NMR spectroscopy probes microstructure, dynamics and doping of metal halide perovskites

Solid-state magic angle spinning NMR spectroscopy is a powerful technique to probe atomiclevel microstructure and structural dynamics in metal halide perovskites (MHPs). It can be used to measure dopant incorporation, phase segregation, halide mixing, decomposition pathways, passivation mechanisms, short- and long-range dynamics and other local properties. This Review describes practical aspects of recording solid-state NMR data on halide perovskites and how these afford unique insights into new compositions, dopants and passivation agents. We discuss the applicability, feasibility and limitations of 1H, 13C, 15N, 14N, 133Cs, 87Rb, 39K, 207Pb, 119Sn, 113Cd, 209Bi, 115In, 19F and 2H NMR in typical experimental scenarios. We highlight the pivotal complementary role of solid-state mechanosynthesis which enables highly sensitive NMR studies by providing large quantities of high-purity materials of arbitrary complexity, and of chemical shifts calculated using density functional theory. We examine the broader impact of solidstate NMR on materials research and how its evolution over seven decades has benefitted structural studies of contemporary materials like halide perovskites. Finally, we summarize some of the open questions in perovskite optoelectronics that could be addressed using solid-state NMR. We thereby hope to stimulate wider use of this technique in materials and optoelectronics research.This work has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 841136. This work was supported by Swiss National Science Foundation Grant No. 200020_178860. S.D.S. acknowledges the Royal Society and Tata Group (UF150033). CPG acknowledges the Royal Society