Crystal morphology of anatase titania nanocrystals used in dye-sensitized solar cells

Anatase TiO2 nanocrystals were synthesized by hydrolysis of titanium isopropoxide followed by crystal growth under hydrothermal conditions in an acidic or basic environment. The crystal phase, crystal shape, and surface orientation of the TiO2 nanocrystals, as well as the photovoltaic performance of DSSCs, was studied by XRD, TEM, HRTEM, FTIR, and DSC-TG. It was found that anatase TiO2 nanocrystals prepared in tetramethylammonium hydroxide contained more [1011 faces and presented a bipyramidal rod-like shape in comparison with the anatase TiO2 nanocrystal with a tetragonal ball-like shape prepared in nitric acid. The anatase-to-rutile phase transition temperature was largely affected by the crystal shape and surface orientation; it was about 950 degrees C for rod-like anatase and 700 degrees C for ball-like anatase. A 6.2% photoelectric conversion efficiency was obtained from the dye-sensitized solar cell (DSSC) with rod-like anatase, and a 5.4% the efficiency was obtained from the DSSC with ball-like anatase, which means that the anatase TiO2 nanocrystal prepared in tetramethylammonium hydroxide should be preferred for DSSCs.