We present a detailed study on the microstructural, structural and optical properties of hydrogen treated (HT) diverse TiO2 nanostructures (TNS) in comparison to the as-prepared (AP) samples. The effect of oxygen vacancies (V-o), introduced in the anatase TiO2 by hydrogenation, on the photovoltaic (PV) characteristics is discussed. Raman spectroscopy shows A(1g) second order scattering modes due to V-o-influenced surface structural changes. EELS confirm the presence of Ti4+/Ti3+ mixed states and oxygen deficiency in all TNS-HT. Bandgap (E-g) of TNS can be tuned by controlling the temperature and/or duration of annealing. The indirect bandgap is found to be larger (similar to 3.2-3.4 eV) for TNS derived from Ti-foil, whereas TNS prepared using wet-chemical methods exhibit E-g in the range of 3.1-3.3 eV. The introduction of V-o red-shifts the band-edge by similar to 0.25 eV. Hydrogenation decreases the PV efficiency (eta) by 2-4 times compared to eta=6-7% observed in DSSCs of diverse nanostructures. Despite the reduction in interfacial resistance enhancing electron generation and transport in TNS-HT samples, EIS studies indicate that the drop in eta (%) is mainly due to the recapture of conduction band electrons via defect states shortening the electron lifetime. (C) 2015 Elsevier B.V. All rights reserved.