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 AGeBr₃ , A=CH₃ NH₃ (MA), CH(NH₂ )₂ (FA), Cs and FAGe0.5 Sn0.5 Br₃ , crystallizing in polar space groups. These compounds exhibit tunable SHG responses, where MAGeBr₃ shows the strongest SHG intensity (5×potassium 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.