We present a one-step layer deposition procedure employing ammonium iodide (NH4I) to achieve photovoltaic quality PbS quantum dot (QD) layers. Ammonium iodide is used to replace the long alkyl organic native ligands binding to the QD surface resulting in iodide terminated QDs that are stabilized in polar solvents such as N,N-dimethylformamide without particle aggregation. We extensively characterized the iodide terminated PbS QD via UV-vis absorption, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), FT-IR transmission spectroscopy, and X-ray photoelectron spectroscopy (XPS). Finally, we fabricated PbS QD photovoltaic cells that employ the iodide terminated PbS QDs. The resulting QD-PV devices achieved a best power conversion efficiency of 2.36% under ambient conditions that is limited by the layer thickness. The PV characteristics compare favorably to similar devices that were prepared using the standard layer-by-layer ethandithiol (EDT) treatment that had a similar layer thickness.

Highly pure metallic single-walled carbon nanotubes were continuously extracted from a mixture of semiconducting and metallic species using a nondestructive, scalable method. Two laminar streams were generated in an H-shaped microfluidic channel with two inlets and two outlets. The flow conditions were carefully controlled to minimize diffusive and convective transport across the boundary between the two flows. Dielectrophoretic force from the embedded electrode at the junction extracted metallic nanotubes from a stream of nanotube suspension toward the other stream of buffer solution without nanotubes. The highly pure metallic and enriched semiconducting nanotubes were obtained simultaneously at each outlet using this novel approach. Excellent selectivity was verified by electrical transport measurement, absorption, and Raman spectroscopic analysis.

Nanocrystal quantum dot (NQD)/single-walled carbon nanotube (SWNT) hybrid nanomaterials were synthesized, assembled into field effect transistors (FETs) via dielectrophoresis (DEP), and characterized optically and electronically. The pyridine moiety functioned as a short, noncovalent linker between the NQDs and SWNTs and allowed more efficient carrier transfer through the assemblies without deleteriously altering electronic structures. Photoluminescence studies of the resulting assemblies support an efficient carrier transfer process in CdSe-py-SWNTs unlike that of CdSe/ZnS-py-SWNTs. The use of DEP as a means of controlling the assembly process allowed the creation of a SWNT array containing densely packed CdSe NQDs across a 2 mum gap between electrodes. Observations and characterization of the photocurrent, resistivity, gate dependence, and optical properties of these systems suggest efficient electron transfer from photoexcited NQDs to SWNTs.