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 (VO), introduced in the anatase TiO2 by hydrogenation, on the photovoltaic (PV) characteristics is discussed. Raman spectroscopy shows A1g second order scattering modes due to VO-influenced surface structural changes. EELS confirm the presence of Ti4+/Ti3+ mixed states and oxygen deficiency in all TNS-HT.
Bandgap (Eg) of TNS can be tuned by controlling the temperature and/or duration of annealing. The indirect bandgap is found to be larger (~3.2–3.4 eV) for TNS derived from Ti-foil, whereas TNS prepared using wet-chemical methods exhibit Eg in the range of 3.1–3.3 eV. The introduction of VO red-shifts the band-edge by ~0.25 eV. Hydrogenation decreases the PV efficiency (η) by 2–4 times compared to η=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 η (%) is mainly due to the recapture of conduction band electrons via defect states shortening the electron lifetime.
Das, T.K., Ilaiyaraja, P., Mocherla, P.S., Bhalerao, G.M. and Sudakar, C., 2016. Influence of surface disorder, oxygen defects and bandgap in TiO 2 nanostructures on the photovoltaic properties of dye sensitized solar cells. Sol Energy Mater Sol Cells, 144, pp.194-209.
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