Surface Effects and Adsorption of Methoxy Anchors on Hybrid Lead Iodide Perovskites: Insights for Spiro-MeOTAD Attachment

Abstract

Despite the intense study that has been carried out on hybrid organic–inorganic perovskites, motivated by the breakthrough of perovskite solar cells, the surface properties of the methylammonium (MA) lead halide perovskites still remain vastly unexplored. The polar structure of the hybrid perovskites suggests that their surface properties are important to the operation of the photovoltaic devices. To gain insight into these properties, we have investigated the (001) the surfaces of the hybrid CH3NH3PbI3 perovskite by a combination of ab initio methods that include the surface relaxation and the molecular dynamics simulations. We also investigated the binding modes of the methoxybenzene (anisole molecule, CH3OC6H5) on the perovskite surface, with the goal of clarifying the perovskite/spiro-MeOTAD attachment mechanisms. It is found that the methoxybenzene can adsorb on the (001) octahedral surface of the MAPbI3 perovskite depleted of the methylammonium cation, where the methoxy group finds a stable minimum of ∼38.6 kJ/mol in the interstice of the corner-sharing PbI6 octahedra. However, there is no stable attachment site for the methoxybenzene on the PbI2 flat (001) surface of the perovskite. The attachment mechanism is governed by the electrostatic interaction of the methoxy group with the surface, which is repulsive with the iodides and attractive with the Pb(II) ion.