Size-controlled anatase titania single crystals with octahedron-like morphology for dye-sensitized solar cells.

A simple hydrothermal method with titanium tetraisopropoxide (TTIP) as a precursor and triethanolamine (TEOA) as a chelating agent enabled growth in the presence of a base (diethylamine, DEA) of anatase titania nanocrystals (HD1–HD5) of controlled size. DEA played a key role to expedite this growth, for which a biphasic crystal growth mechanism is proposed. The produced single crystals of titania show octahedron-like morphology with sizes in a broad range of 30–400 nm; a typical, extra large, octahedral single crystal (HD5) of length 410 nm and width 260 nm was obtained after repeating a sequential hydrothermal treatment using HD3 and then HD4 as a seed crystal. The nanocrystals of size ∼30 nm (HD1) and ∼300 nm (HD5) served as active layer and scattering layer, respectively, to fabricate N719-sensitized solar cells. These HD devices showed greater VOC than devices of conventional nanoparticle (NP) type; the overall device performance of HD attained an efficiency of 10.2% power conversion at a total film t...