Photothermally induced, reversible phase transition in methylammonium lead triiodide

Metal halide perovskites (MHPs) undergo structural phase transi-tions, from lower to higher symmetry, upon heating. Although phase transitions have been investigated by optical, thermal, and diffraction methods, most measurements are quasi-static and do not inform on the fundamental timescale of their phase transitions. Here, we investigate the timescale of the orthorhombic-to-tetragonal phase transition in methylammonium lead triiodide using nano-second transient absorption spectroscopy. Using mid-infrared pulses to impulsively heat the material held right below the phase-transition temperature, we observe a clean signature of transient, reversible orthorhombic-to-tetragonal transition on the tens-of -nanoseconds timescale. A high degree of transient phase transition is observed accounting for one-third of the steady-state counterpart. Compared with inorganic phase-change materials, the orders-of-magnitude-slower phase transition in MAPbI(3) suggests a large energy barrier for activating the hydrogen-bond network and the accompanying cooperative octahedral rotations. Our approach paves the way for unraveling phase-transition dynamics in MHPs and other hybrid materials.

Automated summary

The timescale of the orthorhombic-to-tetragonal phase transition in methylammonium lead triiodide (MAPbI3) was investigated using nanosecond transient absorption spectroscopy. A clean signature of transient, reversible orthorhombic-to-tetragonal transition was observed on the tens-of-nanoseconds timescale. Compared to inorganic phase-change materials, MAPbI3 exhibited orders-of-magnitude-slower phase transition, indicating a large energy barrier for activating the hydrogen-bond network and cooperative octahedral rotations. This approach provides insights into phase-transition dynamics in metal halide perovskites (MHPs) and other hybrid materials.