The materials Fe���(Si,Ge)(S,Se)���, Cu���PS[subscript 4-x]Se[subscript x] (0 ��� x ��� 4), and Cu���PxAs[subscript 1-x]S��� (0 ��� x ��� 1) have been synthesized and studied as new earth-abundant absorbers for single and multijunction photovoltaic cells as well as solar fuel generation. The synthesis, single-crystal growth, and optical and electrical properties of these materials are described and discussed in Chapter 2, 3, and 4. Inspired by the photovoltaic absorber Cu���ZnSnS���, the new compound CuZnPS��� has been discovered; its structure and properties are discussed in Chapter 5, including a comparative analysis to Cu���PS���. The compound YZrF��� (Chapter 6) has been synthesized and evaluated for the first time as a new optical host for green up-conversion. / Graduation date: 2013