Enhanced Photovoltaic Properties of a Cobalt Bipyridyl Redox Electrolyte in Dye-Sensitized Solar Cells Employing Vertically Aligned TiO2 Nanotube Electrodes

Photovoltaic performances of TiO2 nanoparticle (NP) electrodes and TiO2 nanotube (NT) electrodes in dye-sensitized solar cells (DSSCs) employing a cobalt bipyridyl redox electrolyte were compared. The TiO2 NP electrodes had pore sizes ranging from 15 to 20 nm while the NT electrodes had a lager pore size of 80 nm. Highly ordered and vertically oriented TiO2 NT electrodes were prepared by a two-step anodization method. In application to DSSCs employing the cobalt redox electrolyte, the 11-μm-thick NP electrode exhibited an efficiency of 1.60% with a Jsc of 3.96 mA/cm2. Meanwhile, despite nearly half of the amount of adsorbed dye molecules, the 11-μm-thick NT electrode exhibited a slightly enhanced efficiency of 1.84% with a Jsc of 5.86 mA/cm2. In addition, the 35-μm-thick NT electrode showed an efficiency of 2.38% with a Jsc of 9.80 mA/cm2. Compared to the 11-μm-thick NP electrode, the 35-μm-thick NT electrode exhibited a 1.5 times higher efficiency with a 2.5 times higher Jsc in spite of having a similar ...