Atomic-scale imaging of ytterbium ions in lead halide perovskites

Lanthanide-doped lead halide perovskites have demonstrated great potential for photoelectric applications. However, there is a long-standing controversy about the existence of lanthanide ions, e.g., whether the doping of Ln³⁺ is successful or not; the substituting sites of Ln³⁺ in lead halide perovskites are unclear. We directly identify the doped Yb³⁺ in CsPbCl₃ perovskites by using the state-of-the-art transmission electron microscopy and three-dimensional atom probe tomography at atomic scale. Different from the previous assumptions and/or results, we evidence that Yb³⁺ simultaneously replace Pb²⁺ and occupy the lattice interstitial sites. Furthermore, we directly observe the cluster phenomenon of CsPbCl₃ single crystal at near atomic scale. Density functional theory modeling further confirms and explains the mechanisms of our findings. Our findings thus provide an atomic-level understanding of the doping mechanism in perovskites and will stimulate a further thinking of the doping effect on the performance of perovskites.