KCS

PbS nanocrystal quantum dots (NQDs) are very promising for applications in solution- processed photovoltaic device because of their large bulk exciton Bohr radius (20 nm) and size-tunability over the entire near-infrared wavelength region. PbS NQDs, however, have poor air stability for large size PbS NQDs. In this research, we firstly synthesized highly air stable, ultra-small PbS NQDs with diameters as small as 1.5 nm, absorbed at 480 nm using low growth temperature after fast quenching. The PbS NQDs size is controlled from 1.5 to 7.5 nm in diameter. We found a transition at 4 nm in diameter in the air-stability for varying PbS NQDs size. We show this transition is driven by shape transition from octahedron to cuboctahedron due to increasing steric hindrance as large PbS NQDs size using X-ray photoemission spectroscopy (XPS) measurements and density functional theory (DFT) calculations. These studies provide important clues on surface chemistry about air-stability and also can be very useful in the process of designing better stable PbS NQDs under ambient conditions in the future.