All-nano-TiO2 compact film for high-performance dye-sensitized solar cells.

An innovative all-nano-TiO2 thin film capable of enhancing dye-sensitized solar cell (DSC) photoefficiencies was prepared by a layer-by-layer method beneath the meso-TiO2 film, employing acid and basic nano-TiO2 sols as cations and anions, respectively. TiO2 syntheses were performed under absolute control to lead to appropriate morphological and optical properties to yield high-quality compact films using profilometry, tuning, and scanning electron microscopy. A detailed study by photoelectrochemical parameters, incident photon-to-current efficiency, electron lifetime, and electrochemical impedance spectroscopy demonstrates that the physical contact between FTO and the electrolyte is prevented and the role of the compact film has been elucidated. DSCs with TiO2 bilayers on top of FTO improved the conversion efficiency up to 62%, mainly because of the prevention of FTO/I3(-) charge recombination and an improved contact between FTO and TiO2.