High-quality photoelectrodes based on shape-tailored TiO2 nanocrystals for dye-sensitized solar cells

We demonstrate a general approach by which colloidal anatase TiO2 nanocrystals with anisotropically tailored linear and branched shapes can safely be processed into high-quality mesoporous photoelectrodes for dye-sensitized solar cells (DSSCs). A detailed study has been carried out to elucidate how the nanoscale architecture underlying the photoelectrodes impacts their ultimate performances. From the analysis of the most relevant electrochemical parameters,an intrinsic correlation between the photovoltaic performances and the structure of the nanocrystal building blocks has been deduced and explained on the basis of relative contributions of the electron transport and light-harvesting properties of the photoelectrodes. Depending on the nanocrystals incorporated,these devices can exhibit an energy conversion efficiency of 5.2% to 7.8%,which ranks 38% to 53% higher than that achievable with corresponding cells based on reference spherical nanoparticles. It has been ascertained that DSSCs based on high aspect-ratio linear nanorods allow for a remarkable improvement in the charge-collection efficiency due to minimization of detrimental charge-recombination processes at the photoelectrode/electrolyte interface. On the other hand,DSSCs fabricated from branched nanocrystals with a peculiar bundle-like configuration are characterized by a drastic reduction of undesired charge-trapping phenomena. These findings can be useful in the design and fabrication of future generations of high-performing DSSCs based on colloidal nanocrystals with properly engineered size and shape parameters.