Ligand effects on electronic and optoelectronic properties of two-dimensional PbS necking percolative superlattices

The inter-nanocrystal (NC) distance, necking degree, ordering level, and NC surface ligands all affect the electronic and optoelectronic properties of NC solids. Herein, we introduce a unique PbS structure of necking percolative superlattices to exclude the morphological factors and study the effect of ligands on the NC properties. X-ray photoelectron spectroscopy data indicate that 1,2-ethanedithiol (EDT), oxalic acid, mercaptopropionic acid, and NH4SCN (SCN) ligands were attached to the surface of NCs by substrate-supported ligand exchange. Field-effect transistors were tested and photodetector measurements were performed to compare these NC solids. An SCN-treated film had the highest mobility and responsivity under high-power intensity irradiation owing to its high carrier density, whereas an EDT-treated film had the lowest mobility, photocurrent, and dark current. These findings introduce new avenues for choosing suitable ligands for NC applications.