Lead‐Free Semiconductors: Soft Chemistry, Dimensionality Control, and Manganese‐Doping of Germanium Halide Perovskites

Abstract Lead halide perovskites have drawn enormous interest due to their exceptional photovoltaic and optoelectronic properties. However, the heavy metal lead is harmful to humans and the environment resulting in a need for strategies to replace this toxic element. Herein, we report a facile aqueous synthesis of CsGeX₃ (X=I, Br) perovskite nanocrystals with size control achieved by varying the concentration of a cysteammonium halide ligand. We observe a variety of morphologies including pyramidal, hexagonal, and spheroidal. CsGeX₃ nanocrystals undergo a lattice expansion due to partial replacement of Cs⁺ with larger cysteNH₃⁺ cations into their lattice. We successfully dope Mn²⁺ into the CsGeX₃ lattice for the first time with incorporation of up to 29% in bulk and 16% in nano samples. XRD peak shifts and EPR hyperfine splitting strongly indicate that Mn²⁺ is doped into the lattice. Our results introduce a new member to the lead‐free halide perovskite family and set the fundamental stage for their use in optoelectronic devices.