Anatase TiO2 sol as a low reactive precursor to form the photoanodes with compact films of dye-sensitized solar cells

An anatase TiO 2 sol containing ultrafine TiO 2 crystallites (ca. 5   nm) was used to fabricate the dye-sensitized solar cells (DSSCs) with a compact layer, which was prepared by the peptization–hydrothermal method using the CF 3 COOH as peptizing agent. The dried sol was calcined at 300   °C for 1   h to eliminate the organics over the surface of TiO 2 and increase the crystallite size of the TiO 2 nanocrystals (the special surface area of the calcined TiO 2 decreased from 224.7 to 94.9   m 2 /g); and then it was used to prepare the paste for the porous layer of DSSCs. The compact layer was prepared by the diluted sol through the layer-by-layer (LBL) self assembly technique to control its thickness. The compact films derived from LBL self assembly method not only prevented the charge recombination at the conductor substrate/electrolyte interface but also improved the adhesion between the porous layer and the conductive layer on the substrate, which increased the number of the effective electron pathways with the short distance of the porous layer and consequently resulted in a better electrical contact. The photoelectron conversion efficiency of the DSSCs with the LBL films had increased apparently. In particular, a 12-layer TiO 2 /PSS LBL film of the DSSC led to a 24.5% increase in the photoelectron conversion efficiency from 5.93 to 7.38%.