The tunability of the optoelectrical properties upon compositional modification is a key characteristic of metal halide perovskites. In particular, bandgaps narrower than those in conventional lead-based perovskites are essential to achieve the theoretical efficiency limit of single-absorber solar cells, as well as develop multijunction tandem devices. Herein, the solvent-free vacuum deposition of a narrow bandgap perovskite based on tin–lead metal and formamidinium cation is reported. Pinhole-free films with 1.28 eV bandgap are obtained by thermal codeposition of precursors. The optoelectrical quality of these films is demonstrated by their use in solar cells with a power conversion efficiency of 13.98%.