Over the last few years of the heyday of hybrid halide perovskites, so many metal cations additives have been tested to improve their optoelectronic properties that it is already difficult to find an element that has not yet been tried. In general, the variety of these approaches is united under the name doping, however, there is currently no clear understanding of the mechanisms of the influence of the metal ion additives on the properties of the lead halide perovskite materials. For many ions there is even no consensus on the most fundamental questions: what lattice position does a given ion occupy and is it incorporated in the structure at all? Here, we derived a system of effective radii of different metal ions in the iodine environment for the set of iodide compounds and reveal their crystal chemical role in the APbI3 perovskites. We analysed the possible lattice positions for 40 most common monovalent, divalent, and trivalent metals to reveal whether they could successfully enter into the perovskite structures. We show that, at most, three parameters - effective size, electronegativity and the softness of metal ions are the main ones for crystal chemical analysis of the possibility of metal doping of hybrid halide perovskites. Our results provide a useful theoretical guidance to rationalize and improve current doping strategies of hybrid halide perovskites with metal ions.
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