This project will demonstrate an entirely new class of ultrahigh-efficiency solar cells based on merging two highly promising concepts, i.e., 3D-structured nanowire (NW) arrays in conjunction with unique carrier multiplication effects in quantum nanomaterials. Advancement in this highly ambitious frontier will be realized by a well-concerted cooperation between theory and device materials engineering and characterization. In particular, multi-band cellular Monte Carlo simulations will predict the competition between carrier multiplication rates and energy loss mechanisms (electron-phonon interaction and scattering) in strongly confined, ultrathin III-V semiconductor NWs, thereby defining guidelines for the bottom-up growth of complex p-n heterojunction core-shell NW-based solar cells using scalable epitaxial growth methods. Importantly, we will tune core diameter, material composition, electronic band offset, as well as doping concentrations which are the most relevant key parameters governing the scaling behaviour of carrier multiplication and photocurrent properties, as will be evaluated by ultrafast transient absorption spectroscopy. Ultimately, functional solar cells will be fabricated and the key device performance metrics evaluated. This project draws upon the distinct core competences of leading groups in semiconductor NWs and their devices via a strongly multidisciplinary approach including Materials Science & Electrical Engineering (TUM}, Computational Nanoelectronics (ASU), and Solar Energy Conversion Science & Technology (NREL), and presents an excellent opportunity for IGSSE to contribute to the promotion of this high-potential research field.