Synthesis of PbS/TiO2 Colloidal Heterostructures for Photovoltaic Applications

We report on heteroepitaxial growth of nearly monodisperse PbS nanocrystals onto the surface of TiO2 nanoparticles via colloidal hot-injection routes. Fabricated PbS/TiO2 nanocomposites can be dispersed in nonpolar solvents, which enables an easy solution processing of these materials into mesoporous films for use as light-absorbing layers in nanocrystal-sensitized solar cells. High-temperature deposition of the sensitizer material allows controlling both the size and the number of PbS domains grown onto TiO2 nanoparticles, whereby providing synthetic means for tuning the absorbance spectrum of PbS/TiO2 nanocomposites and simultaneously enhancing their photocatalytic response in the visible and near-infrared. Compared with conventional ionic bath deposition of PbS semiconductors onto TiO2, the reported method results in an improved nanocrystal quality and narrower distribution of PbS sizes; meanwhile, the use of hot-temperature deposition of PbS (T = 180 degrees C) promotes the formation of near-epitaxial relationships between PbS and TiO2 domains, leading to fewer interfacial defects. The photovoltaic response of pyridine-treated PbS/TiO2 nanocomposites was investigated using a two-electrode cell filled with polysulfide electrolyte. The measured photocurrent compared favorably to that of PbS/TiO2 electrodes fabricated via chemical bath deposition.