Doping and phase segregation in Mn 2+ - and Co 2+ -doped lead halide perovskites from 133 Cs and 1 H NMR relaxation enhancement

Lead halide perovskites belong to a broad class of compounds with appealing optoelectronic and photovoltaic properties. Doping with transition metal ions such as Mn 2+ and Co 2+ has recently been reported to substantially enhance luminescence and stability of these materials. However, so far atomic-level evidence for incorporation of the dopants into perovskite phases has been missing. Here, we introduce a general and straightforward method for confirming the substitutional doping of bulk perovskite phases with paramagnetic dopants. Using 133 Cs and 1 H solid-state MAS NMR relaxation measurements we provide for the first time direct evidence that, consistent with current understanding, Mn 2+ is incorporated into the perovskite lattice of CsPbCl 3 and CsPbBr 3 and does not form clusters. We also show that, contrary to current conviction, Co 2+ is not incorporated into the perovskite lattice of MAPbI 3 .