Lead-Free, Two-Dimensional Mixed Germanium and Tin Perovskites

Hybrid two-dimensional (2D) organic-inorganic perovskites continue to draw increased attention in view of their outstanding performance in optoelectronic devices such as solar cells and light-emitting devices. Herein, for the first time, we report the synthesis and characterization of lead-free, 2D mixed Ge-Sn halide perovskites, (PEA)₂Ge_{1- x}Sn _xI₄ (where PEA = C₆H₅CH₂CH₂NH₃⁺), and demonstrate that the bandgaps decrease linearly with increasing Sn content. Most importantly, among them, (PEA)₂Ge_0.5Sn_0.5I₄ possesses the smallest bandgap of 1.95 eV. Density functional theory calculations confirm that Sn substitution induces a smaller bandgap and more dispersed band structure, which are desirable characteristics of light-absorbing materials. In addition, conductivity and stability of (PEA)₂Ge_0.5Sn_0.5I₄ have also been assessed.