Facile, Nonhydrothermal, Mass-Producible Synthesis of Mesoporous TiO2 Spheres for Dye-Sensitized Solar Cells

We report a facile, non-hydrothermal (or non-solvothermal) and mass-producible synthesis of mesoporous TiO2 spheres (MTSs) suitable for use in dye-sensitized solar cells (DSSCs). The synthesis is a facile bulk calcination in which the inexpensive polymer ethyl cellulose (EC) is used as a structure-directing agent; the EC concentration is controlled to induce spherical morphology. The size of MTSs can be adjusted by tuning the solute-solvent interactions; for example, the addition of the poor solvent toluene to the solute resulted in the formation of smaller MTSs. A DSSC fabricated using a polymer electrolyte containing ionic liquid and iodine (I-2) and using a layer of MTSs on a nanocrystalline (NC) TiO2 layer exhibited an efficiency of up to 6.3%, which is much higher than those of DSSCs with an NC layer only (5.0%) or with a commercial scattering layer (CSL) on an NC layer (5.7%). A solid-state DSSC (ssDSSC) using a single component solid polymer, namely poly((1-(4-ethenylphenyl) methyl)-3-butyl-imidazolium iodide) (PEBII), also exhibited an excellent efficiency of up to 6.4%. The improved efficiency was due to the role of the MTSs in improving surface area and light harvesting properties, as demonstrated by N-2 adsorption/desorption isotherm, UV-visible light absorption, reflectance spectroscopy, incident photon-to-current efficiency (IPCE), and electrochemical impedance spectroscopy (EIS) analyses. (C) 2015 Elsevier Ltd. All rights reserved.