Photophysical Ion Dynamics in Hybrid Perovskite MAPbX3 (X=Br, Cl) Single Crystals

Journal article, 2024

Hybrid organic–inorganic perovskites (HOIPs) are promising candidates for
next-generation photovoltaic materials. However, there is a debate regarding
the impact of interactions between the organic center and the surrounding
inorganic cage on the solar cell’s high diffusion lengths. It remains unclear
whether the diffusion mechanism is consistent across various halide
perovskite families and how light illumination affects carrier lifetimes. The
focus is on ion kinetics of (CH3NH3)PbX3 (X = Br, Cl) perovskite halide single
crystals. Muon spectroscopy (𝝁+SR)is employed to investigate the
fluctuations and diffusion of ions via the relaxation of muon spins in local
nuclear field environments. Within a temperature range of 30–340 K, ion
kinetics are studied with and without white-light illumination. The results
show a temperature shift of the tetragonal-orthorhombic phase transition on
the illuminated samples, as an effect of increased organic molecule
fluctuations. This relation is supported by density functional theory
(DFT) calculations along the reduction of the nuclear field distribution width
between the phase transitions. The analysis shows that, depending on the
halide ion, the motional narrowing from H and N nuclear moments
represents the molecular fluctuations. The results demonstrate the
importance of the halide ion and the effect of illumination on the compound’s
structural stability and electronic properties.