Layer-by-Layer Structural Identification of 2D Ruddlesden-Popper Hybrid Lead Iodide Perovskites by Solid-State NMR Spectroscopy

Application of two-dimensional (2D) organic-inorganic hybrid halide perovskites for optoelectronic devices requires detailed understanding of the local structural features including the Pb-I bonding in the 2D layers and the capping ligand-perovskite interaction. In this study, we show that 1H and 207Pb solid-state Nuclear Magnetic Resonance (NMR) spectroscopy can serve as a non-invasive and complementary technique to quantify the composition and to probe the local structural features of 2D Ruddlesden-Popper phase BA2MAn-1PbnI3n+1 (n=1-4) with butylammonium (BA) spacers. 207Pb echo and 1H-detected 207Pb→1H heteronuclear correlation (HETCOR) experiments enables layer-by-layer structural detection of 2D halide perovskites. We show that the observed correlation between 207Pb NMR shifts and mean Pb-I bond lengths around each Pb site allows us to probe the local bonding environment of Pb via its 207Pb NMR shift. We envisage that this technique will be vital for better understanding the materials properties as determined by the local atomistic environments in multi-dimensional halide perovskites.