This book provides an overview of select studies from the Army Research Laboratory on nanoparticle applications in solar cells. Topics include altering plasmonic nanoparticle size through thermal annealing for improved photovoltaic devices; a green nanochemistry approach to titanium dioxide nanoparticle, dye-sensitised solar cells; synthesis, characterisation, and application of gold nanoparticles in green nanochemistry dye-sensitised solar cells; and tunable TiO2 nanotube arrays for flexible bio-sensitised solar cells.