Electrochemical properties of TiO ₂ encapsulated ZnO nanorod aggregates dye sensitized solar cells

Dye sensitized solar cells based on TiO ₂ encapsulated ZnO nanorod (NR) aggregates were fabricated and electrochemical performance was analyzed using impedance spectroscopy as a function of forward bias voltage. Charge transfer properties such as electron life time (τ _n), electron diffusion coefficient (D _n) and electron diffusion length (L _n) were calculated in order to ensure the influence of TiO ₂ layer over the ZnO NR aggregates. It is found that the short circuit current density (Jsc = 5.8 mA cm ^-2), open circuit potential (V _oc = 0.743 V), fill factor (FF = 0.57) and conversion efficiency are significantly improved by the introduction of TiO ₂ layer over ZnO photoanode. A power conversion efficiency of about 2.48% has been achieved for TiO ₂/ZnO cell, which is higher than that of bare ZnO NR aggregate based cells (1.73%). The formation of an inherent energy barrier between TiO ₂ and ZnO films and the passivation of surface traps on the ZnO film caused by the introduction of TiO ₂ layer increase the dye absorption and favor the electron transport which may be responsible for the enhanced performance of TiO ₂/ZnO cell.