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)2Ge1- xSn xI4 (where PEA = C6H5CH2CH2NH3+), and demonstrate that the bandgaps decrease linearly with increasing Sn content. Most importantly, among them, (PEA)2Ge0.5Sn0.5I4 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)2Ge0.5Sn0.5I4 have also been assessed.