In quantum dots (QDs), quantum rods (QRs) and unique molecular chromophores that undergo singlet fission (SF) the relaxation pathways of photoexcited states can be modified to produce efficient multiple exciton generation (MEG) from single photons . Efficient MEG in PbSe, PbS, PbTe, and Si QDs and efficient SF in molecules that satisfy specific requirements for their excited state energy levels has been studied and observed at NREL for many years. MEG has been studied in close-packed QD arrays where the QDs are electronically coupled in the films and thus exhibit good transport while still maintaining quantization and MEG. Simple, all-inorganic QD solar cells that produce large short-circuit photocurrents and respectable power conversion efficiencies via both nanocrystalline Schottky junctions and nanocrystalline p-n or p-i-n junctions have been produced. These solar cells also show for the first time external quantum yields (QYs) for photocurrent that exceed 100% in the photon energy regions of the solar spectrum where MEG is possible (i.e.,energy conservation is satisfied); the photocurrent internal QYs from MEG as a function of photon energy match those determined via time-resolved spectroscopy and settles controversy concerning MEG. Very efficient SF in thin films of molecular crystals of 1,3 diphenylisobenzofuran with quantum yields of 200% at the optimum SF threshold of 2Eg (HOMO-LUMO for T1-S0 ), reflecting the creation of two excited triplet states from the first excited singlet state, hs also been observed.. Various possible configurations for novel solar cells based on MEG in QDs and SF in molecules that could produce high conversion efficiencies will be presented, along with progress in developing such new types of solar cells. Recent analyses of the dramatic effects of solar concentration combined with MEG or SF on the conversion efficiency of solar cells to both solar electricity and fuels will also be discussed. The properties required for nanocrystals and SF molecules to achieve the high solar conversion efficiencies predicted by theory will be discussed. .Regarding production of solar fuels, the most efficient systems must have the following features: (1) two photosystems arranged either in a Z-scheme analogous to biological photosynthesis, or two tandem p-n junctions connected in series where sufficient photopotential (1.23 V + overvoltage for H2O splitting) is generated to drive the redox reactions; (2) strong absorption of solar photons; (3) efficient separation of the photogenerated e-h pairs, (4) efficient transport to and collection of the separated carriers at electrocatalytic surfaces; (5) low overvoltages; (6) appropriate alignment of the redox potentials in the photoelectrodes with those of the fuel-producing reactions; and (7) resistance to dark-and photo-corrosion achieving long-term photostability. Progress in this application will also be discussed.