Hybrid Germanium Bromide Perovskites with Tunable Second Harmonic Generation

Ge-based hybrid perovskite materials have demonstrated great potential for second harmonic generation (SHG) due to the geometry and lone-pair induced non-centrosymmetric structures. Here, we report a new family of hybrid 3D Ge-based bromide perovskites AGeBr(3), A=CH3NH3 (MA), CH(NH2)(2) (FA), Cs and FAGe(0.5)Sn(0.5)Br(3), crystallizing in polar space groups. These compounds exhibit tunable SHG responses, where MAGeBr(3) shows the strongest SHG intensity (5xpotassium dihydrogen phosphate, KDP). Structural and theoretical analysis indicate the high SHG efficiency is attributed to the displacement of Ge2+ along [111] direction and the relatively strong interactions between lone pair electrons of Ge2+ and polar MA cations along the c-axis. This work provides new structural insights for designing and fine-tuning the SHG properties in hybrid metal halide materials.