Interface engineering of CsPbI₃-black phosphorus van der Waals heterostructure

Interface Engineering is an effective route to tune structural and electrical properties in semiconductor heterostructures. Two kinds of typical van der Waals (vdW)-type electrical contacts, i.e., the electrical contacts of the Pb-I interface and Cs-I interface with a black phosphorus (BP) monolayer, respectively, in CsPbI₃-BP heterostructures are studied by first-principles calculations. The electronic band structures of both CsPbI₃ slabs and the BP monolayer are preserved in the combined vdW CsPbI₃-BP heterostructures. The heterostructure of the Pb-I interface contacting with BP demonstrates the type-I band alignment, and the Cs-I interface contacting with the BP heterostructure demonstrates the type-II band alignment. The reason for the energy level shift is the work function difference of CsPbI₃ slabs relative to the BP monolayer, which drives electrons and holes to move spontaneously. In addition, the CsPbI₃-BP heterostructures show much better optical properties than CsPbI₃ slabs. The light absorptions are enhanced in the CsPbI₃-BP heterostructures, especially in the infrared region, which would improve the use of infrared light in CsPbI₃ perovskite solar cells. This work suggests that such inorganic perovskite-BP heterostructures have significant potential for future optoelectronic applications and can enable broad possibilities with compositional tunability in inorganic perovskites.