As promising optoelectronic materials, lead sulfide quantum dots (PbS QDs) have attracted great attention. However, their applications are substantially limited by the QD quality and/or complicated synthesis. Herein, a facile new synthesis is developed for highly monodisperse and halide passivated PbS QDs. The new synthesis is based on a heterogeneous system containing a PbCl₂-Pb(OA)₂ solid-liquid precursor solution. The solid PbCl₂ inhibits the diffusion of monomers and maintains a high oversaturation condition for the growth of PbS QDs, resulting in high monodispersities. In addition, the PbCl₂ gives rise to halide passivation on the PbS QDs, showing excellent stability in air. The high monodispersity and good passivation endow these PbS QDs with outstanding optoelectronic properties, demonstrated by a 9.43% power conversion efficiency of PbS QD solar cells with a bandgap of ~ 0.95 eV (1,300 nm). We believe that this heterogeneous strategy opens up a new avenue optimizing for the synthesis and applications of QDs.