| Abstract | Metal halide perovskites remain top candidates for higher-performance photovoltaic devices, but concerns about leading lead-based materials remain. Ge perovskites remain understudied for use in solar cells compared to their Sn-based counterparts. In this work, we undertake a combined ⁷³Ge and ¹³³Cs solid-state Nuclear Magnetic Resonance (NMR) spectroscopy and density functional theory (DFT) study of the bulk CsGeX3 (X = Cl, Br, or I) series. We show how seemingly small structural variations within germanium halide perovskites have major effects on their ⁷³Ge and ¹³³Cs NMR signatures and reveal a near-cubic phase at room temperature for CsGeCl3 with severe local Ge polyhedral distortion. Quantum chemical computations are effective at predicting the structural impact on NMR parameters for ⁷³Ge and ¹³³Cs. This study demonstrates the value of a combined solid-state NMR and DFT approach for investigating promising materials for energy applications, providing information that is out of reach with conventional characterization methods, and adds the challenging ⁷³Ge nucleus to the NMR toolkit. |
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