The role of NaF treatment in the production of SnS thin films and solar cells was investigated. The grain size of SnS films containing Na was large (about 500 nm) compared to that of SnS films prepared by conventional sulfurization (typically 250 nm). The carrier concentration of SnS increased from 5 x 10(16) to 2 x 10(17) cm(-3) by Na diffusion into the SnS film, and Na acted as an acceptor. Moreover, the NaF layer exhibited a capping effect during high-temperature sulfurization at 500 degrees C and suppressed the re-evaporation of SnS. The short-current density tended to increase from 1.1 to 8.8 mA/cm(2) with increasing thickness of the deposited NaF layer from 0 to 200 nm, because of the larger grain size and carrier concentration of SnS. (C) 2016 Elsevier B.V. All rights reserved.