Book excerpt: Solar-cell performance is critically dependent on the optical and electrical properties of their constituent materials. In order to obtain significant improvements in performance for future generations of photovoltaic devices, it will be necessary to either improve the properties of existing materials or engineer new materials and device structures. This book focuses on materials issues and advances for photovoltaics. Topics include: dye-sensitized solar cells; nanoparticle/hybrid solar cells; polymer-based devices; small molecule-based devices; III-V semiconductors; II-VI semiconductors and transparent conducting oxides and silicon thin films.