How Methylammonium Cations and Chlorine Dopants Heal Defects in Lead Iodide Perovskites

Lead tri-iodide methylammonium (MAPbI(3)) perovskite polycrystalline materials show complex optoelectronic behavior, largely because their 3D semiconducting inorganic framework is strongly perturbed by the organic cations and ubiquitous structural or chemical inhomogeneities. Here, a newly developed time-dependent density functional theory-based theoretical formalism is taken advantage of. It treats electron-hole and electron-nuclei interactions on the same footing to assess the many-body excited states of MAPbI(3) perovskites in their pristine state and in the presence of point chemical defects. It is shown that lead and iodine vacancies yield deep trap states that can be healed by dynamic effects, namely rotation of the methylammonium cations in response to point charges, or through slight changes in chemical composition, namely by introducing a tiny amount of chlorine dopants in the defective MAPbI(3). The theoretical results are supported by photoluminescence experiments on MAPbI(3-m)Cl(m) and pave the way toward the design of defect-free perovskite materials with optoelectronic performance approaching the theoretical limits.