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.