Smooth (sub-1% roughness) PbS-nanocrystal films (left) produce spin-cast photoconductive photodetectors that exhibit 10 A W-1 responsivities, low dark current, and respond with a single time constant of 20 ms. The morphology of analogous devices based on previously reported amine-based ligands is shown on the right. ne use of ethanethiol as ligand is responsible for the combination of smooth morphology and low lag.