Liquid-liquid interface assisted synthesis of SnO₂ nanorods with tunable length for enhanced performance in dye-sensitized solar cells

Single-crystalline SnO₂ nanorods with tunable length are synthesized via a facile and surfactant-free solvothermal route based on an aqueous–organic solvent system. The length of the nanorods can be facilely controlled by adjusting the solvent ratio. Particularly, the average length increases from 14.6 to 98.0 nm when the volume ratio of cyclohexane to water is varied from 20:30 to 49:1. The morphological evolution of the SnO₂ nanorods is systematically investigated, and a growth mechanism involving three stages of nucleation, rearrangement and oriented growth is proposed, based on the free migration of the nanoparticles at the two immiscible interfaces thereby offering special path for the self-assembly. The synthesized SnO₂ nanorods are used as photoanodes for dye-sensitized solar cells (DSSCs) and the photovoltaic performance is studied as a function of the morphology. UV–vis absorption spectra show the dye-loading capabilities of the DSSCs are gradually weaken with the length increase of the SnO₂ nanorods. Electrochemical impedance spectroscopy analysis indicates that the charge transfer resistances at the SnO₂/dye/electrolyte interfaces decrease and the electron lifetimes increase along with the increase of nanorod-length. As a consequence, DSSCs fabricated from medium-sized nanorods achieve the best power conversion efficiency of 3.50% due to the equilibrium between fast electron transport and large specific surface area.