A perovskite compound represented by Formula 1, a thin layer including the perovskite compound, and an optoelectronic device including the perovskite compound: [A][B1nB2(1-n)][X]3.  Formula 1 In Formula 1, A may be at least one selected from a monovalent organic cation, monovalent inorganic cation, and combinations thereof; B1 may be a thulium (II) (Tm2+) ion; B2 may be at least one divalent inorganic cation, where B2 is free of (e.g., does not include) Tm2+; n may be a real number that satisfies 0