The heterostructure consisting of lead chalcogenide and halide perovskite materials are recently identified as excellent candidates for optoelectronic devices such as solar cells. Several theoretical works are carried out to understand the nanoscopic structures and properties of halide perovskite/lead chalcogenide heterostructures. However, the detailed features of the heterosystems, including the effects of the solute concentration, types of lead chalcogenide, and polaronic states are not investigated. In this manuscript, we employ first-principles calculations to provide an alternative view of the halide perovskite/lead chalcogenide heterostructure, focusing on CsPbI 3 and the molecular size of PbS/PbSe lead chalcogenide. The calculations confirm the constituent concentration and the elemental substitution can be employed to fine tune the optoelectronic properties of halide perovskite/lead chalcogenide heterostructures. This work facilitates the fundamental understanding of the halide perovskite/lead chalcogenide systems toward optoelectronic applications.