tuned by adjusting particle size, shape, and composition. This talk will also review work on the first photophysical characterization of energy-transfer dynamics in large plasmonic aluminum nanoparticles, which represent an earth-abundant alternative to noble metals that could be used for scalable solar-powered photocatalysis.