Interstitial Nature of Mn²⁺ Doping in 2D Perovskites

Abstract

Halide perovskites doped with magnetic impurities (such as the transition metals Mn 2+ , Co 2+ , Ni 2+ ) are being explored for a wide range of applications beyond photovoltaics, such as spintronic devices, stable lightemitting 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 Cs 2 PbI 2 Cl 2 , we show that doping Mn 2+ 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 Mn 2+ does not replace the Pb 2+ sites. Photoluminescence and electron paramagnetic resonance measurements confirm the presence of Mn 2+ in the lattice, while correlated nano-XRD and X-ray fluorescence track the local strain and chemical composition. Density functional theory calculations predict that Mn 2+ 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.

Luminescence and Mechanism of Mn2+ Substitution in Cs7Cd3Br13 with Two Types of Coordination Number

“…When X ≤ 0.4, there is no obvious change in the diffraction peak positions, and only some of the diffraction peak positions move to higher angles, which indicates that the introduction of Mn 2+ does not change the Cs 7 Cd 3 Br 13 crystal structure, and the movement of the diffraction peak positions to higher angular positions is caused by the lattice contraction due to the replacement of Cd 2+ by Mn 2+ with smaller ionic radii. This is consistent with previous reports , since doping to the interstitial sites leads to lattice expansion. When the ratio of manganese ions in precursors exceeds 0.4, new diffraction peaks appear, indicating that the excess Mn 2+ substituent cannot maintain the original crystal structure.…”

Elucidating the Mn2+ Dopant Sites in Two-Dimensional Na–In Halide Perovskite

“…This type of expansion due to the presence of dopant ions at interstitial sites in perovskites is well-known in the literature. 43,44 Thus, by analyzing the PXRD patterns, we propose the presence of two types of Mn 2+ sites inside the host LDP.…”

Abnormal In-Plane Thermomechanical Behavior of Two-Dimensional Hybrid Organic–Inorganic Perovskites

“…This non-monotonic in-plane thermomechanical behavior can be expected in 2D metal–halide perovskites with organic spacer molecule layers interacting with each other through vdW interfaces, but certainly not in perovskite systems with no vdW interfaces ( e.g. , 2D HOIPs with diammonium spacer molecules) or with no organic spacer molecules ( e.g ., Cs 2 PbI 2 Cl 2 ).…”

“…C4n5 and C4n1 also show non-monotonic thermomechanical behavior similar to that of C4n3 while the onset temperatures of their thermomechanical features correlate well to the order-to-disorder transition temperatures of BA + in the crystals, which supports our proposed mechanism. This nonmonotonic in-plane thermomechanical behavior can be expected in 2D metal−halide perovskites with organic spacer molecule layers interacting with each other through vdW interfaces, but certainly not in perovskite systems with no vdW interfaces (e.g., 2D HOIPs with diammonium spacer molecules 18 ) or with no organic spacer molecules (e.g., Cs 2 PbI 2 Cl 2 68 ). The thermomechanical behavior of 2D HOIPs found here can provide vital guidance to 2D HOIP-based device architecture design to enhance the thermomechanical stability and thus the durability of the devices.…”