Sol-Gel Titanium Dioxide Blocking Layers for Dye-Sensitized Solar Cells: Electrochemical Characterization

• Published in: Chemphyschem 2014-04, Vol.15 (6), p.1056-1061
• Main Authors: Kavan, Ladislav, Zukalova, Marketa, Vik, Ondrej, Havlicek, David
• Format: Article
• Language: English
• Subjects: Applied sciences; Chemistry; Colloidal gels. Colloidal sols; Colloidal state and disperse state; cyclic voltammetry; dye-sensitized solar cells; electrochemical impedance spectroscopy; Electrochemistry; Energy; Exact sciences and technology; General and physical chemistry; Natural energy; Photovoltaic conversion; sol-gel method; Solar cells. Photoelectrochemical cells; Solar energy; titanium dioxide
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.201400026

Compact, thin TiO2 films are grown on F‐doped SnO2 (FTO) by dip‐coating from precursor solutions containing poly(hexafluorobutyl methacrylate) or hexafluorobutyl methacrylate as the structure‐directing agents. The films are quasi‐amorphous, but crystallize to TiO2 (anatase) upon heat treatment at 500 °C in air. Cyclic voltammetry experiments performed using Fe(CN)63−/4− or spiro‐OMeTAD as model redox probes selectively indicate the pinholes, if any, in the layer. The pinhole‐free films on FTO represent an excellent rectifying interface at which no anodic faradaic reactions occur in the depletion state. The flat‐band potentials of the as‐grown films are upshifted by 0.2–0.4 V against the values predicted for a perfect anatase single‐crystal surface, but they still follow the Nernstian pH dependence. The optimized buffer layer is characterized by a combination of quasi‐amorphous morphology (which is responsible for the blocking function) and calcination‐induced crystallinity (which leads to fast electron injection and electron transport in the conduction band). The latter manifests itself by a reversible charging of the chemical capacitance of TiO2 in its accumulation state. The capacitive‐charging capability and pinhole formation significantly depend on the post‐deposition heat treatment. Titania buffer layers for potential application in solid‐state dye‐sensitized solar cells are grown on F‐doped SnO2 by using the sol–gel dip‐coating method. The blocking layers are tested by means of cyclic voltammetry and impedance spectroscopy.