Excess Iodine Improves the Electronic Properties of Zinc Phosphate and Pb‐Halide Perovskite Nanostructured Interfaces

Interfaces between Pb‐halide perovskites and protective layers are of interest for high‐efficiency solar cells and highly luminescent core–shell nanostructures. However, the perovskite crystal structure immediately at such an interface may be highly distorted at the atomic scale, leading to potential degradation of its optoelectronic properties. Here, we show computationally that the electronic structure at an interface between nontoxic, water stable zinc phosphate and Pb‐halide perovskite materials can be improved by excess iodine. After interface equilibration by ab initio molecular dynamics, mid‐gap states involving Zn, O, Pb, and iodine from the original perovskite slab were created by interface disorder. These interface defect states were found to be passivated by experimentally relevant amounts of excess halide. These halide ions drew charge density onto themselves that had previously centred on oxygen ions at the interface. This prevented the perovskite surface, notably Pb, from donating charge to oxygen in the phosphate shell. The excess halide acted as a surface terminating species to the shell material without compromising the bandgap of the perovskite, suggesting a mechanism for the outstanding performance of soft perovskite nanomaterials even in contact with a material that has significant lattice mismatch. The work provides general insight into high‐quality perovskite interfaces, with benefits for solar cells and nanomaterials offering outstanding luminescence.