Well-connected TiO2 nanocrystals via solid-state reaction for dye-sensitized solar cells.

TiO 2 nanocrystals derived from hydrothermal method were widely used as the photoanodes of dye-sensitized solar cells (DSSCs). Developing some alternative routes combining low-cost with high performance is eagerly expected. Well connected anatase TiO 2 nanocrystals were synthesized by one-step thermal decomposition of the double salt (NH 4 ) 2 TiO(SO 4 ) 2 (ammonium titanyl sulfate, ATS) at 700 °C for 2 h, and the fine tuning on aggregate sizes was achieved by adjusting the heating rate. The TiO 2 nanocrystals inside the aggregates were densely packed where each nanocrystal contacted well to neighbouring grains. The connected structure between the crystallites decreases the negative effects of electron grain boundary crossing and reduces recombination within the aggregate when used as photoelectrodes of dye-sensitized solar cells. Moreover, TiO 2 aggregates from ATS calcined at a faster heating rate (5 °C/min) had a wider pore size distribution and exhibited a higher light scattering abilities, while the ones from those calcined at a slower heating rate (3 °C/min) had a narrow pore size distribution but possessed a higher specific surface area (72.8 m 2 g −1 ) for adsorbing more dye. The DSSC based on two kind of TiO 2 nanoparticles as the photoelectrode all exhibited an excellent short-circuit current density (15.21 mA cm −2 and 15.94 mA cm −2 ) and a highly efficient power conversion efficiency (7.78% and 8.16%). The improvements of power conversion efficiency for two kinds of TiO 2 nanoparticles compared to commercial Aerosil process P25 nanoparticles are mainly attributed to a higher light scattering ability and superior dye adsorption property, respectively. The electrochemical impedance spectroscopy (EIS) analysis indicated the DSSCs with TiO 2 nanocrystals derived from solid state reaction had a lower charge transfer resistance than all P25 photoanodes at TiO 2 /dye/electrolyte interface due to the well connected structure provided multiple contacts to neighboring grains. [ABSTRACT FROM AUTHOR]