Lead-Halide Scalar Couplings in 207Pb NMR of APbX3 Perovskites (A=Cs, Methylammonium, Formamidinium; X=Cl, Br, I)

Understanding the structure and dynamics of newcomer optoelectronic materials - lead halide perovskites APbX(3) [A=Cs, methylammonium (CH3NH3+, MA), formamidinium (CH(NH2)(2)(+), FA); X=Cl, Br, I] - has been a major research thrust. In this work, new insights could be gained by using Pb-207 solid-state nuclear magnetic resonance (NMR) spectroscopy at variable temperatures between 100 and 300K. The existence of scalar couplings (1)J(Pb-Cl) of ca. 400Hz and (1)J(Pb-Br) of ca. 2.3kHz could be confirmed for MAPbX(3) and CsPbX3. Diverse and fast structure dynamics, including rotations of A-cations, harmonic and anharmonic vibrations of the lead-halide framework and ionic mobility, affect the resolution of the coupling pattern. Pb-207 NMR can therefore be used to detect the structural disorder and phase transitions. Furthermore, by comparing bulk and nanocrystalline CsPbBr3 a greater structural disorder of the PbBr6-octahedra had been confirmed in a nanoscale counterpart, not readily captured by diffraction-based techniques.