<sup>113</sup>Cd Solid-State NMR at 21.1 T Reveals the Local Structure and Passivation Mechanism of Cadmium in Hybrid and All-Inorganic Halide Perovskites
Dominik J. Kubicki, Daniel Prochowicz, Albert Hofstetter, Brennan J. Walder, Lyndon Emsley
Abstract
Cadmium doping has recently emerged as an efficacious strategy for defect suppression and band gap tuning in hybrid as well as all-inorganic halide perovskites. However, the cadmium speciation in these materials is unknown. Here, we use high-field cadmium-113 NMR spectroscopy in conjunction with chemical shift calculations by fully relativistic density functional theory to establish the phase composition of cadmium-doped lead halide perovskites. We find that cadmium does not incorporate into the 3D perovskite lattice of MA- and FA-based lead halide perovskites (MAPbI3 and the gold-standard triple cation mixed-halide composition). Instead, it forms separate, cadmium-rich nonperovskite phases for as little as 1 mol % Cd2+ doping. Conversely, we find that cadmium can incorporate into the 3D perovskite lattice of CsPbBr3 via homovalent Pb2+ substitution up to around 10 mol %. Our results thus reveal the atomic-level mechanism of this recently developed defect passivation strategy.