Dynamic Lone Pair Expression-Driven Strong Light Emission in a Zero-Dimensional Ge(II)-Based Perovskite

Metal halide perovskites derive their remarkable optoelectronic properties from the combined effects of strong electron-phonon coupling, exciton localization, and the dynamic stereochemical activity of n s 2 lone pairs. However, Ge (II)-based perovskites typically exhibit static lone-pair expression (LPE) and pronounced octahedral distortion, attributed to the second-order Jahn-Teller effect, which leads to severe nonradiative recombination. Here, we demonstrate that incorporating 1-methylpiperazium (MPZ 2+ ), with bidentate coordination sites and balanced polarity, steric effect, and conformational flexibility, can effectively tune the organic-inorganic interactions in a newly synthesized Ge(II)-based zero-dimensional perovskite, (MPZ) 2 GeI 6 , with suppressed LPE in Ge(II) ground states and minimized octahedral distortion. The structural symmetry facilitates strong orbital overlap between Ge 2+ and I − , leading to increased electron-phonon coupling and high defect tolerance. Coupled with the enhanced quantum confinement of isolated 0D [GeI 6 ] octahedra, (MPZ) 2 GeI 6 exhibits a large Stokes shift of 216 nm and a record-high photoluminescence quantum yield of 19.1% among reported Ge 2+ -based perovskites. Additionally, it demonstrates remarkable resistance to moisture, maintaining structural integrity and photoluminescence even after absorbing 0.5 g of water per gram of material, attributable to the polarity of MPZ molecules that help stabilize water molecules. These findings offer new insights into the structural and optical modulation of Ge-based perovskites.