Synthesis of PbS/TiO2 Colloidal Heterostructures for Photovoltaic Applications

We report on heteroepitaxial growth of nearly monodisperse PbS nanocrystals onto the surface of TiO 2 nanoparticles via colloidal hot-injection routes. Fabricated PbS/TiO 2 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 TiO 2 nanoparticles, whereby providing synthetic means for tuning the absorbance spectrum of PbS/TiO 2 nanocomposites and simultaneously enhancing their photocatalytic response in the visible and near-infrared. Compared with conventional ionic bath deposition of PbS semiconductors onto TiO 2, 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 °C) promotes the formation of near-epitaxial relationships between PbS and TiO 2 domains, leading to fewer interfacial defects. The photovoltaic response of pyridine-treated PbS/TiO 2 nanocomposites was investigated using a two-electrode cell filled with polysulfide electrolyte. The measured photocurrent compared favorably to that of PbS/TiO 2 electrodes fabricated via chemical bath deposition.