Ammonium iodide (NH4I) has been shown to have an inhibiting effect on the growth kinetics of lead sulfide films at initial NH4I concentrations in solution from 0.05 M to 0.40 M. The addition of the inhibitor leads to a decrease in grain size, an increase in the fraction of nanoparticles in the PbS films to ~13%, and an increase in the iodine content of the films to 3.7 at %, depending on growth conditions. X-ray diffraction characterization has shown that the films have a B1 cubic structure (sp. gr. (Formula presented.)). Increasing the inhibitor concentration in solution leads to an increase in the lattice parameter of the lead sulfide from 0.59315(1) to 0.59442(3) nm, due to iodine substitution for sulfur in the PbS crystal lattice. The spectral sensitivity peak and the long-wavelength edge of the photoresponse of the PbS films shift to shorter wavelengths from 2.5 to 2.2 and from 3.0 to 2.8 μm, respectively, which is attributable to the formation of the wide-band-gap phase PbI2. Using low-temperature measurements, the thermal band gap of the films grown in the presence of 0.15 and 0.25 mol/L NH4I has been determined to be 0.46 and 0.51 eV. The respective activation energies for acceptor impurity levels are 0.135 and 0.153 eV. The iodine-doped PbS films offer a relatively high voltage responsivity in the IR spectral region owing to an n- to p-type conversion, in combination with an anomalously short response time. © 2023, Pleiades Publishing, Ltd.