“Breathing” organic cation to stabilize multiple structures in low-dimensional Ge-, Sn-, and Pb-based hybrid iodide perovskites

Abstract

Low-dimensional hybrid inorganic–organic perovskites are excellent candidates for stable optoelectronic devices. The dimensionality of these perovskites depends largely on the organic and inorganic compositions, as well as the synthetic conditions. Here, we report five new hybrid iodides, (ETU)₄Ge₅I₁₈, (ETU)GeI₄, (ETU)SnI₄, (ETU)PbI₄, and (ETU)₃Pb₂I₁₀ using only one type of organic cation, namely, S-(2-aminoethyl)isothiouronium (ETU). (ETU)GeI₄ and (ETU)SnI₄ belong to the (110)-oriented structure-type with “3 × 3” sawtooth corrugated layers and crystallize in a structure with the orthorhombic space group Pbca. (ETU)₄Ge₅I₁₈ crystallizes in a structure with the triclinic space group P, featuring a 2D layered structure with combinations of corner, edge, and face-sharing [GeI₆] octahedra. For the Pb-based series, (ETU)PbI₄ has the conventional (100) – oriented 2D type whereas (ETU)₃Pb₂I₁₀ has a unique 0D structure. Remarkably, the unstable 2D orange-phase (ETU)PbI₄ transforms to a stable 0D yellow phase (ETU)₃Pb₂I₁₀, accompanied by the reduction of the C–S–C angle of the organic cation ETU. The optical band gaps are largely regulated by the diverse types of structure and are in the range of 1.8 eV to 2.8 eV. (ETU)SnI₄ is the only material showing notable photoluminescence at room-temperature. Our work showcases the flexibility of the organic cation in determining the structural dimensionality and provides a new strategy in generating new hybrid materials.