Fabrication of MgO-coated TiO₂ nanotubes and application to dye-sensitized solar cells

Dye-sensitized solar cells (DSCs) are more spotlighted than conventional photovoltaic devices due to their relatively low cost, easy fabrication and high efficiency. However, there are limitations to increase the conversion efficiency of DSCs. The limiting factors are the quantity of dye adsorption and charge recombination between TiO₂ electrode and electrolyte. Coating other materials such as high energy band gap insulators or semiconductors on the TiO₂ electrode enhances dye adsorption and reduces charge recombination. We fabricated DSCs based on bare TiO₂ nanotube arrays and 0.02 and 0.04 M MgO coated TiO₂ nanotube arrays. MgO layer increased the photovoltage and photocurrent. The overall conversion efficiency of DSCs using 0.02 M MgO coated TiO₂ nanotubes was 1.61%. MgO formed insulating layers between TiO₂ nanotube array electrode and electrolyte. Charge recombination was inhibited at the interfaces of TiO₂ nanotube array electrode and electrolyte by MgO insulating layers. MgO coating also improved dye adsorption because iso-electric point (IEP) of MgO was larger than TiO₂. When the IEP of coating material is larger than TiO₂, the chemical attraction between the electrode surface and Ru-based dye molecule is increased.