Spatiodynamics, Photodynamics, and Their Correlation in Hybrid Perovskites

The motion of organic cations and its possible correlation with excited-state photodynamics are important to the fundamental understanding of the superior performances of two-dimensional (2D) and three-dimensional (3D) hybrid lead-halide perovskites in optoelectronic applications. Herein, variable-temperature (VT) solid-state 1H and 13C CP (cross polarization) NMR spectroscopy without isotope enrichments, combined with VT powder X-ray diffraction (XRD), differential scanning calorimetry (DSC), and time-resolved photoluminescence (TRPL), was employed to study the phase transition, local structure, motion dynamics, and photodynamic behaviors of organic cations in hybrid 2D Ruddlesden–Popper perovskites (RPPs) (BA)2(MA)n−1PbnI3n+1 (BA denotes butylammonium and MA denotes methylammonium). Two types of BA conformations in various crystalline phases of 2D RPPs and conformational transition associated with phase transition were clearly revealed. Quantitative NMR analyses suggest that the rotation dynamics of MA in 2D RPPs are comparable to that of MA in 3D MAPbI3. A surprising linear relationship was discovered between the estimated activation energy of the MA rotation and the logarithm of photoluminescence (PL) lifetimes (τ) of 2D RPPs and MAPbI3, strongly supporting the presence of coupling between the cation spatial dynamics and the excited-state photodynamic behaviors.