Controlled synthesis of symbiotic structured TiO2 microspheres to improve the performance of dye-sensitized solar cells

Due to the excellent light scattering and dye loading ability, mesoporous TiO₂ microspheres are vastly utilized in dye-sensitized solar cells (DSSCs) to serve as photoanode. Despite of the good electron transport properties due to the unique geometry of mesoporous TiO₂ microspheres, the existence of large holes between adjacent microspheres limits the formation of necking and deteriorates the device performance. In this work, we report a simple 2-step process to synthesize symbiotic structured TiO₂ microspheres treated with different ammonia concentrations. Meanwhile, the nitrogen doping of TiO₂ microspheres is also introduced while ammonia treatment is performed and as a result, the charge transport property is greatly improved. By using the symbiotic structured TiO₂ to substitute pure TiO₂ microspheres photo anode, the photovoltaic performance of DSSCs was greatly improved from 8.77% to 9.58%. It is demonstrated that the improvement is mainly due to the improved charge transportation property of symbiotic structured TiO₂ photoanodes and the effective suppression of carrier recombination. The results give us a comprehensive understanding of electron transport and recombination mechanism in mesoporous TiO₂ microspheres, which will provide significant information for the optimization of TiO₂ structures for DSSC and other optoelectrical applications.