TECHNOLOGY FOCUS - CERAMICS AND GLASS - Preferred Component: The prism material is glass.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The method further comprises depositing an oxidation barrier layer onto the surface of the Group IV subcells, and heating the substrate to remove the oxidation barrier layer. Preferred Component: The inactive substrate comprises germanium and silicon. The photovoltaic cell comprises at least two epitaxial layers comprising Group IV semiconductors. The photovoltaic cell comprises subcell(s) comprising Group IV semiconductors, and subcell(s) comprising Group III-V semiconductors. A first epitaxial layer deposited on the substrate comprises greater than or equal to 95% germanium. The photovoltaic cell may comprise a first subcell comprising germanium or silicon and germanium, where silicon is not greater than 5 atom%, and a second subcell comprising silicon and germanium, where silicon is more than 5 and less than 30 atom%; and subcell(s) comprising Group III-V semiconductors. When the inactive substrate is an inactive germanium substrate, the photovoltaic cell comprises a first subcell comprising germanium, a second subcell comprising silicon and germanium, a third subcell comprising gallium, arsenic and phosphorus, and a fourth subcell comprising indium, gallium and phosphorus. The second subcell comprises 17% silicon and 83% germanium. The third subcell comprises 17% phosphorus and 83% arsenic. The fourth subcell comprises 40% indium and 60% gallium. The photovoltaic cell may comprise a fifth subcell comprising indium, gallium and phosphorus. The fifth subcell comprises 40% indium and 60% gallium. When the inactive substrate is an inactive silicon substrate, the photovoltaic cell comprises a buffer layer deposited on the silicon substrate, subcell(s) comprising Group IV semiconductors deposited on the buffer layer, and subcell(s) comprising Group III-V semiconductors deposited on the Group IV subcells. The buffer layer comprises silicon germanide. The Group V composition of the fourth subcell is approximately 17% phosphorus and 83% arsenic. The group (III) composition of the fifth subcell is approximately 40% indium and 60% gallium. The oxidation barrier layer is germanium. The photovoltaic cell may comprise gridlines containing copper.    TECHNOLOGY FOCUS - POLYMERS - Preferred Component: The prism material is polymer.