Deposition of TiO2 Passivation Layer by Plasma Enhanced Chemical Vapor Deposition between the Transparent Conducting Oxide and Mesoporous TiO2 Electrode in Dye Sensitized Solar Cells

The characteristic of TiO2 passivation layers grown by plasma enhanced chemical vapor deposition as a function of its thickness on F-doped SnO2 (FTO) electrode was investigated. The thickness of TiO2 passivation layer was varied from 30 to 200 nm by controlling the deposition time. The electric resistance of the TiO2 layers was depended on the thickness, so the optimized thickness in enhancing the connection and reducing the recombination of electrons on the surface of FTO electrode was determined. The dye sensitized solar cells fabricated with 40 nm thick TiO2 passivation layer showed the maximum power conversion efficiency of 6.93%. It was due to the effective connection of mesoporous TiO2 and FTO and the prevention of electron recombination from the FTO to electrolyte. The reduced resistance, enlarged electron diffusion length measured by the electrochemical impedance spectroscopy, intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy identified the connection and anti-recombination effect. (C) 2012 The Japan Society of Applied Physics