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

Abstract

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 ns2 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 (MPZ2+), 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)2GeI6, with suppressed LPE in Ge(II) ground states and minimized octahedral distortion. The structural symmetry facilitates strong orbital overlap between Ge2+ and I−, leading to increased electron‐phonon coupling and high defect tolerance. Coupled with the enhanced quantum confinement of isolated 0D [GeI6] octahedra, (MPZ)2GeI6 exhibits a large Stokes shift of 216 nm and a record‐high photoluminescence quantum yield of 19.1% among reported Ge2+‐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.