Optimal conversion of sunlight by a single-threshold converter, whether semiconductor-based or molecular, requires an energy gap near 1.4 eV [1–3], Tandem systems based on two semiconductors or on two light-harvesting molecules require materials with gaps near 1.8 and 1.0 eV [4]. At normal solar irradiance and at 27%, the thermodynamic limit to the solar conversion efficiency is 27% for a single converter and 36% for tandem cells [4]. For nonconcentrated sunlight the actual efficiency that has been attained is 21.9% [5]. Although the thermodynamic efficiency limits for semiconductor and molecular systems are the same, all efficient systems today are semiconductor-based.