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 Ln is successful or not; the substituting sites of Ln in lead halide perovskites are unclear. We directly identify the doped Yb in CsPbCl 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 Yb simultaneously replace Pb and occupy the lattice interstitial sites. Furthermore, we directly observe the cluster phenomenon of CsPbCl 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.