Air-stable PbS quantum dots synthesized with slow reaction kinetics via a PbBr₂ precursor

PbS quantum dots have been synthesized using a PbBr₂ precursor and the halide content has been examined. Slower reaction kinetics for quantum dots growth relative to the use of PbCl₂ was observed for PbBr₂, giving a possible route to increased control over quantum dot size with in situ passivation. Unambiguous determination of the surface conditions of nanomaterials is still a developing area of science, pushing the limits of current microscopy and analytical techniques. Contributions to a rigorous form of nanomaterial surface analysis are made here using X-ray photoelectron spectroscopy to analyse bonding in detail. Atomic resolution TEM is applied to produce energy dispersive X-ray spectroscopy maps with state of the art resolution. This analysis has been applied to air-stable halide terminated PbS nanoparticles, which is a nanomaterial of central importance for quantum confined solar cell applications. Chemical analysis from X-ray photoelectron spectroscopy is consistent with Br surface termination and high resolution energy dispersive X-ray spectroscopy (EDS) maps also show a positive spatial correlation for Br with quantum dot location. An observed excess Br content is attributed to the presence of bromine terminated PbS quantum dots nuclei in the final colloid.