Electron-Selective Layers for Dye-Sensitized Solar Cells Based on TiO2 and SnO2

Titanium dioxide (anatase, rutile) and quasi-amorphous tin dioxide are prepared on F-doped SnO2 in the form of dense thin films, which can serve as electron-selective layers in perovskite solar cells and dye-sensitized solar cells (DSSCs). The present study brings new data about electronic and electrochemical properties of these films at the authentic conditions occurring in a dye-sensitized solar cell (DSSC). Hydrolysis of TiCl4 provides pure rutile TiO2 at low temperatures, but TiO2 (anatase) grows in these layers upon calcination. In acetonitrile medium, the flat band potential of TiO2 (rutile) is more negative than that of TiO2 (anatase). This is opposite ordering to that observed in aqueous media. The energy of conduction band minimum of TiO2 (anatase) equals -4.15 +/- 0.07 eV at the conditions mimicking the DSSC's environment. Electrochemical reductive doping of SnO2 provides a material with the most negative flat band potential and the largest overpotential for the reduction of I-3(-), Co(bpy)(3)(3+), and Cu(tmby)(2)(2+). Voltammetric screening of all the electrode materials in six different electrolyte solutions, relevant to DSSC applications, gives salient information about the mediator type and effects of calcination and the addition of 4-tert-butylpyridine. These data provide novel inputs for optimization of DSSCs and for perovskite photovoltaics, too.