This paper describes our recent developments of intermediate-band solar cells, with a focus on the use of dilute alloys and nanostructured materials such as quantum dots (QDs). The concept of “full-spectrum” solar cells and their working mechanism with various material structures are first illustrated. A comprehensive review of ZnTe:Obased intermediate-band solar cells, including material growth, structural and chemical analysis, device modeling and testing, are presented. Finally, the progress and challenges of quantum-dot-based solar cells are discussed.