Interstitial Nature of Mn<sup>2+</sup> Doping in 2D Perovskites
Andrew J. Torma, Wenbin Li, Hao Zhang, Qing Tu, Vladislav V. Klepov, Michael C. Brennan, Christopher McCleese, Matthew D. Krzyaniak, Michael R. Wasielewski, Claudine Katan, Jacky Even, Martin V. Holt, Tod A. Grusenmeyer, Jie Jiang, Ruth Pachter, Mercouri G. Kanatzidis, Jean‐Christophe Blancon, Aditya D. Mohite
Abstract
Halide perovskites doped with magnetic impurities (such as the transition metals Mn2+, Co2+, Ni2+) are being explored for a wide range of applications beyond photovoltaics, such as spintronic devices, stable light-emitting diodes, single-photon emitters, and magneto-optical devices. However, despite several recent studies, there is no consensus on whether the doped magnetic ions will predominantly replace the octahedral B-site metal via substitution or reside at interstitial defect sites. Here, by performing correlated nanoscale X-ray microscopy, spatially and temporally resolved photoluminescence measurements, and magnetic force microscopy on the inorganic 2D perovskite Cs2PbI2Cl2, we show that doping Mn2+ into the structure results in a lattice expansion. The observed lattice expansion contrasts with the predicted contraction expected to arise from the B-site metal substitution, thus implying that Mn2+ does not replace the Pb2+ sites. Photoluminescence and electron paramagnetic resonance measurements confirm the presence of Mn2+ in the lattice, while correlated nano-XRD and X-ray fluorescence track the local strain and chemical composition. Density functional theory calculations predict that Mn2+ atoms reside at the interstitial sites between two octahedra in the triangle formed by one Cl– and two I– atoms, which results in a locally expanded structure. These measurements show the fate of the transition metal dopants, the local structure, and optical emission when they are doped at dilute concentrations into a wide band gap semiconductor.