FTO/ITO double-layered transparent conductive oxide for dye-sensitized solar cells

New transparent conductive oxide (TCO) films, fluorine-doped tin oxide (FTO) films coated on indium–tin oxide (ITO) films, were developed for dye-sensitized solar cells (DSC). These transparent conductive films were prepared by a spray pyrolysis deposition (SPD) method at a substrate temperature of 350 °C in ITO and 400 °C in FTO. For ITO deposition, an ethanol solution of indium(III) chloride, InCl3·4H2O, and tin(II) chloride, SnCl2·2H2O (Sn/(In+Sn), 5 at.%) was sprayed on a TEMPAX #8330 glass substrate (100×100×1.1 mm3). After the deposition of ITO, FTO films were consecutively deposited for protecting oxidation of ITO films. FTO deposition was carried out by an ethanol solution of tin(IV) chloride, SnCl4·5H2O within the saturated water solution of NH4F. These films achieved the lowest resistivity of 1.4×10−4 Ω cm and the optical transmittance of more than 80% in the visible range of the spectrum. The electrical resistance of these films increased by less than 10% even though exposed to high temperatures of 300–600 °C for 1 h in the air. The DSC composed of the films were fabricated to confirm their availability. The films were of large size, 100×100 mm2. The DSC were made by conventional method. As a result, energy conversion efficiency of η=3.7% was obtained.