Regarding nanowire solar cells, the project will develop new concepts for the efficient use of GaAs nanowires in photovoltaic (PV) devices. It is well known that GaAs-based PV devices represent the most efficient solar cell technology nowadays, offering efficiencies of ~28% in single junction solar cells, and over 42% in multijunction tandem cells. However, the widespread use of this technology is currently limited by its relatively high costs. The basic idea here is to combine the superior photovoltaic properties of GaAs with the cost-reducing advantages of the nanowire configuration, in order to produce high efficiency and low cost cells. The project involves epitaxial growth of III-V nanowire heterostructures in new designs, detailed optical and structural characterization, and PV device processing based on wafers produced in the project. The main innovation aspect of the project will be the development of piezoelectric engineering as a tool to design optimized III-V nanowire heterostructures with enhanced PV properties. In parallel, the project will also investigate the possibility to use semiconductor nanowires as a means for efficient electrical injection of organic semiconductors. In fact, one of the main limiting factors of present-day organic optoelectronic devices is their poor electrical injection characteristics, attributed to the very low carrier mobilities of organic materials. To address this problem, an alternative injection mechanism will be investigated in this project, consisting of developing hybrid inorganic/organic LEDs, in which carriers are electrically injected first in GaN or GaAs nanowires, taking full advantage of the high carrier mobilities in these materials, and are subsequently transferred to the organic chromophores via a rapid Förster resonant energy transfer (FRET) event through the inorganic/organic interface. To enhance the efficiency of the FRET transfer, nanowire surface functionalization will be systematically employed. Clearly, if the above injection scheme proves efficient, it will spur an unprecedented development of organic LEDs bypassing present limitations related to poor injection efficiencies and will pave the way for the realization of currently unavailable high-injection organic devices, such as the organic laser diode. The project will build upon existing know-how, developed in recent years by the host team at FORTH, starting from the design, growth, and characterization of semiconductor nanostructures, and going to the patterning, fabrication, and characterization of optoelectronic and nanophotonic devices. In addition, the host team has included experts on polymer chemistry and surface functionalization, as well as on theoretical modeling of nanostructured materials. The project is complemented by a number of top level participating teams that will provide supplementary expertise and techniques, not available at the host team, covering various aspects of the project. Specifically, high resolution transmission electron microscopy of the nanowire heterostructures and X-ray photoelectron spectroscopy of the functionalized nanowire surfaces will be provided by the specialized teams of the Aristotelian University of Thessaloniki and of the University of Patras, respectively. Finally, the participating team of CEA/Grenoble, France, will provide special nanowire samples that cannot be developed by the host team in the limited duration of the project, as well as some access to a time-resolved photoluminescence setup.