This book provides up-to-date information on the application of nano-sized materials in energy devices. A brief overview on the properties of nano-sized materials introduces the readers to the basics of the application of such materials in energy devices. Among the energy devices covered include third generation solar cells, fuel cells, batteries, and supercapacitors. The book places emphasis on the optical, electrical, morphological, surface, and spectroscopic properties of the materials. It contains both experimental as well as theoretical aspects for different types of nano-sized materials, such as nanoparticles, nanowires, thin film, etc.